Humans retaliate by deactivating mosquito sperm

Adult female Culex mosquito taking a blood meal. Credit: CDC

New research from UC Riverside indicates that it’s likely that proteins responsible for activating mosquito sperm may be shut down, preventing them from swimming or fertilizing eggs.

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

“During mating, the 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 has to get from point A to point B to complete. fertilization,” said Cathy Thaler, UCR. cell biologist and first author of the study.

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

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

The study, detailed in the review PLOS ONEdetails a comprehensive portrait of all of the insect’s sperm proteins, allowing researchers to find those that maintain sperm quality when inactive and also activate them to swim.

Culex species mosquito eggs. Credit: CDC

To get 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 genital tract for mass spectrometry equipment to detect and identify the proteins.

Previously, the team determined that sperm need calcium as they enter the reproductive tract to propel forward movement. “Now we can look into the full 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 on spraying pesticides everywhere because it kills everything, good and bad insects, and harms other animals,” Thaler said.

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

The key word is control rather than eradication. Although sperm immobilization would be 100% effective for treated mosquitoes, it is neither possible nor desirable to kill all mosquitoes. This technology would alter the proportion of fertile males to infertile males in a given mosquito population, rather than wipe them all out.

Culex mosquito larva in standing water. Credit: CDC

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

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

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

Cardullo has long studied mammalian sperm, hoping to develop a male contraceptive. However, just as important as preventing unwanted pregnancies is the effort to help couples conceive. Human fertility rates have been falling for years, in part 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 from our intestines,” 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

Journal information:

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