Injections of porcine sperm extracts trigger fertilization-like calcium oscillations in oocytes of a marine worm

The precise mechanisms by which sperm trigger calcium transients in eggs or oocytes during fertilization remain unknown. Based on time-lapse confocal microscopy, we show that intracellular injections of porcine sperm extracts cause the oocytes of a marine nemertean worm to undergo repetitive calcium oscillations resembling those obtained during normal fertilizations. Such findings are consistent with the view that fertilization involves a soluble sperm factor (SF) which is capable of eliciting calcium transients without binding to externally situated receptors on the oocyte plasmalemma. This s tudy also describes for the first time the wave-like propagation patterns o f SF-induced calcium transients that are generated in a heterologous combin ation of gametes obtained from different phyla of animals. Such cross-react ivity between distantly related taxa suggests that the intracellular signal ing pathways triggered by sperm factors can be well conserved. (C) 2000 Aca demic Press.