Transcriptional and nontranscriptional events are involved in photic entrainment of the circadian clock in the cricket Gryllus bimaculatus

Abstract

Most insects show daily activity rhythms that are controlled by endogenous circadian clocks. A basic property of the clock is entrainment to daily environmental cycles to run with an exact 24-h period. The entrainment is achieved mainly through resetting by light. The present study analyses the light resetting mechanism of the clock in first-instar nymphal and adult crickets Gryllus bimaculatus (De Geer). A 3-h light pulse given at early subjective night and late subjective night causes a phase delay and an advance, respectively, of adult locomotor rhythms. The magnitude of the shift caused by the light pulse at circadian time 12 h in constant darkness is significantly smaller than that caused by a 3-h extension of light phase. Measurement of mRNA levels during the light-induced phase shifts yielded basically similar results for nymphs and adults. When a 3-h light pulse is given at early night by light phase extension, an increase of Pdp1 occurs, which is followed by upregulation of the genes Clk and subsequently by per and tim. These changes are eliminated by RNA interference of opsin-long wavelength, which is expressed in the compound eye and encodes a green-sensitive opsin, the major photoreceptor for photic entrainment of the clock. No clear changes in mRNA levels are observed for light pulses given at late subjective night or at early subjective night after 24 h of constant darkness. These results suggest that the photic entrainment mechanism of the clock may be shared by nymphal and adult crickets, including transcriptional and nontranscriptional events.

A novel photic entrainment mechanism for the circadian clock in an insect: involvement of c-fos and cryptochromes

“…Following RNAi of Gb’opLW , light induced phase shifts were significantly reduced in all light treatments (Fig. 3b, c ), being consistent with previous observations [ 21 , 22 ]. We further examined the effects of Gb’c-fos knock-down on Gb’Pdp1 levels in response to light phase extension.…”

“…2c ). The results were similar to those observed in untreated crickets [ 22 ], suggesting that Gb’cry s are not upstream components of the transcription-dependent entrainment pathway.…”

“…We next examined the effects of Gb’cry1 RNAi and Gb’cry2 RNAi treatment on light-induced Gb’Pdp1 upregulation, which is the first responder to light phase extension at early subjective night [ 22 ]. We measured the mRNA levels of Gb’Pdp1 1 h after light phase extension starting at ZT12, or 1 h after light exposure starting at ZT20 .…”

“…The mRNA levels of Gb’cry1 (GenBank/EMBL/DDBJ Accession No. LC202047), Gb’cry2 (LC202053), Gb’c-fosA ( fra-A , LC215243), Gb’c-fosB ( fra-B , LC215244), and Gb’Pdp1 were measured by quantitative real-time polymerase chain reaction (qPCR) [ 22 ]. Total RNA was extracted and purified from six adult male optic lobes with TRIzol Reagent (Invitrogen, Carlsbad, CA, USA), and treated with DNase I to remove contaminating genomic DNA.…”

“…In the present study, we investigated the role of cry1 and cry2 genes in photic entrainment of the circadian clock in the cricket, Gryllus bimaculatus . In this cricket, photic entrainment solely depends on the compound eye [ 19 , 20 ], and the major circadian photoreceptor molecule in the compound eye is opsin-Long Wavelength ( Gb’ OpLW) [ 21 , 22 ]. We have previously shown that resetting of the clock by the extension of the light phase during the early subjective night includes transcriptional regulation of clock genes, with Pdp1 as the first responder to light [ 22 ].…”