{"gene":"RAB23","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2001,"finding":"Rab23 is an essential negative regulator of the Sonic hedgehog (Shh) signaling pathway, acting downstream of Shh; loss of Rab23 in the open brain (opb) mouse mutant rescues ventral cell types absent in Shh mutants, placing Rab23 genetically downstream of Shh in neural tube patterning.","method":"Genetic epistasis (Shh opb double mutants), map-based cloning of the opb locus","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double mutant rescue, foundational paper replicated extensively","pmids":["11449277"],"is_preprint":false},{"year":2003,"finding":"Rab23 localizes predominantly to the plasma membrane and early endocytic vesicles (colocalizing with Rab5Q79L and internalized transferrin); the constitutively active Q68L mutant shares this distribution while the dominant-negative S23N mutant is cytosolic. Patched colocalizes with intracellular Rab23-GFP vesicles but Smoothened does not, and neither Patched nor Smoothened distribution is altered by Rab23 expression.","method":"Live-cell fluorescence microscopy, immunoelectron microscopy, co-expression with GFP-tagged Rab23 mutants, co-localization with endocytic markers","journal":"Traffic","confidence":"High","confidence_rationale":"Tier 2 — direct localization by light and immunoelectron microscopy with multiple functional mutants and orthogonal markers","pmids":["14617350"],"is_preprint":false},{"year":2005,"finding":"Rab23 acts upstream of Gli transcription factors and downstream of Smoothened in the Shh pathway; double mutant analysis shows the primary target of Rab23 is Gli2 activator function, with additive effects with Gli3 repressor; Rab23 also promotes Gli3 repressor production. Rab23 does not work through Patched or Smoothened.","method":"Genetic epistasis (Rab23/Gli2, Rab23/Gli3, Rab23/Smo double mutants in mouse), Gli3 protein analysis","journal":"Developmental Biology","confidence":"High","confidence_rationale":"Tier 2 — multiple genetic epistasis experiments in mouse, replicated across labs","pmids":["16364285"],"is_preprint":false},{"year":2007,"finding":"RAB23 mutations (truncating and one missense) cause Carpenter syndrome with autosomal recessive inheritance; RAB23 functions as a negative regulator of Hedgehog signaling and is required for cranial suture development, implicating HH signaling in craniosynostosis.","method":"Homozygosity mapping, direct sequencing of RAB23 in 15 families, identification of loss-of-function mutations","journal":"American Journal of Human Genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple independent families with loss-of-function alleles, strong genetic evidence","pmids":["17503333"],"is_preprint":false},{"year":2008,"finding":"Elevated Rab23 expression inhibits chondrogenic differentiation of ATDC5 cells, as shown by retroviral insertion into the Rab23 promoter causing differentiation failure; conversely, stable siRNA knockdown of Rab23 also inhibits differentiation and reduces Sox9 and Gli1 expression, indicating Rab23 regulates chondrogenesis via the Gli1-Sox9 axis.","method":"Retroviral insertion mutagenesis, stable siRNA knockdown, overexpression, RT-PCR for Sox9/Gli1","journal":"Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic perturbation approaches in one study with defined molecular readouts","pmids":["18218620"],"is_preprint":false},{"year":2010,"finding":"Depletion of Rab23 or expression of dominant-negative Rab23 specifically decreases steady-state Smoothened levels in the primary cilium without affecting EB1 or the apical protein Kim1, demonstrating a role for Rab23 in regulating Smoothened protein turnover within the cilium.","method":"FRAP (fluorescence recovery after photobleaching) in MDCK cilia, dominant-negative Rab23 expression, siRNA knockdown","journal":"Journal of Cell Science","confidence":"High","confidence_rationale":"Tier 2 — quantitative ciliary FRAP with multiple perturbation approaches and cargo specificity controls","pmids":["20375059"],"is_preprint":false},{"year":2010,"finding":"Drosophila Rab23 associates with the planar cell polarity protein Prickle and is required for hexagonal packing of wing cells and restriction of prehair initiation; absence of Rab23 leads to increased subapical actin accumulation; Rab23 acts as a dominant enhancer of core polarity mutations and is sensitive to planar polarity effector gene dosage.","method":"Genetic screen, loss-of-function Drosophila mutants, co-association assay with Prickle, actin staining, genetic interaction with PCP effector genes","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 — Drosophila ortholog, genetic epistasis with PCP effectors plus protein association data","pmids":["20124028"],"is_preprint":false},{"year":2012,"finding":"Rab23 directly associates with Su(Fu) (Suppressor of Fused) and inhibits Gli1 transcriptional activity in a Su(Fu)-dependent manner; Rab23 suppresses Gli1 nuclear localization in wild-type but not Su(Fu)-null fibroblasts; GTPase activity of Rab23 is required, as the dominant-negative form cannot suppress Gli1 activity.","method":"Co-immunoprecipitation, confocal microscopy for colocalization, Gli1-luciferase reporter assay in WT vs. Su(Fu) null fibroblasts, GTPase activity assay, dominant-negative mutant analysis","journal":"Cellular Signalling","confidence":"High","confidence_rationale":"Tier 1-2 — co-IP, reporter assay in null cells, in vitro GTPase activity, multiple orthogonal approaches","pmids":["22365972"],"is_preprint":false},{"year":2012,"finding":"Rab23 is recruited to GAS-capturing forming autophagosomes (GcAVs) during Group A Streptococcus infection; knockdown of Rab23 decreases both LC3- and Atg5-positive GAS-associated structures and causes accumulation of LC3-positive structures not associated with intracellular GAS, indicating Rab23 is required for autophagosomal vacuole formation targeting GAS but is dispensable for starvation-induced autophagy.","method":"siRNA knockdown, fluorescence microscopy (LC3/Atg5 colocalization), GcAV formation assay","journal":"Cellular Microbiology","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with specific phenotypic readouts and pathway distinction from starvation autophagy","pmids":["22452336"],"is_preprint":false},{"year":2014,"finding":"Rab23 plays a separate role in Nodal signaling and left-right patterning independently of the Hedgehog pathway; Rab23 is required in the node/Kupffer's vesicle for production of functional Nodal signals (not the response to them), as demonstrated by microinjection of Nodal protein and Nodal cDNA in embryos. Gain- and loss-of-function approaches in both mouse and zebrafish confirm this role.","method":"Mouse double mutant analysis, Nodal protein microinjection, Nodal cDNA transfection in embryo, zebrafish gain/loss-of-function","journal":"Developmental Biology","confidence":"High","confidence_rationale":"Tier 2 — multiple organisms, rescue experiments, epistasis showing independence from Hh pathway","pmids":["24780629"],"is_preprint":false},{"year":2015,"finding":"Rab23 is required for ciliary targeting of the kinesin-2 motor Kif17; wild-type and constitutively active Rab23 Q68L enrich at the primary cilium; Rab23 exists in a complex with Kif17 and importin β2 (as shown by co-immunoprecipitation and affinity-binding); Rab23 depletion disrupts ciliary localization of Kif17 but Rab23 and Ran have distinct roles in Kif17 ciliary import.","method":"Immunofluorescence, co-immunoprecipitation, affinity-binding studies, Rab23 siRNA depletion, GFP-tagged Rab23 localization","journal":"Journal of Cell Science","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP/affinity binding plus functional localization readout, multiple orthogonal methods","pmids":["26136363"],"is_preprint":false},{"year":2015,"finding":"D1-type dopamine receptors are delivered to the ciliary membrane by a mechanism requiring the receptor cytoplasmic tail, IFT-B complex, KIF17, and Rab23; depletion of Rab23 prevents dopamine receptor ciliary access; fusion of Rab23 to a non-ciliary receptor drives its nucleotide-dependent mis-localization to the ciliary membrane.","method":"siRNA depletion, GFP-receptor chimera mis-targeting, live-cell ciliary imaging, IFT-B perturbation","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods including gain-of-function chimera and depletion, nucleotide-dependence demonstrated","pmids":["26182404"],"is_preprint":false},{"year":2016,"finding":"Rab23 promotes squamous cell carcinoma cell migration and invasion in a GTP-dependent manner; Rab23 co-localizes and co-precipitates with integrin β1 and Tiam1 in a GTP-dependent manner at the cell membrane; integrin β1 siRNA disrupts the Rab23-Tiam1 interaction and attenuates Rab23-promoted migration; Rac1 inhibition or silencing attenuates Rab23-promoted invasion, placing Rab23 upstream of integrin β1/Tiam1/Rac1.","method":"Co-immunoprecipitation, siRNA, Transwell invasion assay, Rac1 activity assay, stable overexpression of WT and Q68L Rab23","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP plus functional epistasis in cancer cells, single lab","pmids":["26716504"],"is_preprint":false},{"year":2018,"finding":"Rab23 regulates radial migration of cortical projection neurons via N-cadherin; Rab23-KD neurons show reduced N-cadherin expression and impaired migration; Rab23 silencing impedes ERK1/2 activation via perturbed PDGFRα signaling; pharmacological ERK1/2 inhibition also reduces N-cadherin; restoration of Rab23 or N-cadherin reverses migration defects.","method":"In utero electroporation knockdown, conditional knockout, Western blot (ERK1/2, N-cadherin, PDGFRα), pharmacological inhibition, rescue experiments","journal":"Cerebral Cortex","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo KD/KO with rescue experiments and defined molecular cascade, single lab","pmids":["29420702"],"is_preprint":false},{"year":2019,"finding":"Inturned and Fuzzy, planar cell polarity effector proteins containing multiple longin domains characteristic of Mon1-Ccz1 family Rab7 GEFs, form a specific Rab23 GEF complex; in flies, loss of Rab23 causes planar-polarized trichome defects consistent with this relationship; in cultured cells, Inturned and Fuzzy localize to the basal body/proximal cilia and their depletion arrests ciliogenesis after ciliary vesicle docking but before axoneme elongation.","method":"Biochemical GEF activity assay, Drosophila genetics (loss-of-function), siRNA in human/mouse cells, immunofluorescence localization, longin domain sequence analysis","journal":"Current Biology","confidence":"High","confidence_rationale":"Tier 1-2 — biochemical GEF activity demonstrated, Drosophila genetics, cell biology in multiple systems, multiple orthogonal methods","pmids":["31564489"],"is_preprint":false},{"year":2019,"finding":"GTP-bound Rab23 accumulates at the spindle during mouse oocyte meiosis and promotes migration of Kif17 to spindle poles; depletion of Rab23 or Kif17 causes polar body extrusion failure and perturbs spindle formation, chromosome alignment, and tubulin acetylation; Kif17 regulates tubulin acetylation by associating with αTAT and Sirt2; Kif17 tail domain associates with RhoA-ROCK-LIMK-cofilin pathway components to modulate actin assembly for spindle migration.","method":"siRNA depletion, immunofluorescence (spindle/actin), co-immunoprecipitation (Kif17-αTAT/Sirt2/RhoA-ROCK-LIMK-cofilin), polar body extrusion assay","journal":"Development","confidence":"Medium","confidence_rationale":"Tier 2 — multiple co-IPs and functional readouts in oocytes, single lab","pmids":["30696709"],"is_preprint":false},{"year":2019,"finding":"Rab23 is involved in apical trafficking of influenza hemagglutinin (HA) and neuraminidase (NA); HA associates with Rab23 in lipid raft fractions (co-immunoprecipitation); Rab23 dominant-negative expression impairs cell surface expression of HA; Rab23-positive vesicles transport HA/NA in the apical cytoplasm, downstream of Rab17.","method":"Co-immunoprecipitation, live-cell imaging, dominant-negative expression, cholesterol depletion, immunofluorescence colocalization","journal":"Frontiers in Microbiology","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP in lipid raft fraction plus functional DN perturbation, single lab, partial mechanistic follow-up","pmids":["31456775"],"is_preprint":false},{"year":2020,"finding":"RAB23 deficiency causes premature cranial suture fusion through aberrant osteoprogenitor proliferation driven by elevated FGF10-FGFR1/pERK1/2 signaling; RAB23 acts as an upstream negative regulator of both FGFR and canonical Hh-GLI1 signaling, and also non-canonically regulates GLI1 through pERK1/2; inhibition of pERK1/2 normalizes osteoprogenitor proliferation and prevents craniosynostosis.","method":"Rab23-deficient mouse model, immunostaining, Western blot (pERK1/2, FGFR1, RUNX2, GLI1), pharmacological pERK1/2 inhibition rescue","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO with mechanistic rescue by signaling inhibitor, multiple molecular readouts","pmids":["32662771"],"is_preprint":false},{"year":2021,"finding":"Conditional knockout of Rab23 in mouse brain causes mis-patterning of cerebellar folia and elevated granule cell precursor (GCP) proliferation; Rab23-depleted GCPs show upregulated basal Shh pathway activity but abnormal ciliogenesis; they are desensitized to extrinsic Shh and Smo agonist (SAG) stimulation with attenuated Smo ciliary localization in response to SAG, revealing dual functions: Rab23 represses basal Hh signaling but facilitates cilium-dependent extrinsic Shh activation.","method":"Nestin-Cre conditional KO mouse, immunofluorescence, Gli luciferase reporter, SAG treatment, Smo ciliary localization assay","journal":"Journal of Neuroscience","confidence":"High","confidence_rationale":"Tier 2 — in vivo CKO with multiple functional and molecular readouts, defines dual regulatory role","pmids":["34210780"],"is_preprint":false},{"year":2024,"finding":"Crystal structures of human Rab23 in complex with GDP and with the non-hydrolysable GTP analog GMPPNP were determined, along with the structure of the Carpenter syndrome Y79del clinical mutant; the Y79del mutant shows structural distortions in the switch II region that disrupt binding to interacting partners, causing loss-of-function and Carpenter syndrome pathogenesis.","method":"X-ray crystallography (high-resolution crystal structures of GDP- and GMPPNP-bound forms), in vitro biochemical assays, functional analyses of mutants","journal":"Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with in vitro biochemical validation and mutagenesis-phenotype correlation","pmids":["39615683"],"is_preprint":false},{"year":2007,"finding":"Rab23 is phosphorylated in mouse brain specifically in response to cytidine 3′,5′-cyclic monophosphate (cCMP) but not cAMP or cGMP, identifying Rab23 as the first protein reported to be selectively phosphorylated in response to cCMP.","method":"IMAC phosphoprotein enrichment from mouse brain, MALDI-ToF MS and LC/ESI-MS/MS identification of tryptic phosphopeptides","journal":"Rapid Communications in Mass Spectrometry","confidence":"Low","confidence_rationale":"Tier 3 — single mass spectrometric identification, no writer/eraser/reader characterized","pmids":["17639578"],"is_preprint":false},{"year":2025,"finding":"RAB23 interacts with β-adaptin (AP2β1) subunit of the AP-2 clathrin adaptor complex, with clathrin assembly protein PICALM, with vesicle curvature protein endophilin A2, and with cortactin; RAB23 deficiency reduces AP2β1-clathrin interaction and impairs clathrin-dependent endocytosis (transferrin uptake); BMP-stimulated vesicle formation and signal transduction are aberrant in RAB23-deficient cells, indicating RAB23 functions in clathrin-coated nascent vesicle formation at the plasma membrane.","method":"Co-immunoprecipitation (RAB23/AP2β1/PICALM/endophilin A2/cortactin), time-lapse live-cell imaging of transferrin uptake, RAB23 KD with rescue, microarray-driven hypergeometric test, BMP signaling assay","journal":"Cellular and Molecular Life Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — multiple co-IPs, live imaging, rescue experiment, functional signaling readout; single lab","pmids":["40261407"],"is_preprint":false},{"year":2025,"finding":"RAB23 (in its GDP-bound state) localizes to the basal body just below the transition zone and acts as a RAB18-specific guanine nucleotide exchange factor (GEF); RAB23-GDP activates RAB18-GDP, which then recruits the BBSome as an effector to cross the transition zone for ciliary entry; RAB23-GDP subsequently enters cilia as a BBSome cargo, establishing a RAB23-RAB18 module that mediates inward BBSome transition zone diffusion for proper ciliary signaling.","method":"Chlamydomonas model, GEF activity assay, localization studies, BBSome interaction assays","journal":"bioRxiv (preprint)","confidence":"Low","confidence_rationale":"Tier 1-2 method but preprint not yet peer reviewed, single lab","pmids":["bio_10.1101_2025.02.20.639385"],"is_preprint":true},{"year":2025,"finding":"RAB23 loss-of-function causes context-dependent (cell-type-specific) primary cilia defects in vivo; Rab23-CKO mouse mutants, CS patient iPSC-derived neurons, and zebrafish morphants all show perturbed cilia formation selectively in certain cell types (chondrocytes, neocortical neurons) but not others (epithelial cells, cerebellar granule cells); Rab23-KO neural progenitors are desensitized to cilium-dependent Hedgehog pathway activation, confirming Carpenter syndrome as a ciliopathy.","method":"Conditional knockout mouse (Rab23-CKO), patient iPSC differentiation, zebrafish morpholino knockdown, immunofluorescence of cilia in multiple cell types, Hedgehog pathway activity assay","journal":"PLoS Genetics","confidence":"High","confidence_rationale":"Tier 2 — three independent vertebrate model systems, multiple cell-type analyses, functional Hh pathway readout","pmids":["40825043"],"is_preprint":false},{"year":2025,"finding":"Rab23 and IFT43 are identified as crucial regulators of prostaglandin E receptor 4 (EP4) ciliary trafficking; EP4 physically interacts with IFT43 and Rab23 through its IC3 loop and C-terminal region; high-content siRNA screening and zebrafish/mammalian validation confirm that Rab23 (and IFT43) are required for EP4 delivery to primary cilia.","method":"High-content siRNA screen, co-immunoprecipitation (EP4/IFT43/Rab23), zebrafish embryo localization, mammalian cell ciliary trafficking assay, CRISPR base editing of EP4 LPG motif","journal":"Communications Biology","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus functional siRNA screen plus zebrafish validation; single study","pmids":["41372612"],"is_preprint":false},{"year":2022,"finding":"Rab23 co-localizes with mature melanosomes (TRP-1-positive) and its downregulation by siRNA reduces melanin synthesis, tyrosinase activity, and inhibits UVB-induced melanogenesis via decreased PKA/CREB/MITF pathway activity; Rab23 knockdown also causes abnormal melanosome accumulation around the nucleus, implicating Rab23 in melanosome transport.","method":"siRNA knockdown, melanin quantification, tyrosinase activity assay, immunofluorescence co-localization (Rab23/TRP-1), Western blot (PKA/CREB/MITF pathway)","journal":"Experimental Dermatology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, functional KD with pathway readout but no direct mechanistic interaction established","pmids":["35514241"],"is_preprint":false}],"current_model":"RAB23 is a Rab-family small GTPase that cycles between GDP-bound (inactive) and GTP-bound (active) states, localizes primarily to the plasma membrane and early endosomes (and to primary cilia when active), and functions as a negative regulator of Sonic Hedgehog signaling by acting downstream of Smoothened and upstream of Gli transcription factors (particularly Gli2 activator) in a Su(Fu)-dependent manner; it is activated by the Inturned-Fuzzy GEF complex, regulates Smoothened levels in cilia, mediates ciliary delivery of receptors (including dopamine D1R and EP4) via IFT-B/KIF17, participates in clathrin-coated vesicle formation at the plasma membrane through interactions with AP-2/PICALM/endophilin A2, and has additional Hh-independent roles in Nodal signaling, left-right patterning, cortical neuron radial migration (via ERK1/2-N-cadherin), and GAS-targeting autophagy, with loss-of-function mutations causing Carpenter syndrome through context-dependent primary cilia dysfunction."},"narrative":{"teleology":[{"year":2001,"claim":"The foundational question of where RAB23 acts in development was answered when positional cloning of the mouse open brain locus revealed Rab23 as an essential negative regulator of Shh signaling, establishing the first link between a Rab GTPase and Hedgehog pathway control.","evidence":"Map-based cloning of opb locus and Shh/opb double-mutant epistasis in mouse","pmids":["11449277"],"confidence":"High","gaps":["Mechanism of negative regulation unknown","Subcellular site of action unresolved","No direct biochemical target identified"]},{"year":2003,"claim":"Determining where RAB23 resides in the cell revealed plasma membrane and early endosome localization with GTP-state dependence, and showed Patched but not Smoothened colocalizes with Rab23 vesicles, narrowing the trafficking compartment involved.","evidence":"Live-cell fluorescence, immunoelectron microscopy, GFP-tagged WT/Q68L/S23N Rab23 in cultured cells","pmids":["14617350"],"confidence":"High","gaps":["Ciliary localization not yet examined","No functional connection to Hh signaling components established biochemically"]},{"year":2005,"claim":"Genetic epistasis placed Rab23 downstream of Smoothened and identified Gli2 activator as its primary target, with additional promotion of Gli3 repressor, resolving the signaling hierarchy within the Hh pathway.","evidence":"Rab23/Gli2, Rab23/Gli3, Rab23/Smo double-mutant analysis in mouse","pmids":["16364285"],"confidence":"High","gaps":["Direct biochemical mechanism linking Rab23 to Gli processing or trafficking unknown","Role of Su(Fu) not yet tested"]},{"year":2007,"claim":"Identification of RAB23 loss-of-function mutations in Carpenter syndrome families established the human disease consequence and confirmed the clinical relevance of RAB23-mediated Hedgehog regulation.","evidence":"Homozygosity mapping and sequencing of 15 Carpenter syndrome families","pmids":["17503333"],"confidence":"High","gaps":["Cellular pathomechanism in cranial sutures undefined","Whether cilia defects underlie the syndrome not tested"]},{"year":2010,"claim":"The discovery that Rab23 depletion decreases Smoothened levels in the primary cilium revealed a specific ciliary trafficking function, connecting its GTPase activity to cilium-dependent Hh signaling.","evidence":"FRAP and siRNA/dominant-negative perturbation in MDCK cilia","pmids":["20375059"],"confidence":"High","gaps":["Whether Rab23 itself enters cilia not established","Cargo specificity beyond Smoothened not tested"]},{"year":2012,"claim":"Two distinct roles emerged simultaneously: Rab23 directly associates with Su(Fu) to suppress Gli1 nuclear localization in a GTPase-dependent manner, providing the first biochemical partner in Hh regulation; and Rab23 participates in autophagosome formation targeting Group A Streptococcus independently of starvation autophagy.","evidence":"Co-IP of Rab23–Su(Fu), Gli-luciferase in WT vs Su(Fu)-null fibroblasts [PMID:22365972]; siRNA KD with LC3/Atg5 autophagosome assays for GAS [PMID:22452336]","pmids":["22365972","22452336"],"confidence":"High","gaps":["Whether Su(Fu) interaction occurs at cilia or endosomes unclear","Mechanism of autophagosome recruitment undefined","GAS-targeting specificity mechanism unknown"]},{"year":2014,"claim":"Demonstration that Rab23 is required in the node for Nodal signal production—independent of Hh—revealed a Hedgehog-independent developmental function in left-right axis determination.","evidence":"Mouse/zebrafish double-mutant analysis, Nodal protein and cDNA rescue in embryos","pmids":["24780629"],"confidence":"High","gaps":["Trafficking cargo for Nodal signaling not identified","Whether this involves cilia in the node not resolved"]},{"year":2015,"claim":"Rab23 was shown to form a complex with Kif17 and importin-β2 and to be required for ciliary targeting of Kif17 and dopamine D1 receptors via IFT-B, establishing a general receptor ciliary delivery pathway.","evidence":"Co-IP and affinity binding of Rab23–Kif17–importin-β2 [PMID:26136363]; siRNA depletion and Rab23 chimera mis-targeting for D1R ciliary access [PMID:26182404]","pmids":["26136363","26182404"],"confidence":"High","gaps":["Full repertoire of Rab23-dependent ciliary cargoes unknown","Whether Rab23 enters cilia with cargo not resolved"]},{"year":2018,"claim":"Rab23 was found to regulate cortical neuron radial migration through PDGFRα–ERK1/2–N-cadherin signaling, extending its functions beyond Hh-dependent contexts into neuronal cell biology.","evidence":"In utero electroporation KD/CKO with rescue, Western blot, pharmacological ERK inhibition in mouse cortex","pmids":["29420702"],"confidence":"Medium","gaps":["Whether this involves ciliary or endosomal Rab23 pools not distinguished","Direct binding partners in this pathway not identified"]},{"year":2019,"claim":"Identification of the Inturned–Fuzzy complex as a Rab23-specific GEF resolved how Rab23 GTP loading is regulated and linked planar cell polarity effector proteins to Rab23 activation at the basal body.","evidence":"Biochemical GEF assay, Drosophila loss-of-function genetics, siRNA in mammalian cells, longin domain analysis","pmids":["31564489"],"confidence":"High","gaps":["No GAP for Rab23 identified","Structural basis of GEF specificity unresolved"]},{"year":2020,"claim":"The Carpenter syndrome craniosynostosis mechanism was elucidated: RAB23 deficiency causes osteoprogenitor hyperproliferation via elevated FGF10–FGFR1–pERK1/2 and GLI1 signaling, rescuable by ERK inhibition.","evidence":"Rab23-deficient mouse, immunostaining, Western blot, pharmacological pERK1/2 rescue","pmids":["32662771"],"confidence":"High","gaps":["Whether FGFR trafficking is directly Rab23-dependent not shown","Tissue-specific cilia dependence not yet tested"]},{"year":2021,"claim":"Conditional knockout in cerebellum revealed Rab23 has dual opposing roles: it represses basal Hh pathway activity but facilitates cilium-dependent Smo translocation upon extrinsic Shh stimulation, reconciling apparently conflicting observations.","evidence":"Nestin-Cre CKO mouse, Gli reporter, SAG stimulation, Smo ciliary localization assay","pmids":["34210780"],"confidence":"High","gaps":["How Rab23 simultaneously represses basal and promotes stimulated Hh at the molecular level is mechanistically unresolved"]},{"year":2024,"claim":"Crystal structures of GDP-bound and GTP-analog-bound human RAB23, plus the Carpenter-associated Y79del mutant, provided the first atomic-level view, showing that Y79del distorts switch II to disrupt effector binding.","evidence":"X-ray crystallography, in vitro biochemical and mutant functional assays","pmids":["39615683"],"confidence":"High","gaps":["No co-crystal with Su(Fu) or any effector","Structural basis of GEF (Inturned–Fuzzy) recognition unknown"]},{"year":2025,"claim":"Multiple studies converged to show that RAB23 loss causes context-dependent (cell-type-specific) cilia defects confirming Carpenter syndrome as a ciliopathy, that RAB23 participates in clathrin-coated vesicle formation at the plasma membrane via AP-2/PICALM/endophilin A2, and that EP4 is an additional Rab23-dependent ciliary cargo.","evidence":"CKO mouse/iPSC-neurons/zebrafish cilia analysis [PMID:40825043]; co-IP of RAB23–AP-2–PICALM–endophilin A2 with transferrin uptake assays [PMID:40261407]; siRNA screen and co-IP for EP4 ciliary trafficking [PMID:41372612]","pmids":["40825043","40261407","41372612"],"confidence":"High","gaps":["How Rab23 coordinates clathrin-mediated endocytosis with ciliary trafficking is unknown","Complete set of Rab23-dependent ciliary cargoes undefined","Whether clathrin role is GTP- or GDP-state-dependent not established"]},{"year":null,"claim":"Major open questions include: the identity of the Rab23 GAP, the structural basis of Rab23 interaction with Su(Fu) and the Inturned–Fuzzy GEF, the molecular logic determining cell-type-specific cilia dependence on Rab23, and how Rab23 mechanistically integrates its endosomal, plasma membrane, and ciliary trafficking functions.","evidence":"Not applicable — open questions","pmids":[],"confidence":"High","gaps":["No Rab23 GAP identified","No effector co-structure available","Cell-type specificity mechanism uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[7,14,19]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,7,22]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,12,21]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,16]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[5,10,11]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,5,7,17,18]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,11,21,24]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,2,9,13]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[8]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[3,17]}],"complexes":["IFT-B/KIF17/Rab23 ciliary transport complex","AP-2/PICALM/endophilin A2/Rab23 clathrin vesicle complex"],"partners":["SUFU","KIF17","KPNB2","INTU","FUZ","AP2B1","PICALM","SH3GL1"],"other_free_text":[]},"mechanistic_narrative":"RAB23 is a small GTPase that functions as a negative regulator of Hedgehog signaling and a versatile mediator of membrane trafficking to primary cilia and the plasma membrane. It acts downstream of Smoothened and upstream of Gli transcription factors in a Su(Fu)-dependent manner to suppress Gli2 activator function and promote Gli3 repressor formation, and it regulates Smoothened levels within the cilium [PMID:11449277, PMID:16364285, PMID:22365972, PMID:20375059]. RAB23 is activated by the Inturned–Fuzzy GEF complex, localizes to the plasma membrane, endosomes, and primary cilia in its GTP-bound state, and mediates ciliary delivery of receptors including dopamine D1R and EP4 via IFT-B/KIF17, while also participating in clathrin-coated vesicle formation through interactions with AP-2, PICALM, and endophilin A2 [PMID:31564489, PMID:26182404, PMID:41372612, PMID:40261407]. Loss-of-function mutations in RAB23 cause Carpenter syndrome, a craniosynostosis-polydactyly disorder driven by context-dependent primary cilia dysfunction and deregulated FGF/ERK and Hedgehog signaling [PMID:17503333, PMID:32662771, PMID:40825043]."},"prefetch_data":{"uniprot":{"accession":"Q9ULC3","full_name":"Ras-related protein Rab-23","aliases":[],"length_aa":237,"mass_kda":26.7,"function":"The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes. Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different set of downstream effectors directly responsible for vesicle formation, movement, tethering and fusion. In conjunction with IFT57 and KIF17, it drives the localization of specific G protein-coupled receptors, such as the dopamime receptor DRD1, to primary cilia (PubMed:26182404). Has a critical role in the formation and elongation of neuronal primary cilia, thereby impacting the activation of sonic hedgehog (Shh) signaling (PubMed:40825043). Additionally, it is involved in the down-regulation of Shh signaling by cooperating with SUFU to prevent the nuclear import of GLI1 transcription factor, thus suppressing its transcriptional activity (PubMed:22365972) (PubMed:39615683). Regulates GLI1 in differentiating chondrocytes. Likewise, regulates GLI3 proteolytic processing and modulates GLI2 and GLI3 transcription factor activity. 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genetics","url":"https://pubmed.ncbi.nlm.nih.gov/40825043","citation_count":1,"is_preprint":false},{"pmid":"29437519","id":"PMC_29437519","title":"Molecular Analysis of Gli3, Ihh, Rab23, and Jag1 in a Rabbit Model of Craniosynostosis: Likely Exclusion as the Loci of Origin.","date":"2017","source":"The Cleft palate-craniofacial journal : official publication of the American Cleft Palate-Craniofacial Association","url":"https://pubmed.ncbi.nlm.nih.gov/29437519","citation_count":1,"is_preprint":false},{"pmid":"41372612","id":"PMC_41372612","title":"Rab23 GTPase and IFT43 regulate the trafficking of prostaglandin E receptor 4 to primary cilia.","date":"2025","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/41372612","citation_count":0,"is_preprint":false},{"pmid":"39036858","id":"PMC_39036858","title":"The inhibition roles of RAB23 gene in granulosa cell proliferation and progesterone synthesis of hen ovarian prehierarchical follicles.","date":"2024","source":"British poultry science","url":"https://pubmed.ncbi.nlm.nih.gov/39036858","citation_count":0,"is_preprint":false},{"pmid":"31423247","id":"PMC_31423247","title":"Rab23 contributes to the progression of colorectal cancer via protein kinase B and extracellular signal-regulated kinase signaling pathways.","date":"2019","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/31423247","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.02.10.637381","title":"<i>RAB23</i> loss-of-function mutation causes context-dependent ciliopathy in Carpenter syndrome","date":"2025-02-11","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.10.637381","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.02.20.639385","title":"RAB23 Modulates Signaling Protein Ciliary Homeostasis through Promoting RAB18-mediated Inward BBSome Transition Zone Passage","date":"2025-02-21","source":"bioRxiv","url":"https://doi.org/10.1101/2025.02.20.639385","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":40294,"output_tokens":6878,"usd":0.112026},"stage2":{"model":"claude-opus-4-6","input_tokens":10516,"output_tokens":3637,"usd":0.215257},"total_usd":0.327283,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"Rab23 is an essential negative regulator of the Sonic hedgehog (Shh) signaling pathway, acting downstream of Shh; loss of Rab23 in the open brain (opb) mouse mutant rescues ventral cell types absent in Shh mutants, placing Rab23 genetically downstream of Shh in neural tube patterning.\",\n      \"method\": \"Genetic epistasis (Shh opb double mutants), map-based cloning of the opb locus\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double mutant rescue, foundational paper replicated extensively\",\n      \"pmids\": [\"11449277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Rab23 localizes predominantly to the plasma membrane and early endocytic vesicles (colocalizing with Rab5Q79L and internalized transferrin); the constitutively active Q68L mutant shares this distribution while the dominant-negative S23N mutant is cytosolic. Patched colocalizes with intracellular Rab23-GFP vesicles but Smoothened does not, and neither Patched nor Smoothened distribution is altered by Rab23 expression.\",\n      \"method\": \"Live-cell fluorescence microscopy, immunoelectron microscopy, co-expression with GFP-tagged Rab23 mutants, co-localization with endocytic markers\",\n      \"journal\": \"Traffic\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization by light and immunoelectron microscopy with multiple functional mutants and orthogonal markers\",\n      \"pmids\": [\"14617350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Rab23 acts upstream of Gli transcription factors and downstream of Smoothened in the Shh pathway; double mutant analysis shows the primary target of Rab23 is Gli2 activator function, with additive effects with Gli3 repressor; Rab23 also promotes Gli3 repressor production. Rab23 does not work through Patched or Smoothened.\",\n      \"method\": \"Genetic epistasis (Rab23/Gli2, Rab23/Gli3, Rab23/Smo double mutants in mouse), Gli3 protein analysis\",\n      \"journal\": \"Developmental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic epistasis experiments in mouse, replicated across labs\",\n      \"pmids\": [\"16364285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAB23 mutations (truncating and one missense) cause Carpenter syndrome with autosomal recessive inheritance; RAB23 functions as a negative regulator of Hedgehog signaling and is required for cranial suture development, implicating HH signaling in craniosynostosis.\",\n      \"method\": \"Homozygosity mapping, direct sequencing of RAB23 in 15 families, identification of loss-of-function mutations\",\n      \"journal\": \"American Journal of Human Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple independent families with loss-of-function alleles, strong genetic evidence\",\n      \"pmids\": [\"17503333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Elevated Rab23 expression inhibits chondrogenic differentiation of ATDC5 cells, as shown by retroviral insertion into the Rab23 promoter causing differentiation failure; conversely, stable siRNA knockdown of Rab23 also inhibits differentiation and reduces Sox9 and Gli1 expression, indicating Rab23 regulates chondrogenesis via the Gli1-Sox9 axis.\",\n      \"method\": \"Retroviral insertion mutagenesis, stable siRNA knockdown, overexpression, RT-PCR for Sox9/Gli1\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic perturbation approaches in one study with defined molecular readouts\",\n      \"pmids\": [\"18218620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Depletion of Rab23 or expression of dominant-negative Rab23 specifically decreases steady-state Smoothened levels in the primary cilium without affecting EB1 or the apical protein Kim1, demonstrating a role for Rab23 in regulating Smoothened protein turnover within the cilium.\",\n      \"method\": \"FRAP (fluorescence recovery after photobleaching) in MDCK cilia, dominant-negative Rab23 expression, siRNA knockdown\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative ciliary FRAP with multiple perturbation approaches and cargo specificity controls\",\n      \"pmids\": [\"20375059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Drosophila Rab23 associates with the planar cell polarity protein Prickle and is required for hexagonal packing of wing cells and restriction of prehair initiation; absence of Rab23 leads to increased subapical actin accumulation; Rab23 acts as a dominant enhancer of core polarity mutations and is sensitive to planar polarity effector gene dosage.\",\n      \"method\": \"Genetic screen, loss-of-function Drosophila mutants, co-association assay with Prickle, actin staining, genetic interaction with PCP effector genes\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Drosophila ortholog, genetic epistasis with PCP effectors plus protein association data\",\n      \"pmids\": [\"20124028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Rab23 directly associates with Su(Fu) (Suppressor of Fused) and inhibits Gli1 transcriptional activity in a Su(Fu)-dependent manner; Rab23 suppresses Gli1 nuclear localization in wild-type but not Su(Fu)-null fibroblasts; GTPase activity of Rab23 is required, as the dominant-negative form cannot suppress Gli1 activity.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy for colocalization, Gli1-luciferase reporter assay in WT vs. Su(Fu) null fibroblasts, GTPase activity assay, dominant-negative mutant analysis\",\n      \"journal\": \"Cellular Signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — co-IP, reporter assay in null cells, in vitro GTPase activity, multiple orthogonal approaches\",\n      \"pmids\": [\"22365972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Rab23 is recruited to GAS-capturing forming autophagosomes (GcAVs) during Group A Streptococcus infection; knockdown of Rab23 decreases both LC3- and Atg5-positive GAS-associated structures and causes accumulation of LC3-positive structures not associated with intracellular GAS, indicating Rab23 is required for autophagosomal vacuole formation targeting GAS but is dispensable for starvation-induced autophagy.\",\n      \"method\": \"siRNA knockdown, fluorescence microscopy (LC3/Atg5 colocalization), GcAV formation assay\",\n      \"journal\": \"Cellular Microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with specific phenotypic readouts and pathway distinction from starvation autophagy\",\n      \"pmids\": [\"22452336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rab23 plays a separate role in Nodal signaling and left-right patterning independently of the Hedgehog pathway; Rab23 is required in the node/Kupffer's vesicle for production of functional Nodal signals (not the response to them), as demonstrated by microinjection of Nodal protein and Nodal cDNA in embryos. Gain- and loss-of-function approaches in both mouse and zebrafish confirm this role.\",\n      \"method\": \"Mouse double mutant analysis, Nodal protein microinjection, Nodal cDNA transfection in embryo, zebrafish gain/loss-of-function\",\n      \"journal\": \"Developmental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple organisms, rescue experiments, epistasis showing independence from Hh pathway\",\n      \"pmids\": [\"24780629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Rab23 is required for ciliary targeting of the kinesin-2 motor Kif17; wild-type and constitutively active Rab23 Q68L enrich at the primary cilium; Rab23 exists in a complex with Kif17 and importin β2 (as shown by co-immunoprecipitation and affinity-binding); Rab23 depletion disrupts ciliary localization of Kif17 but Rab23 and Ran have distinct roles in Kif17 ciliary import.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, affinity-binding studies, Rab23 siRNA depletion, GFP-tagged Rab23 localization\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP/affinity binding plus functional localization readout, multiple orthogonal methods\",\n      \"pmids\": [\"26136363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"D1-type dopamine receptors are delivered to the ciliary membrane by a mechanism requiring the receptor cytoplasmic tail, IFT-B complex, KIF17, and Rab23; depletion of Rab23 prevents dopamine receptor ciliary access; fusion of Rab23 to a non-ciliary receptor drives its nucleotide-dependent mis-localization to the ciliary membrane.\",\n      \"method\": \"siRNA depletion, GFP-receptor chimera mis-targeting, live-cell ciliary imaging, IFT-B perturbation\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods including gain-of-function chimera and depletion, nucleotide-dependence demonstrated\",\n      \"pmids\": [\"26182404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Rab23 promotes squamous cell carcinoma cell migration and invasion in a GTP-dependent manner; Rab23 co-localizes and co-precipitates with integrin β1 and Tiam1 in a GTP-dependent manner at the cell membrane; integrin β1 siRNA disrupts the Rab23-Tiam1 interaction and attenuates Rab23-promoted migration; Rac1 inhibition or silencing attenuates Rab23-promoted invasion, placing Rab23 upstream of integrin β1/Tiam1/Rac1.\",\n      \"method\": \"Co-immunoprecipitation, siRNA, Transwell invasion assay, Rac1 activity assay, stable overexpression of WT and Q68L Rab23\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP plus functional epistasis in cancer cells, single lab\",\n      \"pmids\": [\"26716504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Rab23 regulates radial migration of cortical projection neurons via N-cadherin; Rab23-KD neurons show reduced N-cadherin expression and impaired migration; Rab23 silencing impedes ERK1/2 activation via perturbed PDGFRα signaling; pharmacological ERK1/2 inhibition also reduces N-cadherin; restoration of Rab23 or N-cadherin reverses migration defects.\",\n      \"method\": \"In utero electroporation knockdown, conditional knockout, Western blot (ERK1/2, N-cadherin, PDGFRα), pharmacological inhibition, rescue experiments\",\n      \"journal\": \"Cerebral Cortex\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KD/KO with rescue experiments and defined molecular cascade, single lab\",\n      \"pmids\": [\"29420702\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Inturned and Fuzzy, planar cell polarity effector proteins containing multiple longin domains characteristic of Mon1-Ccz1 family Rab7 GEFs, form a specific Rab23 GEF complex; in flies, loss of Rab23 causes planar-polarized trichome defects consistent with this relationship; in cultured cells, Inturned and Fuzzy localize to the basal body/proximal cilia and their depletion arrests ciliogenesis after ciliary vesicle docking but before axoneme elongation.\",\n      \"method\": \"Biochemical GEF activity assay, Drosophila genetics (loss-of-function), siRNA in human/mouse cells, immunofluorescence localization, longin domain sequence analysis\",\n      \"journal\": \"Current Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biochemical GEF activity demonstrated, Drosophila genetics, cell biology in multiple systems, multiple orthogonal methods\",\n      \"pmids\": [\"31564489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"GTP-bound Rab23 accumulates at the spindle during mouse oocyte meiosis and promotes migration of Kif17 to spindle poles; depletion of Rab23 or Kif17 causes polar body extrusion failure and perturbs spindle formation, chromosome alignment, and tubulin acetylation; Kif17 regulates tubulin acetylation by associating with αTAT and Sirt2; Kif17 tail domain associates with RhoA-ROCK-LIMK-cofilin pathway components to modulate actin assembly for spindle migration.\",\n      \"method\": \"siRNA depletion, immunofluorescence (spindle/actin), co-immunoprecipitation (Kif17-αTAT/Sirt2/RhoA-ROCK-LIMK-cofilin), polar body extrusion assay\",\n      \"journal\": \"Development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple co-IPs and functional readouts in oocytes, single lab\",\n      \"pmids\": [\"30696709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Rab23 is involved in apical trafficking of influenza hemagglutinin (HA) and neuraminidase (NA); HA associates with Rab23 in lipid raft fractions (co-immunoprecipitation); Rab23 dominant-negative expression impairs cell surface expression of HA; Rab23-positive vesicles transport HA/NA in the apical cytoplasm, downstream of Rab17.\",\n      \"method\": \"Co-immunoprecipitation, live-cell imaging, dominant-negative expression, cholesterol depletion, immunofluorescence colocalization\",\n      \"journal\": \"Frontiers in Microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP in lipid raft fraction plus functional DN perturbation, single lab, partial mechanistic follow-up\",\n      \"pmids\": [\"31456775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RAB23 deficiency causes premature cranial suture fusion through aberrant osteoprogenitor proliferation driven by elevated FGF10-FGFR1/pERK1/2 signaling; RAB23 acts as an upstream negative regulator of both FGFR and canonical Hh-GLI1 signaling, and also non-canonically regulates GLI1 through pERK1/2; inhibition of pERK1/2 normalizes osteoprogenitor proliferation and prevents craniosynostosis.\",\n      \"method\": \"Rab23-deficient mouse model, immunostaining, Western blot (pERK1/2, FGFR1, RUNX2, GLI1), pharmacological pERK1/2 inhibition rescue\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO with mechanistic rescue by signaling inhibitor, multiple molecular readouts\",\n      \"pmids\": [\"32662771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Conditional knockout of Rab23 in mouse brain causes mis-patterning of cerebellar folia and elevated granule cell precursor (GCP) proliferation; Rab23-depleted GCPs show upregulated basal Shh pathway activity but abnormal ciliogenesis; they are desensitized to extrinsic Shh and Smo agonist (SAG) stimulation with attenuated Smo ciliary localization in response to SAG, revealing dual functions: Rab23 represses basal Hh signaling but facilitates cilium-dependent extrinsic Shh activation.\",\n      \"method\": \"Nestin-Cre conditional KO mouse, immunofluorescence, Gli luciferase reporter, SAG treatment, Smo ciliary localization assay\",\n      \"journal\": \"Journal of Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo CKO with multiple functional and molecular readouts, defines dual regulatory role\",\n      \"pmids\": [\"34210780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Crystal structures of human Rab23 in complex with GDP and with the non-hydrolysable GTP analog GMPPNP were determined, along with the structure of the Carpenter syndrome Y79del clinical mutant; the Y79del mutant shows structural distortions in the switch II region that disrupt binding to interacting partners, causing loss-of-function and Carpenter syndrome pathogenesis.\",\n      \"method\": \"X-ray crystallography (high-resolution crystal structures of GDP- and GMPPNP-bound forms), in vitro biochemical assays, functional analyses of mutants\",\n      \"journal\": \"Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with in vitro biochemical validation and mutagenesis-phenotype correlation\",\n      \"pmids\": [\"39615683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Rab23 is phosphorylated in mouse brain specifically in response to cytidine 3′,5′-cyclic monophosphate (cCMP) but not cAMP or cGMP, identifying Rab23 as the first protein reported to be selectively phosphorylated in response to cCMP.\",\n      \"method\": \"IMAC phosphoprotein enrichment from mouse brain, MALDI-ToF MS and LC/ESI-MS/MS identification of tryptic phosphopeptides\",\n      \"journal\": \"Rapid Communications in Mass Spectrometry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single mass spectrometric identification, no writer/eraser/reader characterized\",\n      \"pmids\": [\"17639578\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAB23 interacts with β-adaptin (AP2β1) subunit of the AP-2 clathrin adaptor complex, with clathrin assembly protein PICALM, with vesicle curvature protein endophilin A2, and with cortactin; RAB23 deficiency reduces AP2β1-clathrin interaction and impairs clathrin-dependent endocytosis (transferrin uptake); BMP-stimulated vesicle formation and signal transduction are aberrant in RAB23-deficient cells, indicating RAB23 functions in clathrin-coated nascent vesicle formation at the plasma membrane.\",\n      \"method\": \"Co-immunoprecipitation (RAB23/AP2β1/PICALM/endophilin A2/cortactin), time-lapse live-cell imaging of transferrin uptake, RAB23 KD with rescue, microarray-driven hypergeometric test, BMP signaling assay\",\n      \"journal\": \"Cellular and Molecular Life Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple co-IPs, live imaging, rescue experiment, functional signaling readout; single lab\",\n      \"pmids\": [\"40261407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAB23 (in its GDP-bound state) localizes to the basal body just below the transition zone and acts as a RAB18-specific guanine nucleotide exchange factor (GEF); RAB23-GDP activates RAB18-GDP, which then recruits the BBSome as an effector to cross the transition zone for ciliary entry; RAB23-GDP subsequently enters cilia as a BBSome cargo, establishing a RAB23-RAB18 module that mediates inward BBSome transition zone diffusion for proper ciliary signaling.\",\n      \"method\": \"Chlamydomonas model, GEF activity assay, localization studies, BBSome interaction assays\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1-2 method but preprint not yet peer reviewed, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.02.20.639385\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAB23 loss-of-function causes context-dependent (cell-type-specific) primary cilia defects in vivo; Rab23-CKO mouse mutants, CS patient iPSC-derived neurons, and zebrafish morphants all show perturbed cilia formation selectively in certain cell types (chondrocytes, neocortical neurons) but not others (epithelial cells, cerebellar granule cells); Rab23-KO neural progenitors are desensitized to cilium-dependent Hedgehog pathway activation, confirming Carpenter syndrome as a ciliopathy.\",\n      \"method\": \"Conditional knockout mouse (Rab23-CKO), patient iPSC differentiation, zebrafish morpholino knockdown, immunofluorescence of cilia in multiple cell types, Hedgehog pathway activity assay\",\n      \"journal\": \"PLoS Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — three independent vertebrate model systems, multiple cell-type analyses, functional Hh pathway readout\",\n      \"pmids\": [\"40825043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Rab23 and IFT43 are identified as crucial regulators of prostaglandin E receptor 4 (EP4) ciliary trafficking; EP4 physically interacts with IFT43 and Rab23 through its IC3 loop and C-terminal region; high-content siRNA screening and zebrafish/mammalian validation confirm that Rab23 (and IFT43) are required for EP4 delivery to primary cilia.\",\n      \"method\": \"High-content siRNA screen, co-immunoprecipitation (EP4/IFT43/Rab23), zebrafish embryo localization, mammalian cell ciliary trafficking assay, CRISPR base editing of EP4 LPG motif\",\n      \"journal\": \"Communications Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus functional siRNA screen plus zebrafish validation; single study\",\n      \"pmids\": [\"41372612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Rab23 co-localizes with mature melanosomes (TRP-1-positive) and its downregulation by siRNA reduces melanin synthesis, tyrosinase activity, and inhibits UVB-induced melanogenesis via decreased PKA/CREB/MITF pathway activity; Rab23 knockdown also causes abnormal melanosome accumulation around the nucleus, implicating Rab23 in melanosome transport.\",\n      \"method\": \"siRNA knockdown, melanin quantification, tyrosinase activity assay, immunofluorescence co-localization (Rab23/TRP-1), Western blot (PKA/CREB/MITF pathway)\",\n      \"journal\": \"Experimental Dermatology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, functional KD with pathway readout but no direct mechanistic interaction established\",\n      \"pmids\": [\"35514241\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAB23 is a Rab-family small GTPase that cycles between GDP-bound (inactive) and GTP-bound (active) states, localizes primarily to the plasma membrane and early endosomes (and to primary cilia when active), and functions as a negative regulator of Sonic Hedgehog signaling by acting downstream of Smoothened and upstream of Gli transcription factors (particularly Gli2 activator) in a Su(Fu)-dependent manner; it is activated by the Inturned-Fuzzy GEF complex, regulates Smoothened levels in cilia, mediates ciliary delivery of receptors (including dopamine D1R and EP4) via IFT-B/KIF17, participates in clathrin-coated vesicle formation at the plasma membrane through interactions with AP-2/PICALM/endophilin A2, and has additional Hh-independent roles in Nodal signaling, left-right patterning, cortical neuron radial migration (via ERK1/2-N-cadherin), and GAS-targeting autophagy, with loss-of-function mutations causing Carpenter syndrome through context-dependent primary cilia dysfunction.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RAB23 is a small GTPase that functions as a negative regulator of Hedgehog signaling and a versatile mediator of membrane trafficking to primary cilia and the plasma membrane. It acts downstream of Smoothened and upstream of Gli transcription factors in a Su(Fu)-dependent manner to suppress Gli2 activator function and promote Gli3 repressor formation, and it regulates Smoothened levels within the cilium [PMID:11449277, PMID:16364285, PMID:22365972, PMID:20375059]. RAB23 is activated by the Inturned–Fuzzy GEF complex, localizes to the plasma membrane, endosomes, and primary cilia in its GTP-bound state, and mediates ciliary delivery of receptors including dopamine D1R and EP4 via IFT-B/KIF17, while also participating in clathrin-coated vesicle formation through interactions with AP-2, PICALM, and endophilin A2 [PMID:31564489, PMID:26182404, PMID:41372612, PMID:40261407]. Loss-of-function mutations in RAB23 cause Carpenter syndrome, a craniosynostosis-polydactyly disorder driven by context-dependent primary cilia dysfunction and deregulated FGF/ERK and Hedgehog signaling [PMID:17503333, PMID:32662771, PMID:40825043].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"The foundational question of where RAB23 acts in development was answered when positional cloning of the mouse open brain locus revealed Rab23 as an essential negative regulator of Shh signaling, establishing the first link between a Rab GTPase and Hedgehog pathway control.\",\n      \"evidence\": \"Map-based cloning of opb locus and Shh/opb double-mutant epistasis in mouse\",\n      \"pmids\": [\"11449277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of negative regulation unknown\", \"Subcellular site of action unresolved\", \"No direct biochemical target identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Determining where RAB23 resides in the cell revealed plasma membrane and early endosome localization with GTP-state dependence, and showed Patched but not Smoothened colocalizes with Rab23 vesicles, narrowing the trafficking compartment involved.\",\n      \"evidence\": \"Live-cell fluorescence, immunoelectron microscopy, GFP-tagged WT/Q68L/S23N Rab23 in cultured cells\",\n      \"pmids\": [\"14617350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ciliary localization not yet examined\", \"No functional connection to Hh signaling components established biochemically\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic epistasis placed Rab23 downstream of Smoothened and identified Gli2 activator as its primary target, with additional promotion of Gli3 repressor, resolving the signaling hierarchy within the Hh pathway.\",\n      \"evidence\": \"Rab23/Gli2, Rab23/Gli3, Rab23/Smo double-mutant analysis in mouse\",\n      \"pmids\": [\"16364285\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical mechanism linking Rab23 to Gli processing or trafficking unknown\", \"Role of Su(Fu) not yet tested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identification of RAB23 loss-of-function mutations in Carpenter syndrome families established the human disease consequence and confirmed the clinical relevance of RAB23-mediated Hedgehog regulation.\",\n      \"evidence\": \"Homozygosity mapping and sequencing of 15 Carpenter syndrome families\",\n      \"pmids\": [\"17503333\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular pathomechanism in cranial sutures undefined\", \"Whether cilia defects underlie the syndrome not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The discovery that Rab23 depletion decreases Smoothened levels in the primary cilium revealed a specific ciliary trafficking function, connecting its GTPase activity to cilium-dependent Hh signaling.\",\n      \"evidence\": \"FRAP and siRNA/dominant-negative perturbation in MDCK cilia\",\n      \"pmids\": [\"20375059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Rab23 itself enters cilia not established\", \"Cargo specificity beyond Smoothened not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Two distinct roles emerged simultaneously: Rab23 directly associates with Su(Fu) to suppress Gli1 nuclear localization in a GTPase-dependent manner, providing the first biochemical partner in Hh regulation; and Rab23 participates in autophagosome formation targeting Group A Streptococcus independently of starvation autophagy.\",\n      \"evidence\": \"Co-IP of Rab23–Su(Fu), Gli-luciferase in WT vs Su(Fu)-null fibroblasts [PMID:22365972]; siRNA KD with LC3/Atg5 autophagosome assays for GAS [PMID:22452336]\",\n      \"pmids\": [\"22365972\", \"22452336\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether Su(Fu) interaction occurs at cilia or endosomes unclear\", \"Mechanism of autophagosome recruitment undefined\", \"GAS-targeting specificity mechanism unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Demonstration that Rab23 is required in the node for Nodal signal production—independent of Hh—revealed a Hedgehog-independent developmental function in left-right axis determination.\",\n      \"evidence\": \"Mouse/zebrafish double-mutant analysis, Nodal protein and cDNA rescue in embryos\",\n      \"pmids\": [\"24780629\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Trafficking cargo for Nodal signaling not identified\", \"Whether this involves cilia in the node not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Rab23 was shown to form a complex with Kif17 and importin-β2 and to be required for ciliary targeting of Kif17 and dopamine D1 receptors via IFT-B, establishing a general receptor ciliary delivery pathway.\",\n      \"evidence\": \"Co-IP and affinity binding of Rab23–Kif17–importin-β2 [PMID:26136363]; siRNA depletion and Rab23 chimera mis-targeting for D1R ciliary access [PMID:26182404]\",\n      \"pmids\": [\"26136363\", \"26182404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full repertoire of Rab23-dependent ciliary cargoes unknown\", \"Whether Rab23 enters cilia with cargo not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Rab23 was found to regulate cortical neuron radial migration through PDGFRα–ERK1/2–N-cadherin signaling, extending its functions beyond Hh-dependent contexts into neuronal cell biology.\",\n      \"evidence\": \"In utero electroporation KD/CKO with rescue, Western blot, pharmacological ERK inhibition in mouse cortex\",\n      \"pmids\": [\"29420702\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this involves ciliary or endosomal Rab23 pools not distinguished\", \"Direct binding partners in this pathway not identified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of the Inturned–Fuzzy complex as a Rab23-specific GEF resolved how Rab23 GTP loading is regulated and linked planar cell polarity effector proteins to Rab23 activation at the basal body.\",\n      \"evidence\": \"Biochemical GEF assay, Drosophila loss-of-function genetics, siRNA in mammalian cells, longin domain analysis\",\n      \"pmids\": [\"31564489\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No GAP for Rab23 identified\", \"Structural basis of GEF specificity unresolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"The Carpenter syndrome craniosynostosis mechanism was elucidated: RAB23 deficiency causes osteoprogenitor hyperproliferation via elevated FGF10–FGFR1–pERK1/2 and GLI1 signaling, rescuable by ERK inhibition.\",\n      \"evidence\": \"Rab23-deficient mouse, immunostaining, Western blot, pharmacological pERK1/2 rescue\",\n      \"pmids\": [\"32662771\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether FGFR trafficking is directly Rab23-dependent not shown\", \"Tissue-specific cilia dependence not yet tested\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Conditional knockout in cerebellum revealed Rab23 has dual opposing roles: it represses basal Hh pathway activity but facilitates cilium-dependent Smo translocation upon extrinsic Shh stimulation, reconciling apparently conflicting observations.\",\n      \"evidence\": \"Nestin-Cre CKO mouse, Gli reporter, SAG stimulation, Smo ciliary localization assay\",\n      \"pmids\": [\"34210780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Rab23 simultaneously represses basal and promotes stimulated Hh at the molecular level is mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Crystal structures of GDP-bound and GTP-analog-bound human RAB23, plus the Carpenter-associated Y79del mutant, provided the first atomic-level view, showing that Y79del distorts switch II to disrupt effector binding.\",\n      \"evidence\": \"X-ray crystallography, in vitro biochemical and mutant functional assays\",\n      \"pmids\": [\"39615683\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No co-crystal with Su(Fu) or any effector\", \"Structural basis of GEF (Inturned–Fuzzy) recognition unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Multiple studies converged to show that RAB23 loss causes context-dependent (cell-type-specific) cilia defects confirming Carpenter syndrome as a ciliopathy, that RAB23 participates in clathrin-coated vesicle formation at the plasma membrane via AP-2/PICALM/endophilin A2, and that EP4 is an additional Rab23-dependent ciliary cargo.\",\n      \"evidence\": \"CKO mouse/iPSC-neurons/zebrafish cilia analysis [PMID:40825043]; co-IP of RAB23–AP-2–PICALM–endophilin A2 with transferrin uptake assays [PMID:40261407]; siRNA screen and co-IP for EP4 ciliary trafficking [PMID:41372612]\",\n      \"pmids\": [\"40825043\", \"40261407\", \"41372612\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Rab23 coordinates clathrin-mediated endocytosis with ciliary trafficking is unknown\", \"Complete set of Rab23-dependent ciliary cargoes undefined\", \"Whether clathrin role is GTP- or GDP-state-dependent not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include: the identity of the Rab23 GAP, the structural basis of Rab23 interaction with Su(Fu) and the Inturned–Fuzzy GEF, the molecular logic determining cell-type-specific cilia dependence on Rab23, and how Rab23 mechanistically integrates its endosomal, plasma membrane, and ciliary trafficking functions.\",\n      \"evidence\": \"Not applicable — open questions\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No Rab23 GAP identified\", \"No effector co-structure available\", \"Cell-type specificity mechanism uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [7, 14, 19]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 7, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 12, 21]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 16]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [5, 10, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 5, 7, 17, 18]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 11, 21, 24]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 2, 9, 13]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [3, 17]}\n    ],\n    \"complexes\": [\n      \"IFT-B/KIF17/Rab23 ciliary transport complex\",\n      \"AP-2/PICALM/endophilin A2/Rab23 clathrin vesicle complex\"\n    ],\n    \"partners\": [\n      \"SUFU\",\n      \"KIF17\",\n      \"KPNB2\",\n      \"INTU\",\n      \"FUZ\",\n      \"AP2B1\",\n      \"PICALM\",\n      \"SH3GL1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}