Diploidization of bovine oocytes matured in vitro and parthenogenetically activated by electric shock

Bovine in vitro matured oocytes were parthenogenetically activated by a single pulse of direct current. Suppression of second polar body extrusion by 60 V DC-pulse followed by cytochalasin B treatment or 240 V DC-pulse were used to diploidize parthenogenones. Analysis of the cytological events 20 h postactivation clearly documented high efficiency of both diploidization techniques. All oocytes exposed to a single 60 V DC-pulse and then to cytochalasin B for 3 to 6 h were activated and 70% to 88% possessed two pronuclei. Exposure to 240-V DC-pulse for 10 and 20 microseconds activated all oocytes, 72% and 62% formed two pronuclei, but a high incidence (22% and 30%) of degenerated oocytes was observed. Prolonged in vitro culture of oocytes after parthenogenetic activation and diploidization treatment showed that formed pronuclei were able to fuse and single prometaphase to telophase mitotic cleavage figures developed in all oocytes fixed 28 h after activation, except one cytochalasin B-treated oocyte with two prometaphase sets of chromosomes.