The adipokinetic hormone system in Culicinae (Diptera: Culicidae): Molecular identification and characterization of two adipokinetic hormone (AKH) precursors from Aedes aegypti and Culex pipiens and two putative AKH receptor variants from A. aegypti

Insect neuropeptides of the adipokinetic hormone (AKH) family induce the mobilization of energy stores to fuel flight, but also affect the nutritional balance during diapause and oogenesis. They are therefore important regulators for flight, hibernation, and reproduction in mosquitoes including those that transmit human pathogens. In this study, we identified and analyzed the genes encoding two AKH preprohormones in the Yellow fever mosquito, Aedes aegypti: Aedae-AKH-I encodes the octapeptide pELFTPSWa and Aedae-AKH-II the decapeptide pEVTFSRDWNAa. Identical AKHs were identified in the West Nile virus vector, Culex pipiens, whose genes were characterized in this study as Culpi-AKH-I and Culpi-AKH-II. Using Northern blot, transcript expression was shown in A. aegypti, for Aedae-AKH-I in the head/thorax tissues of pupae and females, as well as in the abdomen of adult males; Aedae-AKH-II was only expressed in adults. In an immunocytological study using an AKH-antibody, the corpus cardiacum (CC), the intrinsic CC-cells (X-cells), the nervi corporis cardiaci, cells in the brain and thoracic ganglia were stained. In addition, two splice variants of the AKH-receptor gene were characterized in A. aegypti, (Aedae-AKHR-I and -II). RT-PCR revealed that both variants of these typical G-protein-coupled receptors were expressed in all life stages. Aedae-AKHR-I expression was also detected in the ovaries, indicating once more the influence of the AKH/AKHR system during the insect's oogenesis. Based on phylogenetic data, we postulate two closely related types of AKH-receptors that could bind selectively the two AKH peptides found in A. aegypti.