Functional analyses of the neuropeptide Adipokinetic hormone (Akh) -encoding gene in Drosophila. G. Lee, J.H. Park. Dept. of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, TN.

   Adipokinetic hormones (AKHs) have been known to be metabolic neuropeptides that involve homeostatic regulation of physiological levels of energy substrates in the blood of many insects. Despite extensive physiological tests for the action of this substance in many invertebrate species, its genetic roles have not been resolved yet. To understand functions of Drosophila Akh (dAkh), first its expression patterns were examined during various developmental stages. Subsequently, physiological and behavioral consequences of the targeted AKH-cell ablation and ectopic dAkh expression were examined. Expression of dAkh was found exclusively in the corpora cardiaca from late embryo to adult stages. Projection patterns emanating from these AKH-neurons indicate that these neurons have several potential target tissues: the prothoracic gland and aorta in larva, the crop and brain in adult. The absence of AKH-neurons caused significant reduction of hemolymph trehalose levels, whereas ectopic expression of dAkh gave the opposite effect. Ectopic dAkh expression also elevated lipolysis in the fat body, demonstrating that AKH is a principal catabolic inducer. AKH-cell deficient flies were strongly resistant to starvation-induced death. Locomotor activity assays revealed that wild-type flies deprived of food sources displayed prolonged hyperactivity prior to death. Such behavioral patterns could be interpreted to reflect food searching activities that appeared to supersede circadian clock-controlled behavior. Moreover, this type of hyperactive locomotion was not observed for AKH-CD flies. From these data we propose that in response to adverse environmental conditions the neuroendocrine system involving dAkh gene product is activated to stimulate fat body metabolism in order to provide energy substrates. At the same time, AKH, either directly or indirectly, causes behavioral modifications to increase likelihood of animals survival.