COMPLEX N-GLYCANS IN MGAT1 NULL PREIMPLANTATION EMBRYOS ARISE FROM MATERNAL MGAT1 RNA

Mice with a null mutation in the Mgat1 gene lack N-acetylglucosaminylt ransferase I (GlcNAc-TI; EC 2.4.1.101), and die at mid-gestation, This result suggested that development of Mgat1(-/-) blastocysts and their implantation could occur in the absence of complex and hybrid N-glyca ns, However, inner cell mass of all blastocysts from several Mgat1(+/- ) heterozygous crosses bind the lectin E-PHA, indicating that Mgat1 nu ll mutant blastocysts are able to synthesize complex N-glycans (Campbe ll et al,, (1995) Glycobiology, 5, 535-543), In order to directly test this hypothesis, Mgat1(-/-) blastocysts were positively identified by polymerase chain reaction (PCR) of genomic DNA, Reverse transcriptase PCR (RT-PCR) of RNA isolated from the same blastocysts, and restricti on analysis of the PCR products, revealed that Mgat1 null blastocysts contained Mgat1 RNA derived from the wild-type Mgat1 gene, Consistent with this, all 3.5 day blastocysts from five heterozygous crosses boun d the lectin L-PHA, a lectin previously shown not to bind to E8.5 or E 9.5 Mgat1(-/-) embryos that lack complex N-glycans (Ioffe and Stanley (1994) Pi oc. Natl, Acad, Sci,, USA, 91, 728-732), Blastocysts of 4.5 days post-coitum (dpc) obtained by culturing 3.5 dpc blastocysts also bound L-PHA, However, mutant embryos that did not bind L-PHA were pres ent among progeny from E5.5 onward, Therefore, the effects of the Mgat 1 null mutation are not operative until sometime between implantation and E5.5, due to the continued presence of maternally derived Mgat1 mR NA in preimplantation embryos.