Calcineurin dependent protein phosphorylation changes during egg activation in Drosophila melanogaster

In animals studied to date, the crucial process of egg activation, by which an arrested mature oocyte transits into an actively developing embryo, initiates with an increase of Ca2+ in the oocyte’s cytoplasm. This Ca2+ rise sets off a series of downstream events, including the completion of meiosis and the dynamic remodeling of the oocyte transcriptome and proteome, which prepare the oocyte to undertake embryogenesis. Calcineurin is a highly conserved phosphatase that is activated directly by Ca2+ upon egg activation and that is required for the resumption of meiosis in Xenopus, ascidians and Drosophila. The molecular mechanisms by which calcineurin transduces the calcium signal to regulate meiosis and other downstream events are still unclear. In this study, we investigate the regulatory role of calcineurin during egg activation in Drosophila melanogaster. Using mass spectrometry, we quantify the phosphoproteomic and proteomic changes that occur during egg activation, and we examine how these events are affected when calcineurin function is perturbed in female germ cells. Our results show that calcineurin regulates hundreds of phosphosites and also influences the abundance of numerous proteins during egg activation. We find calcineurin-dependent changes in cell cycle regulators including Fzy, Greatwall (Gwl) and Endosulfine (Endos), protein translation modulators including PNG, NAT, eIF4G and eIF4B, and important components of signaling pathways including GSK3β and Akt1. Our results help elucidate the events that occur during the transition from oocyte to embryo