Sperm are expert swimmers. But eggs are tough to breach. And sometimes there is competition from other males' sperm. Paternity in many species depends in part on male sperm-control mechanisms. Image

A gene responsible for sperm production is so vital that its function has remained unaltered throughout evolution and is found in almost all animals, according to a new study. The results suggest the ability to produce sperm originated 600 million years ago.

The gene, called Boule, appears to be the only gene known to be exclusively required for sperm production in animals ranging from an insect to a mammal.

"Our findings also show that humans, despite how complex we are, across the evolutionary lines all the way to flies, which are very simple, still have one fundamental element that's shared," said Eugene Xu, assistant professor of obstetrics and gynecology at Northwestern University Feinberg School of Medicine.

The discovery of Boule's key role in perpetuating animal species offers a better understanding of male infertility, a potential target for a male contraceptive drug, and a new direction for future development of pesticides or medicine to fight infectious parasites.

The study will be published July 15 in the journal PLoS Genetics.

Sperm search

Prior to the new findings, scientists didn't know whether sperm produced by various animal species came from the same prototype. In many evolution scenarios, things develop independently. As an example, birds and insects both fly, but the wings of each originated and evolved completely independently.

For the study, Xu searched for and discovered the presence of the Boule gene in sperm across different evolutionary lines: human, mammal, fish, insect, worm and marine invertebrate. The search required sperm from a sea urchin, a rooster, a fruit fly, a human and a fish.

The findings were unexpected because many sex-specific genes, including other genes involved in sperm production, are usually under evolutionary pressure to change.

"It's really surprising because sperm production gets pounded by natural selection," Xu said. "It tends to change due to strong selective pressures for sperm-specific genes to evolve. There is extra pressure to be a super male to improve reproductive success. This is the one sex-specific element that didn't change across species. This must be so important that it can’t change."

Helping humans

The sperm-gene discovery could have many practical uses for human health. For instance, when the researchers knocked out Boule from a mouse, the animal appeared to be healthy but did not produce sperm.

"A sperm-specific gene like Boule is an ideal target for a male contraceptive drug," Xu said.

Boule also has the potential to reduce diseases caused by mosquitoes and parasites.

"We now have one strong candidate to target for controlling their breeding," Xu said. "Our work suggests that disrupting the function of Boule in animals most likely will disrupt their breeding and put the threatening parasites or germs under control. This could represent a new direction in our future development of pesticides or medicine against infectious parasites or carriers of germs."

The research was supported by the National Institutes of Health and Northwestern Memorial Foundation.