Flowering Plant Sperm Contains a Cytosolic Soluble Protein Factor Which Can Trigger Calcium Oscillations in Mouse Eggs

Abstract

There is evidence showing that the sperm-induced Ca2+ oscillations in mammalian eggs at fertilization are triggered by a sperm-derived protein factor. It was established recently that the activity of the putative sperm protein in causing Ca2+ oscillations in mammalian eggs is not species-specific in vertebrates (1, 16). Here we report that cytosolic soluble extracts derived from flowering plant sperms in Brassica campestris can also induce fertilization-like Ca2+ oscillations when microinjected into mouse eggs. The factor responsible for inducing Ca2+ oscillations in the plant sperm was sperm-specific and heat- or trypsin-labile. Eight to ten sperm equivalents of the plant sperm extracts had enough activity to trigger Ca2+ oscillations in mouse eggs. Our study suggests that, although plant and mammal are evolutionary divergent species, the activity of the putative sperm protein factor in triggering Ca2+ signaling in mammalian eggs is not specific to the animal kingdom.