PLCζ or PAWP: revisiting the putative mammalian sperm factor that triggers egg activation and embryogenesis

In mammals, egg activation is initiated by multiple cytosolic Ca2+ transients (Ca2+ oscillations) that are triggered following delivery of a putative sperm factor from the fertilizing sperm. The identity of this 'sperm factor' thus holds much significance, not only as a vital component in creating a new life, but also for its potential therapeutic and diagnostic value in human infertility. Recent data have emerged suggesting the sperm factor may be a post-acrosomal sheath WW domain-binding protein (PAWP). However, a significant body of research points to a testis-specific phospholipase C zeta (PLC zeta) as the sperm factor. Herein, we examine the evidence presented in favour of PAWP in relation to PLC zeta and the requisite physiological properties of the mammalian sperm factor.