Four of the six Drosophila rhodopsin‐expressing photoreceptors can mediate circadian entrainment in low light

Abstract

Light is the major stimulus for the synchronization of circadian clocks with day-night cycles. The light-driven entrainment of the clock that controls rest-activity rhythms in Drosophila relies on different photoreceptive molecules. Cryptochrome (CRY) is expressed in most brain clock neurons, whereas six different rhodopsins (RH) are present in the light-sensing organs. The compound eye includes outer photoreceptors that express RH1 and inner photoreceptors that each express one of the four rhodopsins RH3-RH6. RH6 is also expressed in the extraretinal Hofbauer-Buchner eyelet, whereas RH2 is only found in the ocelli. In low light, the synchronization of behavioral rhythms relies on either CRY or the canonical rhodopsin phototransduction pathway, which requires the phospholipase C-β encoded by norpA (no receptor potential A). We used norpA(P24) cry(02) double mutants that are circadianly blind in low light and restored NORPA function in each of the six types of photoreceptors, defined as expressing a particular rhodopsin. We first show that the NORPA pathway is less efficient than CRY for synchronizing rest-activity rhythms with delayed light-dark cycles but is important for proper phasing, whereas the two light-sensing pathways can mediate efficient adjustments to phase advances. Four of the six rhodopsin-expressing photoreceptors can mediate circadian entrainment, and all are more efficient for advancing than for delaying the behavioral clock. In contrast, neither RH5-expressing retinal photoreceptors nor RH2-expressing ocellar photoreceptors are sufficient to mediate synchronization through the NORPA pathway. Our results thus reveal different contributions of rhodopsin-expressing photoreceptors and suggest the existence of several circuits for rhodopsin-dependent circadian entrainment. J. Comp. Neurol. 524:2828-2844, 2016. © 2016 Wiley Periodicals, Inc.

Circuit mechanisms underlying chromatic encoding in Drosophila photoreceptors

“…w+ flies were reared on standard molasses-based medium at 25°C - 28°C. The rhodopsin drivers used for imaging photoreceptors Rh3-Gal4 and Rh6-Gal (Cook et al, 2003) along with Rh4-Gal4 and Rh5-Gal4 (Saint-Charles et al, 2016) were expressed heterozygously along with 20X-UAS-GCamp6f, also expressed heterozygously (Bloomington stock center: 52869). Dm9 cells were targeted for imaging, staining and silencing using both the R21A12-Gal4 or the R32E04-Gal4 drivers (Bloomington stock center: 48925 and 49717).…”

Light input pathways to the circadian clock of insects with an emphasis on the fruit fly Drosophila melanogaster

“…The four HB-eyelet cells express Rh6 and the ocelli express rhodopsin 2 (Rh2), which is present neither in the compound eyes nor in the HB eyelets. Saint-Charles et al (2016) tested the re-entrainment of different rhodopsin mutants to 8 h phase-advances and -delays of low-intensity light-dark cycles and found that four of the six rhodopsins can mediate re-entrainment: Rh1, Rh3, Rh4 and Rh6. No re-entrainment was found when all rhodopsins except Rh2 were eliminated, suggesting that the ocelli alone are not able to entrain the clock, at least not to dim light.…”

miR-210 controls the evening phase of circadian locomotor rhythms through repression of Fasciclin 2

“…First, as far as we know, previous genetic manipulations that cause severe defects on sLNv structural plasticity have no effect on evening phase [50,51]. Second, although overexpression or down regulation of Fas2 in the sLNv abolished the arborization rhythms, it does not affect the evening phase either [15].…”

“…Circadian structural plasticity of sLNv dorsal projections has been recently identified [50,51]. The biological function and molecular mechanisms underlying the structural plasticity however remain elusive.…”