Effects of tunicamycin on preimplantation mouse embryos: prevention of molecular differentiation during blastocyst formation.

To examine the role of carbohydrate-containing molecules of preimplantation mouse embryos in early development, effects of tunicamycin were analyzed at the molecular level. Embryos cultured in the presence of tunicamycin (0.1 micrograms/ml) from earlier than the 16-cell stage did not develop into blastocysts, though cell divisions continued normally. Tunicamycin inhibited not only the synthesis of carbohydrate chains of usual N-glycosidic glycoproteins but also that of characteristic large polysaccharides (Mr greater than 9K) of early embryos. Expression of several polypeptides which are characteristic of the blastocyst stage (blastocyst-characteristic proteins: BCPs) was strongly inhibited in the embryos treated by tunicamycin from earlier than the 16-cell stage, while the expression was not inhibited in the embryos treated by the drug after that stage as analyzed by two-dimensional polyacrylamide gel electrophoresis. The expression of BCPs appeared to be dependent on de novo mRNA synthesis, since it was also inhibited by alpha-amanitin treatment. Since tunicamycin was shown not to inhibit expression of most other proteins and the bulk of mRNA, the inhibitory effects of tunicamycin appeared to be specific for the induction of BCPs. These observations suggest that the glycoprotein(s) and/or the characteristic large polysaccharides on the morula stage embryos play an essential role not only for morphological development but also for triggering differentiation at the molecular level.