{"gene":"NEFM","run_date":"2026-06-10T05:19:52","timeline":{"discoveries":[{"year":1987,"finding":"Rat NF-M protein has a calculated molecular weight of 95,600 Da but migrates anomalously on SDS-PAGE; it contains a conserved rod segment and an unusual C-terminal extension rich in glutamic acid that contributes to anomalous migration. In vitro translation of the full-length cDNA produces a product that comigrates with native NF-M even without phosphorylation.","method":"cDNA cloning, sequencing, in vitro transcription/translation in rabbit reticulocyte lysate, SDS-PAGE","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro reconstitution with full-length protein, sequence-based structural inference confirmed by co-migration experiment","pmids":["2441012"],"is_preprint":false},{"year":1984,"finding":"NF-M has a non-alpha-helical arginine-rich head (residues 1–98), a coiled-coil rod domain (residues 99–412), and a ~500-residue carboxy-terminal tailpiece extension rich in lysine and glutamic acid; the rod domain mediates coiled-coil interactions with NF-L for co-polymerization into filaments, while the acidic tailpiece forms an autonomous extra-filamentous domain capable of interactions with other neuronal components.","method":"Direct protein sequencing of porcine NF-M (amino-terminal 436 residues), structural analysis","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct protein sequencing with structural domain identification, foundational architecture paper","pmids":["6439558"],"is_preprint":false},{"year":1987,"finding":"The mouse NF-M gene contains two introns, both located within the conserved rod domain-coding region, in positions that align with two of the NF-L gene introns; the NF-M and NF-L genes are chromosomally linked, and the anomalous intron arrangement compared to other intermediate filament genes suggests an RNA-mediated transposition event in neurofilament gene evolution.","method":"Genomic cloning, sequencing, chromosomal linkage analysis","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genomic sequencing with chromosomal mapping, single lab","pmids":["3036526"],"is_preprint":false},{"year":1989,"finding":"NF-M expressed in fibroblasts (non-neuronal cells) assembles into intermediate filament arrays and co-polymerizes with endogenous vimentin, demonstrating that NF-M assembly does not require neuron-specific factors.","method":"Stable DNA transfection into L cells and 3T6 fibroblasts, immunofluorescence, immunoelectron microscopy","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct co-localization by immunoelectron microscopy confirmed co-assembly; replicated across cell lines","pmids":["2516804"],"is_preprint":false},{"year":1989,"finding":"NF-L and NF-M coassemble with vimentin when expressed in fibroblasts, forming copolymeric intermediate filaments; NF-L accumulation to ~9% of cell protein did not affect cell viability, and vimentin solubility was altered, indicating physical incorporation of NF-L into vimentin filaments.","method":"Transient and stable DNA transfection of mouse fibroblasts, immunofluorescence, solubility fractionation","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional evidence from multiple stable cell lines, solubility change as orthogonal readout","pmids":["2493000"],"is_preprint":false},{"year":1990,"finding":"Deletions into the alpha-helical rod domain of NF-M generate assembly-incompetent or dominant-negative polypeptides; carboxy-terminal rod deletions produce dominant mutants that disrupt vimentin/NF-L filament arrays even at ~1% of wild-type subunit levels, while amino-terminal rod deletions produce pseudo-recessive mutants. Tail and head domain deletions (up to 90% and 70% respectively) do not prevent incorporation into filament networks, establishing the rod domain as essential for assembly.","method":"Site-directed mutagenesis, transient transfection of mouse fibroblasts, immunofluorescence with epitope-tagged constructs","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — systematic deletion mutagenesis with functional readout, dominant-negative titration experiment","pmids":["2121743"],"is_preprint":false},{"year":1992,"finding":"Phosphorylated fragments of the human NF-M C-terminal repeat domain (13-mer and 17-mer KSP-containing peptides) undergo Al3+- and Ca2+-induced conformational changes from random coil to beta-pleated sheet, forming precipitating intermolecular complexes; unphosphorylated peptides do not exhibit this behavior with Al3+.","method":"Circular dichroism spectroscopy with metal-ion titration of synthetic phosphopeptides","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — rigorous biophysical method on synthetic peptides, single lab, peptide model only","pmids":["1542114"],"is_preprint":false},{"year":1992,"finding":"NF-M protein is expressed in myelin-forming Schwann cells (before myelination commitment), co-localizes with vimentin by immunoelectron microscopy, and is induced by elevated intracellular cAMP. Sequencing of the Schwann cell NF-M cDNA confirmed identity with neuronal NF-M.","method":"Immunoelectron microscopy, immunological comparison, cAMP stimulation, cDNA cloning and sequencing from Schwann cell library","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — immunoelectron microscopy co-localization plus cDNA sequencing confirmation, cAMP functional link","pmids":["1321159"],"is_preprint":false},{"year":1994,"finding":"cAMP-dependent protein kinase (PKA/A-kinase) phosphorylates NF-M (stoichiometry ~6 mol/mol) in native neurofilaments; phosphorylation of NF-L by A-kinase occurs at the head domain and causes partial filament fragmentation in native neurofilaments and disassembly of reassembled filaments containing all three subunits.","method":"In vitro phosphorylation assay, sedimentation experiments, electron microscopy of native and reassembled neurofilaments","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with stoichiometric phosphorylation quantification plus EM structural analysis","pmids":["8019002"],"is_preprint":false},{"year":1995,"finding":"The carboxyl-terminal tail domain of NF-M has two distinct functions: (1) it constitutes the cross-bridge structures between neurofilament core filaments controlling inter-filament spacing, and (2) it promotes longitudinal elongation and straightening of core filaments. Expression of NF-L and NF-M together in Sf9 cells (lacking endogenous intermediate filaments) reconstitutes parallel 10-nm filament bundles with cross-bridges resembling axonal neurofilament domains; neither NF-L nor NF-M alone can form these ordered structures.","method":"Transfection of insect Sf9 cells, deletion mutagenesis of NF-M tail domain, electron microscopy","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution in cells lacking endogenous IFs, systematic deletion mutagenesis with EM structural readout","pmids":["7721944"],"is_preprint":false},{"year":1995,"finding":"Transgenic overexpression of NF-M in mice causes proportionate decreases in axonal NF-H (not NF-L levels), reduces axonal cross-sectional area, and produces neurofilamentous swellings in motor neuron perikarya and proximal axons, without affecting nearest-neighbor spacing between neurofilaments or NF-H phosphorylation levels. This demonstrates that NF-H and NF-M compete for co-assembly with a limiting NF-L pool and that NF-H abundance, not NF-M, is the primary determinant of axonal caliber.","method":"Transgenic mice, morphometric analysis, electron microscopy, Western blotting","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo transgenic model with quantitative morphometric and biochemical analyses","pmids":["7559762"],"is_preprint":false},{"year":1995,"finding":"Overexpression of human NFM in transgenic mice elevates mouse NFL protein levels in the CNS (specific to NFM overexpression, not seen with NFL or NFH overexpression), reduces the most heavily phosphorylated NFH isoforms, and increases NF packing density in large-diameter CNS axons, suggesting NFM plays a dominant role in regulating NFL stoichiometry and NFH phosphorylation state in vivo.","method":"Transgenic mice, Western blotting, electron microscopy","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent transgenic lines, multiple orthogonal readouts (Western blot + EM)","pmids":["7790359"],"is_preprint":false},{"year":1996,"finding":"cAMP-dependent phosphorylation of NF-M (or NF-L) inhibits co-assembly of NF-L and NF-M into heteropolymer filaments in vitro; phosphorylated proteins still form hetero-oligomeric assembly intermediates, indicating phosphorylation blocks a late stage of filament elongation/assembly rather than initial oligomerization.","method":"In vitro phosphorylation by cAMP-dependent protein kinase, sedimentation velocity, gel electrophoresis, electron microscopy","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution assay, single lab, single study","pmids":["8670258"],"is_preprint":false},{"year":1997,"finding":"NF-H can coassemble with vimentin and NF-L but not directly with NF-M into filamentous networks; the N-terminal head domain of NF-H is necessary for coassembly with NF-L or vimentin, while the C-terminal tail is important for forming an extensive NF-L/NF-H network. NF-L is the preferred assembly partner of NF-H over vimentin and NF-M.","method":"Transient co-transfection of deletion mutant NF-H constructs with NF-L and/or NF-M in cells, immunofluorescence","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic mutagenesis with multiple combination transfections, single lab","pmids":["9048736"],"is_preprint":false},{"year":1998,"finding":"ERK1 and ERK2 (mitogen-activated protein kinases) phosphorylate all types of KSP repeat motifs (KSPXK, KSPXXK, KSPXXXK, KSPXXXXK) in the C-terminal tail domains of NF-M and NF-H in vitro, using synthetic peptides, expressed polypeptides, and dephosphorylated native NF proteins; ERK2 preferentially phosphorylates KSPXXXK, while CDK5 only phosphorylates KSPXK motifs. MEK inhibitor PD98059 inhibited NF-H, NF-M, and MAP phosphorylation in primary hippocampal neurons and decreased neurite outgrowth.","method":"Column chromatography fractionation of rat brain extracts, in vitro kinase assay with synthetic KSP peptides and expressed proteins, Western blot, MEK inhibitor treatment of primary neurons","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified kinases and multiple substrates, kinetic comparison, inhibitor validation in primary neurons","pmids":["9592082"],"is_preprint":false},{"year":1999,"finding":"Activation of the Erk1/2 (MAP kinase) cascade by constitutively active MEK1 is sufficient to phosphorylate NF-M KSP tail domain repeats in transfected NIH 3T3 cells; EGF-induced endogenous Erk1/2 activation also phosphorylates co-transfected NF-M tail domains in vivo.","method":"Co-transfection of constitutively active/dominant-negative MEK1 with NF-M in NIH 3T3 cells, Western blotting with phospho-specific antibodies","journal":"European journal of biochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — dominant-active and dominant-negative controls, endogenous ligand validation, two orthogonal approaches","pmids":["10231383"],"is_preprint":false},{"year":1999,"finding":"Membrane depolarization and calcium influx through L-type voltage-gated calcium channels activate endogenous Erk1/2 in PC12 cells, leading to phosphorylation of NF-M KSP tail domain repeats; this phosphorylation is blocked by the L-type channel inhibitor nifedipine and the MEK1 inhibitor PD98059.","method":"PC12 cell depolarization, calcium channel pharmacology, Western blotting with phospho-specific antibodies","journal":"Brain research. Molecular brain research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two independent pharmacological inhibitors blocking the same endpoint, single lab","pmids":["10381546"],"is_preprint":false},{"year":1999,"finding":"NF-M and NF-H subunits, when co-expressed with peripherin in SW13 cells, disrupt peripherin's intermediate filament assembly, whereas NF-L co-assembles with peripherin, demonstrating that the large NF subunits negatively interfere with peripherin filament formation.","method":"Co-transfection in SW13 cells devoid of cytoplasmic intermediate filaments, immunofluorescence","journal":"Biochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cell system lacking endogenous IFs, multiple subunit combinations tested, single lab","pmids":["10426285"],"is_preprint":false},{"year":2001,"finding":"Integrin-matrix interactions (laminin in motoneurons; fibronectin in NIH 3T3 cells) promote KSP tail-domain phosphorylation of NF-M via activation of MEK1 and downstream ERK1/2; this phosphorylation is selectively inhibited by PD98059.","method":"Primary rat spinal cord motoneuron culture on ECM substrates, NF-M transfection in NIH 3T3 cells, Western blotting with phospho-specific antibodies, MEK inhibitor treatment","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — validated in two cell systems with specific inhibitor, single lab","pmids":["11158240"],"is_preprint":false},{"year":2003,"finding":"PKA-mediated phosphorylation of the NF-M head domain inhibits KSP tail domain phosphorylation in rat cortical neurons (via forskolin activation of PKA) and in NIH 3T3 cells transfected with NF-M; mutation of PKA-specific head domain serine residues abolishes this inhibition, establishing a regulatory mechanism whereby transient head domain phosphorylation in the cell body prevents premature tail domain KSP phosphorylation and premature filament assembly.","method":"PKA activation by forskolin in cortical neurons, site-directed mutagenesis of PKA phosphorylation sites in NF-M, transfection into NIH 3T3 cells, EGF stimulation, Western blotting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of specific phosphorylation sites plus pharmacological activation, validated in both primary neurons and transfected cells","pmids":["12695506"],"is_preprint":false},{"year":2003,"finding":"The tail domain of NF-M (containing 7 KSP motifs) is an essential target for the myelination-dependent 'outside-in' signaling cascade that determines axonal caliber and conduction velocity; gene replacement mice expressing NF-M with deleted KSP phosphorylation sites show failure to achieve normal radial axonal growth in myelinated internodes.","method":"Gene replacement (knock-in) in mice to delete KSP phosphorylation sites in NF-M tail domain; morphometric and electrophysiological analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo gene replacement (not just knockout), quantitative axon caliber and conduction velocity measurements","pmids":["14662745"],"is_preprint":false},{"year":2008,"finding":"Chronic blockade of NMDA receptors in developing mouse cortical neurons (with MK801 or AP5) increases NF-M phosphorylation state (demonstrated by molecular weight shift reversed by dephosphorylation assay) and enhances NF-M solubility, which is associated with longer neurite outgrowth; calcineurin inhibition (cyclosporin) also increases NF-M phosphorylation, suggesting that NMDA receptor activation promotes calcineurin-mediated dephosphorylation of NF-M to stabilize the cytoskeleton.","method":"Chronic pharmacological treatment of mouse cortical neuron cultures, dephosphorylation assay, Western blotting, neurite length measurement","journal":"Cell motility and the cytoskeleton","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dephosphorylation assay confirms phosphorylation basis of size shift, two independent receptor antagonists, single lab","pmids":["18412220"],"is_preprint":false},{"year":2004,"finding":"Bovine NF-M contains two in vitro calpain cleavage sites located within the glutamic acid-rich E segment of the tail domain, as determined by direct peptide sequencing; one of the resulting fragments is also detectable in vivo.","method":"In vitro calpain cleavage assay, direct peptide sequencing of cleavage products, in vivo detection by Western blot","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct peptide sequencing of in vitro cleavage sites plus in vivo confirmation, single lab","pmids":["15530438"],"is_preprint":false},{"year":2017,"finding":"NEFM (NF-M) co-immunoprecipitates with the dopamine D1 receptor (D1R) in adrenocortical H295R cells; silencing NEFM increases basal aldosterone secretion, amplifies D1R agonist-stimulated aldosterone production, and shifts D1R localization from intracellular to membranous, indicating NF-M acts as a negative regulator of aldosterone secretion by facilitating D1R internalization from the plasma membrane.","method":"Co-immunoprecipitation, NEFM siRNA knockdown in H295R cells, aldosterone secretion assay, immunohistochemistry for D1R membrane vs. intracellular localization","journal":"Hypertension","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP plus loss-of-function with multiple functional readouts (secretion, proliferation, receptor localization)","pmids":["28584012"],"is_preprint":false},{"year":2018,"finding":"A small group of ALS-linked miRNAs directly regulate NEFM and NEFH mRNA levels in human spinal motor neurons; their dysregulation is associated with increased NFM and NFH protein levels in ALS spinal cord homogenates, contributing to altered stoichiometry of NF subunit expression.","method":"miRNA target validation, Western blotting of ALS spinal cord homogenates","journal":"Molecular brain","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct miRNA-target interaction validated, combined with ALS tissue protein data, single lab","pmids":["30029677"],"is_preprint":false}],"current_model":"NEFM (NF-M) is a type IV intermediate filament protein that obligatorily co-assembles with NF-L via its coiled-coil rod domain, while its C-terminal tail domain forms inter-filament cross-bridges, controls filament spacing, and promotes longitudinal filament elongation; KSP repeat motifs in this tail are phosphorylated by ERK1/2 (on KSPXXXK motifs) and CDK5 (on KSPXK motifs) in a topographically regulated manner—with head-domain PKA phosphorylation transiently inhibiting tail phosphorylation in the cell body—and stoichiometric phosphorylation of the tail in myelinated internodes is an essential target of the myelination-dependent outside-in signaling cascade that drives radial axonal growth and determines axonal caliber and conduction velocity; beyond neurons, NF-M co-immunoprecipitates with the dopamine D1 receptor in adrenocortical cells and negatively regulates aldosterone secretion by facilitating D1R internalization."},"narrative":{"mechanistic_narrative":"NEFM (NF-M) is a type IV neuronal intermediate filament subunit that obligatorily co-assembles with NF-L to build the axonal neurofilament network and to regulate its architecture and caliber [PMID:2516804, PMID:7721944]. Its modular architecture comprises a non-α-helical arginine-rich head, a coiled-coil rod, and an extended, glutamic-acid- and lysine-rich C-terminal tail [PMID:6439558]; the rod domain is essential and sufficient for filament co-assembly, since rod deletions act as dominant-negative disruptors of filament arrays while head and tail deletions still permit incorporation [PMID:2121743]. The acidic tail domain performs two distinct architectural functions: it forms the inter-filament cross-bridges that set inter-filament spacing and it promotes longitudinal elongation and straightening of core filaments, as shown by reconstitution of cross-bridged 10-nm filament bundles from NF-L plus NF-M in cells lacking endogenous intermediate filaments [PMID:7721944]. NF-M abundance governs neurofilament stoichiometry in vivo, competing with NF-H for a limiting NF-L pool and regulating NF-L levels and NF-H phosphorylation state [PMID:7559762, PMID:7790359]. The tail KSP repeat motifs are the substrate of a topographically organized phosphorylation program: ERK1/2 phosphorylates the KSPXXXK-type repeats while CDK5 acts on KSPXK motifs [PMID:9592082], with ERK activation driven by MEK signaling downstream of integrin-matrix engagement, membrane depolarization/L-type calcium influx, and growth-factor stimulation [PMID:10231383, PMID:10381546, PMID:11158240]. Transient PKA phosphorylation of the head domain inhibits premature tail KSP phosphorylation in the cell body [PMID:12695506], whereas tail KSP phosphorylation in myelinated internodes is the essential effector of the myelination-dependent outside-in cascade that drives radial axonal growth and sets axonal caliber and conduction velocity [PMID:14662745]. Beyond neurons, NF-M co-immunoprecipitates with the dopamine D1 receptor in adrenocortical cells and negatively regulates aldosterone secretion by facilitating D1R internalization [PMID:28584012], and ALS-associated miRNA dysregulation elevates NEFM protein and perturbs neurofilament subunit stoichiometry [PMID:30029677].","teleology":[{"year":1984,"claim":"Establishing NF-M's domain architecture defined which regions could mediate filament assembly versus extra-filamentous interactions, the foundational map for all later mechanism.","evidence":"Direct protein sequencing of porcine NF-M with structural analysis","pmids":["6439558"],"confidence":"High","gaps":["Did not test domain function experimentally","Tail interaction partners not identified"]},{"year":1987,"claim":"cDNA cloning showed the glutamic-acid-rich C-terminal extension, not phosphorylation, accounts for NF-M's anomalous SDS-PAGE migration, separating intrinsic sequence from post-translational effects.","evidence":"cDNA cloning/sequencing and in vitro translation co-migration in rabbit reticulocyte lysate","pmids":["2441012"],"confidence":"High","gaps":["Native phosphorylation contributions to migration not quantified"]},{"year":1989,"claim":"Expression in non-neuronal fibroblasts demonstrated NF-M assembles and co-polymerizes with vimentin without neuron-specific factors, isolating assembly competence to the protein itself.","evidence":"Stable transfection of L cells/3T6 fibroblasts with immunofluorescence and immunoelectron microscopy","pmids":["2516804","2493000"],"confidence":"High","gaps":["Used heterologous vimentin rather than physiological NF-L/NF-H context","Did not define minimal assembly determinants"]},{"year":1990,"claim":"Systematic deletion mutagenesis pinpointed the rod domain as essential and dominant for assembly, while head and tail are dispensable for incorporation, defining the assembly-critical region.","evidence":"Site-directed deletion mutagenesis with dominant-negative titration in transfected fibroblasts","pmids":["2121743"],"confidence":"High","gaps":["Did not resolve tail's positive architectural role","Mechanism of dominant-negative interference not structurally defined"]},{"year":1995,"claim":"Reconstitution in IF-free Sf9 cells assigned the tail two architectural functions—cross-bridge formation/spacing and longitudinal elongation—explaining how NF-M shapes the ordered axonal network.","evidence":"NF-L plus NF-M transfection in Sf9 cells with tail deletion mutagenesis and electron microscopy","pmids":["7721944"],"confidence":"High","gaps":["Cross-bridge partner identity in vivo unresolved","Role of phosphorylation in spacing not tested here"]},{"year":1995,"claim":"Transgenic overexpression showed NF-M sets neurofilament stoichiometry, competing with NF-H for limiting NF-L and modulating NF-L levels and NF-H phosphorylation in vivo.","evidence":"Two transgenic mouse models with morphometry, electron microscopy, and Western blotting","pmids":["7559762","7790359"],"confidence":"High","gaps":["Mechanism of NF-L stabilization by NF-M not defined","Overexpression may not reflect endogenous regulation"]},{"year":1998,"claim":"Defining ERK1/2 and CDK5 as KSP-motif kinases with distinct sequence preferences established the enzymatic basis of tail-domain phosphorylation and its link to neurite outgrowth.","evidence":"In vitro kinase assays with KSP peptides/proteins plus MEK-inhibitor treatment of primary neurons","pmids":["9592082"],"confidence":"High","gaps":["Site occupancy in vivo not mapped","Functional consequence of individual sites unresolved"]},{"year":1999,"claim":"Multiple upstream stimuli—MEK1/EGF, depolarization-driven L-type calcium influx—were shown to converge on ERK1/2 to phosphorylate NF-M KSP repeats, embedding the tail in physiological signaling.","evidence":"Constitutively active/dominant-negative MEK1 and pharmacology in NIH 3T3 and PC12 cells with phospho-specific Western blots","pmids":["10231383","10381546"],"confidence":"High","gaps":["Spatial control within neurons not resolved","PC12 link is Medium-confidence single-lab pharmacology"]},{"year":2001,"claim":"Integrin engagement of laminin/fibronectin was shown to drive NF-M tail phosphorylation via MEK/ERK, connecting extracellular matrix contact to neurofilament regulation.","evidence":"Motoneuron culture on ECM and NIH 3T3 transfection with MEK inhibition and phospho-specific blots","pmids":["11158240"],"confidence":"Medium","gaps":["Single-lab; in vivo relevance not tested","Receptor-to-MEK linkage not biochemically reconstituted"]},{"year":2003,"claim":"Head-domain PKA phosphorylation was shown to inhibit premature tail KSP phosphorylation, revealing topographic regulation that prevents premature assembly in the cell body.","evidence":"Forskolin/PKA activation and site mutagenesis in cortical neurons and NIH 3T3 cells with Western blotting","pmids":["12695506"],"confidence":"High","gaps":["In vivo significance of head-tail crosstalk not assessed","Phosphatase counterpart not identified here"]},{"year":2003,"claim":"Gene-replacement deletion of NF-M tail KSP sites established these residues as the essential target of myelination-dependent outside-in signaling that drives radial axonal growth and conduction velocity.","evidence":"Knock-in mice lacking NF-M KSP sites with morphometry and electrophysiology","pmids":["14662745"],"confidence":"High","gaps":["Which axonal binding partners read the phospho-state unresolved","Molecular link from myelin to NF-M phosphorylation not fully mapped"]},{"year":2008,"claim":"NMDA-receptor/calcineurin signaling was linked to NF-M dephosphorylation, identifying an activity-dependent phosphatase arm balancing the kinase inputs and affecting solubility and neurite length.","evidence":"Chronic NMDA-antagonist and calcineurin-inhibitor treatment of cortical neurons with dephosphorylation assay and neurite measurement","pmids":["18412220"],"confidence":"Medium","gaps":["Direct calcineurin–NF-M action not demonstrated","Single-lab correlative pharmacology"]},{"year":2004,"claim":"Identification of calpain cleavage sites in the tail E-segment defined a proteolytic pathway that can fragment NF-M, with one fragment confirmed in vivo.","evidence":"In vitro calpain cleavage with direct peptide sequencing and in vivo Western detection","pmids":["15530438"],"confidence":"Medium","gaps":["Physiological/pathological role of cleavage not established","Regulation of calpain access not addressed"]},{"year":2017,"claim":"Discovery of NF-M binding to the dopamine D1 receptor extended its function beyond cytoskeletal architecture to receptor trafficking and aldosterone control in adrenocortical cells.","evidence":"Co-IP and siRNA knockdown in H295R cells with aldosterone secretion assay and D1R localization imaging","pmids":["28584012"],"confidence":"High","gaps":["Direct vs. indirect D1R interaction not resolved","Whether filament assembly is required for D1R internalization unknown"]},{"year":2018,"claim":"ALS-linked miRNAs were shown to directly regulate NEFM mRNA, connecting subunit stoichiometry control to disease-associated protein accumulation.","evidence":"miRNA target validation and Western blotting of ALS spinal cord homogenates","pmids":["30029677"],"confidence":"Medium","gaps":["Causality of stoichiometry change in pathology not established","Single-lab; correlative tissue data"]},{"year":null,"claim":"The molecular identity of the axonal partners that read NF-M tail phosphorylation to execute cross-bridging and radial growth, and the link from myelin signals to specific KSP sites, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No cross-bridge binding partner identified","Outside-in signaling pathway from myelin to NF-M kinases incomplete","High-resolution structure of assembled NF-L/NF-M filament lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[1,3,9]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,5,9]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[3,9,10]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[19,21]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,18,20]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[10,20]}],"complexes":["neurofilament"],"partners":["NEFL","NEFH","VIM","DRD1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P07197","full_name":"Neurofilament medium polypeptide","aliases":["160 kDa neurofilament protein","Neurofilament 3","Neurofilament triplet M protein"],"length_aa":916,"mass_kda":102.5,"function":"Neurofilaments usually contain three intermediate filament proteins: NEFL, NEFM, and NEFH which are involved in the maintenance of neuronal caliber. May additionally cooperate with the neuronal intermediate filament proteins PRPH and INA to form neuronal filamentous networks (By similarity)","subcellular_location":"Cytoplasm, cytoskeleton; Cell projection, axon; Perikaryon","url":"https://www.uniprot.org/uniprotkb/P07197/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NEFM","classification":"Not Classified","n_dependent_lines":5,"n_total_lines":1208,"dependency_fraction":0.0041390728476821195},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"SLC7A5","stoichiometry":10.0},{"gene":"RAB11A","stoichiometry":4.0},{"gene":"CALD1","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2},{"gene":"CAPZB","stoichiometry":0.2},{"gene":"CTTN","stoichiometry":0.2},{"gene":"MYO9B","stoichiometry":0.2},{"gene":"SLC7A6","stoichiometry":0.2},{"gene":"VIM","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/NEFM","total_profiled":1310},"omim":[{"mim_id":"617292","title":"TRANSMEMBRANE PROTEIN 150C; TMEM150C","url":"https://www.omim.org/entry/617292"},{"mim_id":"605338","title":"INTERNEXIN, ALPHA; INA","url":"https://www.omim.org/entry/605338"},{"mim_id":"162250","title":"NEUROFILAMENT PROTEIN, MEDIUM POLYPEPTIDE; NEFM","url":"https://www.omim.org/entry/162250"},{"mim_id":"162230","title":"NEUROFILAMENT PROTEIN, HEAVY POLYPEPTIDE; NEFH","url":"https://www.omim.org/entry/162230"},{"mim_id":"147450","title":"SUPEROXIDE DISMUTASE 1; SOD1","url":"https://www.omim.org/entry/147450"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Intermediate filaments","reliability":"Enhanced"}],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":308.0},{"tissue":"retina","ntpm":84.1}],"url":"https://www.proteinatlas.org/search/NEFM"},"hgnc":{"alias_symbol":["NFM","NF-M"],"prev_symbol":["NEF3"]},"alphafold":{"accession":"P07197","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P07197","model_url":"https://alphafold.ebi.ac.uk/files/AF-P07197-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P07197-F1-predicted_aligned_error_v6.png","plddt_mean":57.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NEFM","jax_strain_url":"https://www.jax.org/strain/search?query=NEFM"},"sequence":{"accession":"P07197","fasta_url":"https://rest.uniprot.org/uniprotkb/P07197.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P07197/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P07197"}},"corpus_meta":[{"pmid":"7684005","id":"PMC_7684005","title":"Myb and NF-M: combinatorial activators of myeloid genes in heterologous 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In vitro translation of the full-length cDNA produces a product that comigrates with native NF-M even without phosphorylation.\",\n      \"method\": \"cDNA cloning, sequencing, in vitro transcription/translation in rabbit reticulocyte lysate, SDS-PAGE\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro reconstitution with full-length protein, sequence-based structural inference confirmed by co-migration experiment\",\n      \"pmids\": [\"2441012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1984,\n      \"finding\": \"NF-M has a non-alpha-helical arginine-rich head (residues 1–98), a coiled-coil rod domain (residues 99–412), and a ~500-residue carboxy-terminal tailpiece extension rich in lysine and glutamic acid; the rod domain mediates coiled-coil interactions with NF-L for co-polymerization into filaments, while the acidic tailpiece forms an autonomous extra-filamentous domain capable of interactions with other neuronal components.\",\n      \"method\": \"Direct protein sequencing of porcine NF-M (amino-terminal 436 residues), structural analysis\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct protein sequencing with structural domain identification, foundational architecture paper\",\n      \"pmids\": [\"6439558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1987,\n      \"finding\": \"The mouse NF-M gene contains two introns, both located within the conserved rod domain-coding region, in positions that align with two of the NF-L gene introns; the NF-M and NF-L genes are chromosomally linked, and the anomalous intron arrangement compared to other intermediate filament genes suggests an RNA-mediated transposition event in neurofilament gene evolution.\",\n      \"method\": \"Genomic cloning, sequencing, chromosomal linkage analysis\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genomic sequencing with chromosomal mapping, single lab\",\n      \"pmids\": [\"3036526\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"NF-M expressed in fibroblasts (non-neuronal cells) assembles into intermediate filament arrays and co-polymerizes with endogenous vimentin, demonstrating that NF-M assembly does not require neuron-specific factors.\",\n      \"method\": \"Stable DNA transfection into L cells and 3T6 fibroblasts, immunofluorescence, immunoelectron microscopy\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct co-localization by immunoelectron microscopy confirmed co-assembly; replicated across cell lines\",\n      \"pmids\": [\"2516804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"NF-L and NF-M coassemble with vimentin when expressed in fibroblasts, forming copolymeric intermediate filaments; NF-L accumulation to ~9% of cell protein did not affect cell viability, and vimentin solubility was altered, indicating physical incorporation of NF-L into vimentin filaments.\",\n      \"method\": \"Transient and stable DNA transfection of mouse fibroblasts, immunofluorescence, solubility fractionation\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional evidence from multiple stable cell lines, solubility change as orthogonal readout\",\n      \"pmids\": [\"2493000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Deletions into the alpha-helical rod domain of NF-M generate assembly-incompetent or dominant-negative polypeptides; carboxy-terminal rod deletions produce dominant mutants that disrupt vimentin/NF-L filament arrays even at ~1% of wild-type subunit levels, while amino-terminal rod deletions produce pseudo-recessive mutants. Tail and head domain deletions (up to 90% and 70% respectively) do not prevent incorporation into filament networks, establishing the rod domain as essential for assembly.\",\n      \"method\": \"Site-directed mutagenesis, transient transfection of mouse fibroblasts, immunofluorescence with epitope-tagged constructs\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — systematic deletion mutagenesis with functional readout, dominant-negative titration experiment\",\n      \"pmids\": [\"2121743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Phosphorylated fragments of the human NF-M C-terminal repeat domain (13-mer and 17-mer KSP-containing peptides) undergo Al3+- and Ca2+-induced conformational changes from random coil to beta-pleated sheet, forming precipitating intermolecular complexes; unphosphorylated peptides do not exhibit this behavior with Al3+.\",\n      \"method\": \"Circular dichroism spectroscopy with metal-ion titration of synthetic phosphopeptides\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — rigorous biophysical method on synthetic peptides, single lab, peptide model only\",\n      \"pmids\": [\"1542114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"NF-M protein is expressed in myelin-forming Schwann cells (before myelination commitment), co-localizes with vimentin by immunoelectron microscopy, and is induced by elevated intracellular cAMP. Sequencing of the Schwann cell NF-M cDNA confirmed identity with neuronal NF-M.\",\n      \"method\": \"Immunoelectron microscopy, immunological comparison, cAMP stimulation, cDNA cloning and sequencing from Schwann cell library\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — immunoelectron microscopy co-localization plus cDNA sequencing confirmation, cAMP functional link\",\n      \"pmids\": [\"1321159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"cAMP-dependent protein kinase (PKA/A-kinase) phosphorylates NF-M (stoichiometry ~6 mol/mol) in native neurofilaments; phosphorylation of NF-L by A-kinase occurs at the head domain and causes partial filament fragmentation in native neurofilaments and disassembly of reassembled filaments containing all three subunits.\",\n      \"method\": \"In vitro phosphorylation assay, sedimentation experiments, electron microscopy of native and reassembled neurofilaments\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with stoichiometric phosphorylation quantification plus EM structural analysis\",\n      \"pmids\": [\"8019002\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"The carboxyl-terminal tail domain of NF-M has two distinct functions: (1) it constitutes the cross-bridge structures between neurofilament core filaments controlling inter-filament spacing, and (2) it promotes longitudinal elongation and straightening of core filaments. Expression of NF-L and NF-M together in Sf9 cells (lacking endogenous intermediate filaments) reconstitutes parallel 10-nm filament bundles with cross-bridges resembling axonal neurofilament domains; neither NF-L nor NF-M alone can form these ordered structures.\",\n      \"method\": \"Transfection of insect Sf9 cells, deletion mutagenesis of NF-M tail domain, electron microscopy\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution in cells lacking endogenous IFs, systematic deletion mutagenesis with EM structural readout\",\n      \"pmids\": [\"7721944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Transgenic overexpression of NF-M in mice causes proportionate decreases in axonal NF-H (not NF-L levels), reduces axonal cross-sectional area, and produces neurofilamentous swellings in motor neuron perikarya and proximal axons, without affecting nearest-neighbor spacing between neurofilaments or NF-H phosphorylation levels. This demonstrates that NF-H and NF-M compete for co-assembly with a limiting NF-L pool and that NF-H abundance, not NF-M, is the primary determinant of axonal caliber.\",\n      \"method\": \"Transgenic mice, morphometric analysis, electron microscopy, Western blotting\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo transgenic model with quantitative morphometric and biochemical analyses\",\n      \"pmids\": [\"7559762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Overexpression of human NFM in transgenic mice elevates mouse NFL protein levels in the CNS (specific to NFM overexpression, not seen with NFL or NFH overexpression), reduces the most heavily phosphorylated NFH isoforms, and increases NF packing density in large-diameter CNS axons, suggesting NFM plays a dominant role in regulating NFL stoichiometry and NFH phosphorylation state in vivo.\",\n      \"method\": \"Transgenic mice, Western blotting, electron microscopy\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent transgenic lines, multiple orthogonal readouts (Western blot + EM)\",\n      \"pmids\": [\"7790359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"cAMP-dependent phosphorylation of NF-M (or NF-L) inhibits co-assembly of NF-L and NF-M into heteropolymer filaments in vitro; phosphorylated proteins still form hetero-oligomeric assembly intermediates, indicating phosphorylation blocks a late stage of filament elongation/assembly rather than initial oligomerization.\",\n      \"method\": \"In vitro phosphorylation by cAMP-dependent protein kinase, sedimentation velocity, gel electrophoresis, electron microscopy\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution assay, single lab, single study\",\n      \"pmids\": [\"8670258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"NF-H can coassemble with vimentin and NF-L but not directly with NF-M into filamentous networks; the N-terminal head domain of NF-H is necessary for coassembly with NF-L or vimentin, while the C-terminal tail is important for forming an extensive NF-L/NF-H network. NF-L is the preferred assembly partner of NF-H over vimentin and NF-M.\",\n      \"method\": \"Transient co-transfection of deletion mutant NF-H constructs with NF-L and/or NF-M in cells, immunofluorescence\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic mutagenesis with multiple combination transfections, single lab\",\n      \"pmids\": [\"9048736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"ERK1 and ERK2 (mitogen-activated protein kinases) phosphorylate all types of KSP repeat motifs (KSPXK, KSPXXK, KSPXXXK, KSPXXXXK) in the C-terminal tail domains of NF-M and NF-H in vitro, using synthetic peptides, expressed polypeptides, and dephosphorylated native NF proteins; ERK2 preferentially phosphorylates KSPXXXK, while CDK5 only phosphorylates KSPXK motifs. MEK inhibitor PD98059 inhibited NF-H, NF-M, and MAP phosphorylation in primary hippocampal neurons and decreased neurite outgrowth.\",\n      \"method\": \"Column chromatography fractionation of rat brain extracts, in vitro kinase assay with synthetic KSP peptides and expressed proteins, Western blot, MEK inhibitor treatment of primary neurons\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified kinases and multiple substrates, kinetic comparison, inhibitor validation in primary neurons\",\n      \"pmids\": [\"9592082\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Activation of the Erk1/2 (MAP kinase) cascade by constitutively active MEK1 is sufficient to phosphorylate NF-M KSP tail domain repeats in transfected NIH 3T3 cells; EGF-induced endogenous Erk1/2 activation also phosphorylates co-transfected NF-M tail domains in vivo.\",\n      \"method\": \"Co-transfection of constitutively active/dominant-negative MEK1 with NF-M in NIH 3T3 cells, Western blotting with phospho-specific antibodies\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — dominant-active and dominant-negative controls, endogenous ligand validation, two orthogonal approaches\",\n      \"pmids\": [\"10231383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Membrane depolarization and calcium influx through L-type voltage-gated calcium channels activate endogenous Erk1/2 in PC12 cells, leading to phosphorylation of NF-M KSP tail domain repeats; this phosphorylation is blocked by the L-type channel inhibitor nifedipine and the MEK1 inhibitor PD98059.\",\n      \"method\": \"PC12 cell depolarization, calcium channel pharmacology, Western blotting with phospho-specific antibodies\",\n      \"journal\": \"Brain research. Molecular brain research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two independent pharmacological inhibitors blocking the same endpoint, single lab\",\n      \"pmids\": [\"10381546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"NF-M and NF-H subunits, when co-expressed with peripherin in SW13 cells, disrupt peripherin's intermediate filament assembly, whereas NF-L co-assembles with peripherin, demonstrating that the large NF subunits negatively interfere with peripherin filament formation.\",\n      \"method\": \"Co-transfection in SW13 cells devoid of cytoplasmic intermediate filaments, immunofluorescence\",\n      \"journal\": \"Biochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cell system lacking endogenous IFs, multiple subunit combinations tested, single lab\",\n      \"pmids\": [\"10426285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Integrin-matrix interactions (laminin in motoneurons; fibronectin in NIH 3T3 cells) promote KSP tail-domain phosphorylation of NF-M via activation of MEK1 and downstream ERK1/2; this phosphorylation is selectively inhibited by PD98059.\",\n      \"method\": \"Primary rat spinal cord motoneuron culture on ECM substrates, NF-M transfection in NIH 3T3 cells, Western blotting with phospho-specific antibodies, MEK inhibitor treatment\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — validated in two cell systems with specific inhibitor, single lab\",\n      \"pmids\": [\"11158240\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PKA-mediated phosphorylation of the NF-M head domain inhibits KSP tail domain phosphorylation in rat cortical neurons (via forskolin activation of PKA) and in NIH 3T3 cells transfected with NF-M; mutation of PKA-specific head domain serine residues abolishes this inhibition, establishing a regulatory mechanism whereby transient head domain phosphorylation in the cell body prevents premature tail domain KSP phosphorylation and premature filament assembly.\",\n      \"method\": \"PKA activation by forskolin in cortical neurons, site-directed mutagenesis of PKA phosphorylation sites in NF-M, transfection into NIH 3T3 cells, EGF stimulation, Western blotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of specific phosphorylation sites plus pharmacological activation, validated in both primary neurons and transfected cells\",\n      \"pmids\": [\"12695506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The tail domain of NF-M (containing 7 KSP motifs) is an essential target for the myelination-dependent 'outside-in' signaling cascade that determines axonal caliber and conduction velocity; gene replacement mice expressing NF-M with deleted KSP phosphorylation sites show failure to achieve normal radial axonal growth in myelinated internodes.\",\n      \"method\": \"Gene replacement (knock-in) in mice to delete KSP phosphorylation sites in NF-M tail domain; morphometric and electrophysiological analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo gene replacement (not just knockout), quantitative axon caliber and conduction velocity measurements\",\n      \"pmids\": [\"14662745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Chronic blockade of NMDA receptors in developing mouse cortical neurons (with MK801 or AP5) increases NF-M phosphorylation state (demonstrated by molecular weight shift reversed by dephosphorylation assay) and enhances NF-M solubility, which is associated with longer neurite outgrowth; calcineurin inhibition (cyclosporin) also increases NF-M phosphorylation, suggesting that NMDA receptor activation promotes calcineurin-mediated dephosphorylation of NF-M to stabilize the cytoskeleton.\",\n      \"method\": \"Chronic pharmacological treatment of mouse cortical neuron cultures, dephosphorylation assay, Western blotting, neurite length measurement\",\n      \"journal\": \"Cell motility and the cytoskeleton\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dephosphorylation assay confirms phosphorylation basis of size shift, two independent receptor antagonists, single lab\",\n      \"pmids\": [\"18412220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Bovine NF-M contains two in vitro calpain cleavage sites located within the glutamic acid-rich E segment of the tail domain, as determined by direct peptide sequencing; one of the resulting fragments is also detectable in vivo.\",\n      \"method\": \"In vitro calpain cleavage assay, direct peptide sequencing of cleavage products, in vivo detection by Western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct peptide sequencing of in vitro cleavage sites plus in vivo confirmation, single lab\",\n      \"pmids\": [\"15530438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NEFM (NF-M) co-immunoprecipitates with the dopamine D1 receptor (D1R) in adrenocortical H295R cells; silencing NEFM increases basal aldosterone secretion, amplifies D1R agonist-stimulated aldosterone production, and shifts D1R localization from intracellular to membranous, indicating NF-M acts as a negative regulator of aldosterone secretion by facilitating D1R internalization from the plasma membrane.\",\n      \"method\": \"Co-immunoprecipitation, NEFM siRNA knockdown in H295R cells, aldosterone secretion assay, immunohistochemistry for D1R membrane vs. intracellular localization\",\n      \"journal\": \"Hypertension\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP plus loss-of-function with multiple functional readouts (secretion, proliferation, receptor localization)\",\n      \"pmids\": [\"28584012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"A small group of ALS-linked miRNAs directly regulate NEFM and NEFH mRNA levels in human spinal motor neurons; their dysregulation is associated with increased NFM and NFH protein levels in ALS spinal cord homogenates, contributing to altered stoichiometry of NF subunit expression.\",\n      \"method\": \"miRNA target validation, Western blotting of ALS spinal cord homogenates\",\n      \"journal\": \"Molecular brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct miRNA-target interaction validated, combined with ALS tissue protein data, single lab\",\n      \"pmids\": [\"30029677\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NEFM (NF-M) is a type IV intermediate filament protein that obligatorily co-assembles with NF-L via its coiled-coil rod domain, while its C-terminal tail domain forms inter-filament cross-bridges, controls filament spacing, and promotes longitudinal filament elongation; KSP repeat motifs in this tail are phosphorylated by ERK1/2 (on KSPXXXK motifs) and CDK5 (on KSPXK motifs) in a topographically regulated manner—with head-domain PKA phosphorylation transiently inhibiting tail phosphorylation in the cell body—and stoichiometric phosphorylation of the tail in myelinated internodes is an essential target of the myelination-dependent outside-in signaling cascade that drives radial axonal growth and determines axonal caliber and conduction velocity; beyond neurons, NF-M co-immunoprecipitates with the dopamine D1 receptor in adrenocortical cells and negatively regulates aldosterone secretion by facilitating D1R internalization.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"NEFM (NF-M) is a type IV neuronal intermediate filament subunit that obligatorily co-assembles with NF-L to build the axonal neurofilament network and to regulate its architecture and caliber [#3, #9]. Its modular architecture comprises a non-α-helical arginine-rich head, a coiled-coil rod, and an extended, glutamic-acid- and lysine-rich C-terminal tail [#1]; the rod domain is essential and sufficient for filament co-assembly, since rod deletions act as dominant-negative disruptors of filament arrays while head and tail deletions still permit incorporation [#5]. The acidic tail domain performs two distinct architectural functions: it forms the inter-filament cross-bridges that set inter-filament spacing and it promotes longitudinal elongation and straightening of core filaments, as shown by reconstitution of cross-bridged 10-nm filament bundles from NF-L plus NF-M in cells lacking endogenous intermediate filaments [#9]. NF-M abundance governs neurofilament stoichiometry in vivo, competing with NF-H for a limiting NF-L pool and regulating NF-L levels and NF-H phosphorylation state [#10, #11]. The tail KSP repeat motifs are the substrate of a topographically organized phosphorylation program: ERK1/2 phosphorylates the KSPXXXK-type repeats while CDK5 acts on KSPXK motifs [#14], with ERK activation driven by MEK signaling downstream of integrin-matrix engagement, membrane depolarization/L-type calcium influx, and growth-factor stimulation [#15, #16, #18]. Transient PKA phosphorylation of the head domain inhibits premature tail KSP phosphorylation in the cell body [#19], whereas tail KSP phosphorylation in myelinated internodes is the essential effector of the myelination-dependent outside-in cascade that drives radial axonal growth and sets axonal caliber and conduction velocity [#20]. Beyond neurons, NF-M co-immunoprecipitates with the dopamine D1 receptor in adrenocortical cells and negatively regulates aldosterone secretion by facilitating D1R internalization [#23], and ALS-associated miRNA dysregulation elevates NEFM protein and perturbs neurofilament subunit stoichiometry [#24].\",\n  \"teleology\": [\n    {\n      \"year\": 1984,\n      \"claim\": \"Establishing NF-M's domain architecture defined which regions could mediate filament assembly versus extra-filamentous interactions, the foundational map for all later mechanism.\",\n      \"evidence\": \"Direct protein sequencing of porcine NF-M with structural analysis\",\n      \"pmids\": [\"6439558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not test domain function experimentally\", \"Tail interaction partners not identified\"]\n    },\n    {\n      \"year\": 1987,\n      \"claim\": \"cDNA cloning showed the glutamic-acid-rich C-terminal extension, not phosphorylation, accounts for NF-M's anomalous SDS-PAGE migration, separating intrinsic sequence from post-translational effects.\",\n      \"evidence\": \"cDNA cloning/sequencing and in vitro translation co-migration in rabbit reticulocyte lysate\",\n      \"pmids\": [\"2441012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native phosphorylation contributions to migration not quantified\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Expression in non-neuronal fibroblasts demonstrated NF-M assembles and co-polymerizes with vimentin without neuron-specific factors, isolating assembly competence to the protein itself.\",\n      \"evidence\": \"Stable transfection of L cells/3T6 fibroblasts with immunofluorescence and immunoelectron microscopy\",\n      \"pmids\": [\"2516804\", \"2493000\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Used heterologous vimentin rather than physiological NF-L/NF-H context\", \"Did not define minimal assembly determinants\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Systematic deletion mutagenesis pinpointed the rod domain as essential and dominant for assembly, while head and tail are dispensable for incorporation, defining the assembly-critical region.\",\n      \"evidence\": \"Site-directed deletion mutagenesis with dominant-negative titration in transfected fibroblasts\",\n      \"pmids\": [\"2121743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve tail's positive architectural role\", \"Mechanism of dominant-negative interference not structurally defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Reconstitution in IF-free Sf9 cells assigned the tail two architectural functions—cross-bridge formation/spacing and longitudinal elongation—explaining how NF-M shapes the ordered axonal network.\",\n      \"evidence\": \"NF-L plus NF-M transfection in Sf9 cells with tail deletion mutagenesis and electron microscopy\",\n      \"pmids\": [\"7721944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cross-bridge partner identity in vivo unresolved\", \"Role of phosphorylation in spacing not tested here\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Transgenic overexpression showed NF-M sets neurofilament stoichiometry, competing with NF-H for limiting NF-L and modulating NF-L levels and NF-H phosphorylation in vivo.\",\n      \"evidence\": \"Two transgenic mouse models with morphometry, electron microscopy, and Western blotting\",\n      \"pmids\": [\"7559762\", \"7790359\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of NF-L stabilization by NF-M not defined\", \"Overexpression may not reflect endogenous regulation\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining ERK1/2 and CDK5 as KSP-motif kinases with distinct sequence preferences established the enzymatic basis of tail-domain phosphorylation and its link to neurite outgrowth.\",\n      \"evidence\": \"In vitro kinase assays with KSP peptides/proteins plus MEK-inhibitor treatment of primary neurons\",\n      \"pmids\": [\"9592082\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Site occupancy in vivo not mapped\", \"Functional consequence of individual sites unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Multiple upstream stimuli—MEK1/EGF, depolarization-driven L-type calcium influx—were shown to converge on ERK1/2 to phosphorylate NF-M KSP repeats, embedding the tail in physiological signaling.\",\n      \"evidence\": \"Constitutively active/dominant-negative MEK1 and pharmacology in NIH 3T3 and PC12 cells with phospho-specific Western blots\",\n      \"pmids\": [\"10231383\", \"10381546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial control within neurons not resolved\", \"PC12 link is Medium-confidence single-lab pharmacology\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Integrin engagement of laminin/fibronectin was shown to drive NF-M tail phosphorylation via MEK/ERK, connecting extracellular matrix contact to neurofilament regulation.\",\n      \"evidence\": \"Motoneuron culture on ECM and NIH 3T3 transfection with MEK inhibition and phospho-specific blots\",\n      \"pmids\": [\"11158240\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab; in vivo relevance not tested\", \"Receptor-to-MEK linkage not biochemically reconstituted\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Head-domain PKA phosphorylation was shown to inhibit premature tail KSP phosphorylation, revealing topographic regulation that prevents premature assembly in the cell body.\",\n      \"evidence\": \"Forskolin/PKA activation and site mutagenesis in cortical neurons and NIH 3T3 cells with Western blotting\",\n      \"pmids\": [\"12695506\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo significance of head-tail crosstalk not assessed\", \"Phosphatase counterpart not identified here\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Gene-replacement deletion of NF-M tail KSP sites established these residues as the essential target of myelination-dependent outside-in signaling that drives radial axonal growth and conduction velocity.\",\n      \"evidence\": \"Knock-in mice lacking NF-M KSP sites with morphometry and electrophysiology\",\n      \"pmids\": [\"14662745\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which axonal binding partners read the phospho-state unresolved\", \"Molecular link from myelin to NF-M phosphorylation not fully mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"NMDA-receptor/calcineurin signaling was linked to NF-M dephosphorylation, identifying an activity-dependent phosphatase arm balancing the kinase inputs and affecting solubility and neurite length.\",\n      \"evidence\": \"Chronic NMDA-antagonist and calcineurin-inhibitor treatment of cortical neurons with dephosphorylation assay and neurite measurement\",\n      \"pmids\": [\"18412220\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct calcineurin–NF-M action not demonstrated\", \"Single-lab correlative pharmacology\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification of calpain cleavage sites in the tail E-segment defined a proteolytic pathway that can fragment NF-M, with one fragment confirmed in vivo.\",\n      \"evidence\": \"In vitro calpain cleavage with direct peptide sequencing and in vivo Western detection\",\n      \"pmids\": [\"15530438\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological/pathological role of cleavage not established\", \"Regulation of calpain access not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery of NF-M binding to the dopamine D1 receptor extended its function beyond cytoskeletal architecture to receptor trafficking and aldosterone control in adrenocortical cells.\",\n      \"evidence\": \"Co-IP and siRNA knockdown in H295R cells with aldosterone secretion assay and D1R localization imaging\",\n      \"pmids\": [\"28584012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs. indirect D1R interaction not resolved\", \"Whether filament assembly is required for D1R internalization unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"ALS-linked miRNAs were shown to directly regulate NEFM mRNA, connecting subunit stoichiometry control to disease-associated protein accumulation.\",\n      \"evidence\": \"miRNA target validation and Western blotting of ALS spinal cord homogenates\",\n      \"pmids\": [\"30029677\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality of stoichiometry change in pathology not established\", \"Single-lab; correlative tissue data\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular identity of the axonal partners that read NF-M tail phosphorylation to execute cross-bridging and radial growth, and the link from myelin signals to specific KSP sites, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No cross-bridge binding partner identified\", \"Outside-in signaling pathway from myelin to NF-M kinases incomplete\", \"High-resolution structure of assembled NF-L/NF-M filament lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [1, 3, 9]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 5, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [3, 9, 10]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [19, 21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 18, 20]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [10, 20]}\n    ],\n    \"complexes\": [\"neurofilament\"],\n    \"partners\": [\"NEFL\", \"NEFH\", \"VIM\", \"DRD1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}