A protein required for development of mosquito eggs may provide a mosquito-selective target for insecticide development, according to a new study publishing on January 8 in the open-access journal PLOS Biology, by Jun Isoe of the University of Arizona and colleagues. Because the protein is specific to mosquitoes, it may be possible to interrupt their egg formation without harming other insects.
To find mosquito-specific proteins, the authors performed data mining and bioinformatic analyses of public genomic databases to identify protein-coding sequences that were restricted to the genomes of three of the most important vectors of human disease: Aedes, Culex, and Anopheles mosquitoes. Among other diseases, yellow fever is spread by Aedes species, West Nile fever by Culex, and malaria by Anopheles. They identified a group of genes expressed in mosquitoes but not in 37 evolutionarily closely related insects, and thus not likely to be found in other animals, plants, fungi, and bacteria.
Using a technique called RNAi, which inactivates messenger RNA and thus blocks expression of the targeted gene, the team investigated the role of 40 genes by blocking their expression in female Aedes aegypti mosquitos just prior to a blood meal, then analyzed the characteristics of the eggs they produced. They identified a protein, called eggshell organizing factor 1 (EOF1), whose inactivation led to fragile, non-melanized eggshells. The authors showed that loss of EOF1 caused multiple defects in egg structure, including a gross increase in size in a layer called the outer chorion. None of the eggs with deficient EOF1 were viable.
"Because EOF1 is restricted to mosquitoes, it may provide a useful target for developing more biosafe mosquito control strategies," Isoe said, "either with small-molecule inhibitors or CRISPR/Cas9 gene-drive genetic manipulation targeting this gene."