Silent X

Upfront is a quick look at the latest developments from Stanford Medicine.

Early in the development of female embryos, one X chromosome is shut down or silenced in each cell, ensuring that females, who have two X chromosomes, and males, who have only one, end up with roughly the same dosage of genes that occur on that chromosome.

Scientists have known about X inactivation for decades. Recently they learned that an RNA molecule called Xist is responsible. But it’s not been clear exactly how Xist silences genes on the X chromosome.

In a study published in Cell, Stanford researchers have outlined the molecular steps of inactivation, showing that it occurs in an orderly fashion as early embryonic cells differentiate into more specialized tissues. They hope their findings will shed light on conditions in humans that are typically more severe in one gender than the other.

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