Parthenogenetic activation of mouse and pig oocytes matured in vitro

Abstract

The objective of this study was to determine if mouse and pig oocytes matured in vitro undergo parthenogenetic activation following exposure to various activation stimuli. Cumulus-intact, germinal vesicle-stage mouse oocytes (n = 151) were collected from pregnant mare serum gonadotropin primed mice and incubated overnight in Brinster's medium. This culture system allowed an 85% maturation to Metaphase II. Pig oocytes (n = 242) were gathered from ovaries collected at an abbattoir and incubated in vitro for 48 h to allow maturation to occur (51% maturation to Metaphase II). Following maturation, mouse and pig oocytes were exposed to various activation stimuli. Mouse oocytes were treated with medium containing ethanol (7%), electricity (85 V, 30 us, one time), or medium; then they were incubated for 6 to 8 h to allow for activation. Pig oocytes were treated with medium containing ethanol (10%), electricity (85 V, 30 us once or twice), ethanol followed by electricity, or medium then incubated for 18 h to allow for activation. A portion of the mouse and pig oocytes were fixed immediately after maturation to serve as a control. The nuclear status of the oocytes was examined after staining with Hoechst 33342. Chi-square procedures were used to analyze the data. The proportion of mouse oocytes which underwent activation was higher (P<0.01) for ethanol and electricity than for the medium (22, 30 and 0%, respectively). The proportion of pig oocytes which underwent activation was higher (P<0.05) for two current exposures (14%) and ethanol followed by current (16%) than for the medium (0%). There was no evidence of spontaneous activation occurring in mouse or pig oocytes during the maturation period. Most of the activated mouse oocytes contained a single haploid pronucleus, as evidenced by two polar bodies and one pronucleus. In contrast, most of the activated pig oocytes were diploid parthenotes, as evidenced by one polar body and one pronucleus. The results show that a portion of in vitro matured mouse and pig oocytes undergo parthenogenetic activation following exposure to activation stimuli.