Mice lacking N-acetylglucosaminyltransferase I activity die at mid- gestation, revealing an essential role for complex or hybrid N-linked carbohydrates

Eukaryotic cells require N-linked carbohydrates for survival. However, the biosynthetic intermediate Man5GlcNAc2Asn, in place of mature N-linked structures, allows glycoprotein synthesis and somatic cell growth to proceed normally. To determine whether the same would be true in a complex biological situation, the gene Mgat-1 was disrupted by homologous recombination in embryonic stem cells and transmitted to the germ line. The Mgat-1 gene encodes N-acetylglucosaminyltransferase I [GlcNAc-TI; α-1,3-mannosyl- glycoprotein β-1,2-N-acetylglucosaminyltransferase; UDP-N-acetyl-D- glucosamine:glycoprotein (N-acetyl-D-glucosamine to α-D-mannosyl-1,3-(R₁)- β-D-mannosyl-R₂) β-1,2-N-acetyl-D-glucosaminyltransferase, EC 2.4.1.101], the transferase that initiates synthesis of hybrid and complex N-linked carbohydrates from Man5GlcNAc2Asn. Mice lacking GlcNAc-TI activity did not survive to term. Biochemical and morphological analyses of embryos from 8.5 to 13.5 days of gestation showed that Mgat-1(-/-) embryos are developmentally retarded, most noticeably in neural tissue, and die between 9.5 and 10.5 days of development.