{"gene":"IGF2","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":1995,"finding":"IGF2 and H19 share the same endoderm-specific enhancers located 3' of H19, but utilize them on different parental chromosomes (IGF2 paternally, H19 maternally). Deletion of these enhancers via homologous recombination abolished H19 expression on maternal inheritance and IGF2 expression on paternal inheritance, establishing that IGFII acts systemically to affect prenatal growth.","method":"Targeted enhancer deletion by homologous recombination in mouse ES cells; analysis of tissue-specific gene expression and growth phenotypes in mice","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct genetic deletion with rigorous developmental and molecular readouts, replicated across multiple tissues and lineages","pmids":["7544754"],"is_preprint":false},{"year":1998,"finding":"Igf2 imprinting does not require its own DNA methylation or H19 RNA. Silencing of Igf2 due to loss of DNA methylation could be overridden by a mutation at H19, and replacement of the H19 gene with a protein-coding gene did not affect Igf2 expression. These epistasis experiments support a transcriptional model in which Igf2 and H19 compete for access to a common set of enhancers.","method":"Genetic epistasis using targeted mutations and H19 gene replacement in mice; allele-specific expression analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal genetic manipulations in vivo, directly addressing mechanism of imprinting","pmids":["9679064"],"is_preprint":false},{"year":1995,"finding":"Translation of the major 6.0-kb IGF2 mRNA (normally stored in a 100S ribonucleoprotein particle) is selectively activated in exponentially growing cells via a rapamycin-sensitive pathway (p70S6k/85S6k kinase signaling), providing post-transcriptional regulation of IGF-II production independent of the constitutively translated 4.8-kb mRNA.","method":"Rapamycin and anisomycin treatment of cultured cells; polysome fractionation; Northern blot analysis of mRNA distribution","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical fractionation combined with pharmacological pathway dissection, two orthogonal methods","pmids":["7566093"],"is_preprint":false},{"year":2006,"finding":"CTCF mediates an interchromosomal colocalization between the Igf2/H19 imprinting control region (ICR) on chromosome 7 and the Wsb1/Nf1 locus on chromosome 11. Omission of CTCF or deletion of the maternal ICR abrogated this association and altered Wsb1/Nf1 gene expression, demonstrating that CTCF-dependent chromosome looping regulates allele-specific long-range gene expression.","method":"Modified chromosome conformation capture (3C) and fluorescence in situ hybridization (FISH); CTCF depletion and ICR deletion experiments","journal":"Science","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — two orthogonal methods (3C and FISH) with genetic loss-of-function controls in single study","pmids":["16614224"],"is_preprint":false},{"year":2007,"finding":"Crystal structures of IGF2R domains 11–12, 11–12–13–14, and the domain 11–12–13/IGF-II complex revealed that domain 11 directly contacts IGF-II while domain 13 modulates binding site flexibility. Phe19 and Leu53 of IGF-II lock into a hydrophobic pocket unique to domain 11 of mammalian IGF2R; mutagenesis confirmed this as the IGF-II binding hotspot, and showed convergent evolution with IGF-binding proteins on the same high-affinity site.","method":"X-ray crystallography; site-directed mutagenesis; binding affinity assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at multiple domain combinations combined with mutagenesis validation","pmids":["18046459"],"is_preprint":false},{"year":2011,"finding":"Hippocampal IGF-II (IGF2) is upregulated after inhibitory avoidance learning in a C/EBPβ-dependent manner, and is required for memory consolidation. Post-training hippocampal injection of recombinant IGF-II enhances memory retention; this requires IGF-II receptors, new protein synthesis, ARC function, and GSK3 activity, and correlates with activation of synaptic GSK3β and increased GluR1 AMPA receptor subunit expression. IGF-II also promotes persistent LTP after weak stimulation in hippocampal slices in an IGF-II receptor-dependent manner.","method":"Recombinant protein injection into rat hippocampus; pharmacological inhibitors; Western blot; electrophysiology (LTP in hippocampal slices); behavioral assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal in vivo and ex vivo approaches with specific pharmacological and molecular dissection, replicated across behavioral and electrophysiological readouts","pmids":["21270887"],"is_preprint":false},{"year":2003,"finding":"IGF-II transcription in skeletal myogenesis is regulated by mTOR (independently of its kinase activity) and by amino acid availability, acting through IGF-II promoter 3 and a downstream enhancer during C2C12 myoblast differentiation. IGF production—not downstream IGF signaling—is the primary mTOR target in initiating differentiation, and mTOR's myogenic signaling is mediated by the PI3K-Akt pathway.","method":"Promoter-reporter assays; pharmacological inhibitors (rapamycin, wortmannin); kinase-dead mTOR constructs; C2C12 myoblast differentiation assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — promoter dissection combined with dominant-negative constructs and pharmacological pathway analysis in two orthogonal approaches","pmids":["14662739"],"is_preprint":false},{"year":2011,"finding":"miR-125b directly targets IGF2 mRNA in myocytes, as demonstrated by luciferase reporter assays with the IGF2 3′UTR. Declining miR-125b during myogenesis de-represses IGF2, promoting myoblast differentiation; mTOR (via kinase-independent signaling) negatively controls miR-125b biogenesis, establishing a dual mechanism for mTOR regulation of IGF2 production.","method":"Luciferase 3′UTR reporter assays; miRNA overexpression/knockdown; in vivo muscle regeneration assays; RT-qPCR","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct 3′UTR reporter validation combined with in vivo and in vitro gain/loss-of-function, multiple orthogonal readouts","pmids":["21200031"],"is_preprint":false},{"year":2002,"finding":"IGF-2 is a downstream mediator of prolactin-induced mammary alveologenesis acting upstream of cyclin D1 transcription. Prolactin induces IGF-2 mRNA; IGF-2 induces cyclin D1 protein in primary MECs; ectopic IGF-2 restores alveologenesis in prolactin receptor-null epithelium; and alveologenesis is retarded in IGF-2-deficient MECs.","method":"Genetic rescue (ectopic IGF-2 expression in PRL-R−/− epithelium); IGF-2 knockout MECs; primary MEC stimulation assays; Northern and Western blot","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic rescue and loss-of-function combined with molecular pathway analysis in primary cells and in vivo models","pmids":["12479812"],"is_preprint":false},{"year":1999,"finding":"Hypoxia activates IGF-II transcription from the P3 promoter in HepG2 cells via increased Egr-1 DNA binding activity. Deletion of Egr-1 binding sites in the P3 promoter abolished hypoxic induction; cotransfection with Egr-1 expression vector synergistically activated P3-driven reporter expression; WT1 (a repressor of IGF-II) was decreased by hypoxia.","method":"Transient promoter-luciferase reporter assays; EMSA with supershift; cotransfection; mRNA stability assays; Western blot; deletion mutagenesis of P3 promoter","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — promoter deletion mutagenesis combined with EMSA and cotransfection rescue, multiple orthogonal methods in single study","pmids":["10606246"],"is_preprint":false},{"year":2000,"finding":"IGF-II promotes mesoderm formation by binding to the IGF1R on mesoderm precursor cells. Androgenetic Igf2-null ES cells (which lack IGF-II) showed severely impaired mesoderm development in teratoma and in vitro differentiation assays, while exogenous IGF-II addition specifically increased expression of mesoderm markers.","method":"Teratoma formation assays using ES cell lines with different Igf2 dosages; in vitro ES cell differentiation with exogenous IGF-II; expression analysis of mesoderm markers","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function combined with exogenous rescue, multiple ES cell genotypes","pmids":["11076682"],"is_preprint":false},{"year":2015,"finding":"Autocrine IGF2 produced and secreted by adult β-cells activates the β-cell IGF-1 receptor signaling pathway. β-cell-specific Igf2 knockout (βIGF2KO) mice showed reduced glucose-stimulated insulin secretion in aging and on high-fat diet, impaired β-cell mass expansion during pregnancy and in response to acute insulin resistance, demonstrating a physiological autocrine role for IGF2 in β-cell function.","method":"Conditional β-cell-specific Igf2 knockout mice; glucose tolerance tests; insulin secretion assays; β-cell mass quantification; metabolic stress experiments","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional knockout with multiple physiological phenotypes and metabolic challenges","pmids":["26384384"],"is_preprint":false},{"year":2013,"finding":"miR-483-5p, encoded within the IGF2 gene, forms a positive feedback loop by binding directly to the 5′UTR of fetal IGF2 mRNA in the nucleus, enhancing recruitment of the RNA helicase DHX9 to the IGF2 transcript and promoting IGF2 transcription from fetal promoters. Ectopic miR-483-5p expression in IGF2-dependent sarcoma cells increased tumorigenesis in vivo.","method":"miRNA screen in primary Wilms' tumors; nuclear pull-down; RNA-protein interaction assays (DHX9); in vivo xenograft tumorigenesis; promoter-reporter assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — direct RNA-protein interaction (pull-down of DHX9) combined with in vivo tumorigenesis and promoter assays, multiple orthogonal methods","pmids":["24298054"],"is_preprint":false},{"year":2006,"finding":"IGF2 allelic dosage directly modulates intestinal adenoma development in Apc(Min/+) mice: biallelic Igf2 expression (LOI) elongated intestinal crypts, increased adenoma growth, and elevated nuclear β-catenin. A soluble form of the IGF2/mannose-6-phosphate receptor (sIGF2R) expressed as a transgenic ligand trap rescued the Igf2-dependent intestinal and adenoma phenotypes, demonstrating functional potency of IGF2 ligand in intestinal cancer.","method":"Genetic crosses of Apc(Min/+) with Igf2 paternal-null or H19 maternal-null mice; sIGF2R ligand-trap transgene rescue; histomorphometry; β-catenin immunostaining","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple allelic dosage models combined with in vivo ligand-trap rescue, genetic epistasis","pmids":["16488992"],"is_preprint":false},{"year":2023,"finding":"The highest hippocampal IGF2 is produced by pericytes. Learning-induced increases in hippocampal Igf2 expression originate specifically from pericytes and require neuronal activity. Conditional Igf2 knockout in pericytes (but not fibroblasts or neurons) impaired long-term memory and blunted learning-dependent neuronal immediate early gene (IEG) induction, establishing a pericyte-to-neuron IGF2 signaling axis for memory consolidation.","method":"Cell-type-specific conditional Igf2 knockout in rats and mice; in situ hybridization and immunofluorescence for cell-type identification; behavioral memory assays; immediate early gene protein quantification","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with multiple controls (fibroblast and neuron KOs as negatives) and orthogonal molecular and behavioral readouts","pmids":["37788670"],"is_preprint":false},{"year":2023,"finding":"IGF2 promotes terminal differentiation of neural stem cells (NSCs) into neurons, astrocytes, and oligodendrocytes by inducing expression of the imprinted gene Cdkn1c (encoding p57). Intraventricular infusion of recombinant IGF2 into mice with Cdkn1c-deficient NSCs confirmed that p57 partially mediates IGF2's differentiation effects independently of cell-cycle progression.","method":"Conditional Cdkn1c-knockout NSCs; intraventricular recombinant IGF2 infusion; in vitro NSC differentiation assays; gene expression analysis","journal":"Development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic rescue/epistasis in vivo combined with in vitro mechanistic dissection using conditional knockout","pmids":["36633189"],"is_preprint":false},{"year":2012,"finding":"IGF2 promotes stemness of neural stem/progenitor cells (NSPs) via the insulin receptor isoform A (IR-A), distinct from IGF-1R-mediated proliferation. IR-A was predominantly expressed in NSPs, and IR knockdown (but not IGF-1R knockdown) impaired self-renewal. IGF-II increased Oct4, Sox1, and FABP7 mRNA levels in NSPs, and NSPs expanded in IGF-II preferentially colonized periventricular niches in vivo.","method":"shRNA knockdown of IR vs IGF-1R; limiting dilution assays; in vivo NSP transplantation; RT-qPCR for stemness markers","journal":"Stem cells","confidence":"High","confidence_rationale":"Tier 2 / Moderate — receptor-specific knockdown combined with in vivo transplantation and molecular markers, orthogonal approaches","pmids":["22593020"],"is_preprint":false},{"year":2008,"finding":"IGF2 activates PI3K and TGFβ signaling pathways in chondrocytes. IGF2 treatment activated phosphorylation of Akt and GSK3β; selective PI3K inhibition (LY294002) blocked Akt phosphorylation and abolished IGF2-driven elevation of proteoglycan (Aggrecan and Versican) mRNA. The TGFβ pathway activation by IGF2 was not suppressed by LY294002, indicating two independent downstream pathways.","method":"Western blot for pathway phosphorylation; pharmacological PI3K inhibition; genome-wide mRNA microarray; RT-PCR","journal":"Cell biology international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological pathway dissection with molecular readouts, but single lab and single inhibitor approach","pmids":["18675921"],"is_preprint":false},{"year":2021,"finding":"Circadian regulators Per1 and Per2 are required for Igf2 transcriptional activation during myoblast differentiation. Per1 and Per2 drive dynamic histone modifications at the Igf2 promoter and enhancer, and promote promoter-enhancer interaction, creating a preferred circadian time window for myoblast differentiation. Muscle regeneration was faster when initiated at night, when Per1, Per2, and Igf2 were highly expressed.","method":"Per1/Per2 knockdown; ChIP for histone modifications and RNA Pol II at Igf2 locus; chromatin conformation assays (promoter-enhancer interaction); muscle regeneration assays in vivo","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — ChIP analysis of histone modifications combined with chromatin conformation capture and in vivo regeneration, multiple orthogonal methods","pmids":["34009269"],"is_preprint":false},{"year":2017,"finding":"Stromal IGF2, derived mainly from cancer-associated fibroblasts (CAFs), activates pro-survival AKT signaling in CRC cells via the paracrine IGF1R/insulin receptor axis. In CAFs, autocrine IGF2/IGF1R signaling induces myofibroblast differentiation (αSMA expression, gel contractility), and IGF2-mediated physical matrix remodeling by CAFs (not soluble factors) facilitates tumor cell invasion in organotypic cultures. IGF2-expressing CAFs co-injected with colon cancer cells increased invasiveness and local recurrence in xenograft models.","method":"CAF isolation; IGF2 siRNA knockdown; organotypic co-culture invasion assays; xenograft mouse models; AKT phosphorylation Western blot; floating collagen gel assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple in vitro and in vivo orthogonal approaches with specific IGF2 knockdown in CAFs and mechanistic pathway readouts","pmids":["28534511"],"is_preprint":false},{"year":2011,"finding":"Endostatin inhibits IGF-II-induced migration and invasion of trophoblasts by suppressing downstream signaling kinases ERK1/2, Akt/mTOR/p70S6K, and focal adhesion kinase. The inhibitory effect on IGF-II-induced Akt phosphorylation is critically dependent on Akt1 expression, as shown by virus-mediated stable Akt1 silencing.","method":"Transwell migration/invasion assays with primary trophoblasts and SGHPL-5 cells; villous explant cultures; Western blot for signaling kinases; stable viral Akt1 knockdown","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — stable gene silencing combined with pharmacological and primary cell assays, single lab","pmids":["21933871"],"is_preprint":false},{"year":2015,"finding":"Paxillin, a focal adhesion protein, acts as a transcriptional regulator of IGF2 by stimulating the chromosomal interaction between the distal shared enhancer and the IGF2 promoter (while restraining the H19 promoter-enhancer interaction). Paxillin interacts with cohesin and the mediator complex, and co-occupies the IGF2/H19 locus, facilitating long-range chromatin looping to activate IGF2 transcription.","method":"Chromosome conformation capture; Co-IP of paxillin with cohesin and mediator; ChIP; allele-specific expression analysis; paxillin overexpression/knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — Co-IP, ChIP, and 3C used in conjunction to establish physical interactions and functional chromatin looping, multiple orthogonal methods","pmids":["26116569"],"is_preprint":false},{"year":2023,"finding":"Fetal manipulation of maternal metabolism is a critical function of placental endocrine Igf2. Igf2 deletion specifically in placental endocrine cells impairs placental hormone production (including prolactins), prevents establishment of pregnancy-related insulin resistance, and restricts nutrient partitioning to the fetus. Mechanistically, Igf2 controls protein synthesis and cellular energy homeostasis in an endocrine cell-type-dependent manner, and has long-lasting effects on offspring metabolism in adulthood.","method":"Conditional Igf2 knockout in placental endocrine cells; placental hormone profiling; metabolic phenotyping of mothers and offspring; molecular analysis of protein synthesis and energy homeostasis pathways","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — cell-type-specific conditional KO with multiple metabolic, endocrine, and molecular readouts in a single rigorous study","pmids":["37544745"],"is_preprint":false},{"year":2011,"finding":"IGF2 precursor isoforms ('big' and pro-IGF-II) are present in normal human plasma (16% and 13%, respectively, of total IGF-II). Mature and 'big' IGF-II exhibit similar activation of IR-A and IR-B signaling, while pro-IGF-II shows significantly less activation. Downstream Akt activation by mature and 'big' IGF-II was greater in IR-A cells than IR-B cells, consistent with higher IR-A affinity for IGF-II.","method":"Human plasma isoform quantification by immunoassay; cell-based receptor activation assays in IGF-1R-deficient cells expressing IR-A or IR-B; Akt phosphorylation by Western blot","journal":"Endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cell system with receptor-specific expression plus plasma biochemistry, single lab","pmids":["21285309"],"is_preprint":false},{"year":2016,"finding":"PHB1 (Prohibitin 1) and CTCF cooperate to negatively regulate the H19-Igf2 axis. PHB1 knockdown reduces CTCF protein levels (~30%) and its binding to the ICR, leading to induction of H19 and Igf2 (~2-fold). PHB1 and CTCF co-immunoprecipitate and co-localize on the ICR element; CTCF overexpression suppresses Phb1-knockdown-mediated H19/Igf2 induction.","method":"Co-IP of PHB1 and CTCF; ChIP at ICR; siRNA knockdown; CTCF overexpression rescue; quantitative RT-PCR","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and ChIP combined with genetic rescue, single lab","pmids":["27687727"],"is_preprint":false},{"year":2012,"finding":"Loss of p53 creates an Igf2-dependent phenotype: developmental lethality occurred in p53-null mice lacking the paternal Igf2 allele, and conditional Igf2 deletion attenuated rapid tumor onset in p53-null mice. Accelerated tumor formation in p53+/- mice with biallelic Igf2 was associated with reductions in p53 loss of heterozygosity and apoptosis, establishing genetic epistasis between Igf2 and p53 pathways in development and tumorigenesis.","method":"Genetic crosses of p53-null and conditional p53-flox with Igf2-null and biallelic Igf2 mice; tumor incidence and phenotype analysis; apoptosis assays; LOH analysis","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple allelic combinations and tumor phenotype readouts in vivo, strong evidence of pathway dependency","pmids":["22674894"],"is_preprint":false},{"year":2022,"finding":"Hepatocyte-specific Igf2 deletion in SRSF3-knockout mice completely prevents hepatic fibrosis, inflammation, and tumor formation. In vitro, IGF2 treatment of HepG2 cells decreases DNA repair enzyme expression and causes DNA damage, linking IGF2 overexpression to homologous recombination and mismatch repair defects in HCC.","method":"Double-conditional knockout mice (Igf2 and Srsf3); tumor incidence assays; in vitro IGF2 treatment of HepG2 cells; DNA damage assays; DNA repair enzyme expression analysis; mutational signature analysis","journal":"Advanced science","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic epistasis with double KO combined with in vitro mechanistic studies, multiple molecular readouts","pmids":["35615981"],"is_preprint":false},{"year":1988,"finding":"Glucocorticoids (cortisone acetate) rapidly extinguish IGF-II mRNA expression in neonatal rat liver (the major endocrine IGF-II production site), while having minimal effect at autocrine/paracrine sites such as skeletal muscle and choroid plexus, demonstrating tissue-specific transcriptional control of the IGF2 gene by glucocorticoids.","method":"Northern blot and in situ hybridization after cortisone acetate administration to neonatal rats; tissue-specific comparison","journal":"Journal of molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo pharmacological manipulation with Northern blot and in situ hybridization across multiple tissues, single lab","pmids":["3255362"],"is_preprint":false},{"year":2020,"finding":"Hippocampal CIM6P/IGF2R is necessary for memory consolidation (but not learning, retrieval, or reconsolidation). CIM6P/IGF2R controls training-induced de novo protein synthesis (including Arc, Egr1, and c-Fos protein but not their mRNAs). Mannose-6-phosphate, like IGF2, enhances memory retention in a CIM6P/IGF2R-dependent manner, establishing that IGF2 acts through this receptor to regulate protein metabolism during memory consolidation.","method":"CIM6P/IGF2R pharmacological inhibition in rats; neuron-specific shRNA knockdown in mice; behavioral memory tests; Western blot for protein synthesis markers; intrahippocampal injections","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological inhibition and genetic knockdown with multiple behavioral and molecular readouts, replication across species","pmids":["32369018"],"is_preprint":false},{"year":2003,"finding":"A methylated oligonucleotide (MON1) complementary to IGF2 promoter P4 induces de novo DNA methylation at that locus, specifically reducing IGF2 mRNA accumulation in HCC cells in vitro. Treatment of nude mice bearing Hep 3B liver tumors with MON1 markedly prolonged survival, demonstrating that epigenetic silencing of IGF2 via targeted DNA methylation inhibits hepatocellular tumor growth in vivo.","method":"Methylated oligonucleotide treatment; bisulfite sequencing for de novo methylation; RT-PCR for IGF2 mRNA; in vivo HCC xenograft mouse model with survival analysis","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro molecular validation combined with in vivo efficacy, but limited mechanistic depth on how methylation is induced, single lab","pmids":["12531883"],"is_preprint":false},{"year":1993,"finding":"IGF-II mRNAs in human, rat, and mouse are subjected to specific endonucleolytic cleavage, indicating post-transcriptional regulation of IGF-II expression by mRNA stability mechanisms. Promoter activity alone does not account for species-specific expression, as maximal promoter activity requires homologous cellular environments, suggesting adaptation to tissue-specific transcription factor levels.","method":"Promoter-luciferase reporter assays in heterologous and homologous cell lines; Northern blot mRNA stability analysis; comparative cross-species promoter analysis","journal":"Regulatory peptides","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter reporter assays combined with mRNA stability analysis across species, single lab","pmids":["8265819"],"is_preprint":false},{"year":2008,"finding":"IGF2 is imprinted and expressed in the marsupial (tammar wallaby) yolk sac placenta. Both IGF1R and IGF2R were present in the placenta, and IGF2 increased vascular endothelial growth factor (VEGF) expression in placental explant cultures, suggesting that IGF2 promotes vascularization of the yolk sac placenta.","method":"RT-PCR and in situ hybridization for IGF2 mRNA; immunohistochemistry for protein localization; placental explant culture with IGF2 treatment; VEGF expression by RT-PCR","journal":"BMC developmental biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — explant culture with functional VEGF readout, plus localization data; indirect evidence for vascularization function","pmids":["18284703"],"is_preprint":false},{"year":2017,"finding":"CTCF-binding site mutations at the Igf2-H19 imprint control region that abolish CTCF insulator activity result in biallelic Igf2 expression (LOI) in prostate, increasing the prevalence and severity of prostatic intraepithelial neoplasia. Prostates with LOI displayed increased MAPK signaling and epithelial proliferation; human prostate tissues showed positive correlation between IGF2 levels and phospho-ERK/phospho-AKT.","method":"CTCF-binding site mutation knock-in mice; PIN histopathology; MAPK/AKT signaling by immunohistochemistry and Western blot; correlation analysis in human prostate tissue arrays","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic knock-in model with defined molecular mechanism (CTCF insulator disruption) and pathway readouts in vivo, plus human tissue validation","pmids":["28775169"],"is_preprint":false},{"year":2012,"finding":"NF-κB, activated by HER2/HER3 signaling, identifies IGF2 as a key target to drive breast cancer stem cell (CSC) tumor sphere formation. IGF2-PI3K signaling induces expression of the stemness transcription factor ID1 and IGF2 itself, forming an IGF2-ID1-IGF2 positive feedback loop. Anti-IGF1/2 antibodies blocked tumorigenesis from the IGF1R-high CSC-enriched population in a patient-derived xenograft model.","method":"Sphere formation assays; shRNA knockdown of ID1 and IGF2; PI3K pathway inhibition; patient-derived xenograft model with anti-IGF1/2 antibodies; gene expression analysis","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple KD experiments combined with in vivo PDX validation, single lab","pmids":["27546618"],"is_preprint":false},{"year":2021,"finding":"IGF2 deficiency in skeletal muscle cells (C2C12 myotubes and primary skeletal muscle cells) causes impaired mitochondrial function, reduced mitochondria-related protein content, and decreased mitochondrial biogenesis. The mechanism involves the IGF2-SIRT1-PGC1α signaling pathway.","method":"IGF2 knockdown in C2C12 myotubes and primary skeletal muscle cells; mitochondrial function assays; Western blot for mitochondrial proteins; pathway inhibitor analysis","journal":"Clinical science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function in two cell systems with molecular pathway analysis, single lab, pathway inferred from inhibitors","pmids":["33825857"],"is_preprint":false},{"year":2013,"finding":"INS-IGF2, a read-through fusion protein consisting of the preproinsulin signal peptide, insulin B-chain, eight C-peptide amino acids, and 138 IGF2-derived amino acids, is expressed primarily in pancreatic beta cells. Autoantibodies against INS-IGF2 are elevated in newly diagnosed type 1 diabetes patients, and INS-IGF2 shares autoantibody-binding sites with insulin.","method":"Immunohistochemistry for INS-IGF2 in human pancreatic islets; autoantibody measurement by radiobinding assay; displacement studies with cold insulin and INS-IGF2","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein localization with displacement assay for shared epitopes, but functional consequence of fusion protein established only for autoimmunity, not canonical IGF2 signaling","pmids":["23935095"],"is_preprint":false}],"current_model":"IGF2 is a secreted growth factor whose expression is regulated by genomic imprinting (paternal-allele-specific expression controlled by CTCF-dependent chromatin insulators and shared enhancers with H19), post-transcriptional mechanisms (rapamycin-sensitive translation of a stored mRNA pool, and targeting by miR-125b), and transcriptional regulators including Egr-1 (under hypoxia), mTOR/amino acid signals (in myogenesis), and Per1/Per2 (circadian priming); it signals through IGF-1R, IR-A, and the mannose-6-phosphate/IGF2R to activate PI3K/AKT and MAPK pathways governing fetal growth, skeletal myogenesis, neural stem cell self-renewal, β-cell mass, placental endocrine function, and memory consolidation—with IGF2R additionally functioning as a lysosomal degradation route and as an independent regulator of protein synthesis during memory consolidation."},"narrative":{"mechanistic_narrative":"IGF2 encodes a secreted growth factor that acts systemically and locally to drive proliferation, differentiation, and tissue growth across fetal and adult contexts [PMID:7544754, PMID:11076682]. Its expression is governed by genomic imprinting: IGF2 (paternal) and the H19 lncRNA (maternal) compete for a shared set of 3' endoderm-specific enhancers, and IGF2 imprinting requires neither its own DNA methylation nor H19 RNA but instead reflects enhancer competition controlled at the imprinting control region (ICR) [PMID:7544754, PMID:9679064]. CTCF binding at the ICR establishes the insulator and long-range chromatin architecture that enforces allele-specific expression; loss of CTCF insulator activity produces biallelic IGF2 (loss of imprinting) that drives MAPK/AKT-dependent neoplasia [PMID:16614224, PMID:28775169], and this regulation is modulated by partner factors including PHB1 and the focal-adhesion protein paxillin, which acts via cohesin and Mediator to favor the enhancer-promoter loop at IGF2 over H19 [PMID:27687727, PMID:26116569]. Beyond transcription, IGF2 output is tuned post-transcriptionally—through rapamycin-sensitive translational activation of a stored mRNA pool [PMID:7566093], miR-125b targeting of its 3'UTR, and a miR-483-5p/DHX9 positive feedback loop on the 5'UTR [PMID:21200031, PMID:24298054]—and by upstream inputs from mTOR/amino acids, Egr-1 under hypoxia, glucocorticoids, and circadian Per1/Per2 priming of the locus [PMID:14662739, PMID:10606246, PMID:3255362, PMID:34009269]. Secreted IGF2 signals through IGF-1R, the insulin receptor isoform A (IR-A), and the mannose-6-phosphate/IGF2R to activate PI3K/AKT and MAPK cascades, governing mesoderm and mammary alveolar development, skeletal myogenesis and muscle mitochondrial biogenesis, neural stem cell self-renewal and terminal differentiation, autocrine β-cell function, and placental endocrine control of maternal metabolism [PMID:11076682, PMID:12479812, PMID:22593020, PMID:36633189, PMID:26384384, PMID:37544745]. Structurally, IGF2R domain 11 contacts IGF-II through a hydrophobic pocket engaging Phe19/Leu53, defining the high-affinity binding hotspot [PMID:18046459]. In the hippocampus, learning-induced IGF2 produced by pericytes signals to neurons and acts through the CIM6P/IGF2R to control de novo protein synthesis required for memory consolidation and persistent LTP [PMID:21270887, PMID:37788670, PMID:32369018]. Dysregulated IGF2 dosage potentiates tumorigenesis in intestinal, prostate, hepatic, and breast contexts and shows genetic epistasis with the p53 pathway [PMID:16488992, PMID:22674894, PMID:35615981, PMID:27546618].","teleology":[{"year":1995,"claim":"Established that IGF2 and H19 are reciprocally imprinted genes sharing common 3' enhancers used on opposite parental chromosomes, defining the architectural logic of the imprinted locus and IGF2's systemic role in prenatal growth.","evidence":"Targeted enhancer deletion by homologous recombination in mice with tissue-specific expression and growth readouts","pmids":["7544754"],"confidence":"High","gaps":["Did not resolve how allele-specific enhancer access is enforced","Mechanism of the insulator not yet identified"]},{"year":1995,"claim":"Showed IGF2 production is regulated post-transcriptionally via rapamycin-sensitive translational activation of a stored mRNA pool, decoupling IGF2 output from transcription alone.","evidence":"Polysome fractionation and Northern blot with rapamycin/anisomycin in growing cells","pmids":["7566093"],"confidence":"High","gaps":["The trans-acting factors mediating 100S particle storage and release not identified","In vivo physiological relevance untested"]},{"year":1998,"claim":"Resolved the imprinting mechanism as enhancer competition, demonstrating IGF2 imprinting requires neither its own methylation nor H19 RNA.","evidence":"Genetic epistasis with H19 gene replacement and allele-specific expression in mice","pmids":["9679064"],"confidence":"High","gaps":["Did not identify the protein factor establishing the insulator boundary"]},{"year":2002,"claim":"Placed IGF2 downstream of prolactin and upstream of cyclin D1 in mammary alveologenesis, defining a developmental hormone-to-growth-factor relay.","evidence":"Genetic rescue in PRL-R-null epithelium and IGF2-null MECs with molecular pathway analysis","pmids":["12479812"],"confidence":"High","gaps":["Receptor mediating IGF2-to-cyclin-D1 induction not specified","Direct vs indirect cyclin D1 induction not distinguished"]},{"year":2003,"claim":"Identified mTOR (kinase-independent) and amino-acid availability as drivers of IGF2 transcription in myogenesis, with IGF production rather than downstream signaling as the primary mTOR target.","evidence":"Promoter-reporter and kinase-dead mTOR constructs in C2C12 differentiation","pmids":["14662739"],"confidence":"High","gaps":["Molecular basis of kinase-independent mTOR action on IGF2 promoter unclear"]},{"year":2006,"claim":"Demonstrated that CTCF organizes interchromosomal looping from the Igf2/H19 ICR, extending imprinting control to trans-acting chromatin architecture.","evidence":"3C and FISH with CTCF depletion and ICR deletion in mice","pmids":["16614224"],"confidence":"High","gaps":["Functional importance of interchromosomal contact for IGF2 dosage in vivo not quantified"]},{"year":2006,"claim":"Showed IGF2 allelic dosage causally modulates intestinal tumor growth, validating IGF2 as a functional oncogenic ligand amenable to ligand-trap inhibition.","evidence":"Apc(Min/+) genetic crosses with Igf2/H19 alleles and sIGF2R transgenic ligand trap","pmids":["16488992"],"confidence":"High","gaps":["Receptor mediating intestinal IGF2 effect not pinned down in this model"]},{"year":2007,"claim":"Defined the structural basis of IGF2 recognition by IGF2R, identifying the domain 11 hydrophobic pocket and the IGF-II Phe19/Leu53 hotspot.","evidence":"X-ray crystallography of IGF2R domains with mutagenesis and binding assays","pmids":["18046459"],"confidence":"High","gaps":["Structures of IGF2 bound to IGF-1R or IR-A not resolved here"]},{"year":2011,"claim":"Established IGF2 as a learning-induced, C/EBPβ-dependent hippocampal factor required for memory consolidation and persistent LTP, acting through IGF-II receptors.","evidence":"Recombinant IGF-II injection, pharmacological inhibitors, LTP electrophysiology and behavior in rats","pmids":["21270887"],"confidence":"High","gaps":["Cellular source of hippocampal IGF2 not yet defined","Receptor identity (IGF2R vs IGF-1R) not fully dissected at this stage"]},{"year":2011,"claim":"Identified miR-125b as a direct 3'UTR repressor of IGF2 whose mTOR-controlled decline de-represses IGF2 during myogenesis, adding a second mTOR-dependent post-transcriptional arm.","evidence":"Luciferase 3'UTR reporters, miRNA gain/loss-of-function, and in vivo muscle regeneration","pmids":["21200031"],"confidence":"High","gaps":["Relative contribution of transcriptional vs miR-125b control in vivo not quantified"]},{"year":2012,"claim":"Distinguished IR-A as the receptor mediating IGF2-driven neural stem/progenitor self-renewal, separate from IGF-1R-mediated proliferation.","evidence":"Receptor-specific shRNA knockdown, limiting dilution, and in vivo transplantation","pmids":["22593020"],"confidence":"High","gaps":["Downstream IR-A signaling effectors driving stemness not mapped"]},{"year":2012,"claim":"Demonstrated genetic epistasis between Igf2 and p53 in both development and tumorigenesis, linking IGF2 dosage to p53-pathway-dependent apoptosis and LOH.","evidence":"Genetic crosses of p53-null/flox with Igf2 allelic models and tumor/apoptosis analysis","pmids":["22674894"],"confidence":"High","gaps":["Molecular node connecting IGF2 signaling to p53 LOH not defined"]},{"year":2013,"claim":"Uncovered a nuclear miR-483-5p/DHX9 positive feedback loop on the IGF2 5'UTR that amplifies fetal-promoter transcription and tumorigenesis.","evidence":"Nuclear pull-down, RNA-protein interaction, promoter reporters, and xenografts","pmids":["24298054"],"confidence":"High","gaps":["Generality of the loop beyond IGF2-dependent sarcoma not established"]},{"year":2015,"claim":"Defined an autocrine IGF2/IGF-1R loop in adult β-cells required for insulin secretion and β-cell mass expansion under metabolic stress and pregnancy.","evidence":"β-cell-specific conditional Igf2 knockout with metabolic and β-cell mass phenotyping","pmids":["26384384"],"confidence":"High","gaps":["Signaling effectors downstream of β-cell IGF-1R not detailed"]},{"year":2015,"claim":"Identified paxillin as a transcriptional regulator that biases enhancer-promoter looping toward IGF2 via cohesin and Mediator.","evidence":"3C, Co-IP of paxillin with cohesin/Mediator, ChIP, and allele-specific expression","pmids":["26116569"],"confidence":"High","gaps":["How a focal-adhesion protein is recruited to the locus mechanistically unclear"]},{"year":2016,"claim":"Showed PHB1 cooperates with CTCF to maintain repression of the H19-Igf2 axis by stabilizing CTCF and its ICR binding.","evidence":"Reciprocal Co-IP, ChIP at ICR, siRNA knockdown, and CTCF overexpression rescue","pmids":["27687727"],"confidence":"Medium","gaps":["Single-lab evidence","Direct PHB1-ICR DNA contact vs CTCF-bridged not distinguished"]},{"year":2017,"claim":"Causally linked CTCF insulator disruption (LOI) to prostate neoplasia driven by IGF2-dependent MAPK/AKT signaling, with human tissue correlation.","evidence":"CTCF-binding-site mutation knock-in mice, PIN histopathology, and human tissue arrays","pmids":["28775169"],"confidence":"High","gaps":["Which receptor transduces IGF2 to ERK/AKT in prostate not resolved"]},{"year":2017,"claim":"Defined a stromal CAF-derived IGF2 paracrine axis promoting CRC survival and invasion via matrix remodeling and autocrine myofibroblast differentiation.","evidence":"CAF isolation, IGF2 siRNA, organotypic invasion, xenografts, and AKT readouts","pmids":["28534511"],"confidence":"High","gaps":["Mechanism by which IGF2 drives physical matrix remodeling not molecularly resolved"]},{"year":2020,"claim":"Established CIM6P/IGF2R as the receptor through which IGF2 controls training-induced de novo protein synthesis necessary for memory consolidation.","evidence":"IGF2R inhibition and neuron-specific shRNA knockdown with protein-synthesis and behavioral readouts","pmids":["32369018"],"confidence":"High","gaps":["How IGF2R, classically a clearance receptor, drives protein synthesis mechanistically unexplained"]},{"year":2021,"claim":"Showed circadian Per1/Per2 prime the Igf2 locus chromatin and promoter-enhancer interaction, creating a time-of-day window favorable for myoblast differentiation and muscle regeneration.","evidence":"Per1/Per2 knockdown, ChIP for histone marks/Pol II, chromatin conformation, and in vivo regeneration","pmids":["34009269"],"confidence":"High","gaps":["Direct vs indirect Per binding at the Igf2 locus not established"]},{"year":2021,"claim":"Linked IGF2 to skeletal muscle mitochondrial biogenesis via a SIRT1-PGC1α pathway.","evidence":"IGF2 knockdown in C2C12 and primary muscle cells with mitochondrial assays and inhibitors","pmids":["33825857"],"confidence":"Medium","gaps":["Pathway inferred from inhibitors, single lab","Receptor mediating the effect not identified"]},{"year":2022,"claim":"Demonstrated hepatocyte IGF2 is required for SRSF3-loss-driven hepatic fibrosis and HCC, and that IGF2 suppresses DNA repair to cause genomic damage.","evidence":"Double-conditional Igf2/Srsf3 knockout mice and in vitro DNA damage/repair assays","pmids":["35615981"],"confidence":"High","gaps":["Mechanism linking IGF2 signaling to DNA repair enzyme downregulation undefined"]},{"year":2023,"claim":"Defined a pericyte-to-neuron IGF2 signaling axis as the source of learning-induced hippocampal IGF2 required for memory and IEG induction.","evidence":"Cell-type-specific conditional Igf2 knockout (pericyte vs fibroblast vs neuron) with behavior and IEG readouts","pmids":["37788670"],"confidence":"High","gaps":["Signal triggering pericyte IGF2 release upon neuronal activity not identified"]},{"year":2023,"claim":"Showed IGF2 drives terminal differentiation of neural stem cells partly via induction of the imprinted CDK inhibitor Cdkn1c/p57, independent of cell-cycle exit.","evidence":"Conditional Cdkn1c-knockout NSCs with intraventricular recombinant IGF2 rescue","pmids":["36633189"],"confidence":"High","gaps":["Receptor and signaling route from IGF2 to Cdkn1c induction not mapped"]},{"year":2023,"claim":"Established placental endocrine IGF2 as a fetal effector reprogramming maternal metabolism and nutrient partitioning, with lifelong offspring metabolic effects.","evidence":"Conditional Igf2 knockout in placental endocrine cells with endocrine and metabolic phenotyping","pmids":["37544745"],"confidence":"High","gaps":["Receptor/signaling controlling endocrine cell protein synthesis and energy homeostasis not detailed"]},{"year":null,"claim":"It remains unresolved how the same IGF2 ligand is routed to distinct receptors (IGF-1R, IR-A, IGF2R) to produce context-specific outcomes, and how IGF2R—a clearance receptor—mechanistically controls protein synthesis.","evidence":"No timeline study reconstitutes receptor-selective IGF2 signaling outcomes across tissues","pmids":[],"confidence":"Medium","gaps":["Receptor-choice determinants per cell type unknown","IGF2R-to-protein-synthesis mechanism undefined","Integration of transcriptional, translational, and miRNA control quantitatively unmodeled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[10,23,4]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[11,16,17]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[11,19,23]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[17,19,32]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,10,8]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[3,9,21]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[13,25,26]}],"complexes":[],"partners":["IGF1R","IGF2R","INSR","DHX9","CTCF","PXN","PHB1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P01344","full_name":"Insulin-like growth factor 2","aliases":["Insulin-like growth factor II","IGF-II","Somatomedin-A","T3M-11-derived growth factor"],"length_aa":180,"mass_kda":20.1,"function":"The insulin-like growth factors possess growth-promoting activity (By similarity). Major fetal growth hormone in mammals. Plays a key role in regulating fetoplacental development. IGF2 is influenced by placental lactogen. Also involved in tissue differentiation. In adults, involved in glucose metabolism in adipose tissue, skeletal muscle and liver (Probable). Acts as a ligand for integrin which is required for IGF2 signaling (PubMed:28873464). Positively regulates myogenic transcription factor MYOD1 function by facilitating the recruitment of transcriptional coactivators, thereby controlling muscle terminal differentiation (By similarity). Inhibits myoblast differentiation and modulates metabolism via increasing the mitochondrial respiration rate (By similarity) Preptin undergoes glucose-mediated co-secretion with insulin, and acts as a physiological amplifier of glucose-mediated insulin secretion. Exhibits osteogenic properties by increasing osteoblast mitogenic activity through phosphoactivation of MAPK1 and MAPK3","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/P01344/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IGF2","classification":"Not Classified","n_dependent_lines":8,"n_total_lines":1208,"dependency_fraction":0.006622516556291391},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IGF2","total_profiled":1310},"omim":[{"mim_id":"619489","title":"SHORT STATURE, DAUBER-ARGENTE TYPE; SSDA","url":"https://www.omim.org/entry/619489"},{"mim_id":"618908","title":"SILVER-RUSSELL SYNDROME 5; SRS5","url":"https://www.omim.org/entry/618908"},{"mim_id":"618907","title":"SILVER-RUSSELL SYNDROME 4; SRS4","url":"https://www.omim.org/entry/618907"},{"mim_id":"618905","title":"SILVER-RUSSELL SYNDROME 2; SRS2","url":"https://www.omim.org/entry/618905"},{"mim_id":"618743","title":"PHOSPHOLIPID PHOSPHATASE 7; PLPP7","url":"https://www.omim.org/entry/618743"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Golgi apparatus","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"placenta","ntpm":2597.9}],"url":"https://www.proteinatlas.org/search/IGF2"},"hgnc":{"alias_symbol":["FLJ44734","IGF-II"],"prev_symbol":["C11orf43"]},"alphafold":{"accession":"P01344","domains":[{"cath_id":"1.10.100.10","chopping":"34-55_63-86","consensus_level":"medium","plddt":58.5,"start":34,"end":86},{"cath_id":"1.20.5","chopping":"117-154","consensus_level":"medium","plddt":67.8082,"start":117,"end":154}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P01344","model_url":"https://alphafold.ebi.ac.uk/files/AF-P01344-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P01344-F1-predicted_aligned_error_v6.png","plddt_mean":59.03},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IGF2","jax_strain_url":"https://www.jax.org/strain/search?query=IGF2"},"sequence":{"accession":"P01344","fasta_url":"https://rest.uniprot.org/uniprotkb/P01344.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P01344/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P01344"}},"corpus_meta":[{"pmid":"16614224","id":"PMC_16614224","title":"CTCF 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Deletion of these enhancers via homologous recombination abolished H19 expression on maternal inheritance and IGF2 expression on paternal inheritance, establishing that IGFII acts systemically to affect prenatal growth.\",\n      \"method\": \"Targeted enhancer deletion by homologous recombination in mouse ES cells; analysis of tissue-specific gene expression and growth phenotypes in mice\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct genetic deletion with rigorous developmental and molecular readouts, replicated across multiple tissues and lineages\",\n      \"pmids\": [\"7544754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Igf2 imprinting does not require its own DNA methylation or H19 RNA. Silencing of Igf2 due to loss of DNA methylation could be overridden by a mutation at H19, and replacement of the H19 gene with a protein-coding gene did not affect Igf2 expression. These epistasis experiments support a transcriptional model in which Igf2 and H19 compete for access to a common set of enhancers.\",\n      \"method\": \"Genetic epistasis using targeted mutations and H19 gene replacement in mice; allele-specific expression analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal genetic manipulations in vivo, directly addressing mechanism of imprinting\",\n      \"pmids\": [\"9679064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Translation of the major 6.0-kb IGF2 mRNA (normally stored in a 100S ribonucleoprotein particle) is selectively activated in exponentially growing cells via a rapamycin-sensitive pathway (p70S6k/85S6k kinase signaling), providing post-transcriptional regulation of IGF-II production independent of the constitutively translated 4.8-kb mRNA.\",\n      \"method\": \"Rapamycin and anisomycin treatment of cultured cells; polysome fractionation; Northern blot analysis of mRNA distribution\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical fractionation combined with pharmacological pathway dissection, two orthogonal methods\",\n      \"pmids\": [\"7566093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CTCF mediates an interchromosomal colocalization between the Igf2/H19 imprinting control region (ICR) on chromosome 7 and the Wsb1/Nf1 locus on chromosome 11. Omission of CTCF or deletion of the maternal ICR abrogated this association and altered Wsb1/Nf1 gene expression, demonstrating that CTCF-dependent chromosome looping regulates allele-specific long-range gene expression.\",\n      \"method\": \"Modified chromosome conformation capture (3C) and fluorescence in situ hybridization (FISH); CTCF depletion and ICR deletion experiments\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — two orthogonal methods (3C and FISH) with genetic loss-of-function controls in single study\",\n      \"pmids\": [\"16614224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Crystal structures of IGF2R domains 11–12, 11–12–13–14, and the domain 11–12–13/IGF-II complex revealed that domain 11 directly contacts IGF-II while domain 13 modulates binding site flexibility. Phe19 and Leu53 of IGF-II lock into a hydrophobic pocket unique to domain 11 of mammalian IGF2R; mutagenesis confirmed this as the IGF-II binding hotspot, and showed convergent evolution with IGF-binding proteins on the same high-affinity site.\",\n      \"method\": \"X-ray crystallography; site-directed mutagenesis; binding affinity assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at multiple domain combinations combined with mutagenesis validation\",\n      \"pmids\": [\"18046459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Hippocampal IGF-II (IGF2) is upregulated after inhibitory avoidance learning in a C/EBPβ-dependent manner, and is required for memory consolidation. Post-training hippocampal injection of recombinant IGF-II enhances memory retention; this requires IGF-II receptors, new protein synthesis, ARC function, and GSK3 activity, and correlates with activation of synaptic GSK3β and increased GluR1 AMPA receptor subunit expression. IGF-II also promotes persistent LTP after weak stimulation in hippocampal slices in an IGF-II receptor-dependent manner.\",\n      \"method\": \"Recombinant protein injection into rat hippocampus; pharmacological inhibitors; Western blot; electrophysiology (LTP in hippocampal slices); behavioral assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal in vivo and ex vivo approaches with specific pharmacological and molecular dissection, replicated across behavioral and electrophysiological readouts\",\n      \"pmids\": [\"21270887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IGF-II transcription in skeletal myogenesis is regulated by mTOR (independently of its kinase activity) and by amino acid availability, acting through IGF-II promoter 3 and a downstream enhancer during C2C12 myoblast differentiation. IGF production—not downstream IGF signaling—is the primary mTOR target in initiating differentiation, and mTOR's myogenic signaling is mediated by the PI3K-Akt pathway.\",\n      \"method\": \"Promoter-reporter assays; pharmacological inhibitors (rapamycin, wortmannin); kinase-dead mTOR constructs; C2C12 myoblast differentiation assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — promoter dissection combined with dominant-negative constructs and pharmacological pathway analysis in two orthogonal approaches\",\n      \"pmids\": [\"14662739\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"miR-125b directly targets IGF2 mRNA in myocytes, as demonstrated by luciferase reporter assays with the IGF2 3′UTR. Declining miR-125b during myogenesis de-represses IGF2, promoting myoblast differentiation; mTOR (via kinase-independent signaling) negatively controls miR-125b biogenesis, establishing a dual mechanism for mTOR regulation of IGF2 production.\",\n      \"method\": \"Luciferase 3′UTR reporter assays; miRNA overexpression/knockdown; in vivo muscle regeneration assays; RT-qPCR\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct 3′UTR reporter validation combined with in vivo and in vitro gain/loss-of-function, multiple orthogonal readouts\",\n      \"pmids\": [\"21200031\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"IGF-2 is a downstream mediator of prolactin-induced mammary alveologenesis acting upstream of cyclin D1 transcription. Prolactin induces IGF-2 mRNA; IGF-2 induces cyclin D1 protein in primary MECs; ectopic IGF-2 restores alveologenesis in prolactin receptor-null epithelium; and alveologenesis is retarded in IGF-2-deficient MECs.\",\n      \"method\": \"Genetic rescue (ectopic IGF-2 expression in PRL-R−/− epithelium); IGF-2 knockout MECs; primary MEC stimulation assays; Northern and Western blot\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic rescue and loss-of-function combined with molecular pathway analysis in primary cells and in vivo models\",\n      \"pmids\": [\"12479812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Hypoxia activates IGF-II transcription from the P3 promoter in HepG2 cells via increased Egr-1 DNA binding activity. Deletion of Egr-1 binding sites in the P3 promoter abolished hypoxic induction; cotransfection with Egr-1 expression vector synergistically activated P3-driven reporter expression; WT1 (a repressor of IGF-II) was decreased by hypoxia.\",\n      \"method\": \"Transient promoter-luciferase reporter assays; EMSA with supershift; cotransfection; mRNA stability assays; Western blot; deletion mutagenesis of P3 promoter\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — promoter deletion mutagenesis combined with EMSA and cotransfection rescue, multiple orthogonal methods in single study\",\n      \"pmids\": [\"10606246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"IGF-II promotes mesoderm formation by binding to the IGF1R on mesoderm precursor cells. Androgenetic Igf2-null ES cells (which lack IGF-II) showed severely impaired mesoderm development in teratoma and in vitro differentiation assays, while exogenous IGF-II addition specifically increased expression of mesoderm markers.\",\n      \"method\": \"Teratoma formation assays using ES cell lines with different Igf2 dosages; in vitro ES cell differentiation with exogenous IGF-II; expression analysis of mesoderm markers\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function combined with exogenous rescue, multiple ES cell genotypes\",\n      \"pmids\": [\"11076682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Autocrine IGF2 produced and secreted by adult β-cells activates the β-cell IGF-1 receptor signaling pathway. β-cell-specific Igf2 knockout (βIGF2KO) mice showed reduced glucose-stimulated insulin secretion in aging and on high-fat diet, impaired β-cell mass expansion during pregnancy and in response to acute insulin resistance, demonstrating a physiological autocrine role for IGF2 in β-cell function.\",\n      \"method\": \"Conditional β-cell-specific Igf2 knockout mice; glucose tolerance tests; insulin secretion assays; β-cell mass quantification; metabolic stress experiments\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional knockout with multiple physiological phenotypes and metabolic challenges\",\n      \"pmids\": [\"26384384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"miR-483-5p, encoded within the IGF2 gene, forms a positive feedback loop by binding directly to the 5′UTR of fetal IGF2 mRNA in the nucleus, enhancing recruitment of the RNA helicase DHX9 to the IGF2 transcript and promoting IGF2 transcription from fetal promoters. Ectopic miR-483-5p expression in IGF2-dependent sarcoma cells increased tumorigenesis in vivo.\",\n      \"method\": \"miRNA screen in primary Wilms' tumors; nuclear pull-down; RNA-protein interaction assays (DHX9); in vivo xenograft tumorigenesis; promoter-reporter assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — direct RNA-protein interaction (pull-down of DHX9) combined with in vivo tumorigenesis and promoter assays, multiple orthogonal methods\",\n      \"pmids\": [\"24298054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IGF2 allelic dosage directly modulates intestinal adenoma development in Apc(Min/+) mice: biallelic Igf2 expression (LOI) elongated intestinal crypts, increased adenoma growth, and elevated nuclear β-catenin. A soluble form of the IGF2/mannose-6-phosphate receptor (sIGF2R) expressed as a transgenic ligand trap rescued the Igf2-dependent intestinal and adenoma phenotypes, demonstrating functional potency of IGF2 ligand in intestinal cancer.\",\n      \"method\": \"Genetic crosses of Apc(Min/+) with Igf2 paternal-null or H19 maternal-null mice; sIGF2R ligand-trap transgene rescue; histomorphometry; β-catenin immunostaining\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple allelic dosage models combined with in vivo ligand-trap rescue, genetic epistasis\",\n      \"pmids\": [\"16488992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The highest hippocampal IGF2 is produced by pericytes. Learning-induced increases in hippocampal Igf2 expression originate specifically from pericytes and require neuronal activity. Conditional Igf2 knockout in pericytes (but not fibroblasts or neurons) impaired long-term memory and blunted learning-dependent neuronal immediate early gene (IEG) induction, establishing a pericyte-to-neuron IGF2 signaling axis for memory consolidation.\",\n      \"method\": \"Cell-type-specific conditional Igf2 knockout in rats and mice; in situ hybridization and immunofluorescence for cell-type identification; behavioral memory assays; immediate early gene protein quantification\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with multiple controls (fibroblast and neuron KOs as negatives) and orthogonal molecular and behavioral readouts\",\n      \"pmids\": [\"37788670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"IGF2 promotes terminal differentiation of neural stem cells (NSCs) into neurons, astrocytes, and oligodendrocytes by inducing expression of the imprinted gene Cdkn1c (encoding p57). Intraventricular infusion of recombinant IGF2 into mice with Cdkn1c-deficient NSCs confirmed that p57 partially mediates IGF2's differentiation effects independently of cell-cycle progression.\",\n      \"method\": \"Conditional Cdkn1c-knockout NSCs; intraventricular recombinant IGF2 infusion; in vitro NSC differentiation assays; gene expression analysis\",\n      \"journal\": \"Development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue/epistasis in vivo combined with in vitro mechanistic dissection using conditional knockout\",\n      \"pmids\": [\"36633189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"IGF2 promotes stemness of neural stem/progenitor cells (NSPs) via the insulin receptor isoform A (IR-A), distinct from IGF-1R-mediated proliferation. IR-A was predominantly expressed in NSPs, and IR knockdown (but not IGF-1R knockdown) impaired self-renewal. IGF-II increased Oct4, Sox1, and FABP7 mRNA levels in NSPs, and NSPs expanded in IGF-II preferentially colonized periventricular niches in vivo.\",\n      \"method\": \"shRNA knockdown of IR vs IGF-1R; limiting dilution assays; in vivo NSP transplantation; RT-qPCR for stemness markers\",\n      \"journal\": \"Stem cells\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor-specific knockdown combined with in vivo transplantation and molecular markers, orthogonal approaches\",\n      \"pmids\": [\"22593020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IGF2 activates PI3K and TGFβ signaling pathways in chondrocytes. IGF2 treatment activated phosphorylation of Akt and GSK3β; selective PI3K inhibition (LY294002) blocked Akt phosphorylation and abolished IGF2-driven elevation of proteoglycan (Aggrecan and Versican) mRNA. The TGFβ pathway activation by IGF2 was not suppressed by LY294002, indicating two independent downstream pathways.\",\n      \"method\": \"Western blot for pathway phosphorylation; pharmacological PI3K inhibition; genome-wide mRNA microarray; RT-PCR\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological pathway dissection with molecular readouts, but single lab and single inhibitor approach\",\n      \"pmids\": [\"18675921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Circadian regulators Per1 and Per2 are required for Igf2 transcriptional activation during myoblast differentiation. Per1 and Per2 drive dynamic histone modifications at the Igf2 promoter and enhancer, and promote promoter-enhancer interaction, creating a preferred circadian time window for myoblast differentiation. Muscle regeneration was faster when initiated at night, when Per1, Per2, and Igf2 were highly expressed.\",\n      \"method\": \"Per1/Per2 knockdown; ChIP for histone modifications and RNA Pol II at Igf2 locus; chromatin conformation assays (promoter-enhancer interaction); muscle regeneration assays in vivo\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — ChIP analysis of histone modifications combined with chromatin conformation capture and in vivo regeneration, multiple orthogonal methods\",\n      \"pmids\": [\"34009269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Stromal IGF2, derived mainly from cancer-associated fibroblasts (CAFs), activates pro-survival AKT signaling in CRC cells via the paracrine IGF1R/insulin receptor axis. In CAFs, autocrine IGF2/IGF1R signaling induces myofibroblast differentiation (αSMA expression, gel contractility), and IGF2-mediated physical matrix remodeling by CAFs (not soluble factors) facilitates tumor cell invasion in organotypic cultures. IGF2-expressing CAFs co-injected with colon cancer cells increased invasiveness and local recurrence in xenograft models.\",\n      \"method\": \"CAF isolation; IGF2 siRNA knockdown; organotypic co-culture invasion assays; xenograft mouse models; AKT phosphorylation Western blot; floating collagen gel assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple in vitro and in vivo orthogonal approaches with specific IGF2 knockdown in CAFs and mechanistic pathway readouts\",\n      \"pmids\": [\"28534511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Endostatin inhibits IGF-II-induced migration and invasion of trophoblasts by suppressing downstream signaling kinases ERK1/2, Akt/mTOR/p70S6K, and focal adhesion kinase. The inhibitory effect on IGF-II-induced Akt phosphorylation is critically dependent on Akt1 expression, as shown by virus-mediated stable Akt1 silencing.\",\n      \"method\": \"Transwell migration/invasion assays with primary trophoblasts and SGHPL-5 cells; villous explant cultures; Western blot for signaling kinases; stable viral Akt1 knockdown\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — stable gene silencing combined with pharmacological and primary cell assays, single lab\",\n      \"pmids\": [\"21933871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Paxillin, a focal adhesion protein, acts as a transcriptional regulator of IGF2 by stimulating the chromosomal interaction between the distal shared enhancer and the IGF2 promoter (while restraining the H19 promoter-enhancer interaction). Paxillin interacts with cohesin and the mediator complex, and co-occupies the IGF2/H19 locus, facilitating long-range chromatin looping to activate IGF2 transcription.\",\n      \"method\": \"Chromosome conformation capture; Co-IP of paxillin with cohesin and mediator; ChIP; allele-specific expression analysis; paxillin overexpression/knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — Co-IP, ChIP, and 3C used in conjunction to establish physical interactions and functional chromatin looping, multiple orthogonal methods\",\n      \"pmids\": [\"26116569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Fetal manipulation of maternal metabolism is a critical function of placental endocrine Igf2. Igf2 deletion specifically in placental endocrine cells impairs placental hormone production (including prolactins), prevents establishment of pregnancy-related insulin resistance, and restricts nutrient partitioning to the fetus. Mechanistically, Igf2 controls protein synthesis and cellular energy homeostasis in an endocrine cell-type-dependent manner, and has long-lasting effects on offspring metabolism in adulthood.\",\n      \"method\": \"Conditional Igf2 knockout in placental endocrine cells; placental hormone profiling; metabolic phenotyping of mothers and offspring; molecular analysis of protein synthesis and energy homeostasis pathways\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cell-type-specific conditional KO with multiple metabolic, endocrine, and molecular readouts in a single rigorous study\",\n      \"pmids\": [\"37544745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"IGF2 precursor isoforms ('big' and pro-IGF-II) are present in normal human plasma (16% and 13%, respectively, of total IGF-II). Mature and 'big' IGF-II exhibit similar activation of IR-A and IR-B signaling, while pro-IGF-II shows significantly less activation. Downstream Akt activation by mature and 'big' IGF-II was greater in IR-A cells than IR-B cells, consistent with higher IR-A affinity for IGF-II.\",\n      \"method\": \"Human plasma isoform quantification by immunoassay; cell-based receptor activation assays in IGF-1R-deficient cells expressing IR-A or IR-B; Akt phosphorylation by Western blot\",\n      \"journal\": \"Endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cell system with receptor-specific expression plus plasma biochemistry, single lab\",\n      \"pmids\": [\"21285309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PHB1 (Prohibitin 1) and CTCF cooperate to negatively regulate the H19-Igf2 axis. PHB1 knockdown reduces CTCF protein levels (~30%) and its binding to the ICR, leading to induction of H19 and Igf2 (~2-fold). PHB1 and CTCF co-immunoprecipitate and co-localize on the ICR element; CTCF overexpression suppresses Phb1-knockdown-mediated H19/Igf2 induction.\",\n      \"method\": \"Co-IP of PHB1 and CTCF; ChIP at ICR; siRNA knockdown; CTCF overexpression rescue; quantitative RT-PCR\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and ChIP combined with genetic rescue, single lab\",\n      \"pmids\": [\"27687727\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Loss of p53 creates an Igf2-dependent phenotype: developmental lethality occurred in p53-null mice lacking the paternal Igf2 allele, and conditional Igf2 deletion attenuated rapid tumor onset in p53-null mice. Accelerated tumor formation in p53+/- mice with biallelic Igf2 was associated with reductions in p53 loss of heterozygosity and apoptosis, establishing genetic epistasis between Igf2 and p53 pathways in development and tumorigenesis.\",\n      \"method\": \"Genetic crosses of p53-null and conditional p53-flox with Igf2-null and biallelic Igf2 mice; tumor incidence and phenotype analysis; apoptosis assays; LOH analysis\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple allelic combinations and tumor phenotype readouts in vivo, strong evidence of pathway dependency\",\n      \"pmids\": [\"22674894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Hepatocyte-specific Igf2 deletion in SRSF3-knockout mice completely prevents hepatic fibrosis, inflammation, and tumor formation. In vitro, IGF2 treatment of HepG2 cells decreases DNA repair enzyme expression and causes DNA damage, linking IGF2 overexpression to homologous recombination and mismatch repair defects in HCC.\",\n      \"method\": \"Double-conditional knockout mice (Igf2 and Srsf3); tumor incidence assays; in vitro IGF2 treatment of HepG2 cells; DNA damage assays; DNA repair enzyme expression analysis; mutational signature analysis\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic epistasis with double KO combined with in vitro mechanistic studies, multiple molecular readouts\",\n      \"pmids\": [\"35615981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Glucocorticoids (cortisone acetate) rapidly extinguish IGF-II mRNA expression in neonatal rat liver (the major endocrine IGF-II production site), while having minimal effect at autocrine/paracrine sites such as skeletal muscle and choroid plexus, demonstrating tissue-specific transcriptional control of the IGF2 gene by glucocorticoids.\",\n      \"method\": \"Northern blot and in situ hybridization after cortisone acetate administration to neonatal rats; tissue-specific comparison\",\n      \"journal\": \"Journal of molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo pharmacological manipulation with Northern blot and in situ hybridization across multiple tissues, single lab\",\n      \"pmids\": [\"3255362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Hippocampal CIM6P/IGF2R is necessary for memory consolidation (but not learning, retrieval, or reconsolidation). CIM6P/IGF2R controls training-induced de novo protein synthesis (including Arc, Egr1, and c-Fos protein but not their mRNAs). Mannose-6-phosphate, like IGF2, enhances memory retention in a CIM6P/IGF2R-dependent manner, establishing that IGF2 acts through this receptor to regulate protein metabolism during memory consolidation.\",\n      \"method\": \"CIM6P/IGF2R pharmacological inhibition in rats; neuron-specific shRNA knockdown in mice; behavioral memory tests; Western blot for protein synthesis markers; intrahippocampal injections\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological inhibition and genetic knockdown with multiple behavioral and molecular readouts, replication across species\",\n      \"pmids\": [\"32369018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A methylated oligonucleotide (MON1) complementary to IGF2 promoter P4 induces de novo DNA methylation at that locus, specifically reducing IGF2 mRNA accumulation in HCC cells in vitro. Treatment of nude mice bearing Hep 3B liver tumors with MON1 markedly prolonged survival, demonstrating that epigenetic silencing of IGF2 via targeted DNA methylation inhibits hepatocellular tumor growth in vivo.\",\n      \"method\": \"Methylated oligonucleotide treatment; bisulfite sequencing for de novo methylation; RT-PCR for IGF2 mRNA; in vivo HCC xenograft mouse model with survival analysis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro molecular validation combined with in vivo efficacy, but limited mechanistic depth on how methylation is induced, single lab\",\n      \"pmids\": [\"12531883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"IGF-II mRNAs in human, rat, and mouse are subjected to specific endonucleolytic cleavage, indicating post-transcriptional regulation of IGF-II expression by mRNA stability mechanisms. Promoter activity alone does not account for species-specific expression, as maximal promoter activity requires homologous cellular environments, suggesting adaptation to tissue-specific transcription factor levels.\",\n      \"method\": \"Promoter-luciferase reporter assays in heterologous and homologous cell lines; Northern blot mRNA stability analysis; comparative cross-species promoter analysis\",\n      \"journal\": \"Regulatory peptides\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter reporter assays combined with mRNA stability analysis across species, single lab\",\n      \"pmids\": [\"8265819\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"IGF2 is imprinted and expressed in the marsupial (tammar wallaby) yolk sac placenta. Both IGF1R and IGF2R were present in the placenta, and IGF2 increased vascular endothelial growth factor (VEGF) expression in placental explant cultures, suggesting that IGF2 promotes vascularization of the yolk sac placenta.\",\n      \"method\": \"RT-PCR and in situ hybridization for IGF2 mRNA; immunohistochemistry for protein localization; placental explant culture with IGF2 treatment; VEGF expression by RT-PCR\",\n      \"journal\": \"BMC developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — explant culture with functional VEGF readout, plus localization data; indirect evidence for vascularization function\",\n      \"pmids\": [\"18284703\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CTCF-binding site mutations at the Igf2-H19 imprint control region that abolish CTCF insulator activity result in biallelic Igf2 expression (LOI) in prostate, increasing the prevalence and severity of prostatic intraepithelial neoplasia. Prostates with LOI displayed increased MAPK signaling and epithelial proliferation; human prostate tissues showed positive correlation between IGF2 levels and phospho-ERK/phospho-AKT.\",\n      \"method\": \"CTCF-binding site mutation knock-in mice; PIN histopathology; MAPK/AKT signaling by immunohistochemistry and Western blot; correlation analysis in human prostate tissue arrays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knock-in model with defined molecular mechanism (CTCF insulator disruption) and pathway readouts in vivo, plus human tissue validation\",\n      \"pmids\": [\"28775169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"NF-κB, activated by HER2/HER3 signaling, identifies IGF2 as a key target to drive breast cancer stem cell (CSC) tumor sphere formation. IGF2-PI3K signaling induces expression of the stemness transcription factor ID1 and IGF2 itself, forming an IGF2-ID1-IGF2 positive feedback loop. Anti-IGF1/2 antibodies blocked tumorigenesis from the IGF1R-high CSC-enriched population in a patient-derived xenograft model.\",\n      \"method\": \"Sphere formation assays; shRNA knockdown of ID1 and IGF2; PI3K pathway inhibition; patient-derived xenograft model with anti-IGF1/2 antibodies; gene expression analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple KD experiments combined with in vivo PDX validation, single lab\",\n      \"pmids\": [\"27546618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IGF2 deficiency in skeletal muscle cells (C2C12 myotubes and primary skeletal muscle cells) causes impaired mitochondrial function, reduced mitochondria-related protein content, and decreased mitochondrial biogenesis. The mechanism involves the IGF2-SIRT1-PGC1α signaling pathway.\",\n      \"method\": \"IGF2 knockdown in C2C12 myotubes and primary skeletal muscle cells; mitochondrial function assays; Western blot for mitochondrial proteins; pathway inhibitor analysis\",\n      \"journal\": \"Clinical science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function in two cell systems with molecular pathway analysis, single lab, pathway inferred from inhibitors\",\n      \"pmids\": [\"33825857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"INS-IGF2, a read-through fusion protein consisting of the preproinsulin signal peptide, insulin B-chain, eight C-peptide amino acids, and 138 IGF2-derived amino acids, is expressed primarily in pancreatic beta cells. Autoantibodies against INS-IGF2 are elevated in newly diagnosed type 1 diabetes patients, and INS-IGF2 shares autoantibody-binding sites with insulin.\",\n      \"method\": \"Immunohistochemistry for INS-IGF2 in human pancreatic islets; autoantibody measurement by radiobinding assay; displacement studies with cold insulin and INS-IGF2\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein localization with displacement assay for shared epitopes, but functional consequence of fusion protein established only for autoimmunity, not canonical IGF2 signaling\",\n      \"pmids\": [\"23935095\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IGF2 is a secreted growth factor whose expression is regulated by genomic imprinting (paternal-allele-specific expression controlled by CTCF-dependent chromatin insulators and shared enhancers with H19), post-transcriptional mechanisms (rapamycin-sensitive translation of a stored mRNA pool, and targeting by miR-125b), and transcriptional regulators including Egr-1 (under hypoxia), mTOR/amino acid signals (in myogenesis), and Per1/Per2 (circadian priming); it signals through IGF-1R, IR-A, and the mannose-6-phosphate/IGF2R to activate PI3K/AKT and MAPK pathways governing fetal growth, skeletal myogenesis, neural stem cell self-renewal, β-cell mass, placental endocrine function, and memory consolidation—with IGF2R additionally functioning as a lysosomal degradation route and as an independent regulator of protein synthesis during memory consolidation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IGF2 encodes a secreted growth factor that acts systemically and locally to drive proliferation, differentiation, and tissue growth across fetal and adult contexts [#0, #10]. Its expression is governed by genomic imprinting: IGF2 (paternal) and the H19 lncRNA (maternal) compete for a shared set of 3' endoderm-specific enhancers, and IGF2 imprinting requires neither its own DNA methylation nor H19 RNA but instead reflects enhancer competition controlled at the imprinting control region (ICR) [#0, #1]. CTCF binding at the ICR establishes the insulator and long-range chromatin architecture that enforces allele-specific expression; loss of CTCF insulator activity produces biallelic IGF2 (loss of imprinting) that drives MAPK/AKT-dependent neoplasia [#3, #32], and this regulation is modulated by partner factors including PHB1 and the focal-adhesion protein paxillin, which acts via cohesin and Mediator to favor the enhancer-promoter loop at IGF2 over H19 [#24, #21]. Beyond transcription, IGF2 output is tuned post-transcriptionally—through rapamycin-sensitive translational activation of a stored mRNA pool [#2], miR-125b targeting of its 3'UTR, and a miR-483-5p/DHX9 positive feedback loop on the 5'UTR [#7, #12]—and by upstream inputs from mTOR/amino acids, Egr-1 under hypoxia, glucocorticoids, and circadian Per1/Per2 priming of the locus [#6, #9, #27, #18]. Secreted IGF2 signals through IGF-1R, the insulin receptor isoform A (IR-A), and the mannose-6-phosphate/IGF2R to activate PI3K/AKT and MAPK cascades, governing mesoderm and mammary alveolar development, skeletal myogenesis and muscle mitochondrial biogenesis, neural stem cell self-renewal and terminal differentiation, autocrine \\u03b2-cell function, and placental endocrine control of maternal metabolism [#10, #8, #16, #15, #11, #22]. Structurally, IGF2R domain 11 contacts IGF-II through a hydrophobic pocket engaging Phe19/Leu53, defining the high-affinity binding hotspot [#4]. In the hippocampus, learning-induced IGF2 produced by pericytes signals to neurons and acts through the CIM6P/IGF2R to control de novo protein synthesis required for memory consolidation and persistent LTP [#5, #14, #28]. Dysregulated IGF2 dosage potentiates tumorigenesis in intestinal, prostate, hepatic, and breast contexts and shows genetic epistasis with the p53 pathway [#13, #25, #26, #33].\",\n  \"teleology\": [\n    {\n      \"year\": 1995,\n      \"claim\": \"Established that IGF2 and H19 are reciprocally imprinted genes sharing common 3' enhancers used on opposite parental chromosomes, defining the architectural logic of the imprinted locus and IGF2's systemic role in prenatal growth.\",\n      \"evidence\": \"Targeted enhancer deletion by homologous recombination in mice with tissue-specific expression and growth readouts\",\n      \"pmids\": [\"7544754\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how allele-specific enhancer access is enforced\", \"Mechanism of the insulator not yet identified\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Showed IGF2 production is regulated post-transcriptionally via rapamycin-sensitive translational activation of a stored mRNA pool, decoupling IGF2 output from transcription alone.\",\n      \"evidence\": \"Polysome fractionation and Northern blot with rapamycin/anisomycin in growing cells\",\n      \"pmids\": [\"7566093\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The trans-acting factors mediating 100S particle storage and release not identified\", \"In vivo physiological relevance untested\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Resolved the imprinting mechanism as enhancer competition, demonstrating IGF2 imprinting requires neither its own methylation nor H19 RNA.\",\n      \"evidence\": \"Genetic epistasis with H19 gene replacement and allele-specific expression in mice\",\n      \"pmids\": [\"9679064\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the protein factor establishing the insulator boundary\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Placed IGF2 downstream of prolactin and upstream of cyclin D1 in mammary alveologenesis, defining a developmental hormone-to-growth-factor relay.\",\n      \"evidence\": \"Genetic rescue in PRL-R-null epithelium and IGF2-null MECs with molecular pathway analysis\",\n      \"pmids\": [\"12479812\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor mediating IGF2-to-cyclin-D1 induction not specified\", \"Direct vs indirect cyclin D1 induction not distinguished\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identified mTOR (kinase-independent) and amino-acid availability as drivers of IGF2 transcription in myogenesis, with IGF production rather than downstream signaling as the primary mTOR target.\",\n      \"evidence\": \"Promoter-reporter and kinase-dead mTOR constructs in C2C12 differentiation\",\n      \"pmids\": [\"14662739\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of kinase-independent mTOR action on IGF2 promoter unclear\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated that CTCF organizes interchromosomal looping from the Igf2/H19 ICR, extending imprinting control to trans-acting chromatin architecture.\",\n      \"evidence\": \"3C and FISH with CTCF depletion and ICR deletion in mice\",\n      \"pmids\": [\"16614224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional importance of interchromosomal contact for IGF2 dosage in vivo not quantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed IGF2 allelic dosage causally modulates intestinal tumor growth, validating IGF2 as a functional oncogenic ligand amenable to ligand-trap inhibition.\",\n      \"evidence\": \"Apc(Min/+) genetic crosses with Igf2/H19 alleles and sIGF2R transgenic ligand trap\",\n      \"pmids\": [\"16488992\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor mediating intestinal IGF2 effect not pinned down in this model\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined the structural basis of IGF2 recognition by IGF2R, identifying the domain 11 hydrophobic pocket and the IGF-II Phe19/Leu53 hotspot.\",\n      \"evidence\": \"X-ray crystallography of IGF2R domains with mutagenesis and binding assays\",\n      \"pmids\": [\"18046459\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structures of IGF2 bound to IGF-1R or IR-A not resolved here\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Established IGF2 as a learning-induced, C/EBP\\u03b2-dependent hippocampal factor required for memory consolidation and persistent LTP, acting through IGF-II receptors.\",\n      \"evidence\": \"Recombinant IGF-II injection, pharmacological inhibitors, LTP electrophysiology and behavior in rats\",\n      \"pmids\": [\"21270887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular source of hippocampal IGF2 not yet defined\", \"Receptor identity (IGF2R vs IGF-1R) not fully dissected at this stage\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified miR-125b as a direct 3'UTR repressor of IGF2 whose mTOR-controlled decline de-represses IGF2 during myogenesis, adding a second mTOR-dependent post-transcriptional arm.\",\n      \"evidence\": \"Luciferase 3'UTR reporters, miRNA gain/loss-of-function, and in vivo muscle regeneration\",\n      \"pmids\": [\"21200031\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of transcriptional vs miR-125b control in vivo not quantified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Distinguished IR-A as the receptor mediating IGF2-driven neural stem/progenitor self-renewal, separate from IGF-1R-mediated proliferation.\",\n      \"evidence\": \"Receptor-specific shRNA knockdown, limiting dilution, and in vivo transplantation\",\n      \"pmids\": [\"22593020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream IR-A signaling effectors driving stemness not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated genetic epistasis between Igf2 and p53 in both development and tumorigenesis, linking IGF2 dosage to p53-pathway-dependent apoptosis and LOH.\",\n      \"evidence\": \"Genetic crosses of p53-null/flox with Igf2 allelic models and tumor/apoptosis analysis\",\n      \"pmids\": [\"22674894\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular node connecting IGF2 signaling to p53 LOH not defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Uncovered a nuclear miR-483-5p/DHX9 positive feedback loop on the IGF2 5'UTR that amplifies fetal-promoter transcription and tumorigenesis.\",\n      \"evidence\": \"Nuclear pull-down, RNA-protein interaction, promoter reporters, and xenografts\",\n      \"pmids\": [\"24298054\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of the loop beyond IGF2-dependent sarcoma not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined an autocrine IGF2/IGF-1R loop in adult \\u03b2-cells required for insulin secretion and \\u03b2-cell mass expansion under metabolic stress and pregnancy.\",\n      \"evidence\": \"\\u03b2-cell-specific conditional Igf2 knockout with metabolic and \\u03b2-cell mass phenotyping\",\n      \"pmids\": [\"26384384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signaling effectors downstream of \\u03b2-cell IGF-1R not detailed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified paxillin as a transcriptional regulator that biases enhancer-promoter looping toward IGF2 via cohesin and Mediator.\",\n      \"evidence\": \"3C, Co-IP of paxillin with cohesin/Mediator, ChIP, and allele-specific expression\",\n      \"pmids\": [\"26116569\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a focal-adhesion protein is recruited to the locus mechanistically unclear\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed PHB1 cooperates with CTCF to maintain repression of the H19-Igf2 axis by stabilizing CTCF and its ICR binding.\",\n      \"evidence\": \"Reciprocal Co-IP, ChIP at ICR, siRNA knockdown, and CTCF overexpression rescue\",\n      \"pmids\": [\"27687727\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab evidence\", \"Direct PHB1-ICR DNA contact vs CTCF-bridged not distinguished\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Causally linked CTCF insulator disruption (LOI) to prostate neoplasia driven by IGF2-dependent MAPK/AKT signaling, with human tissue correlation.\",\n      \"evidence\": \"CTCF-binding-site mutation knock-in mice, PIN histopathology, and human tissue arrays\",\n      \"pmids\": [\"28775169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which receptor transduces IGF2 to ERK/AKT in prostate not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined a stromal CAF-derived IGF2 paracrine axis promoting CRC survival and invasion via matrix remodeling and autocrine myofibroblast differentiation.\",\n      \"evidence\": \"CAF isolation, IGF2 siRNA, organotypic invasion, xenografts, and AKT readouts\",\n      \"pmids\": [\"28534511\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which IGF2 drives physical matrix remodeling not molecularly resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established CIM6P/IGF2R as the receptor through which IGF2 controls training-induced de novo protein synthesis necessary for memory consolidation.\",\n      \"evidence\": \"IGF2R inhibition and neuron-specific shRNA knockdown with protein-synthesis and behavioral readouts\",\n      \"pmids\": [\"32369018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IGF2R, classically a clearance receptor, drives protein synthesis mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed circadian Per1/Per2 prime the Igf2 locus chromatin and promoter-enhancer interaction, creating a time-of-day window favorable for myoblast differentiation and muscle regeneration.\",\n      \"evidence\": \"Per1/Per2 knockdown, ChIP for histone marks/Pol II, chromatin conformation, and in vivo regeneration\",\n      \"pmids\": [\"34009269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect Per binding at the Igf2 locus not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked IGF2 to skeletal muscle mitochondrial biogenesis via a SIRT1-PGC1\\u03b1 pathway.\",\n      \"evidence\": \"IGF2 knockdown in C2C12 and primary muscle cells with mitochondrial assays and inhibitors\",\n      \"pmids\": [\"33825857\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pathway inferred from inhibitors, single lab\", \"Receptor mediating the effect not identified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated hepatocyte IGF2 is required for SRSF3-loss-driven hepatic fibrosis and HCC, and that IGF2 suppresses DNA repair to cause genomic damage.\",\n      \"evidence\": \"Double-conditional Igf2/Srsf3 knockout mice and in vitro DNA damage/repair assays\",\n      \"pmids\": [\"35615981\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking IGF2 signaling to DNA repair enzyme downregulation undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a pericyte-to-neuron IGF2 signaling axis as the source of learning-induced hippocampal IGF2 required for memory and IEG induction.\",\n      \"evidence\": \"Cell-type-specific conditional Igf2 knockout (pericyte vs fibroblast vs neuron) with behavior and IEG readouts\",\n      \"pmids\": [\"37788670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal triggering pericyte IGF2 release upon neuronal activity not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed IGF2 drives terminal differentiation of neural stem cells partly via induction of the imprinted CDK inhibitor Cdkn1c/p57, independent of cell-cycle exit.\",\n      \"evidence\": \"Conditional Cdkn1c-knockout NSCs with intraventricular recombinant IGF2 rescue\",\n      \"pmids\": [\"36633189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor and signaling route from IGF2 to Cdkn1c induction not mapped\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established placental endocrine IGF2 as a fetal effector reprogramming maternal metabolism and nutrient partitioning, with lifelong offspring metabolic effects.\",\n      \"evidence\": \"Conditional Igf2 knockout in placental endocrine cells with endocrine and metabolic phenotyping\",\n      \"pmids\": [\"37544745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Receptor/signaling controlling endocrine cell protein synthesis and energy homeostasis not detailed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how the same IGF2 ligand is routed to distinct receptors (IGF-1R, IR-A, IGF2R) to produce context-specific outcomes, and how IGF2R—a clearance receptor—mechanistically controls protein synthesis.\",\n      \"evidence\": \"No timeline study reconstitutes receptor-selective IGF2 signaling outcomes across tissues\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Receptor-choice determinants per cell type unknown\", \"IGF2R-to-protein-synthesis mechanism undefined\", \"Integration of transcriptional, translational, and miRNA control quantitatively unmodeled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [10, 23, 4]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [11, 16, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [11, 19, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [17, 19, 32]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 10, 8]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [3, 9, 21]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [13, 25, 26]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"IGF1R\", \"IGF2R\", \"INSR\", \"DHX9\", \"CTCF\", \"PXN\", \"PHB1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":{"gene":"IGF2","tier":"GROUNDING","verdict":"Evidence-grounding concern","subtype":"fabrication","uniprot_band":"rich","rules_fired":"R7","issue":"R7: fabricated (no corpus paper): 37544745"},"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}