Injection of a porcine sperm factor induces activation of mouse eggs

Injection of sperm preparations into mammalian oocytes and eggs has been shown to elicit persistent [Ca2+]i oscillations that closely resemble fertilization-associated Ca2+ release. However, the ability of these sperm fractions to initiate egg activation has not been clearly demonstrated. In the present experiments, mouse eggs injected with a porcine sperm preparation were evaluated for early and late events of activation. Events monitored included, among early events, the generation of [Ca2+]i oscillations and cortical granule exocytosis and, among late events, the decrease in histone H1 and myelin basic protein kinase activities, 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 addition, injection of sperm fractions into recently ovulated eggs (experiments were concluded within 15 hr after human chorionic gonadotropin administration) induced high rates of activation, while similarly aged eggs 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 initiating normal egg activation. These results support the hypothesis that a sperm component participates in the generation of fertilization-associated [Ca2+]i oscillations.