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Abstract
The increasing prevalence of obesity as well as its association with many chronic diseases has turned obesity into a major health concern worldwide. Obesity has many underlying environmental and genetic factors that disturb the balance between energy intake and energy expenditure, which is controlled by the central nervous system. The goal of my project is to help further our understanding of these CNS mechanisms by using the powerful tools available in Drosophila melanogaster to identify neuronal genes involved in energy homeostasis. Using the neuronal fru-Gal4 driver we performed an RNAi screen with 1748 genes and assayed for obese or lean phenotypes defined as increases or decreases in triacylglycerol (TAG) levels. After 3 rounds of screening I identified 25 hits that were reproducible and confirmed these phenotypes with independent RNAi lines. One of these hits was Diacylglycerol kinase (Dgk) whose mammalian homologues have been implicated in genome-wide association studies for metabolic defects. Manipulation of neuronal Dgk levels affects TAG and carbohydrate levels but these effects don’t seem to be mediated through Dgk’s regulation of DAG, PA levels or PKC activity. I hypothesized that Dgk acts in the insulin-producing cells (IPCs), a set of neurosecretory neurons that secrete Drosophila insulin-like peptides (dILPs) and are involved in the regulation of dILP secretion. Knockdown or overexpression of Dgk within the IPCs reproduces the same TAG, glucose and glycogen phenotypes seen with fru-Gal4. Moreover, overexpression of kinase-dead Dgk, but not wild-type, decreased circulating dILP2 and dILP5 levels resulting in lower insulin signalling activity. Conversely, despite having higher circulating dILP levels, Dgk RNAi flies have decreased pathway activity suggesting that they are insulin-resistant. Thus, after screening over 1700 genes in vivo I identified 25 genes as potential neuronal mediators of energy homeostasis. My results have also shown that one of these genes, Dgk, acts within the insulin-producing cells to regulate the secretion of dILPs and energy homeostasis in Drosophila.
