One protein controls egg cell maturation and fertility

Egg cells are already present before a girl is born, but they must still mature later in life before fertilisation becomes possible. That maturation process is delicate and can fail. In some women, oocyte maturation arrest means eggs never fully develop, leading to infertility. The molecular causes are largely unknown.

Researchers focused on a protein called MATR3, short for Matrin-3, which is highly expressed in growing egg cells. They deleted the gene for MATR3 specifically in mouse oocytes and observed the consequences. The results were striking: egg cells failed to grow properly, communication between the egg and surrounding support cells (granulosa cells) broke down, and follicles (the fluid-filled sacs in which eggs mature) did not develop normally. The mice were infertile.

Two functions in one protein

What the researchers found mechanistically is that MATR3 operates via two routes. It regulates gene activity by removing a chemical mark from DNA, and it binds directly to the promoter regions of specific genes required for oocyte maturation and cell signalling. The article was published in the journal eLife.

In tissue samples from women with oocyte maturation arrest, MATR3 was found in the wrong location inside the cell: it was absent from the nucleus where it normally resides. This suggests that MATR3 dysfunction contributes to human infertility.

Relevance to the ageing of fertility

Female fertility declines with age, partly because egg quality deteriorates. Whether MATR3 activity changes as ovaries age has not yet been investigated. But if this protein is so central to egg quality, it is a potentially interesting target for research into the biological clock of female fertility. Clinical applications remain speculative at this stage.

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