Transfers N-acetylgalactosamine onto globotriaosylceramide (PubMed:9417047). Plays a critical role in preimplantation stage embryonic development (PubMed:11463849). globoside Gb3Cer (d18:1(4E)) + UDP-N-acetyl-alpha-D-galactosamine = globoside Gb4Cer (d18:1(4E)) + H(+) + UDP Protein modification; protein glycosylation. Detected in brain, ovary, kidney, uterus and stomach (PubMed:9417047, PubMed:11463849). In ovary, specifically expressed in follicular granulosa cells and shows particularly strong expression at later stages of follicle development (PubMed:11463849). Detected in embryos from 12.5 days post coitum (dpc) onwards. Expressed in all four ventricles of the developing brain, with highest expression in the outer ventricular layer. Also found in the limb buds at 12.5 dpc. Detected in the brain (hippocampus) and retina at postnatal day 1. Expression in the retina is localized to the ganglion cell layer. At postnatal day 10, expression remains strong in the hippocampus where it localizes to the four CA fields and the dentate gyrus. Embryonic lethal. Lethality occurs at the preimplantation stage, between 3.5 and 4.5 days post-coitum (dpc). Belongs to the glycosyltransferase 31 family. b3GalT3