ZETA-STIM · The molecular basis for the ability of PLC zeta to stimulate mammalian embryo development

Oocyte activation is the earliest step of embryonic development following mammalian fertilization and is triggered by a characteristic series of cytoplasmic Ca2+ transients, known as Ca2+ oscillations. Over the last decade, growing evidence indicates that the physiological agent responsible for the generation of Ca2+ oscillations and subsequent oocyte activation is a sperm-specific isoform of phospholipase C (PLC), PLC-zeta (PLCz). The sperm-borne PLCz stimulates Ca2+ oscillations in eggs after sperm-egg membrane fusion by promoting Ca2+ release via activation of the inositol 1,4,5-trisphosphate (IP3) signaling pathway. PLCz is the smallest mammalian PLC comprising a tandem pair of EF hand domains, the catalytic X & Y domains and a C2 domain. PLCz hydrolyses the membrane lipid, phosphatidylinositol 4,5- bisphosphate (PIP2), to liberate IP3 which triggers calcium release from the endoplasmic reticulum. The fundamental role of PLCz in mammalian fertilization has been further highlighted by recent clinical studies that have directly linked abnormal expression profiles of PLCz with documented cases of male infertility. This fellowship will establish the molecular mechanism of fertilization in mammals by demonstrating whether PLCz is the sole sperm factor for the generation of Ca2+ oscillations. I will identify distinct intracellular egg proteins that are involved in interaction and targeting to discrete subcellular compartments a process that enables precise modulation of sperm PLCz activity. I will determine how PLCz enzymatic activity is regulated by the binding of the egg protein(s) and to which of the PLCz domains the binding occurs. Gaining an insight on the regulatory mechanism of PLCz action within the egg will facilitate the potential application of PLCz as a therapeutic for PLCz-mediated male infertility and enable a novel treatment to be provided by IVF clinics. PLCz should also help in the breeding of valuable domestic species or propagation of rare animals.