Genome complexity: Inactivating one X chromosome (Introduction)

by David Turell @, Monday, August 10, 2015, 17:56 (1562 days ago) @ David Turell

In mammals one female chromosome is inactivated for proper genome function:

"Nature ensures this does not happen: one of the X chromosomes is completely and permanently inactivated during a female's early development in the womb. The mechanism responsible for this inactivation is not yet fully understood. However, research into mice has shown that a ribonucleic acid (RNA) molecule called Xist plays a pivotal role in the process. Several hundred copies of this molecule attach themselves to one of the two X chromosomes. Scientists believe that these RNA molecules dock onto other molecules which then inactivate the chromosome.


"The scientists were thus able to isolate surviving stem cells and identify seven genes that are central to X inactivation. One of them is called Spen. Scientists were already aware that Spen produces a protein which allows it to bind with RNA and essentially prevents the genes from being read. In other experiments, ETH researchers were able to show that if a mouse cell lacks the Spen gene, the proteins responsible for altering chromosome structure are not able to accumulate as efficiently at the X chromosome.


"The genes for Xist and Spen are found in humans as well. Thus, as Wutz points out, this research offers us some insight into the human system -- at least at the theoretical level, as mouse genetics cannot be mapped directly to humans.

"A few years ago, a team of French researchers postulated that, in addition to Xist, humans also have another system which ensures that the single X chromosome in men and one of the two X chromosomes in women remain active. This activating system does not exist in mice. Due to the interplay of activating and inactivating factors, regulation of X chromosomes in humans might therefore be more complicated than originally thought. Geneticists wanting to understand these processes in detail still have plenty of work ahead of them."

Comment: Sexual reproduction allows for more variation in evolution, but created this problem and required this solution. Still looks planned to me.

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