Cell cycle regulation in the early porcine embryo

The transition from maternal to zygotic control of development occurs during the 4-cell stage of the porcine embryo. This transition is characterized by degradation of maternal transcripts, activation of the embryonic genome, and a qualitative shift in expressed proteins. A better understanding of the regulatory mechanisms operating during this period may provide answers to reduce embryonic loss.; A quantitative reverse transcription-competitive polymerase chain reaction (RT-cPCR) strategy allowed us to address changes in transcript concentrations during the 4-cell stage. Specifically, the transcript quantities of two positive regulators of mitotic entry, cyclin B1 and cdc25c, were determined. After poly(A) RNA had been isolated from single embryos at specific times post-4-cell cleavage (P4CC), RT-cPCR was performed by using introduced truncated mimics for both cyclin B1 and cdc25c in separate experiments. The quantities of cyclin B1 and cdc25c message were calculated.; The quantity of cyclin B1 transcript declined from early to late periods (0- to 33-h) P4CC in both in vivo- and in vitro-derived control embryos. The cyclin B1 transcript concentration was similar to embryos exposed to the RNA polymerase inhibitor, α-amanitin, from specific times P4CC to 33-h P4CC, and did not differ from the 33-h control group.; The quantity of cdc25c poly(A) RNA over the same periods sampled for cyclin B1 revealed no difference between in vivo- and in vitro-derived embryos, but also showed a reduction toward the end of the cell cycle. Embryos treated with α-amanitin over specific time periods ending at 33-h P4CC displayed reduced quantities of cdc25c transcript when the treatment began after 18-h P4CC. A second α-amanitin treatment group was added for these experiments. This treatment consisted of inhibitor exposure from time of cleavage to the 4-cell stage to later time points that corresponded with those from control embryo groups. No difference in transcript quantity was observed between these embryos and controls.; Together, the cyclin B1 and cdc25c transcript results suggested that maternal poly(A) RNA degradation occurred during the 4-cell stage of the porcine embryo. In addition, the cdc25c results indicated that this degradation was dependent on the activation of the zygotic genome after 10-h P4CC.