Activation and Development of Pig Oocytes after Microinjection of Crude Sperm Extract

This work was undertaken to investigate the activation of pig oocytes after microinjection of crude sperm extract prepared from ejaculated boar spermatozoa. The results were compared with those of electro-stimulated oocytes. When in vitro-matured pig oocytes were microinjected with sperm extract and others were electro-stimulated, 100% and 92%, respectively, of the oocytes were released from arrest at metaphase II (MII) and formed female pronuclei. To test their developmental ability, the injected oocytes were treated with cytochalasin B and then cultured in NCSU23 medium. After 168 h, 30% and 44% of the oocytes that had been microinjected with sperm extract and electro-stimulated, respectively, developed to the blastocyst stage. At 6-8 h after the microinjection of sperm extract or electro-stimulation, cortical granules were released from the oocytes. In addition, Cdc2 kinase activity declined to a low level in the treated oocytes. These results indicate that microinjection of crude sperm extract induces the release of in vitro-matured pig oocytes from MII-arrest and leads them into a series of events related to oocyte activation.