Soluble sperm factors and Ca2+ release in eggs at fertilization.
All eggs are activated at fertilization by an increase in intracellular free Ca2+. How the spermatozoa triggers the release of intracellular Ca2+ has not been established in any species. One hypothesis is that spermatozoa introduce a Ca(2+)-releasing factor into the cytoplasm after gamete membrane fusion. It has been suggested that spermatozoa may introduce Ca2+ itself, or a small molecular weight factor that triggers the release of Ca2+ from intracellular stores. However, these suggestions are not consistent with a number of experiments in vertebrate eggs. Here, I present the argument that spermatozoa cause intracellular Ca2+ oscillations in mammalian eggs by introducing a specific protein called an oscillogen. It is suggested that it does not mediate its effects by causing increased inositol, 1,4,5-trisphosphate (InsP3) production, but instead directly affects the ability of the stores to undergo Ca(2+)-induced Ca2+ release. The sperm oscillogen hypothesis may help explain the patterns of intracellular Ca2+ waves that occur during fertilization in hamster eggs, as well as the ability of an injection of live spermatozoa to activate development in human eggs.
Swann
K
K
Department of Anatomy and Developmental Biology, University College, London, UK.
D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000502:physiology*; D006801:Humans; D008297:Male; D008970:Molecular Weight; D011506:Proteins / Q000502:physiology; D013084:Sperm-Ovum Interactions / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology*
D001685:Biological Factors; D011506:Proteins; D002118:Calcium