# Oocyte surface proteins EGG-1 and EGG-2 are required for eggshell integrity in Caenorhabditis elegans

## TL;DR

This study shows that EGG-1 and EGG-2 proteins in C. elegans are not needed for fertilization but help organize the eggshell and membrane proteins.

## Contribution

The study clarifies the specific roles of EGG-1 and EGG-2 in eggshell organization using genome editing.

## Key findings

- EGG-1 and EGG-2 are not required for fertilization but are crucial for eggshell integrity.
- Lack of EGG-1 and EGG-2 leads to mislocalization of CBD-1, CHS-1, and MBK-2 proteins.
- CPG-1 localization remains unaffected in the absence of EGG-1 and EGG-2.

## Abstract

Metazoan eggs are surrounded by a specialized coat of extracellular matrix that mediates sperm-egg interactions. This coat is rapidly remodeled after fertilization to form a barrier that prevents polyspermy, protects against environmental insults, and provides structural support to the developing embryo. In C. elegans, several oocyte surface proteins have been identified that mediate these events. However, whether two of these proteins, EGG-1 and EGG-2, are required for fertilization or downstream events has been unclear. Here, we address this question using more recent advances in genome editing tools through the creation of egg-1  egg-2 deletions of the endogenous loci. We found that egg-1  egg-2 oocytes are fertilization competent and form rudimentary eggshells. While the integrity of the egg-1  egg-2 eggshell is compromised and often ruptures within the uterus, some embryos can undergo several rounds of cell division. Absence of EGG-1 and EGG-2 results in the mislocalization of proteins on the embryo surface and eggshell. CBD-1, CHS-1, and MBK-2, components of the egg activation complex and outermost eggshell layer, were mislocalized, while the localization of CPG-1, a component of an inner eggshell layer, was not perturbed. Overall, our findings demonstrate that EGG-1 and EGG-2 are not required for fertilization but rather are involved in the organization of eggshell structural components and oocyte plasma membrane proteins.