{"gene":"SLC35A2","run_date":"2026-06-10T07:46:33","timeline":{"discoveries":[{"year":2013,"finding":"Mutations in SLC35A2 reduce UDP-galactose transport into the Golgi, leading to galactose-deficient glycoproteins (N-glycosylation defect). The protein is Golgi-localized.","method":"Biochemical UDP-galactose transport assay, whole-exome sequencing, transferrin glycosylation analysis","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct transport assay combined with glycoprotein biochemistry, replicated across multiple families and independent labs","pmids":["23561849"],"is_preprint":false},{"year":2013,"finding":"De novo frameshift mutations in SLC35A2 result in improperly expressed/unstable mutant proteins, while a missense mutant protein localizes correctly to the Golgi apparatus. Only the wild-type allele is expressed in blood leukocytes due to skewed X-inactivation.","method":"Transient expression experiments with Golgi co-localization imaging, X-inactivation analysis, mRNA analysis in lymphoblastoid cells","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment plus functional allele expression analysis, single lab","pmids":["24115232"],"is_preprint":false},{"year":2015,"finding":"A missense mutation (p.G266V) in SLC35A2 abolishes UDP-galactose transporter function as demonstrated by failure to complement UGT-deficient MDCK-RCAr and CHO-Lec8 cells, while wild-type UGT expression rescues galactosylation. Dietary galactose supplementation nearly completely normalizes transferrin glycosylation.","method":"Complementation assay in UGT-deficient cell lines (MDCK-RCAr and CHO-Lec8), transferrin glycosylation analysis","journal":"Journal of inherited metabolic disease","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional complementation assay with two independent deficient cell lines and biochemical readout, single lab but orthogonal methods","pmids":["25778940"],"is_preprint":false},{"year":2015,"finding":"SLC35A2 (UGT1 and UGT2 splice variants) form complexes with mannoside acetylglucosaminyltransferases (Mgat1, Mgat2, Mgat4B, Mgat5) in the Golgi membrane. All four Mgats are in close proximity to NGT (SLC35A3) and UGT1, but only Mgat4B is in close proximity to UGT2 (distance <10 nm), while other Mgats are 10–40 nm from UGT2.","method":"In situ proximity ligation assay (PLA), FLIM-FRET","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal proximity methods (PLA and FLIM-FRET), single lab","pmids":["25944901"],"is_preprint":false},{"year":2011,"finding":"Both splice variants of UDP-galactose transporter (UGT1 and UGT2/SLC35A2) are required for N- and O-glycosylation of proteins, and both are necessary for chondroitin-4-sulfate synthesis. UGT2 is more abundant in most mammalian tissues and cell lines. MDCK-RCAr cells do not produce keratan sulfate, and neither UGT splice variant rescues this defect.","method":"Complementation analysis in UGT-deficient MDCK and CHO cell lines, glycan analysis","journal":"Glycoconjugate journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementation in two independent deficient cell lines with multiple glycan readouts, single lab","pmids":["21894462"],"is_preprint":false},{"year":2014,"finding":"The short N-terminal region of SLC35A2 (first 35 amino acids) is crucial for galactosylation of N-glycans. Chimeric proteins composed of UGT fused to NGT (SLC35A3) but not CMP-sialic acid transporter (CST) corrected galactosylation defects in UGT-deficient cell lines, indicating functional coupling between UGT and NGT.","method":"Chimeric protein complementation in UGT-deficient cell lines, Golgi localization analysis","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain-deletion and chimeric complementation assays in deficient cells, single lab","pmids":["25451267"],"is_preprint":false},{"year":2019,"finding":"Two critical glycine residues (Gly-202, Gly-214) and two lysine residues (Lys-78, Lys-297) in transmembrane segments are required for SLC35A2 transport activity. The N- and C-terminal cytoplasmic loops are dispensable. Disease-associated mutations S213F and G282R completely abolish function; R55L, G266V, and S304P partially inhibit function; V331I, V258M, and Y267C do not impact function. SLC35A2 activity is required for glycosphingolipid Gb3 surface expression.","method":"Structure-guided mutagenesis, activity rescue assay using Shiga toxin binding as readout in ΔSLC35A2 cells","journal":"Glycobiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro mutagenesis of specific residues with functional activity assay and predicted structural model, single lab but multiple orthogonal mutations tested","pmids":["30834435"],"is_preprint":false},{"year":2019,"finding":"A robust biochemical assay measuring SLC35A2-dependent UDP-galactose transport activity in primary fibroblasts shows that transport activity is directly correlated with the ratio of wild-type to mutant alleles.","method":"UDP-galactose transport assay in primary patient fibroblasts","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct transport activity assay in primary cells with quantitative allele ratio correlation, single lab","pmids":["30817854"],"is_preprint":false},{"year":2018,"finding":"Brain somatic mutations in SLC35A2 cause aberrant N-glycan structures, specifically accumulation of high-degree N-acetylglucosamine glycans, in affected brain tissues from patients with intractable focal epilepsy.","method":"Tissue glyco-capture and nanoLC/mass spectrometry N-glycan analysis of brain tissue with somatic SLC35A2 mutations","journal":"Neurology. Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct glycomic analysis of human brain tissue, single lab with mass spectrometry","pmids":["30584598"],"is_preprint":false},{"year":2021,"finding":"SLC35A2 associates with core 1 β-1,3-galactosyltransferase 1 (C1GalT1/T-synthase) and its chaperone Cosmc. In SLC35A2-deficient cells, protein levels of C1GalT1 and Cosmc are decreased and their Golgi localization is less pronounced, suggesting SLC35A2 stabilizes these O-glycosylation pathway components. Endogenous Cosmc localizes to both ER and Golgi in wild-type cells. SLC35A2 was also identified as a novel molecular target of the antifungal agent itraconazole.","method":"Co-immunoprecipitation, western blotting, subcellular fractionation/imaging in SLC35A2-deficient HEK293T cells","journal":"Biochimica et biophysica acta. Molecular cell research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP interaction data with KO cell functional consequence, single lab","pmids":["36933771"],"is_preprint":false},{"year":2021,"finding":"SLC35A2 interacts with ATPases (ATP2A2, ATP2C1), Golgi pH regulator B (GPR89B), calcium channel (TMCO1), and basigin (BSG) as novel interaction partners, confirmed by NanoBiT split-luciferase assay.","method":"Pull-down mass spectrometry, NanoBiT split-luciferase complementation assay","journal":"Journal of proteomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pull-down MS with in vitro NanoBiT confirmation for selected interactions, single lab","pmids":["34242836"],"is_preprint":false},{"year":2022,"finding":"SLC35A2 deficiency in MDCK cells promotes an epithelial-to-mesenchymal transition (EMT)-like phenotype: cells adopt elongated spindle morphology, show impaired cell-cell adhesion, downregulate E-cadherin, upregulate fibronectin and vimentin, reorganize vimentin intermediate filaments, trigger Golgi compaction, and increase motility and invasiveness.","method":"CRISPR/Cas9 knockout of SLC35A2 in MDCK cells, qPCR, western blotting, morphology/motility assays","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO with multiple orthogonal phenotypic readouts (molecular and cellular), single lab","pmids":["35892570"],"is_preprint":false},{"year":2022,"finding":"SLC35A2 activity is required for recruitment of galactosyltransferase B4GalT1 to the Golgi apparatus in hepatocellular carcinoma cells; SLC35A2 depletion alters membrane glycan profiles and dysregulates glycosylation/expression of cell adhesion molecules, promoting invasion and metastasis.","method":"RNA interference knockdown, co-immunoprecipitation, fluorescence microscopy, lectin microarray, in vivo nude mouse metastasis model","journal":"Cellular oncology (Dordrecht, Netherlands)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and localization data plus functional assays, single lab with multiple readouts","pmids":["36454514"],"is_preprint":false},{"year":2024,"finding":"Focal knockout or knockdown of Slc35a2 in developing mouse cortex (via in utero electroporation with CRISPR or shRNA) disrupts radial neuronal migration, causing heterotopic cells in lower cortical layers and subcortical white matter. Slc35a2 KO in neurons does not alter oligodendrocyte number (suggesting oligodendroglial hyperplasia in MOGHE originates from distinct cell-autonomous effects). Focal KO mice show reduced seizure threshold but not spontaneous seizures.","method":"In utero electroporation with CRISPR/Cas9 or shRNA for KO/KD, cortical layer analysis, EEG recording with PTZ challenge","journal":"Neuroscience letters","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent in vivo studies using orthogonal loss-of-function approaches (CRISPR KO and shRNA KD) with convergent neuronal migration phenotype","pmids":["38909838"],"is_preprint":false},{"year":2024,"finding":"Mosaic Slc35a2 knockout in layer 2/3 cortical neuronal progenitors causes heterotopic neurons in white matter, increased dendritic arborisation complexity, reduced action potential firing, increased afterhyperpolarization duration, reduced burst-firing, increased epileptiform spiking, and increased locomotor activity in mice.","method":"In utero electroporation CRISPR/Cas9 mosaic KO, whole-cell electrophysiology, neuronal reconstruction, EEG recording","journal":"Neurobiology of disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo mosaic KO with electrophysiological, morphological, and behavioral readouts, single lab but multiple orthogonal methods","pmids":["39236911"],"is_preprint":false},{"year":2024,"finding":"Slc35a2 conditional knockout from the Emx1 dorsal telencephalic lineage (excitatory neurons and glia) causes early lethality, abnormal cortical development, increased oligodendroglial cell density, early-onset seizures, and developmental delay. EdU birthdating shows Slc35a2 deficiency delays radial neuronal migration from the subventricular zone. Knockout from the Olig2 lineage alone recapitulates increased oligodendroglial density and abnormal EEG but not a clear seizure phenotype, establishing that Slc35a2 deficiency in neurons is required for epileptogenesis.","method":"Conditional knockout mouse models (Emx1-Cre and Olig2-Cre), EdU birthdating, EEG recording, histology","journal":"Epilepsia","confidence":"High","confidence_rationale":"Tier 2 / Strong — two conditional KO lines with lineage-specific epistasis establishing neuronal vs. oligodendroglial contributions, multiple orthogonal readouts","pmids":["39460689"],"is_preprint":false},{"year":2025,"finding":"Loss-of-function variants in SLC35A2 in human iPSC-derived neurons cause disrupted glycomic signatures, precocious neurodevelopment, hypoactive and asynchronous neural networks, and preferential differentiation toward GABAergic fate. Electrophysiology shows increased inhibitory drive at the synaptic level.","method":"Isogenic iPSC-derived neuron model, glycomic analysis, multi-electrode array network dynamics, single-cell electrophysiology, single-cell transcriptomics","journal":"Brain : a journal of neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — isogenic human neuron model with multiple orthogonal methods (glycomics, electrophysiology, transcriptomics), single lab","pmids":["40418734"],"is_preprint":false},{"year":2025,"finding":"SLC35A2 deficiency in a mouse forebrain model causes a specific defect in O-GalNAc glycan synthesis, with absence of O-GalNAc glycans from neuronal tracts in the corpus callosum and accumulation of truncated precursors on extracellular matrix molecules, while other galactose-containing glycoconjugates remain intact. Cultured primary neurons lacking Slc35a2 show impaired development and hyperexcitability. Human brain tissue from SLC35A2-associated intractable epilepsy shows correlation between variant burden and truncated O-GalNAc glycans.","method":"Conditional KO mouse model, chemoenzymatic glycan labeling, glycoproteomic analysis, primary neuron culture electrophysiology, human tissue analysis","journal":"bioRxiv : the preprint server for biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — preprint with multiple orthogonal methods including mouse model and human tissue validation, single lab","pmids":["41867720"],"is_preprint":true},{"year":2025,"finding":"SLC35A2 is essential for paramyxovirus infection: SLC35A2 KO cells show that UGT activity is required for virus-cell fusion during Sendai virus (SeV) entry but not for Newcastle disease virus (NDV) or mumps virus (MuV) entry. SLC35A2 promotes cell-to-cell fusion/syncytia formation during MuV infection, facilitating cell-to-cell spread.","method":"CRISPR loss-of-function screen, SLC35A2 KO cell infection assays with multiple paramyxoviruses, fusion/syncytia assays","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with multiple virus/readout combinations in a single lab, peer-reviewed","pmids":["39792924"],"is_preprint":false},{"year":2025,"finding":"Glycosphingolipid (GSL) synthesis is severely impaired in SLC35A2-CDG patient fibroblasts and CHO-Lec8 cells, with accumulation of glucosylceramide and deficiency of digalactosylated GSLs and complex gangliosides. Galactose supplementation increases UDP-galactose levels and its transport into the Golgi, restoring GSL synthesis by direct galactose incorporation.","method":"Patient-derived fibroblast GSL profiling, CHO-Lec8 model, UDP-galactose transport assay, galactose supplementation experiments","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — direct transport assay plus lipid glycomic profiling in patient cells and an independent cell model, single lab","pmids":["40576648"],"is_preprint":false},{"year":2025,"finding":"SLC35A2 variants in MOGHE brain tissue cause loss-of-function via altered glycan chains with increased truncated N-glycan glycoforms (agalactosylated glycoforms). Glycoproteins bearing agalactosylated N-glycans are enriched in cell adhesion and axon guidance pathways. Heterotopic neurons show N-glycan damage detectable by chemoenzymatic glycan labeling.","method":"Intact glycopeptide profiling, glycan labeling in brain tissue, whole-exome sequencing with ultra-deep amplicon sequencing validation","journal":"Acta neuropathologica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct glycoproteomic and glycan labeling analysis in human brain tissue and cellular models, single lab","pmids":["39900685"],"is_preprint":false},{"year":2023,"finding":"SLC35A2/SLC35A3 double knockout glycosylation defect is fully rescued by hybrid proteins (SLC35A2-SLC35A3 or SLC35A3-SLC35A2), while SLC35A3 alone only partially restores galactosylation, demonstrating that proper N-glycosylation requires balanced cooperation between SLC35A2 and SLC35A3.","method":"CRISPR double KO in HEK293T cells, hybrid protein expression, glycan analysis","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic complementation with hybrid proteins in defined KO background, single lab","pmids":["37552213"],"is_preprint":false},{"year":2025,"finding":"Cytosolic UDP-Gal biosynthesis (via GALE) is required for SLC35A2 to form homomers and to interact with beta-1,4-galactosyltransferase 1 (B4GALT1) in the Golgi membrane. GALE knockout reduces intracellular UDP-Gal and diminishes SLC35A2 homomer formation and SLC35A2-B4GALT1 interaction.","method":"CRISPR/Cas9 KO of GALE/GALT in HEK293T cells, NanoBiT split-luciferase assay, N-glycan profiling","journal":"Frontiers in molecular biosciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined KO with NanoBiT protein interaction assay and glycan readout, single lab","pmids":["40230451"],"is_preprint":false},{"year":2025,"finding":"SLC35A2 missense (p.G282A) and frameshift (p.F280Tfs*10) variants expressed by in utero electroporation in rat cortex cause neuronal heterotopia in white matter and impaired dendritogenesis at postnatal stages. These phenotypes are recapitulated by in utero silencing of rat Slc35a2, demonstrating a cell-autonomous role for SLC35A2 in neuronal development. The variants variably impact SLC35A2 protein stability and expression.","method":"In utero electroporation of rat brain with variant constructs, shRNA knockdown, histology, dendritic morphology analysis","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo variant expression with convergent KD phenotype confirming cell autonomy, single lab","pmids":["41081555"],"is_preprint":false},{"year":2025,"finding":"Drosophila Ugalt (ortholog of SLC35A2) knockdown reduces mucin-type O-glycans on muscles and neuromuscular junctions (NMJs) without affecting N-glycans. Ugalt knockdown causes mislocalization of NMJ boutons with deficiency of basement membrane components. Genetic interaction between Ugalt and dC1GalT1 (confirmed by double knockdown and double heterozygous analyses) places Ugalt upstream in the mucin-type O-glycosylation pathway regulating NMJ architecture.","method":"Drosophila KO/KD model, glycan staining, NMJ morphology analysis, genetic epistasis (double KD, double heterozygous)","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ortholog model with genetic epistasis and glycan-specific phenotype analysis, single lab","pmids":["41008563"],"is_preprint":false}],"current_model":"SLC35A2 encodes a Golgi- and ER-localized UDP-galactose transporter that supplies UDP-galactose for N-glycosylation, O-glycosylation (including mucin-type O-GalNAc and core 1 O-glycans), and glycosphingolipid synthesis; its transmembrane glycine and lysine residues are critical for transport activity, its short N-terminal region is required for N-glycan galactosylation, it forms functional complexes with glycosyltransferases (B4GalT1, C1GalT1, Mgats) and SLC35A3 in the Golgi membrane, and loss of its function disrupts neuronal radial migration, alters inhibitory/excitatory balance, and causes epileptiform activity, linking defective galactosylation—particularly of O-GalNAc glycans on extracellular matrix proteins—to cortical malformation and epilepsy."},"narrative":{"mechanistic_narrative":"SLC35A2 is a Golgi- and ER-localized UDP-galactose transporter that supplies activated galactose to the secretory glycosylation machinery, and its loss disrupts N-glycosylation, O-glycosylation, and glycosphingolipid synthesis [PMID:23561849, PMID:21894462, PMID:40576648]. Transport activity depends on specific transmembrane glycine and lysine residues (Gly-202, Gly-214, Lys-78, Lys-297) and on its short N-terminal region, which is required specifically for N-glycan galactosylation, whereas the cytoplasmic loops are dispensable [PMID:25451267, PMID:30834435]; disease-associated missense and frameshift variants abolish or partially reduce transport in proportion to the wild-type/mutant allele ratio [PMID:30834435, PMID:30817854]. The transporter operates within Golgi glycosylation assemblies, forming homomers and complexes with glycosyltransferases including B4GalT1, the core 1 enzyme C1GalT1 and its chaperone Cosmc, and Mgat enzymes, and acting in balanced cooperation with the UDP-GlcNAc transporter SLC35A3 to achieve proper galactosylation [PMID:25944901, PMID:36933771, PMID:37552213, PMID:40230451]. Functionally, SLC35A2 supports galactosylation of N-glycans, mucin-type O-GalNAc and core 1 O-glycans, and gangliosides, with loss-of-function causing accumulation of truncated and agalactosylated glycans on cell-adhesion and axon-guidance glycoproteins [PMID:30584598, PMID:41867720, PMID:39900685]. In the developing cortex, focal, mosaic, and lineage-restricted loss of Slc35a2 disrupts radial neuronal migration, producing heterotopic neurons, altered dendritic arborization and intrinsic excitability, epileptiform activity, and seizures, with neuronal—rather than oligodendroglial—deficiency required for epileptogenesis [PMID:38909838, PMID:39236911, PMID:39460689]; human iPSC-derived neurons lacking SLC35A2 show disrupted glycomes, skewed GABAergic differentiation, and increased inhibitory drive [PMID:40418734]. The defect underlies a congenital disorder of glycosylation in which dietary galactose supplementation can normalize transferrin glycosylation and restore glycosphingolipid synthesis [PMID:25778940, PMID:40576648].","teleology":[{"year":2013,"claim":"Established that SLC35A2 is the Golgi UDP-galactose transporter whose mutation causes a human congenital disorder of glycosylation, linking a transport defect to galactose-deficient glycoproteins.","evidence":"UDP-galactose transport assay, exome sequencing, and transferrin glycosylation analysis in patient samples; localization and X-inactivation analysis in expression systems","pmids":["23561849","24115232"],"confidence":"High","gaps":["Did not define which transmembrane residues mediate transport","Did not resolve tissue-specific consequences beyond blood glycoproteins"]},{"year":2014,"claim":"Mapped the structural determinants of substrate selectivity by showing the N-terminal 35 residues are required for N-glycan galactosylation and that UGT functionally couples with the GlcNAc transporter NGT/SLC35A3.","evidence":"Domain-deletion and UGT-NGT/CST chimeric complementation in UGT-deficient cell lines","pmids":["25451267"],"confidence":"Medium","gaps":["Did not establish how the N-terminus selects galactosylation over other transport functions","Single lab, no structural model"]},{"year":2011,"claim":"Defined the breadth of glycoconjugates dependent on the transporter, showing both UGT1 and UGT2 splice variants support N-, O-glycosylation and chondroitin-4-sulfate synthesis.","evidence":"Complementation analysis in UGT-deficient MDCK and CHO cell lines with glycan readouts","pmids":["21894462"],"confidence":"Medium","gaps":["Did not explain functional divergence between UGT1 and UGT2","Keratan sulfate defect remained unrescued and unexplained"]},{"year":2015,"claim":"Demonstrated SLC35A2 acts within multi-enzyme Golgi assemblies, positioning the transporter in proximity to Mgat glycosyltransferases and SLC35A3, and showed dietary galactose can rescue glycosylation in patients.","evidence":"Proximity ligation assay and FLIM-FRET for complexes; complementation in UGT-deficient cells with galactose supplementation","pmids":["25944901","25778940"],"confidence":"High","gaps":["Did not establish stoichiometry or stability of the assemblies","Mechanism of galactose rescue at the transporter level not defined here"]},{"year":2019,"claim":"Identified the transmembrane residues essential for transport and built a quantitative genotype-function relationship across disease variants, including a glycosphingolipid (Gb3) readout.","evidence":"Structure-guided mutagenesis with Shiga toxin binding assay in knockout cells; UDP-galactose transport assay in primary fibroblasts correlated to allele ratio","pmids":["30834435","30817854"],"confidence":"High","gaps":["No experimental transporter structure","Did not connect residue-level defects to neuronal phenotypes"]},{"year":2018,"claim":"Connected somatic SLC35A2 mutations to focal epilepsy by demonstrating aberrant brain N-glycans (accumulation of high-GlcNAc structures) in resected epileptogenic tissue.","evidence":"Glyco-capture and nanoLC/MS N-glycan profiling of brain tissue with somatic mutations","pmids":["30584598"],"confidence":"Medium","gaps":["Did not establish causal link from glycan defect to seizures","No cell-type resolution"]},{"year":2022,"claim":"Showed that SLC35A2 controls Golgi recruitment of galactosyltransferases and that its loss reprograms cell-adhesion glycosylation, driving EMT-like and pro-metastatic phenotypes.","evidence":"CRISPR knockout in MDCK cells with morphology/motility readouts; RNAi knockdown, co-IP, lectin microarray, and mouse metastasis model in hepatocellular carcinoma cells","pmids":["35892570","36454514"],"confidence":"Medium","gaps":["Direct B4GalT1-SLC35A2 binding relied on co-IP without structural validation","Causal glycoprotein substrates driving invasion not pinpointed"]},{"year":2021,"claim":"Expanded the SLC35A2 interactome and proposed a stabilizing role, showing association with C1GalT1/Cosmc, Golgi ion/pH regulators, and basigin.","evidence":"Co-immunoprecipitation, western blotting, and imaging in knockout cells; pull-down MS with NanoBiT confirmation","pmids":["36933771","34242836"],"confidence":"Medium","gaps":["Single-lab interaction data, limited reciprocal validation","Functional significance of ion-channel/pH-regulator partners undefined"]},{"year":2023,"claim":"Established that proper N-glycosylation requires balanced cooperation between SLC35A2 and SLC35A3 rather than either transporter alone.","evidence":"CRISPR double knockout in HEK293T cells with hybrid SLC35A2-SLC35A3 protein rescue and glycan analysis","pmids":["37552213"],"confidence":"Medium","gaps":["Molecular basis of the balance requirement not resolved","Did not test relevance in neuronal context"]},{"year":2024,"claim":"Demonstrated a cell-autonomous neurodevelopmental role: Slc35a2 loss disrupts radial migration, producing heterotopic neurons, altered intrinsic excitability, and epileptiform activity, with neuronal deficiency required for epileptogenesis.","evidence":"In utero electroporation CRISPR/shRNA and conditional Emx1-Cre/Olig2-Cre knockout mice with cortical layer analysis, electrophysiology, and EEG","pmids":["38909838","39236911","39460689"],"confidence":"High","gaps":["Did not define the specific glycan substrate driving migration defects","Link between transport defect and altered excitability mechanistically incomplete"]},{"year":2025,"claim":"Linked loss-of-function to specific glycan defects on adhesion/axon-guidance glycoproteins and to altered neuronal network behavior, implicating truncated O-GalNAc and agalactosylated N-glycans in cortical malformation and epilepsy.","evidence":"iPSC-derived neuron glycomics/electrophysiology/transcriptomics; human MOGHE brain glycoproteomics; conditional mouse and primary neuron models (one preprint)","pmids":["40418734","39900685","41867720"],"confidence":"High","gaps":["Direct causal glycoprotein targets mediating epileptogenesis not isolated","O-GalNAc mechanism partly from preprint awaiting peer review"]},{"year":2025,"claim":"Defined cytosolic UDP-galactose supply (via GALE) as a determinant of SLC35A2 homomerization and B4GALT1 interaction, and confirmed galactose-responsive glycosphingolipid synthesis.","evidence":"GALE/GALT knockout with NanoBiT interaction assays; patient fibroblast and CHO-Lec8 GSL profiling with galactose supplementation","pmids":["40230451","40576648"],"confidence":"Medium","gaps":["Causal direction between substrate availability and complex assembly inferred from knockouts","Therapeutic generalizability of galactose rescue across tissues unestablished"]},{"year":2025,"claim":"Extended the functional repertoire to ortholog and pathogen contexts, showing a conserved role in mucin-type O-glycosylation of neuromuscular architecture and a requirement for paramyxovirus fusion/entry.","evidence":"Drosophila Ugalt knockdown with genetic epistasis to dC1GalT1; CRISPR loss-of-function screen and knockout infection/fusion assays with multiple paramyxoviruses","pmids":["41008563","39792924"],"confidence":"Medium","gaps":["Direct glycan target on viral fusion machinery not identified","Conservation of O-GalNAc role to mammalian NMJ not directly tested"]},{"year":null,"claim":"The specific galactosylated glycoproteins whose deficiency causally produces neuronal migration failure and epileptogenesis remain unidentified, and no experimental transporter structure exists.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No isolated causal substrate linking glycan defect to seizures","No high-resolution structure of the human transporter","Mechanism coupling glycan loss to altered intrinsic excitability undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005215","term_label":"transporter activity","supporting_discovery_ids":[0,2,6,7,19]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[0,7,22]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,3,9,12]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,4,5,21]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[6,19]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[13,14,15]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,8,20]}],"complexes":[],"partners":["SLC35A3","B4GALT1","C1GALT1","COSMC","MGAT1","GPR89B","TMCO1","BSG"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P78381","full_name":"UDP-galactose translocator","aliases":["Solute carrier family 35 member A2","UDP-galactose transporter","UDP-Gal-Tr","UGT"],"length_aa":396,"mass_kda":41.3,"function":"Transports uridine diphosphate galactose (UDP-galactose) from the cytosol into the Golgi apparatus, functioning as an antiporter that exchanges UDP-galactose for UMP (PubMed:12682060, PubMed:9010752). It is also able to exchange UDP-galactose for AMP and CMP, and to transport UDP-N-acetylgalactosamine (UDP-GalNAc) and other nucleotide sugars (PubMed:11784306, PubMed:12682060). 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The protein is Golgi-localized.\",\n      \"method\": \"Biochemical UDP-galactose transport assay, whole-exome sequencing, transferrin glycosylation analysis\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct transport assay combined with glycoprotein biochemistry, replicated across multiple families and independent labs\",\n      \"pmids\": [\"23561849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"De novo frameshift mutations in SLC35A2 result in improperly expressed/unstable mutant proteins, while a missense mutant protein localizes correctly to the Golgi apparatus. Only the wild-type allele is expressed in blood leukocytes due to skewed X-inactivation.\",\n      \"method\": \"Transient expression experiments with Golgi co-localization imaging, X-inactivation analysis, mRNA analysis in lymphoblastoid cells\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment plus functional allele expression analysis, single lab\",\n      \"pmids\": [\"24115232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A missense mutation (p.G266V) in SLC35A2 abolishes UDP-galactose transporter function as demonstrated by failure to complement UGT-deficient MDCK-RCAr and CHO-Lec8 cells, while wild-type UGT expression rescues galactosylation. Dietary galactose supplementation nearly completely normalizes transferrin glycosylation.\",\n      \"method\": \"Complementation assay in UGT-deficient cell lines (MDCK-RCAr and CHO-Lec8), transferrin glycosylation analysis\",\n      \"journal\": \"Journal of inherited metabolic disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional complementation assay with two independent deficient cell lines and biochemical readout, single lab but orthogonal methods\",\n      \"pmids\": [\"25778940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SLC35A2 (UGT1 and UGT2 splice variants) form complexes with mannoside acetylglucosaminyltransferases (Mgat1, Mgat2, Mgat4B, Mgat5) in the Golgi membrane. All four Mgats are in close proximity to NGT (SLC35A3) and UGT1, but only Mgat4B is in close proximity to UGT2 (distance <10 nm), while other Mgats are 10–40 nm from UGT2.\",\n      \"method\": \"In situ proximity ligation assay (PLA), FLIM-FRET\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal proximity methods (PLA and FLIM-FRET), single lab\",\n      \"pmids\": [\"25944901\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Both splice variants of UDP-galactose transporter (UGT1 and UGT2/SLC35A2) are required for N- and O-glycosylation of proteins, and both are necessary for chondroitin-4-sulfate synthesis. UGT2 is more abundant in most mammalian tissues and cell lines. MDCK-RCAr cells do not produce keratan sulfate, and neither UGT splice variant rescues this defect.\",\n      \"method\": \"Complementation analysis in UGT-deficient MDCK and CHO cell lines, glycan analysis\",\n      \"journal\": \"Glycoconjugate journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementation in two independent deficient cell lines with multiple glycan readouts, single lab\",\n      \"pmids\": [\"21894462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The short N-terminal region of SLC35A2 (first 35 amino acids) is crucial for galactosylation of N-glycans. Chimeric proteins composed of UGT fused to NGT (SLC35A3) but not CMP-sialic acid transporter (CST) corrected galactosylation defects in UGT-deficient cell lines, indicating functional coupling between UGT and NGT.\",\n      \"method\": \"Chimeric protein complementation in UGT-deficient cell lines, Golgi localization analysis\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain-deletion and chimeric complementation assays in deficient cells, single lab\",\n      \"pmids\": [\"25451267\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Two critical glycine residues (Gly-202, Gly-214) and two lysine residues (Lys-78, Lys-297) in transmembrane segments are required for SLC35A2 transport activity. The N- and C-terminal cytoplasmic loops are dispensable. Disease-associated mutations S213F and G282R completely abolish function; R55L, G266V, and S304P partially inhibit function; V331I, V258M, and Y267C do not impact function. SLC35A2 activity is required for glycosphingolipid Gb3 surface expression.\",\n      \"method\": \"Structure-guided mutagenesis, activity rescue assay using Shiga toxin binding as readout in ΔSLC35A2 cells\",\n      \"journal\": \"Glycobiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro mutagenesis of specific residues with functional activity assay and predicted structural model, single lab but multiple orthogonal mutations tested\",\n      \"pmids\": [\"30834435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A robust biochemical assay measuring SLC35A2-dependent UDP-galactose transport activity in primary fibroblasts shows that transport activity is directly correlated with the ratio of wild-type to mutant alleles.\",\n      \"method\": \"UDP-galactose transport assay in primary patient fibroblasts\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct transport activity assay in primary cells with quantitative allele ratio correlation, single lab\",\n      \"pmids\": [\"30817854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Brain somatic mutations in SLC35A2 cause aberrant N-glycan structures, specifically accumulation of high-degree N-acetylglucosamine glycans, in affected brain tissues from patients with intractable focal epilepsy.\",\n      \"method\": \"Tissue glyco-capture and nanoLC/mass spectrometry N-glycan analysis of brain tissue with somatic SLC35A2 mutations\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct glycomic analysis of human brain tissue, single lab with mass spectrometry\",\n      \"pmids\": [\"30584598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SLC35A2 associates with core 1 β-1,3-galactosyltransferase 1 (C1GalT1/T-synthase) and its chaperone Cosmc. In SLC35A2-deficient cells, protein levels of C1GalT1 and Cosmc are decreased and their Golgi localization is less pronounced, suggesting SLC35A2 stabilizes these O-glycosylation pathway components. Endogenous Cosmc localizes to both ER and Golgi in wild-type cells. SLC35A2 was also identified as a novel molecular target of the antifungal agent itraconazole.\",\n      \"method\": \"Co-immunoprecipitation, western blotting, subcellular fractionation/imaging in SLC35A2-deficient HEK293T cells\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP interaction data with KO cell functional consequence, single lab\",\n      \"pmids\": [\"36933771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SLC35A2 interacts with ATPases (ATP2A2, ATP2C1), Golgi pH regulator B (GPR89B), calcium channel (TMCO1), and basigin (BSG) as novel interaction partners, confirmed by NanoBiT split-luciferase assay.\",\n      \"method\": \"Pull-down mass spectrometry, NanoBiT split-luciferase complementation assay\",\n      \"journal\": \"Journal of proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pull-down MS with in vitro NanoBiT confirmation for selected interactions, single lab\",\n      \"pmids\": [\"34242836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC35A2 deficiency in MDCK cells promotes an epithelial-to-mesenchymal transition (EMT)-like phenotype: cells adopt elongated spindle morphology, show impaired cell-cell adhesion, downregulate E-cadherin, upregulate fibronectin and vimentin, reorganize vimentin intermediate filaments, trigger Golgi compaction, and increase motility and invasiveness.\",\n      \"method\": \"CRISPR/Cas9 knockout of SLC35A2 in MDCK cells, qPCR, western blotting, morphology/motility assays\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO with multiple orthogonal phenotypic readouts (molecular and cellular), single lab\",\n      \"pmids\": [\"35892570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SLC35A2 activity is required for recruitment of galactosyltransferase B4GalT1 to the Golgi apparatus in hepatocellular carcinoma cells; SLC35A2 depletion alters membrane glycan profiles and dysregulates glycosylation/expression of cell adhesion molecules, promoting invasion and metastasis.\",\n      \"method\": \"RNA interference knockdown, co-immunoprecipitation, fluorescence microscopy, lectin microarray, in vivo nude mouse metastasis model\",\n      \"journal\": \"Cellular oncology (Dordrecht, Netherlands)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and localization data plus functional assays, single lab with multiple readouts\",\n      \"pmids\": [\"36454514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Focal knockout or knockdown of Slc35a2 in developing mouse cortex (via in utero electroporation with CRISPR or shRNA) disrupts radial neuronal migration, causing heterotopic cells in lower cortical layers and subcortical white matter. Slc35a2 KO in neurons does not alter oligodendrocyte number (suggesting oligodendroglial hyperplasia in MOGHE originates from distinct cell-autonomous effects). Focal KO mice show reduced seizure threshold but not spontaneous seizures.\",\n      \"method\": \"In utero electroporation with CRISPR/Cas9 or shRNA for KO/KD, cortical layer analysis, EEG recording with PTZ challenge\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent in vivo studies using orthogonal loss-of-function approaches (CRISPR KO and shRNA KD) with convergent neuronal migration phenotype\",\n      \"pmids\": [\"38909838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Mosaic Slc35a2 knockout in layer 2/3 cortical neuronal progenitors causes heterotopic neurons in white matter, increased dendritic arborisation complexity, reduced action potential firing, increased afterhyperpolarization duration, reduced burst-firing, increased epileptiform spiking, and increased locomotor activity in mice.\",\n      \"method\": \"In utero electroporation CRISPR/Cas9 mosaic KO, whole-cell electrophysiology, neuronal reconstruction, EEG recording\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo mosaic KO with electrophysiological, morphological, and behavioral readouts, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"39236911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Slc35a2 conditional knockout from the Emx1 dorsal telencephalic lineage (excitatory neurons and glia) causes early lethality, abnormal cortical development, increased oligodendroglial cell density, early-onset seizures, and developmental delay. EdU birthdating shows Slc35a2 deficiency delays radial neuronal migration from the subventricular zone. Knockout from the Olig2 lineage alone recapitulates increased oligodendroglial density and abnormal EEG but not a clear seizure phenotype, establishing that Slc35a2 deficiency in neurons is required for epileptogenesis.\",\n      \"method\": \"Conditional knockout mouse models (Emx1-Cre and Olig2-Cre), EdU birthdating, EEG recording, histology\",\n      \"journal\": \"Epilepsia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two conditional KO lines with lineage-specific epistasis establishing neuronal vs. oligodendroglial contributions, multiple orthogonal readouts\",\n      \"pmids\": [\"39460689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Loss-of-function variants in SLC35A2 in human iPSC-derived neurons cause disrupted glycomic signatures, precocious neurodevelopment, hypoactive and asynchronous neural networks, and preferential differentiation toward GABAergic fate. Electrophysiology shows increased inhibitory drive at the synaptic level.\",\n      \"method\": \"Isogenic iPSC-derived neuron model, glycomic analysis, multi-electrode array network dynamics, single-cell electrophysiology, single-cell transcriptomics\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isogenic human neuron model with multiple orthogonal methods (glycomics, electrophysiology, transcriptomics), single lab\",\n      \"pmids\": [\"40418734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SLC35A2 deficiency in a mouse forebrain model causes a specific defect in O-GalNAc glycan synthesis, with absence of O-GalNAc glycans from neuronal tracts in the corpus callosum and accumulation of truncated precursors on extracellular matrix molecules, while other galactose-containing glycoconjugates remain intact. Cultured primary neurons lacking Slc35a2 show impaired development and hyperexcitability. Human brain tissue from SLC35A2-associated intractable epilepsy shows correlation between variant burden and truncated O-GalNAc glycans.\",\n      \"method\": \"Conditional KO mouse model, chemoenzymatic glycan labeling, glycoproteomic analysis, primary neuron culture electrophysiology, human tissue analysis\",\n      \"journal\": \"bioRxiv : the preprint server for biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — preprint with multiple orthogonal methods including mouse model and human tissue validation, single lab\",\n      \"pmids\": [\"41867720\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SLC35A2 is essential for paramyxovirus infection: SLC35A2 KO cells show that UGT activity is required for virus-cell fusion during Sendai virus (SeV) entry but not for Newcastle disease virus (NDV) or mumps virus (MuV) entry. SLC35A2 promotes cell-to-cell fusion/syncytia formation during MuV infection, facilitating cell-to-cell spread.\",\n      \"method\": \"CRISPR loss-of-function screen, SLC35A2 KO cell infection assays with multiple paramyxoviruses, fusion/syncytia assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with multiple virus/readout combinations in a single lab, peer-reviewed\",\n      \"pmids\": [\"39792924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Glycosphingolipid (GSL) synthesis is severely impaired in SLC35A2-CDG patient fibroblasts and CHO-Lec8 cells, with accumulation of glucosylceramide and deficiency of digalactosylated GSLs and complex gangliosides. Galactose supplementation increases UDP-galactose levels and its transport into the Golgi, restoring GSL synthesis by direct galactose incorporation.\",\n      \"method\": \"Patient-derived fibroblast GSL profiling, CHO-Lec8 model, UDP-galactose transport assay, galactose supplementation experiments\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct transport assay plus lipid glycomic profiling in patient cells and an independent cell model, single lab\",\n      \"pmids\": [\"40576648\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SLC35A2 variants in MOGHE brain tissue cause loss-of-function via altered glycan chains with increased truncated N-glycan glycoforms (agalactosylated glycoforms). Glycoproteins bearing agalactosylated N-glycans are enriched in cell adhesion and axon guidance pathways. Heterotopic neurons show N-glycan damage detectable by chemoenzymatic glycan labeling.\",\n      \"method\": \"Intact glycopeptide profiling, glycan labeling in brain tissue, whole-exome sequencing with ultra-deep amplicon sequencing validation\",\n      \"journal\": \"Acta neuropathologica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct glycoproteomic and glycan labeling analysis in human brain tissue and cellular models, single lab\",\n      \"pmids\": [\"39900685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SLC35A2/SLC35A3 double knockout glycosylation defect is fully rescued by hybrid proteins (SLC35A2-SLC35A3 or SLC35A3-SLC35A2), while SLC35A3 alone only partially restores galactosylation, demonstrating that proper N-glycosylation requires balanced cooperation between SLC35A2 and SLC35A3.\",\n      \"method\": \"CRISPR double KO in HEK293T cells, hybrid protein expression, glycan analysis\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic complementation with hybrid proteins in defined KO background, single lab\",\n      \"pmids\": [\"37552213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cytosolic UDP-Gal biosynthesis (via GALE) is required for SLC35A2 to form homomers and to interact with beta-1,4-galactosyltransferase 1 (B4GALT1) in the Golgi membrane. GALE knockout reduces intracellular UDP-Gal and diminishes SLC35A2 homomer formation and SLC35A2-B4GALT1 interaction.\",\n      \"method\": \"CRISPR/Cas9 KO of GALE/GALT in HEK293T cells, NanoBiT split-luciferase assay, N-glycan profiling\",\n      \"journal\": \"Frontiers in molecular biosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined KO with NanoBiT protein interaction assay and glycan readout, single lab\",\n      \"pmids\": [\"40230451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SLC35A2 missense (p.G282A) and frameshift (p.F280Tfs*10) variants expressed by in utero electroporation in rat cortex cause neuronal heterotopia in white matter and impaired dendritogenesis at postnatal stages. These phenotypes are recapitulated by in utero silencing of rat Slc35a2, demonstrating a cell-autonomous role for SLC35A2 in neuronal development. The variants variably impact SLC35A2 protein stability and expression.\",\n      \"method\": \"In utero electroporation of rat brain with variant constructs, shRNA knockdown, histology, dendritic morphology analysis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo variant expression with convergent KD phenotype confirming cell autonomy, single lab\",\n      \"pmids\": [\"41081555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Drosophila Ugalt (ortholog of SLC35A2) knockdown reduces mucin-type O-glycans on muscles and neuromuscular junctions (NMJs) without affecting N-glycans. Ugalt knockdown causes mislocalization of NMJ boutons with deficiency of basement membrane components. Genetic interaction between Ugalt and dC1GalT1 (confirmed by double knockdown and double heterozygous analyses) places Ugalt upstream in the mucin-type O-glycosylation pathway regulating NMJ architecture.\",\n      \"method\": \"Drosophila KO/KD model, glycan staining, NMJ morphology analysis, genetic epistasis (double KD, double heterozygous)\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ortholog model with genetic epistasis and glycan-specific phenotype analysis, single lab\",\n      \"pmids\": [\"41008563\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SLC35A2 encodes a Golgi- and ER-localized UDP-galactose transporter that supplies UDP-galactose for N-glycosylation, O-glycosylation (including mucin-type O-GalNAc and core 1 O-glycans), and glycosphingolipid synthesis; its transmembrane glycine and lysine residues are critical for transport activity, its short N-terminal region is required for N-glycan galactosylation, it forms functional complexes with glycosyltransferases (B4GalT1, C1GalT1, Mgats) and SLC35A3 in the Golgi membrane, and loss of its function disrupts neuronal radial migration, alters inhibitory/excitatory balance, and causes epileptiform activity, linking defective galactosylation—particularly of O-GalNAc glycans on extracellular matrix proteins—to cortical malformation and epilepsy.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SLC35A2 is a Golgi- and ER-localized UDP-galactose transporter that supplies activated galactose to the secretory glycosylation machinery, and its loss disrupts N-glycosylation, O-glycosylation, and glycosphingolipid synthesis [#0, #4, #19]. Transport activity depends on specific transmembrane glycine and lysine residues (Gly-202, Gly-214, Lys-78, Lys-297) and on its short N-terminal region, which is required specifically for N-glycan galactosylation, whereas the cytoplasmic loops are dispensable [#5, #6]; disease-associated missense and frameshift variants abolish or partially reduce transport in proportion to the wild-type/mutant allele ratio [#6, #7]. The transporter operates within Golgi glycosylation assemblies, forming homomers and complexes with glycosyltransferases including B4GalT1, the core 1 enzyme C1GalT1 and its chaperone Cosmc, and Mgat enzymes, and acting in balanced cooperation with the UDP-GlcNAc transporter SLC35A3 to achieve proper galactosylation [#3, #9, #21, #22]. Functionally, SLC35A2 supports galactosylation of N-glycans, mucin-type O-GalNAc and core 1 O-glycans, and gangliosides, with loss-of-function causing accumulation of truncated and agalactosylated glycans on cell-adhesion and axon-guidance glycoproteins [#8, #17, #20]. In the developing cortex, focal, mosaic, and lineage-restricted loss of Slc35a2 disrupts radial neuronal migration, producing heterotopic neurons, altered dendritic arborization and intrinsic excitability, epileptiform activity, and seizures, with neuronal—rather than oligodendroglial—deficiency required for epileptogenesis [#13, #14, #15]; human iPSC-derived neurons lacking SLC35A2 show disrupted glycomes, skewed GABAergic differentiation, and increased inhibitory drive [#16]. The defect underlies a congenital disorder of glycosylation in which dietary galactose supplementation can normalize transferrin glycosylation and restore glycosphingolipid synthesis [#2, #19].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"Established that SLC35A2 is the Golgi UDP-galactose transporter whose mutation causes a human congenital disorder of glycosylation, linking a transport defect to galactose-deficient glycoproteins.\",\n      \"evidence\": \"UDP-galactose transport assay, exome sequencing, and transferrin glycosylation analysis in patient samples; localization and X-inactivation analysis in expression systems\",\n      \"pmids\": [\"23561849\", \"24115232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which transmembrane residues mediate transport\", \"Did not resolve tissue-specific consequences beyond blood glycoproteins\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped the structural determinants of substrate selectivity by showing the N-terminal 35 residues are required for N-glycan galactosylation and that UGT functionally couples with the GlcNAc transporter NGT/SLC35A3.\",\n      \"evidence\": \"Domain-deletion and UGT-NGT/CST chimeric complementation in UGT-deficient cell lines\",\n      \"pmids\": [\"25451267\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not establish how the N-terminus selects galactosylation over other transport functions\", \"Single lab, no structural model\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the breadth of glycoconjugates dependent on the transporter, showing both UGT1 and UGT2 splice variants support N-, O-glycosylation and chondroitin-4-sulfate synthesis.\",\n      \"evidence\": \"Complementation analysis in UGT-deficient MDCK and CHO cell lines with glycan readouts\",\n      \"pmids\": [\"21894462\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not explain functional divergence between UGT1 and UGT2\", \"Keratan sulfate defect remained unrescued and unexplained\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated SLC35A2 acts within multi-enzyme Golgi assemblies, positioning the transporter in proximity to Mgat glycosyltransferases and SLC35A3, and showed dietary galactose can rescue glycosylation in patients.\",\n      \"evidence\": \"Proximity ligation assay and FLIM-FRET for complexes; complementation in UGT-deficient cells with galactose supplementation\",\n      \"pmids\": [\"25944901\", \"25778940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish stoichiometry or stability of the assemblies\", \"Mechanism of galactose rescue at the transporter level not defined here\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified the transmembrane residues essential for transport and built a quantitative genotype-function relationship across disease variants, including a glycosphingolipid (Gb3) readout.\",\n      \"evidence\": \"Structure-guided mutagenesis with Shiga toxin binding assay in knockout cells; UDP-galactose transport assay in primary fibroblasts correlated to allele ratio\",\n      \"pmids\": [\"30834435\", \"30817854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental transporter structure\", \"Did not connect residue-level defects to neuronal phenotypes\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected somatic SLC35A2 mutations to focal epilepsy by demonstrating aberrant brain N-glycans (accumulation of high-GlcNAc structures) in resected epileptogenic tissue.\",\n      \"evidence\": \"Glyco-capture and nanoLC/MS N-glycan profiling of brain tissue with somatic mutations\",\n      \"pmids\": [\"30584598\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not establish causal link from glycan defect to seizures\", \"No cell-type resolution\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed that SLC35A2 controls Golgi recruitment of galactosyltransferases and that its loss reprograms cell-adhesion glycosylation, driving EMT-like and pro-metastatic phenotypes.\",\n      \"evidence\": \"CRISPR knockout in MDCK cells with morphology/motility readouts; RNAi knockdown, co-IP, lectin microarray, and mouse metastasis model in hepatocellular carcinoma cells\",\n      \"pmids\": [\"35892570\", \"36454514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct B4GalT1-SLC35A2 binding relied on co-IP without structural validation\", \"Causal glycoprotein substrates driving invasion not pinpointed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Expanded the SLC35A2 interactome and proposed a stabilizing role, showing association with C1GalT1/Cosmc, Golgi ion/pH regulators, and basigin.\",\n      \"evidence\": \"Co-immunoprecipitation, western blotting, and imaging in knockout cells; pull-down MS with NanoBiT confirmation\",\n      \"pmids\": [\"36933771\", \"34242836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab interaction data, limited reciprocal validation\", \"Functional significance of ion-channel/pH-regulator partners undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established that proper N-glycosylation requires balanced cooperation between SLC35A2 and SLC35A3 rather than either transporter alone.\",\n      \"evidence\": \"CRISPR double knockout in HEK293T cells with hybrid SLC35A2-SLC35A3 protein rescue and glycan analysis\",\n      \"pmids\": [\"37552213\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of the balance requirement not resolved\", \"Did not test relevance in neuronal context\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated a cell-autonomous neurodevelopmental role: Slc35a2 loss disrupts radial migration, producing heterotopic neurons, altered intrinsic excitability, and epileptiform activity, with neuronal deficiency required for epileptogenesis.\",\n      \"evidence\": \"In utero electroporation CRISPR/shRNA and conditional Emx1-Cre/Olig2-Cre knockout mice with cortical layer analysis, electrophysiology, and EEG\",\n      \"pmids\": [\"38909838\", \"39236911\", \"39460689\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the specific glycan substrate driving migration defects\", \"Link between transport defect and altered excitability mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked loss-of-function to specific glycan defects on adhesion/axon-guidance glycoproteins and to altered neuronal network behavior, implicating truncated O-GalNAc and agalactosylated N-glycans in cortical malformation and epilepsy.\",\n      \"evidence\": \"iPSC-derived neuron glycomics/electrophysiology/transcriptomics; human MOGHE brain glycoproteomics; conditional mouse and primary neuron models (one preprint)\",\n      \"pmids\": [\"40418734\", \"39900685\", \"41867720\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct causal glycoprotein targets mediating epileptogenesis not isolated\", \"O-GalNAc mechanism partly from preprint awaiting peer review\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined cytosolic UDP-galactose supply (via GALE) as a determinant of SLC35A2 homomerization and B4GALT1 interaction, and confirmed galactose-responsive glycosphingolipid synthesis.\",\n      \"evidence\": \"GALE/GALT knockout with NanoBiT interaction assays; patient fibroblast and CHO-Lec8 GSL profiling with galactose supplementation\",\n      \"pmids\": [\"40230451\", \"40576648\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal direction between substrate availability and complex assembly inferred from knockouts\", \"Therapeutic generalizability of galactose rescue across tissues unestablished\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended the functional repertoire to ortholog and pathogen contexts, showing a conserved role in mucin-type O-glycosylation of neuromuscular architecture and a requirement for paramyxovirus fusion/entry.\",\n      \"evidence\": \"Drosophila Ugalt knockdown with genetic epistasis to dC1GalT1; CRISPR loss-of-function screen and knockout infection/fusion assays with multiple paramyxoviruses\",\n      \"pmids\": [\"41008563\", \"39792924\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct glycan target on viral fusion machinery not identified\", \"Conservation of O-GalNAc role to mammalian NMJ not directly tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The specific galactosylated glycoproteins whose deficiency causally produces neuronal migration failure and epileptogenesis remain unidentified, and no experimental transporter structure exists.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No isolated causal substrate linking glycan defect to seizures\", \"No high-resolution structure of the human transporter\", \"Mechanism coupling glycan loss to altered intrinsic excitability undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005215\", \"supporting_discovery_ids\": [0, 2, 6, 7, 19]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [0, 7, 22]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 3, 9, 12]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 4, 5, 21]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 19]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [13, 14, 15]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 8, 20]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"SLC35A3\", \"B4GALT1\", \"C1GalT1\", \"Cosmc\", \"MGAT1\", \"GPR89B\", \"TMCO1\", \"BSG\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}