Catalyzes the first glycosylation step in glycosphingolipid biosynthesis, the transfer of glucose to ceramide to produce glucosylceramides (GlcCer). GlcCer are known to contribute to the physical properties and physiological functions of membranes and may regulate signal transduction (PubMed:11443131, PubMed:19240113, PubMed:21325339). Only branched-chain sphingoid bases like 15-methylhexadecasphing-4-enine are used for generating complex sphingolipids in Caenorhabditis elegans (PubMed:7651085). an N-acylsphing-4-enine + UDP-alpha-D-glucose = a beta-D-glucosyl-(1<->1')-N-acylsphing-4-enine + H(+) + UDP N-acyl-15-methylhexadecasphing-4-enine + UDP-alpha-D-glucose = H(+) + N-acyl-1-beta-D-glucosyl-15-methylhexadecasphing-4-enine + UDP Lipid metabolism; sphingolipid metabolism. Expressed mostly in intestine and vulva. The D1, D2, D3, (Q/R)XXRW motif is a critical part of the GCS active site, involved in catalysis and UDP-sugar binding. Reduced brood size. Belongs to the glycosyltransferase 2 family.