Humans bite back by disabling mosquito sperm

New research at UC Riverside makes it possible that the proteins responsible for activating mosquito sperm can be disrupted, preventing them from swimming or fertilizing eggs.

The study could help control populations of Culex, the common household mosquito that transmits encephalitis and West Nile virus.

“During mating, mosquitoes mate tail to tail, and the males transfer the sperm into the female reproductive tract. It can be stored there for a while, but it still needs to get from point A to point B to complete fertilization,” said Cathy Thaler, UCR. cell biologist and the first author of the study.

Key to completing this journey are specialized proteins secreted during ejaculation that activate the sperm’s flagella, or “tails,” which power their movement.

“Without these proteins, sperm cannot penetrate eggs. They will remain immobile and eventually degrade,” said Richard Cardullo, UCR biology professor and corresponding author of the new study.

The study, detailed in the journal PLOS ONEdetails a complete portrait of all the proteins in the insect’s sperm, allowing researchers to find the specific ones that maintain sperm quality while dormant and that also enable them to swim.

To obtain this detailed information, the research team worked with a team of graduate and undergraduate students who isolated up to 200 male mosquitoes from a larger population. They then extracted enough sperm from the tiny reproductive tracts for mass spectrometry equipment to locate and identify the proteins.

Previously, the team determined that sperm need calcium upon entering the reproductive tract to trigger forward movement. “Now we can look at the comprehensive protein profile we created, find the calcium channel proteins, and design experiments to target those channels,” Cardullo said.

This type of protein profiling offers a route to mosquito control that is more environmentally friendly than other methods that can have unintended, toxic effects. “We’ve given up spraying pesticides everywhere, because that kills everything, good insects and bad, and it hurts other animals,” Thaler said.

“Our work lays the foundation for a form of biological control that most would agree is preferable,” Cardullo added.

The operative word is control, rather than elimination. Although sperm immobilization would be 100% effective for treated mosquitoes, it is not possible or desirable to kill all mosquitoes. This technology would change the ratio of fertile to infertile males in a given mosquito population, rather than wiping them all out.

“Mosquitoes are the deadliest animals on Earth. But as much as people hate them, most conservationists would oppose a plan to completely eradicate them. They play an important role in the food chain for fish and other animals,” said Cardullo.

The team hopes that the information about regulators of sperm motility in Culex will apply to other mosquito species. As climate change intensifies, many other mosquitoes, such as those that carry malaria, are moving into the northern hemisphere.

Additionally, learning more about Culex sperm motility may have implications for improving human fertility.

Cardullo has long studied mammalian sperm in hopes of developing a male contraceptive. Just as important as preventing unwanted pregnancy, however, is trying to help couples conceive. Human fertility rates have been declining for years, partly due to environmental factors. A better understanding of sperm could help overcome some of these factors.

“Many cells have flagella or tails, including human respiratory cells as well as cells in our intestines,” Cardullo said. “What we learn in one system, like mosquitoes, can be translated to others.”