Research

 

 

Aedes aegypti mosquito

Our overall research focus

The main research focus of the lab is the role of virus-mosquito interactions in the determination of vector competence, which is the ability of a mosquito to transmit a specific pathogen. Vector competence has both genetic and non-genetic determinants, and it can vary between mosquito species or even populations of the same species. It is also selective for different viruses - a specific mosquito population may be a suitable vector for one flavivirus (e.g. West Nile virus), yet incapable of transmitting another flavivirus (such as Zika virus). Our main focus is to study the mosquito immune responses to a set of viruses as potential determinants of vector competence.

 

Arbovirus transmission is an active process, as opposed to mechanical transmission, arboviruses replicate and disseminate through their vector. When a mosquito takes a bloodmeal from a viremic individual, virus enters the mosquito midgut lumen. Arboviruses then need to infect the midgut epithelium, replicate and disseminate from the midgut to the rest of the mosquito. Arboviruses will replicate in a number of peripheral tissues and ultimately infect the salivary glands of the mosquito to be expectorated into a new host with a subsequent bloodmeal. The time it takes for a virus to cross all these barriers and be transmitted again is called the extrinsic incubation period (EIP). The EIP can vary between viruses, mosquito populations and is also dependent on environmental factors, such as temperature.

Antiviral RNA interference

The most important antiviral response in mosquitoes is RNA interference (RNAi). There are three major RNAi, or small RNA, pathways in mosquitoes: the micro RNA (miRNA), the small interfering RNA (siRNA), and the PIWI-interacting RNA (piRNA) pathways. The miRNA pathway is predominantly involved in regulating mosquito gene expression and, as far as we know, only plays an indirect role in controlling virus replication. In contrast, the siRNA pathway is clearly established as an antiviral response in mosquitoes and other arthropods. The antiviral role of the piRNA pathway, however, remains unclear and will form the focus of our first objective. Generally, piRNAs are important suppressors of transposable elements, protecting the germ line of a variety of organisms from random integration of retrotransposons. piRNAs are generated by P-element induced wimpy testis (PIWI) genes expressed exclusively in the gonads of most organisms. These genes have undergone an expansion in Aedes mosquitoes and Culex mosquitoes (7 PIWI proteins). Furthermore, in Aedes mosquitoes, piRNAs are also produced in somatic tissue after virus infection with alphaviruses, flaviviruses, and phleboviruses. These piRNAs generated from virus genomes are referred to as virus-derived piRNAs.

Antiviral RNA interference of Culex spp. mosquitoes

Among other projects, we will study Culex mosquito antiviral responses to a set of arboviruses. We recently found that small RNA responses of Culex mosquitoes differ from those of Aedes mosquitoes. Specifically, while we found evidence for virus-derived piRNAs from Merida virus, an insect-specific negative sense RNA virus, we did not detect any flavivirus-derived piRNAs in Culex cells and mosquitoes. We also found no piRNAs derived from alphaviruses (in unpublished preliminary experiments). These and data from other recent studies may suggest that piRNAs are only produced from negative sense RNA viruses in Culex mosquitoes. We thus aim to establish which small RNAs are generated after infection with additional arboviruses, which of the seven Culex PIWI genes are involved in the generation of virus-derived piRNAs and how these are generated in the first place.