Scientists rebuilt the machinery that sorts chromosomes in eggs, and found a new protein that stops errors.

When cells divide to make eggs and sperm during meiosis, they must split their chromosomes correctly to give half their genetic code to offspring. In human egg cells, mistakes in this splitting cause reproductive failure and link to problems with kinetochores. Kinetochores are complex protein machines built on centromeres, the central pinch points of chromosomes, that pull chromosomes apart. Researchers rebuilt vertebrate centromere chromatin for both rounds of meiosis using natural meiotic proteins. They learned how this machinery works by finding that it gathers a specific set of chromatin regulators along with standard kinetochore proteins. They discovered new kinetochore proteins shared across frogs, mice, and humans that position themselves at egg centromeres. One newly identified protein, HSPBAP1, keeps chromosomes intact and ensures they divide reliably in mouse and human egg cells.

Why it matters

When eggs form, chromosomes must be sorted perfectly. Mistakes cause miscarriages and conditions like Down syndrome. This study found a new protein, HSPBAP1, that keeps chromosomes intact during sorting in both mouse and human eggs. Understanding it could help explain why errors become more common with age.

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