Participates in the initial step of the glucosylceramide-based glycosphingolipid/GSL synthetic pathway at the cytosolic surface of the Golgi. Catalyzes the transfer of glucose from UDP-glucose to ceramide to produce glucosylceramide/GlcCer (such as beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine) (PubMed:18095347). Glucosylceramide is the core component of glycosphingolipids/GSLs, amphipathic molecules consisting of a ceramide lipid moiety embedded in the outer leaflet of the membrane, linked to one of hundreds of different externally oriented oligosaccharide structures. Glycosphingolipids are essential components of membrane microdomains that mediate membrane trafficking and signal transduction. They are implicated in many fundamental cellular processes, including growth, differentiation, migration, morphogenesis, cell-to-cell and cell-to-matrix interactions (PubMed:18095347). Glycosphingolipids are required for convergence extension movements during early development (PubMed:18095347). Catalyzes the synthesis of xylosylceramide/XylCer (such as beta-D-xylosyl-(1<->1')-N-acylsphing-4-enine) using UDP-Xyl as xylose donor (By similarity). an N-acylsphing-4-enine + UDP-alpha-D-glucose = a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + H(+) + UDP an N-acylsphing-4-enine + UDP-alpha-D-xylose = a beta-D-xylosyl-(1<->1')-N-acylsphing-4-enine + H(+) + UDP N-(9Z-octadecenoyl)-sphing-4-enine + UDP-alpha-D-xylose = beta-D-xylosyl-(1<->1')-N-(9Z-octadecenoyl)-sphing-4-enine + H(+) + UDP Lipid metabolism; sphingolipid metabolism. At the late gastrula stage, weakly expressed ubiquitously. As neurulation proceeds (stages 15-16), expression moves towards the dorsal structures: involuted paraxial mesoderm and neural folds. In the tailbud embryo (stage 28), expression is restricted to the notochord. At later stages (stage 35), expression remains in the notochord and also appears weakly in the cephalic region. Expressed both maternally and zygotically. Expressed at all stages of oogenesis except in previtellogenic oocytes. During embryogenesis, weakly expressed as early as the one-cell stage shortly after fertilization, and remains at a relatively uniform level throughout embryogenesis, persisting at least until stage 35 (early tadpole). The D1, D2, D3, (Q/R)XXRW motif is a critical part of the GCS active site, involved in catalysis and UDP-sugar binding. Belongs to the glycosyltransferase 2 family.