{"gene":"SRGAP2","run_date":"2026-06-10T07:46:41","timeline":{"discoveries":[{"year":2009,"finding":"The F-BAR domain of srGAP2 induces filopodia-like membrane protrusions (resembling I-BAR domain activity) in vivo and in vitro, negatively regulates neuronal migration, and promotes neurite outgrowth and branching. srGAP2 knockdown reduces leading process branching and increases neuronal migration rate in vivo.","method":"In utero electroporation knockdown and overexpression in mouse neocortex; in vitro membrane deformation assays; F-BAR domain expression in non-neuronal cells","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KD and OE with defined cellular phenotypes in vivo and in vitro, replicated across multiple cell types and conditions in a single rigorous study","pmids":["19737524"],"is_preprint":false},{"year":2012,"finding":"SRGAP2C, a human-specific truncated paralog encoding only an F-BAR domain, dimerizes with ancestral SRGAP2 (SRGAP2A) to inhibit its function. In mouse neocortex, SRGAP2A promotes spine maturation and limits spine density; expression of SRGAP2C phenocopies SRGAP2 deficiency, leading to increased density of longer, less mature spines (neoteny) and sustained radial migration.","method":"Co-immunoprecipitation of SRGAP2C with SRGAP2A; in utero electroporation of SRGAP2C or SRGAP2 shRNA in mouse neocortex; spine morphology analysis","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP demonstrating dimerization, plus KD and SRGAP2C expression with defined synaptic and migratory phenotypes, replicated by multiple labs","pmids":["22559944"],"is_preprint":false},{"year":2010,"finding":"srGAP2 forms a complex with the formin FMNL1 (FRL1/FRLα); Rac-mediated activation of FMNL1 recruits srGAP2, whose Rac-specific GAP domain then terminates Rac signaling; additionally, the SH3 domain of srGAP2 binds the FH1 domain of FMNL1 to directly inhibit FMNL1-mediated actin severing. Both proteins co-localize to the phagocytic cup.","method":"Co-immunoprecipitation; in vitro actin severing assays; domain mapping; fluorescence microscopy in macrophage-derived cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro actin severing assay plus Co-IP domain mapping and co-localization, multiple orthogonal methods in single lab","pmids":["21148482"],"is_preprint":false},{"year":2010,"finding":"srGAP2 is arginine-methylated at Arg-927 by PRMT5, which binds to the N-terminal region (aa 225–538) of srGAP2. The R927A methylation mutant fails to localize to the plasma membrane leading edge, cannot rescue cell spreading, and disrupts F-BAR domain-mediated srGAP2 homodimerization, linking arginine methylation to membrane localization and cell spreading.","method":"Co-immunoprecipitation; domain mapping; site-directed mutagenesis (R927A); subcellular fractionation/fluorescence localization; cell spreading assays with rescue experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP, mutagenesis, functional rescue, and localization assays combined in one study, multiple orthogonal methods","pmids":["20810653"],"is_preprint":false},{"year":2012,"finding":"The F-BAR domains of srGAP1, srGAP2, and srGAP3 have distinct membrane deformation properties; F-BAR(2) (srGAP2) and F-BAR(3) induce filopodia while F-BAR(1) prevents filopodia in cortical neurons. The three F-BAR domains can heterodimerize and act synergistically in filopodia induction. F-BAR(2) membrane dynamics are partially dependent on F-actin. F-BAR(2) binds negatively charged phospholipids including PtdSer broadly, and PtdIns(4,5)P2 depletion does not displace it from the membrane.","method":"Expression in COS7 cells and cortical neurons; FRAP; phosphoinositide depletion; phospholipid-binding assays; Co-immunoprecipitation of heterodimerization","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (FRAP, lipid-binding, co-IP, KD) in a single rigorous study with functional readouts","pmids":["22467852"],"is_preprint":false},{"year":2015,"finding":"The Slit2-Robo4-srGAP2 signaling axis regulates contact inhibition of locomotion (CIL) in fibroblasts. The srGAP2 F-BAR domain senses membrane curvature to pre-localize srGAP2 to protruding edges, and srGAP2 specifically controls the duration of Rac1 activity in contact protrusions (but not contact-free protrusions) to terminate their extension after cell collision.","method":"FRET-based Rac1 biosensor; srGAP2 knockdown; F-BAR domain overexpression; live-cell imaging of collision events; Slit2/Robo4 perturbations","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — FRET biosensor plus KD with specific cellular phenotype (Rac1 dynamics), multiple orthogonal approaches in single rigorous study","pmids":["26439400"],"is_preprint":false},{"year":2015,"finding":"srGAP2 uses a two-component molecular mechanism for ligand binding through its SH3 domain: one component dramatically tightens ligand association, the other moderately autoinhibits and restricts binding, achieving specificity despite weak isolated SH3-ligand affinity.","method":"Structural analysis; mutagenesis; binding affinity measurements (likely ITC/SPR inferred from structural study context)","journal":"Structure","confidence":"Medium","confidence_rationale":"Tier 1-2 / Weak — structural/mutagenesis study from single lab; abstract does not detail all methods explicitly","pmids":["26365803"],"is_preprint":false},{"year":2017,"finding":"SRGAP2A crystal structure reveals: (1) it homodimerizes through a large interface comprising the F-BAR domain, a newly identified F-BAR extension (Fx) domain, and RhoGAP-SH3 domains; (2) it has an unusual inverse geometry enabling membrane protrusion scaffolding in lamellipodia and dendritic spine heads; (3) SRGAP2C carries a defective Fx domain that severely compromises its solubility and membrane-scaffolding ability; (4) SRGAP2A:SRGAP2C heterodimers form but are insoluble, thereby inhibiting SRGAP2A activity; (5) the primal SRGAP2C (~3.4 Ma) is less effective at heterodimerizing with SRGAP2A than modern SRGAP2C.","method":"X-ray crystallography; biochemical reconstitution; cell culture expression assays; dimerization/solubility assays","journal":"Molecular biology and evolution","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with biochemical reconstitution and functional cell assays; multiple orthogonal methods in single rigorous study","pmids":["28333212"],"is_preprint":false},{"year":2019,"finding":"SRGAP2C and SRGAP2B are intrinsically unstable proteins in neurons; upon heterodimerization with SRGAP2A they reduce SRGAP2A protein levels in a proteasome-dependent manner. SRGAP2C-specific arginine substitutions (non-synonymous mutations) enable it to uniquely induce long-lasting increases in both excitatory and inhibitory synapse density and protracted synapse maturation throughout adulthood, unlike SRGAP2B.","method":"Co-immunoprecipitation; proteasome inhibitor experiments; in utero electroporation; spine/synapse density quantification over developmental time course","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — Co-IP, proteasome inhibition rescue, in vivo neuronal expression with quantitative synaptic phenotyping across multiple time points","pmids":["31822692"],"is_preprint":false},{"year":2017,"finding":"SRGAP2A is primarily localized in podocytes where it co-localizes with synaptopodin, and suppresses podocyte motility through inactivation of RhoA and Cdc42 (but not Rac1). Overexpression of SRGAP2A in db/db mice via adenovirus mitigates podocyte injury and proteinuria.","method":"Immunofluorescence co-localization; Western blot; RhoA/Cdc42/Rac1 activity assays; podocyte migration assays; adenoviral overexpression in diabetic mouse model; zebrafish SRGAP2 knockdown","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GTPase activity assays, in vivo rescue experiment, and zebrafish KD with defined phenotype across multiple orthogonal approaches","pmids":["29242313"],"is_preprint":false},{"year":2020,"finding":"Srgap2 acts as a Rac1-specific GAP in osteoclasts, limiting osteoclastogenesis during TNFα-driven inflammation. Conditional knockout of Srgap2 in the myeloid lineage strongly enhances Rac1 activation in osteoclast precursors. Srgap2 also restricts osteoclast expression of the paracrine clastokine SLIT3, which promotes osteoblast differentiation.","method":"Myeloid-specific conditional knockout (Srgap2 f/f:LysM-Cre); Rac1 activation assays; in vitro osteoclastogenesis; bone histomorphometry; conditioned medium experiments; Western blot","journal":"Journal of bone and mineral research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO model with Rac1 activity assay, in vitro and in vivo phenotyping, and mechanistic pathway identification across multiple orthogonal methods","pmids":["31880824"],"is_preprint":false},{"year":2022,"finding":"srGAP2 acts to deactivate RhoA signaling after thrombin-induced endothelial contraction, allowing cell respreading and restoration of the endothelial barrier. Depletion of srGAP2 increases the magnitude and duration of junctional opening in response to thrombin, TNFα, and angiotensin II. srGAP2 is not required for basal barrier function in resting endothelial cells.","method":"srGAP2 knockdown in endothelial cells; transendothelial electrical resistance measurements; RhoA activity assays; pharmacological perturbations","journal":"Vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KD with defined barrier phenotype and RhoA activity measurement, single lab, single study","pmids":["35441126"],"is_preprint":false},{"year":2022,"finding":"SRGAP2 physically interacts with mitochondrial complex I in colorectal cancer cells and positively modulates its activity. Loss of mitochondrial SRGAP2 decreases mitochondrial respiration and sensitizes CRC cells to chemotherapy, phenocopied by complex I inhibitor treatment.","method":"Co-immunoprecipitation of SRGAP2 with mitochondrial complex I; mitochondrial fractionation; mitochondrial respiration assays; SRGAP2 knockdown; chemosensitivity assays","journal":"Human cell","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — Co-IP and functional respiration assay with KD phenotype, single lab, no mutagenesis or structural validation","pmids":["36059022"],"is_preprint":false},{"year":2023,"finding":"srGAP2 undergoes PKCα-mediated phosphorylation at Ser206 within the F-BAR domain in response to stiff extracellular matrix signals transduced by the mechanoreceptor Syndecan-4 (SDC4). This phosphorylation generates tension gradients within srGAP2 across the cell (higher tension at leading edge), directing persistent cell migration along stiffness gradients (durotaxis) in triple-negative breast cancer cells.","method":"srGAP2 tension FRET probe; phosphomimetic/phosphodeficient mutagenesis (Ser206); Transwell invasion assays; xenograft mouse model; membrane protein fractionation; fluorescence imaging","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FRET tension probe with mutagenesis and in vivo xenograft, multiple orthogonal methods, single lab","pmids":["36593959"],"is_preprint":false},{"year":2024,"finding":"SRGAP2A and its human-specific paralogs SRGAP2B/C are expressed in human microglia. SRGAP2B/C are necessary and sufficient (cell-autonomously) to induce neotenic features of microglial structural and functional maturation, and this neoteny non-cell-autonomously impacts synaptic development in cortical pyramidal neurons.","method":"Xenotransplantation of hiPSC-derived microglia into mouse cortex; mouse genetic models (KD/KO); morphological and functional maturation assays of microglia","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — xenotransplantation with KD/KO and defined cellular phenotype, preprint, single lab","pmids":["38979266"],"is_preprint":true},{"year":2024,"finding":"SRGAP2A levels at synapses are reduced by SRGAP2B/C, leading to increased postsynaptic accumulation of SYNGAP1. The tempo of synaptogenesis is set by reciprocal antagonism between SRGAP2A and SYNGAP1, and this balance is tipped toward neoteny in human cortical pyramidal neurons by SRGAP2B/C.","method":"Human cortical pyramidal neurons xenotransplanted into mouse cortex; combinatorial loss-of-function (SRGAP2A, SYNGAP1, SRGAP2B/C); synaptic density and maturation quantification; Western blot for synaptic protein levels","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Moderate — in vivo xenotransplantation with combinatorial genetic LOF and protein-level measurements, multiple orthogonal approaches, peer-reviewed","pmids":["39406239"],"is_preprint":false},{"year":2013,"finding":"srGAP2 inhibits neuronal differentiation and neurite outgrowth through interaction with srGAP3; the isolated F-BAR domain of srGAP2 (but not srGAP1 or srGAP3 F-BAR) can promote VPA-induced neurite initiation. Knockdown of endogenous srGAP2 promotes neurite outgrowth in differentiated cells without facilitating initial neuronal differentiation.","method":"srGAP2 knockdown and overexpression in mouse Neuro2a cells; RhoGAP-defective mutant expression; GAP-domain point mutants; co-immunoprecipitation of srGAP family interactions","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — KD/OE with domain dissection and Co-IP, multiple approaches but in neuroblastoma cell line, single lab","pmids":["23505444"],"is_preprint":false}],"current_model":"SRGAP2A is a multidomain protein (F-BAR/IF-BAR, RhoGAP, SH3) that uses its inverse F-BAR domain to sense and scaffold membrane protrusions, inhibits Rac1 (and RhoA/Cdc42 in some contexts) via its GAP domain to restrain cell migration and cytoskeletal dynamics, forms homodimers through F-BAR/Fx/RhoGAP-SH3 interfaces, interacts via its SH3 domain with partners including FMNL1 to inhibit actin severing, is arginine-methylated by PRMT5 at Arg-927 to control dimerization and membrane targeting, and is antagonized by human-specific truncated paralogs SRGAP2B/C that heterodimerize with SRGAP2A, reducing its levels via proteasomal degradation to increase synaptic density and prolong synapse maturation—thereby contributing to human-specific neoteny in cortical neurons and microglia."},"narrative":{"mechanistic_narrative":"SRGAP2 (SRGAP2A) is a multidomain Rho-family GAP that couples membrane geometry sensing to local control of cytoskeletal dynamics, restraining cell motility and shaping neuronal architecture [PMID:19737524, PMID:26439400]. Its inverse F-BAR domain senses and deforms membrane to induce filopodia-like protrusions and pre-localizes the protein to protruding edges, while the RhoGAP domain terminates small-GTPase signaling—primarily Rac1 in migrating cells and contact protrusions, and RhoA/Cdc42 in other cell types—to limit protrusion duration and migration [PMID:19737524, PMID:26439400, PMID:29242313, PMID:35441126]. SRGAP2A homodimerizes through an extended interface spanning the F-BAR, a newly defined F-BAR extension (Fx) domain, and RhoGAP-SH3 domains, adopting an unusual inverse geometry suited to scaffolding membrane protrusions in lamellipodia and dendritic spine heads [PMID:28333212]. Through its SH3 domain it engages partners such as the formin FMNL1, inhibiting FMNL1-mediated actin severing while also being recruited to terminate Rac signaling at the phagocytic cup [PMID:21148482]. SRGAP2A activity is tuned by post-translational modification: PRMT5-mediated arginine methylation at Arg-927 controls F-BAR-dependent homodimerization and leading-edge membrane localization [PMID:20810653], and PKCα-mediated phosphorylation at Ser206 transduces ECM stiffness signals into tension gradients that direct durotaxis [PMID:36593959]. In the human lineage, the truncated paralogs SRGAP2B/C heterodimerize with SRGAP2A and—being intrinsically unstable—reduce its levels through proteasomal degradation; SRGAP2C-specific arginine substitutions and a functional Fx domain make it a more effective inhibitor that drives increased synapse density and protracted synaptic maturation (neoteny) in human cortical neurons and microglia, in part by raising postsynaptic SYNGAP1 against which SRGAP2A reciprocally antagonizes [PMID:22559944, PMID:28333212, PMID:31822692, PMID:39406239]. Across non-neuronal contexts SRGAP2 functions broadly as a brake on GTPase-driven remodeling—restraining podocyte motility, osteoclastogenesis, and endothelial barrier opening [PMID:29242313, PMID:31880824, PMID:35441126].","teleology":[{"year":2009,"claim":"Established the founding function of srGAP2: its F-BAR domain deforms membrane to generate filopodia and the protein acts as a negative regulator of neuronal migration while promoting neurite branching.","evidence":"In utero electroporation knockdown/overexpression in mouse neocortex plus in vitro membrane deformation assays","pmids":["19737524"],"confidence":"High","gaps":["Did not define which GTPase the GAP domain targets in this context","Membrane curvature sensing versus generation not structurally resolved"]},{"year":2010,"claim":"Connected srGAP2 to a specific actin effector, showing SH3-domain binding to FMNL1 inhibits actin severing and that Rac-activated FMNL1 recruits srGAP2 to terminate Rac signaling at the phagocytic cup.","evidence":"Co-IP, in vitro actin severing assays, and domain mapping in macrophage-derived cells","pmids":["21148482"],"confidence":"High","gaps":["FMNL1 interaction not validated in neurons","Feedback loop kinetics not quantified"]},{"year":2010,"claim":"Identified PRMT5-mediated arginine methylation at Arg-927 as a regulatory switch controlling F-BAR-dependent dimerization and membrane targeting, linking a post-translational modification to localization and cell spreading.","evidence":"Co-IP, R927A site-directed mutagenesis, localization, and cell-spreading rescue assays","pmids":["20810653"],"confidence":"High","gaps":["Physiological stimuli regulating methylation unknown","Effect on GAP activity not tested"]},{"year":2012,"claim":"Defined the human-specific paralog mechanism: SRGAP2C dimerizes with SRGAP2A to inhibit it, phenocopying SRGAP2 deficiency and producing synaptic neoteny.","evidence":"Reciprocal Co-IP and in utero electroporation of SRGAP2C/shRNA with spine morphology analysis in mouse neocortex","pmids":["22559944"],"confidence":"High","gaps":["Structural basis of inhibitory heterodimer not resolved at this stage","Mechanism reducing SRGAP2A function not yet defined as degradation"]},{"year":2012,"claim":"Distinguished the membrane-deformation properties of the three srGAP F-BAR paralogs and showed they heterodimerize and act synergistically, and that F-BAR(2) binds anionic phospholipids broadly.","evidence":"Expression in COS7/cortical neurons, FRAP, phosphoinositide depletion, lipid-binding assays, and Co-IP","pmids":["22467852"],"confidence":"High","gaps":["Functional consequence of srGAP1/2/3 heterodimers in vivo unclear","Lipid specificity determinants not mapped"]},{"year":2013,"claim":"Showed srGAP2 inhibits neurite outgrowth via interaction with srGAP3 and that the F-BAR domain alone is sufficient for some effects, refining its role in neuronal differentiation.","evidence":"Knockdown/overexpression, GAP-domain point mutants, and Co-IP in Neuro2a cells","pmids":["23505444"],"confidence":"Medium","gaps":["Conducted in a neuroblastoma cell line rather than primary neurons","Separation of differentiation versus outgrowth effects incomplete"]},{"year":2015,"claim":"Resolved the SH3-domain ligand-binding logic, explaining how weak isolated affinity is converted into specific partner selection through a two-component tightening/autoinhibition mechanism.","evidence":"Structural analysis, mutagenesis, and binding affinity measurements","pmids":["26365803"],"confidence":"Medium","gaps":["Specific physiological ligands governed by this mechanism not enumerated","Full method detail not specified in abstract"]},{"year":2015,"claim":"Placed srGAP2 in the Slit2-Robo4 axis controlling contact inhibition of locomotion, showing F-BAR curvature sensing pre-localizes srGAP2 to terminate Rac1 activity specifically in contact protrusions.","evidence":"FRET Rac1 biosensor, knockdown, F-BAR overexpression, and live imaging of cell collisions in fibroblasts","pmids":["26439400"],"confidence":"High","gaps":["How Robo4 engages srGAP2 molecularly not defined","Selectivity for contact versus contact-free protrusions mechanistically unexplained"]},{"year":2017,"claim":"Provided the structural basis for dimerization and human-specific inhibition: a crystal structure revealed the F-BAR/Fx/RhoGAP-SH3 dimer interface and inverse geometry, and showed SRGAP2C's defective Fx domain makes SRGAP2A:SRGAP2C heterodimers insoluble, inhibiting SRGAP2A.","evidence":"X-ray crystallography with biochemical reconstitution and dimerization/solubility assays","pmids":["28333212"],"confidence":"High","gaps":["In-cell consequences of insoluble heterodimers not directly imaged","Membrane-bound conformation not captured"]},{"year":2017,"claim":"Extended the GAP function beyond neurons, showing SRGAP2A restrains podocyte motility via RhoA/Cdc42 (not Rac1) inactivation and protects against diabetic podocyte injury.","evidence":"Co-localization with synaptopodin, GTPase activity assays, podocyte migration, adenoviral rescue in db/db mice, and zebrafish knockdown","pmids":["29242313"],"confidence":"Medium","gaps":["GTPase selectivity switch (RhoA/Cdc42 vs Rac1) across cell types unexplained","Direct GAP activity on RhoA/Cdc42 not biochemically isolated"]},{"year":2019,"claim":"Defined the degradative mechanism of paralog antagonism: unstable SRGAP2B/C reduce SRGAP2A protein via the proteasome upon heterodimerization, and SRGAP2C-specific arginine substitutions confer uniquely durable synaptic neoteny.","evidence":"Co-IP, proteasome inhibitor rescue, and in utero electroporation with synaptic density time courses","pmids":["31822692"],"confidence":"High","gaps":["E3 ligase mediating SRGAP2A degradation unidentified","Why SRGAP2C but not SRGAP2B sustains the effect not fully mechanistic"]},{"year":2020,"claim":"Demonstrated Srgap2 as a Rac1-specific GAP brake on osteoclastogenesis and clastokine SLIT3 expression during inflammation, generalizing its motility/differentiation-restraining role to bone biology.","evidence":"Myeloid conditional knockout, Rac1 activation assays, osteoclastogenesis, bone histomorphometry, and conditioned medium experiments","pmids":["31880824"],"confidence":"High","gaps":["Link between GAP activity and SLIT3 transcriptional control unclear","Whether human paralogs modulate this myeloid role untested"]},{"year":2022,"claim":"Showed srGAP2 deactivates RhoA after agonist-induced endothelial contraction to restore barrier integrity, identifying a vascular role distinct from basal barrier maintenance.","evidence":"Knockdown, transendothelial resistance, RhoA activity assays, and pharmacological perturbations in endothelial cells","pmids":["35441126"],"confidence":"Medium","gaps":["Single-lab study","Recruitment of srGAP2 to junctions after contraction not visualized"]},{"year":2022,"claim":"Reported a non-canonical mitochondrial role, with SRGAP2 interacting with complex I and supporting respiration and chemoresistance in colorectal cancer cells.","evidence":"Co-IP, mitochondrial fractionation, respiration assays, knockdown, and chemosensitivity assays","pmids":["36059022"],"confidence":"Medium","gaps":["No mutagenesis or structural validation of the complex I interaction","How a membrane-deforming GAP localizes to mitochondria unexplained"]},{"year":2023,"claim":"Identified mechanotransduction control of srGAP2: PKCα phosphorylation at Ser206 downstream of SDC4 generates intramolecular tension gradients that direct durotaxis in breast cancer cells.","evidence":"srGAP2 tension FRET probe, Ser206 phosphomimetic/phosphodeficient mutants, invasion assays, and xenografts","pmids":["36593959"],"confidence":"Medium","gaps":["Effect of Ser206 phosphorylation on GAP activity not measured","Single-lab study"]},{"year":2024,"claim":"Extended human-specific neoteny beyond neurons to microglia, showing SRGAP2B/C are necessary and sufficient cell-autonomously for microglial maturation neoteny and non-cell-autonomously affect cortical synaptic development.","evidence":"Xenotransplantation of hiPSC-derived microglia plus mouse KD/KO and maturation assays (preprint)","pmids":["38979266"],"confidence":"Medium","gaps":["Preprint, single lab","Molecular target of paralog action in microglia not defined"]},{"year":2024,"claim":"Defined a molecular partner for setting synaptogenic tempo: SRGAP2B/C reduce synaptic SRGAP2A, increasing postsynaptic SYNGAP1, and reciprocal SRGAP2A-SYNGAP1 antagonism is tipped toward neoteny in human neurons.","evidence":"Xenotransplanted human cortical neurons with combinatorial LOF (SRGAP2A, SYNGAP1, SRGAP2B/C) and synaptic protein quantification","pmids":["39406239"],"confidence":"High","gaps":["Direct physical/biochemical link between SRGAP2A and SYNGAP1 not established","Whether antagonism is competitive at a shared site unknown"]},{"year":null,"claim":"How SRGAP2A's GTPase selectivity (Rac1 vs RhoA/Cdc42) is switched across cell types, and the identity of the E3 ligase driving paralog-induced SRGAP2A degradation, remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mechanism reconciling Rac1-specific versus RhoA/Cdc42-directed GAP activity","Degradation machinery for SRGAP2A unidentified","Mitochondrial localization mechanism unexplained"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,9,10,11,16]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,4]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[4]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[5,13]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[3,4,5,7]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,7]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[12]}],"pathway":[],"complexes":["SRGAP2A homodimer","SRGAP2A:SRGAP2C heterodimer","SRGAP2A:SRGAP2B heterodimer"],"partners":["SRGAP2C","SRGAP2B","FMNL1","SRGAP3","PRMT5","SYNGAP1","ROBO4","SDC4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75044","full_name":"SLIT-ROBO Rho GTPase-activating protein 2","aliases":["Formin-binding protein 2","Rho GTPase-activating protein 34"],"length_aa":1071,"mass_kda":120.9,"function":"Postsynaptic RAC1 GTPase activating protein (GAP) that plays a key role in neuronal morphogenesis and migration mainly during development of the cerebral cortex (PubMed:20810653, PubMed:27373832, PubMed:28333212). Regulates excitatory and inhibitory synapse maturation and density in cortical pyramidal neurons (PubMed:22559944, PubMed:27373832). SRGAP2/SRGAP2A limits excitatory and inhibitory synapse density through its RAC1-specific GTPase activating activity, while it promotes maturation of both excitatory and inhibitory synapses through its ability to bind to the postsynaptic scaffolding protein HOMER1 at excitatory synapses, and the postsynaptic protein GPHN at inhibitory synapses (By similarity). Mechanistically, acts by binding and deforming membranes, thereby regulating actin dynamics to regulate cell migration and differentiation (PubMed:27373832). Promotes cell repulsion and contact inhibition of locomotion: localizes to protrusions with curved edges and controls the duration of RAC1 activity in contact protrusions (By similarity). In non-neuronal cells, may also play a role in cell migration by regulating the formation of lamellipodia and filopodia (PubMed:20810653, PubMed:21148482)","subcellular_location":"Cell membrane; Cell projection, dendritic spine; Postsynaptic density; Postsynaptic cell membrane; Cell projection, lamellipodium; Cytoplasmic vesicle, phagosome; Nucleus; Cytoplasm, cytosol","url":"https://www.uniprot.org/uniprotkb/O75044/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SRGAP2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":74,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CALD1","stoichiometry":0.2},{"gene":"CALM3","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/SRGAP2","total_profiled":1310},"omim":[{"mim_id":"617555","title":"FCH AND DOUBLE SH3 DOMAINS PROTEIN 1; FCHSD1","url":"https://www.omim.org/entry/617555"},{"mim_id":"616853","title":"FAMILY WITH SEQUENCE SIMILARITY 72, MEMBER C: FAM72C","url":"https://www.omim.org/entry/616853"},{"mim_id":"616771","title":"MICRO RNA 218-2; MIR218-2","url":"https://www.omim.org/entry/616771"},{"mim_id":"616770","title":"MICRO RNA 218-1; MIR218-1","url":"https://www.omim.org/entry/616770"},{"mim_id":"614712","title":"FAMILY WITH SEQUENCE SIMILARITY 72, MEMBER D; FAM72D","url":"https://www.omim.org/entry/614712"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Cytosol","reliability":"Uncertain"},{"location":"Centrosome","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":122.7}],"url":"https://www.proteinatlas.org/search/SRGAP2"},"hgnc":{"alias_symbol":["KIAA0456","ARHGAP34","SRGAP2A"],"prev_symbol":["FNBP2"]},"alphafold":{"accession":"O75044","domains":[{"cath_id":"1.20.1270.60","chopping":"13-81_90-196_221-295","consensus_level":"medium","plddt":92.2008,"start":13,"end":295},{"cath_id":"-","chopping":"359-403_432-481","consensus_level":"medium","plddt":91.8184,"start":359,"end":481},{"cath_id":"1.10.555.10","chopping":"506-677","consensus_level":"medium","plddt":89.6703,"start":506,"end":677},{"cath_id":"2.30.30.40","chopping":"730-783","consensus_level":"high","plddt":91.0102,"start":730,"end":783}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75044","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75044-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75044-F1-predicted_aligned_error_v6.png","plddt_mean":71.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SRGAP2","jax_strain_url":"https://www.jax.org/strain/search?query=SRGAP2"},"sequence":{"accession":"O75044","fasta_url":"https://rest.uniprot.org/uniprotkb/O75044.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75044/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75044"}},"corpus_meta":[{"pmid":"22559944","id":"PMC_22559944","title":"Inhibition 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In mouse neocortex, SRGAP2A promotes spine maturation and limits spine density; expression of SRGAP2C phenocopies SRGAP2 deficiency, leading to increased density of longer, less mature spines (neoteny) and sustained radial migration.\",\n      \"method\": \"Co-immunoprecipitation of SRGAP2C with SRGAP2A; in utero electroporation of SRGAP2C or SRGAP2 shRNA in mouse neocortex; spine morphology analysis\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP demonstrating dimerization, plus KD and SRGAP2C expression with defined synaptic and migratory phenotypes, replicated by multiple labs\",\n      \"pmids\": [\"22559944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"srGAP2 forms a complex with the formin FMNL1 (FRL1/FRLα); Rac-mediated activation of FMNL1 recruits srGAP2, whose Rac-specific GAP domain then terminates Rac signaling; additionally, the SH3 domain of srGAP2 binds the FH1 domain of FMNL1 to directly inhibit FMNL1-mediated actin severing. Both proteins co-localize to the phagocytic cup.\",\n      \"method\": \"Co-immunoprecipitation; in vitro actin severing assays; domain mapping; fluorescence microscopy in macrophage-derived cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro actin severing assay plus Co-IP domain mapping and co-localization, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"21148482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"srGAP2 is arginine-methylated at Arg-927 by PRMT5, which binds to the N-terminal region (aa 225–538) of srGAP2. The R927A methylation mutant fails to localize to the plasma membrane leading edge, cannot rescue cell spreading, and disrupts F-BAR domain-mediated srGAP2 homodimerization, linking arginine methylation to membrane localization and cell spreading.\",\n      \"method\": \"Co-immunoprecipitation; domain mapping; site-directed mutagenesis (R927A); subcellular fractionation/fluorescence localization; cell spreading assays with rescue experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, mutagenesis, functional rescue, and localization assays combined in one study, multiple orthogonal methods\",\n      \"pmids\": [\"20810653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The F-BAR domains of srGAP1, srGAP2, and srGAP3 have distinct membrane deformation properties; F-BAR(2) (srGAP2) and F-BAR(3) induce filopodia while F-BAR(1) prevents filopodia in cortical neurons. The three F-BAR domains can heterodimerize and act synergistically in filopodia induction. F-BAR(2) membrane dynamics are partially dependent on F-actin. F-BAR(2) binds negatively charged phospholipids including PtdSer broadly, and PtdIns(4,5)P2 depletion does not displace it from the membrane.\",\n      \"method\": \"Expression in COS7 cells and cortical neurons; FRAP; phosphoinositide depletion; phospholipid-binding assays; Co-immunoprecipitation of heterodimerization\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (FRAP, lipid-binding, co-IP, KD) in a single rigorous study with functional readouts\",\n      \"pmids\": [\"22467852\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The Slit2-Robo4-srGAP2 signaling axis regulates contact inhibition of locomotion (CIL) in fibroblasts. The srGAP2 F-BAR domain senses membrane curvature to pre-localize srGAP2 to protruding edges, and srGAP2 specifically controls the duration of Rac1 activity in contact protrusions (but not contact-free protrusions) to terminate their extension after cell collision.\",\n      \"method\": \"FRET-based Rac1 biosensor; srGAP2 knockdown; F-BAR domain overexpression; live-cell imaging of collision events; Slit2/Robo4 perturbations\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRET biosensor plus KD with specific cellular phenotype (Rac1 dynamics), multiple orthogonal approaches in single rigorous study\",\n      \"pmids\": [\"26439400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"srGAP2 uses a two-component molecular mechanism for ligand binding through its SH3 domain: one component dramatically tightens ligand association, the other moderately autoinhibits and restricts binding, achieving specificity despite weak isolated SH3-ligand affinity.\",\n      \"method\": \"Structural analysis; mutagenesis; binding affinity measurements (likely ITC/SPR inferred from structural study context)\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Weak — structural/mutagenesis study from single lab; abstract does not detail all methods explicitly\",\n      \"pmids\": [\"26365803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SRGAP2A crystal structure reveals: (1) it homodimerizes through a large interface comprising the F-BAR domain, a newly identified F-BAR extension (Fx) domain, and RhoGAP-SH3 domains; (2) it has an unusual inverse geometry enabling membrane protrusion scaffolding in lamellipodia and dendritic spine heads; (3) SRGAP2C carries a defective Fx domain that severely compromises its solubility and membrane-scaffolding ability; (4) SRGAP2A:SRGAP2C heterodimers form but are insoluble, thereby inhibiting SRGAP2A activity; (5) the primal SRGAP2C (~3.4 Ma) is less effective at heterodimerizing with SRGAP2A than modern SRGAP2C.\",\n      \"method\": \"X-ray crystallography; biochemical reconstitution; cell culture expression assays; dimerization/solubility assays\",\n      \"journal\": \"Molecular biology and evolution\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with biochemical reconstitution and functional cell assays; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"28333212\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SRGAP2C and SRGAP2B are intrinsically unstable proteins in neurons; upon heterodimerization with SRGAP2A they reduce SRGAP2A protein levels in a proteasome-dependent manner. SRGAP2C-specific arginine substitutions (non-synonymous mutations) enable it to uniquely induce long-lasting increases in both excitatory and inhibitory synapse density and protracted synapse maturation throughout adulthood, unlike SRGAP2B.\",\n      \"method\": \"Co-immunoprecipitation; proteasome inhibitor experiments; in utero electroporation; spine/synapse density quantification over developmental time course\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, proteasome inhibition rescue, in vivo neuronal expression with quantitative synaptic phenotyping across multiple time points\",\n      \"pmids\": [\"31822692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SRGAP2A is primarily localized in podocytes where it co-localizes with synaptopodin, and suppresses podocyte motility through inactivation of RhoA and Cdc42 (but not Rac1). Overexpression of SRGAP2A in db/db mice via adenovirus mitigates podocyte injury and proteinuria.\",\n      \"method\": \"Immunofluorescence co-localization; Western blot; RhoA/Cdc42/Rac1 activity assays; podocyte migration assays; adenoviral overexpression in diabetic mouse model; zebrafish SRGAP2 knockdown\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GTPase activity assays, in vivo rescue experiment, and zebrafish KD with defined phenotype across multiple orthogonal approaches\",\n      \"pmids\": [\"29242313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Srgap2 acts as a Rac1-specific GAP in osteoclasts, limiting osteoclastogenesis during TNFα-driven inflammation. Conditional knockout of Srgap2 in the myeloid lineage strongly enhances Rac1 activation in osteoclast precursors. Srgap2 also restricts osteoclast expression of the paracrine clastokine SLIT3, which promotes osteoblast differentiation.\",\n      \"method\": \"Myeloid-specific conditional knockout (Srgap2 f/f:LysM-Cre); Rac1 activation assays; in vitro osteoclastogenesis; bone histomorphometry; conditioned medium experiments; Western blot\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO model with Rac1 activity assay, in vitro and in vivo phenotyping, and mechanistic pathway identification across multiple orthogonal methods\",\n      \"pmids\": [\"31880824\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"srGAP2 acts to deactivate RhoA signaling after thrombin-induced endothelial contraction, allowing cell respreading and restoration of the endothelial barrier. Depletion of srGAP2 increases the magnitude and duration of junctional opening in response to thrombin, TNFα, and angiotensin II. srGAP2 is not required for basal barrier function in resting endothelial cells.\",\n      \"method\": \"srGAP2 knockdown in endothelial cells; transendothelial electrical resistance measurements; RhoA activity assays; pharmacological perturbations\",\n      \"journal\": \"Vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KD with defined barrier phenotype and RhoA activity measurement, single lab, single study\",\n      \"pmids\": [\"35441126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SRGAP2 physically interacts with mitochondrial complex I in colorectal cancer cells and positively modulates its activity. Loss of mitochondrial SRGAP2 decreases mitochondrial respiration and sensitizes CRC cells to chemotherapy, phenocopied by complex I inhibitor treatment.\",\n      \"method\": \"Co-immunoprecipitation of SRGAP2 with mitochondrial complex I; mitochondrial fractionation; mitochondrial respiration assays; SRGAP2 knockdown; chemosensitivity assays\",\n      \"journal\": \"Human cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — Co-IP and functional respiration assay with KD phenotype, single lab, no mutagenesis or structural validation\",\n      \"pmids\": [\"36059022\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"srGAP2 undergoes PKCα-mediated phosphorylation at Ser206 within the F-BAR domain in response to stiff extracellular matrix signals transduced by the mechanoreceptor Syndecan-4 (SDC4). This phosphorylation generates tension gradients within srGAP2 across the cell (higher tension at leading edge), directing persistent cell migration along stiffness gradients (durotaxis) in triple-negative breast cancer cells.\",\n      \"method\": \"srGAP2 tension FRET probe; phosphomimetic/phosphodeficient mutagenesis (Ser206); Transwell invasion assays; xenograft mouse model; membrane protein fractionation; fluorescence imaging\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRET tension probe with mutagenesis and in vivo xenograft, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"36593959\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SRGAP2A and its human-specific paralogs SRGAP2B/C are expressed in human microglia. SRGAP2B/C are necessary and sufficient (cell-autonomously) to induce neotenic features of microglial structural and functional maturation, and this neoteny non-cell-autonomously impacts synaptic development in cortical pyramidal neurons.\",\n      \"method\": \"Xenotransplantation of hiPSC-derived microglia into mouse cortex; mouse genetic models (KD/KO); morphological and functional maturation assays of microglia\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — xenotransplantation with KD/KO and defined cellular phenotype, preprint, single lab\",\n      \"pmids\": [\"38979266\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SRGAP2A levels at synapses are reduced by SRGAP2B/C, leading to increased postsynaptic accumulation of SYNGAP1. The tempo of synaptogenesis is set by reciprocal antagonism between SRGAP2A and SYNGAP1, and this balance is tipped toward neoteny in human cortical pyramidal neurons by SRGAP2B/C.\",\n      \"method\": \"Human cortical pyramidal neurons xenotransplanted into mouse cortex; combinatorial loss-of-function (SRGAP2A, SYNGAP1, SRGAP2B/C); synaptic density and maturation quantification; Western blot for synaptic protein levels\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo xenotransplantation with combinatorial genetic LOF and protein-level measurements, multiple orthogonal approaches, peer-reviewed\",\n      \"pmids\": [\"39406239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"srGAP2 inhibits neuronal differentiation and neurite outgrowth through interaction with srGAP3; the isolated F-BAR domain of srGAP2 (but not srGAP1 or srGAP3 F-BAR) can promote VPA-induced neurite initiation. Knockdown of endogenous srGAP2 promotes neurite outgrowth in differentiated cells without facilitating initial neuronal differentiation.\",\n      \"method\": \"srGAP2 knockdown and overexpression in mouse Neuro2a cells; RhoGAP-defective mutant expression; GAP-domain point mutants; co-immunoprecipitation of srGAP family interactions\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — KD/OE with domain dissection and Co-IP, multiple approaches but in neuroblastoma cell line, single lab\",\n      \"pmids\": [\"23505444\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SRGAP2A is a multidomain protein (F-BAR/IF-BAR, RhoGAP, SH3) that uses its inverse F-BAR domain to sense and scaffold membrane protrusions, inhibits Rac1 (and RhoA/Cdc42 in some contexts) via its GAP domain to restrain cell migration and cytoskeletal dynamics, forms homodimers through F-BAR/Fx/RhoGAP-SH3 interfaces, interacts via its SH3 domain with partners including FMNL1 to inhibit actin severing, is arginine-methylated by PRMT5 at Arg-927 to control dimerization and membrane targeting, and is antagonized by human-specific truncated paralogs SRGAP2B/C that heterodimerize with SRGAP2A, reducing its levels via proteasomal degradation to increase synaptic density and prolong synapse maturation—thereby contributing to human-specific neoteny in cortical neurons and microglia.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SRGAP2 (SRGAP2A) is a multidomain Rho-family GAP that couples membrane geometry sensing to local control of cytoskeletal dynamics, restraining cell motility and shaping neuronal architecture [#0, #5]. Its inverse F-BAR domain senses and deforms membrane to induce filopodia-like protrusions and pre-localizes the protein to protruding edges, while the RhoGAP domain terminates small-GTPase signaling—primarily Rac1 in migrating cells and contact protrusions, and RhoA/Cdc42 in other cell types—to limit protrusion duration and migration [#0, #5, #9, #11]. SRGAP2A homodimerizes through an extended interface spanning the F-BAR, a newly defined F-BAR extension (Fx) domain, and RhoGAP-SH3 domains, adopting an unusual inverse geometry suited to scaffolding membrane protrusions in lamellipodia and dendritic spine heads [#7]. Through its SH3 domain it engages partners such as the formin FMNL1, inhibiting FMNL1-mediated actin severing while also being recruited to terminate Rac signaling at the phagocytic cup [#2]. SRGAP2A activity is tuned by post-translational modification: PRMT5-mediated arginine methylation at Arg-927 controls F-BAR-dependent homodimerization and leading-edge membrane localization [#3], and PKCα-mediated phosphorylation at Ser206 transduces ECM stiffness signals into tension gradients that direct durotaxis [#13]. In the human lineage, the truncated paralogs SRGAP2B/C heterodimerize with SRGAP2A and—being intrinsically unstable—reduce its levels through proteasomal degradation; SRGAP2C-specific arginine substitutions and a functional Fx domain make it a more effective inhibitor that drives increased synapse density and protracted synaptic maturation (neoteny) in human cortical neurons and microglia, in part by raising postsynaptic SYNGAP1 against which SRGAP2A reciprocally antagonizes [#1, #7, #8, #15]. Across non-neuronal contexts SRGAP2 functions broadly as a brake on GTPase-driven remodeling—restraining podocyte motility, osteoclastogenesis, and endothelial barrier opening [#9, #10, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"Established the founding function of srGAP2: its F-BAR domain deforms membrane to generate filopodia and the protein acts as a negative regulator of neuronal migration while promoting neurite branching.\",\n      \"evidence\": \"In utero electroporation knockdown/overexpression in mouse neocortex plus in vitro membrane deformation assays\",\n      \"pmids\": [\"19737524\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which GTPase the GAP domain targets in this context\", \"Membrane curvature sensing versus generation not structurally resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected srGAP2 to a specific actin effector, showing SH3-domain binding to FMNL1 inhibits actin severing and that Rac-activated FMNL1 recruits srGAP2 to terminate Rac signaling at the phagocytic cup.\",\n      \"evidence\": \"Co-IP, in vitro actin severing assays, and domain mapping in macrophage-derived cells\",\n      \"pmids\": [\"21148482\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"FMNL1 interaction not validated in neurons\", \"Feedback loop kinetics not quantified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified PRMT5-mediated arginine methylation at Arg-927 as a regulatory switch controlling F-BAR-dependent dimerization and membrane targeting, linking a post-translational modification to localization and cell spreading.\",\n      \"evidence\": \"Co-IP, R927A site-directed mutagenesis, localization, and cell-spreading rescue assays\",\n      \"pmids\": [\"20810653\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological stimuli regulating methylation unknown\", \"Effect on GAP activity not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined the human-specific paralog mechanism: SRGAP2C dimerizes with SRGAP2A to inhibit it, phenocopying SRGAP2 deficiency and producing synaptic neoteny.\",\n      \"evidence\": \"Reciprocal Co-IP and in utero electroporation of SRGAP2C/shRNA with spine morphology analysis in mouse neocortex\",\n      \"pmids\": [\"22559944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of inhibitory heterodimer not resolved at this stage\", \"Mechanism reducing SRGAP2A function not yet defined as degradation\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Distinguished the membrane-deformation properties of the three srGAP F-BAR paralogs and showed they heterodimerize and act synergistically, and that F-BAR(2) binds anionic phospholipids broadly.\",\n      \"evidence\": \"Expression in COS7/cortical neurons, FRAP, phosphoinositide depletion, lipid-binding assays, and Co-IP\",\n      \"pmids\": [\"22467852\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of srGAP1/2/3 heterodimers in vivo unclear\", \"Lipid specificity determinants not mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed srGAP2 inhibits neurite outgrowth via interaction with srGAP3 and that the F-BAR domain alone is sufficient for some effects, refining its role in neuronal differentiation.\",\n      \"evidence\": \"Knockdown/overexpression, GAP-domain point mutants, and Co-IP in Neuro2a cells\",\n      \"pmids\": [\"23505444\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Conducted in a neuroblastoma cell line rather than primary neurons\", \"Separation of differentiation versus outgrowth effects incomplete\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved the SH3-domain ligand-binding logic, explaining how weak isolated affinity is converted into specific partner selection through a two-component tightening/autoinhibition mechanism.\",\n      \"evidence\": \"Structural analysis, mutagenesis, and binding affinity measurements\",\n      \"pmids\": [\"26365803\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific physiological ligands governed by this mechanism not enumerated\", \"Full method detail not specified in abstract\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Placed srGAP2 in the Slit2-Robo4 axis controlling contact inhibition of locomotion, showing F-BAR curvature sensing pre-localizes srGAP2 to terminate Rac1 activity specifically in contact protrusions.\",\n      \"evidence\": \"FRET Rac1 biosensor, knockdown, F-BAR overexpression, and live imaging of cell collisions in fibroblasts\",\n      \"pmids\": [\"26439400\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Robo4 engages srGAP2 molecularly not defined\", \"Selectivity for contact versus contact-free protrusions mechanistically unexplained\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Provided the structural basis for dimerization and human-specific inhibition: a crystal structure revealed the F-BAR/Fx/RhoGAP-SH3 dimer interface and inverse geometry, and showed SRGAP2C's defective Fx domain makes SRGAP2A:SRGAP2C heterodimers insoluble, inhibiting SRGAP2A.\",\n      \"evidence\": \"X-ray crystallography with biochemical reconstitution and dimerization/solubility assays\",\n      \"pmids\": [\"28333212\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In-cell consequences of insoluble heterodimers not directly imaged\", \"Membrane-bound conformation not captured\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended the GAP function beyond neurons, showing SRGAP2A restrains podocyte motility via RhoA/Cdc42 (not Rac1) inactivation and protects against diabetic podocyte injury.\",\n      \"evidence\": \"Co-localization with synaptopodin, GTPase activity assays, podocyte migration, adenoviral rescue in db/db mice, and zebrafish knockdown\",\n      \"pmids\": [\"29242313\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GTPase selectivity switch (RhoA/Cdc42 vs Rac1) across cell types unexplained\", \"Direct GAP activity on RhoA/Cdc42 not biochemically isolated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the degradative mechanism of paralog antagonism: unstable SRGAP2B/C reduce SRGAP2A protein via the proteasome upon heterodimerization, and SRGAP2C-specific arginine substitutions confer uniquely durable synaptic neoteny.\",\n      \"evidence\": \"Co-IP, proteasome inhibitor rescue, and in utero electroporation with synaptic density time courses\",\n      \"pmids\": [\"31822692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase mediating SRGAP2A degradation unidentified\", \"Why SRGAP2C but not SRGAP2B sustains the effect not fully mechanistic\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Demonstrated Srgap2 as a Rac1-specific GAP brake on osteoclastogenesis and clastokine SLIT3 expression during inflammation, generalizing its motility/differentiation-restraining role to bone biology.\",\n      \"evidence\": \"Myeloid conditional knockout, Rac1 activation assays, osteoclastogenesis, bone histomorphometry, and conditioned medium experiments\",\n      \"pmids\": [\"31880824\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Link between GAP activity and SLIT3 transcriptional control unclear\", \"Whether human paralogs modulate this myeloid role untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed srGAP2 deactivates RhoA after agonist-induced endothelial contraction to restore barrier integrity, identifying a vascular role distinct from basal barrier maintenance.\",\n      \"evidence\": \"Knockdown, transendothelial resistance, RhoA activity assays, and pharmacological perturbations in endothelial cells\",\n      \"pmids\": [\"35441126\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab study\", \"Recruitment of srGAP2 to junctions after contraction not visualized\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Reported a non-canonical mitochondrial role, with SRGAP2 interacting with complex I and supporting respiration and chemoresistance in colorectal cancer cells.\",\n      \"evidence\": \"Co-IP, mitochondrial fractionation, respiration assays, knockdown, and chemosensitivity assays\",\n      \"pmids\": [\"36059022\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis or structural validation of the complex I interaction\", \"How a membrane-deforming GAP localizes to mitochondria unexplained\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified mechanotransduction control of srGAP2: PKCα phosphorylation at Ser206 downstream of SDC4 generates intramolecular tension gradients that direct durotaxis in breast cancer cells.\",\n      \"evidence\": \"srGAP2 tension FRET probe, Ser206 phosphomimetic/phosphodeficient mutants, invasion assays, and xenografts\",\n      \"pmids\": [\"36593959\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effect of Ser206 phosphorylation on GAP activity not measured\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended human-specific neoteny beyond neurons to microglia, showing SRGAP2B/C are necessary and sufficient cell-autonomously for microglial maturation neoteny and non-cell-autonomously affect cortical synaptic development.\",\n      \"evidence\": \"Xenotransplantation of hiPSC-derived microglia plus mouse KD/KO and maturation assays (preprint)\",\n      \"pmids\": [\"38979266\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, single lab\", \"Molecular target of paralog action in microglia not defined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined a molecular partner for setting synaptogenic tempo: SRGAP2B/C reduce synaptic SRGAP2A, increasing postsynaptic SYNGAP1, and reciprocal SRGAP2A-SYNGAP1 antagonism is tipped toward neoteny in human neurons.\",\n      \"evidence\": \"Xenotransplanted human cortical neurons with combinatorial LOF (SRGAP2A, SYNGAP1, SRGAP2B/C) and synaptic protein quantification\",\n      \"pmids\": [\"39406239\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct physical/biochemical link between SRGAP2A and SYNGAP1 not established\", \"Whether antagonism is competitive at a shared site unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SRGAP2A's GTPase selectivity (Rac1 vs RhoA/Cdc42) is switched across cell types, and the identity of the E3 ligase driving paralog-induced SRGAP2A degradation, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanism reconciling Rac1-specific versus RhoA/Cdc42-directed GAP activity\", \"Degradation machinery for SRGAP2A unidentified\", \"Mitochondrial localization mechanism unexplained\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 9, 10, 11, 16]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [5, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [3, 4, 5, 7]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0007165\", \"supporting_discovery_ids\": [5, 10]}\n    ],\n    \"complexes\": [\n      \"SRGAP2A homodimer\",\n      \"SRGAP2A:SRGAP2C heterodimer\",\n      \"SRGAP2A:SRGAP2B heterodimer\"\n    ],\n    \"partners\": [\n      \"SRGAP2C\",\n      \"SRGAP2B\",\n      \"FMNL1\",\n      \"SRGAP3\",\n      \"PRMT5\",\n      \"SYNGAP1\",\n      \"ROBO4\",\n      \"SDC4\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}