Phospholipase Cζ, the trigger egg activation in mammals, is present in a non-mammalian species

The activation of the egg to begin development into an embryo is triggered by a sperm-induced increase in intracellular egg Ca²⁺. There has been much controversy about how the sperm induces this fundamental developmental event, but recent studies suggest that, in mammals, egg activation is triggered by a testis-specific phospholipase C: PLCζ. Since the discovery of PLCζ, it has been unclear whether its role in triggering egg activation is common to all vertebrates, or is confined to mammals. Here, we demonstrate for the first time that PLCζ is present in a non-mammalian vertebrate. Using genomic and cDNA databases, we have identified the cDNA encoding a PLCζ orthologue in the domestic chicken that, like the mammalian isoforms, is a testis-specific gene. The chicken PLCζ cDNA is 2152bp in size and encodes an open reading frame of 639 amino acids. When injected into mouse oocytes, chicken PLCζ cRNA triggers Ca²⁺ oscillations, indicating that it has functional properties similar to those of mammalian PLCζ. Our findings suggest that PLCζ may have a universal role in triggering egg activation in vertebrates.