Transcriptional control of development, protein synthesis, and heat-induced heat shock protein 70 synthesis in 2-cell bovine embryos

Experiments were performed to evaluate the role of transcription in early d evelopment of bovine embryos. Two transcription inhibitors-5,6-dichloro-1-b eta-D-ribofuranosylbenzimidazole (DRB) and actinomycin D-were used to test whether 1) the inhibitors alter the rate of early embryonic development and protein synthesis, 2) heat shock increases the steady-state amounts of mRN A for the inducible form of heat shock protein 70 (HSP70) in embryos, and 3 ) this latter effect is blocked by transcription inhibitors. Addition of ei ther DRB or actinomycin D to culture medium beginning 8 h postinsemination (hpi) reduced the proportion of oocytes that had undergone cleavage by 32-3 4 hpi. Both transcription inhibitors also reduced the proportion of cleaved embryos that reached the 4-cell stage by 32-34 hpi. Incorporation of S-35- labeled amino acids into de novo synthesized protein by bovine 2-cell embry os was lower for embryos cultured with DRB. Using reverse transcription-pol ymerase chain reaction, HSP70 mRNA in 2- and 4-cell embryos was increased b y exposure to 42 degrees C. Both inhibitors reduced amounts of HSP70 mRNA a t 42 degrees C. Results indicate that bovine embryos can undergo transcript ion in response to heat shock as early as the 2-cell stage. Moreover, the o bservations that transcription inhibitors reduce rates of cleavage and earl y development point out the importance of transcription for development fro m the earliest period of embryonic life.