It is one of the mysteries of gene regulation. The male of a species has one X-chromosome, the females two. So it would seem that female cells would produce twice as much proteins encoded by X-chromosome as males. But this does not happen. The cells resolve the problem by either deactivating (in females) or hyperactivating (in males) the genetic material to keep protein parity in both sexes. The phenomenon is controlled by an assembly of proteins called the dosage compensation complex (DCC). But there is little understanding about how this complex works. No longer.
A study by a team of scientists from the European Molecular Biology Laboratory in Germany has found a link between the membrane surrounding the nucleus and the male X-chromosome in fruit flies. DCC interacts with molecules that sit on the nuclear membrane where they form gateways to the nucleus. With the molecules removed, hyperactivation did not take place.
Initial studies with human cells indicate a similar phenomenon occurring. Unlike flies, mammals inactivate one of the female X-chromosomes to match the protein contents between the sexes. The study appeared in Molecular Cell (Vol 21, No 6, March 17, 2006).