Degradation of maternal Cdc25c during the maternal to zygotic transition is dependent upon embryonic transcription

To gain a better understanding of the molecular differences that may contri bute to cleavage arrest and the poorer development associated with laborato ry produced embryos, a series of experiments were conducted to quantitate t he message levels of the cell cycle controller cdc25c, over the maternal to zygotic transition (MZT) in 4-cell in vivo- and in vitro-derived porcine e mbryos. The experiments were designed to measure both maternal and embryoni c derived cdc25c transcripts by quantitative reverse transcription-competit ive polymerase chain reaction (RT-cPCR), determine the point of the transit ion to zygotic genome activation, and study the interaction between initial embryonic transcription and maternal cdc25c degradation. Analysis of in vi vo- and in vitro-derived embryos revealed no difference in cdc25c message l evel for any of the times P4CC (P > 0.05). Comparison of control embryos fr om 5- to 33-hr P4CC revealed a reduction in transcript quantities in the 10 -hr P4CC group that was maintained at later time points (P < 0.05). Embryos cultured in the RNA polymerase inhibitor, <alpha>-amanitin, from cleavage to 5-, 10-, 18-, 25-, or 33-hr P4CC displayed no difference in cdc25c level s when compared to controls at similar time points (P > 0.05). However, if embryos were first exposed to alpha -amanitin after 18-hr P4CC with this tr eatment continuing to 33 hr, the levels of cdc25c transcript were reduced ( P<0.04) when compared to those embryos that were first exposed to the inhib itor at either 5- or 10-hr P4CC. This finding and the comparison of these s ame embryos to the 0-33-hr <alpha>-amanitin and control groups allowed us t o conclude that cdc25c transcription began between 10- and 18-hr P4CC, with the degradation of maternal cdc25c message dependent on transcriptional in itiation. Mol. Reprod. Dev. 60: 181-188, 2001. (C) 2001 Wiley-Liss, Inc.