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Comment |
Functional disparity between human PAWP and PLCζ in the generation of Ca2+ oscillations for oocyte activation. Nomikos M et al. (2015) Mammalian oocyte activation is mediated by cytosolic calcium oscillations initiated upon delivery of a putative 'sperm factor' by the fertilizing sperm. Previous studies suggest the identity of this sperm factor as the testis-specific phospholipase C-zeta (PLCζ). Recently, a post-acrosomal sheath WW domain-binding protein (PAWP) has been proposed as an alternative sperm factor candidate, following a report that human PAWP protein and cRNA elicited Ca(2+) oscillations in mouse and human oocytes. Those Ca(2+) oscillations were inhibited by a PAWP-derived peptide corresponding to a functional PPGY binding motif. Herein, using a series of human PAWP expression constructs, we demonstrate that both human PAWP protein and cRNA are, in our experiments, unable to elicit Ca(2+) release following microinjection into mouse oocytes. Parallel experiments performed with human PLCζ elicited the characteristic Ca(2+) oscillations present at mammalian fertilization, which produced oocyte activation and embryo development. Furthermore, sperm-induced Ca(2+) oscillations were not inhibited by the PAWP-derived PPGY peptide following in-vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Thus, the functional disparity with PLCζ leads us to conclude that human PAWP is neither sufficient nor necessary for the Ca(2+) oscillations that initiate mammalian oocyte activation following fertilization.//////////////////
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