A novel signalling mechanism for generating ca2+ oscillations at fertilization in mammals

Abstract

At fertilization in mammals the sperm activates the egg by triggering a series of oscillations in the intracellular free Ca²⁺ concentration. The precise sequence of events that occur between sperm‐egg contact and the increases in intracellular Ca²⁺ remains unknown. Here, we discuss recent evidence supporting the hypothesis that a cytosolic sperm protein enters the egg after gamete membrane fusion and triggers Ca²⁺ oscillations from within the egg cytoplasm. Biochemical studies suggest that there exists a novel sperm protein, named oscillin, that specifically comigrates with Ca²⁺ oscillation‐inducing activity. Oscillin has been immunolocalised to the region of the sperm that first fuses with the egg. The concept of a specific protein that triggers Ca²⁺ oscillations may have wider physiological significance since sperm oscillin can induce Ca²⁺ oscillations in somatic cells, such as neurons and hepatocytes. Unravelling the novel signalling system involved in mammalian fertilization may help reveal some fundamental molecular mechanisms responsible for triggering cytoplasmic Ca²⁺ oscillations.