Humans bite back by deactivating the mosquito’s sperm

An adult female Culex mosquito eating a blood meal. Credit: CDC

New UC Riverside research makes it likely that the proteins responsible for activating mosquito sperm can be shut down, preventing them from swimming to or fertilizing eggs.

The research could help control populations of Culex, brain swelling encephalitis, and the common house mosquito that spreads West Nile virus.

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

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

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

Research, detailed in the journal PLOS ONEcontains a complete picture of all the proteins in the insect’s sperm, allowing researchers to find those that maintain sperm quality when they are inactive and also activate them to swim.

Culex mosquito eggs. Credit: CDC

To obtain this detailed information, the research team worked with a group of graduate and undergraduate students who isolated up to 200 male mosquitoes from a larger population. They then separated enough sperm from small areas of reproduction for mass spectrometry to detect and identify the proteins.

Previously, the team determined that sperm need calcium when they enter the reproductive tract in order to move forward. “Now we can look at the protein profile we’ve created, find the calcium channel proteins, and design experiments to target those channels,” Cardullo said.

Such protein profiling offers a path 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 it kills everything, the good bugs and the bad, and it hurts other animals,” Thaler said.

“Our work lays the foundation for a biological control method that most people prefer,” Cardullo added.

The operative word is control, not destroy. Even if sperm immobilization is 100% effective for treated mosquitoes, it is not possible or desirable to kill all mosquitoes. This technique would change the proportion of fertile and infertile males in a given mosquito population, rather than wiping them all out.

Culex mosquito larva in standing water. Credit: CDC

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

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

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

Cardullo has long studied mammalian sperm, hoping to develop a method of male contraception. However, just as important as preventing unwanted pregnancies is the effort to help couples get pregnant. 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 gut,” Cardullo said. “What we learn in one system, like mosquitoes, can translate to others.”

More information:
Catherine D. Thaler et al., Using the Culex pipiens sperm proteome to identify elements essential for mosquito reproduction, PLOS ONE (2023). DOI: 10.1371/journal.pone.0280013

Details of the magazine:

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