Cloning of a structural and functional homolog of the circadian clock gene period from the giant silkmoth Antheraea pernyi

Role of the clock gene period in regulating circadian rhythm of courtship vibrations in Nilaparvata lugens

Nilaparvata lugens, the brown planthopper (BPH), is a notorious pest threatening rice production across Asia. The heavy reliance on synthetic insecticides for control has led to resistance and raised ecological concerns. Substrate-borne vibrational communication, integral to species-specific mate recognition systems in insects, presents a potential avenue for pest management through mating disruption. However, the molecular mechanisms regulating vibrational signals in BPH remain poorly understood. In this study, we cloned and analyzed the clock gene period from BPH. The open reading frame of Nlper is 3708 bp, encoding a 1235-amino acid protein with two conserved domains: the Per-ARNT-Sim domain and the Period protein 2/3C-terminal region. It shares a closer evolutionary relationship with Laodelphax striatellus and Frankliniella occidentalis. Spatiotemporal expression analysis showed that Nlper was consistently expressed across all life stages and adult tissues, with the highest levels in macropterous males and male head, respectively. Rhythmic expression exhibited significant circadian oscillations under both light-dark and constant darkness conditions, peaking at 00:00 and reaching a trough at 12:00, with fold changes ranging from 2.47 to 3.39. Moreover, after dsRNA injection, Nlper expression decreased by 77.21%-84.26% from day 2 to day 5, disrupting the circadian oscillation of female vibrational signals (FVS) and causing a significant peak shift, along with a 30.56% reduction in FVS frequency on day 5. These findings underscore the essential role of Nlper in regulating the circadian rhythm of courtship vibrational signals, deepening our understanding of the genetic basis of insect communication and opening new possibilities for innovative pest management approaches.

Regulation of feeding dynamics by the circadian clock, light and sex in an adult nocturnal insect

Animals invest crucial resources in foraging to support development, sustenance, and reproduction. Foraging and feeding behaviors are rhythmically expressed by most insects. Rhythmic behaviors are modified by exogenous factors like temperature and photoperiod, and internal factors such as the physiological status of the individual. However, the interactions between these factors and the circadian clock to pattern feeding behavior remains elusive. As Drosophila, a standard insect model, spends nearly all its life on food, we rather chose to focus on the adults of a non-model insect, Agrotis ipsilon, a nocturnal cosmopolitan crop pest moth having structured feeding activity. Our study aimed to explore the impact of environmental cues on directly measured feeding behavior rhythms. We took advantage of a new experimental set-up, mimicking an artificial flower, allowing us to specifically monitor feeding behavior in a naturalistic setting, e.g., the need to enter a flower to get food. We show that the frequency of flower visits is under the control of the circadian clock in males and females. Feeding behavior occurs only during the scotophase, informed by internal clock status and external photic input, and females start to visit flowers earlier than males. Shorter duration visits predominate as the night progresses. Importantly, food availability reorganizes the microstructure of feeding behavior, revealing its plasticity. Interestingly, males show a constant number of daily visits during the 5 days of adult life whereas females decrease visitations after the third day of adult life. Taken together, our results provide evidence that the rhythmicity of feeding behavior is sexually dimorphic and controlled by photoperiodic conditions through circadian clock-dependent and independent pathways. In addition, the use of the new experimental set-up provides future opportunities to examine the regulatory mechanisms of feeding behavior paving the way to investigate complex relationships between feeding, mating, and sleep-wake rhythms in insects.

The clock gene, period, influences migratory flight and reproduction of the oriental armyworm, Mythimna separata (Walker)

The oriental armyworm, Mythimna separata, is a major long-distance migratory insect pest of grain crops in China and other Asian countries. Migratory flights and reproductive behavior usually occur at night, regulated by a circadian rhythm. However, knowledge about the linkages between adult flight, reproduction, and clock genes is still incomplete. To fill this important gap in our knowledge, a clock gene (designated Msper) was identified and phylogenetic analysis indicated that the encoded protein (MsPER) was highly similar to PER proteins from other insect species. Quantitative RT-PCR assays demonstrated that significantly different spatiotemporal and circadian rhythmic accumulations of mRNA encoding MsPER occurred during development under steady 14 h : 10 h light : dark conditions. The highest mRNA accumulation occurred in adult antennae and the lowest in larvae. Msper was expressed rhythmically in adult antennae, relatively less in photophase and more entering scotophase. Injecting small interference RNA (siRNA) into adult heads effectively knocked down Msper mRNA levels within 72 h. Most siRNA-injected adults reduced their evening flight activity significantly and did not exhibit a normal evening peak of flight activity. They also failed to mate and lay eggs within 72 h. Adult mating behavior was restored to control levels by 72 h post injection. We infer that Msper is a prominent clock gene that acts in regulating adult migratory flight and mating behaviors of M. separata. Because of its influence on migration and mating, Msper may be a valuable gene to target for effective management of this migratory insect.

Associations between Melatonin, Neuroinflammation, and Brain Alterations in Depression

Pro-inflammatory systemic conditions that can cause neuroinflammation and subsequent alterations in brain regions involved in emotional regulation have been suggested as an underlying mechanism for the pathophysiology of major depressive disorder (MDD). A prominent feature of MDD is disruption of circadian rhythms, of which melatonin is considered a key moderator, and alterations in the melatonin system have been implicated in MDD. Melatonin is involved in immune system regulation and has been shown to possess anti-inflammatory properties in inflammatory conditions, through both immunological and non-immunological actions. Melatonin has been suggested as a highly cytoprotective and neuroprotective substance and shown to stimulate all stages of neuroplasticity in animal models. The ability of melatonin to suppress inflammatory responses through immunological and non-immunological actions, thus influencing neuroinflammation and neurotoxicity, along with subsequent alterations in brain regions that are implicated in depression, can be demonstrated by the antidepressant-like effects of melatonin. Further studies that investigate the associations between melatonin, immune markers, and alterations in the brain structure and function in patients with depression could identify potential MDD biomarkers.

The inhibitory effect of melatonin on human prostate cancer

Prostate cancer (PCa) is one of the most commonly diagnosed human cancers in males. Nearly 191,930 new cases and 33,330 new deaths of PCa are estimated in 2020. Androgen and androgen receptor pathways played essential roles in the pathogenesis of PCa. Androgen depletion therapy is the most used therapies for primary PCa patients. However, due to the high relapse and mortality of PCa, developing novel noninvasive therapies have become the focus of research. Melatonin is an indole-like neurohormone mainly produced in the human pineal gland with a prominent anti-oxidant property. The anti-tumor ability of melatonin has been substantially confirmed and several related articles have also reported the inhibitory effect of melatonin on PCa, while reviews of this inhibitory effect of melatonin on PCa in recent 10 years are absent. Therefore, we systematically discuss the relationship between melatonin disruption and the risk of PCa, the mechanism of how melatonin inhibited PCa, and the synergistic benefits of melatonin and other drugs to summarize current understandings about the function of melatonin in suppressing human prostate cancer. We also raise several unsolved issues that need to be resolved to translate currently non-clinical trials of melatonin for clinic use. We hope this literature review could provide a solid theoretical basis for the future utilization of melatonin in preventing, diagnosing and treating human prostate cancer.

Melatonin Target Proteins: Too Many or Not Enough?

The neurohormone N-acetyl-5-methoxytryptamine, better known as melatonin, is a tryptophan derivative with a wide range of biological effects that is present in many organisms. These effects are believed to rely either on the chemical properties of melatonin itself as scavenger of free radicals or on the binding of melatonin to protein targets. More than 15 proteins, including receptors (MT1, MT2, Mel1c, CAND2, ROR, VDR), enzymes (QR2, MMP-9, pepsin, PP2A, PR-10 proteins), pores (mtPTP), transporters (PEPT1/2, Glut1), and other proteins (HBS, CaM, tubulin, calreticuline), have been suggested to interact with melatonin at sub-nanomolar to millimolar melatonin concentrations. In this review we assemble for the first time the available information on proposed melatonin targets and discuss them in a comprehensive manner to evaluate the robustness of these findings in terms of methodology, physiological relevance, and independent replication.

Melatonin receptor structures shed new light on melatonin research

The tryptophan derivative melatonin is an evolutionary old molecule that is involved in a pleiotropy of physiological functions. In humans, age-related decline of circulating melatonin levels and/or dysregulation of its circadian synthesis pattern have been associated with several disorders and disease states. Several molecular targets have been proposed for melatonin since its discovery, in 1959. Among them, melatonin MT₁ and MT₂ receptors are the best characterized melatonin targets, mediating melatonin effects in a variety of tissues. They belong to the superfamily of G protein-coupled receptors. Two back-to-back articles published in the "Nature" Journal earlier this year present the first crystal structures of the human MT₁ and MT₂ in its inactive states. Here, we will briefly outline the discovery path of melatonin receptors until their structural elucidation and discuss how these new findings will guide future research toward a better understanding of their function and rational drug design.

No polymorphism of melatonin receptor 1A (MTNR1A) gene was found in Markhoz goat

Melatonin is the main hormone of seasonal breeding in sheep and goat which has an effect on reproductive organs via its receptors. Studies have shown that mutations in melatonin receptor 1A (MTNR1A) gene are related to litter size as well as the ovulation rate in sheep and goats. In this study, polymorphism of two loci in MTNR1A melatonin receptor gene was studied in order to survey their relationship with litter size in Markhoz goats. PCR primers were employed to mask polymorphisms of MTNR1A in 150 does by PCR‐RFLP method. After DNA extraction, the PCR‐RFLP was performed using Ecol31I and HpaI restriction enzymes. Results showed that these loci were not polymorphic. These results show that the fecundity of Markhoz goats is not linked to MTNR1A. No polymorphism in MTNR1A was found in Markhoz goats, therefore, it is essential to test polymorphism of other genes or loci to facilitate marker‐assisted selection techniques to improve reproduction traits in Markhoz goats.

Transcriptome Analysis Reveals Potential Antioxidant Defense Mechanisms in Antheraea pernyi in Response to Zinc Stress

The growth and development of the Chinese oak silkworm, Antheraea pernyi, are strongly influenced by environmental conditions, including heavy metal pollution. An excess of heavy metals causes cellular damage through the production of free radical reactive oxygen species. In this study, transcriptome analysis was performed to investigate global gene expression when A. pernyi was exposed to zinc infection. With RNA sequencing (RNA-Seq), a total of 25 795 510 and 38 158 855 clean reads were obtained from zinc-treated and control fat body libraries, respectively. We identified 2399 differential expression genes (DEGs) (1845 upregulated and 544 downregulated genes) in the zinc-treated library. In addition, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that these DEGs were related to the peroxisome pathway that was associated with antioxidant defense. Our results suggest that fat bodies of A. pernyi constitute a strong antioxidant defense against heavy metal contamination.

Genetic basis of allochronic differentiation in the fall armyworm

BACKGROUND

Very little is known on how changes in circadian rhythms evolve. The noctuid moth Spodoptera frugiperda (Lepidoptera: Noctuidae) consists of two strains that exhibit allochronic differentiation in their mating time, which acts as a premating isolation barrier between the strains. We investigated the genetic basis of the strain-specific timing differences to identify the molecular mechanisms of differentiation in circadian rhythms.

RESULTS

Through QTL analyses we identified one major Quantitative trait chromosome (QTC) underlying differentiation in circadian timing of mating activity. Using RADtags, we identified this QTC to be homologous to Bombyx mori C27, on which the clock gene vrille is located, which thus became the major candidate gene. In S. frugiperda, vrille showed strain-specific polymorphisms. Also, vrille expression differed significantly between the strains, with the rice-strain showing higher expression levels than the corn-strain. In addition, RT-qPCR experiments with the other main clock genes showed that pdp1, antagonist of vrille in the modulatory feedback loop of the circadian clock, showed higher expression levels in the rice-strain than in the corn-strain.

CONCLUSIONS

Together, our results indicate that the allochronic differentiation in the two strains of S. frugiperda is associated with differential transcription of vrille or a cis-acting gene close to vrille, which contributes to the evolution of prezygotic isolation in S. frugiperda.

Distribution of Circadian Clock-Related Proteins in the Cephalic Nervous System of the Silkworm, Bombyx Mori

In the circadian timing systems, input pathways transmit information on the diurnal environmental changes to a core oscillator that generates signals relayed to the body periphery by output pathways. Cryptochrome (CRY) protein participates in the light perception; period (PER), Cycle (CYC), and Doubletime (DBT) proteins drive the core oscillator; and arylalkylamines are crucial for the clock output in vertebrates. Using antibodies to CRY, PER, CYC, DBT, and arylalkylamine N-acetyltransferase (aaNAT), the authors examined neuronal architecture of the circadian system in the cephalic ganglia of adult silkworms. The antibodies reacted in the cytoplasm, never in the nuclei, of specific neurons. Acluster of 4 large Ia1 neurons in each dorsolateral protocerebrum, a pair of cells in the frontal ganglion, and nerve fibers in the corpora cardiaca and corpora allata were stained with all antibodies. The intensity of PER staining in the Ia1 cells and in 2 to 4 adjacent small cells oscillated, being maximal late in subjective day and minimal in early night. No other oscillations were detected in any cell and with any antibody. Six small cells in close vicinity to the Ia1 neurons coexpressed CYC-like and DBT-like, and 4 to 5 of them also coexpressed aaNATlike immunoreactivity; the PER- and CRY-like antigens were each present in separate groups of 4 cells. The CYC- and aaNAT-like antigens were further colocalized in small groups of neurons in the pars intercerebralis, at the venter of the optic tract, and in the subesophageal ganglion. Remaining antibodies reacted with similarly positioned cells in the pars intercerebralis, and the DBT antibody also reacted with the cells in the subesophageal ganglion, but antigen colocalizations were not proven. The results imply that key components of the silkworm circadian system reside in the Ia1 neurons and that additional, hierarchically arranged oscillators contribute to overt pacemaking. The retrocerebral neurohemal organs seem to serve as outlets transmitting central neural oscillations to the hemolymph. The frontal ganglion may play an autonomous function in circadian regulations. The colocalization of aaNAT- and CYC-like antigens suggests that the enzyme is functionally linked to CYC as in vertebrates and that arylalkylamines are involved in the insect output pathway.

Influences of melatonin treatment, melatonin receptor 1A (MTNR1A) and kisspeptin (KiSS-1) gene polymorphisms on first conception in Sarda ewe lambs

In order to investigate if the melatonin receptor 1A (MTNR1A) and kisspeptin (KiSS-1) genes influence the reproductive response to melatonin treatment, 510 Sarda ewe lambs were divided into groups C (control) and M; Group M received one melatonin implant (18 mg). After 35 days rams were introduced for 40 days and subsequent lambing dates and number of newborns were recorded. The MTNR1A gene Exon II and KiSS-1 gene Exon I were amplified and genotyped by restriction fragment length polymorphism (RFLP) and single-strand conformation polymorphism analysis. Two single nucleotide polymorphisms (SNPs; C606T and G612A) in MTNR1A and one (G1035A) in KiSS-1 were found. The most frequent genotypes were G/G (63%) and C/C (53%) for MTNR1A and G/G (92%) for KiSS-1. Treated animals showed a higher lambing rate (P < 0.05) and an advanced lambing date (P < 0.05) compared with controls. The three SNPs did not influence the onset of reproductive activity. The majority of the G/G animals of Group M lambed before 190 days after ram introduction (P < 0.05), while in Group C a higher number of G/G animals lambed after this date. Data revealed the positive effect of melatonin treatment on the time of first conception in ewe lambs and highlighted that the G/G genotype of the MTNR1A gene is able to influence the reproductive response to melatonin treatment.

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. Although the oscillatory mechanisms of the clock are still to be investigated in most insects, RNAi and genome editing technology should accelerate the study, leading toward understanding the origin of variable overt behavioral rhythms such as nocturnal, diurnal, and crepuscular activity rhythms.

Expression of clock genes period and timeless in the central nervous system of the Mediterranean flour moth, Ephestia kuehniella

Homologous circadian genes are found in all insect clocks, but their contribution to species-specific circadian timing systems differs. The aim of this study was to extend research within Lepidoptera to gain a better understanding of the molecular mechanism underlying circadian clock plasticity and evolution. The Mediterranean flour moth, Ephestia kuehniella (Pyralidae), represents a phylogenetically ancestral lepidopteran species. We have identified circadian rhythms in egg hatching, adult emergence, and adult locomotor activity. Cloning full-length complementary DNAs and further characterization confirmed one copy of period and timeless genes in both sexes. Both per and tim transcripts oscillate in their abundance in E. kuehniella heads under light-dark conditions. PER-like immunoreactivity (PER-lir) was observed in nuclei and cytoplasm of most neurons in the central brain, the ventral part of subesophageal complex, the neurohemal organs, the optic lobes, and eyes. PER-lir in photoreceptor nuclei oscillated during the day with maximal intensity in the light phase of the photoperiodic regime and lack of a signal in the middle of the dark phase. Expression patterns of per and tim messenger RNAs (mRNAs) were revealed in the identical location as the PER-lir was detected. In the photoreceptors, a daily rhythm in the intensity of expression of both per mRNA and tim mRNA was found. These findings suggest E. kuehniella as a potential lepidopteran model for circadian studies.

Sequence and expression of per, tim1, and cry2 genes in the Madeira cockroach Rhyparobia maderae

Most of what we know today about the molecular constituents of the insect circadian clock was discovered in the fruit fly Drosophila melanogaster. Various other holometabolous and some hemimetabolous insects have also been examined for the presence of circadian genes. In these insects, per, tim1, and cry2 are part of a core feedback loop system. The proteins inhibit their own expression, leading to circadian oscillations of mRNA and proteins. Although cockroaches are successfully employed circadian model organisms, their clock genes are mostly unknown. Thus, we cloned putative circadian genes in Rhyparobia maderae (synonym Leucophaea maderae), showing the presence of period (per), timeless 1 (tim1), and mammalian-type cryptochrome (cry2). The expression levels of per, tim1, and cry2 in R. maderae were examined in various tissues and photoperiods employing quantitative PCR. In brains and excised accessory medullae, expression levels of rmPer, rmTim1, and rmCry2 oscillated in a circadian manner with peaks in the first half of the night. Oscillations mostly continued in constant conditions. In Malpighian tubules, no significant oscillations were found. In animals raised in different photoperiods (LD 18:6, 12:12, 6:18), the peak levels of rmPer, rmTim1, and rmCry2 expression adjusted with respect to the beginning of the scotophase. The daily mean of expression levels was significantly lower in short-day versus long-day animals. We suggest that rmPer, rmTim1, and rmCry2 are part of the Madeira cockroach nuclear circadian clock, which can adjust to different photoperiods.

Daily Rhythms of PERIOD protein in the eyestalk of the American lobster, Homarus americanus

The daily rhythm of PERIOD protein (PER) expression is an integral component of the circadian clock, which is found among a broad range of animal species including fruit flies, marine mollusks and even humans. The use of antibodies directed against PER has provided a helpful tool in the discovery of PER homologues and the labeling of putative pacemaker cells, especially in animals for which an annotated genome is not readily available. In this study, DrosophilaPER antibodies were used to probe for PER in the American lobster, Homarus americanus. This species exhibits robust endogenous circadian rhythms but the circadian clock has yet to be located or characterized. PER was detected in the eyestalks of the lobster but not in the brain. Furthermore, a significant effect of the LD cycle on daily PER abundance was identified, and PER was significantly more abundant at mid dark than in early light or mid light hours. Our results suggest that PER is a part of the molecular machinery of the circadian clock located in the eyestalk of the lobster.

Insect photoperiodic calendar and circadian clock: independence, cooperation, or unity?

The photoperiodic calendar is a seasonal time measurement system which allows insects to cope with annual cycles of environmental conditions. Seasonal timing of entry into diapause is the most often studied photoperiodic response of insects. Research on insect photoperiodism has an approximately 80-year-old tradition. Despite that long history, the physiological mechanisms underlying functionality of the photoperiodic calendar remain poorly understood. Thus far, a consensus has not been reached on the role of another time measurement system, the biological circadian clock, in the photoperiodic calendar. Are the two systems physically separated and functionally independent, or do they cooperate, or is it a single system with dual output? The relationship between calendar and clock functions are the focus of this review, with particular emphasis on the potential roles of circadian clock genes, and the circadian clock system as a whole, in the transduction pathway for photoperiodic token stimulus to the overt expression of facultative diapause.

Genetic basis of incidence and period length of circadian rhythm for locomotor activity in populations of a seed beetle

Circadian rhythms are ubiquitous in a wide variety of organisms, although their genetic variation has been analyzed in only a few species. We found genetic differences in the circadian rhythm of adult locomotor activity among strains of the adzuki bean beetle, Callosobruchus chinensis, which differed in origin and have been maintained in isolation. All beetles in some strains clearly had free-running rhythms in constant darkness whereas most beetles in other strains were arrhythmic. The period of free-running rhythm varied from approximately 19 to 23 h between the strains. F(1) males from reciprocal crosses among strains with different periods of circadian rhythms had circadian periods that were intermediate between their parental strains. Segregation of the circadian rhythm appeared in the F(2) generation. These findings are consistent with the hypothesis that variation in the period length of circadian rhythm is explained by a major autosomal gene with additive effects and no dominance. This hypothesis was supported by the joint scaling test for the free-running period in the F(1) and F(2) generations. We discuss possible causes for genetic variation in circadian rhythm in the C. chinensis strains in terms of random factors and selection.

The Circadian Control of Eclosion

Eclosion is the stage in development when the adult insect emerges from the shell of its old cuticle. The sequence of behaviors necessary for eclosion is coordinated by an integrated system of hormones and is activated by hormones that relay developmental readiness. The circadian clock, which controls the timing of behaviors such as the rest: activity rhythm of adult insects, also controls eclosion timing. A number of groups are actively investigating the mechanisms by which the circadian clock restricts or gates eclosion to a particular time of day. Data from these studies are beginning to reveal details of the molecular and physiological basis of the eclosion rhythm.

Circadian regulation of olfactory receptor neurons in the cockroach antenna

In the cockroach, olfactory sensitivity as measured by the amplitude of the electroantennogram (EAG) is regulated by the circadian system. We wished to determine how this rhythm in antennal response was reflected in the activity of individual olfactory receptor neurons. The amplitude of the EAG and the activity of olfactory receptor neurons (ORNs) in single olfactory sensilla were recorded simultaneously for 3 to 5 days in constant darkness from an antenna of the cockroach Leucophaea maderae. Both EAG amplitude and the spike frequency of the ORNs exhibited circadian rhythms with peak amplitude/activity occurring in the subjective day. The phases of the rhythms were dependent on the phase of the prior light cycle and thus were entrainable by light. Ablation of the optic lobes abolished the rhythm in EAG amplitude as has been previously reported. In contrast, the rhythm in ORN response persisted following surgery. These results indicated that a circadian clock outside the optic lobes can regulate the responses of olfactory receptor neurons and further that this modulation of the ORN response is not dependent on the circadian rhythm in EAG amplitude.

Polymorphism of the melatonin receptor MT1 gene and its relationship with seasonal reproductive activity in the Sarda sheep breed

The aim was to study the polymorphisms of the melatonin receptor 1A gene (MTNR1A) and its relationship with seasonal reproduction in the Sarda sheep breed. Four-thousand multiparous ewes reared under natural photoperiod were randomly chosen. Genomic DNA was extracted and subjected to PCR for the amplification of the main part of exon II of the ovine MTNR1A gene (GenBank U14109). PCR products were subjected to restriction enzymes MnlI and RsaI and placed into +/+, +/- or -/- group for MnlI and C/C, C/T or T/T group for RsaI. Samples were cloned and sequenced. The sequences were aligned with the U14109 sequence of GenBank. Data were subjected to allelic frequency analysis and to the chi(2) test in order to evaluate the link between genotype and reproductive activity. After MnlI digestion, allelic frequency was 0.78 for allele +and 0.22 for allele -; genotype frequency of the +/+ homozygote was 68%, 20.5% for +/- and 11.5% for -/-. After RsaI, allelic frequency was 0.66 for allele C and 0.34 for allele T; genotype frequency of the C/C homozygote was 53.5%, 26% for C/T and 20.5% for T/T. The population was in Hardy-Weinberg disequilibrium both for the MnlI and RsaI. Lambing frequency of +/+ genotype ewes was higher in the period September-December while for -/- genotype in January-April (P<0.01). Lambing of C/C genotype ewes showed a higher frequency in September-December while for T/T genotype in January-April (P<0.01). Results confirmed that the polymorphism of the MTNR1A locus was also present in the Sarda with a higher incidence of the +/+ and C/C genotypes. The animals that carried one of these two gene isoforms showed a not seasonal reproductive activity with the lambing period in September-December.

Comparative analysis of circadian clock genes in insects

After a slow start, the comparative analysis of clock genes in insects has developed into a mature area of study in recent years. Brain transplant or surgical interventions in larger insects defined much of the early work in this area, before the cloning of clock genes became possible. We discuss the evolution of clock genes, their key sequence differences, and their likely modes of regulation in several different insect orders. We also present their expression patterns in the brain, focusing particularly on Diptera, Lepidoptera, and Orthoptera, the most common non-genetic model insects studied. We also highlight the adaptive involvement of clock molecules in other complex phenotypes which require biological timing, such as social behaviour, diapause and migration.

Casein kinase I epsilon does not rescue double-time function in Drosophila despite evolutionarily conserved roles in the circadian clock

Double-time (dbt) is a casein kinase gene involved in cell survival, proliferation, and circadian rhythms in the fruit fly, Drosophila melanogaster. Genetic and biochemical studies have shown that dbt and its mammalian ortholog casein kinase I epsilon (hckI epsilon) regulate the circadian phosphorylation of period (per), thus controlling per subcellular localization and stability. Mutations in these kinases can shorten the circadian period in both mammals and Drosophila. Since similar activities in circadian clock have been described for these kinases, we investigated whether the expression of mammalian casein kinase I can replace the activity of dbt in flies. Global expression of the full-length dbt rescued lethality of the null mutant dbt revVIII and rescued flies showed normal locomotor activity rhythms. Global expression of dbt also restored the locomotor activity rhythm of the arrhythmic genotype, dbt ar/dbt revVIII. In contrast, global expression of hckI epsilon or hckI alpha did not rescue lethality or locomotor activity of dbt mutants. Furthermore dbt overexpression in wild-type clock cells had only a small effect on period length, whereas hckI epsilon expression in clock cells greatly lengthened period to ~30.5 hours and increased the number of arrhythmic flies. These results indicate that hckI epsilon cannot replace the activity of dbt in flies despite the high degree of similarity in primary sequence and kinase function. Moreover, expression of hck Iepsilon in flies appears to interfere with dbt activity. Thus, caution should be used in interpreting assays that measure activity of mammalian casein kinase mutants in Drosophila, or that employ vertebrate CKI in studies of dPER phosphorylations.

An antennal circadian clock and circadian rhythms in peripheral pheromone reception in the moth Spodoptera littoralis

Circadian rhythms are observed in mating behaviors in moths: females emit sex pheromones and males are attracted by these pheromones in rhythmic fashions. In the moth Spodoptera littoralis, we demonstrated the occurrence of a circadian oscillator in the antenna, the peripheral olfactory organ. We identified different clock genes, period (per), cryptochrome1 (cry1) and cryptochrome2 (cry2), in this organ. Using quantitative real-time PCR (qPCR), we found that their corresponding transcripts cycled circadianly in the antenna as well as in the brain. Electroantennogram (EAG) recordings over 24 h demonstrated for the first time a circadian rhythm in antennal responses of a moth to sex pheromone. qPCR showed that out of one pheromone-binding protein (PBP), one olfactory receptor (OR), and one odorant-degrading enzyme (ODE), all putatively involved in the pheromone reception, only the ODE transcript presented a circadian rhythm that may be related to rhythms in olfactory signal resolution. Peripheral or central circadian clock control of olfaction is then discussed in light of recent data.

Circadian rhythm gene regulation in the housefly Musca domestica

The circadian mechanism appears remarkably conserved between Drosophila and mammals, with basic underlying negative and positive feedback loops, cycling gene products, and temporally regulated nuclear transport involving a few key proteins. One of these negative regulators is PERIOD, which in Drosophila shows very similar temporal and spatial regulation to TIMELESS. Surprisingly, we observe that in the housefly, Musca domestica, PER does not cycle in Western blots of head extracts, in contrast to the TIM protein. Furthermore, immunocytochemical (ICC) localization using enzymatic staining procedures reveals that PER is not localized to the nucleus of any neurons within the brain at any circadian time, as recently observed for several nondipteran insects. However, with confocal analysis, immunofluorescence reveals a very different picture and provides an initial comparison of PER/TIM-containing cells in Musca and Drosophila, which shows some significant differences, but many similarities. Thus, even in closely related Diptera, there is considerable evolutionary flexibility in the number and spatial organization of clock cells and, indeed, in the expression patterns of clock products in these cells, although the underlying framework is similar.

Neuroanatomical approaches to the study of insect photoperiodism

The anatomical locations of three components of insect photoperiodism--the photoperiodic photoreceptor, photoperiodic clock and hormonal effector--are summarized and compared between species. Among photoperiodic photoreceptors, either the retinal or extraretinal types or both are operative, and there is no general relationship between phylogeny and photoreceptor type. The photoperiodic clock comprises time measurement and counter systems. Currently, it is generally accepted that circadian oscillators are involved in the photoperiodic clock. Several recent studies have raised the possibility that timeless, a circadian clock gene, plays a role in the photoperiodic clock in flies. The dorsal protocerebrum has been identified as an important region regulating the endocrine system for adult, pupal and embryonic diapause controlled by photoperiod. In the blow fly Protophormia terraenovae, neural connections between circadian clock neurons and indispensable neurons in the pars lateralis for diapause induction in the dorsal protocerebrum have been demonstrated. This neural network may provide the access needed to investigate the neural components of the photoperiodic clock.

Neurohormones as putative circadian clock output signals in the central nervous system of two cricket species

Antisera to the neuropeptides corazonin (Crz) and crustacean cardioactive peptide (CCAP) and to the diapause hormone (DH) react with small sets of neurones in the cephalic ganglia of the crickets Dianemobius nigrofasciatus and Allonemobius allardi. The distribution of their immunoreactivities is similar in the two species and overlaps with the locations of presumed circadian clock components in the optic lobes, protocerebrum, tritocerebrum, suboesophageal ganglion (SOG) and frontal ganglion. D. nigrofasciatus contains two Crz-immunoreactive (Crz-ir) cells in each optic lobe, six cell groups in the protocerebrum, four in the tritocerebrum, and one in SOG, whereas A. allardi harbours only five Crz-ir groups in the protocerebrum and four in the tritocerebrum. CCAP immunoreactivity occurs in both species in four protocerebrum cell clusters, four tritocerebrum cell clusters, four SOG cell clusters, one frontal ganglion cell cluster, and two optic lobe cell clusters; D. nigrofasciatus possesses two additional cells with unique links to the lamina in the optic lobe. DH-related antigens are present in four cell clusters in the optic lobe, six (D. nigrofasciatus) or eight (A. allardi) in the protocerebrum, four in the tritocerebrum, and three (A. allardi) or five (D. nigrofasciatus) in the SOG. Some of the detected cells also react with antibody to the clock protein Period (PER) or lie close to PER-ir cells. Crickets reared at two different photoperiods do not differ in the distribution and intensity of immunoreactivities. No changes have been detected during the course of diurnal light/dark cycles, possibly because the antisera react with persistent prohormones, whereas circadian fluctuations may occur at the level of their processing or of hormone release. The projection of immunoreactive fibres to several brain regions, the stomatogastric nervous system and the neurohaemal organs indicates multiple functions of the respective hormones.

A nondiapausing variant of the flesh fly, Sarcophaga bullata, that shows arrhythmic adult eclosion and elevated expression of two circadian clock genes, period and timeless

We describe a variant of the flesh fly, Sarcophaga bullata, which fails to enter pupal diapause in response to short daylength and low temperatures. This fly also has an arrhythmic adult eclosion pattern: rather than eclosing in early photophase, the variant ecloses arrhythmically throughout the photophase and scotophase. The loss of both diapause (photoperiodic response) and the gating of adult eclosion (presumably a circadian response) suggests that the same clock system is involved in these two responses. An examination of the expression patterns of the clock genes period and timeless demonstrates that both genes are present in the nondiapausing variant, but surprisingly, both genes are expressed at higher levels. This abnormality we observe, possibly the consequence of an upstream clock gene malfunction or a malfunction of the autoregulatory loop, results in disruption of a component of the clock system that is apparently needed for both photoperiodism and circadian rhythmicity.

Differences in Binding Sites of Two Melatonin Receptors Help to Explain Their Selectivity to Some Melatonin Analogs: A Molecular Modeling Study

Numerous diseases have been linked to the malfunction of G-protein coupled receptors (GPCRs). Their adequate treatment requires rational design of new high-affinity and high-selectivity drugs targeting these receptors. In this work, we report three-dimensional models of the human MT(1) and MT(2) melatonin receptors, members of the GPCR family. The models are based on the X-ray structure of bovine rhodopsin. The computational approach employs an original procedure for optimization of receptor-ligand structures. It includes rotation of one of the transmembrane alpha-helices around its axis with simultaneous assessment of quality of the resulting complexes according to a number of criteria we have developed for this purpose. The optimal geometry of the receptor-ligand binding is selected based on the analysis of complementarity of hydrophobic/hydrophilic properties between the ligand and its protein environment in the binding site. The elaborated "optimized" models are employed to explore the details of protein-ligand interactions for melatonin and a number of its analogs with known affinity to MT(1) and MT(2) receptors. The models permit rationalization of experimental data, including those that were not used in model building. The perspectives opened by the constructed models and by the optimization procedure in the design of new drugs are discussed.

Structure and expressions of two circadian clock genes, period and timeless in the commercial silkmoth, Bombyx mori

We cloned two circadian clock genes period (Bmper) and timeless (Bmtim) from the commercial silkmoth, Bombyx mori. Sequence analysis revealed a high degree of conservation among insects for both genes. BmPER predicted from the DNA sequence is a polypeptide of 1, 113 amino acids with functional domains such as PAS, PAC, nuclear localization signal (NLS) and cytoplasmic localization domain (CLD). Deduced BmTIM consists of 997 amino acids with PER interaction site (PIS) as well as NLS and CLD. Southern blot analyses revealed that Bmper and Bmtim are single copy genes. Northern blot analysis demonstrated that Bmper and Bmtim are expressed both in the head and peripheral tissues. We also examined temporal profiles of Bmper and Bmtim expressions in the head, flight muscle, testis and antenna of adult males under LD12:12 and LD16:8 by Real-Time PCR assays. Our data show that photoperiod differentially affects the temporal expression patterns of Bmper and Bmtim. The mRNA expression of Bmper and Bmtim in the head had a phase lead under LD12:12 compared to that under LD16:8, whereas photoperiod did not affect expression patterns in peripheral tissues relative to light-on. Photoperiod affected not only the phase relationship but also the expression level. In the testis and antenna, the level of transcription of Bmtim was low in LD12:12 but high in LD16:8. The daily differences in amplitudes of the Bmper and Bmtim expression rhythms were 2-fold in the head and 1.5-2.5 folds in the peripheral tissues examined.

Evidence for a putative antennal clock in Mamestra brassicae: molecular cloning and characterization of two clock genes--period and cryptochrome-- in antennae

Circadian rhythms are generated by endogenous circadian clocks, organized in central and peripheral clocks. An antennal peripheral clock has been demonstrated to be necessary and sufficient to generate Drosophila olfactory rhythms in response to food odours. As moth pheromonal communication has been demonstrated to follow daily rhythms, we thus investigated the occurence of a putative antennal clock in the noctuid Mamestra brassicae. From moth antennae, we isolated two full-length cDNAs encoding clock genes, period and cryptochrome, which appeared to be expressed throughout the body. In the antennae, expression of both transcripts was restricted to cells that likely represent olfactory sensory neurones. Our results suggest the occurence of a putative antennal clock that could participate in the pheromonal communication rhythms observed in vivo.

Organization of endogenous clocks in insects

Insect and mammalian circadian clocks show striking similarities. They utilize homologous clock genes, generating self-sustained circadian oscillations in distinct master clocks of the brain, which then control rhythmic behaviour. The molecular mechanisms of rhythm generation were first uncovered in the fruit fly Drosophila melanogaster, whereas cockroaches were among the first animals where the brain master clock was localized. Despite many similarities, there exist obvious differences in the organization and functioning of insect master clocks. These similarities and differences are reviewed on a molecular and anatomical level.

Day/night fluctuations in melatonin content, arylalkylamine N-acetyltransferase activity and NAT mRNA expression in the CNS, peripheral tissues and hemolymph of the cockroach, Periplaneta americana

Melatonin content measured by a radioenzymatic assay in the brain of the American cockroach (Periplaneta americana) showed a day/night fluctuation with higher levels at night under LD 12:12. The activity of arylalkylamine N-acetyltransferase (NAT) in brain was also higher at night and this pattern continued in constant darkness. The results suggest that the rhythmicity in melatonin content can be caused by NAT. Melatonin content in hemolymph showed an even greater day/night difference, more than 12 times that in brain under LD 12:12. Melatonin levels in retina were also higher at night while NAT activity was not significantly higher at night than at daytime. Using a probe designed from NAT cloned from testes we performed Northern blot analysis of total RNA, which revealed that the level of NAT mRNA was higher in midgut, ovary and female accessory glands than in fat body and brain. The level of transcript in midgut was higher at night, but the levels in ovary and female accessory reproductive gland showed the opposite pattern. We also used the antibody to whole Drosophila melanogaster aaNAT1 protein, seeking a homologous antigen in the cephalic ganglia. NAT-like antigen was detected in several restricted populations of cells in the brain that were partially co-localized with PER-like antigen. The results suggest that NAT exists in multiple forms in various tissues of the cockroach and that its functions and regulations can vary among tissues. The results in the brain led to the conclusion that NAT could be a clock-controlled gene functioning as an output regulator of the circadian clock.

The cycling and distribution of PER-like antigen in relation to neurons recognized by the antisera to PTTH and EH in Thermobia domestica

The cephalic nervous system of the firebrat contains antigens recognized by antisera to the clock protein period (PER), the prothoracicotropic hormone (PTTH) and the eclosion hormone (EH). The content of the 115 kDa PER-like antigen visualized on the western blots fluctuates in diurnal rhythm with a maximum in the night. The oscillations entrained in a 12:12 h light/dark (LD) cycle persist in the darkness and disappear in continuous light. They are detected by immunostaining in 14 pairs of the protocerebral neurons and are extreme in four suboesophageal neurons and two cells in each corpus cardiacum that contain PER only during the night phase. No circadian fluctuations occur in three lightly stained perikarya of the optic lobe. Five cell bodies located in each brain hemisphere between the deuto-and the tritocerebrum retain weak immunoreactivity under constant illumination. In all cells, the staining is confined to the cytoplasm and never occurs in the cell nuclei. The cells containing PER-like material do not react with the anti-PTTH and anti-EH antisera, which recognize antigens of about 50 and 20 kDa, respectively. The anti-PTTH antiserum stains in each brain hemisphere seven neurons in the protocerebrum, eight in the optic lobe, and 3-5 in the posterior region of the deutocerebrum. The antiserum to EH reacts in each hemisphere with just two cells located medially to the mushroom bodies. No cycling of the PTTH-like and EH-like antigens was detected.

Constructing a feedback loop with circadian clock molecules from the silkmoth, Antheraea pernyi

Circadian clocks are important regulators of behavior and physiology. The circadian clock of Drosophila depends on an autoinhibitory feedback loop involving dCLOCK, CYCLE (also called dBMAL, for Drosophila brain and muscle ARNT-like protein), dPERIOD, and dTIMELESS. Recent studies suggest that the clock mechanism in other insect species may differ strikingly from that of Drosophila. We cloned Clock, Bmal, and Timeless homologs (apClock, apBmal, and apTimeless) from the silkmoth Antheraea pernyi, from which a Period homolog (apPeriod) has already been cloned. In Schneider 2 (S2) cell culture assays, apCLOCK:apBMAL activates transcription through an E-box enhancer element found in the 5' region of the apPeriod gene. Furthermore, apPERIOD can robustly inhibit apCLOCK: apBMAL-mediated transactivation, and apTIMELESS can augment this inhibition. Thus, a complete feedback loop, resembling that found in Drosophila, can be constructed from silkmoth CLOCK, BMAL, PERIOD, and TIMELESS. Our results suggest that the circadian autoinhibitory feedback loop discovered in Drosophila is likely to be widespread among insects. However, whereas the transactivation domain in Drosophila lies in the C terminus of dCLOCK, in A. pernyi, it lies in the C terminus of apBMAL, which is highly conserved with the C termini of BMALs in other insects (except Drosophila) and in vertebrates. Our analysis sheds light on the molecular function and evolution of clock genes in the animal kingdom.

Development of PDF-immunoreactive cells, possible clock neurons, in the housefly Musca domestica

Even though the housefly Musca domestica shows clear circadian rhythms in its behavioural and physiological processes, a circadian pacemaker system controlling these rhythms has not yet been described morphologically in this species. In M. domestica, neurons immunoreactive to pigment-dispersing factor (PDF), a neurotransmitter/neuromodulator of circadian information arising from a circadian clock and transmitted to target cells, are similar in their number and distribution to the PDF neurons of Drosophila melanogaster. In D. melanogaster these neurons co-localize PER protein and have been identified as clock neurons in that species. Here we report PDF-immunoreactive cells in the housefly's brain during postembryonic development in the larval and pupal stages, as well as in the adult fly soon after eclosion. In the housefly's brain, there are three groups of PDF-immunoreactive neurons: two groups with small (sPDFMe) and large (lPDFMe) cell bodies in the proximal medulla of the optic lobe; and one group in the dorsal protocerebrum (PDFD). Three out of four sPDFMe can be detected during the first hour of larval development, but the fourth sPDFMe is observed in the larva only from 48 hours after hatching, along with five lPDFMe neurons, seen first as two subgroups, and three out of four PDFD neurons. During postembryonic development these neurons show changes in their structure and immunoreactivity. New PDF neurons are observed during pupal development but these neurons mostly do not survive into adulthood. In the adult fly's brain, the PDF neurons have also been examined in double-labelled preparations made with a second antibody directed against the product of one of several clock genes: period (per), timeless (tim), or cryptochrome (cry). Among them, only immunoreactivity to CRY-like protein has been detected in the brain of M. domestica and has shown a daily rhythm in its concentration, as examined immunocytochemically. CRY was co-localized with PDF in the sPDFMe of the housefly's brain fixed during the day. The possibility that the sPDFMe neurons are the housefly's clock neurons is discussed.

Anatomy and functions of brain neurosecretory cells in diptera

In the larval brain of dipteran insects, there are two medial and three lateral groups of neurons innervating the ring gland. One lateral group extends fibers to the corpus allatum. After metamorphosis, a large cluster of the medial group in the pars intercerebralis and two lateral groups in the pars lateralis innervate the retrocerebral complex and some neurons from the lateral group and a few from the medial group extend fibers to the corpus allatum in the adults. Neuropeptides such as insulin-like peptides, FMRFamide related peptides, Locusta-diuretic hormone, beta-pigment dispersing hormone, Manduca sexta-allatostatin, ovary ecdysteroidogenic hormone, and proctolin have been immunocytochemically revealed in medial groups in the pars intercerebralis, and FMRFamide related peptides, beta-pigment dispersing hormone, corazonin, and M. sexta-allatostatin in lateral groups in the pars lateralis of dipteran brains. In mosquitoes after the blood meal, ovary ecdysteroidogenic hormone from 2-3 pairs of medial neurosecretory cells is released at the corpus cardiacum to stimulate the ovaries to secrete ecdysteroid to cause ovarian development. In addition to ovarian development, removal and implantation experiments have shown that neurosecretory cells in the pars intercerebralis and pars lateralis are involved in control of reproductive diapause, cuticular tanning, sugar metabolism, and diures.

Role of neurosecretory cells in the photoperiodic induction of pupal diapause of the tobacco hornworm Manduca sexta

In the tobacco hornworm, Manduca sexta, pupal diapause can be induced by exposure of fifth-instar larvae to a short-day photoperiod. We studied the effect of surgical ablation of tissues containing the neurosecretory cells of the brain of fifth-instar larvae on the photoperiodic induction of pupal diapause. At the end of the experiments, we immunostained the neurosecretory cells to determine the success of the ablations. Under long-day conditions (LD 16:8 at 22 degrees C), all intact larvae, most of the sham-operated larvae, and control-operated larvae developed into nondiapausing pupae. Under short-day conditions (LD 10:14 at 22 degrees C), most intact, sham-operated, and control-operated larvae developed into diapausing pupae. Removal of type-II cells did not interfere with the photoperiodic response. Under long-day conditions, elimination of type-Ia(1) cells did not affect the incidence of nondiapausing pupae. When type-Ia(1) cells were removed under short-day conditions, however, the incidence of nondiapausing pupae was higher (51%, n = 41) than that of the intact (16%, n = 75), sham-operated (24%, n = 88), control-operated larvae (5%, n = 40), and larvae with type-II cells removed (11%, n = 27). Thus, removal of type-Ia(1) cells can impede induction of diapause. These results indicate that the type-Ia(1) neurosecretory cells have an important role in the induction of pupal diapause.

Genetics and molecular biology of rhythms in Drosophila and other insects

Application of generic variants (Sections II-IV, VI, and IX) and molecular manipulations of rhythm-related genes (Sections V-X) have been used extensively to investigate features of insect chronobiology that might not have been experimentally accessible otherwise. Most such tests of mutants and molecular-genetic xperiments have been performed in Drosophila melanogaster. Results from applying visual-system variants have revealed that environmental inputs to the circadian clock in adult flies are mediated by external photoreceptive structures (Section II) and also by direct light reception chat occurs in certain brain neurons (Section IX). The relevant light-absorbing molecuLes are rhodopsins and "blue-receptive" cryptochrome (Sections II and IX). Variations in temperature are another clock input (Section IV), as has been analyzed in part by use of molecular techniques and transgenes involving factors functioning near the heart of the circadian clock (Section VIII). At that location within the fly's chronobiological system, approximately a half-dozen-perhaps up to as many as 10-clock genes encode functions that act and interact to form the circadian pacemaker (Sections III and V). This entity functions in part by transcriptional control of certain clock genes' expressions, which result in the production of key proteins that feed back negatively to regulate their own mRNA production. This occurs in part by interactions of such proteins with others that function as transcriptional activators (Section V). The implied feedback loop operates such that there are daily variations in the abundances of products put out by about one-half of the core clock genes. Thus, the normal expression of these genes defines circadian rhythms of their own, paralleling the effects of mutations at the corresponding genetic loci (Section III), which are to disrupt or apparently eliminate clock functioning. The fluctuations in the abundance of gene products are controlled transciptionally and posttranscriptionally. These clock mechanisms are being analyzed in ways that are increasingly complex and occasionally obscure; not all panels of this picture are comprehensive or clear, including problems revolving round the biological meaning or a given features of all this molecular cycling (Section V). Among the complexities and puzzles that have recently arisen, phenomena that stand out are posttranslational modifications of certain proteins that are circadianly regulated and regulating; these biochemical events form an ancillary component of the clock mechanism, as revealed in part by genetic identification of Factors (Section III) that turned out to encode protein kinases whose substrates include other pacemaking polypeptides (Section V). Outputs from insect circadian clocks have been long defined on formalistic and in some cases concrete criteria, related to revealed rhythms such as periodic eclosion and daily fluctuations of locomotion (Sections II and III). Based on the reasoning that if clock genes can regulate circadian cyclings of their own products, they can do the same for genes that function along output pathways; thus clock-regulated genes have been identified in part by virtue of their products' oscillations (Section X). Those studied most intensively have their expression influenced by circadian-pacemaker mutations. The clock-regulated genes discovered on molecular criteria have in some instances been analyzed further in their mutant forms and found to affect certain features of overt whole-organismal rhythmicity (Sections IV and X). Insect chronogenetics touches in part on naturally occurring gene variations that affect biological rhythmicity or (in some cases) have otherwise informed investigators about certain features of the organism's rhythm system (Section VII). Such animals include at least a dozen insect species other than D. melanogaster in which rhythm variants have been encountered (although usually not looked for systematically). The chronobiological "system" in the fruit fly might better be graced with a plural appellation because there is a myriad of temporally related phenomena that have come under the sway of one kind of putative rhythm variant or the other (Section IV). These phenotypes, which range well beyond the bedrock eclosion and locomotor circadian rhythms, unfortunately lead to the creation of a laundry list of underanalyzed or occult phenomena that may or may not be inherently real, whether or not they might be meaningfully defective under the influence of a given chronogenetic variant. However, such mutants seem to lend themselves to the interrogation of a wide variety of time-based attributes-those that fall within the experimental confines of conventionally appreciated circadian rhythms (Sections II, III, VI, and X); and others that consist of 24-hr or nondaily cycles defined by many kinds of biological, physiological, or biochemical parameters (Section IV).

Distribution of PER protein, pigment-dispersing hormone, prothoracicotropic hormone, and eclosion hormone in the cephalic nervous system of insects

Investigations performed on adult insects revealed that putative components of the central pacemaker, the protein Period (PER) and the pigment-dispersing hormone (PDH), are immunocytochemically detectable in discrete sets of brain neurons throughout the class of Insecta, represented by a bristletail, mayfly, damselfly, 2 locust species, stonefly, 2 bug species, goldsmith beetle, caddisfly, honeybee, and 2 blowfly species. The PER-positive cells are localized in the frontal protocerebrum and in most species also in the optic lobes, which are their only location in damselfly and goldsmith beetle. Additional PER-positive cells occur in a few species either in the deuto- and tritocerebrum or in the suboesophageal ganglion. The PER staining was always confined to the cytoplasm. The PDH immunoreactivity consistently occurs in a cluster of perikarya located frontoventrally at the proximal edge of the medulla. The mayfly and both locust species possess additional PDH neurons in 2 posterior cell clusters at the proximal edge of the medulla, and mayfly, waterstrider, and 1 of the blowfly species in the central brain. PDH-positive fibers form a fanlike arrangement over the frontal side of the medulla. Two or just 1 bundle of PDH-positive fibers run from the optic lobe to the protocerebrum, with collaterals passing over to the contralateral optic lobe. Antisera to the prothoracicotropic (PTTH) and the eclosion (EH) hormones, which in some insects regulate the molting and ecdysis rhythms, respectively, typically react with a few neurons in the frontal protocerebrum. However, the PTTH-positive neurons of the mayfly and the damselfly and the EH-positive neurons of the caddisfly are located in the suboesophageal ganglion. No PTTH-like antigen was detected in locusts, and no EH-like antigens were detected in the damselfly, stonefly, locusts, and the honeybee. There are no signs of co-localization of the PER-, PDH-, PTTH-, and EH-like antigens in identical neurons.

Highly conserved Drosophila ananassae timeless gene functions as a clock component in Drosophila melanogaster

The behavior and physiology of Drosophila are subject to rhythms that are controlled by the circadian clock genes, period, timeless, clock and cycle, all of which are thought to participate in central pacemaker control. The molecular mechanism of rhythm in Drosophila has been studied in detail. However, rhythm and clock genes have mostly been analyzed in Drosophila melanogaster. To confirm whether the tim gene exists and works as a clock component in other Drosophila species, we cloned a tim homolog from Drosophila ananassae that shared 85.9% similarity with Drosophila melanogaster tim at the amino acid level. In addition, the PER interaction domains and NLS were highly conserved. Introduction of the D. ananassae tim homolog rescued the rhythm of the locomotor activity of about 44% of a population of D. melanogaster tim(01) flies. At the molecular level, hs-tim introduced not only TIM but PER oscillation in transgenic flies. These results indicate that the tim gene in D. ananassae functions as a component of the circadian clock in D. melanogaster.

The period gene and allochronic reproductive isolation in Bactrocera cucurbitae

Clock genes that pleiotropically control circadian rhythm and the time of mating may cause allochronic reproductive isolation in the melon fly Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Flies with a shorter circadian period (ca. 22 h of locomotor activity rhythm) mated 5 h earlier in the day than those with a longer circadian period (ca. 30 h). Mate-choice tests demonstrated significant pre-mating isolation between populations with short and long circadian periods. Pre-mating isolation did not occur when the mating time was synchronized between the two populations by photoperiodic controls, indicating that reproductive isolation is due to variations in the time of mating and not any unidentified ethological difference between the two populations. We cloned the period (per) gene of B. cucurbitae that is homologous to the per gene in Drosophila. The relative level of per mRNA in the melon fly exhibited a robust daily fluctuation under light : dark conditions. The fluctuation of per expression under dark : dark conditions is closely correlated to the locomotor rhythm in B. cucurbitae. These results suggest that clock genes can cause reproductive isolation via the pleiotropic effect as a change of mating time.

The period gene of the German cockroach and its novel linking power between vertebrate and invertebrate

Circadian clock protein PERIOD (PER) is essential for the endogenous clockworks in diverse lineages within Metazoa, but the protein sequences, the clock protein interactions, and the photic responses are variant and different between vertebrate and invertebrate PER homologs. Here we identified the German cockroach PER homologs and found it could bridge the huge phylogenetic gap and make possible a more precise protein sequence comparison between vertebrate and invertebrate PER homologs. Seven blocks of conserved regions (c1-c7) interspersed within PER proteins were defined, and two new significant homologies were found in the upstream portion of c3 region and in the c7 region, respectively. In addition, we found all dipteran insects PER homologs lack the c7 region and its following amino acid residues. Our results not only reveal the homology and divergence, but also imply the constraint and plasticity of divergent PER proteins during the course of evolution. These findings lay a solid foundation for understanding the general and divergent properties of circadian clockworks in diverse lineages within Metazoa.

Evolutionary behavioral genetics in Drosophila

Behavioral genes have a special evolutionary interest because they are potentially involved in speciation and in many forms of adaptation. Dozens of loci affecting different aspects of behavior have been already identified and cloned in Drosophila. Some of these genes determine variation in such ethologically complex phenotypes as the male "love song" that is produced during courtship and the locomotor "sleep-wake" activity cycles that are controlled by the circadian clock. Although the evolutionary analysis of most behavioral genes in Drosophila is relatively new, it has already given important insights into the forces shaping the molecular variation at these loci and their functional consequences.

The period gene in two species of tephritid fruit fly differentiated by mating behaviour

The period gene is important for the generation and maintenance of biological rhythms. It served as an ideal candidate for the investigation of the mating time isolation between two sibling Queensland fruit fly species, Bactrocera tryoni and Bactrocera neohumeralis. We have isolated the homologues of the period gene in the two species, and show that their putative amino acid sequences are identical. No length polymorphism was detected in the Thr-Gly repeat region. per mRNA expression, assayed in light-dark diurnal conditions, displayed circadian oscillation in both the head and abdomen of B. tryoni and B. neohumeralis, with the same cycling phase. An alternatively spliced intron was identified in the 3' untranslated region. The effect of temperature on the splicing and mRNA expression was examined.