CAMBRIDGE, Mass. -- Painstaking new analysis of the genetic sequence of the X chromosomelong perceived as the "female" counterpart to the male-associated Y chromosomereveals that large portions of the X have evolved to play a specialized role in sperm production.
This surprising finding, reported by Whitehead Institute scientists in a paper published online this week in the journal Nature Genetics, is paired with another unexpected outcome: despite its reputation as the most stable chromosome of the genome, the X has actually been undergoing relatively swift change. Taken together, these results suggest that it's time to reexamine the biological and medical importance of the X chromosome.
"We view this as the double life of the X chromosome," says Whitehead Institute Director David Page, whose lab conducted this latest research.
"The X is the most famous, most intensely studied chromosome in all of human genetics. And the story of the X has been the story of X-linked recessive diseases, such as color blindness, hemophilia, and Duchenne's muscular dystrophy," Page adds. "But there's another side to the X, a side that is rapidly evolving and seems to be attuned to the reproductive needs of males."
Page's lab, best known for its pioneering investigations of the Y chromosome, embarked on a rigorous comparison of the mouse and human X chromosomes, in part to test the longstanding biological tenet that the gene content of X chromosomes is conserved and shared across mammals. However, to render such a comparison valid, the lab had to upgrade the human X reference sequence, which was originally assembled as a mosaic of sequences from the X chromosomes of at least 16 people. This composite left the reference with errors and gaps that fail to capture so-called ampliconic regions containing segments of nucleotides that are virtually identical. Such near-complete identity prevents recognition of tiny but important differences.
|Contact: Matt Fearer|
Whitehead Institute for Biomedical Research