Tripping along the trail to the molecular mechanisms of biological clocks

Altered Grooming Cycles in Transgenic Drosophila

Head grooming in Drosophila consists of repeated sweeps of the legs across the head, comprising regular cycles. We used the GAL4-UAS system to study the effects of overexpressing shibirets1 and of Adar knockdown via RNA interference, on the period of head-grooming cycles in Drosophila. Overexpressing shibirets1 interferes with synaptic vesicle recycling and thus with cell communication, while Adar knockdown reduces RNA editing of neuronal transcripts for a large number of genes. All transgenic flies and their controls were tested at 22° to avoid temperature effects; in wild type, cycle frequency varied with temperature with a Q10 of 1.3. Two experiments were performed with transgenic shibirets1: (1) each fly was heat-shocked for 10 min at 30° immediately before testing at 22° and (2) flies were not heat shocked. In both experiments, cycle period was increased when shibirets1 was overexpressed in all neurons, but was not increased when shibirets1 was overexpressed in motoneurons alone. We hypothesize that grooming cycles in flies overexpressing shibirets1 are lengthened because of synaptic impairment in neural circuits that control head-grooming cycles. In flies with constitutive, pan-neuronal Adar knockdown, cycle period was more variable within individuals, but mean cycle period was not significantly altered. We conclude that RNA editing is essential for the maintenance of within-individual stereotypy of head-grooming cycles.

Cryptochrome 1 as a state variable of the circadian clockwork of the suprachiasmatic nucleus: Evidence from translational switching

The suprachiasmatic nucleus (SCN) of the hypothalamus is the principal clock driving circadian rhythms of physiology and behavior that adapt mammals to environmental cycles. Disruption of SCN-dependent rhythms compromises health, and so understanding SCN time keeping will inform management of diseases associated with modern lifestyles. SCN time keeping is a self-sustaining transcriptional/translational delayed feedback loop (TTFL), whereby negative regulators inhibit their own transcription. Formally, the SCN clock is viewed as a limit-cycle oscillator, the simplest being a trajectory of successive phases that progresses through two-dimensional space defined by two state variables mapped along their respective axes. The TTFL motif is readily compatible with limit-cycle models, and in Neurospora and Drosophila the negative regulators Frequency (FRQ) and Period (Per) have been identified as state variables of their respective TTFLs. The identity of state variables of the SCN oscillator is, however, less clear. Experimental identification of state variables requires reversible and temporally specific control over their abundance. Translational switching (ts) provides this, the expression of a protein of interest relying on the provision of a noncanonical amino acid. We show that the negative regulator Cryptochrome 1 (CRY1) fulfills criteria defining a state variable: ts-CRY1 dose-dependently and reversibly suppresses the baseline, amplitude, and period of SCN rhythms, and its acute withdrawal releases the TTFL to oscillate from a defined phase. Its effect also depends on its temporal pattern of expression, although constitutive ts-CRY1 sustained (albeit less stable) oscillations. We conclude that CRY1 has properties of a state variable, but may operate among several state variables within a multidimensional limit cycle.

Courtship rhythm in Nasonia vitripennis is affected by the clock gene period

The clock gene period (per) is a regulator of circadian rhythms but may also play a role in the regulation of ultradian rhythms, such as insect courtship. Males of the parasitoid wasp Nasonia vitripennis court females by performing series of head movements (‘head-nods’) and wing vibrations within repeated cycles. The pattern of cycle duration and head-nod number is species-specific and has a genetic basis. In this study, the possible involvement of per in regulating Nasonia courtship rhythms was investigated in a southern and northern European strain that differ in number and timing of courtship components. Knockdown of per via RNA interference (RNAi) resulted in a shortening of the circadian free running period (tau) in constant darkness (DD), and increased both the cycle duration and the number of head-nods per cycle in both strains. These results point at a role of per in the regulation of ultradian rhythms and male courtship behaviour of N. vitripennis and may contribute to resolving the controversy about the role of per in insect courtship behaviour.

Locomotor activity patterns in three spider species suggest relaxed selection on endogenous circadian period and novel features of chronotype

We examined the circadian rhythms of locomotor activity in three spider species in the Family Theridiidae under light-dark cycles and constant darkness. Contrary to previous findings in other organisms, we found exceptionally high variability in endogenous circadian period both within and among species. Many individuals exhibited circadian periods much lower (19-22 h) or much higher (26-30 h) than the archetypal circadian period. These results suggest relaxed selection on circadian period as well as an ability to succeed in nature despite a lack of circadian resonance with the 24-h daily cycle. Although displaying similar entrainment waveforms under light-dark cycles, there were remarkable differences among the three species with respect to levels of apparent masking and dispersion of activity under constant dark conditions. These behavioral differences suggest an aspect of chronotype adapted to the particular ecologies of the different species.

Spontaneous and transient hyperglycemia before sleep in a patient with glaucomatous blindness and diabetes: A case reprt

RATIONALE

The peak of blood glucose was during 9 PM to 3 AM. There is a stable, spontaneous and short-term abnormal increase of blood glucose. The pathophysiological mechanism is unknown. It is speculated that the cause might be the imbalance of the glucose-regulating hormone that is caused by the disorder of the biological clock system.

PATIENT CONCERNS

The case was a 73-year old man with bilateral glaucoma (only mild light perception) and was hospitalized to establish a viable hypoglycemic plan. He received 4 shots of insulin enhancement, oral meditation, pre-mixed insulin treatment during the 22 days. However, his blood glucose had been spontaneously increased from 9 PM to 3 AM which was the highest of the day, and then resumed by itself. Insulin intervention was effective.

DIAGNOSIS

Glaucomatous blindness and diabetes, spontaneous and transient hyperglycemia before sleep.

INTERVENTIONS

We used insulin aspart 3u when we found hyperglycemia three times at 9 PM and it was effective. Without intervention, blood sugar will automatically improve in the morning.

OUTCOMES

During the late night and early morning, there is a stable, spontaneous and short-term transit abnormal increase in blood glucose, which suggests the complexity of blood glucose adjustment.

LESSONS

Due to the case specialty, we could not do the systematic review of the study. However, it improves the awareness of the abnormal periodically increase of blood glucose during the special periods, and provides with a reference for clinical research of dawn and dusk phenomenon. Multi-point blood glucose monitoring or dynamic blood glucose monitoring throughout the day is of great significance for the detection of special types of hyperglycemia.

The Circadian Clock of the Ant Camponotus floridanus Is Localized in Dorsal and Lateral Neurons of the Brain

The circadian clock of social insects has become a focal point of interest for research, as social insects show complex forms of timed behavior and organization within their colonies. These behaviors include brood care, nest maintenance, foraging, swarming, defense, and many other tasks, of which several require social synchronization and accurate timing. Ants of the genus Camponotus have been shown to display a variety of daily timed behaviors such as the emergence of males from the nest, foraging, and relocation of brood. Nevertheless, circadian rhythms of isolated individuals have been studied in few ant species, and the circadian clock network in the brain that governs such behaviors remains completely uncharacterized. Here we show that isolated minor workers of Camponotus floridanus exhibit temperature overcompensated free-running locomotor activity rhythms under constant darkness. Under light-dark cycles, most animals are active during day and night, with a slight preference for the night. On the neurobiological level, we show that distinct cell groups in the lateral and dorsal brain of minor workers of C. floridanus are immunostained with an antibody against the clock protein Period (PER) and a lateral group additionally with an antibody against the neuropeptide pigment-dispersing factor (PDF). PER abundance oscillates in a daily manner, and PDF-positive neurites invade most parts of the brain, suggesting that the PER/PDF-positive neurons are bona fide clock neurons that transfer rhythmic signals into the relevant brain areas controlling rhythmic behavior.

REVIEW ■ : The Suprachiasmatic Nucleus: A Circadian Oscillator

The suprachiasmatic nucleus (SCN) is considered to be a circadian oscillator that regulates a set of phys iological aspects of behavior, including sleep-wakefulness and hormone release in mammalian species. In this review, we describe recent research that has begun to reveal the functional organization of the SCN. The SCN, which consists of a bilateral pair of tiny nuclei located just above the optic chiasm, contains several kinds of peptidergic neurons, but vasoactive intestinal peptide (VIP), arginine vasopressin (AVP), and somatostatin (SOM) neurons are the main components. VIP neurons and AVP neurons show distinctly different locations in the SCN; the former are found in the ventrolateral portion, whereas the latter are localized in the dorsomedial portion. VIP neurons receive all neuronal inputs from other regions of the CNS, such as those evoked by photic stimulation via the retinal ganglion cells and those relayed by 5HT inner vation from the raphe nuclei. VIP neurons relay their information to other kinds of neurons in the SCN, such as AVP and SOM neurons. VIP neurons, thus, may play a significant role in entrainment of circadian rhythm. VIP, AVP, SOM, and their mRNAs show rhythmic fluctuations that are predicted by this model; VIP and its mRNA show diurnal variation under the influence of photic stimulation, whereas AVP, SOM, and their mRNAs show endogenous rhythms. Immediate early genes (lEGs), such as c-fos mRNA, are also expressed in VIP neurons in the SCN, and IEG expression in the cells appears to be modified by photic stimuli. Together with transplantation studies showing that exogenous SCN tissue tends to restore circadian rhythm in arrhythmic animals, these results are beginning to clarify the function of the SCN in setting, maintaining, and resetting the biological clock. NEUROSCIENTIST 3:215-225, 1997

Function of wheat phosphate transporter gene TaPHT2;1 in Pi translocation and plant growth regulation under replete and limited Pi supply conditions

Several phosphate transporters (PTs) that belong to the Pht2 family have been released in bioinformatics databases, but only a few members of this family have been functionally characterized. In this study, we found that wheat TaPHT2;1 shared high identity with a subset of Pht2 in diverse plants. Expression analysis revealed that TaPHT2;1 was strongly expressed in the leaves, was up-regulated by low Pi stress, and exhibited a circadian rhythmic expression pattern. TaPHT2;1-green fluorescent protein fusions in the leaves of tobacco and wheat were specifically detected in the chloroplast envelop. TaPHT2;1 complemented the Pi transporter activities in a yeast mutant with a defect in Pi uptake. Knockdown expression of TaPHT2;1 significantly reduced Pi concentration in the chloroplast under sufficient (2 mM Pi) and deficient Pi (100 μM Pi) conditions, suggesting that TaPHT2;1 is crucial in the mediation of Pi translocation from the cytosol to the chloroplast. The down-regulated expression of TaPHT2;1 resulted in reduced photosynthetic capacities, total P contents, and accumulated P amounts in plants under sufficient and deficient Pi conditions, eventually leading to worse plant growth phenotypes. The TaPHT2;1 knockdown plants exhibited pronounced decrease in accumulated phosphorus in sufficient and deficient Pi conditions, suggesting that TaPHT2;1 is an important factor to associate with a distinct P signaling that up-regulates other PT members to control Pi acquisition and translocation within plants. Therefore, TaPHT2;1 is a key member of the Pht2 family involved in Pi translocation, and that it can function in the improvement of phosphorus usage efficiency in wheat.

Cloning, tissue expression pattern and daily rhythms of Period1, Period2, and Clock transcripts in the flatfish Senegalese sole, Solea senegalensis

An extensive network of endogenous oscillators governs vertebrate circadian rhythmicity. At the molecular level, they are composed of a set of clock genes that participate in transcriptional-translational feedback loops to control their own expression and that of downstream output genes. These clocks are synchronized with the environment, although entrainment by external periodic cues remains little explored in fish. In this work, partial cDNA sequences of clock genes representing both positive (Clock) and negative (Period1, Period2) elements of the molecular feedback loops were obtained from the nocturnal flatfish Senegalese sole, a relevant species for aquaculture and chronobiology. All of the above genes exhibited high identities with their respective teleost clock genes, and Per-Arnt-Sim or basic helix-loop-helix binding domains were recognized in their primary structure. They showed a widespread distribution through the animal body and some of them displayed daily mRNA rhythms in central (retina, optic tectum, diencephalon, and cerebellum) and peripheral (liver) tissues. These rhythms were most robust in retina and liver, exhibiting marked Period1 and Clock daily oscillations in transcript levels as revealed by ANOVA and cosinor analysis. Interestingly, expression profiles were inverted in retina and optic tectum compared to liver. Such differences suggest the existence of tissue-dependent zeitgebers for clock gene expression in this species (i.e., light for retina and optic tectum and feeding time for liver). This study provides novel insight into the location of the molecular clocks (central vs. peripheral) and their different phasing and synchronization pathways, which contributes to better understand the teleost circadian systems and its plasticity.

The gliocentric hypothesis of the pathophysiology of the sudden infant death syndrome (SIDS)

The hypothesis is based on glial-neuronal interactions in the cardio-respiratory centre of the brainstem. Recently, it has been experimentally verified that glial cells, especially astrocytes, exert a modulatory function in the maintenance of homeostasis in this brain region. In addition, astrocytes may also control the rhythms of heartbeat and breathing in a pulsatile manner. Based on a model of the glial-neuronal-vascular interactions in the networks of the cardio-respiratory centre in the brainstem, possible impairments of glial function that may be responsible for the sudden infant death syndrome (SIDS) are proposed. Finally, general approaches for testing the hypothesis are outlined.

Unique Self-Sustaining Circadian Oscillators Within the Brain ofDrosophila melanogaster

In Drosophila circadian rhythms persist in constant darkness (DD). The small ventral Lateral Neurons (s-LNv) mainly control the behavioral circadian rhythm in consortium with the large ventral Lateral Neurons (l-LNv) and dorsal Lateral Neurons (LNd). It is believed that the molecular oscillations of clock genes are the source of this persistent behavior. Indeed the s-LNv, LNd, Dorsal Neurons (DN)-DN2 and DN3 displayed self-sustained molecular oscillations in DD both at RNA and protein levels, except the DN2 oscillates in anti-phase. In contrast, the l-LNv and DN1 displayed self-sustained oscillations at the RNA level, but protein oscillations quickly dampened. Having self-sustained and dampened molecular oscillators together in the DN groups suggested that they play different roles. However, all DN groups seemed to contribute together to the light-dark (LD) behavioral rhythm. The LD entrainment of LN oscillators is achieved through Rhodopsin (RH) and Cryptochrome (CRY). CRY's expression in all DN groups implicates also its role in LD entrainment of DN, like in DN1. However, mutations in cry and glass that did not inflict LD synchronization of the DN2, DN3 oscillator implicate the existence of a novel photoreceptor at least in DN3.

Circadian changes in Drosophila motor terminals

In Drosophila melanogaster, as in most other higher organisms, a circadian clock controls the rhythmic distribution of rest/sleep and locomotor activity. Here we report that the morphology of Drosophila flight neuromuscular terminals changes between day and night, with a rhythm in synaptic bouton size that continues in constant darkness, but is abolished during aging. Furthermore, arrhythmic mutations in the clock genes timeless and period also disrupt this circadian rhythm. Finally, these clock mutants also have an opposing effect on the nonrhythmic phenotype of neuronal branching, with tim mutants showing a dramatic hyperbranching morphology and per mutants having fewer branches than wild-type flies. These unexpected results reveal further circadian as well as nonclock related pleiotropic effects for these classic behavioral mutants.

Temperature-compensated chemical reactions

Circadian rhythms are daily oscillations in behaviors that persist in constant light/dark conditions with periods close to 24 h. A striking feature of these rhythms is that their periods remain fairly constant over a wide range of physiological temperatures, a feature called temperature compensation. Although circadian rhythms have been associated with periodic oscillations in mRNA and protein levels, the question of how to construct a network of chemical reactions that is temperature compensated remains unanswered. We discuss a general framework for building such a network.

Principles and problems revolving around rhythm-related genetic variants

Much of what is known about the regulation of circadian rhythms has stemmed from the induction, recognition, or manufacture of genetic variants. Such investigations have been especially salient in chronobiological analyses of Drosophila. Many starting points for elucidation of rhythmic processes operating in this insect entailed the isolation of mutants or the design of engineered gene modifications. Various features of the principles and practices associated with the genetic approach toward understanding clock functions, and chronobiologically related ones, are discussed from perspectives that are largely genetic as such, although intertwined with certain neurogenetic and molecular-genetic concerns when appropriate. Key themes in this treatment connect with the power and problems associated with multiply mutant forms of rhythm-related genes, with the opportunistic or problematical aspects of multigenic variants that are in play (sometimes surprisingly), and with a question as to how forceful chronogenetic inferences have been in terms of elucidating the mechanisms of circadian pacemaking.

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.

Molecular characterization and expression of the UV opsin in bumblebees: three ommatidial subtypes in the retina and a new photoreceptor organ in the lamina

Ultraviolet-sensitive photoreceptors have been shown to be important for a variety of visual tasks performed by bees, such as orientation, color and polarization vision, yet little is known about their spatial distribution in the compound eye or optic lobe. We cloned and sequenced a UV opsin mRNA transcript from Bombus impatiens head-specific cDNA and, using western blot analysis, detected an eye protein band of approximately 41 kDa, corresponding to the predicted molecular mass of the encoded opsin. We then characterized UV opsin expression in the retina, ocelli and brain using immunocytochemistry. In the main retina, we found three different ommatidial types with respect to the number of UV opsin-expressing photoreceptor cells, namely ommatidia containing two, one or no UV opsin-immunoreactive cells. We also observed UV opsin expression in the ocelli. These results indicate that the cloned opsin probably encodes the P350 nm pigment, which was previously characterized by physiological recordings. Surprisingly, in addition to expression in the retina and ocelli, we found opsin expression in different parts of the brain. UV opsin immunoreactivity was detected in the proximal rim of the lamina adjacent to the first optic chiasm, which is where studies in other insects have found expression of proteins involved in the circadian clock, period and cryptochrome. We also found UV opsin immunoreactivity in the core region of the antennal lobe glomeruli and different clusters of perikarya within the protocerebrum, indicating a putative function of these brain regions, together with the lamina organ, in the entrainment of circadian rhythms. In order to test for a possible overlap of clock protein and UV opsin spatial expression, we also examined the expression of the period protein in these regions.

Temperature Synchronization of the Drosophila Circadian Clock

BACKGROUND

Circadian clocks are synchronized by both light:dark cycles and by temperature fluctuations. Although it has long been known that temperature cycles can robustly entrain Drosophila locomotor rhythms, nothing is known about the molecular mechanisms involved.

RESULTS

We show here that temperature cycles induce synchronized behavioral rhythms and oscillations of the clock proteins PERIOD and TIMELESS in constant light, a situation that normally leads to molecular and behavioral arrhythmicity. We show that expression of the Drosophila clock gene period can be entrained by temperature cycles in cultured body parts and isolated brains. Further, we show that the phospholipase C encoded by the norpA gene contributes to thermal entrainment, suggesting that a receptor-coupled transduction cascade signals temperature changes to the circadian clock. We initiated the further genetic dissection of temperature-entrainment and isolated the novel Drosophila mutation nocte, which is defective in molecular and behavioral entrainment by temperature cycles but synchronizes normally to light:dark cycles.

CONCLUSIONS

We conclude that temperature synchronization of the circadian clock is a tissue-autonomous process that is able to override the arrhythmia-inducing effects of constant light. Our data suggest that it involves a cell-autonomous signal-transduction cascade from a thermal receptor to the circadian clock. This process includes the function of phospholipase C and the product specified by the novel mutation nocte.

FLR-4, a novel serine/threonine protein kinase, regulates defecation rhythm in Caenorhabditis elegans

The defecation behavior of the nematode Caenorhabditis elegans is controlled by a 45-s ultradian rhythm. An essential component of the clock that regulates the rhythm is the inositol trisphosphate receptor in the intestine, but other components remain to be discovered. Here, we show that the flr-4 gene, whose mutants exhibit very short defecation cycle periods, encodes a novel serine/threonine protein kinase with a carboxyl terminal hydrophobic region. The expression of functional flr-4::GFP was detected in the intestine, part of pharyngeal muscles and a pair of neurons, but expression of flr-4 in the intestine was sufficient for the wild-type phenotype. Furthermore, laser killing of the flr-4-expressing neurons did not change the defecation phenotypes of wild-type and flr-4 mutant animals. Temperature-shift experiments with a temperature-sensitive flr-4 mutant suggested that FLR-4 acts in a cell-functional rather than developmental aspect in the regulation of defecation rhythms. The function of FLR-4 was impaired by missense mutations in the kinase domain and near the hydrophobic region, where the latter allele seemed to be a weak antimorph. Thus, a novel protein kinase with a unique structural feature acts in the intestine to increase the length of defecation cycle periods.

Systems approaches to biological rhythms in Drosophila

The chronobiological system of Drosophila is considered from the perspective of rhythm-regulated genes. These factors are enumerated and discussed not so much in terms of how the gene products are thought to act on behalf of circadian-clock mechanisms, but with special emphasis on where these molecules are manufactured within the organism. Therefore, with respect to several such cell and tissue types in the fly head, what is the "systems meaning" of a given structure's function insofar as regulation of rest-activity cycles is concerned? (Systematic oscillation of daily behavior is the principal overt phenotype analyzed in studies of Drosophila chronobiology). In turn, how do the several separate sets of clock-gene-expressing cells interact--or in some cases act in parallel--such that intricacies of the fly's sleep-wake cycles are mediated? Studying Drosophila chrono-genetics as a system-based endeavor also encompasses the fact that rhythm-related genes generate their products in many tissues beyond neural ones and during all stages of the life cycle. What, then, is the meaning of these widespread gene-expression patterns? This question is addressed with regard to circadian rhythms outside the behavioral arena, by considering other kinds of temporally based behaviors, and by contemplating how broadly systemic expression of rhythm-related genes connects with even more pleiotropic features of Drosophila biology. Thus, chronobiologically connected factors functioning within this insect comprise an increasingly salient example of gene versatility--multi-faceted usages of, and complex interactions among, entities that set up an organism's overall wherewithal to form and function. A corollary is that studying Drosophila development and adult-fly actions, even when limited to analysis of rhythm-systems phenomena, involves many of the animal's tissues and phenotypic capacities. It follows that such chronobiological experiments are technically demanding, including the necessity for investigators to possess wide-ranging expertise. Therefore, this chapter includes several different kinds of Methods set-asides. These techniques primers necessarily lack comprehensiveness, but they include certain discursive passages about why a given method can or should be applied and concerning real-world applicability of the pertinent rhythm-related technologies.

E pluribus unum, ex uno plura: quantitative and single-gene perspectives on the study of behavior

Genetic studies of behavior have traditionally come in two flavors: quantitative genetic studies of natural variants and single-gene studies of induced mutants. Each employed different techniques and methods of analysis toward the common, ultimate goal of understanding how genes influence behavior. With the advent of new genomic technologies, and also the realization that mechanisms underlying behavior involve a considerable degree of complex gene interaction, the traditionally separate strands of behavior genetics are merging into a single, synthetic strategy.

A portrait of locomotor behaviour in Drosophila determined by a video-tracking paradigm

This paper presents a detailed characterisation of locomotor behaviour of a single Drosophila fly freely walking in a small square arena. Locomotor activity is monitored by a video-tracking paradigm. Multiple parameters are extracted to construct the portrait of locomotor activity: the total distance moved, the number of episodes of activity and inactivity, the duration of activity, and the mean walking speed. To initiate a quantification of the fly's spatial walking movements, the number of passages in a virtual centre zone has also been determined. Moreover, to reveal the trajectory, as an index of fly's navigation ability, the turning angle, the angular velocity and the meander have been measured. Finally, we show that the number of episodes of inactivity as function of their duration follows a power law, while its counterpart, the episodes of activity does not, suggesting that the overall pattern of locomotor activity adheres to a fractal-like structure. Remarkably, the majority of these parameters are sexually dimorphic. This fine description of locomotor activity represents a new tool which will facilitate the study of the role of the different brain structures in the organisation of locomotor activity and the localisation of the fly's central pattern generator for locomotion and its motivational control.

Male courtship song in circadian rhythm mutants of Bactrocera cucurbitae (Tephritidae: Diptera)

Pulse train intervals (PTI) of courtship song were differentiated between circadian clock mutants of the melon fly, Bactrocera cucurbitae (Coquillett) (Tephritidae: Diptera). We analysed the male mating song of B. cucurbitae flies of two mutant strains that differed in circadian locomotor rhythm by a LabVIEW programming system. Flies with a short circadian rhythm (S-strain) had shorter PTI than those with a long circadian rhythm (L-strain) in the two age groups tested, young and old. Young flies showed longer PTI than old flies, but no interaction between strain and age was found in PTI. There was a significant interaction between strain and age for pulse train duration (PTD), whereas no stable difference was found in PTD between S- and L-strains. These results suggest a positive correlation between the length of the circadian locomotor rhythm and PTI of courtship song sounds in B. cucurbitae.

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.

Locomotor activity: a complex behavioural trait to unravel

Locomotor activity in Drosophila, as in other organisms, is an important trait since it is at the basis of almost all behaviours. Indeed, the locomotor centre is implicated in all complex behaviours consisting of a change in the position of the animal with respect to its environment. Despite its importance, locomotor activity itself has received sparse attention for the following two reasons: first, until recently, the study of locomotor activity has lacked a well automated and standardised paradigm which is necessary for a detailed description. Second, locomotor activity is complicated by many factors (genetic, feeding, temperature), and as such is rather difficult to study. With recent technological developments, locomotor activity is now more accessible to automated paradigms. These have permitted us to reveal that locomotor activity is a very complex and rich behaviour that follows strict rules, harbours an organised (fractal-like) structure, and consequently might adhere to highly organised neurophysiological processes. Undoubtedly, locomotor activity has now reached a scientific maturity that allows it to be studied with the panoply of neuroethological approaches, in particular genetic, to unravel its mechanisms and neural circuitry. Consequently, we propose that locomotor activity can now represent a relevant biomarker to study various model diseases such as addiction, Parkinson, Alzheimer, Huntington, and diabetes.

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).

The self-composing brain: towards a glial-neuronal brain theory

A brain model is proposed which describes its structural organization and the related functions as compartments organized in time and space. On a molecular level the negative feedback loops of clock-controlled genes are interpreted as compartments. This spatio-temporal operational principle may also work on the cellular level as glial-neuronal interactions, wherein glia have a spatio-temporal boundary setting function. The synchronization of the multi-compartmental operations of the brain is compared to the harmonization in a symphony and appears as an integrated behavior of the whole organism, defined as modes of behavior. For explanation of the principle of harmonization, an example from Schubert's Symphony No. 8 has been chosen. While harmonization refers to the synchronization of diverse systems, it seems appropriate to select the brain of a composer and the structure of musical composition as a paradigm towards a glial-neuronal brain theory. Finally, some limitations of experimental brain research are discussed and robotics are proposed as a promising alternative.

Targeted expression of tetanus toxin: a new tool to study the neurobiology of behavior

Over the past few decades, the explosion of molecular genetic knowledge, particularly in the fruit fly Drosophila melanogaster, has led to the identification of a large number of genes, which, when mutated, directly or indirectly affect fly behavior. Beyond the genetic and molecular characterization of genes and their associated molecular pathways, recent advances in molecular genetics also have allowed the development of new tools dedicated more directly to the dissection of the neural bases for various behaviors. In particular, the conjunction of the development of two techniques--the enhancer-trap detection system and the targeted gene expression system, based on the yeast GAL4 transcription factor--has led to the development of the binary enhancer-trap P[GAL4] expression system, which allows the selective activation of any cloned gene in a wide variety of tissue- and cell-specific patterns. Thus, this development, in addition to allowing the anatomical characterization of neuronal circuitry, also allows, via the expression of tetanus toxin light chain (known to specifically block synaptic transmission), an investigation of the role of specific neurons in certain behaviors. Using this system of "toxigenetics," several forms of behavior--from those mediated by sensory systems, such as olfaction, mechanoreception, and vision, to those mediated by higher brain function, such as learning, memory and locomotion--have been studied. These studies aim to map neuronal circuitry underlying specific behaviors and thereby unravel relevant neurophysiological mechanisms. The advantage of this approach is that it is noninvasive and permits the investigation of behavior in the free moving animal. We review a number of behavioral studies that have successfully employed this toxigenetic approach, and we hope to persuade the reader that transgenic tetanus toxin light chain is a useful and appropriate tool for the armory of neuroethologists.

Neuroanatomical studies of period gene expression in the hawkmoth, Manduca sexta

In the nervous system of the hawkmoth, Manduca sexta, cells expressing the period (per)gene were mapped by in situ hybridization and immunocytochemical methods. Digoxigenin-labeled riboprobes were transcribed from a 1-kb M. sexta per cDNA. Monoclonal anti-PER antibodies were raised to peptide antigens translated from both M. sexta and Drosophila melanogaster per cDNAs. These reagents revealed a widespread distribution of per gene products in M. sexta eyes, optic lobes, brains, and retrocerebral complexes. Labeling for per mRNA was prominent in photoreceptors and in glial cells throughout the brain, and in a cluster of 100-200 neurons adjacent to the accessory medulla of the optic lobes. Daily rhythms of per mRNA levels were detected only in glial cells. PER-like immunoreactivity was observed in nuclei of most neurons and glial cells and in many photoreceptor nuclei. Four neurosecretory cells in the pars lateralis of each brain hemisphere exhibited both nuclear and cytoplasmic staining with anti-PER antibodies. These cells were positively identified as Ia(1) neurosecretory cells that express corazonin immunoreactivity. Anti-corazonin labeled their projections in the brain and their neurohemal endings in the corpora cardiaca and corpora allata. Four pairs of PER-expressing neurosecretory cells previously described in the silkmoth, Anthereae pernyi, are likely to be homologous to these PER/corazonin-expressing Ia(1) cells of M. sexta. Other findings, such as widespread nuclear localization of M. sexta PER and rhythmic expression in glial cells, are reminiscent of the period gene of D. melanogaster, suggesting that some functions of per may be conserved in this lepidopteran species.

Loss of circadian clock function decreases reproductive fitness in males of Drosophila melanogaster

Circadian coordination of life functions is believed to contribute to an organism's fitness; however, such contributions have not been convincingly demonstrated in any animal. The most significant measure of fitness is the reproductive output of the individual and species. Here we examined the consequences of loss of clock function on reproductive fitness in Drosophila melanogaster with mutated period (per(0)), timeless (tim(0)), cycle (cyc(0)), and Clock (Clk(Jrk)) genes. Single mating among couples with clock-deficient phenotypes resulted in approximately 40% fewer progeny compared with wild-type flies, because of a decreased number of eggs laid and a greater rate of unfertilized eggs. Male contribution to this phenotype was demonstrated by a decrease in reproductive capacity among per(0) and tim(0) males mated with wild-type females. The important role of clock genes for reproductive fitness was confirmed by reversal of the low-fertility phenotype in flies with rescued per or tim function. Males lacking a functional clock showed a significant decline in the quantity of sperm released from the testes to seminal vesicles, and these tissues displayed rhythmic and autonomous expression of clock genes. By combining molecular and physiological approaches, we identified a circadian clock in the reproductive system and defined its role in the sperm release that promotes reproductive fitness in D. melanogaster.

Identification of circadian-clock-regulated enhancers and genes of Drosophila melanogaster by transposon mobilization and luciferase reporting of cyclical gene expression

A new way was developed to isolate rhythmically expressed genes in Drosophila by modifying the classic enhancer-trap method. We constructed a P element containing sequences that encode firefly luciferase as a reporter for oscillating gene expression in live flies. After generation of 1176 autosomal insertion lines, bioluminescence screening revealed rhythmic reporter-gene activity in 6% of these strains. Rhythmically fluctuating reporter levels were shown to be altered by clock mutations in genes that specify various circadian transcription factors or repressors. Intriguingly, rhythmic luminescence in certain lines was affected by only a subset of the pacemaker mutations. By isolating genes near 13 of the transposon insertions and determining their temporal mRNA expression pattern, we found that four of the loci adjacent to the trapped enhancers are rhythmically expressed. Therefore, this approach is suitable for identifying genetic loci regulated by the circadian clock. One transposon insert caused a mutation in the rhythmically expressed gene numb. This novel numb allele, as well as previously described ones, was shown to affect the fly's rhythm of locomotor activity. In addition to its known role in cell fate determination, this gene and the phosphotyrosine-binding protein it encodes are likely to function in the circadian system.

Implications of circadian gene expression in kidney, liver and the effects of fasting on pharmacogenomic studies

Pharmacogenomics offers the potential to define metabolic pathways and to provide increased knowledge of drug actions. We studied relative levels of gene expression in the rat using a microarray with 8448 rat UniGenes (1928 known genes, 6520 unknown ESTs) in the liver and kidney as a function of time of day and then of feeding regime, which are common variables in preclinical pharmacogenomic studies. We identified 597 genes, including several key metabolic pathways, whose relative expression levels are significantly affected by time of day: expression of some was further modified by feeding state. These would have sparked interest in a pharmacogenomic study. Our study demonstrates that two common variables in pharmacogenomic studies can have dramatic effects on gene expression. This study provides investigators with baseline information for both kidney and liver with respect to 'normal' changes in gene expression influenced by time of day and feeding state. It also identifies 18 new genes that should be investigated for a role in circadian rhythms in peripheral tissues.

Peripheral clocks and their role in circadian timing: insights from insects

Impressive advances have been made recently in our understanding of the molecular basis of the cell-autonomous circadian feedback loop; however, much less is known about the overall organization of the circadian systems. How many clocks tick in a multicellular animal, such as an insect, and what are their roles and the relationships between them? Most attempts to locate clock-containing tissues were based on the analysis of behavioural rhythms and identified brain-located timing centres in a variety of animals. Characterization of several essential clock genes and analysis of their expression patterns revealed that molecular components of the clock are active not only in the brain, but also in many peripheral organs of Drosophila and other insects as well as in vertebrates. Subsequent experiments have shown that isolated peripheral organs can maintain self-sustained and light sensitive cycling of clock genes in vitro. This, together with earlier demonstrations that physiological output rhythms persist in isolated organs and tissues, provide strong evidence for the existence of functionally autonomous local circadian clocks in insects and other animals. Circadian systems in complex animals may include many peripheral clocks with tissue-specific functions and a varying degree of autonomy, which seems to be correlated with their sensitivity to external entraining signals.

Behavioral rhythmicity, age, division of labor and period expression in the honey bee brain

Young adult honey bees work inside the beehive "nursing" brood around the clock with no circadian rhythms; older bees forage for nectar and pollen outside with strong circadian rhythms. Previous research has shown that the development of an endogenous rhythm of activity is also seen in the laboratory in a constant environment. Newly emerging bees maintained in isolation are typically arrhythmic during the first few days of adult life and develop strong circadian rhythms by about a few days of age. In addition, average daily levels of period (per) mRNA in the brain are higher in foragers or forager-age bees (> 21 days of age) relative to young nest bees (approximately 7 days of age). The authors used social manipulations to uncouple behavioral rhythmicity, age, and task to determine the relationship between these factors and per. There was no obligate link between average daily levels of per brain mRNA and either behavioral rhythmicity or age. There also were no differences in per brain mRNA levels between nurse bees and foragers in social environments that promote precocious or reversed behavioral development. Nurses and other hive-age bees can have high or low levels of per mRNA levels in the brain, depending on the social environment, while foragers and foraging-age bees always have high levels. These findings suggest a link between honey bee foraging behavior and per up-regulation. Results also suggest task-related differences in the amplitude of per mRNA oscillation in the brain, with foragers having larger diurnal fluctuation in per than nurses, regardless of age. Taken together, these results suggest that social factors may exert potent influences on the regulation of clock genes.

Localization of the clock controlling circadian rhythms in the first neuropile of the optic lobe in the housefly

The visual system of a fly expresses several circadian rhythms that have been detected in the photoreceptors of the compound eye and in the first neuropile, the lamina, of the underlying optic lobe. In the lamina, axons of two classes of interneuron, L1 and L2, exhibit cyclical size changes, swelling by day and shrinking by night. These rhythmic size changes may be generated by circadian oscillators located inside and/or outside the optic lobe. To localize such oscillators, we have examined changes in the axonal cross-sectional areas of L1 and L2 within the lamina of the housefly (Musca domestica) under conditions of 12 h of light and 12 h of darkness (LD12:12), constant darkness (DD) or continuous light (LL) 24 h after the medulla was severed from the rest of the brain. After the lesion, the axon size changes of L1 and L2 were maintained only in LD conditions, but were weaker than in control flies. In DD and LL conditions, they were eliminated. This indicates that circadian rhythms in the lamina of a fly are generated central to the lamina and medulla neuropiles of the optic lobe. Cyclical changes of light and darkness in LD conditions are still able, however, to induce a weak daily rhythm in the axon sizes of L1 and L2.

Does the difference in the timing of eclosion of the fruit fly Drosophila melanogaster reflect differences in the circadian organization?

The eclosion rhythm of a laboratory population of Drosophila melanogaster was studied under 12h light, 12h dark (LD 12:12) cycles. Although most of the flies were found to eclose just after "lights on" in LD 12:12, termed within gate (WG) flies, a few flies were found to eclose nearly 10h after peak eclosion, termed outside gate (OG) flies. The circadian parameters of the clocks controlling oviposition rhythms in the WG and the OG flies were estimated to understand the cause of such differences in the timing of eclosion. The distribution of the fraction of individual flies exhibiting single, multiple, and no significant period in the WG flies was significantly different from distribution in the OG flies. Compared to the WG flies, more OG flies were found to exhibit oviposition rhythm with multiple periodicity, whereas more WG flies exhibited an oviposition rhythm with a single significant period. The fraction of flies with arrhythmic oviposition was similar in both the WG and the OG flies. Free-running period tau in constant darkness (DD) and the phase angle difference psi in LD 12:12 for the oviposition rhythm of WG and OG flies were significantly different. These results suggest that the differences in the time of eclosion between the flies eclosing within the gate and outside the gate of eclosion are probably due to differences in the circadian system controlling eclosion, which is reflected by the differences in their oviposition rhythm.

Circadian photoreception in Drosophila: functions of cryptochrome in peripheral and central clocks

In Drosophila melanogaster, disruption of night by even short light exposures results in degradation of the clock protein TIMELESS (TIM), leading to shifts in the fly molecular and behavioral rhythms. Several lines of evidence indicate that light entrainment of the brain clock involves the blue-light photoreceptor cryptochrome (CRY). In cryptochrome-depleted Drosophila (cry(b)), the entrainment of the brain clock by short light pulses is impaired but the clock is still entrainable by light-dark cycles, probably due to light input from the visual system. Whether cryptochrome and visual transduction pathways play a role in entrainment of noninnervated, directly photosensitive peripheral clocks is not known and the subject of this study. The authors monitored levels of the clock protein TIM in the lateral neurons (LNs) of larval brains and in the renal Malpighian tubules (MTs) of flies mutant for the cryptochrome gene (cry(b)) and in mutants that lack signaling from the visual photopigments (norpA(P41)). In cry(b) flies, light applied during the dark period failed to induce degradation of TIM both in MTs and in LNs, yet attenuated cycling of TIM was observed in both tissues in LD. This cycling was abolished in LNs, but persisted in MTs, of norpA(P41);cry(b) double mutants. Furthermore, the activity of the tim gene in the MTs of cry(b) flies, reported by luciferase, seemed stimulated by lights-on and suppressed by lights-off, suggesting that the absence of functional cryptochrome uncovered an additional light-sensitive pathway synchronizing the expression of TIM in this tissue. In constant darkness, cycling of TIM was abolished in MTs; however, it persisted in LNs of cry(b) flies. The authors conclude that cryptochrome is involved in TIM-mediated entrainment of both central LN and peripheral MT clocks. Cryptochrome is also an indispensable component of the endogenous clock mechanism in the examined peripheral tissue, but not in the brain. Thus, although neural and epithelial cells share the core clock mechanism, some clock components and light-entrainment pathways appear to have tissue-specific roles.