Sperm-activating proteins obtained from the herring eggs are homologous totrypsin inhibitors and synthesized in follicle cells

The activation of sperm motility by the egg is an ubiquitous phenomenon in the animal kingdom, but the molecules by which the egg activates sperm moti lity have been clarified in only a few invertebrate species. In the Pacific herring, Clupea pallasii, mature unfertilized eggs release the sperm-activ ating proteins which are prerequisite to successful fertilization. Compleme ntary DNA clones encoding herring sperm-activating proteins were isolated f rom a herring ovarian complementary DNA library and amino acid sequences we re deduced. The herring sperm-activating protein(s) is a secretory product( s) with a strong homology to Kazal-type trypsin inhibitors, such as mammali an acrosin inhibitors. The sperm-activating proteins were globally distribu ted in the outermost layer of the egg chorion and its gene was found to be expressed in the follicle cells which surround developing oocytes. These re sults suggest that in the Pacific herring, trypsin inhibitor-like proteins are synthesized in the follicle cells, secreted, accumulated in the egg cho rion during oocyte development, and released into the milieu at spawning to activate the motility of spermatozoa at the time of gamete interaction. (C ) 1998 Academic Press.