Because of mosquitos’ ability to transmit viruses (Zika virus) and other parasites (such as Plasmodium, the agent causing malaria), the World Health Organization considers them to be one of the world’s deadliest organisms1 and the Bill and Melinda Gates Foundation is making enormous financial contributions to research to counter the mosquito threat. It is estimated that more than half the human population is exposed to mosquito-borne diseases with more than 300 million people per year becoming sick2. Even this enormous figure is likely to increase because of global warming and other human activities that will expand the range of mosquitos into more temperate regions (including the United Kingdom)3,4.
Recently, we have generated some interesting results5 suggesting that the genes encoding light-sensitive opsin pigments underwent substantial molecular divergence in mosquitos suggesting a potential link with prey recognition. Furthermore, recent work from Zhang and collaborators6 showed that mutations in the opsin genes in Aedes aegypti abolish vision-guided target recognition suggesting the possibility for using a gene-drive approach to target these sequences in order to interfere with the insect’s visual attraction to humans. Opsin genes in mosquitos remain poorly understood7, so the study of their expression in sensory structures that underlie circadian behaviour, mating and target recognition is fundamental to developing a gene drive approach6.
The aim of this project is to characterize the expression of the opsin genes in the mosquitos’ sensory system. To do this, we shall integrate genomics and molecular approaches in two species that represent an extreme health concern for humans: Aedes albopictus, one of the dengue fever carriers and Anopheles gambiae/stephanesi, the main vector of malaria.
To achieve our aim, we have three objectives which will form three chapters in the PhD thesis:
1. To characterize at the molecular level, the sensory neurons in these two species. This will be achieved by sequencing the relevant sensory structure in mosquitos (antenna and head) using RNA-seq methods under different light condition (e.g. dusk and night)
2. These data will be then clarified using single-cell RNA-seq for the whole head.
3. To characterize the spatial expression of the opsin genes using immunohistochemistry and in situ hybridization.
This project is timely because the single-cell RNA-sequencing approach has significantly enhanced the possibility of conducting unbiased classifications of neuronal types and expression patterns8,9. In the short term, we can use the results from this project to clarify which sensory stimuli mosquitos use to perceive their environment and how this differs amongst different species. In the long term, having a list of candidate genes with specific functions will allow us to control mosquito populations by knocking down rhodopsin using Crisper/Cas9 technology and evaluated the effect on target recognition6.
1 WHO Available at: http://www.who.int/vector-control/publications/global-control-response/en/. (Accessed: 13th April 2020)
2 Franklinos, LHV et al. (2019). The Lancet Infectious Diseases 19, e302–e312
3 Medlock, JM & Leach, SA. (2015). The Lancet Infectious Diseases 15, 721–730
4 Simons, RRL et al. (2019). PLOS ONE 14, e0225250
5 Feuda, R et al. (2020). bioRxiv 2020.06.29.177931 doi:10.1101/2020.06.29.177931
6 Zhan, Y et al. (2020). bioRxiv 2020.07.01.182899 doi:10.1101/2020.07.01.182899
7 Montell, C & Zwiebel, LJ. (2016) Chapter Ten - Mosquito Sensory Systems. Academic Press in Advances in Insect Physiology (ed. Raikhel, A. S.) 51, 293–328
8 Davis, FP et al. (2020). eLife 9, e50901
9 Konstantinides, N et al. (2018). Cell 174, 622-635.e13