Peptides from sperm acrosomal protein that initiate egg development

Abstract

How sperm initiate egg development is being investigated with gametes of the marine worm Urechis. Sperm acrosomal protein, previously shown to activate eggs ( Gould et al., 1986, Dev. Biol. 117, 306–318 ; Gould and Stephano, 1987, Science 235, 1654–1656 ), was enzymatically cleaved into soluble peptide fragments. When this mixture was added to eggs they activated, and parthenogenetic cleavage often occurred. An active peptide (P23) was purified from the mixture and its sequence was determined to be Val-Ala-Lys-Lys-Pro-Lys. Synthetic peptide had the same biological activity. P23 induced eggs to undergo the complete sequence of changes that normally follows fertilization, including the fertilization potential, completion of meiosis, and DNA replication. When a sperm centrosome was introduced into eggs by prefertilization without activation, and the eggs were subsequently activated by P23, they developed normally to trochophore larvae (the contribution of another sperm component is not ruled out by this experiment). P23 covalently coupled to bovine serum albumin also activated eggs, showing that it acted on the external surface of the egg. The peptide did not activate sea urchin eggs, but did cause oyster eggs to undergo germinal vesicle breakdown.