Male infertility-linked point mutation reveals a vital binding role for the C2 domain of sperm PLCζ

Sperm-specific phospholipase C zeta (PLCζ) is widely considered to be the physiological stimulus that evokes intracellular calcium (Ca ) oscillations that are essential for the initiation of egg activation during mammalian fertilisation. A recent genetic study reported a male infertility case that was directly associated with a point mutation in the PLCζ C2 domain, where an isoleucine residue had been substituted with a phenylalanine (I489F). Here, we have analysed the effect of this mutation on the Ca oscillation-inducing activity and the biochemical properties of human PLCζ. Microinjection of cRNA or recombinant protein corresponding to PLCζ mutant at physiological concentrations completely failed to cause Ca oscillations and trigger development. However, this infertile phenotype could be effectively rescued by microinjection of relatively high (non-physiological) amounts of recombinant mutant PLCζ protein, leading to Ca oscillations and egg activation. Our biochemical analysis suggested that the PLCζ mutant displayed similar enzymatic properties, but dramatically reduced binding to PI(3)P and PI(5)P-containing liposomes compared with wild-type PLCζ. Our findings highlight the importance of PLCζ at fertilisation and the vital role of the C2 domain in PLCζ function, possibly due to its novel binding characteristics.