Dual specificity glycosyltransferase that catalyzes the transfer of glucose and xylose from UDP-glucose and UDP-xylose, respectively, to a serine residue found in the consensus sequence of C-X-S-X-P-C (PubMed:21949356, PubMed:26496195). Specifically targets extracellular EGF repeats of protein such as CRB2, F7, F9 and NOTCH2 (PubMed:21949356, PubMed:26496195). Acts as a positive regulator of Notch signaling by mediating O-glucosylation of Notch, leading to regulate muscle development (By similarity). Notch glucosylation does not affect Notch ligand binding (By similarity). Required during early development to promote gastrulation: acts by mediating O-glucosylation of CRB2, which is required for CRB2 localization to the cell membrane (PubMed:26496195). L-seryl-[EGF-like domain protein] + UDP-alpha-D-xylose = 3-O-(beta-D-xylosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP L-seryl-[EGF-like domain protein] + UDP-alpha-D-glucose = 3-O-(beta-D-glucosyl)-L-seryl-[EGF-like domain protein] + H(+) + UDP Protein modification; protein glycosylation. Widely expressed in newborn and adult tissues (at protein level). Mutant embryos die at or before 9.5 dpc. At 7.0 to 7.5 dpc, they cannot be morphologically distinguished from wild-type littermates (PubMed:21490058, PubMed:26496195). At 8.0 dpc, mutant embryos exhibit an abnormally expanded neural plate that does not fold properly, absence of heart rudiments and posterior axis truncation (PubMed:21490058). Defects are caused by a deficit of mesoderm caused by impaired gastrulation. Belongs to the glycosyltransferase 90 family.