Diabetic larvae and obese flies-emerging studies of metabolism in Drosophila

A glucagon-like endocrine pathway in Drosophila modulates both lipid and carbohydrate homeostasis

The regulation of energy homeostasis is fundamental to all organisms. The Drosophila fat body serves as a repository for both triglycerides and glycogen, combining the energy storage functions of mammalian adipose and hepatic tissues, respectively. Here we show that mutation of the Drosophila adipokinetic hormone receptor (AKHR), a functional analog of the mammalian glucagon receptor, leads to abnormal accumulation of both lipid and carbohydrate. As a consequence of their obese phenotypes, AKHR mutants are markedly starvation resistant. We show that AKHR is expressed in the fat body, and, intriguingly, in a subset of gustatory neurons that mediate sweet taste. Genetic rescue experiments establish that the metabolic phenotypes arise exclusively from the fat body AKHR expression. Behavioral experiments demonstrate that AKHR mutants are neither sedentary nor hyperphagic, suggesting the metabolic abnormalities derive from a genetic propensity to retain energy stores. Taken together, our results indicate that a single endocrine pathway contributes to both lipid and carbohydrate catabolism in the Drosophila fat body.

Drosophila melanogaster as a model system for genetics of postnatal cardiac function

The fruit fly, Drosophila melanogaster, is an excellent model system that has a vast set of molecular tools and mutants to dissect the genetic pathways that are responsible for the normal and abnormal cardiac function. While the majority of studies have focused on heart development in the Drosophila embryo, attention has recently focused on the structure and function of the adult fly heart as a model of human heart failure. Here we review strategies to identify novel genes and pathways that cause or modify dilated cardiomyopathy in adult Drosophila.

A nucleostemin family GTPase, NS3, acts in serotonergic neurons to regulate insulin signaling and control body size

Growth and body size are regulated by the CNS, integrating the genetic developmental program with assessments of an animal's current energy state and environmental conditions. CNS decisions are transmitted to all cells of the animal by insulin/insulin-like signals. The molecular biology of the CNS growth control system has remained, for the most part, elusive. Here we identify NS3, a Drosophila nucleostemin family GTPase, as a powerful regulator of body size. ns3 mutants reach <60% of normal size and have fewer and smaller cells, but exhibit normal body proportions. NS3 does not act cell-autonomously, but instead acts at a distance to control growth. Rescue experiments were performed by expressing wild-type ns3 in many different cells of ns3 mutants. Restoring NS3 to only 106 serotonergic neurons rescued global growth defects. These neurons are closely apposed with those of insulin-producing neurons, suggesting possible communication between the two neuronal systems. In the brains of ns3 mutants, excess serotonin and insulin accumulate, while peripheral insulin pathway activation is low. Peripheral insulin pathway activation rescues the growth defects of ns3 mutants. The findings suggest that NS3 acts in serotonergic neurons to regulate insulin signaling and thus exert global growth control.