Mosquito vision: Molecular evolution and functional characterization of the opsins in Anopheles gambiae and Aedes aegypti

New control strategies against the malaria mosquito Anopheles gambiae and the yellow fever mosquito Aedes aegypti target behaviors influenced by vision.  Disruption of mating, host location or oviposition by manipulating mosquito vision could reduce survival and vector capacity.  An understanding of mosquito vision at the molecular level is fundamental toward accomplishing these objectives.  Opsins are G-protein coupled receptors that interact with photons and then initiate a phototransduction signaling cascade resulting in a visual response. Typically, insects possess opsin genes in three classes (UV, short-, and long-wavelength) that are expressed in the eye, and usually a related brain protein, pteropsin, which is speculated to regulate circadian rhythm.  We previously identified 11 and 10 opsins (GPRop) in An. gambiae and Ae. aegypti, respectively. Here we report an updated manual annotation of these opsins based on EST- and homology-based evidence. The PhyML and PAML4 programs (maximum likelihood) were used to analyze the molecular evolution of mosquito opsins and to predict opsin function.  Anopheles and Aedes have orthologs of UV, short-, and long-wavelength opsins and pteropsins identified in other insects. Both mosquitoes have an expansion in the number of putative long-wavelength opsins compared to other insects. These opsins may facilitate vision during periods of low light intensity, such as dusk/dawn, when these mosquitoes are active. Using real-time RT-PCR, expression was confirmed for all opsins, except GPRop7 and GPRop11, in males and females of An. gambiae. RT-PCR and in situ hybridization were used to study Ae. aegypti opsin expression in tissues and developmental stages. Future work will involve opsin spectral sensitivity studies in Ae. aegypti.