Reciprocal Coupling of Circadian Clocks in the Compound Eye and Optic Lobe in the Cricket .

The circadian system comprises multiple clocks, including central and peripheral clocks. The central clock generally governs peripheral clocks to synchronize circadian rhythms throughout the animal body. However, whether the peripheral clock influences the central clock is unclear.

OpsinLW2 serves as a circadian photoreceptor in the entrainment of circadian locomotor rhythm of a firebrat.

Photic entrainment is an essential function of the circadian clock, which enables organisms to set the appropriate timing of daily behavioral and physiological events. Recent studies have shown that the mechanisms of the circadian clock and photic entrainment vary among insect species. This study aimed to elucidate the circadian photoreceptors necessary for photic entrainment in firebrats Thermobia domestica, one of the most primitive apterygote insects.

The Compound Eye Regulates Free-Running Period and Stability of the Circadian Locomotor Rhythm in the Cricket .

The circadian system of many multicellular organisms consists of a hierarchical structure of multiple clocks, including central and peripheral clocks. The temporal structure has been analyzed in terms of central-to-peripheral regulation but rarely from the opposite perspective. In this study, the potential control of the central clock in the optic lobe by the peripheral clock in the compound eye was investigated in the cricket .

Regulates the Photic Entrainment of Circadian Locomotor Rhythms in the Cricket .

Photic entrainment is an essential property of the circadian clock that sets the appropriate timing of daily behavioral and physiological events. However, the molecular mechanisms underlying the entrainment remain largely unknown. In the cricket the immediate early gene plays an important role in photic entrainment, followed by a mechanism involving s (s).

Constant Light, , and Exert Influence on Free-Running Period of Locomotor Rhythms in the Cricket .

Most insects show circadian rhythms of which the free-running period changes in a light-dependent manner and is generally longer under constant light (LL) than under constant dark conditions in nocturnal animals. However, the mechanism underlying this LL-dependent period change remains unclear. Here, using the cricket , we examined the effects of long-term LL exposure on the free-running period of locomotor rhythms.

Plays an Important Role in Compound Eye-Dependent Photic Entrainment of the Circadian Rhythm in the Cricket .

The light cycle is the most powerful Zeitgeber entraining the circadian clock in most organisms. Insects use CRYPTOCHROMEs (CRYs) and/or the compound eye for the light perception necessary for photic entrainment. The molecular mechanism underlying CRY-dependent entrainment is well understood, while that of the compound eye-dependent entrainment remains to be elucidated.

The Compound Eye Possesses a Self-Sustaining Circadian Oscillator in the Cricket .

Many insects show daily and circadian changes in morphology and physiology in their compound eye. In this study, we investigated whether the compound eye had an intrinsic circadian rhythm in the cricket . We found that clock genes (), (), (), and () were rhythmically expressed in the compound eye under 12-h light/12-h dark cycles (LD 12:12) and constant darkness (DD) at a constant temperature.

The role of clockwork orange in the circadian clock of the cricket Gryllus bimaculatus.

The circadian clock generates rhythms of approximately 24 h through periodic expression of the clock genes. In insects, the major clock genes period (per) and timeless (tim) are rhythmically expressed upon their transactivation by CLOCK/CYCLE, with peak levels in the early night. In Drosophila, clockwork orange (cwo) is known to inhibit the transcription of per and tim during the daytime to enhance the amplitude of the rhythm, but its function in other insects is largely unknown.

Functional analysis of Pdp1 and vrille in the circadian system of a cricket.

Circadian rhythms are generated by a circadian clock for which oscillations are based on the rhythmic expression of the so-called clock genes. The present study investigated the role of Gryllus bimaculatus vrille (Gb'vri) and Par domain protein 1 (Gb'Pdp1) in the circadian clock of the cricket Gryllus bimaculatus. Structural analysis of Gb'vri and Gb'Pdp1 cDNAs revealed that they are a member of the bZIP transcription factors.

Photoperiod and temperature separately regulate nymphal development through JH and insulin/TOR signaling pathways in an insect.

Insects living in the temperate zone enter a physiological state of arrested or slowed development to overcome an adverse season, such as winter. Developmental arrest, called diapause, occurs at a species-specific developmental stage, and embryonic and pupal diapauses have been extensively studied in mostly holometabolous insects. Some other insects overwinter in the nymphal stage with slow growth for which the mechanism is poorly understood.

Temperature Entrainment of Circadian Locomotor and Transcriptional Rhythms in the Cricket, .

Most animals exhibit circadian rhythms in various physiological and behavioral functions regulated by circadian clock that resides in brain and in many peripheral tissues. Temperature cycle is an important time cue for entrainment, even in mammals, since the daily change in body temperature is thought to be used for phase regulation of clocks in peripheral tissues. However, little is known about the mechanisms by which temperature resets the clock.

A novel photic entrainment mechanism for the circadian clock in an insect: involvement of and s.

Background: Entrainment to the environmental light cycle is an essential property of the circadian clock. Although the compound eye is known to be the major photoreceptor necessary for entrainment in many insects, the molecular mechanisms of photic entrainment remain to be explored.

Results: We found  that s (s) and mediate photic entrainment of the circadian clock in a hemimetabolous insect, the cricket .

timeless2 plays an important role in reproduction and circadian rhythms in the cricket Gryllus bimaculatus.

The timeless2 (tim2) gene is an insect orthologue of the mammalian clock gene Timeless (mTim). Although its functional role has been extensively studied in mammals, little is known regarding its role in insects. In the present study, we obtained tim2 cDNA (Gb'tim2) from the cricket Gryllus bimaculatus and characterized its functional role in embryonic development, egg production, and circadian rhythms.

The effect of Wolbachia on diapause, fecundity, and clock gene expression in Trichogramma brassicae (Hymenoptera: Trichogrammatidae).

The short day lengths of late summer in moderate regions are used to induce diapause in various insects. Many studies have shown the maternal effect of photoperiod on diapause induction of Trichogramma wasps, but there is no study to show the relationship between photoperiodic regimes and clock genes in these useful biological control agents. Here, we investigated the role of photoperiods on diapause, fecundity, and clock gene expression (clk, cyc, cry2, per, and timeout) in asexual and sexual Trichogramma brassicae as a model insect to find any differences between two strains.

A Tug-of-War between Cryptochrome and the Visual System Allows the Adaptation of Evening Activity to Long Photoperiods in Drosophila melanogaster.

In many animals, the circadian clock plays a role in adapting to the coming season by measuring day length. The mechanism for measuring day length and its neuronal circuits remains elusive, however. Under laboratory conditions, the fruit fly, Drosophila melanogaster, displays 2 activity peaks: one in the morning and one in the evening.

genes form an oscillatory loop independent of the / loop in the circadian clockwork of the cricket .

Background: Animals exhibit circadian rhythms with a period of approximately 24 h in various physiological functions, including locomotor activity. This rhythm is controlled by an endogenous oscillatory mechanism, or circadian clock, which consists of cyclically expressed clock genes and their product proteins. () genes are thought to be involved in the clock mechanism, and their functions have been examined extensively in holometabolous insects, but in hemimetabolous insects their role is less well understood.

TGF-β signaling in insects regulates metamorphosis via juvenile hormone biosynthesis.

Although butterflies undergo a dramatic morphological transformation from larva to adult via a pupal stage (holometamorphosis), crickets undergo a metamorphosis from nymph to adult without formation of a pupa (hemimetamorphosis). Despite these differences, both processes are regulated by common mechanisms that involve 20-hydroxyecdysone (20E) and juvenile hormone (JH). JH regulates many aspects of insect physiology, such as development, reproduction, diapause, and metamorphosis.

Enhancer of zeste plays an important role in photoperiodic modulation of locomotor rhythm in the cricket, Gryllus bimaculatus.

Introduction: Insects show daily behavioral rhythms controlled by an endogenous oscillator, the circadian clock. The rhythm synchronizes to daily light-dark cycles (LD) and changes waveform in association with seasonal change in photoperiod.

Results: To explore the molecular basis of the photoperiod-dependent changes in circadian locomotor rhythm, we investigated the role of a chromatin modifier, Enhancer of zeste (Gb'E(z)), in the cricket, Gryllus bimaculatus.

Heterogeneity of the Peripheral Circadian Systems in Drosophila melanogaster: A Review.

Circadian rhythms in organisms are involved in many aspects of metabolism, physiology, and behavior. In many animals, these rhythms are produced by the circadian system consisting of a central clock located in the brain and peripheral clocks in various peripheral tissues. The oscillatory machinery and entrainment mechanism of peripheral clocks vary between different tissues and organs.

Green-sensitive opsin is the photoreceptor for photic entrainment of an insect circadian clock.

Introduction: Entrainment to light cycle is a prerequisite for circadian rhythms to set daily physiological events to occur at an appropriate time of day. In hemimetabolous insects, the photoreceptor molecule for photic entrainment is still unknown. Since the compound eyes are the only circadian photoreceptor in the cricket Gryllus bimaculatus, we have investigated the role of three opsin genes expressed there, opsin-Ultraviolet (opUV), opsin-Blue (opB), and opsin-Long Wave (opLW) encoding a green-sensitive opsin in photic entrainment.

Leg regeneration is epigenetically regulated by histone H3K27 methylation in the cricket Gryllus bimaculatus.

Hemimetabolous insects such as the cricket Gryllus bimaculatus regenerate lost tissue parts using blastemal cells, a population of dedifferentiated proliferating cells. The expression of several factors that control epigenetic modification is upregulated in the blastema compared with differentiated tissue, suggesting that epigenetic changes in gene expression might control the differentiation status of blastema cells during regeneration. To clarify the molecular basis of epigenetic regulation during regeneration, we focused on the function of the Gryllus Enhancer of zeste [Gb'E(z)] and Ubiquitously transcribed tetratricopeptide repeat gene on the X chromosome (Gb'Utx) homologues, which regulate methylation and demethylation of histone H3 lysine 27 (H3K27), respectively.

Cryptochrome-dependent and -independent circadian entrainment circuits in Drosophila.

Entrainment to environmental light/dark (LD) cycles is a central function of circadian clocks. In Drosophila, entrainment is achieved by Cryptochrome (CRY) and input from the visual system. During activation by brief light pulses, CRY triggers the degradation of TIMELESS and subsequent shift in circadian phase.

Circadian molecular clockworks in non-model insects.

The recent development of molecular genetic technology is promoting studies on the clock mechanism of various non-model insect species, revealing diversity and commonality of their molecular clock machinery. Like in Drosophila, their clocks generally consist of clock genes including period, timeless, Clock, and cycle, except for hymenopteran species which lack timeless in their genome. Unlike in Drosophila, however, some insects show vertebrate-like traits: The clock machinery involves mammalian type cryptochrome, cycle is rhythmically expressed, and Clock is constitutively expressed.

The nuclear receptor genes HR3 and E75 are required for the circadian rhythm in a primitive insect.

Insect circadian rhythms are generated by a circadian clock consisting of transcriptional/translational feedback loops, in which CYCLE and CLOCK are the key elements in activating the transcription of various clock genes such as timeless (tim) and period (per). Although the transcriptional regulation of Clock (Clk) has been profoundly studied, little is known about the regulation of cycle (cyc). Here, we identify the orphan nuclear receptor genes HR3 and E75, which are orthologs of mammalian clock genes, Rorα and Rev-erbα, respectively, as factors involved in the rhythmic expression of the cyc gene in a primitive insect, the firebrat Thermobia domestica.