Control of Gene Expression at the Onset of Bovine Embryonic Development1

The objective of this study was to examine the timing and mechanisms involved in transcription initiation in bovine embryos. Transcriptional activity and its regulation were explored by labeling 1-cell zygotes and 2-cell embryos with [(3)H]uridine in the presence or absence of alpha-amanitin, aphidicolin, and tricostatin A (TSA) (inhibitors of mRNA synthesis, DNA replication, and histone deacetylases, respectively) followed by a total RNA isolation and determination of [(3)H]uridine incorporation. We also analyzed translation of zygotic/embryonic mRNAs by labeling zygotes and 2-cell embryos with [(35)S]methionine in the presence or absence of alpha-amanitin, aphidicolin, and TSA followed by two-dimensional PAGE and autoradiography. We show that bovine 1-cell zygotes and 2-cell embryos are transcriptionally and translationally active. The first and second rounds of DNA replication are important regulators of early gene expression as the inhibition of DNA replication resulted in a dramatic decrease in both transcriptional and translational activity. Moreover, acetylation of histones plays an important role in this early gene activation at the onset of embryonic development in the cow.