{"gene":"CBLN3","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":2000,"finding":"CBLN3 was identified as a novel Cbln1-binding protein via yeast two-hybrid screen. CBLN3 binds avidly to CBLN1 to form heteromeric complexes, while CBLN3 homomeric association is weak. This interaction is specific, as C1qB binds to neither CBLN1 nor CBLN3. CBLN3 contains a C1q signature domain and signal sequence for secretion.","method":"Yeast two-hybrid screen, in vitro binding assays","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 1-2 — original discovery with direct binding assays and specificity controls, replicated by subsequent studies","pmids":["10964938"],"is_preprint":false},{"year":2006,"finding":"CBLN3 cannot form homomeric complexes and is retained in the endoplasmic reticulum unless bound to CBLN1. A single arginine residue in CBLN3 creates a steric clash that causes ER retention, which is masked upon CBLN1 binding — a 'hide-and-run' mechanism. CBLN1 is essential for CBLN3 secretion; in cbln1-null mice, CBLN3 is absent (degraded), while in cbln3-null mice, CBLN1 levels increase ~sixfold. Double-null mice phenocopy cbln1 single knockouts.","method":"cbln1-null and cbln3-null mouse analysis, mutation analysis, structural modeling, secretion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods including KO mice, mutagenesis, and structural modeling with clear mechanistic resolution","pmids":["17030622"],"is_preprint":false},{"year":2007,"finding":"CBLN3 is not secreted when expressed alone but is retained in the endoplasmic reticulum or cis-Golgi due to its N-terminal domain. When co-expressed with CBLN1 in heterologous cells, a proportion of CBLN3 is secreted together with CBLN1. In cbln1-null granule cells, CBLN3 is almost completely degraded, confirming CBLN1 dependence for CBLN3 trafficking.","method":"Heterologous cell expression, co-expression experiments, analysis of cbln1-null granule cells, immunofluorescence","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 — independent replication of CBLN1-dependent CBLN3 secretion with multiple orthogonal approaches","pmids":["17331201"],"is_preprint":false},{"year":2006,"finding":"Cbln3 mRNA expression is selective to cerebellar granule cells throughout development, with onset as late as postnatal day 7-10, distinguishing it from other Cbln family members.","method":"RT-PCR, Northern blot, in situ hybridization","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods but limited to expression/localization without direct functional manipulation","pmids":["16930405"],"is_preprint":false},{"year":2009,"finding":"CBLN1 and CBLN3 co-accumulate at parallel fiber-Purkinje cell synaptic clefts, where they colocalize with GluRdelta2, providing anatomical evidence that all three molecules operate together in a common signaling pathway regulating cerebellar circuit development and synaptic plasticity.","method":"Light and electron microscopic immunohistochemistry with pepsin pretreatment and postembedding immunogold","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization with antigen-exposing methods showing synaptic cleft co-accumulation, but no functional manipulation of CBLN3 specifically","pmids":["19250438"],"is_preprint":false},{"year":2007,"finding":"In cbln3-null mice, Cbln1 immunoreactivity in the cerebellum increases dramatically, but is unchanged in extracerebellar neurons, indicating CBLN3 regulates CBLN1 levels via the endolysosomal degradation pathway specifically in cerebellar granule cells. Cbln1 localizes to the endolysosomal compartment of neurons.","method":"Immunohistochemistry of cbln3-null mice, colocalization with cathepsin D (lysosomal marker), cbln1-lacZ transgenic mice","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — direct subcellular localization combined with genetic KO showing regulatory relationship","pmids":["18001291"],"is_preprint":false},{"year":2017,"finding":"Unlike CBLN1, CBLN2, and CBLN4 which autonomously assemble into homohexamers, CBLN3 requires CBLN1 for assembly and secretion, forming heteromeric complexes. This was confirmed in reporter knockin mice and cell expression studies.","method":"Knockin reporter mice, expression studies in heterologous cells","journal":"The Journal of comparative neurology","confidence":"Medium","confidence_rationale":"Tier 2 — independent confirmation of CBLN1-dependent CBLN3 assembly with in vivo reporter models","pmids":["28714144"],"is_preprint":false}],"current_model":"CBLN3 is a secreted C1q-family glycoprotein that cannot form homomers or be secreted independently due to an ER-retention mechanism mediated by a single arginine residue in its N-terminal domain; it requires CBLN1 binding (via a 'hide-and-run' mechanism) for ER export, heteromeric complex assembly, and secretion, after which the CBLN1-CBLN3 complex accumulates in the synaptic cleft of parallel fiber-Purkinje cell synapses alongside GluRdelta2, where it participates in regulating cerebellar synapse integrity and plasticity."},"narrative":{"teleology":[{"year":2000,"claim":"Identification of CBLN3 as a CBLN1-binding partner established the existence of a heteromeric cerebellin complex, resolving the question of whether cerebellin family members interact directly.","evidence":"Yeast two-hybrid screen with specificity controls and in vitro binding assays","pmids":["10964938"],"confidence":"High","gaps":["Whether CBLN3 is secreted or has independent function outside the CBLN1 complex was unknown","No in vivo localization or functional evidence"]},{"year":2006,"claim":"Demonstration that CBLN3 is ER-retained unless bound to CBLN1 — via a steric clash from a single arginine — defined a 'hide-and-run' secretion mechanism and showed that CBLN3 loss elevates CBLN1 levels sixfold, revealing a reciprocal regulatory relationship.","evidence":"cbln1-null and cbln3-null mouse phenotyping, site-directed mutagenesis, structural modeling, and secretion assays in heterologous cells","pmids":["17030622"],"confidence":"High","gaps":["The stoichiometry of the CBLN1–CBLN3 complex was not resolved","Whether the sixfold CBLN1 increase in cbln3-null mice has functional consequences at the synapse was untested"]},{"year":2006,"claim":"Mapping Cbln3 mRNA expression exclusively to postnatal cerebellar granule cells defined its spatiotemporal expression domain, separating it from other family members.","evidence":"RT-PCR, Northern blot, and in situ hybridization across developmental stages","pmids":["16930405"],"confidence":"Medium","gaps":["Protein-level expression was not directly assessed","No functional manipulation to test whether the late postnatal onset is functionally significant"]},{"year":2007,"claim":"Independent replication confirmed CBLN3 ER/cis-Golgi retention and CBLN1-dependent secretion, and showed that CBLN3 is nearly completely degraded in cbln1-null granule cells, solidifying the obligate dependence model.","evidence":"Co-expression in heterologous cells, immunofluorescence, and cbln1-null granule cell analysis","pmids":["17331201"],"confidence":"High","gaps":["The degradation pathway for CBLN3 in the absence of CBLN1 was not defined","Whether CBLN3 modifies CBLN1 signaling properties or merely alters its levels was unresolved"]},{"year":2007,"claim":"Showing that CBLN3 loss increases CBLN1 specifically in cerebellum via diversion from endolysosomal degradation revealed a cell-type-specific regulatory mechanism controlling CBLN1 abundance.","evidence":"Immunohistochemistry in cbln3-null mice with lysosomal marker colocalization","pmids":["18001291"],"confidence":"Medium","gaps":["Direct biochemical demonstration of CBLN1 endolysosomal routing by CBLN3 was not provided","Whether the increased CBLN1 in cbln3-null cerebellum alters synaptic function was not tested"]},{"year":2009,"claim":"Ultrastructural co-localization of CBLN1, CBLN3, and GluRδ2 at parallel fiber–Purkinje cell synaptic clefts placed the heteromeric complex at its site of action, linking it to trans-synaptic signaling.","evidence":"Pre-embedding immunohistochemistry with pepsin antigen retrieval and postembedding immunogold electron microscopy","pmids":["19250438"],"confidence":"Medium","gaps":["No direct functional evidence that CBLN3 modulates GluRδ2 signaling at the synapse","Whether CBLN3 contacts GluRδ2 directly or only through CBLN1 was unknown"]},{"year":2017,"claim":"Reporter knockin mice confirmed that CBLN3 uniquely among the family requires CBLN1 for assembly into secreted hexameric complexes, reinforcing its obligate heteromeric nature.","evidence":"Knockin reporter mice and heterologous cell expression studies","pmids":["28714144"],"confidence":"Medium","gaps":["Exact stoichiometry (e.g., trimer-of-dimers composition) of CBLN1–CBLN3 heterohexamers was not determined","Functional distinction between CBLN1 homohexamers and CBLN1–CBLN3 heterohexamers at the synapse remains unknown"]},{"year":null,"claim":"It remains unknown whether CBLN3 incorporation into CBLN1 complexes changes the binding affinity or signaling output at GluRδ2-containing synapses, and whether CBLN3 loss produces distinct behavioral or synaptic phenotypes beyond those explained by altered CBLN1 levels.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of the CBLN1–CBLN3 heteromeric complex","No direct electrophysiological or behavioral analysis specifically attributable to CBLN3 function","Whether CBLN3 interacts with neurexins or other synaptic organizers independent of CBLN1 is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1,2,4]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[3,4]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,2,6]}],"complexes":["CBLN1-CBLN3 heterohexamer"],"partners":["CBLN1","GRID2"],"other_free_text":[]},"mechanistic_narrative":"CBLN3 is a secreted C1q-domain glycoprotein expressed selectively in cerebellar granule cells that functions exclusively as a heteromeric partner of CBLN1 to regulate cerebellar synapse integrity [PMID:10964938, PMID:16930405]. Unlike other cerebellin family members, CBLN3 cannot form homomers or be secreted independently; a single arginine residue in its N-terminal domain causes ER retention, which is relieved upon CBLN1 binding through a 'hide-and-run' mechanism, making CBLN1 obligatory for CBLN3 trafficking and secretion [PMID:17030622, PMID:17331201]. In the absence of CBLN3, CBLN1 levels increase approximately sixfold in the cerebellum due to escape from endolysosomal degradation, indicating that CBLN3 quantitatively regulates CBLN1 availability [PMID:17030622, PMID:18001291]. The CBLN1–CBLN3 heteromeric complex accumulates in the synaptic cleft of parallel fiber–Purkinje cell synapses where it colocalizes with GluRδ2, positioning it as a trans-synaptic signaling component in cerebellar circuit development and plasticity [PMID:19250438]."},"prefetch_data":{"uniprot":{"accession":"Q6UW01","full_name":"Cerebellin-3","aliases":[],"length_aa":205,"mass_kda":21.5,"function":"May be involved in synaptic functions in the CNS","subcellular_location":"Endoplasmic reticulum; Golgi apparatus, cis-Golgi network; Secreted; Synapse","url":"https://www.uniprot.org/uniprotkb/Q6UW01/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CBLN3","classification":"Not Classified","n_dependent_lines":16,"n_total_lines":1208,"dependency_fraction":0.013245033112582781},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CBLN3","total_profiled":1310},"omim":[{"mim_id":"615029","title":"PRECEREBELLIN 4; CBLN4","url":"https://www.omim.org/entry/615029"},{"mim_id":"612978","title":"PRECEREBELLIN 3; CBLN3","url":"https://www.omim.org/entry/612978"},{"mim_id":"600433","title":"PRECEREBELLIN 2; CBLN2","url":"https://www.omim.org/entry/600433"},{"mim_id":"600432","title":"PRECEREBELLIN 1; CBLN1","url":"https://www.omim.org/entry/600432"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Tissue enriched","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":365.9}],"url":"https://www.proteinatlas.org/search/CBLN3"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q6UW01","domains":[{"cath_id":"2.60.120.40","chopping":"72-203","consensus_level":"high","plddt":89.0114,"start":72,"end":203}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UW01","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UW01-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6UW01-F1-predicted_aligned_error_v6.png","plddt_mean":76.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CBLN3","jax_strain_url":"https://www.jax.org/strain/search?query=CBLN3"},"sequence":{"accession":"Q6UW01","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6UW01.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6UW01/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6UW01"}},"corpus_meta":[{"pmid":"16930405","id":"PMC_16930405","title":"Distinct expression of Cbln family mRNAs in developing and adult mouse brains.","date":"2006","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/16930405","citation_count":92,"is_preprint":false},{"pmid":"10964938","id":"PMC_10964938","title":"Cbln3, a novel member of the precerebellin family that binds specifically to Cbln1.","date":"2000","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/10964938","citation_count":68,"is_preprint":false},{"pmid":"28714144","id":"PMC_28714144","title":"Cerebellins are differentially expressed in selective subsets of neurons throughout the brain.","date":"2017","source":"The Journal of comparative neurology","url":"https://pubmed.ncbi.nlm.nih.gov/28714144","citation_count":53,"is_preprint":false},{"pmid":"17030622","id":"PMC_17030622","title":"Cbln1 is essential for interaction-dependent secretion of Cbln3.","date":"2006","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17030622","citation_count":49,"is_preprint":false},{"pmid":"17331201","id":"PMC_17331201","title":"Characterization of a transneuronal cytokine family Cbln--regulation of secretion by heteromeric assembly.","date":"2007","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/17331201","citation_count":47,"is_preprint":false},{"pmid":"19250438","id":"PMC_19250438","title":"Cbln1 accumulates and colocalizes with Cbln3 and GluRdelta2 at parallel fiber-Purkinje cell synapses in the mouse cerebellum.","date":"2009","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/19250438","citation_count":31,"is_preprint":false},{"pmid":"18001291","id":"PMC_18001291","title":"Mapping of Cbln1-like immunoreactivity in adult and developing mouse brain and its localization to the endolysosomal compartment of neurons.","date":"2007","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/18001291","citation_count":31,"is_preprint":false},{"pmid":"18813864","id":"PMC_18813864","title":"Expression of precerebellins in cultured rat calvaria osteoblast-like cells.","date":"2008","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/18813864","citation_count":16,"is_preprint":false},{"pmid":"19082514","id":"PMC_19082514","title":"Precerebellin-related genes and precerebellin 1 peptide in endocrine glands of the rat - pattern of their expression.","date":"2009","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/19082514","citation_count":14,"is_preprint":false},{"pmid":"19481574","id":"PMC_19481574","title":"Insulinostatic activity of cerebellin--evidence from in vivo and in vitro studies in rats.","date":"2009","source":"Regulatory 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CBLN3 binds avidly to CBLN1 to form heteromeric complexes, while CBLN3 homomeric association is weak. This interaction is specific, as C1qB binds to neither CBLN1 nor CBLN3. CBLN3 contains a C1q signature domain and signal sequence for secretion.\",\n      \"method\": \"Yeast two-hybrid screen, in vitro binding assays\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — original discovery with direct binding assays and specificity controls, replicated by subsequent studies\",\n      \"pmids\": [\"10964938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CBLN3 cannot form homomeric complexes and is retained in the endoplasmic reticulum unless bound to CBLN1. A single arginine residue in CBLN3 creates a steric clash that causes ER retention, which is masked upon CBLN1 binding — a 'hide-and-run' mechanism. CBLN1 is essential for CBLN3 secretion; in cbln1-null mice, CBLN3 is absent (degraded), while in cbln3-null mice, CBLN1 levels increase ~sixfold. Double-null mice phenocopy cbln1 single knockouts.\",\n      \"method\": \"cbln1-null and cbln3-null mouse analysis, mutation analysis, structural modeling, secretion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods including KO mice, mutagenesis, and structural modeling with clear mechanistic resolution\",\n      \"pmids\": [\"17030622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"CBLN3 is not secreted when expressed alone but is retained in the endoplasmic reticulum or cis-Golgi due to its N-terminal domain. When co-expressed with CBLN1 in heterologous cells, a proportion of CBLN3 is secreted together with CBLN1. In cbln1-null granule cells, CBLN3 is almost completely degraded, confirming CBLN1 dependence for CBLN3 trafficking.\",\n      \"method\": \"Heterologous cell expression, co-expression experiments, analysis of cbln1-null granule cells, immunofluorescence\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — independent replication of CBLN1-dependent CBLN3 secretion with multiple orthogonal approaches\",\n      \"pmids\": [\"17331201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Cbln3 mRNA expression is selective to cerebellar granule cells throughout development, with onset as late as postnatal day 7-10, distinguishing it from other Cbln family members.\",\n      \"method\": \"RT-PCR, Northern blot, in situ hybridization\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods but limited to expression/localization without direct functional manipulation\",\n      \"pmids\": [\"16930405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CBLN1 and CBLN3 co-accumulate at parallel fiber-Purkinje cell synaptic clefts, where they colocalize with GluRdelta2, providing anatomical evidence that all three molecules operate together in a common signaling pathway regulating cerebellar circuit development and synaptic plasticity.\",\n      \"method\": \"Light and electron microscopic immunohistochemistry with pepsin pretreatment and postembedding immunogold\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization with antigen-exposing methods showing synaptic cleft co-accumulation, but no functional manipulation of CBLN3 specifically\",\n      \"pmids\": [\"19250438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In cbln3-null mice, Cbln1 immunoreactivity in the cerebellum increases dramatically, but is unchanged in extracerebellar neurons, indicating CBLN3 regulates CBLN1 levels via the endolysosomal degradation pathway specifically in cerebellar granule cells. Cbln1 localizes to the endolysosomal compartment of neurons.\",\n      \"method\": \"Immunohistochemistry of cbln3-null mice, colocalization with cathepsin D (lysosomal marker), cbln1-lacZ transgenic mice\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct subcellular localization combined with genetic KO showing regulatory relationship\",\n      \"pmids\": [\"18001291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Unlike CBLN1, CBLN2, and CBLN4 which autonomously assemble into homohexamers, CBLN3 requires CBLN1 for assembly and secretion, forming heteromeric complexes. This was confirmed in reporter knockin mice and cell expression studies.\",\n      \"method\": \"Knockin reporter mice, expression studies in heterologous cells\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — independent confirmation of CBLN1-dependent CBLN3 assembly with in vivo reporter models\",\n      \"pmids\": [\"28714144\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CBLN3 is a secreted C1q-family glycoprotein that cannot form homomers or be secreted independently due to an ER-retention mechanism mediated by a single arginine residue in its N-terminal domain; it requires CBLN1 binding (via a 'hide-and-run' mechanism) for ER export, heteromeric complex assembly, and secretion, after which the CBLN1-CBLN3 complex accumulates in the synaptic cleft of parallel fiber-Purkinje cell synapses alongside GluRdelta2, where it participates in regulating cerebellar synapse integrity and plasticity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CBLN3 is a secreted C1q-domain glycoprotein expressed selectively in cerebellar granule cells that functions exclusively as a heteromeric partner of CBLN1 to regulate cerebellar synapse integrity [PMID:10964938, PMID:16930405]. Unlike other cerebellin family members, CBLN3 cannot form homomers or be secreted independently; a single arginine residue in its N-terminal domain causes ER retention, which is relieved upon CBLN1 binding through a 'hide-and-run' mechanism, making CBLN1 obligatory for CBLN3 trafficking and secretion [PMID:17030622, PMID:17331201]. In the absence of CBLN3, CBLN1 levels increase approximately sixfold in the cerebellum due to escape from endolysosomal degradation, indicating that CBLN3 quantitatively regulates CBLN1 availability [PMID:17030622, PMID:18001291]. The CBLN1–CBLN3 heteromeric complex accumulates in the synaptic cleft of parallel fiber–Purkinje cell synapses where it colocalizes with GluRδ2, positioning it as a trans-synaptic signaling component in cerebellar circuit development and plasticity [PMID:19250438].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Identification of CBLN3 as a CBLN1-binding partner established the existence of a heteromeric cerebellin complex, resolving the question of whether cerebellin family members interact directly.\",\n      \"evidence\": \"Yeast two-hybrid screen with specificity controls and in vitro binding assays\",\n      \"pmids\": [\"10964938\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether CBLN3 is secreted or has independent function outside the CBLN1 complex was unknown\",\n        \"No in vivo localization or functional evidence\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstration that CBLN3 is ER-retained unless bound to CBLN1 — via a steric clash from a single arginine — defined a 'hide-and-run' secretion mechanism and showed that CBLN3 loss elevates CBLN1 levels sixfold, revealing a reciprocal regulatory relationship.\",\n      \"evidence\": \"cbln1-null and cbln3-null mouse phenotyping, site-directed mutagenesis, structural modeling, and secretion assays in heterologous cells\",\n      \"pmids\": [\"17030622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The stoichiometry of the CBLN1–CBLN3 complex was not resolved\",\n        \"Whether the sixfold CBLN1 increase in cbln3-null mice has functional consequences at the synapse was untested\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Mapping Cbln3 mRNA expression exclusively to postnatal cerebellar granule cells defined its spatiotemporal expression domain, separating it from other family members.\",\n      \"evidence\": \"RT-PCR, Northern blot, and in situ hybridization across developmental stages\",\n      \"pmids\": [\"16930405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Protein-level expression was not directly assessed\",\n        \"No functional manipulation to test whether the late postnatal onset is functionally significant\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Independent replication confirmed CBLN3 ER/cis-Golgi retention and CBLN1-dependent secretion, and showed that CBLN3 is nearly completely degraded in cbln1-null granule cells, solidifying the obligate dependence model.\",\n      \"evidence\": \"Co-expression in heterologous cells, immunofluorescence, and cbln1-null granule cell analysis\",\n      \"pmids\": [\"17331201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The degradation pathway for CBLN3 in the absence of CBLN1 was not defined\",\n        \"Whether CBLN3 modifies CBLN1 signaling properties or merely alters its levels was unresolved\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing that CBLN3 loss increases CBLN1 specifically in cerebellum via diversion from endolysosomal degradation revealed a cell-type-specific regulatory mechanism controlling CBLN1 abundance.\",\n      \"evidence\": \"Immunohistochemistry in cbln3-null mice with lysosomal marker colocalization\",\n      \"pmids\": [\"18001291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct biochemical demonstration of CBLN1 endolysosomal routing by CBLN3 was not provided\",\n        \"Whether the increased CBLN1 in cbln3-null cerebellum alters synaptic function was not tested\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Ultrastructural co-localization of CBLN1, CBLN3, and GluRδ2 at parallel fiber–Purkinje cell synaptic clefts placed the heteromeric complex at its site of action, linking it to trans-synaptic signaling.\",\n      \"evidence\": \"Pre-embedding immunohistochemistry with pepsin antigen retrieval and postembedding immunogold electron microscopy\",\n      \"pmids\": [\"19250438\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No direct functional evidence that CBLN3 modulates GluRδ2 signaling at the synapse\",\n        \"Whether CBLN3 contacts GluRδ2 directly or only through CBLN1 was unknown\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Reporter knockin mice confirmed that CBLN3 uniquely among the family requires CBLN1 for assembly into secreted hexameric complexes, reinforcing its obligate heteromeric nature.\",\n      \"evidence\": \"Knockin reporter mice and heterologous cell expression studies\",\n      \"pmids\": [\"28714144\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Exact stoichiometry (e.g., trimer-of-dimers composition) of CBLN1–CBLN3 heterohexamers was not determined\",\n        \"Functional distinction between CBLN1 homohexamers and CBLN1–CBLN3 heterohexamers at the synapse remains unknown\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown whether CBLN3 incorporation into CBLN1 complexes changes the binding affinity or signaling output at GluRδ2-containing synapses, and whether CBLN3 loss produces distinct behavioral or synaptic phenotypes beyond those explained by altered CBLN1 levels.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structure of the CBLN1–CBLN3 heteromeric complex\",\n        \"No direct electrophysiological or behavioral analysis specifically attributable to CBLN3 function\",\n        \"Whether CBLN3 interacts with neurexins or other synaptic organizers independent of CBLN1 is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0005198\",\n        \"supporting_discovery_ids\": [0, 1, 6]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005783\",\n        \"supporting_discovery_ids\": [1, 2]\n      },\n      {\n        \"term_id\": \"GO:0005576\",\n        \"supporting_discovery_ids\": [1, 2, 4]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-112316\",\n        \"supporting_discovery_ids\": [3, 4]\n      },\n      {\n        \"term_id\": \"R-HSA-9609507\",\n        \"supporting_discovery_ids\": [1, 2, 6]\n      }\n    ],\n    \"complexes\": [\n      \"CBLN1-CBLN3 heterohexamer\"\n    ],\n    \"partners\": [\n      \"CBLN1\",\n      \"GRID2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}