Transgenic mosquito resistant to multiple serotypes of the dengue virus

Development of the first transgenic Animal in Sri Lanka
Department of Chemistry, Faculty of Science, University of Colombo in collaboration with the Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya

The dengue virus causes epidemics in more than 100 tropical and sub-tropical countries, where over 2.5 billion people (over 40% of the world’s population) are currently at risk of dengue infections. In recent years, dengue has become the number one vector-borne disease in Sri Lanka. The worst ever dengue virus outbreaks experienced in 2009, 2010, and 2013 transformed dengue into a major health issue in Sri Lanka.

Figure 1: Red fluorescence expression in transgenic mosquito eyes

There are no medicines or effective vaccines developed for dengue; therefore, mosquito vector control is the most promising option to control dengue virus transmission. The conventional vector control methods used currently have only limited success. In an attempt to find a solution to this problem, the research team lead by Professor Ranil Dassanayake, Department of Chemistry, University of Colombo in collaboration with Professor Nilmini Gunawardene, Molecular Medicine Unit, Faculty of Medicine, University of Kelaniya undertook to develop a dengue virus resistant transgenic Aedes aegypti mosquito (the primary vector of dengue virus transmission) line using an RNA interference (RNAi) based technology, as a component of the Ph.D. research project of Mr. Kalindu Ramyasoma.

Figure 2: Dengue challenging studies in transgenic mosquitoes

Transgenic animals are those that have a foreign gene deliberately inserted into their genome. The dengue resistant gene (multiple sh-RNA molecule) inserted into the mosquito was designed bioinformatically and was expressed under the control of Ae. aegypti carboxypeptidase – a blood inducible promoter- which is switched on only at the time the dengue virus enters the mosquito body through a blood meal. In the process of development, the dengue resistant gene was coupled with a red fluorescent reporter gene to be expressed in the ommatidium units of the mosquito eyes. This gene was introduced into the Ae. aegypti mosquito eggs using the advanced gene transformation technique, microinjection. Transgenic mosquito lines were selected based on the red fluorescent protein found in their eyes (Figure 1). Thus this research group was able to develop the first transgenic mosquito as the first transgenic animal in Sri Lanka. Later, based on expression analyses and dengue challenging experiments, it was revealed the multiple sh-RNA molecule processed into si-RNA (small molecular scissors to cleave the dengue virus) in transgenic mosquito lines, and is resistant to dengue virus serotypes 2 and 4 (Figure 2) by the action of si-RNA and this is the first ever reported transgenic mosquito resistant to multiple dengue virus sero types developed in the world.

Figure 3: Microinjections of mosquito eggs and laboratory & semi-field studies of transgenic mosquitoes

This transgenic mosquito-based vector control strategy has also been successfully semi-field tested (Figure 3) and will be of immence national importance in its efforts towards the control of dengue virus transmission. This research entails not only the development of products to fight against the dengue virus but also used advanced- cutting edge technologies that can be applied to control both other mosquito-borne diseases and pest insects affecting Sri Lanka. This work has been published in prestigious peer reviewed international research journals, RNA Biology and BioMed Research. The project was funded by the National Research Council of Sri Lanka [grant TO 14-04].