{"gene":"MOSMO","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":2017,"finding":"MOSMO (named 'Atthog' in this paper, an unannotated tetraspan protein) was identified as a negative regulator of Hedgehog signaling; in its absence, Smoothened (SMO) was stabilized at the cell surface and concentrated in the ciliary membrane, boosting cell sensitivity to Sonic Hedgehog (SHH) and altering SHH-guided neural cell-fate decisions.","method":"Genome-wide CRISPR screen followed by multiple signaling and differentiation assays in two cell types; loss-of-function phenotypic readout of SMO localization and SHH-guided neural differentiation","journal":"Developmental Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide CRISPR screen validated with multiple orthogonal assays in two cell types, replicated by subsequent independent studies","pmids":["29290584"],"is_preprint":false},{"year":2021,"finding":"MOSMO is a component of the MMM (MEGF8-MOSMO-MGRN1) membrane protein complex that promotes degradation of the Hedgehog transducer SMO; loss of MOSMO results in elevated SMO levels and increased Hedgehog signaling, causing multiple birth defects in mouse embryos. In utero exposure to a SMO-inhibiting teratogen rescued these defects, demonstrating quantitative modulation of signaling strength through SMO abundance.","method":"Mosmo-/- mouse knockout with in vivo birth defect phenotyping; pharmacological rescue with SMO inhibitor teratogen in utero; genetic and biochemical dissection of the MMM complex","journal":"Development (Cambridge, England)","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout mouse with defined molecular mechanism (SMO abundance), pharmacological epistasis rescue, and placement within the MMM complex","pmids":["34486668"],"is_preprint":false},{"year":2021,"finding":"In zebrafish, MOSMO (Mosmoa) localizes at the plasma membrane, cytoplasmic vesicles, and the primary cilium. CRISPR/Cas9 inactivation of both zebrafish paralogs (mosmoa and mosmob) causes frontonasal hypoplasia and craniofacial skeleton defects, consistent with its role in promoting SMO internalization and degradation to down-modulate Hedgehog pathway activation.","method":"CRISPR/Cas9 knockout of both zebrafish mosmo paralogs; subcellular localization by fluorescence imaging in zebrafish and chick embryos; craniofacial phenotyping in adult fish","journal":"Frontiers in Cell and Developmental Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional consequence, clean CRISPR KO with defined phenotype, single lab","pmids":["34746155"],"is_preprint":false},{"year":2026,"finding":"Cryo-electron microscopy of the human MEGF8-MOSMO-MGRN1 (MMM) complex revealed that MOSMO and MEGF8 are the two transmembrane components, with a long helix engaging SMO via an intramembrane degron and extending into the cytoplasm to position the MGRN1 RING domain for ubiquitylation of the cytoplasmic surface of SMO, thereby reducing SMO abundance at primary cilia and attenuating Hedgehog signaling.","method":"Cryo-electron microscopy (structure determination) integrated with biophysical and functional studies; structure-function analysis of SMO ubiquitylation by the MMM complex","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure of the human complex integrated with biophysical and functional assays, defining the molecular mechanism of SMO ubiquitylation","pmids":["42190653"],"is_preprint":false},{"year":2021,"finding":"In Drosophila and Xenopus laevis models, homologs of MOSMO (a 16p12.1 gene) interact genetically with homologs of SETD5 (a 'second-hit' gene), synergistically producing modified cellular and brain phenotypes, as well as axon outgrowth defects not observed with knockdown of either gene alone.","method":"Pairwise RNAi knockdown epistasis in Drosophila and X. laevis; phenotypic readouts including brain morphology, cellular proliferation, and axon outgrowth","journal":"PLoS Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis across two model organisms, multiple phenotypic readouts, single lab","pmids":["33819264"],"is_preprint":false},{"year":2022,"finding":"In Xenopus laevis, mosmo knockdown significantly disrupts craniofacial and cartilage formation, pharyngeal arch migration, and neural crest cell specification and motility, indicating a role for MOSMO in vertebrate craniofacial patterning through regulation of neural crest cell development.","method":"Morpholino-mediated knockdown in X. laevis; phenotypic readouts of craniofacial structure, pharyngeal arch migration, and neural crest cell specification and motility","journal":"Frontiers in Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — loss-of-function with defined cellular phenotype (NCC migration/specification), single lab, single organism","pmids":["35401697"],"is_preprint":false}],"current_model":"MOSMO is a transmembrane tetraspan protein that forms the MEGF8-MOSMO-MGRN1 (MMM) E3 ubiquitin ligase complex; cryo-EM structures show that MOSMO and MEGF8 anchor the complex in the membrane, where a long helix engages the GPCR Smoothened (SMO) via an intramembrane degron and positions the MGRN1 RING domain to ubiquitylate SMO's cytoplasmic surface, driving SMO removal from primary cilia and attenuating Hedgehog signaling; loss of MOSMO stabilizes SMO at the cell surface and cilia, hyperactivating Hedgehog signaling and causing craniofacial and multi-organ birth defects in vertebrate models."},"narrative":{"mechanistic_narrative":"MOSMO is a transmembrane tetraspan protein that functions as a negative regulator of Hedgehog signaling by promoting the removal of the GPCR Smoothened (SMO) from the cell surface and primary cilium [PMID:29290584]. It is a core subunit of the MEGF8-MOSMO-MGRN1 (MMM) membrane E3 ubiquitin ligase complex, in which MOSMO and MEGF8 serve as the transmembrane components; a long helix engages SMO through an intramembrane degron and extends into the cytoplasm to position the MGRN1 RING domain for ubiquitylation of SMO's cytoplasmic surface, driving SMO degradation and attenuating pathway output [PMID:34486668, PMID:42190653]. Loss of MOSMO stabilizes SMO at the plasma membrane and ciliary membrane, hyperactivating Hedgehog signaling and quantitatively raising cellular sensitivity to Sonic Hedgehog, an effect reversible by pharmacological SMO inhibition [PMID:29290584, PMID:34486668]. Through this control of signaling strength, MOSMO localizes to the plasma membrane, cytoplasmic vesicles, and primary cilium [PMID:34746155] and is required for vertebrate craniofacial patterning, neural crest cell specification and migration, and prevention of multi-organ birth defects [PMID:34486668, PMID:34746155, PMID:35401697].","teleology":[{"year":2017,"claim":"Established MOSMO as a previously unannotated negative regulator of Hedgehog signaling, answering whether an unknown tetraspan protein controls SMO localization and SHH responsiveness.","evidence":"Genome-wide CRISPR screen with SMO localization and SHH-guided neural differentiation readouts in two cell types","pmids":["29290584"],"confidence":"High","gaps":["Did not define the molecular mechanism of SMO removal","No binding partners or complex membership identified","Did not establish in vivo developmental consequences"]},{"year":2021,"claim":"Placed MOSMO within the MEGF8-MOSMO-MGRN1 complex and showed that SMO abundance is the quantitative effector linking MOSMO loss to developmental defects.","evidence":"Mosmo-/- mouse knockout with birth-defect phenotyping and pharmacological SMO-inhibitor rescue in utero, plus biochemical dissection of the MMM complex","pmids":["34486668"],"confidence":"High","gaps":["Did not resolve the structural basis of SMO recognition by the complex","Stoichiometry and assembly of MMM left undefined","Direct ubiquitylation mechanism not yet visualized"]},{"year":2021,"claim":"Defined the subcellular distribution of MOSMO and confirmed its role in craniofacial development across a second vertebrate model.","evidence":"CRISPR/Cas9 knockout of both zebrafish paralogs with fluorescence localization in zebrafish and chick embryos and craniofacial phenotyping","pmids":["34746155"],"confidence":"Medium","gaps":["Localization based on imaging in single lab without complex co-localization","Did not biochemically link localization to SMO degradation"]},{"year":2021,"claim":"Tested whether MOSMO acts within a genetic interaction network, revealing synergistic phenotypes with SETD5 relevant to neurodevelopmental defects.","evidence":"Pairwise RNAi knockdown epistasis in Drosophila and X. laevis with brain morphology and axon outgrowth readouts","pmids":["33819264"],"confidence":"Medium","gaps":["Genetic interaction not connected to a molecular mechanism","Relationship to Hedgehog/SMO pathway not established","Relies on knockdown rather than null alleles"]},{"year":2022,"claim":"Resolved the cellular basis of MOSMO craniofacial requirement by linking it to neural crest cell specification and migration.","evidence":"Morpholino knockdown in X. laevis with readouts of craniofacial structure, pharyngeal arch migration, and neural crest specification/motility","pmids":["35401697"],"confidence":"Medium","gaps":["Single-organism, single-lab morpholino study without rescue","Mechanistic link from SMO regulation to neural crest behavior not directly tested"]},{"year":2026,"claim":"Defined the molecular mechanism of SMO ubiquitylation, answering how MOSMO and MEGF8 anchor the complex and orient MGRN1 toward SMO.","evidence":"Cryo-EM structure of the human MEGF8-MOSMO-MGRN1 complex integrated with biophysical and functional ubiquitylation assays","pmids":["42190653"],"confidence":"High","gaps":["Dynamics of SMO capture and release in cilia not visualized","Regulation of MMM assembly/activity in vivo unresolved","Substrate range beyond SMO not addressed"]},{"year":null,"claim":"How MMM complex activity is regulated spatially and temporally during development, and whether MOSMO has substrates or roles beyond SMO, remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No regulatory inputs controlling MMM activity identified","No substrates other than SMO characterized","Connection between neural crest phenotypes and SMO regulation not mechanistically closed"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,3]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[0,2]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,2,5]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,3]}],"complexes":["MEGF8-MOSMO-MGRN1 (MMM) complex"],"partners":["MEGF8","MGRN1","SMO"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NHV5","full_name":"Modulator of smoothened protein","aliases":["Attenuator of hedgehog"],"length_aa":167,"mass_kda":18.2,"function":"Acts as a negative regulator of hedgehog signaling probably by promoting internalization and subsequent degradation of smoothened protein (SMO) present in the ciliary membrane. Plays a role in sonic hedgehog (SHH)-induced spinal neural progenitor cells differentiation","subcellular_location":"Cell projection, cilium membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q8NHV5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MOSMO","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MOSMO","total_profiled":1310},"omim":[],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MOSMO"},"hgnc":{"alias_symbol":["ATTHOG","BC030336"],"prev_symbol":["C16orf52"]},"alphafold":{"accession":"Q8NHV5","domains":[{"cath_id":"1.20.140.150","chopping":"2-158","consensus_level":"high","plddt":90.3338,"start":2,"end":158}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NHV5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NHV5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NHV5-F1-predicted_aligned_error_v6.png","plddt_mean":88.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MOSMO","jax_strain_url":"https://www.jax.org/strain/search?query=MOSMO"},"sequence":{"accession":"Q8NHV5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NHV5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NHV5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NHV5"}},"corpus_meta":[{"pmid":"29290584","id":"PMC_29290584","title":"CRISPR Screens Uncover Genes that Regulate Target Cell Sensitivity to the Morphogen Sonic Hedgehog.","date":"2017","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/29290584","citation_count":84,"is_preprint":false},{"pmid":"6276018","id":"PMC_6276018","title":"Analysis of transforming gene products from Moloney murine sarcoma virus.","date":"1981","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/6276018","citation_count":60,"is_preprint":false},{"pmid":"33819264","id":"PMC_33819264","title":"Functional assessment of the \"two-hit\" model for neurodevelopmental defects in Drosophila and X. laevis.","date":"2021","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33819264","citation_count":18,"is_preprint":false},{"pmid":"35817504","id":"PMC_35817504","title":"Receptor control by membrane-tethered ubiquitin ligases in development and tissue homeostasis.","date":"2022","source":"Current topics in developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/35817504","citation_count":13,"is_preprint":false},{"pmid":"34486668","id":"PMC_34486668","title":"Gene-teratogen interactions influence the penetrance of birth defects by altering Hedgehog signaling strength.","date":"2021","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/34486668","citation_count":12,"is_preprint":false},{"pmid":"7175503","id":"PMC_7175503","title":"Characterization of a large genomic size Moloney murine sarcoma virus produced by a transformed rat cell line.","date":"1982","source":"The Journal of general virology","url":"https://pubmed.ncbi.nlm.nih.gov/7175503","citation_count":9,"is_preprint":false},{"pmid":"34746155","id":"PMC_34746155","title":"Mosmo Is Required for Zebrafish Craniofacial Formation.","date":"2021","source":"Frontiers in cell and developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/34746155","citation_count":5,"is_preprint":false},{"pmid":"6180181","id":"PMC_6180181","title":"Identification of proteins encoded by the Gazdar murine sarcoma virus genome by in vitro translation and comparison with Moloney murine sarcoma virus 124.","date":"1982","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/6180181","citation_count":4,"is_preprint":false},{"pmid":"41000701","id":"PMC_41000701","title":"\"Design principles of a membrane-spanning ubiquitin ligase\".","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/41000701","citation_count":2,"is_preprint":false},{"pmid":"35401697","id":"PMC_35401697","title":"16p12.1 Deletion Orthologs are Expressed in Motile Neural Crest Cells and are Important for Regulating Craniofacial Development in Xenopus laevis.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35401697","citation_count":2,"is_preprint":false},{"pmid":"42190653","id":"PMC_42190653","title":"Design principles of a membrane-spanning ubiquitin ligase.","date":"2026","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/42190653","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.09.11.675358","title":"“Design principles of a membrane-spanning ubiquitin ligase”","date":"2025-09-16","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.11.675358","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7316,"output_tokens":1742,"usd":0.024039,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8590,"output_tokens":2495,"usd":0.052663,"stage2_stop_reason":"end_turn"},"total_usd":0.076702,"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\": 2017,\n      \"finding\": \"MOSMO (named 'Atthog' in this paper, an unannotated tetraspan protein) was identified as a negative regulator of Hedgehog signaling; in its absence, Smoothened (SMO) was stabilized at the cell surface and concentrated in the ciliary membrane, boosting cell sensitivity to Sonic Hedgehog (SHH) and altering SHH-guided neural cell-fate decisions.\",\n      \"method\": \"Genome-wide CRISPR screen followed by multiple signaling and differentiation assays in two cell types; loss-of-function phenotypic readout of SMO localization and SHH-guided neural differentiation\",\n      \"journal\": \"Developmental Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide CRISPR screen validated with multiple orthogonal assays in two cell types, replicated by subsequent independent studies\",\n      \"pmids\": [\"29290584\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MOSMO is a component of the MMM (MEGF8-MOSMO-MGRN1) membrane protein complex that promotes degradation of the Hedgehog transducer SMO; loss of MOSMO results in elevated SMO levels and increased Hedgehog signaling, causing multiple birth defects in mouse embryos. In utero exposure to a SMO-inhibiting teratogen rescued these defects, demonstrating quantitative modulation of signaling strength through SMO abundance.\",\n      \"method\": \"Mosmo-/- mouse knockout with in vivo birth defect phenotyping; pharmacological rescue with SMO inhibitor teratogen in utero; genetic and biochemical dissection of the MMM complex\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout mouse with defined molecular mechanism (SMO abundance), pharmacological epistasis rescue, and placement within the MMM complex\",\n      \"pmids\": [\"34486668\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In zebrafish, MOSMO (Mosmoa) localizes at the plasma membrane, cytoplasmic vesicles, and the primary cilium. CRISPR/Cas9 inactivation of both zebrafish paralogs (mosmoa and mosmob) causes frontonasal hypoplasia and craniofacial skeleton defects, consistent with its role in promoting SMO internalization and degradation to down-modulate Hedgehog pathway activation.\",\n      \"method\": \"CRISPR/Cas9 knockout of both zebrafish mosmo paralogs; subcellular localization by fluorescence imaging in zebrafish and chick embryos; craniofacial phenotyping in adult fish\",\n      \"journal\": \"Frontiers in Cell and Developmental Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional consequence, clean CRISPR KO with defined phenotype, single lab\",\n      \"pmids\": [\"34746155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Cryo-electron microscopy of the human MEGF8-MOSMO-MGRN1 (MMM) complex revealed that MOSMO and MEGF8 are the two transmembrane components, with a long helix engaging SMO via an intramembrane degron and extending into the cytoplasm to position the MGRN1 RING domain for ubiquitylation of the cytoplasmic surface of SMO, thereby reducing SMO abundance at primary cilia and attenuating Hedgehog signaling.\",\n      \"method\": \"Cryo-electron microscopy (structure determination) integrated with biophysical and functional studies; structure-function analysis of SMO ubiquitylation by the MMM complex\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure of the human complex integrated with biophysical and functional assays, defining the molecular mechanism of SMO ubiquitylation\",\n      \"pmids\": [\"42190653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In Drosophila and Xenopus laevis models, homologs of MOSMO (a 16p12.1 gene) interact genetically with homologs of SETD5 (a 'second-hit' gene), synergistically producing modified cellular and brain phenotypes, as well as axon outgrowth defects not observed with knockdown of either gene alone.\",\n      \"method\": \"Pairwise RNAi knockdown epistasis in Drosophila and X. laevis; phenotypic readouts including brain morphology, cellular proliferation, and axon outgrowth\",\n      \"journal\": \"PLoS Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis across two model organisms, multiple phenotypic readouts, single lab\",\n      \"pmids\": [\"33819264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Xenopus laevis, mosmo knockdown significantly disrupts craniofacial and cartilage formation, pharyngeal arch migration, and neural crest cell specification and motility, indicating a role for MOSMO in vertebrate craniofacial patterning through regulation of neural crest cell development.\",\n      \"method\": \"Morpholino-mediated knockdown in X. laevis; phenotypic readouts of craniofacial structure, pharyngeal arch migration, and neural crest cell specification and motility\",\n      \"journal\": \"Frontiers in Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — loss-of-function with defined cellular phenotype (NCC migration/specification), single lab, single organism\",\n      \"pmids\": [\"35401697\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MOSMO is a transmembrane tetraspan protein that forms the MEGF8-MOSMO-MGRN1 (MMM) E3 ubiquitin ligase complex; cryo-EM structures show that MOSMO and MEGF8 anchor the complex in the membrane, where a long helix engages the GPCR Smoothened (SMO) via an intramembrane degron and positions the MGRN1 RING domain to ubiquitylate SMO's cytoplasmic surface, driving SMO removal from primary cilia and attenuating Hedgehog signaling; loss of MOSMO stabilizes SMO at the cell surface and cilia, hyperactivating Hedgehog signaling and causing craniofacial and multi-organ birth defects in vertebrate models.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MOSMO is a transmembrane tetraspan protein that functions as a negative regulator of Hedgehog signaling by promoting the removal of the GPCR Smoothened (SMO) from the cell surface and primary cilium [#0]. It is a core subunit of the MEGF8-MOSMO-MGRN1 (MMM) membrane E3 ubiquitin ligase complex, in which MOSMO and MEGF8 serve as the transmembrane components; a long helix engages SMO through an intramembrane degron and extends into the cytoplasm to position the MGRN1 RING domain for ubiquitylation of SMO's cytoplasmic surface, driving SMO degradation and attenuating pathway output [#1, #3]. Loss of MOSMO stabilizes SMO at the plasma membrane and ciliary membrane, hyperactivating Hedgehog signaling and quantitatively raising cellular sensitivity to Sonic Hedgehog, an effect reversible by pharmacological SMO inhibition [#0, #1]. Through this control of signaling strength, MOSMO localizes to the plasma membrane, cytoplasmic vesicles, and primary cilium [#2] and is required for vertebrate craniofacial patterning, neural crest cell specification and migration, and prevention of multi-organ birth defects [#1, #2, #5].\",\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Established MOSMO as a previously unannotated negative regulator of Hedgehog signaling, answering whether an unknown tetraspan protein controls SMO localization and SHH responsiveness.\",\n      \"evidence\": \"Genome-wide CRISPR screen with SMO localization and SHH-guided neural differentiation readouts in two cell types\",\n      \"pmids\": [\"29290584\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not define the molecular mechanism of SMO removal\",\n        \"No binding partners or complex membership identified\",\n        \"Did not establish in vivo developmental consequences\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placed MOSMO within the MEGF8-MOSMO-MGRN1 complex and showed that SMO abundance is the quantitative effector linking MOSMO loss to developmental defects.\",\n      \"evidence\": \"Mosmo-/- mouse knockout with birth-defect phenotyping and pharmacological SMO-inhibitor rescue in utero, plus biochemical dissection of the MMM complex\",\n      \"pmids\": [\"34486668\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not resolve the structural basis of SMO recognition by the complex\",\n        \"Stoichiometry and assembly of MMM left undefined\",\n        \"Direct ubiquitylation mechanism not yet visualized\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the subcellular distribution of MOSMO and confirmed its role in craniofacial development across a second vertebrate model.\",\n      \"evidence\": \"CRISPR/Cas9 knockout of both zebrafish paralogs with fluorescence localization in zebrafish and chick embryos and craniofacial phenotyping\",\n      \"pmids\": [\"34746155\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Localization based on imaging in single lab without complex co-localization\",\n        \"Did not biochemically link localization to SMO degradation\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Tested whether MOSMO acts within a genetic interaction network, revealing synergistic phenotypes with SETD5 relevant to neurodevelopmental defects.\",\n      \"evidence\": \"Pairwise RNAi knockdown epistasis in Drosophila and X. laevis with brain morphology and axon outgrowth readouts\",\n      \"pmids\": [\"33819264\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Genetic interaction not connected to a molecular mechanism\",\n        \"Relationship to Hedgehog/SMO pathway not established\",\n        \"Relies on knockdown rather than null alleles\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the cellular basis of MOSMO craniofacial requirement by linking it to neural crest cell specification and migration.\",\n      \"evidence\": \"Morpholino knockdown in X. laevis with readouts of craniofacial structure, pharyngeal arch migration, and neural crest specification/motility\",\n      \"pmids\": [\"35401697\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Single-organism, single-lab morpholino study without rescue\",\n        \"Mechanistic link from SMO regulation to neural crest behavior not directly tested\"\n      ]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined the molecular mechanism of SMO ubiquitylation, answering how MOSMO and MEGF8 anchor the complex and orient MGRN1 toward SMO.\",\n      \"evidence\": \"Cryo-EM structure of the human MEGF8-MOSMO-MGRN1 complex integrated with biophysical and functional ubiquitylation assays\",\n      \"pmids\": [\"42190653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Dynamics of SMO capture and release in cilia not visualized\",\n        \"Regulation of MMM assembly/activity in vivo unresolved\",\n        \"Substrate range beyond SMO not addressed\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How MMM complex activity is regulated spatially and temporally during development, and whether MOSMO has substrates or roles beyond SMO, remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No regulatory inputs controlling MMM activity identified\",\n        \"No substrates other than SMO characterized\",\n        \"Connection between neural crest phenotypes and SMO regulation not mechanistically closed\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0162582\", \"supporting_discovery_ids\": []},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 2, 5]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"complexes\": [\n      \"MEGF8-MOSMO-MGRN1 (MMM) complex\"\n    ],\n    \"partners\": [\n      \"MEGF8\",\n      \"MGRN1\",\n      \"SMO\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}