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Role of Rhodopsins as Circadian Photoreceptors in the Drosophila melanogaster

Neurobiology & Genetics, Theodor-Boveri Institute, Biocenter, Julius-Maximilians University Würzburg, Am Hubland, 97074 Würzburg, Germany
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Received: 3 October 2018 / Revised: 14 December 2018 / Accepted: 4 January 2019 / Published: 10 January 2019
(This article belongs to the Special Issue Biological Clocks)
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Abstract

Light profoundly affects the circadian clock and the activity levels of animals. Along with the systematic changes in intensity and spectral composition, over the 24-h day, light shows considerable irregular fluctuations (noise). Using light as the Zeitgeber for the circadian clock is, therefore, a complex task and this might explain why animals utilize multiple photoreceptors to entrain their circadian clock. The fruit fly Drosophila melanogaster possesses light-sensitive Cryptochrome and seven Rhodopsins that all contribute to light detection. We review the role of Rhodopsins in circadian entrainment, and of direct light-effects on the activity, with a special emphasis on the newly discovered Rhodopsin 7 (Rh7). We present evidence that Rhodopsin 6 in receptor cells 8 of the compound eyes, as well as in the extra retinal Hofbauer-Buchner eyelets, plays a major role in entraining the fly’s circadian clock with an appropriate phase-to-light–dark cycles. We discuss recent contradictory findings regarding Rhodopsin 7 and report original data that support its role in the compound eyes and in the brain. While Rhodopsin 7 in the brain appears to have a minor role in entrainment, in the compound eyes it seems crucial for fine-tuning light sensitivity to prevent overshooting responses to bright light. View Full-Text
Keywords: Rhodopsins; electroretinogram; immunocytochemistry; entrainment, Rhodopsin 7; retina Rhodopsins; electroretinogram; immunocytochemistry; entrainment, Rhodopsin 7; retina
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Senthilan, P.R.; Grebler, R.; Reinhard, N.; Rieger, D.; Helfrich-Förster, C. Role of Rhodopsins as Circadian Photoreceptors in the Drosophila melanogaster. Biology 2019, 8, 6.

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