A recessive deletion in the GlcNAc-1-phosphotransferase gene results in periimplantation embryonic lethality

Formation of the dolichol oligosaccharide precursor is essential for the pr oduction of asparagine- (N-) linked oligosaccharides (N-glycans) in eukaryo tic cells. The first step in precursor biosynthesis requires the enzyme UDP -Glc-NAc: dolichol phosphate N-acetylglucosamine-1-phosphate transferase (G PT), Without GPT activity, subsequent steps necessary in constructing the o ligosaccharide precursor cannot occur, Inhibition of this biosynthetic step using tunicamycin, a GlcNAc analog, produces a deficiency in N-glycosylati on in cell lines and embryonic lethality during preimplantation development in vitro, suggesting that N-glycan formation is essential in early embryog enesis. In exploring structure-function relationships among N-glycans, and since tunicamycin has various reported biochemical activities; we have gene rated a germline deletion in the mouse GPT gene. GPT mutant embryos were an alyzed and the phenotypes obtained were compared with previous studies usin g tunicamycin, We find that embryos homozygous for a deletion in the GPT ge ne complete preimplantation development and also implant in the uterine epi thelium, but die shortly thereafter between days 4-5 postfertilization with cell degeneration apparent among both embryonic and extraembryonic cell ty pes. Of cells derived from these early embryos, neither trophoblast nor emb ryonic endodermal lineages are able to survive in culture in vitro. These r esults indicate that GPT function is essential in early embryogenesis and s uggest that N-glycosylation is needed for the viability of cells comprising the peri-implantation stage embryo.