Drosophila model to investigate the tripartite relationship between symbiont, trypanosomes and tsetse flies

Tsetse flies (genus Glossina) are the sole vectors of the zoonotic disease African Trypanosomiasis, which causes sleeping sickness in humans and nagana in animals. The World Health Organisation (WHO) has estimated that there are currently 300,000 - 500,000 cases of trypanosomiasis with 60 million people at risk of contracting the disease in 37 African countries (WHO Committee, 2001). In addition to the human cost, trypanosomiasis has severely restricted cattle and dairy production in Africa, resulting in substantial economic losses. To increase agricultural production in Africa it is very important that cattle can be used for traction for ploughing.
In this proposal we will investigate the tripartite interactions of the fly, trypanosome and a symbiotic bacterium called Sodalis glossinidius. The presence of Sodalis in tsetse has been linked to the fly being more capable of transmitting the trypanosome parasite. We will identify the mechanisms through which Sodalis makes the fly a better vector by analysing how Sodalis interacts with cells and guts of insects. We expect that Sodalis can change the way an insect's immune system responds to Sodalis and this creates a "blind spot" in the insect's defenses that allow the parasite to survive and divide in tsetse. This will be investigated by looking at how insect gene expression changes as a result of exposure to Sodalis and trypanosomes. The work will provide fundamental understanding of the biology of tsetse as a disease vector by identifying the key genes underpinning symbiotic and parasitic interactions.
A greater understanding of how insect guts respond to challenge by microbes will lead to new targets for disease control strategies. The knowledge gained will be of direct relevance to the control of other medical, veterinary and agriculturally important diseases vectored by arthropods. For example zoonosis such as Leishmania, animal diseases like Bluetongue and plant diseases vectored by aphids such as Potato leaf roll virus.

The presence of Sodalis glossinidius in the midgut of tsetse has been linked to increased establishment of trypanosomes in the insect's midgut. This suggests that Sodalis is changing the status of the tsetse gut allowing trypanosomes to establish. The central hypothesis of this study is that the symbiotic interaction of Sodalis with the tsetse host results in the fly being more susceptible to trypanosome infection. The most likely explanation for this is that tsetse immunity is compromised by the Sodalis symbiosis.
Tsetse are very difficult and expensive insects to work with due to their slow reproductive rate and complex symbiont biology. We take the novel approach of using Drosophila as a model system for tsetse biology. This overcomes a number of tsetse research problems and opens up the opportunity to use the vast molecular genetic toolbox provided by Drosophila research. Unusually for insect symbionts Sodalis is amenable to culture and genetic manipulation. Therefore we will use a unique Sodalis/Drosophila experimental symbiosis to investigate 1) how Sodalis establishes a symbiotic relationship with Drosophila and 2) how the symbiotic interaction of Sodalis with tsetse results in the fly becoming more susceptible to trypanosome infection. This project will use transcriptomic (RNAseq- Sodalis and microarray - Drosophila), proteomics and genomics information to identify bacterial and insect genes involved in the establishment and persistence of symbiosis using parallel analysis of symbiont and host gene expression in cells. Candidate genes which may make the tsetse fly immune-incompetent to trypanosomes will be validated in the Drosophila model and tsetse gut using functional genetics.
The work will provide fundamental understanding of the tsetse biology as a disease vector but will also provide insight into novel ways to target important vector of animal, plant and human disease.

The knowledge collected by this project has the potential to directly benefit the control of trypanosomiasis in Africa. Therefore, this project will potentially bring benefits to some of the poorest communities in developing countries by providing novel strategies for disease control promoting stable agriculture and food security.
While this will not directly benefit the UK in terms of economic growth it is now widely accepted that food security is a global issue and helping farming and economic development in Africa will undoubtedly have wide ranging benefits to society in the UK.

To help ensure that the data from this project are utilised in endemic countries we will be running a workshop in Africa as part of the proposed impact activities.

The outcomes of this project have a direct overlap with the interests of a commercial partner Oxitec and we will ensure that any gene targets identified are communicated to Oxitec who are world leaders in genetic insect control.

In addition this project addresses a universal feature of vector-borne diseases as they all interact with the alimentary canal of the vector. A greater understanding of how vector guts respond to challenge by microbes will lead to new targets for disease control strategies. The knowledge gained will be of direct relevance to the control of medical, veterinary and agriculturally important diseases vectored by arthropods. For example animal diseases like Bluetongue and plant diseases vectored by aphids such as Potato leaf roll virus which potential could have a direct impact on the UK economy.