# Egg Overactivation—An Overlooked Phenomenon of Gamete Physiology

## TL;DR

This paper explores the phenomenon of egg overactivation in frogs, focusing on how different stressors trigger abnormal activation and subsequent cell death.

## Contribution

The paper provides a comparative analysis of spontaneous and stress-induced overactivation in Xenopus laevis eggs, highlighting distinct cell death mechanisms.

## Key findings

- Overactivation in Xenopus eggs can be triggered by oxidative or mechanical stress.
- Spontaneous and stress-induced overactivation lead to different cell death outcomes.
- Calcium signaling plays a central role in both normal activation and overactivation processes.

## Abstract

In many vertebrates, mature ovulated eggs are arrested at metaphase II prior to fertilization. The eggs exit meiotic arrest after fertilization-induced or parthenogenetic activation, followed by embryo development or egg degradation, respectively. Calcium-dependent activation of meiotically-arrested eggs has been thoroughly investigated in various species. In addition, several recent studies have detailed the excessive activation of ovulated frog eggs, so-called overactivation. This overview highlights the major events of overactivation observed in mature ovulated eggs of the African clawed frog Xenopus laevis with a focus on similarities and differences between spontaneous, oxidative stress-induced, and mechanical stress-induced overactivation. The dramatically different cell death scenarios that unfold in activated and overactivated eggs are also exposed in the article.