A genetic discovery from the University of California – Riverside (UCR) could permanently transform disease-carrying mosquitoes into adolescents, never developing or reproducing.
Contrary to conventional scientific thinking, UCR entomologist Naoki Yamanaka discovered in 2018 that a crucial steroid hormone needs transporter proteins to enter or depart fruit fly cells. Ecdysone, a hormone, is referred to as the “molting hormone.” Flies cannot develop into adults or breed without it.
Before his discovery, textbooks taught that ecdysone travels freely across cell membranes, slipping past them with ease. “We now know that’s not true,” Yamanaka said.
Ecdysone is necessary for some stage of every insect species’ life cycle, from the egg to the offspring-producing adult. The ecdysone transporter that Yamanaka discovered in 2018 as well as a few others discovered in recent research are present in every insect that Yamanaka has tested. He discovered, however, that mosquitoes are unique in this new study.
Only three of the four transporter proteins found in fruit flies are present in mosquitoes. They are lacking in the primary and most crucial ecdysone transporter.
“This primary one is somehow, mysteriously, missing in mosquitoes,” Yamanaka said.
These findings have recently been published in the Proceedings of the National Academy of Sciences.
The discovery opens the door to a mosquito-specific insecticide that would not harm beneficial bees or other pollinators. It would, however, affect mosquitoes like the ones used in the study, Aedes aegypti, which spread Zika, dengue, yellow fever, chikungunya, and other viruses.
“We can develop chemicals to block the functions of these ecdysone transporters but do not affect the original transporter that is so key for other insects,” Yamanaka said. “The chances for off-target effects would be low.”
A related UC Riverside study, led by cell biologist Sachiko Haga-Yamanaka, is attempting to locate similar hormone transporting machinery in humans.
“Textbooks say that steroid hormones transport freely into and out of human cells, but based on our insect research, we doubt that to be the case,” Yamanaka said.
Yamanaka’s research has been funded by the National Institutes of Health. His laboratory is now screening for chemicals that can block mosquitoes’ ecdysone importers. He is also investigating ecdysone transporters in other animals.
Other methods do exist of ensuring local populations of mosquitoes cannot breed. Releasing sterile, irradiated male mosquitoes into the wild to mate with females results in eggs that do not hatch, a technique that eliminates the need for insecticides.
Though there are effective methods like this for controlling local populations of mosquitoes, Yamanaka feels it is important to develop additional tools so we can handle mosquito-related issues in many different scenarios.
“It is impossible to make mosquitoes go extinct,” Yamanaka said. “Depending on one tool to control them is dangerous. As the climate heats up, it creates even more favorable conditions for them to multiply, and they’re only likely to become a bigger problem, especially in Southern California.”
The study was funded by the NIH/National Institutes of Health.
Reference: “Essential functions of mosquito ecdysone importers in development and reproduction” by Lewis V. Hun, Naoki Okamoto, Eisuke Imura, Roilea Maxson, Riyan Bittar and Naoki Yamanaka, 13 June 2022, Proceedings of the National Academy of Sciences.
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