Initiation of cleavage in starfish eggs by the injection of triton-treated spermatozoa

Triton X-100-treated spermatozoa were injected into immature (fully grown, germinal vesicle stage) or mature (pronuclear stage) oocytes of the starfish, Asterina pectinifera, to study relation between initiation of cleavage and cortical reaction. Immature oocytes into which Triton X-100-treated spermatozoa were injected were treated with 1-methyladenine. Such immature oocytes initiated cleavage after completion of meiosis without formation of the fertilization membrane. The same results were obtained when Triton X-100-treated spermatozoa were injected into mature oocytes. Control oocytes into which only calcium-free sea water was injected did not cleave. These results indicate that the initiation of cleavage is independent of the cortical reaction but dependent on the existence of spermatozoa (spermatozoon) in the egg cytoplasm.