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The later activation of the X chromosome may enhance cognitive function, which could partly explain why women tend to have longer lifespans.
Each of us inherits our genetic background from our parents, grandparents, and even distant ancestors that we may have forgotten. Humans have 23 pairs of chromosomes, with one set coming from each parent. The chromosome inherited from the father determines the biological sex of the child, but we receive genes from both parents equally. The dominant genes are sometimes expressed during development and in life outside the womb, while recessive genes may remain hidden and not visibly affect traits.
The X chromosome is present in the gametes of both women and men, while men also receive a Y chromosome, the determinant of male sex. This results in women having two X chromosomes (XX) and men having one X and one Y chromosome (XY). In women, the second X chromosome, known as the silent X, is inactivated during the developmental stage and early life to prevent a double dose of X-linked genes.
When silent genes awake
Recently, scientists from the University of California, San Francisco, published a study in ,,Science Advances” claiming that this silent X chromosome is activated later in life as aging begins, particularly with expression in the hippocampus, a crucial part of the brain for learning and memory. This activation occurs due to elevated levels of a specific protein linked to the protection of signaling pathways in the brain. The researchers suggest that this phenomenon may enhance cognitive abilities and influence longevity in both women and men. However, they noted that the elevated levels of this protein are found to be naturally higher in women.
The X chromosome is about 155 million DNA building blocks long (base pairs) and accounts for roughly 5 percent of the total DNA in cells. Individuals with two X chromosomes have only one functional copy of the X chromosome in each cell. X-inactivation occurs randomly, so it is unclear whether the X chromosome inherited from the mother or the one from the father will be switched off.
Researchers in California have found that, alongside aging, the previously silent chromosome X activates about 20 additional genes that were expected to remain inactive.
Aging had awakened the sleeping X,
says Dena Dubal of the University of California, San Francisco, USA.
How does all of this contribute to brain function? The activation of the second X chromosome, driven by a specific protein, enhances the brain’s connections and increases cognitive abilities. Simplifying the chromosome can suddenly cause it to detach from its loci, which typically happens during cell division when a piece of genetic material separates in the cell’s nucleus.
The escapee activates when a protein, a component of myelin that protects nerve fibers, triggers the process. This causes previously silent genes to express, enhancing connections between brain cells and improving communication. As a result, signal transmission improves, boosting cognitive function. In the hippocampus, crucial for memory and emotion, this slows cognitive decline and helps women better resist the effects of aging.
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