Expression of LacZ Gene Controlled by Various Promoters in Mouse Preimplantation Embryos

In this study, the activity of mouse phosphoglycerate kinase promoter (PGK) and murine embryonic stem cell virus promoter (MESV), enhanced by the connection of the R-segment and part of the U5 sequence (RU5) of the long terminal repeat of human T-cell leukemia virus type 1, was compared with that of simian virus 40 early promoter (SV40) and human cytomegalovirus early promoter (CMV). Escherichia coli β-galactosidase (LacZ) reporter gene connected to these promoters was microinjected into pronuclei of mouse zygotes, and their expression of developing embryos during the preimplantation period was evaluated histochemically with X-gal. No difference was observed in the proportion of embryos which developed into the morula stage among the promoter sequences at 96 h after hCG injection, but the expression of LacZ gene connected to MESV-RU5 (MESV-LacZ) was lower than that to PGK-RU5 (PGK-LacZ), CMV (CMV-LacZ) and SV40 (SV40-LacZ) in the morula stage embryos (P<0.05). In another experiment, more than 50% of embryos microinjected with PGK- and CMV-LacZ responded positively to X-gal staining at 48 h after hCG injection and the activity of these promoters continued at nearly the same rate from there onwards. However, the rate of expression of SV40- and MESV-LacZ was lower than that of PGK- and CMV-LacZ at 48 h after hCG injection (P<0.05). Although expression of MESV-LacZ was consistently low in proportion and weak in intensity, that of SV40-LacZ was high at 72 h after hCG injection and was equivalent to that of PGK- and CMV-LacZ at 96 h after hCG injection. Regardless of the promoters used, the expression of LacZ gene in the embryos showed various intensities of blue staining. The frequency of mosaic patterns and a weak intensity of gene expression in morphologically normal embryos had a tendency to be higher than in degenerated embryos or those whose development had been arrested.