Early research suggests SGO1 may reduce chromosome separation errors in older eggs

A 2026 study suggests that restoring the protein SGO1 can reduce early chromosome separation in eggs, a process that might help reduce embryo aneuploidy, though this was not directly tested.

One of the main causes of age-related infertility is chromosome errors in eggs. As women get older, eggs are more likely to make mistakes when chromosomes separate during cell division, a process called meiosis. This can lead to aneuploid embryos that have too many or too few chromosomes. Aneuploid embryos are a major cause of implantation failure and miscarriage.

Human eggs pause meiosis for decades. Over time, the systems that hold chromosomes together and pull them apart can weaken. When the egg finally resumes division at ovulation, chromosomes are more likely to separate incorrectly.

Proteins called cohesins help keep chromosomes together until the right moment. These proteins can weaken with age, allowing chromosomes to separate too early and increasing the risk of aneuploidy.

A new study by Saha et al. (2026) looked at another protein called Shugoshin 1 (SGO1), which also helps prevent chromosomes from separating too soon. Earlier studies in animals suggested that loss of SGO1 may increase chromosome errors with age, but it was unclear whether this also happens in human eggs, or whether restoring SGO1 could help reduce these errors.

Note that this study is a preprint, meaning it hasn’t been peer reviewed yet and some details could change once the review process is complete.

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SGO1 and early chromosome separation in mouse eggs

To better understand what SGO1 does, the researchers first studied mouse eggs.

When SGO1 was depleted in mouse eggs, chromosomes were far more likely to separate too early during meiosis. This occurred in about 10% of control eggs but increased to roughly 50–60% after SGO1 depletion, and these eggs also showed clear chromosome alignment defects.

The researchers also compared eggs from young and aged mice. Premature chromosome separation occurred in about 10% of eggs from young mice, compared with roughly 70–80% of eggs from older mice, along with signs that the structures holding chromosomes together were weakened.

Importantly, adding SGO1 back to aged mouse eggs reduced early chromosome separation toward levels seen in young eggs, showing that SGO1 loss directly contributes to this defect.

Together, these mouse experiments show that SGO1 is directly involved in keeping chromosomes paired during meiosis, and that losing SGO1 leads to early chromosome separation, which is an important step toward chromosome errors and aneuploidy.

SGO1 and early chromosome separation in human eggs

The researchers next examined human eggs donated by women of different ages. These were fresh, immature eggs (GV or MI) that were not used clinically and were donated for research.

Like mice, eggs from women 35 and older had lower levels of SGO1 and higher rates of early chromosome separation than eggs from younger donors.

Immature eggs were microinjected with either SGO1 mRNA or a control mRNA (the mRNA allows the egg to produce the SGO1 protein itself). When SGO1 was added back to human eggs in this way, several improvements were seen:

• Across all eggs, early chromosome separation dropped from about 53% to 29%
• In eggs from women under 35, rates fell from about 49% to 24% (statistically significant). In eggs from women 35 and older, rates fell from about 65% to 44%, but this was not statistically significant, likely because of the lower sample size (n= 9).
• The number of single chromatids per egg was reduced, indicating stronger chromosome cohesion, but this again wasn’t statistically significant for older eggs.
• In paired comparisons, treated eggs consistently showed less early chromosome separation than untreated eggs from the same donor

Overall, these results suggest that SGO1 levels decline with age in human eggs and that restoring SGO1 can improve chromosome cohesion, which might be more effective in younger eggs (but larger studies are needed).

Conclusion

This study suggests that SGO1 helps keep chromosomes together during egg division, a process that is linked to aneuploidy risk.

In mice, losing SGO1 caused chromosomes to separate too early, while supplementing it back reduced this problem.

In human eggs, SGO1 levels were lower with age and were linked to higher rates of early chromosome separation. Adding SGO1 reduced these errors, especially in eggs from younger women, though results in older eggs weren’t statistically significant possibly because of the low sample size.

While this is exciting research, it is still early and leaves several important questions unanswered:

• No embryos were created, so it is unclear whether delivering SGO1 mRNA could affect embryo health.
• No IVF outcomes were reported, such as fertilization, embryo development, implantation, or live birth.
• The study focused on early chromosome separation in eggs, a risk factor for aneuploidy, but did not examine embryo aneuploidy itself. No PGT-A was performed.
• The study suggests that older eggs have lower SGO1 levels and a higher risk of early chromosome separation, but the older patient group was small and results in this group were not statistically significant. This makes age-specific conclusions uncertain in humans.

Overall, this work suggests that restoring SGO1 might one day help reduce chromosome errors in older eggs, but more research is needed to see if this improves clinical outcomes.

Want to read more about egg quality and aneuploidy?

Reference

Restoring Shugoshin 1 reduces chromosome errors in human eggs. Debojit Saha, Saba Manshaei, Tommaso Cavazza, Zuzana Holubcová, Barbora Maierova, Agata P. Zielinska, Lena Wartosch, Martyn Blaney, Kay Elder, Melina Schuh. doi: https://doi.org/10.64898/2026.01.08.698387

 

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About Embryoman

Embryoman (Sean Lauber) is a former embryologist and the founder of Remembryo, an IVF research and fertility education website. After working in an IVF lab in the US, he returned to Canada and now focuses on making fertility research more accessible. He holds a Master’s in Immunology and launched Remembryo in 2018 to help patients and professionals make sense of IVF research. Sean shares weekly study updates on Facebook, Instagram, and Reddit regularly. He also answers questions on Reddit or in his private Facebook group.

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