Calcineurin-dependent Protein Phosphorylation Changes During Egg Activation in Drosophila melanogaster

Phosphoproteomic and global proteomic changes that occur during egg activation were quantified for the oocytes and eggs of Drosophila melanogaster, with normal (control) or perturbed (CanB2, knockdown) calcineurin functions. We discovered broad influences of calcineurin on protein phosphorylation states in maturing oocytes and activating eggs. Our results illuminate the molecular mechanisms through which calcineurin regulates meiosis progression, protein translation, and signaling pathways during this critical developmental transition. [Display omitted] Highlights •Calcineurin controls proteomic phosphorylation in fly oocytes and activating eggs.•Without CanB2, activated eggs arrest in an M-phase like cell cycle state.•Calcineurin is a key regulator of translation factors during egg activation.•In egg activation, phosphorylation of GSK3β via Akt1 is calcineurin-dependent. In almost all animals studied to date, the crucial process of egg activation, by which an arrested mature oocyte transitions into an actively developing embryo, initiates with an increase in 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 prepares the oocyte for embryogenesis. Calcineurin is a highly conserved phosphatase that is activated 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 Fizzy (Fzy), Greatwall (Gwl) and Endosulfine (Endos); in protein translation modulators including PNG, NAT, eIF4G, and eIF4B; and in important components of signaling pathways including GSK3β and Akt1. Our results help elucidate the events that occur during the transition from oocyte to embryo.