This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: It's known that the Y chromosome, which confers male sex, plays a big role in development and health, despite its small size. As cells age they frequently lose their Y chromosomes, which is associated with conditions like cancer, Alzheimer's disease and heart disease.
"The Y chromosome is vulnerable as cells divide, with consequences for health," says James Turner, who runs the Crick's Sex Chromosome Biology Laboratory. "But what happens if it's lost in the earliest days of development when it needs to switch on male sex in the embryo?" Embryos don't usually survive if a chromosome is lost early in development. However, individuals can have a condition where most or some of their cells have only one X chromosome, called Turner syndrome.
This affects growth and fertility and causes potential cardiovascular, renal and autoimmune complications. Turner syndrome is often thought to be linked to the loss of the second X, but it can also result from the loss of a Y chromosome, which Turner believes may happen more often than previously thought. In a new study published in Science Advances, Turner and Agata Zielinska, a former postdoctoral researcher in the lab, explored how embryos protect the Y chromosome in their earliest days.
"Once a sperm and egg have fused together, the first division into two cells is a huge challenge," says Zielinska. "And the Y chromosome starts off at a disadvantage, with much lower levels of a protein that helps keep cell division on track." Before cell division, two copies of each chromosome line up in the middle of the cell and then ropes called "spindles" pull them apart into each new cell. These spindles attach to a landing pad, or centromere, on each chromosome pair.
The Y chromosome has unusually low levels of a protein that forms the foundations of the landing pad. So how do embryos with two sex chromosomes emerge if the odds are stacked against the Y? To find out, Zielinska fluorescently labeled chromosomes in mouse zygotes (the first cell formed when a sperm and egg fuse) during their first division.
She recorded the chromosomes duplicating, lining up in the center and splitting into two new cells under a microscope. In normal conditions, most Y chromosome pairs separated in the first division. Zielinska discovered safeguards that help the vulnerable Y pairs separate successfully, including finely balanced spindle forces, which meant the Y was under less tension than other chromosomes.
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