Developmental and molecular correlates of bovine preimplantation embryos.

Expression of embryonic genes is altered in different culture conditions, which influence developmental potential both during preimplantation and fetal development. The objective of this study was to define the effects of culture conditions on: bovine embryonic development to blastocyst stage, blastocyst cell number, apoptosis and expression patterns of a panel of developmentally important genes. Bovine embryos were cultured in vitro in three culture media containing amino acids, namely potassium simplex optimization medium (KSOMaa), Charles Rosenkrans 1 (CR1aa) and synthetic oviductal fluid (SOFaa). Apoptosis in blastocysts was determined by TUNEL assay and expression profiles of developmentally important genes were assayed by real-time PCR. In vivo-produced bovine blastocysts were used as controls for experiments determining gene expression patterns. While the cleavage rates did not differ, embryos cultured in SOFaa had higher rates of development to blastocyst stage (P < 0.05). Mean cell numbers and percentages of apoptotic cells per blastocyst did not differ among the groups. Expression of the heat shock protein 70 (Hsp70) gene was significantly up-regulated in both CR1aa and KSOMaa when compared with SOFaa (P < 0.001). DNA methyltransferase 3a (Dnmt3a) expression was higher in embryos cultured in CR1aa than in those cultured in SOFaa (P < 0.001). Expression of interferon tau (IF-tau) and insulin-like growth factor II receptor (Igf-2r) genes was significantly up-regulated in KSOMaa when compared with CR1aa (P < 0.001). Gene expression did not differ between in vivo-derived blastocysts and their in vitro-derived counterparts. In conclusion, SOFaa supports higher development to blastocyst stage than KSOMaa and CR1aa, and the culture conditions influence gene expression.