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:21081508, PubMed:21490058, PubMed:21949356, PubMed:27807076, PubMed:28775322). Specifically targets extracellular EGF repeats of protein such as CRB2, F7, F9 and NOTCH2 (PubMed:21081508, PubMed:21490058, PubMed:21949356, PubMed:27807076, PubMed:28775322). Acts as a positive regulator of Notch signaling by mediating O-glucosylation of Notch, leading to regulate muscle development (PubMed:27807076). Notch glucosylation does not affect Notch ligand binding (PubMed:21490058). Required during early development to promote gastrulation: acts by mediating O-glucosylation of CRB2, which is required for CRB2 localization to the cell membrane (By similarity). {ECO:0000250|UniProtKB:Q8BYB9, ECO:0000269|PubMed:21081508, ECO:0000269|PubMed:21490058, ECO:0000269|PubMed:21949356, ECO:0000269|PubMed:27807076, ECO:0000269|PubMed:28775322}. This is the function of POGLUT1 (protein O-glucosyltransferase 1, ENSG00000163389).