Unravelling a mystery

Mary Buhr is an expert on sperm—and a bit of a film noir buff.

So if ‘membrane-based signalling pathways controlling sperm capacitation’ does not paint a picture in your mind, she suggests imagining a mysterious character going down a shadowy back alley.

“The sperm is wearing a disguise and a hat pulled down low and knocking on a door with a little grill in it,” she said. “When the grill opens, he takes off the hat and disguise and shows who he really is. And then the door opens.”

That moment when the disguise comes off is capacitation, a series of molecular changes that allow the head membrane of a sperm to first fuse with and then penetrate the egg. The rough outline of the process has been known since the days when wisecracking gumshoes and femme fatales still ruled the box office, but the precise details remain a mystery.

“Basically, the egg has to recognize the sperm as being of her species and being healthy before the egg will let the sperm in to fertilize,” said Buhr. “What we don’t know is what those specific molecules are and how they function.”

Artificial insemination has been a tremendous boon to livestock breeding because you can freeze sperm from top males and send it around the world. The result is offspring that produce more meat or milk, utilize feed more efficiently or have other desirable attributes.

“The problem is that when you store these little guys, you’re freezing them to -196 C and some don’t live through the process,” noted Buhr. “We’re thinking that if we can identify the molecules that are crucial for fertility, then we could custom design a cryoprotectant—a freezing solution—targeted specifically to protect those molecules.”

What could also be huge in the effort to save endangered species.

While the reproductive biology of livestock (such as details of the estrous cycle or where to place sperm) is very well known, that is not the case for wild animals. And collecting sperm from wildlife (think elephants or cheetahs) is not the easiest thing, either. So being able to preserve sperm is critical—you do not want to be unthawing this extremely valuable genetic resource decades from now and discover it isn’t viable because of freezer burn.

Better cryopreservation would also help honeybees, the major pollinator of agricultural crops. The honeybee sector suffers big losses each winter and has been plagued by colony collapse disorder in recent years. Replacing those lost colonies means importing new ones from the U.S., which can also bring in varroa mites (a deadly parasite), diseases and Africanized, killer bee hybrids. Using bee semen tested for genetic purity and presence of disease bypasses all those problems.

“You just overwinter and then inseminate the queen and—presto—we don’t have to import colonies anymore,” she said. “The problem, again, is that bee semen is incredibly hard to preserve.”

Being a specialist in sperm physiology has led Buhr into areas she never imagined, but that makes it all the more interesting, she said.

“There’s not a whole lot of people working with sperm but what we’re learning can be applied in many areas, so it really is important work.”