Investigating the role of microRNAs in Wolbachia-Aedes aegypti-dengue virus interactions

Abstract

More than a third of the world's population is at risk of infection from various arboviruses transmitted by mosquitoes. One particularly destructive example of these is dengue virus (DENV), which is the causative agent of dengue haemorrhagic fever and is responsible for as many as 390 million infections annually across the tropical and sub-tropical regions of the world.Unfortunately, there has been limited effectiveness of vaccines against DENV to date and preventative efforts have focused largely on vector control through the use of pesticides. There exist several drawbacks to such strategies including possible off-target effects of pesticides as well as the potential for development of resistant insects. These challenges have necessitated novel approaches to restricting the prevalence of DENV such as the use of biocontrol agents. Recent research efforts in this field have successfully demonstrated that the endosymbiotic bacterium Wolbachia pipientis holds the potential to inhibit the ability of several viral pathogens to replicate in their insect hosts.Infecting up to two thirds of all insect species, this Gram-negative bacterium encompasses several distinct strains that produce a diverse array of impacts on their respective hosts physiology. In some cases, these effects are pathogenic, such as male killing, reduced lifespan, and reduced fecundity, and yet others are less so, such as increased resistance to particular pathogens and cytoplasmic incompatibility. When a non-native strain of Wolbachia (wMelPop-CLA) was introduced into the DENV vector Aedes aegypti, it had the impact of drastically restricting the ability of several viruses, including DENV, to successfully replicate and disseminate through the mosquito tissues. Despite this impactful discovery, very little is known about the physiological and molecular mechanisms that mediate this ability of Wolbachia to impinge DENV success in its host. One demonstrable effect of Wolbachia colonisation of its mosquito host is the marked induction of the key transcription factor GATA4.This versatile transcription factor has a wide array of tissue specific developmental functions in mammals including effects on ovary and teste development. This activity in ovarian development is at least partially conserved in Ae. aegypti as GATA4 has been shown to induce vitellogenesis in response iii to blood meal and thus play a key role in embryo development. Our observations of GATA4s behaviour in response to Wolbachia led us to investigate potential genes under GATA4 regulatory control. We determine two genes, Blastoderm specific gene 25D (BSG25D) and Imaginal disc growth factor (disc) expressed in the ovaries, to be transcriptionally repressed in vitro by GATA4. When we reproduced this suppression of the disc gene in vivo it led to delayed emergence of eggs giving some insight into the effects Wolbachia may produce by suppressing this gene.Despite this work and the work of others, the mechanism of GATA4 induction as well as several other transcriptional changes induced by Wolb...