CLEAVAGE AND H-3 URIDINE INCORPORATION IN BOVINE EMBRYOS OF HIGH IN-VITRO DEVELOPMENTAL POTENTIAL

The timing of genome activation in bovine embryos is still not well defined. The objective of this study was therefore to investigate transcription in bovine embryos with a high potential to develop in culture after in Vitro fertilization, by examining, autoradiographically, their incorporation of H-3-uridine. Initial experiments determined that developmental potential in vitro could be related to the time of first division of the zygote. Embryos that completed their first cleavage within 30 hours of exposure to sperm were more likely to develop into blastocysts (65.7%) and to hatch (50.9%). Using such embryos, it was found that 10 of 12 8-cell and all 11 4-cell stage embryos were labeled after a 2-4-hr exposure to H-3-Uridine. Among 2-cell stage embryos, 0 of 23, 3 of 17, 8 of 15, and 3 of 4 were labeled after exposure to H-3-uridine of 2, 4, 7, and 10 hr, respectively. Treatment with alpha-amanatin (10-100 mu g/ ml) blocked H-3-uridine incorporation but did not inhibit cleavage during the first 4 cell cycles. It was concluded that transcription occurs as early as the 2-cell stage in bovine embryos in vitro but is not critical to the first four cell cycles. (C) 1994 Wiley-Liss, Inc.