Catalyzes the synthesis of lactosylceramide (LacCer) via the transfer of galactose from UDP-galactose to glucosylceramide (GlcCer). Required for proper patterning of the dorsoventral axis during embryogenesis through the regulation of BMP signaling. Plays a role in proteoglycan glycosylation that is required for BMP-dependent specification of the dorsoventral axis