Genetic Analysis of Sleep in Drosophila Melanogaster

Sleep is phylogenetically ubiquitous and important for survival. Although the essential role of sleep is well recognised, the molecular mechanisms that control it still remain largely unknown. In the last decade, Drosophila has emerged as a valid and a powerful model for sleep research, and has been extensively used to explore the underlying molecular mechanisms. The major aim of the current work was to explore natural variation in sleep and identify genetic variations that contribute to phenotypic variation and consequently important for evolution of this trait. A biometric analysis of 16 reciprocal crosses using two inbred strains revealed an extensive phenotypic variation and substantial heritability. Interestingly, these experiments showed the significant contribution of maternal factors to variation in sleep. Subsequently, QTL mapping was carried using a set of 187 recombinant inbred lines, derived from a North-American population. Five QTL associated with different sleep parameters have been identified. Complementation tests using deficiency strains spanning the QTL intervals, and P-element insertion in candidate genes, allowed refining of the QTL interval and identifying few candidate genes, including CG9328 and Rab9, which are likely to underlie these QTL. In addition, the role of dopamine-acetyltransferase (Dat) in sleep was investigated, by generating a dat-GAL4 construct that allowed identifying Dat neurons in the brain. Genetic ablation of Dat neurons caused sleep fragmentation, with flies exhibiting shorter bouts of sleep. The GAL4/UAS system has also been used to explore the brain regions underlying sleep sexual dimorphism. Miss-expressing the female-specific form of transformer allowed feminising or masculinisation of specific regions in the brain and indicated a role of the mushroom bodies. The role of DNA methylation in sleep regulation was also investigated. Miss-expressing Dnmt2 (DNA methyl-transferase) demonstrated that homeostasis of methylation is important for normal levels of sleep, and may explain the link between sleep and life-span.