Abstract
The aim of this study was to determine the influence of the homogeneity of genomic components and ploidy on the in vitro development of porcine parthenogenetic oocytes to the blastocyst stage. In vitro matured oocytes were subjected to a single pulse of electro-stimulation (El-St; 100 μsec, 1,500 V/cm) for activation. First, the activated oocytes were cultured for 6, 16, 18, 20 and 22 h after El-St, and examined for the timing of the first cleavage of parthenogenetic haploids. Next, the effects of the timing and duration of cytochalasin B (CB) treatment on inhibition of the first cleavage of haploids were examined in order to produce homogenous parthenogenetic diploids. Then the developmental ability to the blastocyst stage was compared among activated oocytes with genomic components of haploid (without CB treatment), homogeneous diploid (nn-diploid, CB treatment for 6 h from 20 h after El-St), and heterogeneous diploid (nn'-diploid, CB treatment for 4 h immediately after El-St). Most haploids were at the prophase to telophase of the first cleavage between 16 and 22 h after El-St. When the haploids were treated with 5.0 μg/ml CB for 6 h from 20 h after El-St, their first cleavage was efficiently suppressed, and most of them (84%) became diploids. The frequency of parthenogenetic development to the blastocyst stage was significantly lower in haploids (5%) than in nn-diploids (48%, P<0.01) or nn'-diploids (57%, P<0.01). These results shows that ploidy of activated oocytes, but not the homology of genomic components, affects the development of porcine parthenogenetic oocytes to the blastocyst stage.
