Genome complexity: Inactivating one X chromosome (Introduction)

by David Turell , Monday, August 10, 2015, 17:56 (3179 days ago) @ David Turell

In mammals one female chromosome is inactivated for proper genome function:-http://www.sciencedaily.com/releases/2015/08/150810110747.htm-"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.