A component of the sperm membrane tightly controls a crucial step in fertilization, making it a prime target for efforts to either assist fertilization or prevent it.
A new study shows that as a sperm approaches an egg, GM1 in the sperm membrane controls the opening and closing of a specific calcium channel on the surface of the sperm head, allowing a small amount of calcium into the sperm.
This tiny movement of calcium must be completed in order for the sperm to release the enzymes that help it pass through the egg’s thick outer coating. The release process, called acrosome exocytosis, is an irreversible step toward fertilization.
“By defining how GM1 regulates this calcium channel, we can now look for compounds that block or mimic that interaction,” says Alexander Travis, associate professor of reproductive biology at Cornell University. “It potentially gives you a new approach for a spermicide.”
The only spermicide that’s commercially available is detergent-based, a formulation that makes certain users more susceptible to sexually transmitted diseases. A new approach could work without detergents, mimicking GM1’s effect on sperm and triggering them to burst open and die long before they reach an egg.
Male fertility testing
On the other hand, the information might help guide the development of new cryopreservatives for use in fertility treatments in humans, livestock, or endangered species.
Some current cryopreservative formulations contain mixtures of lipids, including GM1, an ingredient that may trigger premature acrosome exocytosis and actually reduce the length of time sperm can survive after thawing, Travis says.
Meanwhile, an immediate application for GM1 is male fertility testing. Since the presence and location of GM1 in the sperm membrane must be finely tuned to accomplish fertilization, defects in these aspects can adversely affect sperm function, making GM1 a potentially useful biomarker for male fertility.
The new findings, published in the journal Developmental Cell, may also provide answers to other health-related questions, Travis says. The particular calcium channels that are active in sperm and regulated by GM1 are also found in other parts of the body. Researchers will now explore whether the GM1-calcium channel interaction they’ve identified in sperm also holds true in those organs.
Source: Cornell University