Haploidy influences Bak and Bcl-xL mRNA expression and increases incidence of apoptosis in porcine embryos.

The objective of this study was to determine developmental pattern, total cell number, apoptosis and apoptosis-related gene expression in haploid and diploid embryos following parthenogenetic activation. In vitro-matured porcine oocytes were activated by electrical pulses and cultured in the absence or presence of cytochalasin B for 3 h. Zygotes with two polar bodies (haploid) and one polar body (diploid) were carefully selected and were further cultured in NCSU 23 medium containing 0.4% bovine serum albumin (BSA) for 7 days. The percentage of development to blastocyst stage was higher (p < 0.01) in the diploid than in the haploid parthenotes. In haploid blastocysts, average total cell number was significantly reduced (p < 0.05) and apoptosis was increased at day 7. The relative abundance of Bcl-xL and Bak mRNA in the diploid blastocysts was similar to that of in vivo-fertilized embryos. However, Bcl-xL was significantly decreased, and Bak mRNA was significantly increased (p < 0.05) in haploid parthenotes compared with the diploid parthenotes. These results suggest that the haploid state affects apoptosis-related gene expression which results in increased apoptosis and decreased developmental competence of haploid parthenotes.