Title: Investigating the molecular basis of sleep homeostasis in Drosophila

Sleep is a near-universal yet mysterious behaviour. Whilst the circadian processes that time sleep are well-defined, the homeostatic mechanism which drives the need to sleep remains relatively obscure. Sleep loss increases the likeliness of road traffic collisions as well as being implicated in the pathogenesis of a wide range of diseases from psychiatric to metabolic.

Despite the high prevalence of sleep disorders, current pharmacological interventions are limited; available drugs have limited efficacy and significant side-effects. Dissecting the neural and biochemical basis of sleep homeostasis will provide an understanding of the purpose of sleep and may identify novel therapeutic targets.

My project will follow on from previous work in the lab which has used the fruit fly Drosophila melanogaster as a model. Optogenetic activation of a cluster of neurons in the Drosophila dorsal fan-shaped body (dFB) induces sleep. These neurons fire during sleep but are silent during wake.

The voltage-gated potassium channel Shaker and its beta subunit Hyperkinetic are essential for neuronal activity during sleep; their loss renders flies insomniac. Conversely, the two-pore domain channel Sandman provides the hyperpolarising clamp on neuronal activity during waking hours. Therefore, Drosophila sleep homeostasis represents the balance of the potassium currents carried by Shaker and Sandman.

Reactive oxygen species (ROS) accumulate during wake and activate Shaker, increasing the chance of dFB neurons spiking. However, the neurons will not fire, and therefore sleep will not be induced, until Sandman's hyperpolarising clamp is released. This digitises the gradual accumulation of sleep pressure into a sharp sleep-wake switch.

The project will initially focus on how the voltage-gated potassium channel Shaker senses sleep pressure and tracks its accumulation over time as a molecular memory. Experimental approaches will be varied including enzyme biochemistry, single channel recordings, Drosophila genetics, and whole-organismal sleep measurement. As this project lies in the intersection of cellular neuroscience, ion channel biophysics and enzyme kinetics, it will facilitate the development of interdisciplinary skills. Quantitative skills will be developed during statistical analysis and modelling.