Embryonic transcription in in vitro cultured bovine embryos

The rate of cleavage and the onset of embryonic transcription of bovine embryos cultured in vitro (IVC) has been investigated. Embryos were derived from in vitro matured, in vitro fertilized oocytes (IVM/IVF) to improve developmental synchrony. The rate of cleavage was assessed by morphological evaluation between the one- and eight- to 16-cell stage. The rate of cleavage was found to be equivalent to that reported for in vivo recovered embryos. To assess the onset of embryonic transcription, embryos were cultured to the eight- to 16-cell stage in the presence of alpha-amanitin for various periods of time followed by two-dimensional polyacrylamide gel electrophoresis. Embryos readily cleaved to the eight- to 16-cell stage in the presence of inhibitor. alpha-Amanitin-sensitive protein synthesis was first detected at 36-48 h post-insemination (hpi) and continued up to 84 hpi. We conclude that bovine embryos produced by IVM/IVF/IVC are competent to initiate embryonic transcription at 36-48 h post-insemination and suggest that in vitro-induced cleavage arrest is not due to failure of the embryonic genome to initiate transcription.