Researchers at the University of Arizona have discovered a protein in mosquitos that is critical to the process of producing viable eggs and can be exploited to control mosquito populations. Named Eggshell Organizing Factor 1 (EOF-1), the selective blocking of this protein in female mosquitos results in them laying eggs with defective shells, causing the death of the embryos inside.
The researchers are confident that using this mechanism would only affect mosquito populations and not other beneficial insects such as bees, as EOF-1 only exists in mosquitos.
“We specifically looked for genes that were unique to mosquitoes and then tested for their functional role in eggshell synthesis,” says lead author Jun Isoe. “We think there are other discoveries to be made using this same species-directed approach.”
Isoe first used a bioinformatics approach to search for and identify genes that are unique to mosquitoes. None of those genes were previously known with regard to their function. The research team then created small RNA molecules that specifically inhibit each of the proteins the genes code for. Known as RNA interference, or RNAi, the technique works by suppressing messenger RNA molecules that serve as blueprints for proteins.
The RNAi molecules were injected into female mosquitoes right before a blood meal. Only female mosquitoes bite because they need a blood meal to produce eggs; the males visit flowers to drink nectar. Once a female mosquito has had a blood meal, her follicles develop and it takes three days to lay eggs. Each individual mosquito was screened for viable offspring. Out of the 40 mosquito-specific genes the team tested, only one, the EOF-1 gene, was found to disrupt eggshell formation and result in the death of the mosquito embryo.
Usually, the effects of RNAi injection last only through one egg-laying cycle, but in the case of EOF-1, the researchers were surprised to find that treated females could no longer produce viable eggs for the rest of their two- to three-week life span, even after three consecutive blood meals.
Electron microscopy revealed that when mosquitoes are deficient in the EOF-1 protein, the females lay eggs with abnormal-looking egg shells. Although the exact function of the protein have not yet been determined, the University of Arizona researchers believe that EOF-1 might act as a master switch at the onset of the insects’ ability to produce viable eggs in response to a blood meal.
These results have led to the team coming up with a strategy that utilizes small molecule drugs that selectively interfere with mosquito EOF-1 in areas of the world where mosquito-borne human diseases are prevalent, resulting in eggs that never hatch into larvae.
More than 500 million people suffer from diseases transmitted by the blood-feeding insects, including malaria, Dengue Fever, Zika, and West Nile, and nearly a million deaths are attributed to mosquito-borne illnesses each year.