Humans bite back by deactivating mosquito sperm

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

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

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

“During mating, mosquitoes mate tail to tail, and the males transfer sperm to 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,” Cathy said Thaler, UCR cell biologist and the study’s first author.

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

“Without these proteins, the sperm cannot enter the eggs. They remain immobile and will eventually just break down,” says Richard Cardullo, UCR biology professor and corresponding author of the new study.

The study, described in the journal PLOS ONEdescribes a full portrait of all the proteins in the insect’s sperm, helping researchers find the specific proteins that maintain sperm quality while inactive, as well as triggering them to swim.

Mosquito eggs of the Culex genus. Credit: CDC

To get this detailed information, the research team teamed up with a team of graduate and undergraduate students who isolated as many as 200 male mosquitoes from a larger population. They then extracted enough sperm from the small reproductive organs for mass spectrometry equipment to detect and identify the proteins.

Previously, the team determined that sperm need calcium when entering a reproductive tract to enable forward movement. “Now we can look into the finished protein profile we created, find the calcium channel proteins and design experiments to target these channels,” Cardullo said.

This kind of protein profiling offers a way to control mosquitoes that is more environmentally friendly than other methods that can have unintended, toxic effects. “We stopped spraying pesticides everywhere because that kills everything, good bugs and bad, and harms other animals,” Thaler said.

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

The operative word is control, rather than extermination. While immobilizing the sperm would be 100% effective for the 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 eradicate them all.

Culex mosquito larva in stagnant water. Credit: CDC

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

The team hopes that information about sperm motility regulators in Culex will also apply to other species of mosquitoes. As climate change intensifies, many other mosquitoes, such as those that transmit malaria, are migrating to the Northern Hemisphere.

In addition, more information about Culex sperm motility may have implications for improving fertility in humans.

Cardullo has long studied mammalian sperm, hoping to develop a male contraceptive. Just as important as preventing unwanted pregnancies, however, is the effort to help couples conceive. Human fertility rates have been declining for years, partly due to environmental factors. A better understanding of sperm may help overcome some of these factors.

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

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

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