Porcine oocyte activation induced by a cytosolic sperm factor

It is not known how the fertilizing sperm elicits the release of Ca2+ from the oocyte's intracellular stores. We investigated whether a crude extract isolated from boar sperm could induce the Ca2+ release and trigger subsequent early and late activation events upon injection into matured porcine oocytes. The sperm extract induced an immediate rise in the intracellular free Ca2+ concentration in all oocytes tested, which was followed by repetitive Ca2+ transients in 11 out of 14 oocytes. Heat or trypsin treatment of the extract totally abolished the Ca2+ releasing activity of the sperm factor. The injected oocytes showed cortical granule exocytosis, they resumed meiosis and entered first interphase: pronuclei were formed in 89.2% (132/148) of the cases. Pronuclear formation was accompanied by the appearance of a new 22 kDa protein as normally seen at fertilization. Of the successfully injected oocytes 51.7% (105/203) cleaved and 2.0% (4/203) developed to the blastocyst stage after being cultured for 7 days in NCSU 23 medium. Injection of the carrier medium could not trigger these changes. The results indicate that the sperm might activate porcine oocytes by introducing a soluble factor into the oocyte's cytoplasm after gamete fusion. Mel. Reprod. Dev. 57:290-295, 2000. (C) 2000 Wiley-Liss, Inc.