Egg Timer

Our cells are replaced every few weeks as they accumulate damage. But there’s one big exception: egg cells. In a seemingly high-risk strategy, women are born with all the eggs they will ever have, yet an egg may wait decades before creating healthy offspring. So how do they avoid the damage that other cells are subjected to (image shows a human egg cell (crescent shape) surrounded by granulosa cells which nurture the egg cell)? They go into ‘standby mode’. Cell damage is often caused by reactive oxygen species (ROS), which are created in the mitochondria, specifically in a compartment called complex I. In egg cells, this complex is inactive which creates less ROS and reduces the chance of developing damaging mutations. By adding a dye to the eggs, researchers saw that their mitochondria are less active (green) compared to those of the surrounding granulosa cells, which are producing more damaging ROS (red).

Written by Sophie Arthur

Sophie Arthur

former Science Communications Officer MRC LMS

Formerly a stem cell biologist, Sophie has since moved into science communication working at the MRC LMS. She also writes an award winning science and education blog Soph talks science.

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• Image adapted from work by Aida Rodríguez-Nuevo and colleagues
• Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain
• Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Published in Nature, July 2022