Molecular mechanisms of how increased sleep propensity promotes activation of a sleep-active neuron

• Applicant: Professor Dr. Henrik Bringmann
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 462461613

Sleep is an essential physiological state in animals that have a nervous system. Central to the induction of sleep are sleep-active sleep-promoting neurons that express inhibitory neurotransmitters, GABA and neuropeptides. Sleep-active neurons depolarize specifically at the onset of sleep to inhibit wake-promoting circuits and thus to promote sleep. During normal wakefulness in the absence of sleep drive, neuronal circuits that can promote sleep-active neuron depolarization do not seem to be active, thus permitting wakefulness. During phases of increased sleep propensity, these neuronal circuits promote the depolarization of sleep-active neurons to turn on sleep. However, how sleep circuits are engaged at the molecular level to turn on sleep-active neurons during phases of increased sleep propensity is not understood in any system. We found that sleep in the nematode Caenorhabditis elegans requires crucially the sleep-active RIS neuron. Using optogenetics in C. elegans, we recently solved the presynaptic circuit for depolarization of RIS when the animal is set to sleep. The circuit that we have identified can explain RIS activation at the circuit level during lethargus, a developmental period of increased sleep propensity. We showed that a key activating input for RIS activation is the PVC neuron. PVC activates RIS more strongly and also becomes resistant to inhibition during lethargus. But how this PVC-RIS circuit is engaged at the molecular level is not known. Here, we will use the regulation of the PVC-to-RIS circuit as a model system to study how increased sleep propensity during lethargus turns on a sleep circuit at the molecular level to activate a sleep-active neuron. In this proposal we will understand 1) the molecular mechanism of resistance of PVC to inhibition and 2) the molecular mechanism of increased capacity of PVC to activate RIS during lethargus. To achieve these goals, we will combine optogenetic and imaging assays with genetics. We will identify the key molecular players that determine excitability of PVC and the signaling mechanism from PVC to RIS. This will be achieved by genetically screening through PVC- and RIS-expressed genes in optogenetic and imaging assays that probe the functioning of the sleep circuit. We will then test how the activity of these signaling pathways are changed during lethargus. Thus, we will obtain a molecular-mechanistic understanding for how increased sleep propensity activates a circuit for sleep-active neuron depolarization. The results of this work will provide a roadmap also for understanding sleep in other systems, including mammalian sleep. It will provide testable hypotheses and key molecular pathways that can be followed up by using mouse models and will thus lead to the understanding of sleep evolution and also of human sleep, how it its triggered and what defines increased sleep propensity at the molecular level.

• DFG Programme: Research Grants
• Major Instrumentation: DMD System mit Adapteroptik, LEDs und Software
• Instrumentation Group: 5080 Optisches Mikroskopzubehör