Expression of a mouse metallothionein-Escherichia coli beta-galactosidase fusion gene (MT-beta gal) in early mouse embryos.

We have microinjected DNA containing the inducible mouse metallothionein-I (MT-I) promoter, coupled to the structural gene for Escherichia coli beta-galactosidase (lacZ), into the pronuclei of one-cell mouse embryos. A qualitative histochemical assay, with 5-bromo-4-chloro-3-indolyl beta-D-galactopyranoside (X-Gal) as a substrate, was used to detect expression of lacZ at several preimplantation stages. We observed staining indicative of exogenous beta-galactosidase activity in 5-17% of DNA-injected embryos assayed at preimplantation stages after 16-24 h treatment with ZnSO4. Thus, lacZ can be used as an indicator gene for promoter function during early mouse embryogenesis, and the incorporation of the MT-I promoter into fusion genes can be a useful means of controlling the expression of exogenous genes in preimplantation mouse embryos.