Abstract: 415

APOPTOSIS IN BOVINE OOCYTES AND IN PREIMPLANTATION EMBRYOS: THE ROLE OF Bcl-2 AND Bax GENES.

Ming Yuan Yang¹ , Rajaduri Rajamahendran^{1 *}
Department of Animal Science, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 ¹

Studies have shown that fragmented embryos are associated with decreased pregnancy rate following embryo transfer and with poor survival following cryopreservation. The objectives of this study are: a) to investigate whether apoptosis could be an underlying mechanism of bovine embryo fragmentation and; b) to study the pattern of Bcl-2 and Bax expression to help elucidate their potential roles in the regulation of apoptosis during embryo development. Bovine oocytes were obtained from slaughterhouse ovaries. Embryos were obtained via IVM, IVF, and IVC procedures. The morphological analysis of apoptosis in blastocysts was carried out using PI staining and TUNEL technique. DNA was extracted from pooled blastocysts and DNA fragments were detected by 2% agrose gel electrophoresis for biochemical detection of apoptosis. Expression of Bcl-2 and Bax in oocytes and embryos of different qualities and stages was determined by western blotting. The results showed that the blastocyst cells displayed the characteristics of apoptosis, suggesting that this may be the mechanism of cell deletion and embryonic loss during bovine embryo development. Bcl-2 expression was higher in good quality oocytes and embryos and hardly detectable in poor quality oocytes (denuded). Expression of Bax was found in all oocytes and embryos with the highest expression in poor quality oocytes, implying that the ratio of Bcl-2 to Bax may determine the sensitivity of an embryo towards survival or apoptosis. In summary, our study suggests that apoptosis is an underlying mechanism of the high incidence of fragmented bovine embryos obtained through IVF. To our knowledge, we are the first to demonstrate that the ratio of Bcl-2 family dimers may play a critical role in preimplantation embryo development. These findings could have important implications for improving IVF and related techniques.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.