Human Eggs Go Dormant to Remain Healthy for Decades

By Medscape Staff

November 02, 2022

Human egg cells can alter their metabolic activity, which allows some of them to remain viable for reproduction for up to 50 years, according to fertility experts at the Centre for Genomic Regulation. 

What to know:

  • Human eggs are first formed in the ovaries during fetal development, but during the early stages of their maturation process, immature egg cells known as oocytes are put into cellular arrest, remaining dormant for up to 50 years in the ovaries.

  • Like all other eukaryotic cells, oocytes have mitochondria that act as batteries of the cell and help generate energy for their needs during this period of dormancy; it's a process that is not unlike putting batteries on standby mode.

  • Immature human egg cells skip a fundamental metabolic reaction thought to be essential for generating energy to avoid creating reactive oxygen species, which are harmful molecules that can accumulate, damage DNA, and cause cell death.

  • A complex protein and enzyme known as complex I is the usual 'gatekeeper' that initiates the reactions required to generate energy in mitochondria, and although it is fundamental in the cells of living organisms, it is virtually absent in oocytes.

  • The discovery explains why some women with mitochondrial conditions linked to complex I do not experience reduced fertility compared to women with conditions affecting other mitochondrial respiratory complexes, yet 1 in 4 cases of female infertility are unexplained.

This is a summary of the article, "Oocytes maintain ROS-free mitochondrial metabolism by suppressing complex I" published by Nature on July 20, 2022. The full article can be found on

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