Parthenogenic activation of pig oocytes by protein kinase inhibition.

Previous studies have shown that protein kinase stimulators can induce the release of the metaphase II arrest in mouse ova. The present report is about the role of protein kinase in parthenogenic activation of pig oocytes, which was studied using a broad-spectrum protein kinase inhibitor. Metaphase II oocytes were obtained via in vitro maturation. Two sources of H7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine, HCl] were tested--Sigma (H7s) and Calbiochem (H7c). Both were found to be equally effective in promoting release of the metaphase II block. Activation, release of the metaphase II arrest, and progression to the first interphase could be induced at the highest percentage with an exposure to 2.0 mM H7s for 80 min (68.1%). In another experiment, H7c resulted in 69.5% activation, while iso-H7 [1-(5-isoquinolinesulfonyl)-3-methylpiperazine, HCl] at a similar concentration and exposure duration resulted in 25.7% activation. H7s and H7c were more effective than iso-H7 in inducing the appearance of a 22-kDa protein that is associated with normal fertilization in the pig. In contrast, although pronuclei could form and the protein profiles were indicative of activation, cortical granule exocytosis did not occur, and oocytes failed to develop to the blastocyst stage after H7 treatment. In contrast to the H7-treated oocytes, electrostimulation resulted in pronuclear formation, the appearance of the 22-kDa protein, release of cortical granules, and development to the blastocyst stage. These data demonstrate that broad-spectrum inhibitors of protein kinase are unable to induce all the events associated with normal fertilization.