Egg-Cortex · Actomyosin driven force-generation at the egg surface during fertilization

The fusion of two specialized gametes represents the starting point of life in sexually reproductive organisms. Despite this fundamental role in the creation of life, the molecular and biophysical mechanisms underlying this process remain largely elusive. It is evident that the dynamic modulation of the egg actomyosin cortex plays a central role during different steps of fertilization including cortical granule exocytosis, Ca2+ signaling and sperm uptake. How this high plasticity of the actin cortex is regulated during fertilization has not been studied in detail. In the past, research of this dynamic process has been limited by live-cell microscopy techniques lacking the needed spatiotemporal resolution. Gamete interaction is not only a very fast process; in mammals, it also occurs synchronously with gamete activation. To overcome these limitations, we propose utilizing eggs isolated from zebrafish that can be activated independently of interaction with sperm. Specifically, we will comparatively characterize the dynamic egg actomyosin cortex properties during fertilization using advanced single-molecule imaging techniques and biophysical tools like optical tweezers. We will specifically address whether the egg actin cortex has mechanosensitive properties that might facilitate gamete fusion, as has been shown for other cell-cell fusion events. It is our goal to identify the basic molecular and biophysical mechanisms underlying fertilization, and the comprehensive quantitative study of actin structures within the egg cortex will establish an essential step in addressing this question.