Medical Research Council - London Institute of Medical Sciences

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The X Factor

Insight into the cycle of inactivation–reactivation of one of females' two X-chromosomes necessary for functional germ cells

01 August 2022

The X Factor

We have 23 pairs of chromosomes, but our gametes, sperm and eggs, only carry one copy of each. To achieve that, precursors called germ cells undergo a form of cell division known as meiosis: in this artificial ovary, lab-grown female germ cells are shown in purple, with those undergoing meiosis in yellow, and supporting cells in cyan. Meiosis has added complications for females, who possess two copies of the X chromosome. To avoid producing a harmful excess of X-linked proteins, one copy of X is inactivated in every cell, but it needs to be re-activated in germ cells. Researchers tracking the status of X chromosomes in cultured mouse cells found that this cycle of inactivation and re-activation is hugely important for efficient meiosis. This could help explain why producing immature eggs, or oocytes, in the laboratory is so difficult; improvements to the process would ultimately benefit research on female fertility.

Written by Emmanuelle Briolat

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