“Female” X chromosome may have an important role in sperm production in men, researchers have found.
Genetically, women carry two X chromosomes, while men carry an X and Y chromosome. The study, published in the journal Nature Genetics, reveals that large portions of the X chromosome have a specialized role in sperm production.
“We view this as the double life of the X chromosome,” study’s lead researcher, David Page, director at the Whitehead Institute for Biomedical Research in Cambridge, Mass. noted.
“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 said.
“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.”
For the study, researchers looked at mouse and human X chromosomes.
Using single-haplotype iterative mapping and sequencing (SHIMS), a unique sequencing method created by David Page along with developers at Washington University in St. Louis, the researchers discovered the human X reference sequence.
Comparisons revealed that nearly 95 percent of their X-linked, single-copy genes were common. Moreover, nearly all these genes were expressed in both males and females.
However, the study also uncovered the presence of 340 genes that were not shared between mice and humans.
Most of these genes were active almost exclusively in testicular germ cells, likely contributing to sperm production.
“These genes are more likely to have roles in diseases that are related to reproduction, infertility, perhaps even testis cancer. There’s a whole other book to be written about this aspect of the X,” Page noted.
“This is a collection of genes that has largely eluded medical geneticists. None of these genes have been associated with a Mendelian trait. Now that we are confident of the assembly and gene content of these highly repetitive regions on the X chromosome, we can start to dissect their biological significance,” Jacob Mueller, a postdoctoral researcher at the Whitehead Institute, said.
The findings of the study are reported in the current issue of the medical journal Nature Genetics.