Beta-1,3-N-acetylglucosaminyltransferase that plays a key role in the synthesis of lacto- or neolacto-series carbohydrate chains on glycolipids, notably by participating in biosynthesis of HNK-1 and Lewis X carbohydrate structures. Has strong activity toward lactosylceramide (LacCer) and neolactotetraosylceramide (nLc(4)Cer; paragloboside), resulting in the synthesis of Lc(3)Cer and neolactopentaosylceramide (nLc(5)Cer), respectively. Plays a central role in regulating neolacto-series glycolipid synthesis during embryonic development. a beta-D-Gal-(1->4)-beta-D-Glc-(1<->1)-Cer(d18:1(4E)) + UDP-N-acetyl-alpha-D-glucosamine = a beta-D-GlcNAc-(1->3)-beta-D-Gal-(1->4)-beta-D-Glc-(1<->1)-Cer(d18:1(4E)) + H(+) + UDP a neolactoside nLc4Cer(d18:1(4E)) + UDP-N-acetyl-alpha-D-glucosamine = a neolactoside IV(3)-beta-GlcNAc-nLc4Cer(d18:1(4E)) + H(+) + UDP Protein modification; protein glycosylation. Highly expressed in adult spleen, placenta and cerebellar Purkinje cells where it colocalized with HNK-1. Expressed at lower level in brain, lung, thymus and muscle. Mainly expressed during embryonic development. Expressed in most tissues at embryonic day 11 with elevated expression in the developing central nervous system. Belongs to the glycosyltransferase 31 family.