The story of sperm meets egg sounds pretty simple, but there are a lot of factors driving that all-important meeting. Now, researchers at Yale University have identified a key molecule that helps activate sperm and guide them to the egg. This could make it a target for both infertility treatments and new contraceptive methods.

Sperm have a calcium channel complex called CatSper, which they use to detect their surroundings, such as acidity levels in the female reproductive tract, and decide when to race off in search of an egg. At least, that's the idea – nobody really knew exactly how they do that.

So the researchers on the new study set out to find which molecules are interacting with CatSper. After screening all sperm proteins, one in particular caught their eye – known as EFCAB9, the protein appears to act like a sensor that opens the channels when it's time to swim.

"This molecule is a long-sought sensor for the CatSper channel, which is essential to fertilization, and explains how sperm respond to physiological cues," says Jean-Ju Chung, senior author of the study.

To test the protein's role, the researchers then engineered male mice that were missing the gene that encodes for EFCAB9. Sure enough, those mice were found to impregnate fewer females, and when they did, fewer babies were born. In vitro, sperm from engineered mice were seen to be less active and generally had a harder time fertilizing eggs.

With that mechanism uncovered, scientists could target the protein in two opposite types of treatments. For one, boosting it could help men with fertility problems to conceive. On the other hand, blocking it could lead to new types of contraceptives, which wouldn't require messing with hormones.

The research was published in the journal Cell. The team describes the work in the video below.