{"gene":"KIF21A","run_date":"2026-04-28T18:30:27","timeline":{"discoveries":[{"year":1999,"finding":"KIF21A is a plus-end-directed kinesin motor protein containing seven WD-40 repeats; it localizes throughout neurons (axons and dendrites), whereas the paralog KIF21B is enriched specifically in dendrites, demonstrating a novel kinesin sorting mechanism in neurons.","method":"Identification of novel kinesin-like proteins, immunolocalization in neurons, domain architecture analysis","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 3 — single study with immunolocalization and domain analysis, foundational characterization","pmids":["10225949"],"is_preprint":false},{"year":2003,"finding":"Heterozygous missense mutations in KIF21A, predominantly in the third coiled-coil stalk domain, cause CFEOM1, identifying the stalk as critical for KIF21A function in oculomotor axis formation.","method":"Direct DNA sequencing of KIF21A in 45 CFEOM1 probands; mutation mapping to stalk domain","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — large cohort, replicated across multiple labs, foundational genetic identification","pmids":["14595441"],"is_preprint":false},{"year":2008,"finding":"KIF21A physically interacts with BIG1 (brefeldin A-inhibited guanine nucleotide-exchange protein 1); the C-terminal WD-40 repeat tail of KIF21A interacts with the C-terminal region of BIG1. ARF1 activity modulates this interaction, and KIF21A depletion alters BIG1 distribution without changing intrinsic Golgi membrane protein distribution.","method":"LC-MS/MS of co-precipitated proteins, reciprocal co-immunoprecipitation, overexpression of full-length and fragment constructs, siRNA knockdown, immunofluorescence","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, fragment mapping, siRNA functional validation, multiple orthogonal methods in single study","pmids":["19020088"],"is_preprint":false},{"year":2009,"finding":"KIF21A interacts with KANK1 via the third and fourth coiled-coil domains of KIF21A and the ankyrin-repeat domain of KANK1. CFEOM1 mutations (R954W, M947T) enhance heterodimer formation with wild-type KIF21A and increase KANK1 translocation to the membrane fraction, suggesting KIF21A regulates KANK1 subcellular distribution.","method":"Co-immunoprecipitation, subcellular fractionation, knockdown experiments","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP and fractionation, single study, moderate follow-up","pmids":["19559006"],"is_preprint":false},{"year":2012,"finding":"KIF21A mediates anterograde axonal transport of NCKX2 via direct interaction between the intracellular loop of NCKX2 and the WD-40 repeat domain of KIF21A. Dominant-negative KIF21A or KIF21A knockdown inhibits axonal transport of NCKX2 and causes calcium dysregulation at axonal boutons.","method":"Co-immunoprecipitation, dominant-negative overexpression, siRNA knockdown, live-cell imaging of NCKX2-GFP transport, calcium imaging","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction mapping, dominant-negative and knockdown with specific functional readout (calcium dysregulation), multiple orthogonal methods","pmids":["22442075"],"is_preprint":false},{"year":2013,"finding":"KIF21A acts as a cortical microtubule growth inhibitor: in vitro it suppresses microtubule growth and inhibits catastrophes; in cells it restricts microtubule growth at the cell edge. KIF21A is recruited to the cortex by KANK1, which co-clusters with liprin-α1/β1 and LL5β-containing complexes. CFEOM1 mutations relieve autoinhibition of KIF21A motor activity, leading to enhanced KIF21A accumulation in axonal growth cones, aberrant axon morphology, and reduced responsiveness to inhibitory cues.","method":"In vitro microtubule dynamics assay, live-cell imaging, TIRF microscopy, co-immunoprecipitation, dominant-negative and overexpression constructs, primary neuron culture assays","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution assay plus cellular functional assays and mutant analysis, replicated mechanistic insight","pmids":["24120883"],"is_preprint":false},{"year":2014,"finding":"CFEOM1 mutations in both the motor domain and third coiled-coil stalk of KIF21A attenuate autoinhibition (gain-of-function mechanism). Knockin mice with the most common human mutation develop CFEOM with oculomotor axon stalling, enlarged growth cones, excessive filopodia, and random trajectories. MAP1B was identified as a KIF21A-interacting protein, and Map1b-null mice also develop CFEOM.","method":"Knockin mouse model, axon tracing, growth cone morphology analysis, co-immunoprecipitation (KIF21A–MAP1B interaction), in vitro autoinhibition assays","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 — knockin mouse with defined cellular phenotype, gain-of-function mechanism established, Co-IP for binding partner, replicated across multiple methods","pmids":["24656932"],"is_preprint":false},{"year":2016,"finding":"The KIF21A stalk regulatory domain containing all CFEOM1-associated substitutions forms an intramolecular antiparallel coiled coil that inhibits the motor domain. CFEOM1 mutations disrupt the structural integrity of this antiparallel coiled coil or its autoinhibitory binding interface, reducing affinity for the motor domain and causing KIF21A hyperactivation. This regulatory mechanism is conserved in KIF21B, KIF7, and KIF27.","method":"Crystal structure of regulatory domain, in vitro binding assays, mutagenesis, analytical ultracentrifugation","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and in vitro binding validation","pmids":["27485312"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of the KANK1 ankyrin repeat domain (ANKRD) in complex with a short KIF21A peptide at high resolution reveals that the ANKRD uses two distinct interfaces (combinatorial use) to recognize KIF21A. Mutations at either interface disrupt the KANK1–KIF21A interaction and block KIF21A recruitment to focal adhesions.","method":"Crystal structure (high-resolution), site-directed mutagenesis, biochemical binding assays, cellular immunofluorescence localization","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and cellular functional validation","pmids":["29217769"],"is_preprint":false},{"year":2017,"finding":"Crystal structure of the KANK1·KIF21A complex at 2.1 Å resolution reveals that a five-helix-bundle-capping domain immediately preceding the ANK repeats of KANK1 forms a structural and functional supramodule with its ANK repeats to bind an evolutionarily conserved KIF21A peptide. Cancer-associated missense mutations at the KANK1–KIF21A interface destabilize complex formation.","method":"Crystal structure (2.1 Å), biochemical binding assays, mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with mutagenesis validation","pmids":["29158259"],"is_preprint":false},{"year":2017,"finding":"A stretch of ~22 amino acids in KIF21A is sufficient for binding to both KANK1 and KANK2 ankyrin domains. Structures of KIF21A peptide complexed with KANK1 and KANK2 ankyrin domains show KIF21A adopts helical conformations recognized by two distinct pockets of the ankyrin domain.","method":"Crystal structure of KIF21A peptide–KANK1 ANK domain and KIF21A peptide–KANK2 ANK domain complexes, site-directed mutagenesis, biochemical binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structures of two complexes with mutagenesis","pmids":["29183992"],"is_preprint":false},{"year":2021,"finding":"An NS-associated KANK2 mutation (S684F) induces abnormal binding of eIF4A1 to KANK2 at the physiological KIF21A-binding site; eIF4A1 can competitively displace KIF21A from this site. This pathological competition disrupts KANK2/KIF21A interaction and impairs focal adhesion and cell adhesion in podocytes.","method":"Structural analysis, competitive binding assays, co-immunoprecipitation, KANK2 knockout podocyte rescue experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — structural, biochemical, and cellular evidence with multiple orthogonal methods","pmids":["34274317"],"is_preprint":false},{"year":2023,"finding":"KIF21A localizes to a subset of dendritic spines in neurons; KIF21A-positive spines are larger and more structurally plastic. The KIF21A–KANK1 interaction is required for dendritic spine morphogenesis and synaptic plasticity; knockdown of either protein inhibits spine morphogenesis and dendritic branching, and hippocampal KIF21A knockdown impairs long-term potentiation and cognitive function in rats.","method":"Immunofluorescence, shRNA knockdown in primary neurons and in vivo rat hippocampus, rescue with wild-type vs. binding-deficient mutants, electrophysiology (LTP), behavioral assays","journal":"Neural regeneration research","confidence":"High","confidence_rationale":"Tier 2 — knockdown with specific cellular and in vivo phenotypes, binding-deficient mutant rescue experiments, multiple methods","pmids":["38767486"],"is_preprint":false},{"year":2023,"finding":"Kif21a localizes specifically to podocytes in the zebrafish glomerulus; its deficiency causes podocyte foot process effacement, altered slit diaphragm formation, and severe proteinuria, establishing a role for KIF21A in maintaining glomerular filtration barrier integrity.","method":"Zebrafish loss-of-function model, immunolocalization, electron microscopy (foot process morphology), functional proteinuria assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO in vertebrate model with defined cellular phenotype and functional readout, single study","pmids":["37932480"],"is_preprint":false},{"year":2025,"finding":"A novel KIF21A variant (p.Leu664Pro) in the second coiled-coil domain causes decreased binding of KIF21A to TUBB3 (β-tubulin III) as demonstrated by co-immunoprecipitation, defining a KIF21A–TUBB3 interaction whose disruption produces peripheral neuropathy, corpus callosum hypoplasia, and strabismus without classic CFEOM.","method":"Co-immunoprecipitation (KIF21A p.Leu664Pro vs. reference with TUBB3 in vitro), protein structure modelling","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2-3 — Co-IP with defined functional consequence, single lab, novel finding","pmids":["39643435"],"is_preprint":false}],"current_model":"KIF21A is an anterograde kinesin-4 motor protein that uses its WD-40 repeat tail to transport cargo (e.g., NCKX2) in axons and is recruited to the cell cortex by KANK1 (via a conserved peptide recognized by KANK1's ankyrin-repeat supramodule), where it suppresses microtubule growth and catastrophes; its motor activity is kept in check by autoinhibitory antiparallel coiled-coil interactions between the stalk regulatory domain and the motor domain, and CFEOM1-associated missense mutations in either the motor or stalk domain relieve this autoinhibition, causing oculomotor axon stalling and growth-cone dysregulation in vivo."},"narrative":{"teleology":[{"year":1999,"claim":"Establishing that KIF21A exists as a distinct plus-end kinesin with WD-40 repeats and pan-neuronal distribution resolved the identity of this motor and distinguished it from the dendrite-restricted paralog KIF21B.","evidence":"Identification via novel kinesin screen, domain architecture analysis, and immunolocalization in neurons","pmids":["10225949"],"confidence":"Medium","gaps":["No cargo or functional role identified","Motor directionality inferred from kinesin family membership, not directly measured for KIF21A"]},{"year":2003,"claim":"Discovery that heterozygous KIF21A stalk-domain mutations cause CFEOM1 established the gene as essential for oculomotor circuit development and pinpointed the third coiled-coil as a functionally critical region.","evidence":"Direct sequencing of KIF21A in 45 CFEOM1 probands with mutation clustering in third coiled-coil stalk domain","pmids":["14595441"],"confidence":"High","gaps":["Mechanism by which stalk mutations alter motor function unknown","No animal model to confirm causality"]},{"year":2008,"claim":"Identification of the BIG1–KIF21A interaction via the WD-40 tail showed that KIF21A connects to Arf-GTPase signaling and membrane trafficking, broadening its functional scope beyond simple cargo transport.","evidence":"LC-MS/MS, reciprocal co-immunoprecipitation, fragment mapping, siRNA knockdown altering BIG1 distribution","pmids":["19020088"],"confidence":"High","gaps":["Physiological cargo transported via BIG1 link unclear","Whether BIG1 interaction is relevant to CFEOM pathogenesis untested"]},{"year":2009,"claim":"Demonstration that KIF21A binds KANK1 through its coiled-coil domains—and that CFEOM1 mutations enhance this interaction—revealed a cortical recruitment axis and suggested disease mutations are gain-of-function.","evidence":"Co-immunoprecipitation and subcellular fractionation comparing wild-type and CFEOM1 mutant KIF21A","pmids":["19559006"],"confidence":"Medium","gaps":["No structural basis for KANK1 binding determined","Single-study observation of enhanced binding by mutants"]},{"year":2012,"claim":"Establishing NCKX2 as a WD-40-dependent KIF21A cargo that requires KIF21A for anterograde axonal transport linked this motor to calcium homeostasis at presynaptic terminals.","evidence":"Co-immunoprecipitation, dominant-negative and siRNA experiments with live-cell NCKX2-GFP tracking and calcium imaging","pmids":["22442075"],"confidence":"High","gaps":["Whether NCKX2 transport defects contribute to CFEOM unknown","Additional axonal cargoes not systematically identified"]},{"year":2013,"claim":"Reconstitution of KIF21A's microtubule growth-inhibitory activity in vitro, combined with demonstration that CFEOM1 mutations relieve autoinhibition and cause growth-cone accumulation, unified the transport and cytoskeletal regulation functions and provided the first mechanistic disease model.","evidence":"In vitro microtubule dynamics assays, TIRF microscopy, KANK1-dependent cortical recruitment, primary neuron assays with CFEOM1 mutants","pmids":["24120883"],"confidence":"High","gaps":["Structural basis of autoinhibition not yet resolved","Relative contribution of growth inhibition vs. cargo transport to CFEOM unclear"]},{"year":2014,"claim":"A knockin mouse carrying the commonest human CFEOM1 mutation recapitulated oculomotor axon stalling and growth-cone defects, confirming the gain-of-function mechanism in vivo and identifying MAP1B as an interacting partner whose loss phenocopies CFEOM.","evidence":"Knockin mouse model with axon tracing and growth-cone morphology; co-immunoprecipitation for MAP1B; Map1b-null mouse phenotyping","pmids":["24656932"],"confidence":"High","gaps":["How MAP1B functionally intersects KIF21A autoinhibition unknown","Whether MAP1B interaction is direct or bridged not resolved"]},{"year":2016,"claim":"The crystal structure of the KIF21A stalk regulatory domain revealed an antiparallel coiled-coil fold whose disruption by CFEOM1 mutations weakens motor-domain binding, providing the atomic-level explanation for disease-associated hyperactivation.","evidence":"Crystal structure, analytical ultracentrifugation, in vitro binding assays with disease-mimicking mutations","pmids":["27485312"],"confidence":"High","gaps":["Full-length structure of autoinhibited KIF21A not available","Dynamics of autoinhibition relief in vivo uncharacterized"]},{"year":2017,"claim":"High-resolution crystal structures of KANK1 and KANK2 ankyrin domains complexed with a short KIF21A peptide defined the cortical recruitment interface at atomic detail, showing a supramodule recognition mechanism conserved across KANK family members.","evidence":"Crystal structures (2.1 Å for KANK1·KIF21A; separate KANK2·KIF21A structure), mutagenesis disrupting binding and focal-adhesion recruitment","pmids":["29217769","29158259","29183992"],"confidence":"High","gaps":["How KANK-mediated cortical anchoring coordinates with autoinhibition release unknown","Whether all KANK family members equally recruit KIF21A in vivo untested"]},{"year":2021,"claim":"Discovery that a nephrotic syndrome-associated KANK2 mutation allows eIF4A1 to competitively displace KIF21A from the shared binding site demonstrated that the KANK–KIF21A axis operates in podocyte adhesion and can be pathologically disrupted by heterologous competitors.","evidence":"Structural analysis, competitive binding assays, co-immunoprecipitation, KANK2-knockout podocyte rescue","pmids":["34274317"],"confidence":"High","gaps":["Whether KIF21A loss per se drives podocyte pathology or acts through KANK2 dysfunction unresolved"]},{"year":2023,"claim":"Identification of KIF21A in dendritic spines and demonstration that the KIF21A–KANK1 axis drives spine morphogenesis, LTP, and cognitive function extended the motor's role from axonal guidance to postsynaptic plasticity.","evidence":"shRNA knockdown in primary neurons and rat hippocampus in vivo, rescue with binding-deficient mutants, electrophysiology, behavioral assays","pmids":["38767486"],"confidence":"High","gaps":["Cargo transported by KIF21A into spines not identified","Whether microtubule growth inhibition or transport underlies spine effects unknown"]},{"year":2023,"claim":"Zebrafish loss-of-function showed KIF21A is required in podocytes for foot process formation and slit diaphragm integrity, establishing an in vivo role in glomerular filtration.","evidence":"Zebrafish knockout, electron microscopy of foot processes, proteinuria assay","pmids":["37932480"],"confidence":"Medium","gaps":["Not replicated in mammalian kidney models","Molecular mechanism of podocyte foot process regulation by KIF21A unclear"]},{"year":2025,"claim":"A novel KIF21A coiled-coil variant that reduces TUBB3 binding defined a direct KIF21A–TUBB3 interaction and a distinct clinical phenotype (peripheral neuropathy, corpus callosum hypoplasia) outside classic CFEOM.","evidence":"Co-immunoprecipitation comparing mutant vs. reference KIF21A with TUBB3, protein modelling, clinical phenotyping","pmids":["39643435"],"confidence":"Medium","gaps":["Single family; independent replication needed","Mechanism by which reduced TUBB3 binding alters neuronal development not established"]},{"year":null,"claim":"Key unresolved questions include the full-length structure of autoinhibited KIF21A, the identity of dendritic-spine cargoes, the relative contributions of microtubule regulation versus transport to each tissue-specific phenotype, and whether KIF21A has catalytic or regulatory roles beyond its motor activity.","evidence":"","pmids":[],"confidence":"High","gaps":["No full-length autoinhibited structure","Spine-specific cargo unknown","Relative contribution of growth inhibition vs. transport to axonal and podocyte phenotypes unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003774","term_label":"cytoskeletal motor activity","supporting_discovery_ids":[0,4,5]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[5,6,14]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[5,6]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,8]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,4]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,6]},{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[4,12]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,5]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[5,6]}],"complexes":[],"partners":["KANK1","KANK2","BIG1","NCKX2","MAP1B","TUBB3"],"other_free_text":[]},"mechanistic_narrative":"KIF21A is a plus-end-directed kinesin-4 family motor protein that functions both as an anterograde axonal transporter and as a cortical microtubule growth inhibitor, with critical roles in oculomotor axon guidance, dendritic spine morphogenesis, and glomerular podocyte integrity. Its C-terminal WD-40 repeat domain engages cargo such as the sodium/calcium exchanger NCKX2 for axonal transport and interacts with the Arf-GEF BIG1, while its coiled-coil stalk mediates recruitment to the cell cortex through binding to KANK1/KANK2 ankyrin-repeat supramodules, where KIF21A suppresses microtubule growth and catastrophes [PMID:24120883, PMID:29158259, PMID:22442075]. Motor activity is held in check by an intramolecular antiparallel coiled-coil autoinhibitory interaction between the stalk regulatory domain and the motor domain; heterozygous missense mutations in either domain relieve this autoinhibition, causing the congenital eye movement disorder CFEOM1 through oculomotor axon stalling, growth-cone enlargement, and aberrant pathfinding [PMID:14595441, PMID:27485312, PMID:24656932]. KIF21A also directly binds TUBB3, and disruption of this interaction by a coiled-coil variant produces a neurological syndrome distinct from classic CFEOM [PMID:39643435]."},"prefetch_data":{"uniprot":{"accession":"Q7Z4S6","full_name":"Kinesin-like protein KIF21A","aliases":["Kinesin-like protein KIF2","Renal carcinoma antigen NY-REN-62"],"length_aa":1674,"mass_kda":187.2,"function":"Processive microtubule plus-end directed motor protein involved in neuronal axon guidance. Is recruited by KANK1 to cortical microtubule stabilizing complexes (CMSCs) at focal adhesions (FAs) rims where it promotes microtubule capture and stability. Controls microtubule polymerization rate at axonal growth cones and suppresses microtubule growth without inducing microtubule disassembly once it reaches the cell cortex","subcellular_location":"Cytoplasm, cytoskeleton; Cytoplasm, cell cortex; Cell projection, axon; Cell projection, dendrite; Cell projection, growth cone","url":"https://www.uniprot.org/uniprotkb/Q7Z4S6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/KIF21A","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/KIF21A","total_profiled":1310},"omim":[{"mim_id":"608322","title":"KINESIN FAMILY MEMBER 21B; KIF21B","url":"https://www.omim.org/entry/608322"},{"mim_id":"608283","title":"KINESIN FAMILY MEMBER 21A; KIF21A","url":"https://www.omim.org/entry/608283"},{"mim_id":"602661","title":"TUBULIN, BETA-3; TUBB3","url":"https://www.omim.org/entry/602661"},{"mim_id":"600638","title":"FIBROSIS OF EXTRAOCULAR MUSCLES, CONGENITAL, 3A, WITH OR WITHOUT EXTRAOCULAR INVOLVEMENT; CFEOM3A","url":"https://www.omim.org/entry/600638"},{"mim_id":"167410","title":"PAIRED BOX GENE 7; PAX7","url":"https://www.omim.org/entry/167410"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"retina","ntpm":71.9}],"url":"https://www.proteinatlas.org/search/KIF21A"},"hgnc":{"alias_symbol":["FLJ20052"],"prev_symbol":["FEOM1"]},"alphafold":{"accession":"Q7Z4S6","domains":[{"cath_id":"3.40.850.10","chopping":"12-164_174-242_262-379","consensus_level":"medium","plddt":88.9711,"start":12,"end":379},{"cath_id":"-","chopping":"940-1083","consensus_level":"medium","plddt":81.6947,"start":940,"end":1083},{"cath_id":"2.130.10.10","chopping":"1323-1438_1450-1654","consensus_level":"medium","plddt":90.6566,"start":1323,"end":1654},{"cath_id":"1.10.287","chopping":"643-704_712-827","consensus_level":"medium","plddt":80.8466,"start":643,"end":827}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7Z4S6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q7Z4S6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q7Z4S6-F1-predicted_aligned_error_v6.png","plddt_mean":70.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=KIF21A","jax_strain_url":"https://www.jax.org/strain/search?query=KIF21A"},"sequence":{"accession":"Q7Z4S6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q7Z4S6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q7Z4S6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q7Z4S6"}},"corpus_meta":[{"pmid":"14595441","id":"PMC_14595441","title":"Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1).","date":"2003","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/14595441","citation_count":201,"is_preprint":false},{"pmid":"24120883","id":"PMC_24120883","title":"CFEOM1-associated kinesin KIF21A is a cortical microtubule growth inhibitor.","date":"2013","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/24120883","citation_count":152,"is_preprint":false},{"pmid":"10225949","id":"PMC_10225949","title":"Novel dendritic kinesin sorting identified by different process targeting of two related kinesins: KIF21A and KIF21B.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10225949","citation_count":140,"is_preprint":false},{"pmid":"24656932","id":"PMC_24656932","title":"Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling.","date":"2014","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/24656932","citation_count":94,"is_preprint":false},{"pmid":"15223798","id":"PMC_15223798","title":"Identification of KIF21A mutations as a rare cause of congenital fibrosis of the extraocular muscles type 3 (CFEOM3).","date":"2004","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/15223798","citation_count":74,"is_preprint":false},{"pmid":"16157808","id":"PMC_16157808","title":"A novel KIF21A mutation in a patient with congenital fibrosis of the extraocular muscles and Marcus Gunn jaw-winking phenomenon.","date":"2005","source":"Archives of ophthalmology (Chicago, Ill. : 1960)","url":"https://pubmed.ncbi.nlm.nih.gov/16157808","citation_count":41,"is_preprint":false},{"pmid":"17511870","id":"PMC_17511870","title":"Three novel mutations in KIF21A highlight the importance of the third coiled-coil stalk domain in the etiology of CFEOM1.","date":"2007","source":"BMC genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17511870","citation_count":41,"is_preprint":false},{"pmid":"34740919","id":"PMC_34740919","title":"Bi-allelic loss-of-function variants in KIF21A cause severe fetal akinesia with arthrogryposis multiplex.","date":"2021","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/34740919","citation_count":36,"is_preprint":false},{"pmid":"22442075","id":"PMC_22442075","title":"KIF21A-mediated axonal transport and selective endocytosis underlie the polarized targeting of NCKX2.","date":"2012","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/22442075","citation_count":30,"is_preprint":false},{"pmid":"19559006","id":"PMC_19559006","title":"A major mutation of KIF21A associated with congenital fibrosis of the extraocular muscles type 1 (CFEOM1) enhances translocation of Kank1 to the membrane.","date":"2009","source":"Biochemical and 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ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/19551685","citation_count":7,"is_preprint":false},{"pmid":"22968744","id":"PMC_22968744","title":"KIF21A mRNA expression in patients with Down syndrome.","date":"2012","source":"Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/22968744","citation_count":7,"is_preprint":false},{"pmid":"34274317","id":"PMC_34274317","title":"Nephrotic-syndrome-associated mutation of KANK2 induces pathologic binding competition with physiological interactor KIF21A.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34274317","citation_count":5,"is_preprint":false},{"pmid":"16939002","id":"PMC_16939002","title":"Mutation p.Arg954Trp of KIF21A causes congenital fibrosis of the extraocular muscles in a Chinese family.","date":"2006","source":"Yi chuan xue bao = Acta genetica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/16939002","citation_count":5,"is_preprint":false},{"pmid":"23799907","id":"PMC_23799907","title":"Inherited KIF21A and PAX6 gene mutations in a boy with congenital fibrosis of extraocular muscles and aniridia.","date":"2013","source":"BMC medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/23799907","citation_count":5,"is_preprint":false},{"pmid":"28930843","id":"PMC_28930843","title":"Clinical characteristics of a KIF21A mutation in a Chinese family with congenital fibrosis of the extraocular muscles type 1.","date":"2017","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/28930843","citation_count":4,"is_preprint":false},{"pmid":"24426772","id":"PMC_24426772","title":"Maternal germline mosaicism of kinesin family member 21A (KIF21A) mutation causes complex phenotypes in a Chinese family with congenital fibrosis of the extraocular muscles.","date":"2014","source":"Molecular 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it localizes throughout neurons (axons and dendrites), whereas the paralog KIF21B is enriched specifically in dendrites, demonstrating a novel kinesin sorting mechanism in neurons.\",\n      \"method\": \"Identification of novel kinesin-like proteins, immunolocalization in neurons, domain architecture analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single study with immunolocalization and domain analysis, foundational characterization\",\n      \"pmids\": [\"10225949\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Heterozygous missense mutations in KIF21A, predominantly in the third coiled-coil stalk domain, cause CFEOM1, identifying the stalk as critical for KIF21A function in oculomotor axis formation.\",\n      \"method\": \"Direct DNA sequencing of KIF21A in 45 CFEOM1 probands; mutation mapping to stalk domain\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — large cohort, replicated across multiple labs, foundational genetic identification\",\n      \"pmids\": [\"14595441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"KIF21A physically interacts with BIG1 (brefeldin A-inhibited guanine nucleotide-exchange protein 1); the C-terminal WD-40 repeat tail of KIF21A interacts with the C-terminal region of BIG1. ARF1 activity modulates this interaction, and KIF21A depletion alters BIG1 distribution without changing intrinsic Golgi membrane protein distribution.\",\n      \"method\": \"LC-MS/MS of co-precipitated proteins, reciprocal co-immunoprecipitation, overexpression of full-length and fragment constructs, siRNA knockdown, immunofluorescence\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, fragment mapping, siRNA functional validation, multiple orthogonal methods in single study\",\n      \"pmids\": [\"19020088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"KIF21A interacts with KANK1 via the third and fourth coiled-coil domains of KIF21A and the ankyrin-repeat domain of KANK1. CFEOM1 mutations (R954W, M947T) enhance heterodimer formation with wild-type KIF21A and increase KANK1 translocation to the membrane fraction, suggesting KIF21A regulates KANK1 subcellular distribution.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, knockdown experiments\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and fractionation, single study, moderate follow-up\",\n      \"pmids\": [\"19559006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"KIF21A mediates anterograde axonal transport of NCKX2 via direct interaction between the intracellular loop of NCKX2 and the WD-40 repeat domain of KIF21A. Dominant-negative KIF21A or KIF21A knockdown inhibits axonal transport of NCKX2 and causes calcium dysregulation at axonal boutons.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative overexpression, siRNA knockdown, live-cell imaging of NCKX2-GFP transport, calcium imaging\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction mapping, dominant-negative and knockdown with specific functional readout (calcium dysregulation), multiple orthogonal methods\",\n      \"pmids\": [\"22442075\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"KIF21A acts as a cortical microtubule growth inhibitor: in vitro it suppresses microtubule growth and inhibits catastrophes; in cells it restricts microtubule growth at the cell edge. KIF21A is recruited to the cortex by KANK1, which co-clusters with liprin-α1/β1 and LL5β-containing complexes. CFEOM1 mutations relieve autoinhibition of KIF21A motor activity, leading to enhanced KIF21A accumulation in axonal growth cones, aberrant axon morphology, and reduced responsiveness to inhibitory cues.\",\n      \"method\": \"In vitro microtubule dynamics assay, live-cell imaging, TIRF microscopy, co-immunoprecipitation, dominant-negative and overexpression constructs, primary neuron culture assays\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution assay plus cellular functional assays and mutant analysis, replicated mechanistic insight\",\n      \"pmids\": [\"24120883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"CFEOM1 mutations in both the motor domain and third coiled-coil stalk of KIF21A attenuate autoinhibition (gain-of-function mechanism). Knockin mice with the most common human mutation develop CFEOM with oculomotor axon stalling, enlarged growth cones, excessive filopodia, and random trajectories. MAP1B was identified as a KIF21A-interacting protein, and Map1b-null mice also develop CFEOM.\",\n      \"method\": \"Knockin mouse model, axon tracing, growth cone morphology analysis, co-immunoprecipitation (KIF21A–MAP1B interaction), in vitro autoinhibition assays\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — knockin mouse with defined cellular phenotype, gain-of-function mechanism established, Co-IP for binding partner, replicated across multiple methods\",\n      \"pmids\": [\"24656932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The KIF21A stalk regulatory domain containing all CFEOM1-associated substitutions forms an intramolecular antiparallel coiled coil that inhibits the motor domain. CFEOM1 mutations disrupt the structural integrity of this antiparallel coiled coil or its autoinhibitory binding interface, reducing affinity for the motor domain and causing KIF21A hyperactivation. This regulatory mechanism is conserved in KIF21B, KIF7, and KIF27.\",\n      \"method\": \"Crystal structure of regulatory domain, in vitro binding assays, mutagenesis, analytical ultracentrifugation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and in vitro binding validation\",\n      \"pmids\": [\"27485312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of the KANK1 ankyrin repeat domain (ANKRD) in complex with a short KIF21A peptide at high resolution reveals that the ANKRD uses two distinct interfaces (combinatorial use) to recognize KIF21A. Mutations at either interface disrupt the KANK1–KIF21A interaction and block KIF21A recruitment to focal adhesions.\",\n      \"method\": \"Crystal structure (high-resolution), site-directed mutagenesis, biochemical binding assays, cellular immunofluorescence localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and cellular functional validation\",\n      \"pmids\": [\"29217769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Crystal structure of the KANK1·KIF21A complex at 2.1 Å resolution reveals that a five-helix-bundle-capping domain immediately preceding the ANK repeats of KANK1 forms a structural and functional supramodule with its ANK repeats to bind an evolutionarily conserved KIF21A peptide. Cancer-associated missense mutations at the KANK1–KIF21A interface destabilize complex formation.\",\n      \"method\": \"Crystal structure (2.1 Å), biochemical binding assays, mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with mutagenesis validation\",\n      \"pmids\": [\"29158259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A stretch of ~22 amino acids in KIF21A is sufficient for binding to both KANK1 and KANK2 ankyrin domains. Structures of KIF21A peptide complexed with KANK1 and KANK2 ankyrin domains show KIF21A adopts helical conformations recognized by two distinct pockets of the ankyrin domain.\",\n      \"method\": \"Crystal structure of KIF21A peptide–KANK1 ANK domain and KIF21A peptide–KANK2 ANK domain complexes, site-directed mutagenesis, biochemical binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures of two complexes with mutagenesis\",\n      \"pmids\": [\"29183992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"An NS-associated KANK2 mutation (S684F) induces abnormal binding of eIF4A1 to KANK2 at the physiological KIF21A-binding site; eIF4A1 can competitively displace KIF21A from this site. This pathological competition disrupts KANK2/KIF21A interaction and impairs focal adhesion and cell adhesion in podocytes.\",\n      \"method\": \"Structural analysis, competitive binding assays, co-immunoprecipitation, KANK2 knockout podocyte rescue experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — structural, biochemical, and cellular evidence with multiple orthogonal methods\",\n      \"pmids\": [\"34274317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KIF21A localizes to a subset of dendritic spines in neurons; KIF21A-positive spines are larger and more structurally plastic. The KIF21A–KANK1 interaction is required for dendritic spine morphogenesis and synaptic plasticity; knockdown of either protein inhibits spine morphogenesis and dendritic branching, and hippocampal KIF21A knockdown impairs long-term potentiation and cognitive function in rats.\",\n      \"method\": \"Immunofluorescence, shRNA knockdown in primary neurons and in vivo rat hippocampus, rescue with wild-type vs. binding-deficient mutants, electrophysiology (LTP), behavioral assays\",\n      \"journal\": \"Neural regeneration research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — knockdown with specific cellular and in vivo phenotypes, binding-deficient mutant rescue experiments, multiple methods\",\n      \"pmids\": [\"38767486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Kif21a localizes specifically to podocytes in the zebrafish glomerulus; its deficiency causes podocyte foot process effacement, altered slit diaphragm formation, and severe proteinuria, establishing a role for KIF21A in maintaining glomerular filtration barrier integrity.\",\n      \"method\": \"Zebrafish loss-of-function model, immunolocalization, electron microscopy (foot process morphology), functional proteinuria assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO in vertebrate model with defined cellular phenotype and functional readout, single study\",\n      \"pmids\": [\"37932480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A novel KIF21A variant (p.Leu664Pro) in the second coiled-coil domain causes decreased binding of KIF21A to TUBB3 (β-tubulin III) as demonstrated by co-immunoprecipitation, defining a KIF21A–TUBB3 interaction whose disruption produces peripheral neuropathy, corpus callosum hypoplasia, and strabismus without classic CFEOM.\",\n      \"method\": \"Co-immunoprecipitation (KIF21A p.Leu664Pro vs. reference with TUBB3 in vitro), protein structure modelling\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP with defined functional consequence, single lab, novel finding\",\n      \"pmids\": [\"39643435\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"KIF21A is an anterograde kinesin-4 motor protein that uses its WD-40 repeat tail to transport cargo (e.g., NCKX2) in axons and is recruited to the cell cortex by KANK1 (via a conserved peptide recognized by KANK1's ankyrin-repeat supramodule), where it suppresses microtubule growth and catastrophes; its motor activity is kept in check by autoinhibitory antiparallel coiled-coil interactions between the stalk regulatory domain and the motor domain, and CFEOM1-associated missense mutations in either the motor or stalk domain relieve this autoinhibition, causing oculomotor axon stalling and growth-cone dysregulation in vivo.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"KIF21A is a plus-end-directed kinesin-4 family motor protein that functions both as an anterograde axonal transporter and as a cortical microtubule growth inhibitor, with critical roles in oculomotor axon guidance, dendritic spine morphogenesis, and glomerular podocyte integrity. Its C-terminal WD-40 repeat domain engages cargo such as the sodium/calcium exchanger NCKX2 for axonal transport and interacts with the Arf-GEF BIG1, while its coiled-coil stalk mediates recruitment to the cell cortex through binding to KANK1/KANK2 ankyrin-repeat supramodules, where KIF21A suppresses microtubule growth and catastrophes [PMID:24120883, PMID:29158259, PMID:22442075]. Motor activity is held in check by an intramolecular antiparallel coiled-coil autoinhibitory interaction between the stalk regulatory domain and the motor domain; heterozygous missense mutations in either domain relieve this autoinhibition, causing the congenital eye movement disorder CFEOM1 through oculomotor axon stalling, growth-cone enlargement, and aberrant pathfinding [PMID:14595441, PMID:27485312, PMID:24656932]. KIF21A also directly binds TUBB3, and disruption of this interaction by a coiled-coil variant produces a neurological syndrome distinct from classic CFEOM [PMID:39643435].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Establishing that KIF21A exists as a distinct plus-end kinesin with WD-40 repeats and pan-neuronal distribution resolved the identity of this motor and distinguished it from the dendrite-restricted paralog KIF21B.\",\n      \"evidence\": \"Identification via novel kinesin screen, domain architecture analysis, and immunolocalization in neurons\",\n      \"pmids\": [\"10225949\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No cargo or functional role identified\", \"Motor directionality inferred from kinesin family membership, not directly measured for KIF21A\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovery that heterozygous KIF21A stalk-domain mutations cause CFEOM1 established the gene as essential for oculomotor circuit development and pinpointed the third coiled-coil as a functionally critical region.\",\n      \"evidence\": \"Direct sequencing of KIF21A in 45 CFEOM1 probands with mutation clustering in third coiled-coil stalk domain\",\n      \"pmids\": [\"14595441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which stalk mutations alter motor function unknown\", \"No animal model to confirm causality\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of the BIG1–KIF21A interaction via the WD-40 tail showed that KIF21A connects to Arf-GTPase signaling and membrane trafficking, broadening its functional scope beyond simple cargo transport.\",\n      \"evidence\": \"LC-MS/MS, reciprocal co-immunoprecipitation, fragment mapping, siRNA knockdown altering BIG1 distribution\",\n      \"pmids\": [\"19020088\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological cargo transported via BIG1 link unclear\", \"Whether BIG1 interaction is relevant to CFEOM pathogenesis untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstration that KIF21A binds KANK1 through its coiled-coil domains—and that CFEOM1 mutations enhance this interaction—revealed a cortical recruitment axis and suggested disease mutations are gain-of-function.\",\n      \"evidence\": \"Co-immunoprecipitation and subcellular fractionation comparing wild-type and CFEOM1 mutant KIF21A\",\n      \"pmids\": [\"19559006\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural basis for KANK1 binding determined\", \"Single-study observation of enhanced binding by mutants\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Establishing NCKX2 as a WD-40-dependent KIF21A cargo that requires KIF21A for anterograde axonal transport linked this motor to calcium homeostasis at presynaptic terminals.\",\n      \"evidence\": \"Co-immunoprecipitation, dominant-negative and siRNA experiments with live-cell NCKX2-GFP tracking and calcium imaging\",\n      \"pmids\": [\"22442075\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NCKX2 transport defects contribute to CFEOM unknown\", \"Additional axonal cargoes not systematically identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Reconstitution of KIF21A's microtubule growth-inhibitory activity in vitro, combined with demonstration that CFEOM1 mutations relieve autoinhibition and cause growth-cone accumulation, unified the transport and cytoskeletal regulation functions and provided the first mechanistic disease model.\",\n      \"evidence\": \"In vitro microtubule dynamics assays, TIRF microscopy, KANK1-dependent cortical recruitment, primary neuron assays with CFEOM1 mutants\",\n      \"pmids\": [\"24120883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of autoinhibition not yet resolved\", \"Relative contribution of growth inhibition vs. cargo transport to CFEOM unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"A knockin mouse carrying the commonest human CFEOM1 mutation recapitulated oculomotor axon stalling and growth-cone defects, confirming the gain-of-function mechanism in vivo and identifying MAP1B as an interacting partner whose loss phenocopies CFEOM.\",\n      \"evidence\": \"Knockin mouse model with axon tracing and growth-cone morphology; co-immunoprecipitation for MAP1B; Map1b-null mouse phenotyping\",\n      \"pmids\": [\"24656932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How MAP1B functionally intersects KIF21A autoinhibition unknown\", \"Whether MAP1B interaction is direct or bridged not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"The crystal structure of the KIF21A stalk regulatory domain revealed an antiparallel coiled-coil fold whose disruption by CFEOM1 mutations weakens motor-domain binding, providing the atomic-level explanation for disease-associated hyperactivation.\",\n      \"evidence\": \"Crystal structure, analytical ultracentrifugation, in vitro binding assays with disease-mimicking mutations\",\n      \"pmids\": [\"27485312\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length structure of autoinhibited KIF21A not available\", \"Dynamics of autoinhibition relief in vivo uncharacterized\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"High-resolution crystal structures of KANK1 and KANK2 ankyrin domains complexed with a short KIF21A peptide defined the cortical recruitment interface at atomic detail, showing a supramodule recognition mechanism conserved across KANK family members.\",\n      \"evidence\": \"Crystal structures (2.1 Å for KANK1·KIF21A; separate KANK2·KIF21A structure), mutagenesis disrupting binding and focal-adhesion recruitment\",\n      \"pmids\": [\"29217769\", \"29158259\", \"29183992\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How KANK-mediated cortical anchoring coordinates with autoinhibition release unknown\", \"Whether all KANK family members equally recruit KIF21A in vivo untested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Discovery that a nephrotic syndrome-associated KANK2 mutation allows eIF4A1 to competitively displace KIF21A from the shared binding site demonstrated that the KANK–KIF21A axis operates in podocyte adhesion and can be pathologically disrupted by heterologous competitors.\",\n      \"evidence\": \"Structural analysis, competitive binding assays, co-immunoprecipitation, KANK2-knockout podocyte rescue\",\n      \"pmids\": [\"34274317\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KIF21A loss per se drives podocyte pathology or acts through KANK2 dysfunction unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of KIF21A in dendritic spines and demonstration that the KIF21A–KANK1 axis drives spine morphogenesis, LTP, and cognitive function extended the motor's role from axonal guidance to postsynaptic plasticity.\",\n      \"evidence\": \"shRNA knockdown in primary neurons and rat hippocampus in vivo, rescue with binding-deficient mutants, electrophysiology, behavioral assays\",\n      \"pmids\": [\"38767486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo transported by KIF21A into spines not identified\", \"Whether microtubule growth inhibition or transport underlies spine effects unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Zebrafish loss-of-function showed KIF21A is required in podocytes for foot process formation and slit diaphragm integrity, establishing an in vivo role in glomerular filtration.\",\n      \"evidence\": \"Zebrafish knockout, electron microscopy of foot processes, proteinuria assay\",\n      \"pmids\": [\"37932480\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Not replicated in mammalian kidney models\", \"Molecular mechanism of podocyte foot process regulation by KIF21A unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A novel KIF21A coiled-coil variant that reduces TUBB3 binding defined a direct KIF21A–TUBB3 interaction and a distinct clinical phenotype (peripheral neuropathy, corpus callosum hypoplasia) outside classic CFEOM.\",\n      \"evidence\": \"Co-immunoprecipitation comparing mutant vs. reference KIF21A with TUBB3, protein modelling, clinical phenotyping\",\n      \"pmids\": [\"39643435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single family; independent replication needed\", \"Mechanism by which reduced TUBB3 binding alters neuronal development not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the full-length structure of autoinhibited KIF21A, the identity of dendritic-spine cargoes, the relative contributions of microtubule regulation versus transport to each tissue-specific phenotype, and whether KIF21A has catalytic or regulatory roles beyond its motor activity.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length autoinhibited structure\", \"Spine-specific cargo unknown\", \"Relative contribution of growth inhibition vs. transport to axonal and podocyte phenotypes unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003774\", \"supporting_discovery_ids\": [0, 4, 5]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [5, 6, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 8]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4, 12]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"KANK1\",\n      \"KANK2\",\n      \"BIG1\",\n      \"NCKX2\",\n      \"MAP1B\",\n      \"TUBB3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}