Starfish sperm-oocyte jelly binding triggers functional changes in cortical granules

Summary Starfish oocytes were examined before fertilization, immediately after insemination, and during the cortical reaction by means of acid phosphatase and ruthenium red ultrastructural histochemistry. Oocyte cortical granules are composed of a lamellar body and a surrounding matrix which is subdivided into dense and light portions. In unfertilized oocytes cortical granules are not stained by ruthenium red but show a weak acid phosphatase activity in the light portion of the granule matrix. Immediately after the adhesion of the spermatozoon to the oocyte jelly coat, the light matrix portion of cortical granules appears stained by ruthenium red and shows a strong acid phosphatase activity. During the cortical reaction, cortical granules are released into the perivitelline space and the lamellar body, surrounded by the stained matrix, fuses with the fertilization envelope. Our data suggest that membrane permeability changes and enzyme activation occur in the egg when the spermatozoon binds to the oocyte jelly coat.