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

Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK, ¹ MRC Functional Genetics Unit, Department of Human Anatomy and Genetics, University of Oxford, Oxford OX1 3QX, UK, ² Cell and Developmental Physiology Research Group, Institute for Cell and Molecular Biosciences, The Medical School, Framlington Place, University of Newcastle NE2 4HH, UK and ³ Department of Biotechnology, Royal Institute of Technology, SE-10691 Stockholm, Sweden

Correspondence should be addressed to K Coward; Email: kevin.coward{at}pharm.ox.ac.uk

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: PLC. Since the discovery of PLC, 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 PLC is present in a non-mammalian vertebrate. Using genomic and cDNA databases, we have identified the cDNA encoding a PLC orthologue in the domestic chicken that, like the mammalian isoforms, is a testis-specific gene. The chicken PLC cDNA is 2152 bp in size and encodes an open reading frame of 639 amino acids. When injected into mouse oocytes, chicken PLC cRNA triggers Ca²⁺ oscillations, indicating that it has functional properties similar to those of mammalian PLC. Our findings suggest that PLC may have a universal role in triggering egg activation in vertebrates.

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