Mechanisms of Sleep Regulation in C. elegans

Project Summary Sleep is a fundamental biological process that is essential for survival in animals. Humans normally spend ~ 30% of our lifetime sleeping, but sleep disorders are prevalent in modern societies. Sleep abnormalities not only affect daily performance but also lead to adverse effects on neuronal function and contribute to neurological and other diseases. Thus, it is imperative to understand how and why we sleep. However, it remains largely unclear how sleep is controlled at the molecular, cellular, and circuit levels, partially due to the complexity of sleep regulation. A fundamental question about sleep is how the brain controls different sleep-associated behavioral changes to induce a robust sleep state. Our long-term goal is to build a comprehensive understanding of basic genetic pathways and neural mechanisms underlying sleep regulation. Sleep is an evolutionarily conserved process, with shared features across different organisms that include behavioral quiescence, increased arousal threshold, and rapid reversibility to wakefulness. In line with this, recent studies in simple model organisms, such as worms, fruit flies, and zebrafish, have yielded valuable insights into sleep regulation. We propose to study a simple and robust stress-induced sleep (SIS) state in C. elegans: cellular stress activates epidermal growth factor (EGF) signaling primarily within a single neuron (ALA) to induce sleep. How does a single neuron control a 302-neuron brain to drive C. elegans into a sleep state? To address this question, we will exploit the advantages of C. elegans, such as powerful genetics, short life cycle, optical transparency, and a compact nervous system. Our central hypothesis is that activation of EGF signaling in the ALA neuron induces sleep through the actions of distinct yet potentially overlapping molecular pathways and neural circuits that coordinate various sleep behavioral phenotypes. To test this hypothesis, we propose two projects: 1) perform a set of genetic screens and mutant analyses to identify new sleep regulatory genes and 2) perform brain-wide functional circuit mapping to identify the neural basis for SIS at single-neuron resolution. We will systematically manipulate and visualize the activity of individual neurons in the entire nervous system of C. elegans through a combination of optogenetics, chemogenetics, in vivo calcium imaging, and a powerful GAL4-based bipartite expression system (cGAL) we developed. The proposed research is significant because it will provide a mechanistic view of how sleep operates at the molecular, cellular, and circuit levels. This study will also potentially transform approaches of functional circuit analyses in C. elegans because the cGAL reagents produced in this study will become a powerful resource for the entire research community and can be readily used to dissect underlying neural circuits for other behaviors.