A multi-component screen for feeding behaviour and nutritional status in Drosophila to interrogate mammalian appetite-related genes

Abstract

More than 300 genetic variants have been robustly associated with measures of human adiposity. Highly penetrant mutations causing human obesity do so largely by disrupting satiety pathways in the brain and increasing food intake. Most of the common obesity-predisposing variants are in, or near, genes that are expressed highly in the brain, but little is known about their function. Exploring the biology of these genes at scale in mammalian systems is challenging. We therefore sought to establish and validate the use of a multicomponent screen for feeding behaviour and nutrient status taking advantage of the tractable model organism Drosophila melanogaster. We validated our screen by demonstrating its ability to distinguish the effect of disrupting neuronal expression of four genes known to influence energy balance in flies from ten control genes. We then used our screen to interrogate two genetic data sets. Firstly, we investigated 53 genes that have been implicated in energy homeostasis by human genome wide association studies (GWASs): of the 53 Drosophila orthologues studied, we found that 16 significantly influenced feeding behaviour or nutrient status. Secondly, we looked at genes which are expressed and nutritionally responsive in specific populations of hypothalamic neurons involved in feeding/fasting (POMC and AgRP neurons): 50 Drosophila orthologues of 47 murine genes were studied, and 10 found by our screen to influence feeding behaviour or nutrient status in flies. In conclusion, Drosophila provide a valuable model system for high throughput interrogation of genes implicated in feeding behaviour and obesity in mammals. Author SummaryNew high-throughput technologies have resulted in large numbers of candidate genes that are potentially involved in the control of food intake and body-weight, many of which are highly expressed in the brain. How, though, are we to find the functionally most relevant genes from these increasingly long lists? Appetite needs to be explored in context of a whole animal, but studies in humans and mice take a long time and are expensive. The fruit fly, while clearly evolutionarily distant, shares a surprising amount of biology with mammals, with 75% of genes involved in inherited human diseases having an equivalent in flies. In particular, the fruit fly has surprisingly conserved neuronal circuitry when it comes to food intake. Here we have developed a suite of four different functional assays for studying the feeding behaviour and energy balance in flies. We then used these assays to explore the effects of disrupting the expression of genes in the neurons of flies, that either are implicated in body weight through human genetic studies or are expressed and nutritionally responsive in specific populations of neurons involved in feeding. We show that the use of fruit flies are time and cost efficient, and are a valuable model system for studying genes implicated in feeding behaviour and obesity in mammals.