{"gene":"CSF1","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":1985,"finding":"The c-fms proto-oncogene product is the receptor for CSF-1 (M-CSF); the 165 kDa murine c-fms glycoprotein specifically binds CSF-1 and exhibits ligand-dependent tyrosine kinase activity and tyrosine autophosphorylation in membrane preparations.","method":"Immunoprecipitation with anti-v-fms antisera, radioligand binding with 125I-CSF-1, and in vitro tyrosine kinase assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus receptor binding, foundational paper with >1500 citations","pmids":["2408759"],"is_preprint":false},{"year":1985,"finding":"Molecular cloning of a CSF-1 cDNA encoding a 224-amino-acid mature polypeptide (plus 32-aa leader) that directs synthesis of biologically active CSF-1 in COS cells; multiple mRNA species arise from a single-copy gene.","method":"cDNA cloning, COS-cell expression, radioreceptor assay, macrophage colony assay, antibody neutralization","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — reconstituted biological activity from recombinant protein with multiple validation assays","pmids":["2996129"],"is_preprint":false},{"year":1987,"finding":"A 4-kb CSF-1 cDNA encodes a longer 522-amino-acid precursor containing a C-terminal extension not found in the 1.6-kb cDNA product; both isoforms are structurally and functionally equivalent, arising from alternative splicing of the CSF-1 pre-mRNA.","method":"cDNA cloning, direct protein sequencing, mammalian cell expression","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — direct structural analysis plus expression of recombinant protein","pmids":["3493529"],"is_preprint":false},{"year":1987,"finding":"Human CSF-1 gene contains 10 exons spanning 20 kb; alternative splicing at exon 6 and alternative 3′ noncoding exons produce transcripts encoding either 224 or 522 amino-acid forms of CSF-1.","method":"Genomic cloning, RNA analysis, exon mapping","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 — direct gene structure determination with functional implications for isoform production","pmids":["3500041"],"is_preprint":false},{"year":1987,"finding":"CSF-1 is synthesized as an integral transmembrane homodimeric glycoprotein (disulfide-linked) on the cell surface; extracellular proteolysis by trypsin-like proteases cleaves this membrane-bound precursor to release the soluble secreted form. Autocrine CSF-1/c-fms co-expression transforms NIH 3T3 cells.","method":"Cotransfection of CSF-1 and c-fms genes, surface trypsin cleavage, receptor downmodulation assays, transformation assay","journal":"Molecular and Cellular Biology","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution of membrane processing and autocrine signaling with structural validation","pmids":["3039346"],"is_preprint":false},{"year":1986,"finding":"CSF-1 regulates survival, proliferation, and differentiation of mononuclear phagocytes exclusively via a cell-surface receptor (165 kDa glycoprotein) that undergoes CSF-1-dependent tyrosine autophosphorylation; receptor levels increase on CFU-C just before differentiation to mononuclear phagocytes, marking lineage determination.","method":"Purified receptor characterization, tyrosine kinase assay, developmental receptor expression analysis","journal":"Ciba Foundation symposium","confidence":"High","confidence_rationale":"Tier 1 — purified receptor biochemistry with functional validation","pmids":["3015514"],"is_preprint":false},{"year":1992,"finding":"X-ray crystal structure of recombinant human M-CSF dimer at 2.5 Å reveals two four-helix bundles laid end-to-end with an inter-chain disulfide bond; individual monomers share structural similarity with GM-CSF and growth hormone, suggesting common receptor-binding determinants.","method":"X-ray crystallography at 2.5 Å resolution","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional implications, >160 citations","pmids":["1455231"],"is_preprint":false},{"year":1991,"finding":"Mutation of autophosphorylation site Y809 (Phe substitution) in CSF-1R does not reduce kinase activity, PI3K binding, or immediate-early gene (c-fos, junB) induction, but abolishes CSF-1-dependent mitogenesis and c-myc induction; enforced c-myc expression rescues proliferation, demonstrating a bifurcation of signaling pathways at the receptor level with c-Myc as a central mitogenic mediator downstream of Y809.","method":"Site-directed mutagenesis of CSF-1R Y809, serum-free growth assay, colony assay, Northern blot for c-myc, c-myc overexpression rescue","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis plus epistasis rescue experiment, highly cited foundational paper","pmids":["1833648"],"is_preprint":false},{"year":1992,"finding":"CSF-1 gene expression is induced in vascular endothelial and smooth muscle cells by IL-1α, TNF-α, and LPS; locally produced CSF-1 promotes macrophage scavenger receptor and apolipoprotein E mRNA accumulation in monocytes, linking vascular CSF-1 production to macrophage foam cell development in atherosclerosis.","method":"Northern blot, immunostaining, ELISA, PCR on human/rabbit atheromata, monocyte culture","journal":"The American Journal of Pathology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods in both cultured cells and tissue, single lab","pmids":["1739124"],"is_preprint":false},{"year":1994,"finding":"Structure-function analysis of recombinant human M-CSF by site-directed mutagenesis identifies residues His-9 and His-15 in the N-terminal region (helix A) as critical for receptor binding; double mutation H9A/H15A reduces bioactivity 9,100-fold and receptor affinity equivalently; X-ray crystallography at 2.5 Å confirms no structural change, indicating direct involvement in receptor contact.","method":"Site-directed mutagenesis, radioreceptor binding assay, bioactivity assay, X-ray crystallography at 2.5 Å","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis + receptor binding + crystal structure in single study","pmids":["7983059"],"is_preprint":false},{"year":1997,"finding":"CSF-1 stimulates macrophage proliferation through signaling cascades that include PI3K, ERK1/2, cyclin D1/D2, cdk4, Rb phosphorylation, and E2F activation; IFN-α/β acts as an endogenous inhibitor of CSF-1-driven cell cycle progression in bone marrow-derived macrophages, acting at least partly via down-regulation of c-myc and cyclin D.","method":"Pharmacological inhibitors, cyclin/CDK immunoprecipitation kinase assays, Northern blot, knockout macrophages, cell-cycle analysis","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical assays with genetic controls, single lab","pmids":["8981359"],"is_preprint":false},{"year":1997,"finding":"CSF-1R autophosphorylation site Y807 (murine numbering) is essential for macrophage differentiation signaling and its mutation totally abrogates differentiation of FDC-P1 myeloid cells while increasing proliferation, suggesting Y807 controls a proliferation/differentiation switch; sites Y697, Y706, Y721 in the kinase insert augment but are not essential for differentiation.","method":"Site-directed mutagenesis of individual CSF-1R tyrosines, differentiation and proliferation assays in FDC-P1 myeloid cells","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2 — systematic mutagenesis with functional readout, single lab","pmids":["8981370"],"is_preprint":false},{"year":1997,"finding":"CSF-1R phosphorylation of Y721 in the kinase insert domain is the primary site mediating association with PI3K, which activates the major macrophage motility signaling pathways.","method":"Receptor mutagenesis, phosphotyrosine co-immunoprecipitation with p85 PI3K subunit, chemotaxis assays","journal":"International journal of cell biology (review citing original data)","confidence":"Medium","confidence_rationale":"Tier 2 — receptor mutagenesis + PI3K co-IP, summarized in multiple review contexts","pmids":["22505929","9261328"],"is_preprint":false},{"year":1997,"finding":"CSF-1 stimulates macrophage proliferation through the Raf-1/MEK/ERK pathway; downstream, ERK activation is required for macrophage differentiation. New myeloid-specific substrate p150 (Shc/Grb2 complex partner via PTB domain) is identified as a CSF-1R signaling component specific to hematopoietic cells.","method":"Co-immunoprecipitation, tyrosine phosphorylation assays, cDNA cloning of p150","journal":"Molecular reproduction and development","confidence":"Medium","confidence_rationale":"Tier 2/3 — co-IP and phosphorylation data in multiple hematopoietic cell lines","pmids":["8981370"],"is_preprint":false},{"year":1997,"finding":"CSF-1 produced by estrogen-deficient stromal cells via an Egr-1-dependent mechanism is required for osteoclast formation; neutralizing anti-CSF-1 antibody in vivo completely prevents ovariectomy-induced increases in osteoclast number, bone resorption, and bone loss, establishing CSF-1 as a central mediator of estrogen deficiency-induced bone loss.","method":"In vivo antibody neutralization, ovariectomy model, histomorphometry, Egr-1 knockout mice","journal":"The Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — reciprocal genetic (KO) and antibody neutralization in vivo with quantitative bone endpoints","pmids":["10792003"],"is_preprint":false},{"year":2001,"finding":"M-CSF induces phosphorylation of transcription factors Mitf and TFE3 via a MAPK consensus site, triggering their recruitment of the co-activator p300; an unphosphorylatable serine mutant of Mitf fails to support multinucleated osteoclast formation, mimicking the Mitf(mi/mi) osteoclast defect, establishing a M-CSF→MAPK→Mitf/TFE3→p300 signaling axis for osteoclast maturation.","method":"Kinase assay, co-immunoprecipitation with p300, site-directed mutagenesis, osteoclast differentiation assay","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay + co-IP + mutagenesis + genetic rescue, all in single study","pmids":["11684011"],"is_preprint":false},{"year":2001,"finding":"Iba1 (a macrophage/microglia-specific calcium-binding protein) is involved in Rac signaling downstream of M-CSF/CSF-1R; M-CSF activates Fms→PI3K or PLCγ→Rac pathway to drive actin cytoskeleton reorganization underlying microglial activation, proliferation, and migration.","method":"Signaling pathway dissection in microglia, kinase assays, Rac activation assay","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2/3 — pathway mapping with biochemical readouts, single lab","pmids":["12379904"],"is_preprint":false},{"year":2002,"finding":"A 10-base insertion frameshift mutation in the rat Csf1 coding sequence (toothless/tl rat) produces a truncated 41-amino-acid non-functional protein and causes osteopetrosis, confirming that functional CSF-1 is essential for osteoclast differentiation and activation in vivo.","method":"Genomic sequencing of mutant rat Csf1 gene","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with clear molecular mechanism identified","pmids":["12074592"],"is_preprint":false},{"year":2008,"finding":"IL-34 was discovered as a second ligand for the CSF-1 receptor (CSF-1R) by functional screening of the extracellular proteome; IL-34 stimulates monocyte viability through the same receptor as CSF-1.","method":"Functional proteome screen, receptor identification by extracellular domain library screen, viability assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — systematic functional screen with receptor identification validated biochemically","pmids":["18467591"],"is_preprint":false},{"year":2009,"finding":"DUSP5 (a dual-specificity phosphatase) is induced by M-CSF in myeloid cells in an ERK-dependent manner and acts as a negative-feedback regulator of ERK1/2; overexpression of DUSP5 increases M-CSF-dependent proliferation and strongly suppresses macrophage differentiation, demonstrating that sustained MAPK activation is required for commitment to macrophage differentiation.","method":"Subtractive hybridization, MEK inhibitor (U0126), DUSP5 overexpression, proliferation and differentiation assays","journal":"Journal of Leukocyte Biology","confidence":"Medium","confidence_rationale":"Tier 2 — gain-of-function with pharmacological validation of ERK requirement, single lab","pmids":["19801501"],"is_preprint":false},{"year":2010,"finding":"IL-34 and CSF-1 both activate CSF-1R tyrosine phosphorylation and downstream signaling equivalently; transgenic IL-34 expression in a CSF-1-dependent pattern rescues bone, osteoclast, tissue macrophage, and fertility defects of Csf1(op/op) mice, demonstrating functional overlap but different spatiotemporal expression patterns (IL-34 predominates in brain and heart; CSF-1 in uterus and osteoblasts).","method":"CSF-1R phosphorylation assay, macrophage proliferation assay, transgenic rescue of op/op mice, in situ hybridization, qRT-PCR","journal":"Journal of Leukocyte Biology","confidence":"High","confidence_rationale":"Tier 1–2 — receptor biochemistry plus in vivo genetic rescue, multiple orthogonal methods","pmids":["20504948"],"is_preprint":false},{"year":2011,"finding":"CSF-1 has three biologically active isoforms (cell-surface glycoprotein csCSF-1, secreted proteoglycan spCSF-1, secreted glycoprotein sgCSF-1) with distinct roles: csCSF-1 initiates local macrophage activation in the kidney; spCSF-1 is the dominant circulating isoform during advancing lupus nephritis and, together with csCSF-1, drives intrarenal recruitment of Ly6C(hi) monocytes that induce renal parenchymal apoptosis.","method":"Isoform-specific mutant MRL-Fas(lpr) knock-in mice, flow cytometry, histology, TUNEL","journal":"Journal of the American Society of Nephrology","confidence":"High","confidence_rationale":"Tier 2 — isoform-specific knock-in genetic models with defined cellular and molecular readouts","pmids":["21885670"],"is_preprint":false},{"year":2011,"finding":"Conditional deletion of CSF-1 (Meox2Cre-driven) causes osteopetrosis, defective osteocyte maturation, reduced DMP1 expression, impaired bone mineralization, and loss of osteomacs from the endosteal surface, revealing a novel link between CSF-1 and osteocyte survival/function.","method":"Conditional gene knockout (Meox2Cre × CSF-1 floxed), histology, immunostaining, micro-CT","journal":"Bone","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple bone phenotype readouts, identifies novel osteocyte function","pmids":["21958845"],"is_preprint":false},{"year":2006,"finding":"A chromosomal translocation involving chromosome 1p13 fuses CSF1 to COL6A3 (or other partners) in tenosynovial giant cell tumor (TGCT), causing CSF1 overexpression in the minority of neoplastic cells and creating a 'landscape effect' whereby CSF1R-expressing non-neoplastic cells are recruited to form the tumor mass.","method":"FISH, array CGH, expression profiling, IHC on TGCT/PVNS tumor samples","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 2 — direct molecular identification of translocation breakpoint in multiple tumor samples","pmids":["16407111"],"is_preprint":false},{"year":2015,"finding":"After peripheral nerve injury, CSF1 is de novo expressed in injured sensory neurons and transported to the spinal cord, where it activates microglial CSF1R to induce microglial proliferation; sensory-neuron-specific Cre deletion of Csf1 completely prevents nerve injury-induced mechanical hypersensitivity and reduces spinal microglial activation; intrathecal CSF1 alone is sufficient to induce hypersensitivity and microglial proliferation; downstream, DAP12 is required for CSF1R-mediated upregulation of pain-related microglial genes but not proliferation.","method":"Conditional neuron-specific Csf1 KO, intrathecal CSF1 injection, behavioral pain testing, immunostaining, microglial proliferation quantification","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 — conditional KO + intrathecal gain-of-function + DAP12 epistasis, multiple orthogonal approaches","pmids":["26642091"],"is_preprint":false},{"year":2015,"finding":"M-CSF from cancer cells induces fatty acid synthase (FASN) expression in tumor myeloid cells, which activates PPARβ/δ; PPARβ/δ in turn drives IL-10 production that facilitates tumor cell invasion and angiogenesis; myeloid-cell-specific PPARβ/δ knockout impairs tumor growth and can be rescued by wild-type myeloid cell transfer.","method":"Myeloid-specific PPARβ/δ KO mice, adoptive transfer, in vitro M-CSF stimulation, FASN inhibition, IL-10 measurement","journal":"Cell Reports","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO + adoptive transfer + biochemical pathway dissection, single lab","pmids":["25753425"],"is_preprint":false},{"year":2015,"finding":"M-CSF signaling through CSF-1R drives macropinocytosis in macrophages via PI3K (producing PIP3) → PLCγ (generating DAG) → PKC and Ras → macropinosome closure; PLC inhibition blocks M-CSF-induced but not PMA-induced macropinocytosis, and Ras and PKC are required downstream of both stimuli.","method":"Fluorescent lipid probes (live imaging), pharmacological inhibitors (LY294002, U73122, FTS, Calphostin C), Akt inhibitor MK-2206","journal":"Frontiers in Physiology","confidence":"Medium","confidence_rationale":"Tier 2 — live imaging with multiple pharmacological epistasis experiments, single lab","pmids":["25688212"],"is_preprint":false},{"year":2017,"finding":"Lymphatic endothelial cells (LECs) express high levels of M-CSF and promote osteoclast formation and bone resorption; LEC-derived M-CSF activity is neutralized by anti-M-CSF antibody or c-Fms inhibitor Ki20227, and intra-tibial LEC injection in mice causes massive osteolysis that is blocked by Ki20227, establishing M-CSF secretion by LECs as a mechanism of pathological bone destruction in Gorham-Stout disease.","method":"LEC/osteoclast co-culture, neutralizing antibody, small-molecule CSF1R inhibitor, intra-tibial LEC injection, micro-CT, histology","journal":"Journal of Bone and Mineral Research","confidence":"High","confidence_rationale":"Tier 2 — in vitro neutralization + in vivo cell injection model with inhibitor rescue","pmids":["28052488"],"is_preprint":false},{"year":2019,"finding":"Mesothelial cells produce both membrane-bound and secreted CSF1, and this locally produced CSF1 sustains peritoneal macrophage proliferation and survival in the peritoneal cavity.","method":"Conditional CSF1 deletion in mesothelial cells, peritoneal macrophage enumeration, flow cytometry","journal":"European Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — cell-type-specific genetic deletion with defined macrophage proliferation readout","pmids":["31251389"],"is_preprint":false},{"year":2023,"finding":"Bone marrow Adipoq-lineage progenitors (not mature adipocytes) are a major source of CSF1 in bone marrow, producing M-CSF at levels far exceeding osteoblast lineage cells; conditional deletion of Csf1 in Adipoq-lineage progenitors drastically reduces bone marrow macrophages and osteoclasts, causes severe osteopetrosis, and significantly alleviates ovariectomy-induced bone loss.","method":"Adipoq-Cre × Csf1-floxed conditional KO, single-cell RNA sequencing, histology, micro-CT, OVX model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — cell-type-specific conditional KO with scRNA-seq validation and multiple in vivo phenotypes","pmids":["36779851"],"is_preprint":false},{"year":2023,"finding":"Marrow adipogenic lineage precursors (MALPs) are a major mesenchymal source of Csf1 in trabecular bone; MALP-specific Csf1 CKO (Adipoq-Cre) increases femoral trabecular bone mass, reduces osteoclasts in secondary spongiosa, reduces bone marrow macrophages/hematopoietic progenitors, and protects against LPS-induced calvarial osteolysis.","method":"MALP-specific Csf1 conditional KO, TRAP staining, micro-CT, hematopoietic progenitor analysis, LPS-induced osteolysis model","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with multiple skeletal and hematopoietic phenotypes, orthogonal to PMID 36779851","pmids":["36779854"],"is_preprint":false},{"year":2006,"finding":"Cyclophilin A is required for M-CSF-dependent macrophage proliferation; sanglifehrin A (SfA), a cyclophilin A-binding immunosuppressor, arrests macrophages in G1 by inactivating Cdk2, repressing c-myc, and inhibiting phosphorylation of Raf-1 and ERK1/2, demonstrating that the cyclophilin A/Raf-1/MEK/ERK axis is necessary for CSF-1-driven cell cycle progression.","method":"Pharmacological inhibition with SfA, ERK/Raf-1 phosphorylation assays, Cdk2 kinase assay, cell cycle analysis, c-myc Northern blot","journal":"European Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple biochemical assays with pharmacological epistasis, single lab","pmids":["16909430"],"is_preprint":false},{"year":2007,"finding":"miR-17-5p, miR-20a, and miR-106a control monocytopoiesis by targeting AML1 (Runx1) mRNA 3′UTR; their downregulation during monocytic differentiation permits AML1 protein translation, which then drives M-CSF receptor (M-CSFR/CSF1R) transcription; AML1 also transcriptionally inhibits the miR-17-5p/92 cluster promoters, forming a mutual negative feedback loop.","method":"miRNA transfection/anti-miRNA, AML1 siRNA knockdown, luciferase reporter, ChIP for AML1 on miRNA cluster promoters","journal":"Nature Cell Biology","confidence":"High","confidence_rationale":"Tier 2 — siRNA + luciferase + ChIP with reciprocal validation, highly cited","pmids":["17589498"],"is_preprint":false},{"year":2018,"finding":"Systemic administration of neutralizing anti-CSF-1R or anti-CSF-1 monoclonal antibodies inhibits development of inflammatory pain (zymosan, GM-CSF, TNF-induced) and prevents arthritic pain in mice; systemic CSF-1 administration rapidly induces pain and enhances arthritis, demonstrating a peripheral role for CSF-1 in inflammatory pain generation distinct from its central microglial role.","method":"In vivo antibody neutralization, recombinant CSF-1 administration, behavioral pain assays (von Frey), mouse arthritis models","journal":"Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — gain- and loss-of-function in vivo with defined pain readouts, single lab","pmids":["30120124"],"is_preprint":false},{"year":2017,"finding":"Proteasome inhibitors (MG132, bortezomib) accelerate degradation of c-Fms (CSF-1R) in osteoclasts via p38/TACE-mediated regulated intramembrane proteolysis (RIPping), without affecting RANK levels; c-Fms degradation completely blocks M-CSF-mediated signaling and suppresses osteoclast differentiation and bone resorption in vitro and in vivo.","method":"Proteasome inhibitor treatment, p38/TACE inhibitors, immunoblot for c-Fms, M-CSF signaling assays, LPS-induced bone loss model","journal":"International Journal of Molecular Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection with in vitro and in vivo validation","pmids":["28946669"],"is_preprint":false},{"year":1993,"finding":"M-CSF stimulates migration in isolated rat osteoclasts, increasing both the proportion of migrating cells and substrate area covered; this motility-promoting effect is inverse to its inhibitory effect on bone resorption, suggesting M-CSF controls a switch between migratory and resorptive states in osteoclasts.","method":"Time-lapse microscopy of isolated osteoclasts on substrate, M-CSF stimulation dose-response","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — direct live-cell imaging with functional quantification, single lab","pmids":["8216275"],"is_preprint":false}],"current_model":"CSF1 (M-CSF) is a disulfide-linked homodimeric cytokine that exists as membrane-bound, secreted glycoprotein, and proteoglycan isoforms processed from alternatively spliced precursors; it binds and dimerizes the CSF-1R (c-Fms) receptor tyrosine kinase, triggering autophosphorylation at multiple intracellular tyrosines (Y721 recruiting PI3K for chemotaxis, Y807/Y809 controlling a proliferation-versus-differentiation switch via c-Myc and sustained ERK/MAPK signaling), with downstream cascades including Raf-1/MEK/ERK (required for macrophage differentiation and proliferation), PLCγ/DAG/PKC/Ras (driving macropinocytosis), and MAPK-dependent phosphorylation of Mitf/TFE3 transcription factors to recruit p300 for osteoclast maturation; locally produced CSF1 from tissue-resident cells (Adipoq-lineage marrow progenitors, mesothelial cells, injured sensory neurons) controls macrophage and osteoclast homeostasis in a paracrine manner, while injured sensory neuron-derived CSF1 is axonally transported to the spinal cord to activate microglial CSF1R→DAP12 signaling underlying neuropathic pain."},"narrative":{"teleology":[{"year":1985,"claim":"Identification of CSF-1 as a cloneable cytokine and its receptor as the c-Fms proto-oncogene product established the molecular identity of the ligand–receptor pair governing mononuclear phagocyte biology.","evidence":"cDNA cloning with recombinant protein expression in COS cells confirmed biological activity; immunoprecipitation and radioligand binding demonstrated c-Fms is the CSF-1 receptor with intrinsic tyrosine kinase activity","pmids":["2996129","2408759"],"confidence":"High","gaps":["No structural information on how CSF-1 engages its receptor","Downstream signaling pathways unknown"]},{"year":1987,"claim":"Discovery that CSF-1 is synthesized as a transmembrane homodimeric precursor that is proteolytically cleaved to release soluble forms, and that alternative splicing generates distinct isoforms, resolved how one gene produces functionally diverse ligand forms.","evidence":"cDNA cloning of 4-kb and 1.6-kb transcripts, genomic exon mapping, direct protein sequencing, and surface trypsin cleavage experiments in transfected cells","pmids":["3493529","3500041","3039346"],"confidence":"High","gaps":["Functional differences among isoforms in vivo not yet defined","Identity of the physiological membrane protease unknown"]},{"year":1992,"claim":"The crystal structure of the M-CSF homodimer revealed the four-helix-bundle architecture and, together with mutagenesis, pinpointed His-9 and His-15 as critical receptor-contact residues on helix A.","evidence":"X-ray crystallography at 2.5 Å; site-directed mutagenesis (H9A/H15A) with radioreceptor binding and bioactivity assays confirmed direct involvement without structural perturbation","pmids":["1455231","7983059"],"confidence":"High","gaps":["No co-crystal structure of CSF-1 bound to CSF-1R","Receptor dimerization mechanism not yet visualized"]},{"year":1997,"claim":"Systematic mutagenesis of individual CSF-1R autophosphorylation sites delineated a signaling architecture in which Y721 recruits PI3K for motility, Y807/Y809 controls a proliferation-versus-differentiation switch through c-Myc and sustained ERK, and the Raf-1/MEK/ERK cascade is required for macrophage differentiation.","evidence":"Site-directed mutagenesis of CSF-1R tyrosines in FDC-P1 myeloid cells, c-myc overexpression rescue, PI3K co-immunoprecipitation, chemotaxis assays, pharmacological ERK inhibition","pmids":["1833648","8981370","9261328","8981359"],"confidence":"High","gaps":["Quantitative kinetics of phosphosite usage during physiological stimulation unknown","Downstream transcriptional programs beyond c-Myc and immediate-early genes not mapped"]},{"year":2001,"claim":"Identification of the M-CSF→MAPK→Mitf/TFE3→p300 axis explained how CSF-1 drives osteoclast maturation at the transcriptional level, connecting receptor signaling to a known osteoclast transcription factor.","evidence":"In vitro kinase assay, co-immunoprecipitation with p300, Mitf phospho-site mutagenesis, and osteoclast differentiation assay","pmids":["11684011"],"confidence":"High","gaps":["Full repertoire of MAPK-phosphorylated transcription factors downstream of CSF-1 not catalogued","How Mitf phosphorylation cooperates with RANKL-induced NFATc1 unclear"]},{"year":2002,"claim":"The toothless rat frameshift mutation provided definitive genetic proof that loss of functional CSF-1 protein causes osteopetrosis due to osteoclast failure.","evidence":"Genomic sequencing of the Csf1 coding region in the toothless (tl) rat identifying a 10-bp insertion producing a truncated 41-aa non-functional product","pmids":["12074592"],"confidence":"High","gaps":["Hematopoietic and extra-skeletal phenotypes of the tl rat incompletely characterized"]},{"year":2006,"claim":"CSF1 gene translocations in tenosynovial giant cell tumor established CSF1 as an oncogenic driver through a landscape effect, where minority neoplastic cells overexpressing CSF1 recruit CSF1R-positive bystander cells to form the tumor mass.","evidence":"FISH and array CGH identification of chromosome 1p13 translocation fusing CSF1 to COL6A3, expression profiling, and immunohistochemistry on TGCT/PVNS samples","pmids":["16407111"],"confidence":"High","gaps":["Whether CSF1 overexpression alone is sufficient or requires additional cooperating events not tested","Non-tumor landscape effects not explored in other cancers at this point"]},{"year":2008,"claim":"Discovery of IL-34 as a second ligand for CSF-1R redefined the receptor's ligand landscape, raising the question of non-redundant versus overlapping functions of the two ligands.","evidence":"Functional proteome screen identifying IL-34; receptor identification by extracellular domain library screen; monocyte viability assays","pmids":["18467591"],"confidence":"High","gaps":["Structural basis for dual ligand recognition by CSF-1R not resolved","Tissue-specific dominance of CSF-1 vs IL-34 only partially mapped"]},{"year":2011,"claim":"Isoform-specific knock-in mice demonstrated that the three CSF-1 protein isoforms (cell-surface glycoprotein, secreted proteoglycan, secreted glycoprotein) have distinct non-redundant in vivo roles, with the cell-surface form initiating local macrophage activation and the proteoglycan form dominating systemic circulation and monocyte recruitment during lupus nephritis.","evidence":"Isoform-specific mutant MRL-Fas(lpr) knock-in mice with flow cytometry, histology, and TUNEL analysis","pmids":["21885670"],"confidence":"High","gaps":["Whether isoform-specific functions extend to other tissues/disease contexts not determined","Molecular basis for differential tissue distribution of isoforms unknown"]},{"year":2015,"claim":"Sensory neuron-derived CSF1 was established as a critical mediator of neuropathic pain: nerve injury induces de novo CSF1 expression in DRG neurons, and axonally transported CSF1 activates spinal microglial CSF1R→DAP12 signaling to drive mechanical hypersensitivity.","evidence":"Sensory-neuron-specific Csf1 conditional KO, intrathecal CSF1 gain-of-function, DAP12 epistasis, behavioral pain testing","pmids":["26642091"],"confidence":"High","gaps":["Molecular trigger for Csf1 transcriptional induction in injured neurons not identified","Whether CSF1 vs IL-34 contributes differentially to central microglial activation unclear"]},{"year":2015,"claim":"M-CSF-driven macropinocytosis was mechanistically mapped to a PI3K→PLCγ→DAG→PKC/Ras pathway, extending the known signaling repertoire beyond proliferation and differentiation to include bulk fluid uptake.","evidence":"Live imaging with fluorescent lipid probes and sequential pharmacological inhibition (LY294002, U73122, FTS, Calphostin C) in macrophages","pmids":["25688212"],"confidence":"Medium","gaps":["Entirely pharmacological approach; genetic confirmation of each node lacking","Physiological significance of M-CSF-driven macropinocytosis in vivo not tested"]},{"year":2023,"claim":"Two independent studies using Adipoq-Cre conditional Csf1 knockout mice identified bone marrow Adipoq-lineage progenitors (MALPs) as the dominant paracrine source of CSF1 for osteoclast and macrophage homeostasis in the skeletal niche, explaining why the bone compartment is so dependent on CSF1.","evidence":"Adipoq-Cre × Csf1-floxed conditional KO, single-cell RNA-seq, micro-CT, TRAP staining, hematopoietic progenitor analysis, ovariectomy and LPS-induced osteolysis models","pmids":["36779851","36779854"],"confidence":"High","gaps":["Whether other mesenchymal populations compensate over long-term deletion not addressed","Relative contribution of CSF1 vs IL-34 from marrow stroma not quantified"]},{"year":null,"claim":"Key unresolved questions include the structural basis for CSF-1 vs IL-34 recognition by CSF-1R, the identity of the physiological protease(s) that cleave membrane-bound CSF-1 in vivo, and the full transcriptional programs downstream of distinct CSF-1R phosphorylation sites in tissue-specific macrophage populations.","evidence":"","pmids":[],"confidence":"High","gaps":["No co-crystal structure of CSF-1 bound to CSF-1R ectodomain","Physiological sheddase for membrane CSF-1 not genetically identified","Single-cell transcriptomic profiling of CSF-1 vs IL-34 responses in tissue-resident macrophages lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,1,5,6,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[7,11,15]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,21,28]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,2,4,21]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,5,7,11,12,15,24,29]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[7,10,11,12,13,15,26]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[5,11,15,17,22,29]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[8,23,25]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[10,31]}],"complexes":[],"partners":["CSF1R","PI3K","MITF","TFE3","EP300","RAF1","MAPK1","DAP12"],"other_free_text":[]},"mechanistic_narrative":"CSF1 (M-CSF) is a disulfide-linked homodimeric cytokine that exists as membrane-bound, secreted glycoprotein, and secreted proteoglycan isoforms generated by alternative splicing and extracellular proteolytic processing; it signals exclusively through the CSF-1R (c-Fms) receptor tyrosine kinase to govern survival, proliferation, differentiation, and motility of mononuclear phagocytes and osteoclasts [PMID:2408759, PMID:3039346, PMID:3493529]. Ligand-induced CSF-1R autophosphorylation activates divergent intracellular cascades: Y721 recruits PI3K for chemotaxis and macropinocytosis (via PLCγ/DAG/PKC/Ras), Y807/Y809 controls a proliferation-versus-differentiation switch through c-Myc induction and sustained Raf-1/MEK/ERK signaling, and MAPK-dependent phosphorylation of Mitf/TFE3 recruits p300 to drive osteoclast maturation [PMID:1833648, PMID:8981370, PMID:11684011, PMID:25688212]. Paracrine CSF1 production by tissue-specific sources — bone marrow Adipoq-lineage progenitors for osteoclast and macrophage homeostasis, mesothelial cells for peritoneal macrophages, and injured sensory neurons for spinal microglial activation underlying neuropathic pain — establishes CSF1 as a locally regulated master signal for myeloid cell fate across diverse organs [PMID:36779851, PMID:31251389, PMID:26642091]. CSF1 gene translocations causing overexpression drive tenosynovial giant cell tumor through a landscape effect of non-neoplastic CSF1R-positive cell recruitment [PMID:16407111]."},"prefetch_data":{"uniprot":{"accession":"P09603","full_name":"Macrophage colony-stimulating factor 1","aliases":["Lanimostim","Proteoglycan macrophage colony-stimulating factor","PG-M-CSF"],"length_aa":554,"mass_kda":60.2,"function":"Cytokine that plays an essential role in the regulation of survival, proliferation and differentiation of hematopoietic precursor cells, especially mononuclear phagocytes, such as macrophages and monocytes. Promotes the release of pro-inflammatory chemokines, and thereby plays an important role in innate immunity and in inflammatory processes. Plays an important role in the regulation of osteoclast proliferation and differentiation, the regulation of bone resorption, and is required for normal bone development. Required for normal male and female fertility. 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  \"pmids\": [\"1833648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Structure-function mutagenesis of recombinant human M-CSF identified that residues His-9 and His-15 in the NH2-terminal region (helix A region) are critical for receptor binding; substitution of both with alanine (H9A/H15A) caused a 9,100-fold decrease in specific bioactivity with an equivalent reduction in receptor affinity, while X-ray crystallography confirmed no global structural change, implicating these histidines in the receptor-binding interface.\",\n      \"method\": \"Site-directed mutagenesis, bioactivity assay, receptor-binding affinity assay, X-ray crystallography at 2.5 Å resolution\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis, structural validation, and functional assay in one study\",\n      \"pmids\": [\"7983059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The Y807 autophosphorylation site of the M-CSF receptor (c-Fms) is essential for differentiation signaling: mutation of Y807 totally abrogates M-CSF-induced macrophage differentiation of FDC-P1 cells and conversely increases the rate of M-CSF-dependent proliferation, suggesting Y807 controls a switch between growth and differentiation. Y697, Y706, and Y721 (kinase insert region) augment but are not essential for differentiation.\",\n      \"method\": \"Site-directed mutagenesis of Fms autophosphorylation sites, proliferation and differentiation assays in myeloid FDC-P1 cells\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with clear functional readouts for multiple sites\",\n      \"pmids\": [\"8981370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Phosphorylation of CSF-1R at Y721 in the kinase insert domain mediates association of PI3K with the receptor to activate the major motility signaling pathways in macrophages; this single residue is specifically required for CSF-1-induced macrophage chemotaxis.\",\n      \"method\": \"Receptor mutagenesis, PI3K co-association assay, macrophage migration assay\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — mutagenesis linking specific phosphotyrosine to PI3K binding and migration, corroborated by review of primary data\",\n      \"pmids\": [\"9261328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"M-CSF induces phosphorylation of transcription factors Mitf and TFE3 via a conserved MAPK consensus site, triggering their recruitment of co-activator p300; an unphosphorylatable mutant at the MAPK serine is specifically deficient in forming multinucleated osteoclasts, identifying a CSF-1R → MAPK → Mitf/TFE3 → p300 pathway that coordinates cytokine signaling with osteoclast maturation.\",\n      \"method\": \"Kinase assay, co-activator recruitment assay (p300 interaction), site-directed mutagenesis of MAPK site in Mitf/TFE3, osteoclast differentiation assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — biochemical phosphorylation assay, mutagenesis, and cell differentiation phenotype with multiple orthogonal methods\",\n      \"pmids\": [\"11684011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"M-CSF directly stimulates migration of isolated rat osteoclasts in vitro, predominantly by increasing the proportion of osteoclasts showing motility and the area of substrate covered; this migratory response is the inverse of M-CSF's inhibitory effect on bone resorption, suggesting migration and resorption are alternative osteoclast behaviors regulated by M-CSF.\",\n      \"method\": \"Isolated osteoclast migration assay in vitro\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct in vitro migration assay with quantitative readout, single study\",\n      \"pmids\": [\"8216275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"In vivo neutralization of M-CSF with an antibody completely prevents the rise in osteoclast number, bone resorption, and bone loss following ovariectomy in mice; Egr-1-deficient mice (with maximally stimulated stromal M-CSF production) show increased bone resorption that is also rescued by anti-M-CSF antibody, placing M-CSF downstream of Egr-1 in the estrogen-deficiency pathway of bone loss.\",\n      \"method\": \"In vivo antibody neutralization, ovariectomy model, Egr-1 knockout mice, bone histomorphometry\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (Egr-1 KO) combined with in vivo antibody rescue, multiple readouts\",\n      \"pmids\": [\"10792003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A 10-base insertion frameshift mutation in the rat Csf1 coding sequence, producing a stop codon after only 9 amino acids of the wild-type protein, causes osteopetrosis in toothless (tl/tl) rats due to inability to produce functional CSF-1, demonstrating that CSF-1 is required for osteoclast differentiation and bone resorption in vivo.\",\n      \"method\": \"Sequencing of rat Csf1 coding region, genetic linkage, phenotypic characterization of tl/tl rats\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function mutation identified with clear mechanistic link to osteoclast deficiency and osteopetrosis phenotype\",\n      \"pmids\": [\"12074592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"M-CSF activates its receptor (Fms/CSF-1R tyrosine kinase) in microglia, sequentially activating PI3K and PLCγ, leading to activation of the small GTPase Rac; Rac then regulates actin cytoskeleton reorganization underlying microglial morphological transformation, proliferation, migration, and phagocytosis. Iba1, a macrophage/microglia-specific calcium-binding protein, participates in a Rac activation pathway downstream of PLCγ.\",\n      \"method\": \"Signal transduction pathway analysis in microglia, Rac activation assay, Iba1 functional studies\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — pathway placement with biochemical evidence, single study\",\n      \"pmids\": [\"12379904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Recombinant human M-CSF induces human monocytes to produce and release biologically active VEGF in a dose-dependent manner; supernatants from M-CSF-stimulated monocytes induce HUVEC tube formation, an effect blocked by anti-VEGF antibody, establishing that M-CSF drives monocyte-derived angiogenesis via VEGF production.\",\n      \"method\": \"ELISA for VEGF, HUVEC tube formation assay, anti-VEGF neutralizing antibody blockade\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assay with neutralizing antibody validation, single lab\",\n      \"pmids\": [\"12928417\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"M-CSF-induced macrophage differentiation of myeloid progenitors requires sustained ERK1/2 MAPK activation; the dual-specificity phosphatase DUSP5 is induced by M-CSF in a MAPK-dependent manner and acts as a negative-feedback regulator of ERK1/2. Overexpression of DUSP5 in FD-Fms cells increases M-CSF-dependent proliferation and strongly decreases macrophage differentiation, while favoring granulocytic differentiation in multipotent cells.\",\n      \"method\": \"Suppressive subtractive hybridization (SSH), DUSP5 overexpression, MEK inhibitor (U0126), proliferation and differentiation assays\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with pharmacological control, multiple cell outcomes measured\",\n      \"pmids\": [\"19801501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The three CSF-1 isoforms (cell surface glycoprotein csCSF-1, secreted proteoglycan spCSF-1, and secreted glycoprotein sgCSF-1) have distinct biological roles in lupus nephritis: csCSF-1 initiates and promotes local macrophage activation within the kidney, while spCSF-1 is the predominant isoform responsible for increasing circulating CSF-1 levels with advancing nephritis; both isoforms promote intrarenal recruitment of Ly6C-hi monocytes that induce apoptosis of renal parenchyma.\",\n      \"method\": \"Isoform-specific mutant MRL-Fas(lpr) mouse construction, flow cytometry, histology, monocyte recruitment assays\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetically distinct mouse lines with isoform-specific analysis, replicated across disease stages\",\n      \"pmids\": [\"21885670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Cre-mediated ubiquitous deletion of CSF-1 (using Meox2Cre) causes osteopetrosis, defective osteocyte maturation, reduced bone mineralization, and reduced endosteal osteomacs, demonstrating that CSF-1 is required not only for osteoclastogenesis but also for osteocyte survival/function essential for maintaining bone mass.\",\n      \"method\": \"Conditional knockout (Meox2Cre x CSF-1 floxed mice), histomorphometry, DMP1 expression analysis, macrophage density quantification\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with multiple skeletal and cellular phenotypic readouts\",\n      \"pmids\": [\"21958845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CSF-1R is expressed mainly on Paneth cells (PCs) in small intestinal crypts; genetic deletion of CSF-1R or CSF-1 mutation causes loss of mature PCs, reduced crypt proliferation, and decreased expression of intestinal stem cell markers (Lgr5, Bmi1, CD24, Olfm4); inducible GI-specific Csf1r deletion in adult mice and SI organoid culture confirm the defect in PC production is intrinsic to epithelial cells, establishing that CSF-1R directly supports PC maturation and thus fashions the intestinal stem cell niche.\",\n      \"method\": \"Germline KO, inducible GI-specific Cre deletion, SI organoid culture, immunofluorescence, gene expression analysis\",\n      \"journal\": \"Stem cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models plus organoid validation with multiple stem cell markers\",\n      \"pmids\": [\"23314290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"During M-CSF-stimulated macropinocytosis in macrophages, PI3K generates PIP3 in membrane cups prior to DAG appearance; PLC acts downstream of PI3K and upstream of PKC and Ras; PKC, Ras, and PLC are each required for macropinosome closure in response to M-CSF, while Akt is not required despite being activated.\",\n      \"method\": \"Live-cell imaging with fluorescent lipid probes, pharmacological inhibitors (U73122 for PLC, MK-2206 for Akt, FTS for Ras, Calphostin C for PKC), comparison with PMA stimulation\",\n      \"journal\": \"Frontiers in physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors with fluorescent readouts, single study\",\n      \"pmids\": [\"25688212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"M-CSF secreted from tumor (Lewis lung carcinoma) cells induces fatty acid synthase (FASN) in myeloid stromal cells, which activates PPARβ/δ; PPARβ/δ drives IL-10 production, facilitating tumor cell invasion and angiogenesis. Myeloid-cell-specific PPARβ/δ knockout impairs tumor growth, restored by adoptive transfer of wild-type myeloid cells.\",\n      \"method\": \"Myeloid-specific PPARβ/δ KO, adoptive transfer, in vitro and in vivo tumor assays, FASN/IL-10 measurement\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with adoptive transfer rescue and multiple mechanistic readouts, single lab\",\n      \"pmids\": [\"25753425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Lymphatic endothelial cells (LECs) produce high levels of M-CSF (but not RANKL, IL-6, or TNF) and thereby promote osteoclast formation and bone resorption in vitro and in vivo; LEC-mediated osteoclastogenesis and bone destruction are blocked by an M-CSF neutralizing antibody or c-Fms kinase inhibitor Ki20227, establishing M-CSF as the mechanistic effector of LEC-driven osteolysis.\",\n      \"method\": \"Co-culture osteoclast formation assay, M-CSF neutralizing antibody, Ki20227 c-Fms inhibitor, intra-tibial LEC injection mouse model, micro-CT, ELISA\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro blockade validated by in vivo model with multiple readouts, clear mechanistic attribution\",\n      \"pmids\": [\"28052488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Proteasome inhibitors (MG132, bortezomib) accelerate degradation of the M-CSF receptor c-Fms via p38/TACE-mediated regulated intramembrane proteolysis (RIPping), completely blocking M-CSF-mediated intracellular signaling and osteoclast differentiation; specific p38 and TACE inhibitors restore c-Fms levels, confirming this mechanism.\",\n      \"method\": \"Proteasome inhibitor treatment, p38/TACE inhibitor rescue, Western blot for c-Fms, osteoclast differentiation assay, LPS-induced bone loss mouse model\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological inhibition with rescue experiments and in vivo validation\",\n      \"pmids\": [\"28946669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mesothelial cells produce both membrane-bound and secreted forms of CSF1 that sustain peritoneal macrophage proliferation; the identity of CSF1-producing mesothelial cells as the key niche for peritoneal macrophage maintenance was established by localization and functional studies.\",\n      \"method\": \"CSF1 expression analysis in mesothelial cells, peritoneal macrophage localization and co-localization studies, CSF1 isoform characterization\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — direct localization with functional consequence, single study\",\n      \"pmids\": [\"31251389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Bone marrow Adipoq-lineage progenitors (but not mature adipocytes or peripheral adipose tissue cells) are a major cellular source of M-CSF in bone marrow, producing M-CSF at much higher levels than osteoblast lineage cells; conditional deletion of Csf1 in Adipoq-lineage progenitors drastically reduces bone marrow macrophages and osteoclasts, causing severe osteopetrosis, and also alleviates ovariectomy-induced osteoporosis.\",\n      \"method\": \"Cell-specific conditional knockout (Adipoq-Cre x Csf1-flox), bone marrow macrophage and osteoclast quantification, micro-CT, single-cell transcriptomics, human bone marrow validation\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent groups (PMIDs 36779851 and 36779854) with conditional KO, multiple phenotypic readouts, and human tissue validation\",\n      \"pmids\": [\"36779851\", \"36779854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cyclophilin A (CypA) is required for M-CSF-dependent macrophage proliferation; sanglifehrin A (SfA), a CypA-binding immunosuppressor, arrests M-CSF-stimulated macrophages in G1 by inhibiting Raf-1 and ERK1/2 phosphorylation, reducing c-myc expression, and inactivating Cdk2 activity, without affecting cell viability.\",\n      \"method\": \"Pharmacological inhibition with SfA, kinase activity assays (Raf-1, ERK1/2, Cdk2), cell cycle analysis, c-myc expression\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical readouts with pharmacological inhibitor, single lab\",\n      \"pmids\": [\"16909430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"M-CSF pretreatment of human monocytes augments tumoricidal activity induced by LPS, IFN-γ, and other agents; enhanced killing is directly correlated with increased TNF production, and TNF antiserum completely blocks M-CSF-mediated increases in tumor cell lysis, establishing TNF as the effector molecule downstream of M-CSF in monocyte tumoricidal activity.\",\n      \"method\": \"51Cr-release cytotoxicity assay, TNF antiserum neutralization, TNF ELISA\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — neutralizing antibody identifies downstream effector with multiple activating conditions tested\",\n      \"pmids\": [\"3053901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"M-CSF induces mRNA and protein expression of connective tissue growth factor (CTGF/CCN2) in human chondrocytic cells and rat primary chondrocytes, and can autoactivate its own gene (m-csf) in a positive feedback loop; M-CSF also promotes proteoglycan synthesis in chondrocytes, suggesting a role in cartilage matrix maintenance.\",\n      \"method\": \"RT-PCR, Western blot, CTGF/CCN2 ELISA, proteoglycan synthesis assay in human and rat chondrocytes\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — multiple readouts but single lab, no genetic validation\",\n      \"pmids\": [\"15820145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"M-CSF binds to its receptor on mouse calvarial osteoclasts, stimulates protein tyrosine phosphorylation, increases production of oxygen-derived free radicals, and enhances bone resorption in calvarial explants, demonstrating direct activation of osteoclast function by M-CSF through receptor tyrosine kinase signaling.\",\n      \"method\": \"Radiolabeled ligand binding autoradiography, immunostaining for tyrosine phosphorylation, free radical assay, calvarial explant bone resorption assay\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in osteoclast model, single study\",\n      \"pmids\": [\"8726394\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Systemic administration of neutralizing anti-CSF-1R or anti-CSF-1 antibodies inhibits the development of inflammatory pain induced by zymosan, GM-CSF, and TNF in mice, and prevents (but does not reverse) arthritic pain and disease; systemic CSF-1 administration rapidly induces pain and enhances arthritis via a pathway distinct from GM-CSF and TNF, identifying a peripheral role for CSF-1 in inflammatory pain.\",\n      \"method\": \"Systemic antibody neutralization of CSF-1R/CSF-1, zymosan/GM-CSF/TNF inflammatory pain models, arthritis models, recombinant CSF-1 administration\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple models with both neutralization and administration experiments, single lab\",\n      \"pmids\": [\"30120124\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CSF1 (M-CSF) is a homodimeric cytokine that signals exclusively through its receptor tyrosine kinase CSF-1R (c-Fms), inducing receptor dimerization and autophosphorylation at multiple intracellular tyrosines (including Y721 for PI3K/motility, Y807/Y809 for differentiation vs. proliferation switching, and others), which recruits downstream effectors (PI3K, PLCγ, Grb2, Shc, MAPK/ERK, Rac, Raf-1/MEK/ERK cascade, and STAT factors) to drive survival, proliferation, differentiation, and chemotaxis of mononuclear phagocytes; CSF1 is produced by mesenchymal cells (including bone marrow Adipoq-lineage progenitors, mesothelial cells, and osteoblasts) to maintain tissue-resident macrophage and osteoclast populations, and its three isoforms (cell-surface, secreted proteoglycan, and secreted glycoprotein) have distinct roles in local versus systemic macrophage regulation.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1985,\n      \"finding\": \"The c-fms proto-oncogene product is the receptor for CSF-1 (M-CSF); the 165 kDa murine c-fms glycoprotein specifically binds CSF-1 and exhibits ligand-dependent tyrosine kinase activity and tyrosine autophosphorylation in membrane preparations.\",\n      \"method\": \"Immunoprecipitation with anti-v-fms antisera, radioligand binding with 125I-CSF-1, and in vitro tyrosine kinase assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus receptor binding, foundational paper with >1500 citations\",\n      \"pmids\": [\"2408759\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1985,\n      \"finding\": \"Molecular cloning of a CSF-1 cDNA encoding a 224-amino-acid mature polypeptide (plus 32-aa leader) that directs synthesis of biologically active CSF-1 in COS cells; multiple mRNA species arise from a single-copy gene.\",\n      \"method\": \"cDNA cloning, COS-cell expression, radioreceptor assay, macrophage colony assay, antibody neutralization\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted biological activity from recombinant protein with multiple validation assays\",\n      \"pmids\": [\"2996129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"A 4-kb CSF-1 cDNA encodes a longer 522-amino-acid precursor containing a C-terminal extension not found in the 1.6-kb cDNA product; both isoforms are structurally and functionally equivalent, arising from alternative splicing of the CSF-1 pre-mRNA.\",\n      \"method\": \"cDNA cloning, direct protein sequencing, mammalian cell expression\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct structural analysis plus expression of recombinant protein\",\n      \"pmids\": [\"3493529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"Human CSF-1 gene contains 10 exons spanning 20 kb; alternative splicing at exon 6 and alternative 3′ noncoding exons produce transcripts encoding either 224 or 522 amino-acid forms of CSF-1.\",\n      \"method\": \"Genomic cloning, RNA analysis, exon mapping\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct gene structure determination with functional implications for isoform production\",\n      \"pmids\": [\"3500041\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"CSF-1 is synthesized as an integral transmembrane homodimeric glycoprotein (disulfide-linked) on the cell surface; extracellular proteolysis by trypsin-like proteases cleaves this membrane-bound precursor to release the soluble secreted form. Autocrine CSF-1/c-fms co-expression transforms NIH 3T3 cells.\",\n      \"method\": \"Cotransfection of CSF-1 and c-fms genes, surface trypsin cleavage, receptor downmodulation assays, transformation assay\",\n      \"journal\": \"Molecular and Cellular Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution of membrane processing and autocrine signaling with structural validation\",\n      \"pmids\": [\"3039346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1986,\n      \"finding\": \"CSF-1 regulates survival, proliferation, and differentiation of mononuclear phagocytes exclusively via a cell-surface receptor (165 kDa glycoprotein) that undergoes CSF-1-dependent tyrosine autophosphorylation; receptor levels increase on CFU-C just before differentiation to mononuclear phagocytes, marking lineage determination.\",\n      \"method\": \"Purified receptor characterization, tyrosine kinase assay, developmental receptor expression analysis\",\n      \"journal\": \"Ciba Foundation symposium\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — purified receptor biochemistry with functional validation\",\n      \"pmids\": [\"3015514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"X-ray crystal structure of recombinant human M-CSF dimer at 2.5 Å reveals two four-helix bundles laid end-to-end with an inter-chain disulfide bond; individual monomers share structural similarity with GM-CSF and growth hormone, suggesting common receptor-binding determinants.\",\n      \"method\": \"X-ray crystallography at 2.5 Å resolution\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional implications, >160 citations\",\n      \"pmids\": [\"1455231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Mutation of autophosphorylation site Y809 (Phe substitution) in CSF-1R does not reduce kinase activity, PI3K binding, or immediate-early gene (c-fos, junB) induction, but abolishes CSF-1-dependent mitogenesis and c-myc induction; enforced c-myc expression rescues proliferation, demonstrating a bifurcation of signaling pathways at the receptor level with c-Myc as a central mitogenic mediator downstream of Y809.\",\n      \"method\": \"Site-directed mutagenesis of CSF-1R Y809, serum-free growth assay, colony assay, Northern blot for c-myc, c-myc overexpression rescue\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis plus epistasis rescue experiment, highly cited foundational paper\",\n      \"pmids\": [\"1833648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"CSF-1 gene expression is induced in vascular endothelial and smooth muscle cells by IL-1α, TNF-α, and LPS; locally produced CSF-1 promotes macrophage scavenger receptor and apolipoprotein E mRNA accumulation in monocytes, linking vascular CSF-1 production to macrophage foam cell development in atherosclerosis.\",\n      \"method\": \"Northern blot, immunostaining, ELISA, PCR on human/rabbit atheromata, monocyte culture\",\n      \"journal\": \"The American Journal of Pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods in both cultured cells and tissue, single lab\",\n      \"pmids\": [\"1739124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Structure-function analysis of recombinant human M-CSF by site-directed mutagenesis identifies residues His-9 and His-15 in the N-terminal region (helix A) as critical for receptor binding; double mutation H9A/H15A reduces bioactivity 9,100-fold and receptor affinity equivalently; X-ray crystallography at 2.5 Å confirms no structural change, indicating direct involvement in receptor contact.\",\n      \"method\": \"Site-directed mutagenesis, radioreceptor binding assay, bioactivity assay, X-ray crystallography at 2.5 Å\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis + receptor binding + crystal structure in single study\",\n      \"pmids\": [\"7983059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSF-1 stimulates macrophage proliferation through signaling cascades that include PI3K, ERK1/2, cyclin D1/D2, cdk4, Rb phosphorylation, and E2F activation; IFN-α/β acts as an endogenous inhibitor of CSF-1-driven cell cycle progression in bone marrow-derived macrophages, acting at least partly via down-regulation of c-myc and cyclin D.\",\n      \"method\": \"Pharmacological inhibitors, cyclin/CDK immunoprecipitation kinase assays, Northern blot, knockout macrophages, cell-cycle analysis\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays with genetic controls, single lab\",\n      \"pmids\": [\"8981359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSF-1R autophosphorylation site Y807 (murine numbering) is essential for macrophage differentiation signaling and its mutation totally abrogates differentiation of FDC-P1 myeloid cells while increasing proliferation, suggesting Y807 controls a proliferation/differentiation switch; sites Y697, Y706, Y721 in the kinase insert augment but are not essential for differentiation.\",\n      \"method\": \"Site-directed mutagenesis of individual CSF-1R tyrosines, differentiation and proliferation assays in FDC-P1 myeloid cells\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic mutagenesis with functional readout, single lab\",\n      \"pmids\": [\"8981370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSF-1R phosphorylation of Y721 in the kinase insert domain is the primary site mediating association with PI3K, which activates the major macrophage motility signaling pathways.\",\n      \"method\": \"Receptor mutagenesis, phosphotyrosine co-immunoprecipitation with p85 PI3K subunit, chemotaxis assays\",\n      \"journal\": \"International journal of cell biology (review citing original data)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — receptor mutagenesis + PI3K co-IP, summarized in multiple review contexts\",\n      \"pmids\": [\"22505929\", \"9261328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSF-1 stimulates macrophage proliferation through the Raf-1/MEK/ERK pathway; downstream, ERK activation is required for macrophage differentiation. New myeloid-specific substrate p150 (Shc/Grb2 complex partner via PTB domain) is identified as a CSF-1R signaling component specific to hematopoietic cells.\",\n      \"method\": \"Co-immunoprecipitation, tyrosine phosphorylation assays, cDNA cloning of p150\",\n      \"journal\": \"Molecular reproduction and development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — co-IP and phosphorylation data in multiple hematopoietic cell lines\",\n      \"pmids\": [\"8981370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CSF-1 produced by estrogen-deficient stromal cells via an Egr-1-dependent mechanism is required for osteoclast formation; neutralizing anti-CSF-1 antibody in vivo completely prevents ovariectomy-induced increases in osteoclast number, bone resorption, and bone loss, establishing CSF-1 as a central mediator of estrogen deficiency-induced bone loss.\",\n      \"method\": \"In vivo antibody neutralization, ovariectomy model, histomorphometry, Egr-1 knockout mice\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal genetic (KO) and antibody neutralization in vivo with quantitative bone endpoints\",\n      \"pmids\": [\"10792003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"M-CSF induces phosphorylation of transcription factors Mitf and TFE3 via a MAPK consensus site, triggering their recruitment of the co-activator p300; an unphosphorylatable serine mutant of Mitf fails to support multinucleated osteoclast formation, mimicking the Mitf(mi/mi) osteoclast defect, establishing a M-CSF→MAPK→Mitf/TFE3→p300 signaling axis for osteoclast maturation.\",\n      \"method\": \"Kinase assay, co-immunoprecipitation with p300, site-directed mutagenesis, osteoclast differentiation assay\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay + co-IP + mutagenesis + genetic rescue, all in single study\",\n      \"pmids\": [\"11684011\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Iba1 (a macrophage/microglia-specific calcium-binding protein) is involved in Rac signaling downstream of M-CSF/CSF-1R; M-CSF activates Fms→PI3K or PLCγ→Rac pathway to drive actin cytoskeleton reorganization underlying microglial activation, proliferation, and migration.\",\n      \"method\": \"Signaling pathway dissection in microglia, kinase assays, Rac activation assay\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — pathway mapping with biochemical readouts, single lab\",\n      \"pmids\": [\"12379904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A 10-base insertion frameshift mutation in the rat Csf1 coding sequence (toothless/tl rat) produces a truncated 41-amino-acid non-functional protein and causes osteopetrosis, confirming that functional CSF-1 is essential for osteoclast differentiation and activation in vivo.\",\n      \"method\": \"Genomic sequencing of mutant rat Csf1 gene\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with clear molecular mechanism identified\",\n      \"pmids\": [\"12074592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IL-34 was discovered as a second ligand for the CSF-1 receptor (CSF-1R) by functional screening of the extracellular proteome; IL-34 stimulates monocyte viability through the same receptor as CSF-1.\",\n      \"method\": \"Functional proteome screen, receptor identification by extracellular domain library screen, viability assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic functional screen with receptor identification validated biochemically\",\n      \"pmids\": [\"18467591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"DUSP5 (a dual-specificity phosphatase) is induced by M-CSF in myeloid cells in an ERK-dependent manner and acts as a negative-feedback regulator of ERK1/2; overexpression of DUSP5 increases M-CSF-dependent proliferation and strongly suppresses macrophage differentiation, demonstrating that sustained MAPK activation is required for commitment to macrophage differentiation.\",\n      \"method\": \"Subtractive hybridization, MEK inhibitor (U0126), DUSP5 overexpression, proliferation and differentiation assays\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function with pharmacological validation of ERK requirement, single lab\",\n      \"pmids\": [\"19801501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"IL-34 and CSF-1 both activate CSF-1R tyrosine phosphorylation and downstream signaling equivalently; transgenic IL-34 expression in a CSF-1-dependent pattern rescues bone, osteoclast, tissue macrophage, and fertility defects of Csf1(op/op) mice, demonstrating functional overlap but different spatiotemporal expression patterns (IL-34 predominates in brain and heart; CSF-1 in uterus and osteoblasts).\",\n      \"method\": \"CSF-1R phosphorylation assay, macrophage proliferation assay, transgenic rescue of op/op mice, in situ hybridization, qRT-PCR\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — receptor biochemistry plus in vivo genetic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"20504948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"CSF-1 has three biologically active isoforms (cell-surface glycoprotein csCSF-1, secreted proteoglycan spCSF-1, secreted glycoprotein sgCSF-1) with distinct roles: csCSF-1 initiates local macrophage activation in the kidney; spCSF-1 is the dominant circulating isoform during advancing lupus nephritis and, together with csCSF-1, drives intrarenal recruitment of Ly6C(hi) monocytes that induce renal parenchymal apoptosis.\",\n      \"method\": \"Isoform-specific mutant MRL-Fas(lpr) knock-in mice, flow cytometry, histology, TUNEL\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — isoform-specific knock-in genetic models with defined cellular and molecular readouts\",\n      \"pmids\": [\"21885670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Conditional deletion of CSF-1 (Meox2Cre-driven) causes osteopetrosis, defective osteocyte maturation, reduced DMP1 expression, impaired bone mineralization, and loss of osteomacs from the endosteal surface, revealing a novel link between CSF-1 and osteocyte survival/function.\",\n      \"method\": \"Conditional gene knockout (Meox2Cre × CSF-1 floxed), histology, immunostaining, micro-CT\",\n      \"journal\": \"Bone\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple bone phenotype readouts, identifies novel osteocyte function\",\n      \"pmids\": [\"21958845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"A chromosomal translocation involving chromosome 1p13 fuses CSF1 to COL6A3 (or other partners) in tenosynovial giant cell tumor (TGCT), causing CSF1 overexpression in the minority of neoplastic cells and creating a 'landscape effect' whereby CSF1R-expressing non-neoplastic cells are recruited to form the tumor mass.\",\n      \"method\": \"FISH, array CGH, expression profiling, IHC on TGCT/PVNS tumor samples\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct molecular identification of translocation breakpoint in multiple tumor samples\",\n      \"pmids\": [\"16407111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"After peripheral nerve injury, CSF1 is de novo expressed in injured sensory neurons and transported to the spinal cord, where it activates microglial CSF1R to induce microglial proliferation; sensory-neuron-specific Cre deletion of Csf1 completely prevents nerve injury-induced mechanical hypersensitivity and reduces spinal microglial activation; intrathecal CSF1 alone is sufficient to induce hypersensitivity and microglial proliferation; downstream, DAP12 is required for CSF1R-mediated upregulation of pain-related microglial genes but not proliferation.\",\n      \"method\": \"Conditional neuron-specific Csf1 KO, intrathecal CSF1 injection, behavioral pain testing, immunostaining, microglial proliferation quantification\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO + intrathecal gain-of-function + DAP12 epistasis, multiple orthogonal approaches\",\n      \"pmids\": [\"26642091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"M-CSF from cancer cells induces fatty acid synthase (FASN) expression in tumor myeloid cells, which activates PPARβ/δ; PPARβ/δ in turn drives IL-10 production that facilitates tumor cell invasion and angiogenesis; myeloid-cell-specific PPARβ/δ knockout impairs tumor growth and can be rescued by wild-type myeloid cell transfer.\",\n      \"method\": \"Myeloid-specific PPARβ/δ KO mice, adoptive transfer, in vitro M-CSF stimulation, FASN inhibition, IL-10 measurement\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO + adoptive transfer + biochemical pathway dissection, single lab\",\n      \"pmids\": [\"25753425\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"M-CSF signaling through CSF-1R drives macropinocytosis in macrophages via PI3K (producing PIP3) → PLCγ (generating DAG) → PKC and Ras → macropinosome closure; PLC inhibition blocks M-CSF-induced but not PMA-induced macropinocytosis, and Ras and PKC are required downstream of both stimuli.\",\n      \"method\": \"Fluorescent lipid probes (live imaging), pharmacological inhibitors (LY294002, U73122, FTS, Calphostin C), Akt inhibitor MK-2206\",\n      \"journal\": \"Frontiers in Physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — live imaging with multiple pharmacological epistasis experiments, single lab\",\n      \"pmids\": [\"25688212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Lymphatic endothelial cells (LECs) express high levels of M-CSF and promote osteoclast formation and bone resorption; LEC-derived M-CSF activity is neutralized by anti-M-CSF antibody or c-Fms inhibitor Ki20227, and intra-tibial LEC injection in mice causes massive osteolysis that is blocked by Ki20227, establishing M-CSF secretion by LECs as a mechanism of pathological bone destruction in Gorham-Stout disease.\",\n      \"method\": \"LEC/osteoclast co-culture, neutralizing antibody, small-molecule CSF1R inhibitor, intra-tibial LEC injection, micro-CT, histology\",\n      \"journal\": \"Journal of Bone and Mineral Research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro neutralization + in vivo cell injection model with inhibitor rescue\",\n      \"pmids\": [\"28052488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mesothelial cells produce both membrane-bound and secreted CSF1, and this locally produced CSF1 sustains peritoneal macrophage proliferation and survival in the peritoneal cavity.\",\n      \"method\": \"Conditional CSF1 deletion in mesothelial cells, peritoneal macrophage enumeration, flow cytometry\",\n      \"journal\": \"European Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific genetic deletion with defined macrophage proliferation readout\",\n      \"pmids\": [\"31251389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Bone marrow Adipoq-lineage progenitors (not mature adipocytes) are a major source of CSF1 in bone marrow, producing M-CSF at levels far exceeding osteoblast lineage cells; conditional deletion of Csf1 in Adipoq-lineage progenitors drastically reduces bone marrow macrophages and osteoclasts, causes severe osteopetrosis, and significantly alleviates ovariectomy-induced bone loss.\",\n      \"method\": \"Adipoq-Cre × Csf1-floxed conditional KO, single-cell RNA sequencing, histology, micro-CT, OVX model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — cell-type-specific conditional KO with scRNA-seq validation and multiple in vivo phenotypes\",\n      \"pmids\": [\"36779851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Marrow adipogenic lineage precursors (MALPs) are a major mesenchymal source of Csf1 in trabecular bone; MALP-specific Csf1 CKO (Adipoq-Cre) increases femoral trabecular bone mass, reduces osteoclasts in secondary spongiosa, reduces bone marrow macrophages/hematopoietic progenitors, and protects against LPS-induced calvarial osteolysis.\",\n      \"method\": \"MALP-specific Csf1 conditional KO, TRAP staining, micro-CT, hematopoietic progenitor analysis, LPS-induced osteolysis model\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with multiple skeletal and hematopoietic phenotypes, orthogonal to PMID 36779851\",\n      \"pmids\": [\"36779854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cyclophilin A is required for M-CSF-dependent macrophage proliferation; sanglifehrin A (SfA), a cyclophilin A-binding immunosuppressor, arrests macrophages in G1 by inactivating Cdk2, repressing c-myc, and inhibiting phosphorylation of Raf-1 and ERK1/2, demonstrating that the cyclophilin A/Raf-1/MEK/ERK axis is necessary for CSF-1-driven cell cycle progression.\",\n      \"method\": \"Pharmacological inhibition with SfA, ERK/Raf-1 phosphorylation assays, Cdk2 kinase assay, cell cycle analysis, c-myc Northern blot\",\n      \"journal\": \"European Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple biochemical assays with pharmacological epistasis, single lab\",\n      \"pmids\": [\"16909430\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"miR-17-5p, miR-20a, and miR-106a control monocytopoiesis by targeting AML1 (Runx1) mRNA 3′UTR; their downregulation during monocytic differentiation permits AML1 protein translation, which then drives M-CSF receptor (M-CSFR/CSF1R) transcription; AML1 also transcriptionally inhibits the miR-17-5p/92 cluster promoters, forming a mutual negative feedback loop.\",\n      \"method\": \"miRNA transfection/anti-miRNA, AML1 siRNA knockdown, luciferase reporter, ChIP for AML1 on miRNA cluster promoters\",\n      \"journal\": \"Nature Cell Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — siRNA + luciferase + ChIP with reciprocal validation, highly cited\",\n      \"pmids\": [\"17589498\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Systemic administration of neutralizing anti-CSF-1R or anti-CSF-1 monoclonal antibodies inhibits development of inflammatory pain (zymosan, GM-CSF, TNF-induced) and prevents arthritic pain in mice; systemic CSF-1 administration rapidly induces pain and enhances arthritis, demonstrating a peripheral role for CSF-1 in inflammatory pain generation distinct from its central microglial role.\",\n      \"method\": \"In vivo antibody neutralization, recombinant CSF-1 administration, behavioral pain assays (von Frey), mouse arthritis models\",\n      \"journal\": \"Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain- and loss-of-function in vivo with defined pain readouts, single lab\",\n      \"pmids\": [\"30120124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Proteasome inhibitors (MG132, bortezomib) accelerate degradation of c-Fms (CSF-1R) in osteoclasts via p38/TACE-mediated regulated intramembrane proteolysis (RIPping), without affecting RANK levels; c-Fms degradation completely blocks M-CSF-mediated signaling and suppresses osteoclast differentiation and bone resorption in vitro and in vivo.\",\n      \"method\": \"Proteasome inhibitor treatment, p38/TACE inhibitors, immunoblot for c-Fms, M-CSF signaling assays, LPS-induced bone loss model\",\n      \"journal\": \"International Journal of Molecular Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with in vitro and in vivo validation\",\n      \"pmids\": [\"28946669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"M-CSF stimulates migration in isolated rat osteoclasts, increasing both the proportion of migrating cells and substrate area covered; this motility-promoting effect is inverse to its inhibitory effect on bone resorption, suggesting M-CSF controls a switch between migratory and resorptive states in osteoclasts.\",\n      \"method\": \"Time-lapse microscopy of isolated osteoclasts on substrate, M-CSF stimulation dose-response\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct live-cell imaging with functional quantification, single lab\",\n      \"pmids\": [\"8216275\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CSF1 (M-CSF) is a disulfide-linked homodimeric cytokine that exists as membrane-bound, secreted glycoprotein, and proteoglycan isoforms processed from alternatively spliced precursors; it binds and dimerizes the CSF-1R (c-Fms) receptor tyrosine kinase, triggering autophosphorylation at multiple intracellular tyrosines (Y721 recruiting PI3K for chemotaxis, Y807/Y809 controlling a proliferation-versus-differentiation switch via c-Myc and sustained ERK/MAPK signaling), with downstream cascades including Raf-1/MEK/ERK (required for macrophage differentiation and proliferation), PLCγ/DAG/PKC/Ras (driving macropinocytosis), and MAPK-dependent phosphorylation of Mitf/TFE3 transcription factors to recruit p300 for osteoclast maturation; locally produced CSF1 from tissue-resident cells (Adipoq-lineage marrow progenitors, mesothelial cells, injured sensory neurons) controls macrophage and osteoclast homeostasis in a paracrine manner, while injured sensory neuron-derived CSF1 is axonally transported to the spinal cord to activate microglial CSF1R→DAP12 signaling underlying neuropathic pain.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CSF1 (macrophage colony-stimulating factor, M-CSF) is a homodimeric cytokine that signals through the receptor tyrosine kinase CSF-1R (c-Fms) to drive the survival, proliferation, differentiation, migration, and functional activation of mononuclear phagocytes and osteoclasts. Binding of CSF1 to CSF-1R triggers receptor autophosphorylation at distinct tyrosines that recruit specific effectors — Y721 recruits PI3K to mediate chemotaxis [PMID:9261328], Y807 controls a differentiation-versus-proliferation switch [PMID:8981370], and Y809 is required for c-myc induction and mitogenesis [PMID:1833648] — while downstream MAPK/ERK signaling drives osteoclast maturation via Mitf/TFE3 phosphorylation [PMID:11684011] and sustained ERK activation controls macrophage differentiation fate [PMID:19801501]. CSF1 exists as three isoforms (cell-surface glycoprotein, secreted proteoglycan, and secreted glycoprotein) with distinct roles in local versus systemic macrophage regulation [PMID:21885670]; it is produced by mesenchymal cells including bone marrow Adipoq-lineage progenitors and mesothelial cells to maintain tissue-resident macrophage and osteoclast populations, and its loss-of-function causes osteopetrosis due to osteoclast deficiency [PMID:12074592, PMID:36779851]. CSF1 also supports non-myeloid functions including Paneth cell maturation in the intestinal stem cell niche [PMID:23314290] and contributes to inflammatory pain, tumor-associated macrophage polarization, and monocyte-derived angiogenesis via VEGF induction [PMID:30120124, PMID:25753425, PMID:12928417].\",\n  \"teleology\": [\n    {\n      \"year\": 1986,\n      \"claim\": \"Establishing the fundamental signaling mechanism: CSF-1 was shown to bind a dedicated receptor (CSF-1R, Mr 165 kDa) on mononuclear phagocytes that exhibits ligand-dependent tyrosine autophosphorylation, providing the first biochemical framework for how this cytokine activates target cells.\",\n      \"evidence\": \"Receptor purification, ligand-binding assay, and tyrosine autophosphorylation assay in vitro\",\n      \"pmids\": [\"3015514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling pathways not yet mapped\", \"Role of individual autophosphorylation sites unknown\", \"In vivo relevance not tested\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"CSF1 was linked to innate immune effector function: M-CSF priming of monocytes augmented tumoricidal activity via TNF production, establishing that CSF1 does not merely expand macrophages but actively modulates their inflammatory outputs.\",\n      \"evidence\": \"51Cr-release cytotoxicity assay with TNF antiserum neutralization in human monocytes\",\n      \"pmids\": [\"3053901\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling intermediates between CSF-1R and TNF induction not identified\", \"Whether this extends to non-tumor targets unknown\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Receptor autophosphorylation site Y809 was shown to specifically control c-myc induction and mitogenesis without affecting kinase activity or PI3K binding, revealing that CSF-1R bifurcates signaling through distinct phosphotyrosines to separate proliferation from other responses.\",\n      \"evidence\": \"Site-directed mutagenesis of CSF-1R Y809 with proliferation assay and c-myc overexpression rescue in myeloid cells\",\n      \"pmids\": [\"1833648\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adaptor proteins recruited to Y809 not identified\", \"Differentiation-specific sites not yet mapped\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"The receptor-binding interface of CSF1 was resolved: His-9 and His-15 in helix A were shown by mutagenesis and crystallography to be critical for receptor engagement, providing the first structural definition of how CSF1 contacts CSF-1R.\",\n      \"evidence\": \"Alanine mutagenesis with bioactivity/binding assays plus X-ray crystallography at 2.5 Å\",\n      \"pmids\": [\"7983059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full co-crystal structure of CSF1–CSF-1R complex not solved\", \"Contribution of receptor residues to binding not mapped\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Two additional phosphotyrosines were functionally resolved: Y807 was shown essential for macrophage differentiation (acting as a proliferation-differentiation switch), while Y721 was identified as the PI3K docking site required for CSF-1-induced chemotaxis, establishing a phosphotyrosine code for distinct cellular outcomes.\",\n      \"evidence\": \"Site-directed mutagenesis of multiple CSF-1R autophosphorylation sites with proliferation, differentiation, and migration assays in myeloid cells\",\n      \"pmids\": [\"8981370\", \"9261328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for selective adaptor recruitment unknown\", \"Whether Y807 and Y721 signaling interact in vivo not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"M-CSF was placed as the critical downstream effector of estrogen-deficiency bone loss: in vivo neutralization completely prevented ovariectomy-induced osteoclast expansion and bone loss, and epistasis with Egr-1 knockout confirmed M-CSF acts downstream of transcriptional de-repression following estrogen withdrawal.\",\n      \"evidence\": \"Anti-M-CSF antibody neutralization in ovariectomized and Egr-1 knockout mice with bone histomorphometry\",\n      \"pmids\": [\"10792003\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cell types producing M-CSF in response to estrogen withdrawal not identified\", \"Whether this pathway operates in humans not directly tested\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"A CSF-1R → MAPK → Mitf/TFE3 → p300 transcriptional axis was delineated for osteoclast multinucleation, revealing how receptor tyrosine kinase signaling converges on transcription factor phosphorylation to drive terminal osteoclast maturation.\",\n      \"evidence\": \"Kinase assay, p300 co-activator recruitment assay, Mitf/TFE3 MAPK-site mutagenesis, osteoclast formation assay\",\n      \"pmids\": [\"11684011\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Mitf and TFE3 are redundant or synergistic not resolved\", \"Target genes of this complex in osteoclasts not identified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Loss-of-function genetics confirmed CSF1 is essential for osteoclastogenesis in vivo: a frameshift mutation in rat Csf1 causes osteopetrosis in toothless rats, providing definitive genetic proof that CSF1 is non-redundant for bone resorption.\",\n      \"evidence\": \"Sequencing of Csf1 coding region and phenotypic characterization of tl/tl rats\",\n      \"pmids\": [\"12074592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether IL-34 (the second CSF-1R ligand, identified later) can partially compensate not addressed\", \"Human genetic counterpart not identified\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"CSF-1R signaling was mapped in microglia: PI3K and PLCγ sequentially activate Rac to reorganize the actin cytoskeleton, explaining how M-CSF drives microglial morphological transformation, proliferation, migration, and phagocytosis through a common GTPase node.\",\n      \"evidence\": \"Rac activation assay and signal transduction pathway analysis in microglia with Iba1 functional studies\",\n      \"pmids\": [\"12379904\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relative contributions of PI3K versus PLCγ to Rac not quantified\", \"In vivo relevance in CNS injury not tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Sustained ERK1/2 activation was identified as a critical determinant of M-CSF-driven macrophage differentiation: DUSP5 phosphatase acts as a MAPK-dependent negative feedback regulator, and its overexpression shifts the proliferation-differentiation balance toward proliferation and granulocytic fate.\",\n      \"evidence\": \"DUSP5 overexpression, MEK inhibitor U0126, proliferation and differentiation assays in FD-Fms and multipotent progenitors\",\n      \"pmids\": [\"19801501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether DUSP5 is the dominant ERK phosphatase in vivo macrophage differentiation unknown\", \"Transcription factor targets of sustained ERK not identified\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"CSF1 isoform-specific functions were resolved: cell-surface CSF1 initiates local macrophage activation while secreted proteoglycan CSF1 elevates circulating levels and mediates systemic effects; conditional knockout also revealed CSF1 is required for osteocyte maturation beyond osteoclastogenesis.\",\n      \"evidence\": \"Isoform-specific mutant MRL-Fas(lpr) mice for nephritis; Meox2Cre conditional Csf1 knockout with bone histomorphometry\",\n      \"pmids\": [\"21885670\", \"21958845\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Secreted glycoprotein isoform function not fully dissected\", \"Signaling differences between isoforms at the receptor level unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"An unexpected non-myeloid role emerged: CSF-1R expressed on Paneth cells mediates CSF1-dependent Paneth cell maturation and maintenance of the intestinal stem cell niche, extending CSF1 function beyond the mononuclear phagocyte lineage.\",\n      \"evidence\": \"Germline KO, inducible GI-specific Csf1r deletion, SI organoid culture with stem cell marker analysis\",\n      \"pmids\": [\"23314290\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream signaling in Paneth cells not mapped\", \"Whether CSF1 or IL-34 is the physiological ligand in intestine not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Lymphatic endothelial cells were identified as an M-CSF source for pathological osteoclastogenesis, and proteasome inhibitor-induced CSF-1R degradation via p38/TACE-mediated RIPping was shown to block M-CSF signaling, revealing both new cellular sources and a novel receptor turnover mechanism.\",\n      \"evidence\": \"LEC co-culture with osteoclasts plus anti-M-CSF antibody blockade and in vivo LEC injection; proteasome inhibitor treatment with p38/TACE inhibitor rescue\",\n      \"pmids\": [\"28052488\", \"28946669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of LEC-derived CSF1 in normal bone homeostasis not established\", \"Whether RIPping of CSF-1R is constitutive or signal-dependent not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The dominant cellular source of M-CSF in bone marrow was identified as Adipoq-lineage progenitors rather than mature adipocytes or osteoblasts; conditional deletion causes severe osteopetrosis and also alleviates ovariectomy-induced bone loss, closing the loop on the cellular origin of M-CSF that drives both normal and pathological osteoclastogenesis.\",\n      \"evidence\": \"Adipoq-Cre conditional Csf1 knockout, micro-CT, single-cell transcriptomics, human bone marrow validation by two independent groups\",\n      \"pmids\": [\"36779851\", \"36779854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether these progenitors also supply M-CSF for tissue macrophage maintenance beyond bone not addressed\", \"Regulation of Csf1 transcription in Adipoq-lineage progenitors not characterized\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of CSF1–CSF-1R co-engagement at atomic resolution, how the three CSF1 isoforms differentially activate receptor signaling, the identity of CSF-1R signaling intermediates in non-myeloid cells such as Paneth cells, and whether CSF1 versus IL-34 have distinct physiological roles in each tissue.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No co-crystal structure of CSF1–CSF-1R complex\", \"Isoform-specific receptor activation mechanisms uncharacterized\", \"CSF1 versus IL-34 partitioning in tissues not genetically resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 2, 7, 17, 25]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [12, 19, 20]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [12, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": [0, 1, 3, 4, 9]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 7, 9, 20, 22]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 8, 13, 14]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CSF1R\",\n      \"PI3K\",\n      \"MITF\",\n      \"TFE3\",\n      \"DUSP5\",\n      \"RAC1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CSF1 (M-CSF) is a disulfide-linked homodimeric cytokine that exists as membrane-bound, secreted glycoprotein, and secreted proteoglycan isoforms generated by alternative splicing and extracellular proteolytic processing; it signals exclusively through the CSF-1R (c-Fms) receptor tyrosine kinase to govern survival, proliferation, differentiation, and motility of mononuclear phagocytes and osteoclasts [PMID:2408759, PMID:3039346, PMID:3493529]. Ligand-induced CSF-1R autophosphorylation activates divergent intracellular cascades: Y721 recruits PI3K for chemotaxis and macropinocytosis (via PLCγ/DAG/PKC/Ras), Y807/Y809 controls a proliferation-versus-differentiation switch through c-Myc induction and sustained Raf-1/MEK/ERK signaling, and MAPK-dependent phosphorylation of Mitf/TFE3 recruits p300 to drive osteoclast maturation [PMID:1833648, PMID:8981370, PMID:11684011, PMID:25688212]. Paracrine CSF1 production by tissue-specific sources — bone marrow Adipoq-lineage progenitors for osteoclast and macrophage homeostasis, mesothelial cells for peritoneal macrophages, and injured sensory neurons for spinal microglial activation underlying neuropathic pain — establishes CSF1 as a locally regulated master signal for myeloid cell fate across diverse organs [PMID:36779851, PMID:31251389, PMID:26642091]. CSF1 gene translocations causing overexpression drive tenosynovial giant cell tumor through a landscape effect of non-neoplastic CSF1R-positive cell recruitment [PMID:16407111].\",\n  \"teleology\": [\n    {\n      \"year\": 1985,\n      \"claim\": \"Identification of CSF-1 as a cloneable cytokine and its receptor as the c-Fms proto-oncogene product established the molecular identity of the ligand–receptor pair governing mononuclear phagocyte biology.\",\n      \"evidence\": \"cDNA cloning with recombinant protein expression in COS cells confirmed biological activity; immunoprecipitation and radioligand binding demonstrated c-Fms is the CSF-1 receptor with intrinsic tyrosine kinase activity\",\n      \"pmids\": [\"2996129\", \"2408759\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural information on how CSF-1 engages its receptor\", \"Downstream signaling pathways unknown\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"Discovery that CSF-1 is synthesized as a transmembrane homodimeric precursor that is proteolytically cleaved to release soluble forms, and that alternative splicing generates distinct isoforms, resolved how one gene produces functionally diverse ligand forms.\",\n      \"evidence\": \"cDNA cloning of 4-kb and 1.6-kb transcripts, genomic exon mapping, direct protein sequencing, and surface trypsin cleavage experiments in transfected cells\",\n      \"pmids\": [\"3493529\", \"3500041\", \"3039346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional differences among isoforms in vivo not yet defined\", \"Identity of the physiological membrane protease unknown\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"The crystal structure of the M-CSF homodimer revealed the four-helix-bundle architecture and, together with mutagenesis, pinpointed His-9 and His-15 as critical receptor-contact residues on helix A.\",\n      \"evidence\": \"X-ray crystallography at 2.5 Å; site-directed mutagenesis (H9A/H15A) with radioreceptor binding and bioactivity assays confirmed direct involvement without structural perturbation\",\n      \"pmids\": [\"1455231\", \"7983059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of CSF-1 bound to CSF-1R\", \"Receptor dimerization mechanism not yet visualized\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Systematic mutagenesis of individual CSF-1R autophosphorylation sites delineated a signaling architecture in which Y721 recruits PI3K for motility, Y807/Y809 controls a proliferation-versus-differentiation switch through c-Myc and sustained ERK, and the Raf-1/MEK/ERK cascade is required for macrophage differentiation.\",\n      \"evidence\": \"Site-directed mutagenesis of CSF-1R tyrosines in FDC-P1 myeloid cells, c-myc overexpression rescue, PI3K co-immunoprecipitation, chemotaxis assays, pharmacological ERK inhibition\",\n      \"pmids\": [\"1833648\", \"8981370\", \"9261328\", \"8981359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative kinetics of phosphosite usage during physiological stimulation unknown\", \"Downstream transcriptional programs beyond c-Myc and immediate-early genes not mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of the M-CSF→MAPK→Mitf/TFE3→p300 axis explained how CSF-1 drives osteoclast maturation at the transcriptional level, connecting receptor signaling to a known osteoclast transcription factor.\",\n      \"evidence\": \"In vitro kinase assay, co-immunoprecipitation with p300, Mitf phospho-site mutagenesis, and osteoclast differentiation assay\",\n      \"pmids\": [\"11684011\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full repertoire of MAPK-phosphorylated transcription factors downstream of CSF-1 not catalogued\", \"How Mitf phosphorylation cooperates with RANKL-induced NFATc1 unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The toothless rat frameshift mutation provided definitive genetic proof that loss of functional CSF-1 protein causes osteopetrosis due to osteoclast failure.\",\n      \"evidence\": \"Genomic sequencing of the Csf1 coding region in the toothless (tl) rat identifying a 10-bp insertion producing a truncated 41-aa non-functional product\",\n      \"pmids\": [\"12074592\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Hematopoietic and extra-skeletal phenotypes of the tl rat incompletely characterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"CSF1 gene translocations in tenosynovial giant cell tumor established CSF1 as an oncogenic driver through a landscape effect, where minority neoplastic cells overexpressing CSF1 recruit CSF1R-positive bystander cells to form the tumor mass.\",\n      \"evidence\": \"FISH and array CGH identification of chromosome 1p13 translocation fusing CSF1 to COL6A3, expression profiling, and immunohistochemistry on TGCT/PVNS samples\",\n      \"pmids\": [\"16407111\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CSF1 overexpression alone is sufficient or requires additional cooperating events not tested\", \"Non-tumor landscape effects not explored in other cancers at this point\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery of IL-34 as a second ligand for CSF-1R redefined the receptor's ligand landscape, raising the question of non-redundant versus overlapping functions of the two ligands.\",\n      \"evidence\": \"Functional proteome screen identifying IL-34; receptor identification by extracellular domain library screen; monocyte viability assays\",\n      \"pmids\": [\"18467591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for dual ligand recognition by CSF-1R not resolved\", \"Tissue-specific dominance of CSF-1 vs IL-34 only partially mapped\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Isoform-specific knock-in mice demonstrated that the three CSF-1 protein isoforms (cell-surface glycoprotein, secreted proteoglycan, secreted glycoprotein) have distinct non-redundant in vivo roles, with the cell-surface form initiating local macrophage activation and the proteoglycan form dominating systemic circulation and monocyte recruitment during lupus nephritis.\",\n      \"evidence\": \"Isoform-specific mutant MRL-Fas(lpr) knock-in mice with flow cytometry, histology, and TUNEL analysis\",\n      \"pmids\": [\"21885670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether isoform-specific functions extend to other tissues/disease contexts not determined\", \"Molecular basis for differential tissue distribution of isoforms unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Sensory neuron-derived CSF1 was established as a critical mediator of neuropathic pain: nerve injury induces de novo CSF1 expression in DRG neurons, and axonally transported CSF1 activates spinal microglial CSF1R→DAP12 signaling to drive mechanical hypersensitivity.\",\n      \"evidence\": \"Sensory-neuron-specific Csf1 conditional KO, intrathecal CSF1 gain-of-function, DAP12 epistasis, behavioral pain testing\",\n      \"pmids\": [\"26642091\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger for Csf1 transcriptional induction in injured neurons not identified\", \"Whether CSF1 vs IL-34 contributes differentially to central microglial activation unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"M-CSF-driven macropinocytosis was mechanistically mapped to a PI3K→PLCγ→DAG→PKC/Ras pathway, extending the known signaling repertoire beyond proliferation and differentiation to include bulk fluid uptake.\",\n      \"evidence\": \"Live imaging with fluorescent lipid probes and sequential pharmacological inhibition (LY294002, U73122, FTS, Calphostin C) in macrophages\",\n      \"pmids\": [\"25688212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Entirely pharmacological approach; genetic confirmation of each node lacking\", \"Physiological significance of M-CSF-driven macropinocytosis in vivo not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Two independent studies using Adipoq-Cre conditional Csf1 knockout mice identified bone marrow Adipoq-lineage progenitors (MALPs) as the dominant paracrine source of CSF1 for osteoclast and macrophage homeostasis in the skeletal niche, explaining why the bone compartment is so dependent on CSF1.\",\n      \"evidence\": \"Adipoq-Cre × Csf1-floxed conditional KO, single-cell RNA-seq, micro-CT, TRAP staining, hematopoietic progenitor analysis, ovariectomy and LPS-induced osteolysis models\",\n      \"pmids\": [\"36779851\", \"36779854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other mesenchymal populations compensate over long-term deletion not addressed\", \"Relative contribution of CSF1 vs IL-34 from marrow stroma not quantified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for CSF-1 vs IL-34 recognition by CSF-1R, the identity of the physiological protease(s) that cleave membrane-bound CSF-1 in vivo, and the full transcriptional programs downstream of distinct CSF-1R phosphorylation sites in tissue-specific macrophage populations.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal structure of CSF-1 bound to CSF-1R ectodomain\", \"Physiological sheddase for membrane CSF-1 not genetically identified\", \"Single-cell transcriptomic profiling of CSF-1 vs IL-34 responses in tissue-resident macrophages lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 1, 5, 6, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [7, 11, 15]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 21, 28]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1, 2, 4, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 5, 7, 11, 12, 15, 24, 29]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [7, 10, 11, 12, 13, 15, 26]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [5, 11, 15, 17, 22, 29]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [8, 23, 25]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [10, 31]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CSF1R\",\n      \"PI3K\",\n      \"MITF\",\n      \"TFE3\",\n      \"EP300\",\n      \"RAF1\",\n      \"MAPK1\",\n      \"DAP12\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}