Is PAWP the “real” sperm factor?

Mammalian embryo development is initiated by intracellular Ca(2+) oscillations that result in oocyte activation following gamete membrane fusion. It is widely believed that oocyte Ca(2+) oscillations are triggered by a sperm-specific protein, phospholipase C-zeta (PLCζ) that activates InsP3 production leading to repetitive Ca(2+) release from intracellular stores. However, a recent report in the FASEB Journal by Aarabi et al. challenges this view by proposing postacrosomal WW domain-binding protein (PAWP) as another sperm-derived protein that can also initiate Ca(2+) oscillations and zygotic development at fertilization. Here we discuss these new findings and examine the evidence suggesting PAWP as the “real” sperm factor.