Medical Research Council - London Institute of Medical Sciences

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Egg Timer

How egg cells – present at birth – avoid damage as females age: clues for infertility treatment

13 November 2022

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

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