Researchers Probe Sex Chromosome's Virgin Territory
The male sex chromosome has long been called our genetic junkyard, a clutter of meaningless DNA surrounding a handful of genes--and those only good for making more men. But after rummaging through the scrap heap, two biologists say they have discovered five genes that are used throughout the body to help keep cells working properly. The researchers also describe in today's issue of Science another seven genes that are unique to the Y chromosome and lie in regions known to be involved in infertility.
Massachusetts Institute of Technology biologists Bruce Lahn and David Page knew that the Y chromosome's barren reputation rested on limited evidence. Panning for gold, the researchers examined cells from human testes, where they guessed genes on the Y chromosome should be particularly active. They collected messenger RNA (mRNA), which is made from active genes and eventually codes for proteins; because each gene has a unique corresponding mRNA strand, mRNA levels reveal which genes are actively making proteins. The researchers next copied the mRNA into a more stable form called cDNA. By making these fragments radioactive, Lahn and Page could identify which ones stuck to the Y chromosome. In all, they identified cDNAs representing 12 new Y chromosome genes.
Five of the new Y genes are found on the X chromosome and are expressed in many tissues, where they play an important role in cell "housekeeping," such as ensuring normal ribosome function. The other seven new genes are even more intriguing: They are unique to the Y chromosome and seem to be expressed just in the testes. What's more, they lie in regions that, when missing, cause male infertility. Although the Y chromosome evolved from the X, Lahn is not surprised that the Y would have unique genes. "Since the Y chromosome is passed through males, it is reasonable that it would acquire genes that function only in males," he says.
Experts say the findings should help give a fuller picture of the Y chromosome's role in making men the way they are. "This work really forms a basis of what people will be studying in the future," says Renee Reijo, a reproductive biologist at the University of California, San Francisco. She says that besides fertility, there are hints that the new Y genes might be a factor in why men tend to be taller than women and in a rare cancer called gonadoblastoma.