Joshua Ibukun Raji
Highly motivated to understand the molecular mechanism underlying mosquito host-seeking behavior, I traveled six thousand miles to the United States to study the world’s deadliest animal. My previous research experience involves screening botanicals that can ward off mosquitoes from humans and testing the genotoxicity of antimalarial drugs. I received my M.Sc. with a distinction in Cell Biology and Genetics from the University of Lagos in Nigeria. Prior to that, my undergraduate training was at the Federal University of Technology, Akure for which I received a B. Tech. in Biology. I am currently pursuing a Ph.D. at FIU in the DeGennaro Lab.
Detection of volatile chemicals is essential for mosquitoes to find their human hosts and spread diseases. Human odor, a blend of volatile chemicals derived from the metabolism of sweat by skin microbiota and exhaled carbon dioxide (CO2) strongly attract mosquitoes. The molecular mechanism by which mosquitoes translate host odor information into host-seeking behavior has until recently only begun to be understood. Insects use three families of chemoreceptors to sense odors. The ionotropic receptors (IRs) and the odorant receptors (ORs) are expressed in the antenna and maxillary palp and detect a near complete repertoire of volatile chemicals that an insect would encounter. CO2 is detected by three gustatory receptors (GRs) that are co-expressed in capitate peg sensilla on the mosquito maxillary palp. Connecting the chemical cues that attract and repel mosquitoes with their cognate genes and neural circuits will inform new strategies to control mosquito behavior. A necessary step to achieving this goal is to identify the receptors that detect attractive volatile chemicals.
We have identified and dissected in detail the role of IR8a in human host-seeking by female Aedes aegypti mosquitoes and showed how it interacts with other olfactory receptor families, the Odorant Receptors and carbon dioxide-sensitive gustatory receptors. Unlike previous work that showed how CO2 can rescue host-seeking defect in orco mutants, the loss of the Ir8a gene cannot be rescued by the addition of carbon dioxide to our assays. This suggests that IR8a olfactory receptor pathway activation by acidic volatiles that are a component of human skin odor and sweat cannot be rescued by other olfactory receptors pathways. Our behavior assays and electrophysiology experiment showed that Ir8a is required for sensing lactic acid, a human sweat component. This makes the IR8a pathway an important molecular target for novel behavioral vector control strategies.