{"gene":"MAB21L2","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2004,"finding":"MAB21L2 binds single-stranded RNA, as predicted by structural homology; this RNA-binding activity is abolished in disease-associated missense variants (Glu49Lys, Arg51Cys, Arg51His, Arg247Gln). MAB21L2 showed no detectable nucleotidyltransferase activity in vitro.","method":"In vitro RNA-binding assay; in vitro nucleotidyltransferase assay; structural homology modeling","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro biochemical assay for RNA binding and enzymatic activity, but single lab and abstracts lack full methodological detail","pmids":["24906020"],"is_preprint":false},{"year":2014,"finding":"Wild-type MAB21L2 expression in HEK293 cells increased phospho-ERK1/2 (pERK) signaling; disease-associated variants at Glu49 and Arg51 showed increased protein stability compared to wild-type and the Arg247Gln variant, suggesting abnormal persistence of pERK signaling as a pathogenic mechanism for the heterozygous mutations.","method":"Overexpression in HEK293 cells; western blot for phospho-ERK1/2; protein stability assessment","journal":"American journal of human genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single cellular assay (gain-of-function overexpression), no reciprocal validation or mechanistic follow-up","pmids":["24906020"],"is_preprint":false},{"year":2004,"finding":"MAB21L2 antagonizes BMP4 signaling in vivo: overexpression of Mab21l2 in Xenopus gastrulae rescues the dorsalized axis caused by BMP4 overexpression and restores wild-type distribution of Chordin and Xvent2 transcripts. MAB21L2 immunoprecipitates with BMP4 effector SMAD1 in vivo, and binds SMAD1 and the SMAD1-SMAD4 complex in vitro. When targeted to a heterologous promoter, MAB21L2 acts as a transcriptional repressor.","method":"Xenopus gain-of-function overexpression; in vivo co-immunoprecipitation; in vitro binding assay with SMAD1 and SMAD1-SMAD4; heterologous promoter transcriptional repressor assay; whole-mount in situ hybridization for Chordin and Xvent2","journal":"BMC cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus in vitro binding plus functional rescue in Xenopus, single lab but multiple orthogonal methods","pmids":["15613244"],"is_preprint":false},{"year":2004,"finding":"In C. elegans genetic epistasis, mab-21 is epistatic to genes encoding members of a TGF-beta signaling pathway involved in male-specific sensory organ formation, placing MAB21L2 orthologs downstream of or parallel to TGF-beta/BMP pathway components.","method":"Genetic epistasis analysis in C. elegans double mutants (cited from prior literature within this paper)","journal":"BMC cell biology","confidence":"Low","confidence_rationale":"Tier 2 / Weak — epistasis data cited from prior C. elegans literature, not directly performed in this corpus paper; indirect evidence","pmids":["15613244"],"is_preprint":false},{"year":2004,"finding":"Mab21l2 is required downstream of rx3 in zebrafish eye development: mab21l2 expression is absent in the eye field of rx3 (chokh) mutants, and morpholino-mediated knockdown of Mab21l2 partially phenocopies the rx3 mutation (microphthalmia, incomplete eye maturation, dramatic increase in apoptotic eye progenitors), placing mab21l2 as an early downstream effector of rx3 for survival of eye progenitors.","method":"Antisense morpholino knockdown in zebrafish; in situ hybridization; apoptosis assay; epistasis through rx3 mutant analysis","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via morpholino knockdown plus expression analysis in mutant background, single lab","pmids":["15183718"],"is_preprint":false},{"year":2004,"finding":"Mab21l2 knockout in mouse causes insufficient optic vesicle invagination due to deficient proliferation, leading to rudimentary retina and absent lens. Loss of Mab21l2 specifically reduces Chx10 expression, while Rx, Lhx2, and Pax6 are not significantly affected, placing Mab21l2 upstream of Chx10 in the retinal development pathway.","method":"Mouse genetic knockout; histology; in situ hybridization for retinal transcription factors (Chx10, Rx, Lhx2, Pax6)","journal":"Developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined cellular phenotype and marker gene analysis, single lab","pmids":["15385160"],"is_preprint":false},{"year":2012,"finding":"Mab21l2 is required for cardiomyocyte proliferation and trabecular/compact myocardium formation; Mab21l2-deficient mouse embryos show decreased expression of genes regulating cell proliferation and apoptosis in the heart. Additionally, Mab21l2 is required in the septum transversum mesenchyme for proepicardial cell proliferation and migration (dependent on α4 integrin expression), epicardial formation, and hepatoblast proliferation/liver morphogenesis.","method":"Mouse genetic knockout; histology; gene expression analysis; immunostaining for α4 integrin; assessment of cell proliferation in proepicardium","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple defined cellular phenotypes and molecular marker analysis, single lab","pmids":["22412967"],"is_preprint":false},{"year":2018,"finding":"In chick, Mab21l2 loss-of-function (RNAi) prior to optic vesicle formation causes anophthalmia; inhibition at optic cup stage causes microphthalmic colobomatous phenotype. Mab21l2 knockdown affects cell proliferation, cell cycle exit, and expression of Atoh7/Ath5, NeuroD4/Ath3, Isl1, Pax6, AP-2α, and Prox1. Mab21l2 overexpression hampers cell cycle exit and differentiation of retinal progenitor cells, demonstrating a stage-dependent requirement for regulated Mab21l2 expression in retinogenesis.","method":"In ovo RNAi electroporation in chick; gain-of-function electroporation; immunostaining for apoptosis, proliferation, and differentiation markers; in situ hybridization","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss- and gain-of-function with multiple molecular markers, single lab","pmids":["30073347"],"is_preprint":false},{"year":2019,"finding":"In zebrafish mab21l2 mutants, loss of mab21l2 function causes decreased proliferation and increased cell death in the lens, elevated cell death in the optic stalk, failure of basement membrane breakdown between choroid fissure edges (preventing fissure closure/coloboma), and corneal dysgenesis with ectopic proliferation and failure to differentiate the corneal stroma. Neuronal differentiation in the retina was normal.","method":"Zebrafish genetic mutant; histology; immunostaining for proliferation (BrdU/pH3) and apoptosis (TUNEL/caspase); marker gene expression analysis","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mutant with multiple cellular phenotype readouts and orthogonal methods, single lab","pmids":["31037784"],"is_preprint":false},{"year":2023,"finding":"Yeast two-hybrid screens identified klhl31, tnpo1, TNPO2/tnpo2, KLC2/klc2, and SPTBN1/sptbn1 as binding partners of wild-type MAB21L2/mab21l2. HSPA8 and HSPA5 interact with both wild-type and disease-variant MAB21L2-p.(Arg51Gly), validated by 1-by-1 Y2H, co-immunoprecipitation, and mass spectrometry. hspa8 zebrafish mutants display severe ocular defects, and hspa8/mab21l2 double mutants are more severely affected than single mutants, suggesting a functional interaction in eye development.","method":"Yeast two-hybrid screening; co-immunoprecipitation; mass spectrometry; in situ hybridization; zebrafish double mutant genetic analysis","journal":"Developmental dynamics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Y2H + Co-IP + MS + double mutant genetics) in single lab","pmids":["36576422"],"is_preprint":false},{"year":2025,"finding":"Conditional knockout of Mab21l2 using Prx1-Cre in mouse early limb mesenchyme causes humerus/stylopod malformation with a 3-day delay in endochondral ossification. Mab21l2 is expressed in the distal mesenchyme of forelimb buds at E9.5-10.5, and its deletion reduces chondrocyte proliferation in the prospective humerus region at E10.5, leading to a smaller cartilage template and humerus shortening. The effect is proposed to be non-cell-autonomous.","method":"Conditional knockout mouse (Prx1-Cre; Mab21l2flox/flox); histology; micro-CT; BrdU/Ki67 proliferation assay; in situ hybridization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional genetic KO with defined cellular phenotype and proliferation assay, single lab","pmids":["40054064"],"is_preprint":false},{"year":2024,"finding":"A ~113.5 kb homozygous deletion 19.38 kb upstream of MAB21L2 causes microphthalmia in a human patient. Conservation analysis identified 15 non-coding conserved elements (CEs) in this region; ChIP-seq data showed that CE13 and CE14 bind the transcription factor Otx2 in mouse embryonic stem cells. Targeted disruption of CE14 alone in Xenopus tropicalis recapitulates ocular coloboma, identifying CE14 as a functional regulatory element for MAB21L2 eye expression.","method":"Human genomic deletion mapping; zebrafish and Xenopus tropicalis modeling of deletion; ChIP-seq data analysis for Otx2 binding; CRISPR/Cas9 targeted disruption of CE14 in Xenopus; phenotypic analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — regulatory element identified by conservation + ChIP-seq and functionally validated by targeted disruption in Xenopus, single study","pmids":["39455595"],"is_preprint":false},{"year":2026,"finding":"MAB21L2 knockdown in neuroblastoma cells inhibits tumor cell growth in vitro and in vivo, and RNA-seq analysis revealed that MAB21L2 enhances cell migration capacity in neuroblastoma cells.","method":"siRNA/shRNA knockdown; in vitro proliferation assay; in vivo xenograft; RNA-seq; migration assay","journal":"Experimental cell research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, loss-of-function with phenotypic readout in cancer cells, limited mechanistic pathway placement","pmids":["41651436"],"is_preprint":false}],"current_model":"MAB21L2 is a single-exon gene encoding a conserved protein that binds single-stranded RNA (with disease mutations abolishing this activity), lacks nucleotidyltransferase activity, antagonizes BMP4/SMAD1 signaling as a transcriptional repressor, interacts physically with SMAD1/SMAD4, and is required downstream of Rx3 for survival and proliferation of eye progenitors; it also regulates cell proliferation in the developing retina, lens, cornea, heart (cardiomyocytes and proepicardium), liver (septum transversum mesenchyme), and limb stylopods, with HSPA8/HSPA5 identified as binding partners relevant to its ocular function."},"narrative":{"mechanistic_narrative":"MAB21L2 is a conserved single-stranded RNA-binding protein that controls progenitor cell proliferation and survival across multiple developing tissues, with its principal characterized role in eye morphogenesis [PMID:24906020, PMID:15385160]. It binds single-stranded RNA in vitro—an activity abolished by disease-associated missense variants—but shows no detectable nucleotidyltransferase activity [PMID:24906020]. Functionally, MAB21L2 antagonizes BMP4/SMAD signaling: it physically associates with SMAD1 and the SMAD1–SMAD4 complex, acts as a transcriptional repressor when tethered to a promoter, and rescues BMP4-induced axial dorsalization in Xenopus [PMID:15613244]. In eye development it operates downstream of Rx3 and upstream of Chx10, where its loss causes deficient optic vesicle invagination, increased apoptosis of eye progenitors, and microphthalmia/anophthalmia, while regulating proliferation, cell-cycle exit, and differentiation in retina, lens, and cornea [PMID:15183718, PMID:15385160, PMID:30073347, PMID:31037784]. Beyond the eye, MAB21L2 drives proliferation in cardiomyocytes and the proepicardium/septum transversum mesenchyme, hepatoblasts, and limb-bud chondrocyte precursors [PMID:22412967, PMID:40054064]. The chaperones HSPA8 and HSPA5 are direct binding partners relevant to its ocular function, and eye-specific expression is governed by a distal Otx2-bound regulatory element whose disruption causes microphthalmia and coloboma [PMID:36576422, PMID:39455595]. Loss of human MAB21L2 function or its regulatory elements causes ocular malformations including microphthalmia and coloboma [PMID:24906020, PMID:39455595].","teleology":[{"year":2004,"claim":"Establishing what biochemical activity MAB21L2 carries, the protein was shown to bind single-stranded RNA while lacking nucleotidyltransferase activity, redefining its molecular identity away from a presumed enzyme.","evidence":"In vitro RNA-binding and nucleotidyltransferase assays with structural homology modeling, including disease variants","pmids":["24906020"],"confidence":"Medium","gaps":["No RNA target specificity or sequence motif identified","Functional consequence of RNA binding for downstream signaling not established","Single lab, abstract-level methodological detail"]},{"year":2004,"claim":"To place MAB21L2 in a signaling pathway, it was shown to antagonize BMP4 by binding SMAD1/SMAD1-SMAD4 and acting as a transcriptional repressor, connecting it to TGF-beta/BMP signal output.","evidence":"Xenopus overexpression rescue, in vivo Co-IP and in vitro binding with SMAD1/SMAD4, heterologous promoter repressor assay","pmids":["15613244"],"confidence":"Medium","gaps":["Target genes repressed by MAB21L2 not defined","Mechanism linking RNA binding to SMAD repression unknown","Direct DNA binding not demonstrated"]},{"year":2004,"claim":"Genetic epistasis in C. elegans placed mab-21 orthologs downstream of or parallel to TGF-beta pathway components, supporting a conserved role in signaling-dependent organ patterning.","evidence":"C. elegans double-mutant epistasis cited from prior literature","pmids":["15613244"],"confidence":"Low","gaps":["Epistasis data cited, not directly performed in this corpus","Molecular relationship to mammalian BMP signaling indirect"]},{"year":2004,"claim":"Positioning MAB21L2 in the eye gene network, it was shown to act downstream of rx3 and to be required for survival of eye progenitors, defining it as an early effector of retinal field specification.","evidence":"Zebrafish morpholino knockdown, in situ hybridization in rx3 mutants, apoptosis assays","pmids":["15183718"],"confidence":"Medium","gaps":["Morpholino knockdown not confirmed by stable mutant in this study","Direct transcriptional regulators downstream of MAB21L2 not defined"]},{"year":2004,"claim":"A mouse knockout established that MAB21L2 drives optic vesicle invagination through proliferation and lies upstream of Chx10, distinguishing it from Rx/Lhx2/Pax6 inputs.","evidence":"Mouse genetic knockout with histology and marker in situ hybridization","pmids":["15385160"],"confidence":"Medium","gaps":["Mechanism linking MAB21L2 to Chx10 regulation unknown","Whether effect is cell-autonomous not resolved"]},{"year":2012,"claim":"Extending MAB21L2 beyond the eye, knockout mice revealed requirements for proliferation in heart, proepicardium/septum transversum mesenchyme, and liver, defining a broad role in progenitor proliferation.","evidence":"Mouse genetic knockout with histology, gene expression, and integrin immunostaining","pmids":["22412967"],"confidence":"Medium","gaps":["Molecular pathway linking MAB21L2 to α4 integrin and proliferation not defined","Direct versus indirect effects on each tissue unresolved"]},{"year":2018,"claim":"Chick loss- and gain-of-function defined a stage-dependent requirement for MAB21L2 in regulating proliferation, cell-cycle exit, and differentiation across retinogenesis.","evidence":"In ovo RNAi and overexpression electroporation with proliferation/differentiation markers","pmids":["30073347"],"confidence":"Medium","gaps":["Direct transcriptional targets among affected markers not established","Mechanism of bidirectional dose sensitivity unknown"]},{"year":2019,"claim":"Zebrafish mutants dissected tissue-specific MAB21L2 roles, linking it to lens proliferation/survival, choroid fissure basement-membrane breakdown (coloboma), and corneal stromal differentiation.","evidence":"Zebrafish genetic mutant with proliferation/apoptosis assays and marker analysis","pmids":["31037784"],"confidence":"Medium","gaps":["Molecular control of basement-membrane breakdown not defined","Cell-autonomy of corneal phenotype unresolved"]},{"year":2023,"claim":"Interactome screens identified physical partners including HSPA8/HSPA5, and double-mutant genetics linked hspa8 to MAB21L2 in eye development, providing a chaperone-associated molecular context.","evidence":"Yeast two-hybrid, Co-IP, mass spectrometry, and zebrafish double-mutant analysis","pmids":["36576422"],"confidence":"Medium","gaps":["Functional consequence of HSPA8/HSPA5 binding unknown","Roles of klhl31/tnpo1/TNPO2/KLC2/SPTBN1 interactions not characterized"]},{"year":2024,"claim":"Identifying how MAB21L2 eye expression is controlled, a distal Otx2-bound conserved element (CE14) was shown to be a functional regulatory element whose disruption causes ocular defects.","evidence":"Human deletion mapping, ChIP-seq for Otx2, CRISPR disruption of CE14 in Xenopus","pmids":["39455595"],"confidence":"Medium","gaps":["Direct Otx2 regulation of MAB21L2 in human cells not shown","Roles of other conserved elements not tested"]},{"year":2025,"claim":"Conditional knockout extended MAB21L2 function to skeletal development, showing it promotes chondrocyte proliferation in limb stylopod formation, likely non-cell-autonomously.","evidence":"Prx1-Cre conditional knockout mouse with micro-CT and proliferation assays","pmids":["40054064"],"confidence":"Medium","gaps":["Non-cell-autonomous signal not identified","Mechanism linking MAB21L2 to chondrocyte proliferation unknown"]},{"year":2026,"claim":"MAB21L2 was implicated in cancer, with knockdown inhibiting neuroblastoma growth and migration, suggesting a pro-tumorigenic role.","evidence":"siRNA/shRNA knockdown, xenograft, RNA-seq, migration assay in neuroblastoma cells","pmids":["41651436"],"confidence":"Low","gaps":["No mechanistic pathway placement in cancer","Single lab, limited validation","Relationship to developmental BMP/proliferation roles unclear"]},{"year":null,"claim":"How MAB21L2's RNA-binding activity mechanistically connects to its SMAD-repressing, proliferation-promoting functions across diverse tissues remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No RNA target identified that links biochemistry to transcriptional/proliferative output","No structural model of partner or RNA engagement in cells","Unified mechanism across eye, heart, liver, limb, and cancer not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[2]}],"localization":[],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[4,5,6,7,10]}],"complexes":[],"partners":["SMAD1","SMAD4","HSPA8","HSPA5","TNPO2","KLC2","SPTBN1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y586","full_name":"Protein mab-21-like 2","aliases":[],"length_aa":359,"mass_kda":40.9,"function":"Required for several aspects of embryonic development including normal development of the eye","subcellular_location":"Nucleus; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9Y586/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAB21L2","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/MAB21L2","total_profiled":1310},"omim":[{"mim_id":"615877","title":"MICROPHTHALMIA/COLOBOMA AND SKELETAL DYSPLASIA SYNDROME; MCSKS","url":"https://www.omim.org/entry/615877"},{"mim_id":"604357","title":"MAB21-LIKE 2; MAB21L2","url":"https://www.omim.org/entry/604357"},{"mim_id":"601280","title":"MAB21-LIKE 1; MAB21L1","url":"https://www.omim.org/entry/601280"},{"mim_id":"309800","title":"MICROPHTHALMIA, SYNDROMIC 1; MCOPS1","url":"https://www.omim.org/entry/309800"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":170.0}],"url":"https://www.proteinatlas.org/search/MAB21L2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9Y586","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y586","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y586-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y586-F1-predicted_aligned_error_v6.png","plddt_mean":94.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAB21L2","jax_strain_url":"https://www.jax.org/strain/search?query=MAB21L2"},"sequence":{"accession":"Q9Y586","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y586.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y586/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y586"}},"corpus_meta":[{"pmid":"24906020","id":"PMC_24906020","title":"Monoallelic and biallelic mutations in MAB21L2 cause a spectrum of major eye malformations.","date":"2014","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/24906020","citation_count":74,"is_preprint":false},{"pmid":"15183718","id":"PMC_15183718","title":"Zebrafish rx3 and mab21l2 are required during eye morphogenesis.","date":"2004","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/15183718","citation_count":69,"is_preprint":false},{"pmid":"15385160","id":"PMC_15385160","title":"Requirement for Mab21l2 during development of murine retina and ventral body wall.","date":"2004","source":"Developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/15385160","citation_count":66,"is_preprint":false},{"pmid":"25719200","id":"PMC_25719200","title":"Mutations in MAB21L2 result in ocular Coloboma, microcornea and cataracts.","date":"2015","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25719200","citation_count":53,"is_preprint":false},{"pmid":"15613244","id":"PMC_15613244","title":"MAB21L2, a vertebrate member of the Male-abnormal 21 family, modulates BMP signaling and interacts with SMAD1.","date":"2004","source":"BMC cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/15613244","citation_count":42,"is_preprint":false},{"pmid":"11857508","id":"PMC_11857508","title":"Depletion of Mab21l1 and Mab21l2 messages in mouse embryo arrests axial turning, and impairs notochord and neural tube differentiation.","date":"2002","source":"Teratology","url":"https://pubmed.ncbi.nlm.nih.gov/11857508","citation_count":32,"is_preprint":false},{"pmid":"10495284","id":"PMC_10495284","title":"Developmental expression of Mab21l2 during mouse embryogenesis.","date":"1999","source":"Mechanisms of development","url":"https://pubmed.ncbi.nlm.nih.gov/10495284","citation_count":31,"is_preprint":false},{"pmid":"22412967","id":"PMC_22412967","title":"Mab21l2 is essential for embryonic heart and liver development.","date":"2012","source":"PloS 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zazhi = Chinese journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35929935","citation_count":1,"is_preprint":false},{"pmid":"40054064","id":"PMC_40054064","title":"Mab21l2 is required to promote cell proliferation in stylopods during early limb development.","date":"2025","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/40054064","citation_count":0,"is_preprint":false},{"pmid":"41651436","id":"PMC_41651436","title":"Targeting super-enhancer-driven MAB21L2 suppresses neuroblastoma growth and migration.","date":"2026","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/41651436","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12466,"output_tokens":3633,"usd":0.045947,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11225,"output_tokens":3730,"usd":0.074688,"stage2_stop_reason":"end_turn"},"total_usd":0.120635,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"MAB21L2 binds single-stranded RNA, as predicted by structural homology; this RNA-binding activity is abolished in disease-associated missense variants (Glu49Lys, Arg51Cys, Arg51His, Arg247Gln). MAB21L2 showed no detectable nucleotidyltransferase activity in vitro.\",\n      \"method\": \"In vitro RNA-binding assay; in vitro nucleotidyltransferase assay; structural homology modeling\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro biochemical assay for RNA binding and enzymatic activity, but single lab and abstracts lack full methodological detail\",\n      \"pmids\": [\"24906020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Wild-type MAB21L2 expression in HEK293 cells increased phospho-ERK1/2 (pERK) signaling; disease-associated variants at Glu49 and Arg51 showed increased protein stability compared to wild-type and the Arg247Gln variant, suggesting abnormal persistence of pERK signaling as a pathogenic mechanism for the heterozygous mutations.\",\n      \"method\": \"Overexpression in HEK293 cells; western blot for phospho-ERK1/2; protein stability assessment\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single cellular assay (gain-of-function overexpression), no reciprocal validation or mechanistic follow-up\",\n      \"pmids\": [\"24906020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"MAB21L2 antagonizes BMP4 signaling in vivo: overexpression of Mab21l2 in Xenopus gastrulae rescues the dorsalized axis caused by BMP4 overexpression and restores wild-type distribution of Chordin and Xvent2 transcripts. MAB21L2 immunoprecipitates with BMP4 effector SMAD1 in vivo, and binds SMAD1 and the SMAD1-SMAD4 complex in vitro. When targeted to a heterologous promoter, MAB21L2 acts as a transcriptional repressor.\",\n      \"method\": \"Xenopus gain-of-function overexpression; in vivo co-immunoprecipitation; in vitro binding assay with SMAD1 and SMAD1-SMAD4; heterologous promoter transcriptional repressor assay; whole-mount in situ hybridization for Chordin and Xvent2\",\n      \"journal\": \"BMC cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus in vitro binding plus functional rescue in Xenopus, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"15613244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In C. elegans genetic epistasis, mab-21 is epistatic to genes encoding members of a TGF-beta signaling pathway involved in male-specific sensory organ formation, placing MAB21L2 orthologs downstream of or parallel to TGF-beta/BMP pathway components.\",\n      \"method\": \"Genetic epistasis analysis in C. elegans double mutants (cited from prior literature within this paper)\",\n      \"journal\": \"BMC cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 / Weak — epistasis data cited from prior C. elegans literature, not directly performed in this corpus paper; indirect evidence\",\n      \"pmids\": [\"15613244\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Mab21l2 is required downstream of rx3 in zebrafish eye development: mab21l2 expression is absent in the eye field of rx3 (chokh) mutants, and morpholino-mediated knockdown of Mab21l2 partially phenocopies the rx3 mutation (microphthalmia, incomplete eye maturation, dramatic increase in apoptotic eye progenitors), placing mab21l2 as an early downstream effector of rx3 for survival of eye progenitors.\",\n      \"method\": \"Antisense morpholino knockdown in zebrafish; in situ hybridization; apoptosis assay; epistasis through rx3 mutant analysis\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via morpholino knockdown plus expression analysis in mutant background, single lab\",\n      \"pmids\": [\"15183718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Mab21l2 knockout in mouse causes insufficient optic vesicle invagination due to deficient proliferation, leading to rudimentary retina and absent lens. Loss of Mab21l2 specifically reduces Chx10 expression, while Rx, Lhx2, and Pax6 are not significantly affected, placing Mab21l2 upstream of Chx10 in the retinal development pathway.\",\n      \"method\": \"Mouse genetic knockout; histology; in situ hybridization for retinal transcription factors (Chx10, Rx, Lhx2, Pax6)\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined cellular phenotype and marker gene analysis, single lab\",\n      \"pmids\": [\"15385160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mab21l2 is required for cardiomyocyte proliferation and trabecular/compact myocardium formation; Mab21l2-deficient mouse embryos show decreased expression of genes regulating cell proliferation and apoptosis in the heart. Additionally, Mab21l2 is required in the septum transversum mesenchyme for proepicardial cell proliferation and migration (dependent on α4 integrin expression), epicardial formation, and hepatoblast proliferation/liver morphogenesis.\",\n      \"method\": \"Mouse genetic knockout; histology; gene expression analysis; immunostaining for α4 integrin; assessment of cell proliferation in proepicardium\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple defined cellular phenotypes and molecular marker analysis, single lab\",\n      \"pmids\": [\"22412967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In chick, Mab21l2 loss-of-function (RNAi) prior to optic vesicle formation causes anophthalmia; inhibition at optic cup stage causes microphthalmic colobomatous phenotype. Mab21l2 knockdown affects cell proliferation, cell cycle exit, and expression of Atoh7/Ath5, NeuroD4/Ath3, Isl1, Pax6, AP-2α, and Prox1. Mab21l2 overexpression hampers cell cycle exit and differentiation of retinal progenitor cells, demonstrating a stage-dependent requirement for regulated Mab21l2 expression in retinogenesis.\",\n      \"method\": \"In ovo RNAi electroporation in chick; gain-of-function electroporation; immunostaining for apoptosis, proliferation, and differentiation markers; in situ hybridization\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss- and gain-of-function with multiple molecular markers, single lab\",\n      \"pmids\": [\"30073347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In zebrafish mab21l2 mutants, loss of mab21l2 function causes decreased proliferation and increased cell death in the lens, elevated cell death in the optic stalk, failure of basement membrane breakdown between choroid fissure edges (preventing fissure closure/coloboma), and corneal dysgenesis with ectopic proliferation and failure to differentiate the corneal stroma. Neuronal differentiation in the retina was normal.\",\n      \"method\": \"Zebrafish genetic mutant; histology; immunostaining for proliferation (BrdU/pH3) and apoptosis (TUNEL/caspase); marker gene expression analysis\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mutant with multiple cellular phenotype readouts and orthogonal methods, single lab\",\n      \"pmids\": [\"31037784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Yeast two-hybrid screens identified klhl31, tnpo1, TNPO2/tnpo2, KLC2/klc2, and SPTBN1/sptbn1 as binding partners of wild-type MAB21L2/mab21l2. HSPA8 and HSPA5 interact with both wild-type and disease-variant MAB21L2-p.(Arg51Gly), validated by 1-by-1 Y2H, co-immunoprecipitation, and mass spectrometry. hspa8 zebrafish mutants display severe ocular defects, and hspa8/mab21l2 double mutants are more severely affected than single mutants, suggesting a functional interaction in eye development.\",\n      \"method\": \"Yeast two-hybrid screening; co-immunoprecipitation; mass spectrometry; in situ hybridization; zebrafish double mutant genetic analysis\",\n      \"journal\": \"Developmental dynamics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Y2H + Co-IP + MS + double mutant genetics) in single lab\",\n      \"pmids\": [\"36576422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Conditional knockout of Mab21l2 using Prx1-Cre in mouse early limb mesenchyme causes humerus/stylopod malformation with a 3-day delay in endochondral ossification. Mab21l2 is expressed in the distal mesenchyme of forelimb buds at E9.5-10.5, and its deletion reduces chondrocyte proliferation in the prospective humerus region at E10.5, leading to a smaller cartilage template and humerus shortening. The effect is proposed to be non-cell-autonomous.\",\n      \"method\": \"Conditional knockout mouse (Prx1-Cre; Mab21l2flox/flox); histology; micro-CT; BrdU/Ki67 proliferation assay; in situ hybridization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional genetic KO with defined cellular phenotype and proliferation assay, single lab\",\n      \"pmids\": [\"40054064\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A ~113.5 kb homozygous deletion 19.38 kb upstream of MAB21L2 causes microphthalmia in a human patient. Conservation analysis identified 15 non-coding conserved elements (CEs) in this region; ChIP-seq data showed that CE13 and CE14 bind the transcription factor Otx2 in mouse embryonic stem cells. Targeted disruption of CE14 alone in Xenopus tropicalis recapitulates ocular coloboma, identifying CE14 as a functional regulatory element for MAB21L2 eye expression.\",\n      \"method\": \"Human genomic deletion mapping; zebrafish and Xenopus tropicalis modeling of deletion; ChIP-seq data analysis for Otx2 binding; CRISPR/Cas9 targeted disruption of CE14 in Xenopus; phenotypic analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — regulatory element identified by conservation + ChIP-seq and functionally validated by targeted disruption in Xenopus, single study\",\n      \"pmids\": [\"39455595\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MAB21L2 knockdown in neuroblastoma cells inhibits tumor cell growth in vitro and in vivo, and RNA-seq analysis revealed that MAB21L2 enhances cell migration capacity in neuroblastoma cells.\",\n      \"method\": \"siRNA/shRNA knockdown; in vitro proliferation assay; in vivo xenograft; RNA-seq; migration assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, loss-of-function with phenotypic readout in cancer cells, limited mechanistic pathway placement\",\n      \"pmids\": [\"41651436\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAB21L2 is a single-exon gene encoding a conserved protein that binds single-stranded RNA (with disease mutations abolishing this activity), lacks nucleotidyltransferase activity, antagonizes BMP4/SMAD1 signaling as a transcriptional repressor, interacts physically with SMAD1/SMAD4, and is required downstream of Rx3 for survival and proliferation of eye progenitors; it also regulates cell proliferation in the developing retina, lens, cornea, heart (cardiomyocytes and proepicardium), liver (septum transversum mesenchyme), and limb stylopods, with HSPA8/HSPA5 identified as binding partners relevant to its ocular function.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAB21L2 is a conserved single-stranded RNA-binding protein that controls progenitor cell proliferation and survival across multiple developing tissues, with its principal characterized role in eye morphogenesis [#0, #5]. It binds single-stranded RNA in vitro—an activity abolished by disease-associated missense variants—but shows no detectable nucleotidyltransferase activity [#0]. Functionally, MAB21L2 antagonizes BMP4/SMAD signaling: it physically associates with SMAD1 and the SMAD1–SMAD4 complex, acts as a transcriptional repressor when tethered to a promoter, and rescues BMP4-induced axial dorsalization in Xenopus [#2]. In eye development it operates downstream of Rx3 and upstream of Chx10, where its loss causes deficient optic vesicle invagination, increased apoptosis of eye progenitors, and microphthalmia/anophthalmia, while regulating proliferation, cell-cycle exit, and differentiation in retina, lens, and cornea [#4, #5, #7, #8]. Beyond the eye, MAB21L2 drives proliferation in cardiomyocytes and the proepicardium/septum transversum mesenchyme, hepatoblasts, and limb-bud chondrocyte precursors [#6, #10]. The chaperones HSPA8 and HSPA5 are direct binding partners relevant to its ocular function, and eye-specific expression is governed by a distal Otx2-bound regulatory element whose disruption causes microphthalmia and coloboma [#9, #11]. Loss of human MAB21L2 function or its regulatory elements causes ocular malformations including microphthalmia and coloboma [#0, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Establishing what biochemical activity MAB21L2 carries, the protein was shown to bind single-stranded RNA while lacking nucleotidyltransferase activity, redefining its molecular identity away from a presumed enzyme.\",\n      \"evidence\": \"In vitro RNA-binding and nucleotidyltransferase assays with structural homology modeling, including disease variants\",\n      \"pmids\": [\"24906020\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No RNA target specificity or sequence motif identified\", \"Functional consequence of RNA binding for downstream signaling not established\", \"Single lab, abstract-level methodological detail\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"To place MAB21L2 in a signaling pathway, it was shown to antagonize BMP4 by binding SMAD1/SMAD1-SMAD4 and acting as a transcriptional repressor, connecting it to TGF-beta/BMP signal output.\",\n      \"evidence\": \"Xenopus overexpression rescue, in vivo Co-IP and in vitro binding with SMAD1/SMAD4, heterologous promoter repressor assay\",\n      \"pmids\": [\"15613244\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target genes repressed by MAB21L2 not defined\", \"Mechanism linking RNA binding to SMAD repression unknown\", \"Direct DNA binding not demonstrated\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Genetic epistasis in C. elegans placed mab-21 orthologs downstream of or parallel to TGF-beta pathway components, supporting a conserved role in signaling-dependent organ patterning.\",\n      \"evidence\": \"C. elegans double-mutant epistasis cited from prior literature\",\n      \"pmids\": [\"15613244\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Epistasis data cited, not directly performed in this corpus\", \"Molecular relationship to mammalian BMP signaling indirect\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Positioning MAB21L2 in the eye gene network, it was shown to act downstream of rx3 and to be required for survival of eye progenitors, defining it as an early effector of retinal field specification.\",\n      \"evidence\": \"Zebrafish morpholino knockdown, in situ hybridization in rx3 mutants, apoptosis assays\",\n      \"pmids\": [\"15183718\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Morpholino knockdown not confirmed by stable mutant in this study\", \"Direct transcriptional regulators downstream of MAB21L2 not defined\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"A mouse knockout established that MAB21L2 drives optic vesicle invagination through proliferation and lies upstream of Chx10, distinguishing it from Rx/Lhx2/Pax6 inputs.\",\n      \"evidence\": \"Mouse genetic knockout with histology and marker in situ hybridization\",\n      \"pmids\": [\"15385160\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking MAB21L2 to Chx10 regulation unknown\", \"Whether effect is cell-autonomous not resolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Extending MAB21L2 beyond the eye, knockout mice revealed requirements for proliferation in heart, proepicardium/septum transversum mesenchyme, and liver, defining a broad role in progenitor proliferation.\",\n      \"evidence\": \"Mouse genetic knockout with histology, gene expression, and integrin immunostaining\",\n      \"pmids\": [\"22412967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular pathway linking MAB21L2 to α4 integrin and proliferation not defined\", \"Direct versus indirect effects on each tissue unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Chick loss- and gain-of-function defined a stage-dependent requirement for MAB21L2 in regulating proliferation, cell-cycle exit, and differentiation across retinogenesis.\",\n      \"evidence\": \"In ovo RNAi and overexpression electroporation with proliferation/differentiation markers\",\n      \"pmids\": [\"30073347\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional targets among affected markers not established\", \"Mechanism of bidirectional dose sensitivity unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Zebrafish mutants dissected tissue-specific MAB21L2 roles, linking it to lens proliferation/survival, choroid fissure basement-membrane breakdown (coloboma), and corneal stromal differentiation.\",\n      \"evidence\": \"Zebrafish genetic mutant with proliferation/apoptosis assays and marker analysis\",\n      \"pmids\": [\"31037784\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular control of basement-membrane breakdown not defined\", \"Cell-autonomy of corneal phenotype unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Interactome screens identified physical partners including HSPA8/HSPA5, and double-mutant genetics linked hspa8 to MAB21L2 in eye development, providing a chaperone-associated molecular context.\",\n      \"evidence\": \"Yeast two-hybrid, Co-IP, mass spectrometry, and zebrafish double-mutant analysis\",\n      \"pmids\": [\"36576422\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of HSPA8/HSPA5 binding unknown\", \"Roles of klhl31/tnpo1/TNPO2/KLC2/SPTBN1 interactions not characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying how MAB21L2 eye expression is controlled, a distal Otx2-bound conserved element (CE14) was shown to be a functional regulatory element whose disruption causes ocular defects.\",\n      \"evidence\": \"Human deletion mapping, ChIP-seq for Otx2, CRISPR disruption of CE14 in Xenopus\",\n      \"pmids\": [\"39455595\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct Otx2 regulation of MAB21L2 in human cells not shown\", \"Roles of other conserved elements not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Conditional knockout extended MAB21L2 function to skeletal development, showing it promotes chondrocyte proliferation in limb stylopod formation, likely non-cell-autonomously.\",\n      \"evidence\": \"Prx1-Cre conditional knockout mouse with micro-CT and proliferation assays\",\n      \"pmids\": [\"40054064\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Non-cell-autonomous signal not identified\", \"Mechanism linking MAB21L2 to chondrocyte proliferation unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"MAB21L2 was implicated in cancer, with knockdown inhibiting neuroblastoma growth and migration, suggesting a pro-tumorigenic role.\",\n      \"evidence\": \"siRNA/shRNA knockdown, xenograft, RNA-seq, migration assay in neuroblastoma cells\",\n      \"pmids\": [\"41651436\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mechanistic pathway placement in cancer\", \"Single lab, limited validation\", \"Relationship to developmental BMP/proliferation roles unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MAB21L2's RNA-binding activity mechanistically connects to its SMAD-repressing, proliferation-promoting functions across diverse tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No RNA target identified that links biochemistry to transcriptional/proliferative output\", \"No structural model of partner or RNA engagement in cells\", \"Unified mechanism across eye, heart, liver, limb, and cancer not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [4, 5, 6, 7, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SMAD1\", \"SMAD4\", \"HSPA8\", \"HSPA5\", \"TNPO2\", \"KLC2\", \"SPTBN1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}