Introduction and Expression of Recombinant β-Galactosidase Genes in Cleavage Stage Mouse Embryos

In an attempt to study gene regulation in very early stages of mouse embryogenesis, we injected genes constructed by joining the coding sequence of the bacterial β-galactosidase gene to four different animal gene enhancers/promoters and to poly (A) signals, and examined the gene expression in cleavage stage embryos.
With appropriate injection volumes for each embryonic stage, ranging from 0.2 to 1.3 pl, the majority of the injected embryos underwent at least one further cleavage. Expression of injected genes, which occurred transiently after injection, required the promoter sequences but without much distinction of the source of enhancer/promoter complexes. This result was in a sharp contrast to transfection of mouse cell lines where the recombinant genes were variably expressed reflecting differential enhancer effects.
By injection at the 1-cell stage, expression of injected genes was low while the expression by injection at the 2-cell or later stages was several fold higher, which may correlate with the fact that most zygotic gene expression begins after the 2-cell stage. The low expression at the 1-cell stage was augmented by the conditions causing clea***age arrest such as inhibition of DNA synthesis with aphidicolin.