Disrupting female flight in the vectorAedes aegypti

Abstract

Aedes aegypti is a vector of dengue, chikungunya, and Zika viruses. Current vector control strategies such as community engagement, source reduction, and insecticides have not been sufficient to prevent viral outbreaks. Thus, interest in novel strategies involving genetic engineering is growing. Female mosquitoes rely on flight to mate with males and obtain a bloodmeal from a host. We hypothesized that knockout of genes specifically expressed in female mosquitoes associated with the indirect flight muscles would result in a flightless female mosquito.With the CRISPR-Cas9 system, we performed embryonic microinjections of Cas9 protein and guide RNAs specific to genes hypothesized to control flight in mosquitoes, and have obtained genetic knockouts in several genes specifically expressed in the flight-muscle, including those specific to female flight muscle. Analysis of the phenotype of these female-specific gene knockout mutants resulted in flightless females and flying males. While further assessment is required, this work lays the groundwork for a mechanism of population control that is female-specific for the Ae.aegypti vector. Introduction:The yellow fever mosquito Aedes aegypti is a vector for many viruses of medical significance, such as dengue, Zika, chikungunya, and yellow fever. They can be found in tropical, subtropical, and temperate regions of the world, with outbreaks occurring in the US within the last century [1]. Only female Ae. aegypti bite to obtain a blood meal, which is required for egg production. After hatching from the embryo, Ae. aegypti like all other mosquito species will progress through the aquatic larval and pupal stages of their life, before emerging as an adult from the pupal casing to fly away [2,3].Currently, there is a safe and effective vaccine available for yellow fever [4], but not yet for dengue or Zika virus. Control efforts largely focus on reducing vector abundance, and include source reduction, and chemical methods like insecticides or larvicides [3,5]. The short-term effect and high financial cost, along with the need for trained staff, presents challenges to the implementation, scaling, and maintenance of these control methods. With chemical methods, additional concerns relating to the emergence of resistance and effects on off-target species are increasing [6]. Because of these limitations, the need for novel vector control strategies is growing.Genetic control strategies are receiving an increased amount of attention as viable vector control approaches, and include sterile insect technique (SIT) [7-9], release of an insect carrying a dominant lethal (RIDL) [7,10], and gene drive. Population suppression approaches to vector control with genetic modifications seek to, in some way, prevent the female mosquito from being able to bloodfeed or mate, thus producing fewer or no offspring, leading to a population decline or collapse. Gene drive involves the spread of a genetic element beyond Mendelian rates of inheritance [11,12]. Synthetic gene drive mechanisms can take advanta...

Nixalone is sufficient to convert femaleAedes aegyptiinto fertile males andmyo-sexis needed for male flight

“…In addition to Nix , a myosin heavy-chain gene, myo-sex ( 19 ) is also located in the M-locus ( 15 ). Myo-sex and its closest autosomal paralog (AAEL005656) show sex-specific expression in males and females, respectively ( 19 – 21 ), and could be involved in sex-specific muscle functions. Therefore, we hypothesized that the flightless phenotype observed in N1 (m/m) and N2 (m/m) males is caused by the lack of the myo-sex gene associated with the M-locus.…”

Double drives and private alleles for localised population genetic control

“…Such genes are not common, but there are some possible candidates [50][51][52], and our modelling motivates the search for others. Finally, performance (in terms of being able to cope with ever higher frequencies of pre-existing resistance) could presumably also be improved by using a third construct, to construct a triple drive, though modelling would be required to explore the implications of the many different configurations this extension would allow.…”

Double drives and private alleles for localised population genetic control

“…The most powerful design we considered targets a female-specific haplo-insufficient gene, or otherwise causes dominant female sterility or lethality. Such genes are not common, but there are some possible candidates [57][58][59][60], and our modelling motivates the search for others. Finally, performance (in terms of being able to cope with ever higher frequencies of pre-existing resistance) could presumably also be improved by using a third construct, to construct a triple drive, though modelling would be required to explore the implications of the many different configurations this extension would allow.…”