Japanese researchers discover protein that may shed light on fertility decline

Japanese researchers have discovered a protein that helps preserve chromosomes in egg cells over long periods. The finding could help explain why fertility in those who ovulate declines with age and potentially pave the way for new fertility treatments.

The research team, led by scientists from Chiba University, Kumamoto University and the Riken research institute, identified the protein — which they named OMC1 — that plays a crucial role in maintaining the bonds between chromosomes in egg cells throughout reproductive life.

The findings, published Thursday in the scientific journal Nature Aging, could provide new insights into why older people who ovulate face greater risks of infertility, miscarriage and their children having chromosomal disorders such as Down syndrome.

Unlike most cells in the human body, egg cells begin a specialized process of division, known as meiosis, during the fetal period of a person with ovaries and remain dormant after their birth until ovulation potentially decades later.

During this dormant period, a protein complex called REC8 cohesin acts as a molecular glue, holding chromosomes together. These bonds gradually weaken with age, increasing the likelihood of errors when chromosomes separate during cell division.

Using mice, the researchers discovered that OMC1 helps prevent REC8 cohesin from declining, allowing chromosomes to remain properly connected.

When the scientists genetically removed OMC1, even young mice exhibited chromosome abnormalities resembling those typically seen in older eggs. The researchers also found that embryos produced from eggs lacking OMC1 were less likely to develop normally after fertilization.

However, when researchers artificially reintroduced OMC1 into deficient eggs, premature chromosome separation was suppressed.

The team also investigated a mutation corresponding to one in the human gene CCDC201, which previous research has linked to premature menopause.

A 2024 study found that people who ovulate and carry two copies of a particular CCDC201 mutation experienced menopause approximately nine years earlier than others.

Keiichiro Ishiguro, a professor at the Graduate School of Medicine at Chiba University who led the research, told reporters at a news conference Thursday the protein discovery could eventually contribute to technologies aimed at preventing age-related deterioration in egg quality.

However, the findings are based primarily on experiments in mice, and further research is needed to establish whether the protein plays the same role in human eggs and whether the discovery could be applied to fertility treatments, the team said.