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Prof Hilary HurdResearch group
Current research projectsAnti-malaria effector molecules that block the transmission of Plasmodium falciparum ((Hilary Hurd, Vicky Carter and Ann Underhill, in collaboration with Paul Eggleston and Frederic Tripet (Keele), Sekou Traore, Marmadou Coulibaly, and Barber Ibrahima and Mahamoudou Toure (University of Bamako, Mali), Ingrid Faye and Ulo Langel (University of Stockholm, Sweden) and Laszol Otvos (Temple University, Philadelphia) and John Wade (Howard Florey Institute of Experimental Physiology and Medicine, Australia) This project is one of three work programmes in the project "Genetic engineering of refractory mosquito vectors for the control of malaria transmission" which is a collaborative project supported by The Wellcome Trust. The aim is to insert genes that code for effective anti-parasite molecules into the genome of Anopheles gambiae from a colony of mosquitoes frequently refreshed from our field site in Mali and to evaluate the effectiveness of these transgenic mosquitoes in transmitting human malaria. We are evaluating a number of small peptides with antimicrobial activity to determine their toxicity to mosquito cell lines and their effect on mosquito longevity and reproductive success. Those with no or very low toxicity are being screened for their effect against mosquito stages of a rodent malaria and the human malaria Plasmodium falciparum. Genes that code for peptides with optimal activity will be inserted into the mosquito genome to be expressed in a tissue and time specific manner. Ultimately we will assess the fitness and vectorial competence of these genetically transformed mosquitoes. A large element of the work is associated with capacity building and training in Mali, where much of the work will be done. Mechanisms underlying fecundity reduction in malaria infected and immune stimulated mosquitoes (Hilary Hurd and Ann Underhill) Infected Anopheles gambiae have reduced reproductive fitness compared with uninfected mosquitoes. We have shown that several aspects of the process of yolk synthesis and uptake are affected by infection. The abundance of vitellogenin gene mRNA is significantly reduced when oocysts are developing and the accumulation of vitellin in ovaries is reduced both when ookinetes are penetrating the midgut and when early oocysts are present. Many follicles begin to develop then are resorbed by a process which initially involves the programmed cell death of patches of follicular epithelial cells. We have been investigating the molecular mechanisms underlying apoptosis and the signals that induce it in the infected-mosquito ovary (Hurd, 2003, Annual Review of Entomology 48: 141-161; Hurd & Carter, 2004, International Journal for Parasitology, 34: 1459-1472; Hurd, H. 2009, Advances in Parasitology 68, 85-110. We have also demonstrated that mosquitoes suffer fitness costs when their defence systems are stimulated by injection of the artificial elicitors, lipopolysaccharide or glass beads. Fewer eggs are produced and ovarian follicles are resorbed during the development of a batch of eggs. As with malaria infection, resorption occurs because follicular epithelial cells are dying by apoptosis (Ahmed and Hurd, 2006). Fitness costs of refractoriness to malaria (Hilary Hurd, Maarten Voordouw (now at University of Pennsylvania, Philadelphia) and Jacob Koella (Imperial College)) We now have selected several lines of Anopheles gambiae that are refractory or highly susceptible to infection, all were selected from our outbred Keele strain. Parasites are melanized as they cross the midgut epithelium or lysed before transforming into oocysts. Mosquitoes that have been selected to be highly susceptible or refractory/resistant to malaria infection show no difference in survivorship compared with the unselected lines. In addition, we have found that founder effects have created some difference between lines in the utilization of the blood meal for egg production, egg hatching rate and the production of larvae, but refractory and resistant mosquitoes did not gain a fitness advantage by eliminating the parasite. We have concluded that it is as costly to resist the parasite as it is to be infected. Refractoriness may thus not have a large selective advantage and this may explain why totally refractory mosquitoes may not be found in the wild. We also investigated the effect of selection for refractoriness on male mosquito fitness. Although males from isofemale lines refractory to malaria infection had no detectable fitness disadvantage we were able to show a correlation between sperm mobility and the oviposition success of inseminated females (Voordouw, M.J., Koella, J.C. and Hurd, H. 2008. Malaria Journal, 7:103; Voordouw, M.J., Koella, J.C. and Hurd, H. 2008. Malaria Journal 7:214. Apoptosis and the malaria parasite (Hilary Hurd, Shashini Arambage and Medhat Ali in collaboration with Gwyn Williams and Anne Loweth (Keele University), Karen Grant (University of Lancaster) and Sarah Reece (University of Edinburgh)). We have previously demonstrated that many zygotes and ookinetes of the rodent malaria parasite, Plasmodium berghei, undergo apoptosis-like death whilst in the midgut lumen of the mosquito. They also die in this manner in vitro. The proportion of ookinetes displaying various apoptosis markers have been mapped over time in culture. Many of the markers of eukaryote apoptosis are exhibited and they react with caspase detectors although no homologues of caspase appear to be present in the genome. We are using a proteomics approach to identify the caspase-like molecule(s) that are activated in ookinetes. We are also investigating the effect of nitric oxide and other potential signalling molecules on the induction of apoptosis-like death in vivo and in vitro. In collaboration with Sarah Reece (Edinburgh University) we are also investigating hypotheses concerning the evolution of programmed cell death in malaria parasites.
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