A sleep promoting role of phototransduction in Drosophila melanogaster

Daily sleep-wake cycle is a conserved behaviour defined by locomotion quiescence and enhanced responsive threshold to sensory stimuli. Both circadian rhythm and a homeostatic process determine the daily sleep profile, which is also regulated by environmental light, a major sensory input to regulate circadian rhythm and alertness. With decades of investigation in Drosophila , the cellular and circuital mechanism underlying light-mediated circadian synchronization are well-established, yet the direct relationship between light/visual input and sleep remains unclear. To address this knowledge gap, we have started an investigatory survey of sleep behaviour using classic mutant lines to manipulate phototransduction and downstream neural transmission. We observed consistent day sleep fragmentation in flies with mutations in multiple phototransduction components. We also found hyperpolarised Drosophila photoreceptor resulted in shorter day sleep. We found a severe reduction in locomotor speed in several visual mutants during normal waking time preventing assessment of their sleep-linked immobility. In summary, we provide a rigorous quantification of several phototransduction genes and reveal the key role of visual input to promote sleep.