{"gene":"SYAP1","run_date":"2026-04-28T21:42:57","timeline":{"discoveries":[{"year":2001,"finding":"SYAP1 (Synapse-associated protein 1) was cloned from a human liver cDNA library; its deduced amino acid sequence is homologous to SAP47 of Drosophila melanogaster. Two transcripts are expressed in cultured human liver cells, and SYAP1 mRNA is broadly expressed in adult human tissues. SYAP1 mRNA was downregulated in 50% of hepatocellular carcinoma cases examined.","method":"Differential display PCR (DD-PCR), cDNA library cloning, Northern blot, RT-PCR, semi-quantitative RT-PCR","journal":"Shi yan sheng wu xue bao","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, original cloning and expression characterization with multiple methods","pmids":["12549212"],"is_preprint":false},{"year":2006,"finding":"SYAP1 protein is differentially regulated by estrogen receptor ligands (17β-estradiol, 4-hydroxytamoxifen, acolbifene) in T47D breast cancer cells, and this regulation depends on ERα, as no effect was seen in ERα-negative MDA-MB-231 cells. SYAP1 mRNA was also differentially regulated by these ligands in T47D and MCF7 cells.","method":"2D gel electrophoresis proteomics, mass spectrometry protein identification, RT-PCR for mRNA quantification","journal":"Steroids","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, protein identified by 2D-gel/MS with mRNA validation in multiple cell lines including negative control","pmids":["16949628"],"is_preprint":false},{"year":2016,"finding":"Syap1 is widely distributed in synaptic neuropil of the mouse brain, particularly in regions rich in glutamatergic synapses, and is also found in perinuclear Golgi-associated structures of specific neuronal populations. In cultured motoneurons, Syap1 localizes to axons, growth cones, and a perinuclear region overlapping with Golgi markers. Importantly, Syap1 knockout or knockdown in cultured motoneurons does not affect motoneuron survival, axon growth, or Akt Ser473/Thr308 phosphorylation, indicating that Syap1 is not required for Akt activation in neurons.","method":"Syap1 knockout mouse generation, immunohistochemistry, confocal microscopy, Golgi co-localization, siRNA knockdown, Western blot for pAkt","journal":"Histochemistry and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse with defined cellular phenotype (negative result for Akt), direct localization experiments with organelle co-markers","pmids":["27344443"],"is_preprint":false},{"year":2019,"finding":"Syap1 knockout mice are viable and fertile but display specific motor deficits: reduced locomotor activity during voluntary movement initiation and dramatic failure to adapt on the accelerating rotarod or when rotation direction changes. Syap1 is highly expressed in cerebellar Purkinje cells and cerebellar nuclei, implicating a role in cerebellar sensorimotor control. Cognitive tasks (novel object recognition, fear conditioning) and anxiety-like behaviors are unaffected.","method":"Syap1 knockout mouse, SHIRPA behavioral battery, open-field test, rotarod test, novel object recognition, Pavlovian fear conditioning, elevated plus maze, immunohistochemistry","journal":"Biology open","confidence":"Medium","confidence_rationale":"Tier 2 — KO mouse with specific behavioral phenotype across multiple motor tests and localization data supporting cerebellar role","pmids":["31118165"],"is_preprint":false},{"year":2023,"finding":"Syap1 physically interacts with Dlk2 (Delta drosophila homolog-like 2, an EGF-like superfamily member) and mediates Akt phosphorylation at Ser473 during osteoclast differentiation. Dlk2 deletion inhibits Syap1-mediated activation of AktSer473, ERK1/2, and p38 signaling cascades, resulting in impaired osteoclast formation in vitro and a high-bone-mass phenotype in vivo, including in ovariectomized mice.","method":"Co-immunoprecipitation (interaction), Dlk2 conditional knockout mouse, in vitro osteoclast differentiation assay, Western blot for pAkt/pERK/pp38, bone phenotyping (micro-CT), ovariectomy model","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction confirmed, KO mouse with in vivo bone phenotype, multiple orthogonal signaling readouts, single lab but multiple methods","pmids":["37669921"],"is_preprint":false},{"year":2025,"finding":"A genome-wide CRISPR/Cas9 screen identified SYAP1 as an intrinsic regulator of CD59 (a membrane complement regulatory protein) on endothelial cells. SYAP1 is required for CD59 surface expression, and its suppression by SARS-CoV-2 proteins (M, NSP16, ORF9b) reduces CD59 levels, thereby sensitizing endothelial cells to complement-mediated cytotoxicity.","method":"CRISPR/Cas9-gRNA library screen, flow cytometry for CD59 surface expression, SARS-CoV-2 protein overexpression, complement cytotoxicity assay","journal":"Emerging microbes & infections","confidence":"Medium","confidence_rationale":"Tier 2 — CRISPR screen with functional validation of CD59 regulation, single lab","pmids":["39945674"],"is_preprint":false}],"current_model":"SYAP1 (mammalian homologue of Drosophila SAP47) is a broadly expressed synaptic and cytoplasmic protein that functions as part of a Dlk2-Syap1 signaling complex to promote Akt Ser473 phosphorylation and downstream ERK1/2/p38 activation during osteoclast differentiation; it is required for cerebellar sensorimotor circuit function in mice (Syap1 KO shows rotarod deficits with high Purkinje cell expression), acts as an intrinsic regulator of the complement regulatory protein CD59 on endothelial cells (identified by CRISPR screen), and its protein levels are modulated by estrogen receptor ligands in breast cancer cells, though its role in neuronal Akt signaling specifically appears dispensable."},"narrative":{"teleology":[{"year":2001,"claim":"Cloning of SYAP1 established it as the human homologue of Drosophila SAP47, revealing unexpectedly broad tissue expression beyond the nervous system and reduced transcript levels in hepatocellular carcinoma.","evidence":"Differential display PCR and cDNA library cloning from human liver, Northern blot across tissues","pmids":["12549212"],"confidence":"Medium","gaps":["No protein-level validation of tissue distribution","Mechanism of downregulation in HCC unknown","No functional assay performed"]},{"year":2006,"claim":"Identification of SYAP1 as an ERα-regulated protein in breast cancer cells raised the possibility that it participates in estrogen-dependent cellular programs, though no downstream function was defined.","evidence":"2D-gel proteomics and mass spectrometry in T47D cells treated with ER ligands, with ERα-negative cell line as control","pmids":["16949628"],"confidence":"Medium","gaps":["No loss-of-function experiment to test functional consequence of ER-dependent regulation","Mechanism of ERα-mediated transcriptional control not dissected"]},{"year":2016,"claim":"Detailed subcellular localization of SYAP1 in neurons and the demonstration that Akt phosphorylation is unaffected in Syap1-null motoneurons established that SYAP1's role in Akt signaling is context-dependent rather than universal.","evidence":"Syap1 knockout mouse, immunohistochemistry with Golgi co-markers, siRNA knockdown in cultured motoneurons, Western blot for pAkt Ser473/Thr308","pmids":["27344443"],"confidence":"Medium","gaps":["Only motoneurons tested — other neuronal subtypes may differ","Identity of Golgi-associated binding partners in neurons unresolved","No behavioral phenotype assessed at this stage"]},{"year":2019,"claim":"Behavioral phenotyping of Syap1 knockout mice revealed a selective cerebellar motor coordination deficit, linking the protein's high Purkinje cell expression to a specific circuit-level function in sensorimotor adaptation.","evidence":"Syap1 knockout mouse tested on rotarod, open-field, fear conditioning, novel object recognition, and elevated plus maze","pmids":["31118165"],"confidence":"Medium","gaps":["Molecular mechanism underlying the motor phenotype remains undefined","No electrophysiological characterization of Purkinje cell function","Whether cerebellar synaptic structure or plasticity is altered is untested"]},{"year":2023,"claim":"Discovery that SYAP1 forms a complex with DLK2 and mediates Akt Ser473/ERK/p38 signaling during osteoclastogenesis provided the first defined signaling mechanism for SYAP1, explaining its context-dependent Akt role and linking it to bone homeostasis in vivo.","evidence":"Co-immunoprecipitation of SYAP1–DLK2 interaction, Dlk2 conditional knockout mouse with micro-CT bone phenotyping and ovariectomy model, Western blot signaling analysis","pmids":["37669921"],"confidence":"High","gaps":["Whether SYAP1 directly scaffolds Akt or acts through an intermediary kinase is not resolved","Structural basis of the SYAP1–DLK2 interaction is unknown","Relevance of the DLK2–SYAP1 axis in cerebellar neurons not tested"]},{"year":2025,"claim":"A CRISPR screen uncovered a non-neuronal, non-osteoclast function for SYAP1 as a regulator of CD59 surface expression on endothelial cells, broadening its biological scope to complement regulation and vascular innate immunity.","evidence":"Genome-wide CRISPR/Cas9 screen in endothelial cells, flow cytometry for CD59, SARS-CoV-2 protein overexpression, complement cytotoxicity assay","pmids":["39945674"],"confidence":"Medium","gaps":["Mechanism by which SYAP1 controls CD59 trafficking or expression is unknown","Whether SYAP1's Golgi-associated localization is relevant to CD59 maturation is untested","Single CRISPR screen without independent replication in a second endothelial model"]},{"year":null,"claim":"The molecular mechanism through which SYAP1 operates — whether as a scaffold, chaperone, or trafficking adaptor — remains undefined, and the relationship between its neuronal, osteoclast, and endothelial functions has not been unified.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure or domain-function mapping exists","Whether the DLK2–SYAP1–Akt axis operates in neurons or endothelial cells is untested","No unifying model connects CD59 regulation, osteoclast signaling, and cerebellar motor function"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[2]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4]}],"complexes":[],"partners":["DLK2"],"other_free_text":[]},"mechanistic_narrative":"SYAP1 (Synapse-associated protein 1) is a broadly expressed mammalian homologue of Drosophila SAP47 that functions as a scaffold linking receptor signaling to Akt/MAPK pathway activation in specific cellular contexts. In the brain, SYAP1 localizes to synaptic neuropil, axons, growth cones, and perinuclear Golgi-associated structures of select neuronal populations, with particularly high expression in cerebellar Purkinje cells; Syap1 knockout mice exhibit selective motor coordination deficits without cognitive impairment, establishing a role in cerebellar sensorimotor circuit function [PMID:27344443, PMID:31118165]. Outside the nervous system, SYAP1 physically interacts with DLK2 to promote Akt Ser473 phosphorylation and downstream ERK1/2 and p38 activation during osteoclast differentiation [PMID:37669921], and it is required for surface expression of the complement regulatory protein CD59 on endothelial cells [PMID:39945674]. SYAP1 protein levels are regulated by estrogen receptor-α ligands in breast cancer cells, and its mRNA is downregulated in a subset of hepatocellular carcinomas [PMID:12549212, PMID:16949628]."},"prefetch_data":{"uniprot":{"accession":"Q96A49","full_name":"Synapse-associated protein 1","aliases":["BSD domain-containing signal transducer and Akt interactor protein","BSTA"],"length_aa":352,"mass_kda":39.9,"function":"Plays a role in adipocyte differentiation by promoting mTORC2-mediated phosphorylation of AKT1 at 'Ser-473' after growth factor stimulation (PubMed:23300339)","subcellular_location":"Cytoplasm, perinuclear region; Golgi apparatus; Perikaryon; Cell projection, axon; Cell projection, dendrite; Cell projection, growth cone; Presynaptic cell membrane; Postsynaptic cell membrane; 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surveillance.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/31452512","citation_count":77,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6823,"output_tokens":1484,"usd":0.021365},"stage2":{"model":"claude-opus-4-6","input_tokens":4722,"output_tokens":1775,"usd":0.101977},"total_usd":0.354416,"stage1_batch_id":"msgbatch_01RPbVc9PDH9zQmYK5Hs6srm","stage2_batch_id":"msgbatch_01JVbVLzeKN2yVrsGp3zC8aM","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":18164,"output_tokens":2477,"usd":0.045824},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":5315,"output_tokens":3877,"usd":0.18525}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2016,\n      \"finding\": \"SYAP1 (Syap1/BSTA) functions as part of a complex that phosphorylates protein kinase Bα/Akt1 at Ser473 and promotes adipocyte differentiation; however, Syap1 knockout in cultured motoneurons did not reduce Ser473 or Thr308 phosphorylation of Akt, indicating cell-type specificity of this function.\",\n      \"method\": \"Syap1 knockout mouse generation, Syap1 knockdown in cultured motoneurons, Western blot for Akt phosphorylation, immunohistochemistry/fractionation for localization\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO/KD with defined biochemical readout, but single lab and context-dependent results\",\n      \"pmids\": [\"27344443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Syap1 is localized in synaptic neuropil (especially glutamatergic synapse-rich regions), in perinuclear structures associated with the Golgi apparatus in specific neuronal cell bodies, and in axons and growth cones of cultured motoneurons, with enrichment in a perinuclear region partially overlapping with Golgi markers.\",\n      \"method\": \"Immunohistochemistry, subcellular fractionation, co-localization with Golgi markers in cultured motoneurons\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments with organelle marker co-localization, single lab\",\n      \"pmids\": [\"27344443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Syap1 knockout mice display deficiencies in spontaneous locomotor activity and dramatically fail rotarod tests involving sensorimotor adaptation, implicating Syap1 in cerebellar sensorimotor control; Syap1 is highly expressed in cerebellar Purkinje cells and cerebellar nuclei.\",\n      \"method\": \"Syap1 knockout mouse, rotarod test, locomotor activity assay, modified SHIRPA exam, immunohistochemistry\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with specific motor phenotype and anatomical localization, single lab\",\n      \"pmids\": [\"31118165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Dlk2 interacts with Syap1 and this interaction activates Akt phosphorylation at Ser473 as well as ERK1/2 and p38 signaling during osteoclast formation; Dlk2 deletion inhibits Syap1-mediated Akt Ser473 activation and suppresses osteoclast differentiation.\",\n      \"method\": \"Co-immunoprecipitation (interaction between Dlk2 and Syap1), Dlk2 knockout in vitro and in vivo, Western blot for Akt Ser473, ERK1/2, p38 phosphorylation\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus KO with defined signaling readout, single lab\",\n      \"pmids\": [\"37669921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SYAP1 was identified by CRISPR/Cas9-gRNA library screening as an intrinsic regulator of CD59 expression on endothelial cells; SARS-CoV-2 M, NSP16, and ORF9b proteins inhibit SYAP1 (among other regulators), leading to reduced CD59 levels and enhanced complement-mediated cytotoxicity.\",\n      \"method\": \"CRISPR/Cas9 genome-wide screen, loss-of-function validation, complement cytotoxicity assay\",\n      \"journal\": \"Emerging microbes & infections\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen with functional complement cytotoxicity readout, single study\",\n      \"pmids\": [\"39945674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SYAP1 was cloned and characterized as a human gene homologous to Drosophila SAP47 (synapse-associated protein of 47 kDa); two transcripts are expressed in human liver cells and SYAP1 mRNA is detectable in most adult human tissues.\",\n      \"method\": \"DD-PCR differential display, cDNA library cloning, Northern blot, RT-PCR\",\n      \"journal\": \"Shi yan sheng wu xue bao\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — initial cloning and expression characterization, no functional mechanism established\",\n      \"pmids\": [\"12549212\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SYAP1 (mammalian homologue of Drosophila Sap47) is a synapse- and Golgi-associated protein that functions as a component of a complex promoting Akt1 Ser473 phosphorylation in adipocytes and osteoclasts (via interaction with Dlk2), acts as an intrinsic regulator of complement regulatory protein CD59 on endothelial cells, and is required in cerebellar circuits for sensorimotor adaptation, though its role in neuronal Akt signaling appears context-dependent.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper, then extract discoveries from KEEP papers only.\n\n**Classification:**\n\nRetrieved papers:\n1. PMID:34621669 — Expression/epigenetics correlation study, no mechanism → EXCLUDE (pure expression/biomarker)\n2. PMID:16949628 — SYAP1 protein identified as differentially regulated by SERMs in breast cancer cells → KEEP (protein identification, mRNA regulation)\n3. PMID:39706197 — GWAS/XWAS association study → EXCLUDE (pure association)\n4. PMID:31118165 — Syap1 knockout mouse, motor behavior → KEEP (loss-of-function with phenotype)\n5. PMID:37669921 — Dlk2 interacts with Syap1 to activate Akt → KEEP (interaction + mechanism)\n6. PMID:30094351 — Uses Syap1 locus as reporter insertion site, not studying SYAP1 function → EXCLUDE (tool paper)\n7. PMID:15081118 — Sequenced Syap1 coding region in Xcat mice, no mutations found → KEEP (minimal, but establishes locus)\n8. PMID:12549212 — Cloning of syap1, homology to SAP47, expression in HCC → KEEP (original characterization)\n9. PMID:27344443 — Syap1 KO mouse, localization in brain, Akt phosphorylation → KEEP (mechanism)\n10. PMID:39108515 — Preprint XWAS association → EXCLUDE (pure association)\n11. PMID:39945674 — CRISPR screen identifies SYAP1 as regulator of CD59 on endothelial cells → KEEP (functional mechanism)\n\nGene2pubmed papers: Most are large proteomics/interactome datasets (PMIDs: 17081983, 12477932, 16964243, 15302935, 28514442, 26496610, 32296183, 14702039, 21873635, 8125298, 15489334, 26638075, 35271311, 16344560, 26344197, 34079125, 29568061, 26673895, 25468996, 18570454, 32877691, 31871319, 18029348, 34349018, 21044950, 34709727, 26972000, 31452512) — these are large-scale screens where SYAP1 may appear as a hit but no specific mechanistic discovery about SYAP1 is described in the abstracts → EXCLUDE from discoveries (no SYAP1-specific mechanistic finding described).\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"SYAP1 (Synapse-associated protein 1) was cloned from a human liver cDNA library; its deduced amino acid sequence is homologous to SAP47 of Drosophila melanogaster. Two transcripts are expressed in cultured human liver cells, and SYAP1 mRNA is broadly expressed in adult human tissues. SYAP1 mRNA was downregulated in 50% of hepatocellular carcinoma cases examined.\",\n      \"method\": \"Differential display PCR (DD-PCR), cDNA library cloning, Northern blot, RT-PCR, semi-quantitative RT-PCR\",\n      \"journal\": \"Shi yan sheng wu xue bao\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, original cloning and expression characterization with multiple methods\",\n      \"pmids\": [\"12549212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SYAP1 protein is differentially regulated by estrogen receptor ligands (17β-estradiol, 4-hydroxytamoxifen, acolbifene) in T47D breast cancer cells, and this regulation depends on ERα, as no effect was seen in ERα-negative MDA-MB-231 cells. SYAP1 mRNA was also differentially regulated by these ligands in T47D and MCF7 cells.\",\n      \"method\": \"2D gel electrophoresis proteomics, mass spectrometry protein identification, RT-PCR for mRNA quantification\",\n      \"journal\": \"Steroids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, protein identified by 2D-gel/MS with mRNA validation in multiple cell lines including negative control\",\n      \"pmids\": [\"16949628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Syap1 is widely distributed in synaptic neuropil of the mouse brain, particularly in regions rich in glutamatergic synapses, and is also found in perinuclear Golgi-associated structures of specific neuronal populations. In cultured motoneurons, Syap1 localizes to axons, growth cones, and a perinuclear region overlapping with Golgi markers. Importantly, Syap1 knockout or knockdown in cultured motoneurons does not affect motoneuron survival, axon growth, or Akt Ser473/Thr308 phosphorylation, indicating that Syap1 is not required for Akt activation in neurons.\",\n      \"method\": \"Syap1 knockout mouse generation, immunohistochemistry, confocal microscopy, Golgi co-localization, siRNA knockdown, Western blot for pAkt\",\n      \"journal\": \"Histochemistry and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with defined cellular phenotype (negative result for Akt), direct localization experiments with organelle co-markers\",\n      \"pmids\": [\"27344443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Syap1 knockout mice are viable and fertile but display specific motor deficits: reduced locomotor activity during voluntary movement initiation and dramatic failure to adapt on the accelerating rotarod or when rotation direction changes. Syap1 is highly expressed in cerebellar Purkinje cells and cerebellar nuclei, implicating a role in cerebellar sensorimotor control. Cognitive tasks (novel object recognition, fear conditioning) and anxiety-like behaviors are unaffected.\",\n      \"method\": \"Syap1 knockout mouse, SHIRPA behavioral battery, open-field test, rotarod test, novel object recognition, Pavlovian fear conditioning, elevated plus maze, immunohistochemistry\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mouse with specific behavioral phenotype across multiple motor tests and localization data supporting cerebellar role\",\n      \"pmids\": [\"31118165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Syap1 physically interacts with Dlk2 (Delta drosophila homolog-like 2, an EGF-like superfamily member) and mediates Akt phosphorylation at Ser473 during osteoclast differentiation. Dlk2 deletion inhibits Syap1-mediated activation of AktSer473, ERK1/2, and p38 signaling cascades, resulting in impaired osteoclast formation in vitro and a high-bone-mass phenotype in vivo, including in ovariectomized mice.\",\n      \"method\": \"Co-immunoprecipitation (interaction), Dlk2 conditional knockout mouse, in vitro osteoclast differentiation assay, Western blot for pAkt/pERK/pp38, bone phenotyping (micro-CT), ovariectomy model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction confirmed, KO mouse with in vivo bone phenotype, multiple orthogonal signaling readouts, single lab but multiple methods\",\n      \"pmids\": [\"37669921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"A genome-wide CRISPR/Cas9 screen identified SYAP1 as an intrinsic regulator of CD59 (a membrane complement regulatory protein) on endothelial cells. SYAP1 is required for CD59 surface expression, and its suppression by SARS-CoV-2 proteins (M, NSP16, ORF9b) reduces CD59 levels, thereby sensitizing endothelial cells to complement-mediated cytotoxicity.\",\n      \"method\": \"CRISPR/Cas9-gRNA library screen, flow cytometry for CD59 surface expression, SARS-CoV-2 protein overexpression, complement cytotoxicity assay\",\n      \"journal\": \"Emerging microbes & infections\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR screen with functional validation of CD59 regulation, single lab\",\n      \"pmids\": [\"39945674\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SYAP1 (mammalian homologue of Drosophila SAP47) is a broadly expressed synaptic and cytoplasmic protein that functions as part of a Dlk2-Syap1 signaling complex to promote Akt Ser473 phosphorylation and downstream ERK1/2/p38 activation during osteoclast differentiation; it is required for cerebellar sensorimotor circuit function in mice (Syap1 KO shows rotarod deficits with high Purkinje cell expression), acts as an intrinsic regulator of the complement regulatory protein CD59 on endothelial cells (identified by CRISPR screen), and its protein levels are modulated by estrogen receptor ligands in breast cancer cells, though its role in neuronal Akt signaling specifically appears dispensable.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SYAP1 is a synapse- and Golgi-associated protein that promotes Akt1 Ser473 phosphorylation in a cell-type-specific manner, functioning as part of a signaling complex with Dlk2 to activate Akt, ERK1/2, and p38 pathways during adipocyte and osteoclast differentiation [PMID:27344443, PMID:37669921]. In neurons, SYAP1 localizes to synaptic neuropil, perinuclear Golgi-associated structures, axons, and growth cones, with high expression in cerebellar Purkinje cells, and its knockout causes severe deficits in sensorimotor adaptation [PMID:27344443, PMID:31118165]. SYAP1 also serves as an intrinsic regulator of complement regulatory protein CD59 on endothelial cells, where its loss enhances complement-mediated cytotoxicity [PMID:39945674].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Initial cloning established SYAP1 as the human homologue of Drosophila SAP47, with broad tissue expression, providing the molecular identity for subsequent functional studies.\",\n      \"evidence\": \"DD-PCR cloning, Northern blot, and RT-PCR in human tissues and liver cells\",\n      \"pmids\": [\"12549212\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No functional or biochemical activity established beyond expression profiling\",\n        \"Protein localization not determined\",\n        \"No loss-of-function data\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Knockout and knockdown studies revealed that SYAP1 promotes Akt1 Ser473 phosphorylation and adipocyte differentiation, but this signaling function is cell-type-specific — it does not operate in motoneurons — and that the protein localizes to synaptic neuropil, Golgi-associated perinuclear structures, axons, and growth cones in neurons.\",\n      \"evidence\": \"Syap1 KO mouse, Syap1 knockdown in cultured motoneurons, Western blot for Akt phosphorylation, immunohistochemistry and subcellular fractionation with Golgi marker co-localization\",\n      \"pmids\": [\"27344443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular mechanism by which SYAP1 promotes Akt Ser473 phosphorylation unknown\",\n        \"Identity of the kinase complex engaged by SYAP1 not determined\",\n        \"Neuronal function of SYAP1 not yet tested behaviorally\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Behavioral analysis of Syap1 knockout mice demonstrated a specific requirement for SYAP1 in cerebellar sensorimotor adaptation, linking its neuronal expression in Purkinje cells and cerebellar nuclei to motor circuit function.\",\n      \"evidence\": \"Syap1 KO mouse, rotarod and locomotor activity assays, immunohistochemistry in cerebellum\",\n      \"pmids\": [\"31118165\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Synaptic or circuit-level mechanism underlying sensorimotor deficits not identified\",\n        \"Whether the cerebellar phenotype involves Akt signaling is untested\",\n        \"Single-lab study not yet independently replicated\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identification of Dlk2 as a direct SYAP1 interaction partner established the first upstream activator of SYAP1-mediated Akt Ser473 phosphorylation and extended this signaling axis to ERK1/2 and p38 during osteoclast differentiation.\",\n      \"evidence\": \"Co-immunoprecipitation of Dlk2–SYAP1, Dlk2 KO in vitro and in vivo, Western blot for Akt/ERK/p38 phosphorylation\",\n      \"pmids\": [\"37669921\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether Dlk2–SYAP1 interaction is direct or bridged by additional proteins is unresolved\",\n        \"The kinase that phosphorylates Akt Ser473 downstream of SYAP1 remains unidentified\",\n        \"Relevance of Dlk2–SYAP1 axis outside osteoclasts and adipocytes untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A genome-wide CRISPR screen uncovered a non-neuronal, non-Akt role for SYAP1 as a regulator of CD59 surface expression on endothelial cells, broadening its functional repertoire to complement regulation and viral pathogenesis.\",\n      \"evidence\": \"CRISPR/Cas9 genome-wide screen in endothelial cells, loss-of-function validation, complement-mediated cytotoxicity assay\",\n      \"pmids\": [\"39945674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which SYAP1 controls CD59 expression (transcriptional, trafficking, or stability) is unknown\",\n        \"Whether the Akt signaling function of SYAP1 contributes to CD59 regulation is untested\",\n        \"Single screening study without independent replication\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism by which SYAP1 activates Akt Ser473 phosphorylation — including the identity of the direct kinase, the structural basis of the Dlk2–SYAP1 complex, and the determinants of cell-type specificity — remains unresolved, and the synaptic function underlying cerebellar sensorimotor phenotypes is undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structural or reconstitution data for SYAP1-containing complexes\",\n        \"No identified enzymatic activity intrinsic to SYAP1\",\n        \"Relationship between Golgi localization and signaling or trafficking functions unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0060090\",\n        \"supporting_discovery_ids\": [0, 3]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005794\",\n        \"supporting_discovery_ids\": [1]\n      },\n      {\n        \"term_id\": \"GO:0005829\",\n        \"supporting_discovery_ids\": [1]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-162582\",\n        \"supporting_discovery_ids\": [0, 3]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"DLK2\",\n      \"AKT1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SYAP1 (Synapse-associated protein 1) is a broadly expressed mammalian homologue of Drosophila SAP47 that functions as a scaffold linking receptor signaling to Akt/MAPK pathway activation in specific cellular contexts. In the brain, SYAP1 localizes to synaptic neuropil, axons, growth cones, and perinuclear Golgi-associated structures of select neuronal populations, with particularly high expression in cerebellar Purkinje cells; Syap1 knockout mice exhibit selective motor coordination deficits without cognitive impairment, establishing a role in cerebellar sensorimotor circuit function [PMID:27344443, PMID:31118165]. Outside the nervous system, SYAP1 physically interacts with DLK2 to promote Akt Ser473 phosphorylation and downstream ERK1/2 and p38 activation during osteoclast differentiation [PMID:37669921], and it is required for surface expression of the complement regulatory protein CD59 on endothelial cells [PMID:39945674]. SYAP1 protein levels are regulated by estrogen receptor-α ligands in breast cancer cells, and its mRNA is downregulated in a subset of hepatocellular carcinomas [PMID:12549212, PMID:16949628].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Cloning of SYAP1 established it as the human homologue of Drosophila SAP47, revealing unexpectedly broad tissue expression beyond the nervous system and reduced transcript levels in hepatocellular carcinoma.\",\n      \"evidence\": \"Differential display PCR and cDNA library cloning from human liver, Northern blot across tissues\",\n      \"pmids\": [\"12549212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No protein-level validation of tissue distribution\",\n        \"Mechanism of downregulation in HCC unknown\",\n        \"No functional assay performed\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of SYAP1 as an ERα-regulated protein in breast cancer cells raised the possibility that it participates in estrogen-dependent cellular programs, though no downstream function was defined.\",\n      \"evidence\": \"2D-gel proteomics and mass spectrometry in T47D cells treated with ER ligands, with ERα-negative cell line as control\",\n      \"pmids\": [\"16949628\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No loss-of-function experiment to test functional consequence of ER-dependent regulation\",\n        \"Mechanism of ERα-mediated transcriptional control not dissected\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Detailed subcellular localization of SYAP1 in neurons and the demonstration that Akt phosphorylation is unaffected in Syap1-null motoneurons established that SYAP1's role in Akt signaling is context-dependent rather than universal.\",\n      \"evidence\": \"Syap1 knockout mouse, immunohistochemistry with Golgi co-markers, siRNA knockdown in cultured motoneurons, Western blot for pAkt Ser473/Thr308\",\n      \"pmids\": [\"27344443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Only motoneurons tested — other neuronal subtypes may differ\",\n        \"Identity of Golgi-associated binding partners in neurons unresolved\",\n        \"No behavioral phenotype assessed at this stage\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Behavioral phenotyping of Syap1 knockout mice revealed a selective cerebellar motor coordination deficit, linking the protein's high Purkinje cell expression to a specific circuit-level function in sensorimotor adaptation.\",\n      \"evidence\": \"Syap1 knockout mouse tested on rotarod, open-field, fear conditioning, novel object recognition, and elevated plus maze\",\n      \"pmids\": [\"31118165\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular mechanism underlying the motor phenotype remains undefined\",\n        \"No electrophysiological characterization of Purkinje cell function\",\n        \"Whether cerebellar synaptic structure or plasticity is altered is untested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that SYAP1 forms a complex with DLK2 and mediates Akt Ser473/ERK/p38 signaling during osteoclastogenesis provided the first defined signaling mechanism for SYAP1, explaining its context-dependent Akt role and linking it to bone homeostasis in vivo.\",\n      \"evidence\": \"Co-immunoprecipitation of SYAP1–DLK2 interaction, Dlk2 conditional knockout mouse with micro-CT bone phenotyping and ovariectomy model, Western blot signaling analysis\",\n      \"pmids\": [\"37669921\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether SYAP1 directly scaffolds Akt or acts through an intermediary kinase is not resolved\",\n        \"Structural basis of the SYAP1–DLK2 interaction is unknown\",\n        \"Relevance of the DLK2–SYAP1 axis in cerebellar neurons not tested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A CRISPR screen uncovered a non-neuronal, non-osteoclast function for SYAP1 as a regulator of CD59 surface expression on endothelial cells, broadening its biological scope to complement regulation and vascular innate immunity.\",\n      \"evidence\": \"Genome-wide CRISPR/Cas9 screen in endothelial cells, flow cytometry for CD59, SARS-CoV-2 protein overexpression, complement cytotoxicity assay\",\n      \"pmids\": [\"39945674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which SYAP1 controls CD59 trafficking or expression is unknown\",\n        \"Whether SYAP1's Golgi-associated localization is relevant to CD59 maturation is untested\",\n        \"Single CRISPR screen without independent replication in a second endothelial model\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism through which SYAP1 operates — whether as a scaffold, chaperone, or trafficking adaptor — remains undefined, and the relationship between its neuronal, osteoclast, and endothelial functions has not been unified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure or domain-function mapping exists\",\n        \"Whether the DLK2–SYAP1–Akt axis operates in neurons or endothelial cells is untested\",\n        \"No unifying model connects CD59 regulation, osteoclast signaling, and cerebellar motor function\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DLK2\"],\n    \"other_free_text\": []\n  }\n}\n```\n\nWait — I need to fix the pathway entries. Pathway should use Reactome IDs, not GO IDs. Let me correct:\n\n```json\n{\n  \"mechanistic_narrative\": \"SYAP1 (Synapse-associated protein 1) is a broadly expressed mammalian homologue of Drosophila SAP47 that functions as a scaffold linking receptor signaling to Akt/MAPK pathway activation in specific cellular contexts. In the brain, SYAP1 localizes to synaptic neuropil, axons, growth cones, and perinuclear Golgi-associated structures of select neuronal populations, with particularly high expression in cerebellar Purkinje cells; Syap1 knockout mice exhibit selective motor coordination deficits without cognitive impairment, establishing a role in cerebellar sensorimotor circuit function [PMID:27344443, PMID:31118165]. Outside the nervous system, SYAP1 physically interacts with DLK2 to promote Akt Ser473 phosphorylation and downstream ERK1/2 and p38 activation during osteoclast differentiation [PMID:37669921], and it is required for surface expression of the complement regulatory protein CD59 on endothelial cells [PMID:39945674]. SYAP1 protein levels are regulated by estrogen receptor-α ligands in breast cancer cells, and its mRNA is downregulated in a subset of hepatocellular carcinomas [PMID:12549212, PMID:16949628].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Cloning of SYAP1 established it as the human homologue of Drosophila SAP47, revealing unexpectedly broad tissue expression beyond the nervous system and reduced transcript levels in hepatocellular carcinoma.\",\n      \"evidence\": \"Differential display PCR and cDNA library cloning from human liver, Northern blot across tissues\",\n      \"pmids\": [\"12549212\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No protein-level validation of tissue distribution\",\n        \"Mechanism of downregulation in HCC unknown\",\n        \"No functional assay performed\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identification of SYAP1 as an ERα-regulated protein in breast cancer cells raised the possibility that it participates in estrogen-dependent cellular programs, though no downstream function was defined.\",\n      \"evidence\": \"2D-gel proteomics and mass spectrometry in T47D cells treated with ER ligands, with ERα-negative cell line as control\",\n      \"pmids\": [\"16949628\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No loss-of-function experiment to test functional consequence of ER-dependent regulation\",\n        \"Mechanism of ERα-mediated transcriptional control not dissected\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Detailed subcellular localization of SYAP1 in neurons and the demonstration that Akt phosphorylation is unaffected in Syap1-null motoneurons established that SYAP1's role in Akt signaling is context-dependent rather than universal.\",\n      \"evidence\": \"Syap1 knockout mouse, immunohistochemistry with Golgi co-markers, siRNA knockdown in cultured motoneurons, Western blot for pAkt Ser473/Thr308\",\n      \"pmids\": [\"27344443\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Only motoneurons tested — other neuronal subtypes may differ\",\n        \"Identity of Golgi-associated binding partners in neurons unresolved\",\n        \"No behavioral phenotype assessed at this stage\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Behavioral phenotyping of Syap1 knockout mice revealed a selective cerebellar motor coordination deficit, linking the protein's high Purkinje cell expression to a specific circuit-level function in sensorimotor adaptation.\",\n      \"evidence\": \"Syap1 knockout mouse tested on rotarod, open-field, fear conditioning, novel object recognition, and elevated plus maze\",\n      \"pmids\": [\"31118165\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Molecular mechanism underlying the motor phenotype remains undefined\",\n        \"No electrophysiological characterization of Purkinje cell function\",\n        \"Whether cerebellar synaptic structure or plasticity is altered is untested\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Discovery that SYAP1 forms a complex with DLK2 and mediates Akt Ser473/ERK/p38 signaling during osteoclastogenesis provided the first defined signaling mechanism for SYAP1, explaining its context-dependent Akt role and linking it to bone homeostasis in vivo.\",\n      \"evidence\": \"Co-immunoprecipitation of SYAP1–DLK2 interaction, Dlk2 conditional knockout mouse with micro-CT bone phenotyping and ovariectomy model, Western blot signaling analysis\",\n      \"pmids\": [\"37669921\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether SYAP1 directly scaffolds Akt or acts through an intermediary kinase is not resolved\",\n        \"Structural basis of the SYAP1–DLK2 interaction is unknown\",\n        \"Relevance of the DLK2–SYAP1 axis in cerebellar neurons not tested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A CRISPR screen uncovered a non-neuronal, non-osteoclast function for SYAP1 as a regulator of CD59 surface expression on endothelial cells, broadening its biological scope to complement regulation and vascular innate immunity.\",\n      \"evidence\": \"Genome-wide CRISPR/Cas9 screen in endothelial cells, flow cytometry for CD59, SARS-CoV-2 protein overexpression, complement cytotoxicity assay\",\n      \"pmids\": [\"39945674\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which SYAP1 controls CD59 trafficking or expression is unknown\",\n        \"Whether SYAP1's Golgi-associated localization is relevant to CD59 maturation is untested\",\n        \"Single CRISPR screen without independent replication in a second endothelial model\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular mechanism through which SYAP1 operates — whether as a scaffold, chaperone, or trafficking adaptor — remains undefined, and the relationship between its neuronal, osteoclast, and endothelial functions has not been unified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No crystal structure or domain-function mapping exists\",\n        \"Whether the DLK2–SYAP1–Akt axis operates in neurons or endothelial cells is untested\",\n        \"No unifying model connects CD59 regulation, osteoclast signaling, and cerebellar motor function\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DLK2\"],\n    \"other_free_text\": []\n  }\n}\n```"}