{"gene":"CBLN3","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2000,"finding":"CBLN3 was identified as a novel binding partner of CBLN1 via yeast two-hybrid screen. CBLN1 binds avidly to CBLN3 and also forms homomeric complexes, whereas CBLN3 homomeric association is weak. This interaction is specific, as C1qB bound neither CBLN1 nor CBLN3.","method":"Yeast two-hybrid screen, protein interaction assays","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus binding specificity controls in a single study; homomeric/heteromeric distinction established with multiple interaction tests","pmids":["10964938"],"is_preprint":false},{"year":2006,"finding":"CBLN3 is secreted from cerebellar granule cells only when bound to CBLN1 (interaction-dependent secretion). In cbln1-null mice, Cbln3 is completely absent (degraded), whereas in cbln3-null mice, Cbln1 levels increase approximately sixfold. CBLN3 cannot form homomeric complexes and is retained in the endoplasmic reticulum when expressed alone. A single arginine residue in CBLN3 creates a steric clash that is masked upon Cbln1 binding ('hide-and-run' ER retention mechanism), conferring its unique secretion dependency.","method":"Knockout mouse analysis (cbln1-null, cbln3-null, double-null), structural modeling, site-directed mutagenesis, cell secretion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple knockout mouse lines, mutagenesis identifying the critical arginine, structural modeling, and secretion assays all converging on the same mechanism in a single rigorous study","pmids":["17030622"],"is_preprint":false},{"year":2007,"finding":"When expressed alone in mammalian heterologous cells, CBLN3 is not secreted but is retained in the endoplasmic reticulum or cis-Golgi due to its N-terminal domain. Co-expression of CBLN1 and CBLN3 results in partial secretion of CBLN3 together with CBLN1. In wild-type granule cells (which co-express CBLN1 and CBLN3), CBLN3 is partially secreted and reaches postsynaptic sites on Purkinje cell dendrites; in cbln1-null granule cells, CBLN3 is almost completely degraded.","method":"Heterologous cell expression, co-expression assays, immunohistochemistry in wild-type and cbln1-null granule cells","journal":"The European journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — replicates and extends the CBLN1-dependent secretion mechanism using both heterologous cells and primary neurons with genetic controls, consistent with PMID 17030622","pmids":["17331201"],"is_preprint":false},{"year":2006,"finding":"CBLN3 mRNA expression in the brain is selective to cerebellar granule cells throughout development, with onset as late as postnatal day 7-10, distinguishing it from other Cbln family members which appear earlier in development.","method":"RT-PCR, Northern blot, high-resolution in situ hybridization","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple complementary expression methods (RT-PCR, Northern blot, ISH) in a single study; localization finding with temporal precision","pmids":["16930405"],"is_preprint":false},{"year":2009,"finding":"CBLN1 and CBLN3 co-localize with GluRdelta2 at parallel fiber-Purkinje cell synaptic clefts, as revealed by antigen-exposing immunohistochemical methods. CBLN1 accumulates in the synaptic cleft specifically at PF-PC synapses (not at other PC synapses), and co-localizes almost completely with CBLN3 and GluRdelta2 at these sites.","method":"Light and electron microscopic immunohistochemistry with pepsin pretreatment and postembedding immunogold","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct subcellular localization by electron microscopy immunogold, single lab, with synapse-specificity controls","pmids":["19250438"],"is_preprint":false},{"year":2007,"finding":"In cbln3-null mice, CBLN1-like immunoreactivity in the cerebellum is dramatically increased (consistent with CBLN1 upregulation when not complexed with CBLN3), but CLI is unchanged in extracerebellar neurons. CBLN1 localizes to the endolysosomal compartment (co-localizing with cathepsin D) in neurons, suggesting that regulated degradation of Cbln proteins occurs through endosome/lysosome processing.","method":"Immunohistochemistry, cbln1-lacZ transgenic mice, cbln3-null mice, co-localization with lysosomal marker cathepsin D","journal":"The European journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic mouse models combined with subcellular marker co-localization, single lab","pmids":["18001291"],"is_preprint":false},{"year":2017,"finding":"CBLN3 requires CBLN1 for assembly and secretion, unlike CBLN1, CBLN2, and CBLN4 which autonomously assemble into homohexamers. This property distinguishes CBLN3 functionally from other cerebellin family members.","method":"Biochemical assembly and secretion assays in heterologous expression systems, knockin reporter mice","journal":"The Journal of comparative neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — replication of CBLN1-dependent secretion mechanism across labs with additional comparative family analysis; consistent with prior work","pmids":["28714144"],"is_preprint":false}],"current_model":"CBLN3 is a secreted C1q-family glycoprotein expressed selectively in cerebellar granule cells that cannot form homomeric complexes or be secreted independently; instead, a single arginine in its N-terminal domain causes ER retention via steric clash, which is masked upon heteromeric complex formation with CBLN1 ('hide-and-run' mechanism), allowing co-secretion of CBLN1-CBLN3 heteromers that accumulate at parallel fiber–Purkinje cell synaptic clefts together with the postsynaptic receptor GluRdelta2, while in the absence of CBLN1, CBLN3 is degraded via the endolysosomal pathway."},"narrative":{"mechanistic_narrative":"CBLN3 is a secreted C1q-family glycoprotein expressed selectively in cerebellar granule cells, where it functions as an obligate heteromeric partner of CBLN1 at parallel fiber–Purkinje cell synapses [PMID:10964938, PMID:17030622, PMID:19250438]. Unlike CBLN1, CBLN2, and CBLN4, which autonomously assemble into homohexamers and are secreted independently, CBLN3 cannot form stable homomeric complexes and is retained in the endoplasmic reticulum when expressed alone [PMID:17030622, PMID:28714144]. A single arginine residue in its N-terminal domain creates a steric clash that drives this ER retention; the clash is masked upon binding to CBLN1, permitting co-secretion of CBLN1–CBLN3 heteromers ('hide-and-run' mechanism) [PMID:17030622, PMID:17331201]. Following secretion, CBLN1 and CBLN3 co-localize with the postsynaptic receptor GluRdelta2 at parallel fiber–Purkinje cell synaptic clefts [PMID:19250438]. In the absence of CBLN1, CBLN3 is almost completely degraded, with regulated turnover of cerebellin proteins occurring through the endosomal/lysosomal pathway [PMID:17030622, PMID:18001291]. CBLN3 expression onset is delayed to postnatal day 7–10, distinguishing it temporally from other family members [PMID:16930405].","teleology":[{"year":2000,"claim":"Establishing that CBLN3 binds CBLN1 reframed CBLN3 from an isolated C1q-family protein into a partner-dependent member of a heteromeric system.","evidence":"Yeast two-hybrid screen with binding specificity assays","pmids":["10964938"],"confidence":"Medium","gaps":["Stoichiometry and assembly architecture of the CBLN1-CBLN3 complex not resolved","Functional consequence of the interaction not addressed"]},{"year":2006,"claim":"Defining CBLN3 as selectively expressed in cerebellar granule cells with late postnatal onset localized its site of action and distinguished it temporally from related cerebellins.","evidence":"RT-PCR, Northern blot, and in situ hybridization across development","pmids":["16930405"],"confidence":"Medium","gaps":["Does not address whether expression timing correlates with synapse formation","Protein-level localization not established"]},{"year":2006,"claim":"Identifying interaction-dependent secretion mediated by a single arginine resolved why CBLN3 cannot leave the cell alone and established the molecular basis of its obligate partnership with CBLN1.","evidence":"Knockout mouse lines (cbln1-null, cbln3-null, double-null), structural modeling, site-directed mutagenesis, and secretion assays","pmids":["17030622"],"confidence":"High","gaps":["High-resolution structure of the steric clash and its masking not determined","Downstream synaptic function of secreted heteromer not directly tested here"]},{"year":2007,"claim":"Showing ER/cis-Golgi retention in heterologous cells and CBLN1-dependent partial secretion in primary granule cells confirmed the retention mechanism operates both in reconstituted systems and native neurons.","evidence":"Heterologous cell co-expression and immunohistochemistry in wild-type and cbln1-null granule cells","pmids":["17331201"],"confidence":"High","gaps":["Efficiency and regulation of partial secretion not quantified","Trafficking route of the secreted complex to synapses unmapped"]},{"year":2007,"claim":"Demonstrating CBLN1 upregulation and endolysosomal localization in cbln3-null mice revealed that cerebellin protein levels are reciprocally regulated and turned over via lysosomal processing.","evidence":"Immunohistochemistry in cbln1-lacZ and cbln3-null mice with cathepsin D co-localization","pmids":["18001291"],"confidence":"Medium","gaps":["Mechanism coupling complex formation to degradation routing unknown","Whether endolysosomal targeting is specific to uncomplexed protein not directly shown"]},{"year":2009,"claim":"Co-localization of CBLN1, CBLN3, and GluRdelta2 at parallel fiber–Purkinje cell synaptic clefts placed the secreted heteromer at a defined postsynaptic receptor site, indicating a trans-synaptic role.","evidence":"Light and electron microscopic immunohistochemistry with pepsin pretreatment and postembedding immunogold","pmids":["19250438"],"confidence":"Medium","gaps":["Direct binding between the heteromer and GluRdelta2 not demonstrated here","Functional synaptic consequence of co-localization not tested"]},{"year":2017,"claim":"Comparative assembly analysis confirmed CBLN3 is uniquely unable to homo-assemble whereas CBLN1/2/4 form homohexamers, formalizing CBLN3's dependence within the family.","evidence":"Biochemical assembly and secretion assays in heterologous systems plus knockin reporter mice","pmids":["28714144"],"confidence":"Medium","gaps":["Quantitative subunit composition of native heteromers not defined","Physiological role distinct from CBLN1 not isolated"]},{"year":null,"claim":"The specific synaptic function of CBLN3 and its individual contribution to GluRdelta2 signaling beyond serving as a CBLN1-dependent passenger remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No direct receptor-binding assay for CBLN3 itself","No behavioral or synaptic phenotype attributable specifically to CBLN3 reported in the corpus","Structural basis of the arginine steric clash unresolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[4]}],"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":[2,4]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-112316","term_label":"Neuronal System","supporting_discovery_ids":[4]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,2]}],"complexes":["CBLN1-CBLN3 heteromer"],"partners":["CBLN1","GRID2"],"other_free_text":[]}},"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":56,"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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yeast two-hybrid screen. CBLN1 binds avidly to CBLN3 and also forms homomeric complexes, whereas CBLN3 homomeric association is weak. This interaction is specific, as C1qB bound neither CBLN1 nor CBLN3.\",\n      \"method\": \"Yeast two-hybrid screen, protein interaction assays\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus binding specificity controls in a single study; homomeric/heteromeric distinction established with multiple interaction tests\",\n      \"pmids\": [\"10964938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CBLN3 is secreted from cerebellar granule cells only when bound to CBLN1 (interaction-dependent secretion). In cbln1-null mice, Cbln3 is completely absent (degraded), whereas in cbln3-null mice, Cbln1 levels increase approximately sixfold. CBLN3 cannot form homomeric complexes and is retained in the endoplasmic reticulum when expressed alone. A single arginine residue in CBLN3 creates a steric clash that is masked upon Cbln1 binding ('hide-and-run' ER retention mechanism), conferring its unique secretion dependency.\",\n      \"method\": \"Knockout mouse analysis (cbln1-null, cbln3-null, double-null), structural modeling, site-directed mutagenesis, cell secretion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple knockout mouse lines, mutagenesis identifying the critical arginine, structural modeling, and secretion assays all converging on the same mechanism in a single rigorous study\",\n      \"pmids\": [\"17030622\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"When expressed alone in mammalian heterologous cells, CBLN3 is not secreted but is retained in the endoplasmic reticulum or cis-Golgi due to its N-terminal domain. Co-expression of CBLN1 and CBLN3 results in partial secretion of CBLN3 together with CBLN1. In wild-type granule cells (which co-express CBLN1 and CBLN3), CBLN3 is partially secreted and reaches postsynaptic sites on Purkinje cell dendrites; in cbln1-null granule cells, CBLN3 is almost completely degraded.\",\n      \"method\": \"Heterologous cell expression, co-expression assays, immunohistochemistry in wild-type and cbln1-null granule cells\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — replicates and extends the CBLN1-dependent secretion mechanism using both heterologous cells and primary neurons with genetic controls, consistent with PMID 17030622\",\n      \"pmids\": [\"17331201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CBLN3 mRNA expression in the brain is selective to cerebellar granule cells throughout development, with onset as late as postnatal day 7-10, distinguishing it from other Cbln family members which appear earlier in development.\",\n      \"method\": \"RT-PCR, Northern blot, high-resolution in situ hybridization\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple complementary expression methods (RT-PCR, Northern blot, ISH) in a single study; localization finding with temporal precision\",\n      \"pmids\": [\"16930405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CBLN1 and CBLN3 co-localize with GluRdelta2 at parallel fiber-Purkinje cell synaptic clefts, as revealed by antigen-exposing immunohistochemical methods. CBLN1 accumulates in the synaptic cleft specifically at PF-PC synapses (not at other PC synapses), and co-localizes almost completely with CBLN3 and GluRdelta2 at these sites.\",\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 / Moderate — direct subcellular localization by electron microscopy immunogold, single lab, with synapse-specificity controls\",\n      \"pmids\": [\"19250438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In cbln3-null mice, CBLN1-like immunoreactivity in the cerebellum is dramatically increased (consistent with CBLN1 upregulation when not complexed with CBLN3), but CLI is unchanged in extracerebellar neurons. CBLN1 localizes to the endolysosomal compartment (co-localizing with cathepsin D) in neurons, suggesting that regulated degradation of Cbln proteins occurs through endosome/lysosome processing.\",\n      \"method\": \"Immunohistochemistry, cbln1-lacZ transgenic mice, cbln3-null mice, co-localization with lysosomal marker cathepsin D\",\n      \"journal\": \"The European journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic mouse models combined with subcellular marker co-localization, single lab\",\n      \"pmids\": [\"18001291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CBLN3 requires CBLN1 for assembly and secretion, unlike CBLN1, CBLN2, and CBLN4 which autonomously assemble into homohexamers. This property distinguishes CBLN3 functionally from other cerebellin family members.\",\n      \"method\": \"Biochemical assembly and secretion assays in heterologous expression systems, knockin reporter mice\",\n      \"journal\": \"The Journal of comparative neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — replication of CBLN1-dependent secretion mechanism across labs with additional comparative family analysis; consistent with prior work\",\n      \"pmids\": [\"28714144\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CBLN3 is a secreted C1q-family glycoprotein expressed selectively in cerebellar granule cells that cannot form homomeric complexes or be secreted independently; instead, a single arginine in its N-terminal domain causes ER retention via steric clash, which is masked upon heteromeric complex formation with CBLN1 ('hide-and-run' mechanism), allowing co-secretion of CBLN1-CBLN3 heteromers that accumulate at parallel fiber–Purkinje cell synaptic clefts together with the postsynaptic receptor GluRdelta2, while in the absence of CBLN1, CBLN3 is degraded via the endolysosomal pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CBLN3 is a secreted C1q-family glycoprotein expressed selectively in cerebellar granule cells, where it functions as an obligate heteromeric partner of CBLN1 at parallel fiber–Purkinje cell synapses [#0, #1, #4]. Unlike CBLN1, CBLN2, and CBLN4, which autonomously assemble into homohexamers and are secreted independently, CBLN3 cannot form stable homomeric complexes and is retained in the endoplasmic reticulum when expressed alone [#1, #6]. A single arginine residue in its N-terminal domain creates a steric clash that drives this ER retention; the clash is masked upon binding to CBLN1, permitting co-secretion of CBLN1–CBLN3 heteromers ('hide-and-run' mechanism) [#1, #2]. Following secretion, CBLN1 and CBLN3 co-localize with the postsynaptic receptor GluRdelta2 at parallel fiber–Purkinje cell synaptic clefts [#4]. In the absence of CBLN1, CBLN3 is almost completely degraded, with regulated turnover of cerebellin proteins occurring through the endosomal/lysosomal pathway [#1, #5]. CBLN3 expression onset is delayed to postnatal day 7–10, distinguishing it temporally from other family members [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that CBLN3 binds CBLN1 reframed CBLN3 from an isolated C1q-family protein into a partner-dependent member of a heteromeric system.\",\n      \"evidence\": \"Yeast two-hybrid screen with binding specificity assays\",\n      \"pmids\": [\"10964938\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and assembly architecture of the CBLN1-CBLN3 complex not resolved\", \"Functional consequence of the interaction not addressed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining CBLN3 as selectively expressed in cerebellar granule cells with late postnatal onset localized its site of action and distinguished it temporally from related cerebellins.\",\n      \"evidence\": \"RT-PCR, Northern blot, and in situ hybridization across development\",\n      \"pmids\": [\"16930405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not address whether expression timing correlates with synapse formation\", \"Protein-level localization not established\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identifying interaction-dependent secretion mediated by a single arginine resolved why CBLN3 cannot leave the cell alone and established the molecular basis of its obligate partnership with CBLN1.\",\n      \"evidence\": \"Knockout mouse lines (cbln1-null, cbln3-null, double-null), structural modeling, site-directed mutagenesis, and secretion assays\",\n      \"pmids\": [\"17030622\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the steric clash and its masking not determined\", \"Downstream synaptic function of secreted heteromer not directly tested here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showing ER/cis-Golgi retention in heterologous cells and CBLN1-dependent partial secretion in primary granule cells confirmed the retention mechanism operates both in reconstituted systems and native neurons.\",\n      \"evidence\": \"Heterologous cell co-expression and immunohistochemistry in wild-type and cbln1-null granule cells\",\n      \"pmids\": [\"17331201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Efficiency and regulation of partial secretion not quantified\", \"Trafficking route of the secreted complex to synapses unmapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating CBLN1 upregulation and endolysosomal localization in cbln3-null mice revealed that cerebellin protein levels are reciprocally regulated and turned over via lysosomal processing.\",\n      \"evidence\": \"Immunohistochemistry in cbln1-lacZ and cbln3-null mice with cathepsin D co-localization\",\n      \"pmids\": [\"18001291\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism coupling complex formation to degradation routing unknown\", \"Whether endolysosomal targeting is specific to uncomplexed protein not directly shown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Co-localization of CBLN1, CBLN3, and GluRdelta2 at parallel fiber–Purkinje cell synaptic clefts placed the secreted heteromer at a defined postsynaptic receptor site, indicating a trans-synaptic role.\",\n      \"evidence\": \"Light and electron microscopic immunohistochemistry with pepsin pretreatment and postembedding immunogold\",\n      \"pmids\": [\"19250438\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct binding between the heteromer and GluRdelta2 not demonstrated here\", \"Functional synaptic consequence of co-localization not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Comparative assembly analysis confirmed CBLN3 is uniquely unable to homo-assemble whereas CBLN1/2/4 form homohexamers, formalizing CBLN3's dependence within the family.\",\n      \"evidence\": \"Biochemical assembly and secretion assays in heterologous systems plus knockin reporter mice\",\n      \"pmids\": [\"28714144\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Quantitative subunit composition of native heteromers not defined\", \"Physiological role distinct from CBLN1 not isolated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The specific synaptic function of CBLN3 and its individual contribution to GluRdelta2 signaling beyond serving as a CBLN1-dependent passenger remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No direct receptor-binding assay for CBLN3 itself\", \"No behavioral or synaptic phenotype attributable specifically to CBLN3 reported in the corpus\", \"Structural basis of the arginine steric clash unresolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-112316\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 2]}\n    ],\n    \"complexes\": [\"CBLN1-CBLN3 heteromer\"],\n    \"partners\": [\"CBLN1\", \"GRID2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":6,"faith_total":6,"faith_pct":100.0}}