Investigating the mechanisms of Drosophila Egg Activation

My PhD focuses on understanding the processes that occur during the universal process of egg activation, an event in which calcium entry triggers multiple downstream events in a mature oocyte, such as the resumption of meiosis, changes in the translational landscape, and broad changes in the actin cytoskeleton. This process is usually triggered by fertilization, however in Drosophila, the process is triggered as the mature oocyte undergoes ovulation, likely due to increased turgor pressure as the oocyte takes up fluid in the oviduct.

It is thought that the swelling of the oocyte opens mechanically gated TrpM channels enabling the calcium to enter. Thus my project focuses largely on how the process of calcium entry is regulated, firstly through the identification of calcium channels involved in this process, and secondly through the understanding what the involvement of the actin cytoskeleton could be. This poses an interesting question, as data suggests that the actin cortex poses great influence over calcium entry, and as such, what is the mechanism behind this? My project will show data that presents the actin network as a key regulator of calcium flux, acting as a barrier for calcium entry in the oocyte. I show that actin is depleted at the cortex where the egg is primed for calcium entry, and that manipulating the level of actin at the cortex affects calcium entry and calcium wave speed propagation. Additionally, pharmacological manipulation of the actin cytoskeleton actively prevents calcium wave propagation.

Questions thus remain as to how actin mechanistically controls calcium entry? I will investigate further whether it is due to the physical connection of mechanically gated channels that actin is able to transduce a physical force that opens gated calcium channels, or whether the calcium entry acts to dissociate the actin cortex and thus disrupt the barrier to calcium entry.