Unravelling the role of the male accessory glands in the fertility of the malaria mosquito Anopheles gambiae

Mosquitoes represent a major threat for human health, as they transmit a variety of infectious diseases that cause the death and suffering of millions of people each year. Among the most prominent infectious diseases is malaria, which is transmitted exclusively by mosquitoes of the Anopheles genus. Current strategies aimed at tackling this disease rely extensively on the control of vector populations in the field, mainly through the use of insecticide indoor residual sprays and insecticide-impregnated bednets. However, insurgence of resistance in mosquitoes and the lack of novel insecticidal compounds are major hurdles in the fight against malaria, and novel ideas and tools are urgently needed. This proposal focuses on the reproductive biology of the species of mosquito primarily responsible for the transmission of malaria in Africa, known as Anopheles gambiae. An. gambiae mosquitoes mate only once in their lifetime, which means that disrupting the reproductive process offers a good way of dramatically reducing natural populations in Africa. When they mate, the male mosquito transfers sperm to the female and then afterwards transfers a coagulated mass of proteins and seminal fluids known as a mating plug, which is formed in the male accessory glands (MAGs), the mosquito equivalent of the human prostate. The MAGs have been shown by a number of studies to play a very important role in An. gambiae fertility. Transfer of MAG secretions (mainly proteins and lipids) to female mosquitoes has been shown to reduce the female willingness to mate again. Furthermore, our previous studies have shown that transfer of the mating plug is essential for the correct storage of sperm in the female, and hence for female fertility. A deeper knowledge of factors and mechanisms shaping the function of the MAGs would undoubtedly provide novel tools and ideas for the control of mosquito populations in the field through the manipulation of their fertility. As an example, if molecular mechanisms ensuring male fertility were identified, then we could design chemicals to inhibit such mechanisms that could be delivered to field mosquitoes in order to limit their reproductive output. In this project we will perform a detailed analysis of the MAGs, unravelling their functions in regulating mosquito reproductive success. In particular, we will assess whether the MAGs are regulating male behaviour, and we will analyse the roles in fertility of small peptide hormones produced in these reproductive organs. The results obtained here will remarkably improve our knowledge of the reproductive processes occurring in Anopheles mosquitoes, and will provide us with tremendous opportunities to translate this knowledge into practical tools for vector control. To achieve our goals, we will validate the results obtained in the laboratory in field mosquitoes, in collaboration with Professor Dan Masiga, from the International Centre of Insect Physiology and Ecology (ICIPE), Kenya. Strong collaborative links are already established between our groups within the framework of EU projects and in the form of a joint PhD studentship. Our study will focus on An. gambiae mosquitoes, however it could subsequently be extended to other insect pests of medical and agricultural importance. We anticipate that this project will have a profound impact on malaria research, and will contribute to the training and scientific excellence of the next generation of scientists.

Anopheles gambiae mosquitoes are the major vectors of malaria, a disease with devastating consequences for human health. Given the evolution of insecticide resistance in mosquitoes and the lack of new insecticidal compounds, novel methods for controlling the natural vector populations are urgently needed. A deeper understanding of the processes shaping the biology of these mosquitoes would undoubtedly help to develop tools aimed at limiting the spread of malaria. In this proposal, we will target mosquito reproduction, a major determinant of the An. gambiae capacity to transmit disease. We will focus our analyses on the male accessory gland (MAGs), a major player of mosquito reproduction, in both laboratory and field settings. We will then set the scene for translating this information into the identification of tools for the manipulation of fertility of field populations. The experimental activities will be divided in three objectives. In Objective 1, we will unravel the role of the MAGs in shaping mosquito fertility and behaviour, by performing a combination of transcriptional and functional studies that will reveal the multifaceted activities of these tissues. In Objective 2 we will instead focus on the assessment of the role of peptide hormones produced in the MAGs on the fertility and reproductive behaviour of mosquitoes. Results obtained in both objectives will then be validated in field mosquitoes in Objective 3. This study will reveal as yet unknown molecular mechanisms underlying reproductive success in mosquitoes, considerably increasing our knowledge beyond the state-of-the-art and critically contributing with innovative tools and ideas to the fight against malaria. Our results will also be instrumental for the study of reproduction in other insect pests of medical and agricultural importance.

Expanding our knowledge beyond the state-of-the-art. This project will considerably expand our knowledge of the reproductive biology of Anopheles mosquitoes, major vectors of human malaria. Importantly, it is very likely that the extensive knowledge gained here will be directly applicable to many other insects, providing the means for applying our findings to other systems for the reduction of field populations, for instance through the generation of sterile males in Sterile Insect Technique programmes. As such this can be considered as a founding study. By expanding our general knowledge of reproductive processes crucial to the high reproductive rate of these mosquitoes, we will contribute towards the development of innovative ideas and novel tools for the reduction or eradication of natural mosquito populations. Training of staff and students This project will crucially contribute to the training of next generation of scientists, in the UK and in the collaborating disease endemic country (Kenya). The interdisciplinary approach utilized here will greatly enhance the scientific skills and knowledge of the postdoctoral fellow that will be hired on the project, providing them with an excellent opportunity to learn state-of-the-art techniques, to collaborate with international groups of the highest scientific caliber, to participate to international conferences and to perform field studies. Such trained postdocs are likely to benefit biotechnology and pharmaceutical industries, as well as academic Institutions based in the UK and abroad. Furthermore, our collaboration with ICIPE, Kenya, will provide young African scientists with an invaluable opportunity for training in their everyday scientific work, also through their participation at project meetings and international conferences. Dissemination of results The results of this project will be mainly disseminated by: 1) publication as research articles in a variety of specialised and high-impact journals; 2) scientific lectures/talks at international conferences; 3) review articles and book chapters; 4) websites, bloggers, podcasts interviews. Our group is actively disseminating results to scientific audiences and to the general public, as our results have been made available. We will also give talks to schools and societies. Social and economic impact Malaria constitutes a terrible burden for health services and economies in disease endemic countries, and it also represents an increasing health and economic problem for European countries. By elucidating the molecular mechanisms of vector reproduction that are so crucial to the mosquito capacity to transmit malaria, this project will impact global health issues. Moreover, it will provide a strong contribution to UK scientific competitiveness. This will be achieved through the development of highly innovative ideas and findings that in future studies will be translated into powerful and novel tools for insect control. As an example of possible applications, once identified in Objective 2, peptide hormones affecting mosquito fertility could be modified to block the events leading to successful fertilization. These would therefore act as a novel generation of insecticide-like compounds to reduce the size of field populations, with the possible advantage of a species-specific mode of action to target only transmission-competent species. Alternatively, genetic traits conferring a male sterility phenotype could be introduced into field populations by transgenic means, thereby preventing insemination. It is anticipate that the involvement of industrial partners will be sought at some stage for the development of these tools.