Abstract
Two different cDNAs similar to Bombyx mori aquaporins (Bommo AQPs) were identified and characterized from the larval alimentary canal of the oriental fruit moth, Grapholita molesta. The first cDNA (AQP-Gra1) encodes a 28 380 Da protein similar to the water-specific AQPs isolated from several liquid-feeding insects such as Haematobia irritans exigua, Aedes aegypti and Cicadella viridis, and from Drosophila melanogaster (DRIP) as well as one of Bommo AQPs (AQP-Bom1). The second cDNA (AQP-Gra2) encodes a 27 929Da protein similar to the other Bommo AQP (AQP-Bom2) and other putative AQPs from D. melanogaster (Aqp17662 and Aqp17664). Functional analysis in Xenopus oocytes microinjected with the capped RNA of G. molesta AQPs revealed that both stimulated osmotic water permeability in a mercury-sensitive manner. The water-specific AQP property in AQP-Gra1 and its higher identity of the deduced amino acid sequence (>70%) with AQP-Bom1 suggests that it is a hindgut-type AQP, likely involved in water-recycling functioning of G. molesta larvae. The AQP-Gra2, most similar (~40% identity) to AQP-Bom2, is considered as a midgut-type and it also increased glycerol and urea permeability. This is the second to demonstrate a member of the aquaglyceroporin family in insects after the first identification of insect aquaglyceroporin from B. mori by our group. The occurrence of two types of AQP, namely aquaporin (water channel) and aquaglyceroporin, appears to be characteristic of fluid-transpoting epithelia in lepidopteran larvae.
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