Before They're Hatched

Female mammals are born with a lifetime’s supply of eggs in their ovaries. They must protect their long-term egg supply while allowing some egg cells to mature, ready for ovulation. Here researchers use a sensitive single-plane illumination microscopy to take virtual slices through a 5-day old mouse ovary. Artificial intelligence helps to analyse the pictures, highlighting individual eggs in bright colours, also shown in a 3D reconstruction at the end of the video. The team analyse ovaries of different ages, finding the total number of eggs drastically reduces with age. What doesn’t change, however, is the percentage of eggs getting ready. The team suggest that, rather than simply being a 'reservoir', the ovary must actively count its eggs, preparing the same proportion for ovulation, at different stages of life. Discovering how the ovaries count their eggs may suggest treatments to help similar processes in human fertility.

Written by John Ankers

John Ankers

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A former researcher in systems biology, John is now an online biology tutor and professional coach supporting the wellbeing of scientists and NHS professionals. He's writing, too, of course.

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• Video from work by Arturo D’Angelo and colleagues
• Centre for Genomic Regulation, The Barcelona Institute of Science and Technology, Barcelona, Spain ICREA, Barcelona, Spain
• Video originally published with a Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)
• Published in Nature Aging, August 2026