Presynaptic Active Zone Plasticity Encodes Sleep Need in Drosophila

Abstract

Sleep is universal across species and essential for quality of life and health, as evidenced by the consequences of sleep loss. Sleep might homeostatically normalize synaptic gains made over wake states in order to reset information processing and storage and support learning, and sleep-associated synaptic (ultra)structural changes have been demonstrated recently. However, causal relationships between the molecular and (ultra)structural status of synapses, sleep homeostatic regulation, and learning processes have yet to be established. We show here that the status of the presynaptic active zone can directly control sleep in Drosophila. Short sleep mutants showed a brain-wide upregulation of core presynaptic scaffold proteins and release factors. Increasing the gene copy number of ELKS-family scaffold master organizer Bruchpilot (BRP) not only mimicked changes in the active zone scaffold and release proteins but importantly provoked sleep in a dosage-dependent manner, qualitatively and quantitatively reminiscent of sleep deprivation effects. Conversely, reducing the brp copy number decreased sleep in short sleep mutant backgrounds, suggesting a specific role of the active zone plasticity in homeostatic sleep regulation. Finally, elimination of BRP specifically in the sleep-promoting R2 neurons of 4xBRP animals partially restored sleep patterns and rescued learning deficits. Our results suggest that the presynaptic active zone plasticity driven by BRP operates as a sleep homeostatic actuator that also restricts periods of effective learning.

Keywords: active zone; learning and memory; sleep; sleep homeostasis; sleep need; synapse; synaptic plasticity.