Infertility is a significant global health challenge, impacting 8 to 12% of couples of reproductive age. Traditionally, infertility research has heavily focused on sperm cells, with discoveries in sperm motility and activation propelling advancements in in vitro fertilization (IVF) techniques. However, this has led to a relative under-exploration of the egg's role in fertilization. Notably, while eggs are known to actively prevent polyspermy and facilitate cell-cell fusion, the intricate subcellular mechanisms underpinning these processes remain largely uncharted. This project is conceived in light of the critical knowledge gap in understanding the egg's active role in fertilization. Specifically, it seeks to elucidate the dynamic modulation of the egg actomyosin cortex, a crucial player during the fertilization process. Given the complex and rapid nature of fertilization, involving overlapping stages of gamete activation, adhesion, fusion, and sperm incorporation, previous research has been limited by the lack of suitable live-cell microscopy techniques.
To overcome these limitations, our project will employ an innovative methodological framework using eggs isolated from zebrafish. This model organism offers a unique advantage as its eggs can be activated independently of sperm interaction, allowing for detailed observation and analysis of the fertilization process. In total, we have set forth four interrelated objectives:
Objective I revolves around a detailed characterization of the actin cortex in zebrafish eggs. We plan to investigate how this cortex changes over time, both before and after the egg is activated. A special emphasis will be placed on understanding the variations in intracellular calcium levels and the process of Cortical Granule Exocytosis (CGE), as these are pivotal in egg activation and the prevention of polyspermy.
Objective II aims to shed light on the role of the egg actin cortex in the fusion of gametes. We seek to unravel how this cortex facilitates the process of sperm uptake, a vital step for successful fertilization. Understanding this interaction at a molecular level could offer new insights into the fertilization process.
In Objective III, we explore a novel concept – the oocyte surface as a mechanosensory interface. This objective is focused on understanding how the egg's surface reacts to physical forces during sperm interaction. Specifically, we are interested in how these interactions might alter the cortical stiffness, potentially making the egg more conducive to cell-cell fusion.
Finally, Objective IV involves a targeted interference approach to strategically disrupt actin structures within the egg. By doing so, we aim to gauge the effects of such disruptions on fertilization rates. This objective is particularly crucial as it will allow us to connect our findings back to the specific structures and processes identified in the previous objectives, offering a comprehensive understanding of their physiological significance.
The outcomes of this project are anticipated to significantly advance our understanding of the egg's role in fertilization, particularly regarding the function of the actin cortex.
