A gene required for sperm production in humans is also required to make sperm in mice, flies, worms and even sea anemones — some of the most primitive animals alive.

The gene called boule is expressed in the testes of sea urchins and fish — as well as those of roosters, fruit flies, fish, mice and humans. (Dr. Scott M. Lieberman/Associated Press) The findings published Thursday in the journal PLoS Genetics suggest that the gene — and sperm production as we know it — is ancient, arising about 600 million years ago with some of the first animals.

"That machinery … has been maintained and now humans and mammals still use that," said Eugene Xu, a professor of obstetrics and gynecology at Northwestern University Feinberg School of Medicine in Chicago, Ill., who led the study.

Xu said it's unusual for such a specialized process or function to be maintained through so many animals that are otherwise very different. It's especially surprising because in general, sperm change quickly through natural selection and vary widely through the animal kingdom.

Researchers first discovered the gene in flies and found that it disrupted sperm production. They named the gene "boule" — the French word for marble — because the resulting cells in the flies' testes were shiny, like marbles, Xu said.

Xu discovered the same gene in humans in 2001.

Knowing it was found in both flies and people, he decided to figure out how widespread boule was in the animal kingdom. He was surprised to find the same gene expressed in the testes of sea urchins, roosters, fruit flies and fish.

To test whether boule was also required for sperm production in mammals, he knocked out the gene in some mice. The males were unable to produce sperm as a result.

When their testes were viewed under a microscope, the undeveloped cells inside also resembled marbles, Xu said.

The findings may lead to a new kind of male contraceptive drug, Xu suggested.

"A gene like boule whose only function is sperm production, has no effect on your normal other functions … so that's an ideal target," he said.

It might also be used to control pests such as mosquitoes and worms, he thinks. While the gene has some key parts that are the same in animals, it also has parts that differ from animal to animal. That means it could be possible to develop boule-disrupting pesticides that target certain species.

Sperm can be seen in the testes of normal mice, left, but when the boule gene is knocked out, the sperm fail to develop. In their place are round, marble-like cells. (Eugene Xu/PLoS Genetics)