Divergent effect of mammalian PLCζ in generating Ca 2+ oscillations in somatic cells compared with eggs

Abstract

Sperm PLCζ (phospholipase Cζ) is a distinct phosphoinositide- specific PLC isoform that is proposed to be the physiological trigger of egg activation and embryo development at mammalian fertilization. Recombinant PLCζ has the ability to trigger Ca 2+ oscillations when expressed in eggs, but it is not known how PLCζ activity is regulated in sperm or eggs. In the present study, we have transfected CHO (Chinese-hamster ovary) cells with PLCζ fused with either YFP (yellow fluorescent protein) or luciferase and found that PLCζ-transfected cells did not display cytoplasmic Ca 2+ oscillations any differently from control cells. PLCζ expression was not associated with changes in CHO cell resting Ca 2+ levels, nor with a significantly changed Ca 2+ response to extracellular ATP compared with control cells transfected with either YFP alone, a catalytically inactive PLCζ or luciferase alone. Sperm extracts containing PLCζ also failed to cause Ca 2+ oscillations in CHO cells. Despite these findings, PLCζ -transfected CHO cell extracts exhibited high recombinant protein expression and PLC activity. Furthermore, either PLCζ-transfected CHO cells or derived cell extracts could specifically cause cytoplasmic Ca 2+ oscillations when microinjected into mouse eggs. These data suggest that PLCζ-mediated Ca 2+ oscillations may require specific factors that are only present within the egg cytoplasm or be inhibited by factors present only in somatic cell lines. © 2011 The Author(s).