INJECTION OF A PORCINE SPERM FACTOR INDUCES ACTIVATION OF MOUSE EGGS

Injection of sperm preparations into mammalian oocytes and eggs has be en shown to elicit persistent [Ca2+]i oscillations that closely resemb le fertilization-associated Ca2+ release. However, the ability of thes e sperm fractions to initiate egg activation has not been clearly demo nstrated. In the present experiments, mouse eggs injected with a porci ne sperm preparation were evaluated for early and late events of activ ation. Events monitored included, among early events, the generation o f [Ca2+]i oscillations and cortical granule exocytosis and, among late events, the decrease in histone H1 and myelin basic protein kinase ac tivities, polar body extrusion, pronuclear formation, and cleavage to the two-cell stage. Injection of sperm fractions consistently evoked [ Ca2+]i oscillations that, in turn, initiated all events of activation. Uninjected control eggs or eggs injected with buffer or heat-treated sperm fractions failed to show Ca2+ responses or activation. In additi on, injection of sperm fractions into recently ovulated eggs (experime nts were concluded within 15 hr after human chorionic gonadotropin adm inistration) induced high rates of activation, while similarly aged eg gs exposed to 7% ethanol for 5 min, a known parthenogenetic treatment, failed to activate. Together these results indicate that injection of sperm fractions elicits [Ca2+]i oscillations that are capable of init iating normal egg activation. These results support the hypothesis tha t a sperm component participates in the generation of fertilization-as sociated [Ca2+]i oscillations. (C) 1998 Wiley-Liss, Inc.