The expression of β‐galactosidase during preimplantation mouse embryogenesis

Lysosomal acid hydrolase expression during preimplantation mouse embryogenesis has proved useful in estimating when mRNA transcription commences during this period. Previous work from this laboratory has shown that α‐galactosidase and β‐glucuronidase undergo 50‐ to 100‐fold increases in activity between the two‐cell stage and the blastocyst stage [1, 2]. Here we show that β‐galactosidase activity levels undergo a similar change. We also demonstrate that mouse strains with the Bgl‐sh allele produce cleavage stage embryos with 2–4‐fold higher activity levels than strains with the Bgl‐sd allele. Bgl has been shown to control β‐galactosidase levels in adult mouse tissues [3]. Unfertilized egg β‐galactosidase levels are also regulated by Bgl, but loci distant from Bgl modify egg expression. The distant sites are not observed to act during cleavage. Hybrid embryos (Bgl‐sd/h) show intermediate activity levels to the parental types. The timing of the deviation of hybrid embryo β‐galactosidase activity levels from maternal‐type activity levels is used to estimate when transcription of genes governing β‐galactosidase expression occurs.