Activation of mouse metallothionein-I promoter in mouse preimplantation embryos after pronuclear microinjection.

摘要

Pronuclei of in vitro-fertilized eggs were microinjected with a fusion gene composed of the mouse metallothionein-I promoter and the Escherichia coli beta-galactosidase reporter gene (lacZ). The eggs were cultured up to the blastocyst stage in Whitten's medium supplemented with 100 鍹 EDTA. Expression of the reporter gene was first detected at the 2-cell stage. The proportion of embryos expressing the lacZ gene reached a maximum of 80% at 33-48 h after fertilization. The proportion declined from the 4-cell stage onward, but some embryos still showed positive staining at the blastocyst stage. alpha-Amanitin blocked the expression of lacZ gene only when added before 12 h after fertilization, suggesting that transcription had started during the pronuclear stage rather than in cleavage stages. The presence of EDTA in the culture medium reduced the expression markedly from the morula stage onwards, but 25 鍹 ZnCl2 enhanced expression after the 4-cell stage in the presence of EDTA.