A new mutation at the period locus of Drosophila melanogaster with some novel effects on circadian rhythms

Integration of photoperiodic and temperature cues by the circadian clock to regulate insect seasonal adaptations

Organisms adapt to unfavorable seasonal conditions to survive. These seasonal adaptations rely on the correct interpretation of environmental cues such as photoperiod, and temperature. Genetic studies in several organisms, including the genetic powerhouse Drosophila melanogaster, indicate that circadian clock components, such as period and timeless, are involved in photoperiodic-dependent seasonal adaptations, but our understanding of this process is far from complete. In particular, the role of temperature as a key factor to complement photoperiodic response is not well understood. The development of new sequencing technologies has proven extremely useful in understanding the plastic changes that the clock and other cellular components undergo in different environmental conditions, including changes in gene expression and alternative splicing. This article discusses the integration of photoperiod and temperature for seasonal biology as well as downstream molecular and cellular pathways involved in the regulation of physiological adaptations that occur with changing seasons. We focus our discussion on the current understanding of the involvement of the molecular clock and the circadian clock neuronal circuits in these adaptations in D. melanogaster.

Dietary acrylamide disrupts the functioning of the biological clock

Acrylamide (ACR) is a known carcinogen and neurotoxin. It is chronically consumed in carbohydrate-rich snacks processed at high temperatures. This calls for systematic research into the effects of ACR intake, best performed in an experimental model capable of detecting symptoms of its neurotoxicity at both high and low doses. Here, we study the influence of 10 µg/g (corresponding to the concentrations found in food products) and, for comparison, 60, 80 and 110 µg/g dietary ACR, on the fruit fly Drosophila melanogaster. We show that chronic administration of ACR affects lifespan, activity level and, most importantly, the daily and circadian pattern of locomotor activity of Drosophila. ACR-treated flies show well-defined and concentration-dependent symptoms of ACR neurotoxicity; a reduced anticipation of upcoming changes in light conditions and increased arrhythmicity in constant darkness. The results suggest that the rhythm-generating neural circuits of their circadian oscillator (biological clock) are sensitive to ACR even at low concentrations if the exposure time is sufficiently long. This makes the behavioural readout of the clock, the rhythm of locomotor activity, a useful tool for studying the adverse effects of ACR and probably other compounds.

CRUMB: a shiny-based app to analyze rhythmic feeding in Drosophila using the FLIC system

Rhythmic feeding activity has become an important research area for circadian biologists as it is now clear that metabolic input is critical for regulating circadian rhythms, and chrononutrition has been shown to promote health span. In contrast to locomotor activity rhythm, studies conducting high throughput analysis of Drosophila rhythmic food intake have been limited and few monitoring system options are available. One monitoring system, the Fly Liquid-Food Interaction Counter (FLIC) has become popular, but there is a lack of efficient analysis toolkits to facilitate scalability and ensure reproducibility by using unified parameters for data analysis. Here, we developed Circadian Rhythm Using Mealtime Behavior (CRUMB), a user-friendly Shiny app to analyze data collected using the FLIC system. CRUMB leverages the 'plotly' and 'DT' packages to enable interactive raw data review as well as the generation of easily manipulable graphs and data tables. We used the main features of the FLIC master code provided with the system to retrieve feeding events and provide a simplified pipeline to conduct circadian analysis. We also replaced the use of base functions in time-consuming processes such as 'rle' and 'read.csv' with faster versions available from other packages to optimize computing time. We expect CRUMB to facilitate analysis of feeding-fasting rhythm as a robust output of the circadian clock.

The Underlying Genetics of Drosophila Circadian Behaviors

Life is shaped by circadian clocks. This review focuses on how behavioral genetics in the fruit fly unveiled what is known today about circadian physiology. We will briefly summarize basic properties of the clock and focus on some clock-controlled behaviors to highlight how communication between central and peripheral oscillators defines their properties.

Daytime CLOCK Dephosphorylation Is Controlled by STRIPAK Complexes in Drosophila

In the Drosophila circadian oscillator, the CLOCK/CYCLE complex activates transcription of period (per) and timeless (tim) in the evening. PER and TIM proteins then repress CLOCK (CLK) activity during the night. The pace of the oscillator depends upon post-translational regulation that affects both positive and negative components of the transcriptional loop. CLK protein is highly phosphorylated and inactive in the morning, whereas hypophosphorylated active forms are present in the evening. How this critical dephosphorylation step is mediated is unclear. We show here that two components of the STRIPAK complex, the CKA regulatory subunit of the PP2A phosphatase and its interacting protein STRIP, promote CLK dephosphorylation during the daytime. In contrast, the WDB regulatory PP2A subunit stabilizes CLK without affecting its phosphorylation state. Inhibition of the PP2A catalytic subunit and CKA downregulation affect daytime CLK similarly, suggesting that STRIPAK complexes are the main PP2A players in producing transcriptionally active hypophosphorylated CLK.

Ultradian components in the locomotor activity rhythms of the genetically normal mouse, Mus musculus

Ultradian periodicities in physiological processes have been reported for a wide variety of organisms and may appear as bouts in locomotor activity. In some instances, this temporal organization can be related to some ethological strategy. In mice, however, ultradian rhythms have been reported largely in animals with circadian pacemakers disrupted either by genetic or surgical manipulation. Using analysis techniques capable of resolving periodicities in the ultradian range in the presence of strong diel periodicity, we found unequivocal evidence of ultradian rhythms in mice entrained to an light:dark cycle. We collected locomotor activity data of individuals from 11 genetically disparate strains of mice whose activity was recorded in 12 h:12 h L:D photoperiods for 3 days. Data were subjected to maximum entropy spectral analysis and autocorrelation, both before and after filtering to remove the 24-h periodicity. We found that every strain had a majority of individuals with strong ultradian rhythms ranging from ~3 to ~5 h. These periodicities were commonly visible in individual animals both in high-pass-filtered and in unfiltered data. Furthermore, when all raw data from a given strain were pooled to get a 24-h ensemble average across all animals and days, the rhythms continued to be discernable. We fitted Fourier series to these form estimates to model the frequency structure of each strain and found significant effects of strain and an interaction between period and strain indicating significant genetic variation for rhythmicity in the ultradian range. The techniques employed in this study should have wider use in a range of organisms and fields.

Influence of sex on sleep regulatory mechanisms

The ability of biological sex and sex-driven characteristics to alter sleep states may contribute to gender disparities in sleep disorders. Sex influences sleep-wake amount, the daily timing of the sleep-wake cycle, and the ability to restore sleep after extended wakefulness. Several lines of evidence suggest that in mammals, reproductive hormones are responsible for the effects of sex on sleep and may have organizational and activational influences on sleep regulatory mechanisms. In humans, exogenously administered estrogens and progestins generally enhance sleep amount and continuity, whereas androgens appear to have a positive impact on rapid eye movement (REM) sleep but disrupt sleep consolidation. In rodent studies, however, female reproductive hormones appear to enhance wakefulness, and male gonadal hormones reinforce sleep. Rodent studies have also revealed that neonatal exposure to reproductive hormones organizes adult sleep-wake architecture. This paper reviews how sex and reproductive hormones interact with circadian and homeostatic sleep regulatory mechanisms in humans and animal models. We examine the organizational and activational nature of these interactions and also review how these interactions change with advancing age. Finally, we discuss the potential for genetic sex to influence sleep states. It is our hope that a better understanding of the mechanisms through which sex influences sleep-wake states will lead to improvements in the design of studies that examine gender disparities in sleep-wake disorders.

Analyses for physiological and behavioral rhythmicity

Biological data that contain cycles require specialized statistical and analytical procedures. Techniques for analysis of time series from three types of systems are considered with the intent that the choice of examples is sufficiently broad that the processes described can be generalized to most other types of physiological or behavioral work. Behavioral circadian rhythms, acoustic signals in fly mating, and the Drosophila melanogaster cardiac system have been picked as typical in three broad areas. Worked examples from the fly cardiac system are studied in full detail throughout. The nature of the data streams and how they are acquired is first discussed with attention paid to ensuring satisfactory subsequent statistical treatment. Analysis in the time domain, namely simple and advanced plotting of data, autocorrelation analysis, and cross-correlation, is described. The search for periodicity is conducted through examples of analysis in the frequency domain, primarily spectral analysis. Nonstationary time series pose a particular problem, and wavelet analysis of Drosophila mating song is described in detail as an example. Conditioning of data to improve output with digital filters, Fourier filtering, and trend removal is described. Finally, two tests for noise levels and regularity are considered. All the nonproprietary software used throughout the work is available from the author free of charge and can be specifically tailored to the needs of individual systems.

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.

Circadian output, input, and intracellular oscillators: insights into the circadian systems of single cells

Circadian output comprises the business end of circadian systems in terms of adaptive significance. Work on Neurospora pioneered the molecular analysis of circadian output mechanisms, and insights from this model system continue to illuminate the pathways through which clocks control metabolism and overt rhythms. In Neurospora, virtually every strain examined in the context of rhythms bears the band allele that helps to clarify the overt rhythm in asexual development. Recent cloning of band showed it to be an allele of ras-1 and to affect a wide variety of signaling pathways yielding enhanced light responses and asexual development. These can be largely phenocopied by treatments that increase levels of intracellular reactive oxygen species. Although output is often unidirectional, analysis of the prd-4 gene provided an alternative paradigm in which output feeds back to affect input. prd-4 is an allele of checkpoint kinase-2 that bypasses the requirement for DNA damage to activate this kinase; FRQ is normally a substrate of activated Chk2, so in Chk2(PRD-4), FRQ is precociously phosphorylated and the clock cycles more quickly. Finally, recent adaptation of luciferase to fully function in Neurospora now allows the core FRQ/WCC feedback loop to be followed in real time under conditions where it no longer controls the overt rhythm in development. This ability can be used to describe the hierarchical relationships among FRQ-Less Oscillators (FLOs) and to see which are connected to the circadian system. The nitrate reductase oscillator appears to be connected, but the oscillator controlling the long-period rhythm elicited upon choline starvation appears completely disconnected from the circadian system; it can be seen to run with a very long noncompensated 60-120-hour period length under conditions where the circadian FRQ/WCC oscillator continues to cycle with a fully compensated circadian 22-hour period.

Genetic screens for clock mutants in Drosophila

The isolation and analysis of mutant flies (Drosophila melanogaster) with altered circadian rhythms have led to an understanding of circadian rhythms at the molecular level. This molecular mechanism elucidated in fruit flies is similar to the mechanism of the human circadian clock, which confers 24-h rhythmicity to our sleep/wake behavior, as well as to many other aspects of our cellular and organismal physiology. In fruit flies, genes can be mutated to abolish circadian rhythms (i.e., produce arrhythmia) or alter the period of the circadian rhythm; these genes encode key components of the circadian oscillator mechanism. Other mutations have identified components of the input pathways (by which light and temperature synchronize the circadian clock to environmental cycles) or output pathways (which connect the circadian oscillator to the physiological response). Mutations in genes are typically generated by chemical mutagenesis or mutagenesis with transposable elements. Flies with mutagenized chromosomes are processed in a series of genetic crosses, which allow specific chromosomes to be screened for semidominant mutations, recessive mutations, enhancer/suppressor mutations, or genes that can be overexpressed to alter circadian rhythms. Circadian phenotypes, which are assayed to identify mutants, include eclosion (emergence of the adult from the pupal case), locomotor activity (similar to human sleep?wake behavior), and circadian oscillations of gene expression. It is argued that screens for new circadian genes will continue to reveal novel components of the circadian mechanism.

Regulation of copulation duration by period and timeless in Drosophila melanogaster

The circadian clock involves several clock genes encoding interacting transcriptional regulators. Mutations in clock genes in Drosophila melanogaster, period (per), timeless (tim), Clock (Clk), and cycle (cyc), produce multiple phenotypes associated with physiology, behavior, development, and morphology. It is not clear whether these genes always work as clock components or may also act in some unknown pleiotropic fashion. We report here that per and tim are involved in a novel, male-specific phenotype that affects behavioral timing on the order of minutes. Males lacking per or tim copulate significantly longer than males with normal per or tim function, while females do not show this effect. No correlation between fertility and extended copulation duration was found. Several lines of evidence suggest that the time in copula (TIC) is not regulated by the known clock mechanism. First, the period of free-running clock oscillations does not appear to affect this phenotype. Second, constant light, which abolishes the clock function, does not alter TIC. Finally, mutations in the positively acting clock transcription factors, Clk and cyc, do not affect TIC. Our study extends the repertoire of behavioral functions involving per and tim genes and uncovers another time scale over which these genes may act.

Noncircadian regulation and function of clock genes period and timeless in oogenesis of Drosophila melanogaster

Circadian clock genes are ubiquitously expressed in the nervous system and peripheral tissues of complex animals. While clock genes in the brain are essential for behavioral rhythms, the physiological roles of these genes in the periphery are not well understood. Constitutive expression of the clock gene period was reported in the ovaries of Drosophila melanogaster; however, its molecular interactions and functional significance remained unknown. This study demonstrates that period (per) and timeless (tim) are involved in a novel noncircadian function in the ovary. PER and TIM are constantly expressed in the follicle cells enveloping young oocytes. Genetic evidence suggests that PER and TIM interact in these cells, yet they do not translocate to the nucleus. The levels of TIM and PER in the ovary are affected neither by light nor by the lack of clock-positive elements Clock (Clk) and cycle (cyc). Taken together, these data suggest that per and tim are regulated differently in follicle cells than in clock cells. Experimental evidence suggests that a novel fitness-related phenotype may be linked to noncircadian expression of clock genes in the ovaries. Mated females lacking either per or tim show nearly a 50% decline in progeny, and virgin females show a similar decline in the production of mature oocytes. Disruption of circadian mechanism by either the depletion of TIM via constant light treatment or continuous expression of PER via GAL4/UAS expression system has no adverse effect on the production of mature oocytes.

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).

Genetic analysis of the circadian system in Drosophila melanogaster and mammals

The fruit fly, Drosophila melanogaster, has been a grateful object for circadian rhythm researchers over several decades. Behavioral, genetic, and molecular studies helped to reveal the genetic bases of circadian time keeping and rhythmic behaviors. Contrary, mammalian rhythm research until recently was mainly restricted to descriptive and physiologic approaches. As in many other areas of research, the surprising similarity of basic biologic principles between the little fly and our own species, boosted the progress of unraveling the genetic foundation of mammalian clock mechanisms. Once more, not only the basic mechanisms, but also the molecules involved in establishing our circadian system are taken or adapted from the fly. This review will try to give a comparative overview about the two systems, highlighting similarities as well as specifics of both insect and murine clocks.

Giant neuron pathway neurophysiological activity in per(0) mutants of Drosophila melanogaster

In Drosophila melanogaster, the clock gene period (per) has a clearly defined role in the molecular machinery involved in generating free-running circadian rhythms. per mutations also influence rhythms in the Drosophila love song and in the ultradian timescale. The relationship between these two phenomena has so far escaped satisfactory explanation. Here we analyzed the neurophysiological activity of the giant fiber neural pathway in per(0) flies. Under constant light, and at relatively low stimulation frequencies (1-2 Hz), per(01) flies habituate significantly earlier than they do under 12 h light-dark cycles. The results suggest an involvement of per in phenomena of short-term neural plasticity.

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.

Signal analysis of behavioral and molecular cycles

BACKGROUND

Circadian clocks are biological oscillators that regulate molecular, physiological, and behavioral rhythms in a wide variety of organisms. While behavioral rhythms are typically monitored over many cycles, a similar approach to molecular rhythms was not possible until recently; the advent of real-time analysis using transgenic reporters now permits the observations of molecular rhythms over many cycles as well. This development suggests that new details about the relationship between molecular and behavioral rhythms may be revealed. Even so, behavioral and molecular rhythmicity have been analyzed using different methods, making such comparisons difficult to achieve. To address this shortcoming, among others, we developed a set of integrated analytical tools to unify the analysis of biological rhythms across modalities.

RESULTS

We demonstrate an adaptation of digital signal analysis that allows similar treatment of both behavioral and molecular data from our studies of Drosophila. For both types of data, we apply digital filters to extract and clarify details of interest; we employ methods of autocorrelation and spectral analysis to assess rhythmicity and estimate the period; we evaluate phase shifts using crosscorrelation; and we use circular statistics to extract information about phase.

CONCLUSION

Using data generated by our investigation of rhythms in Drosophila we demonstrate how a unique aggregation of analytical tools may be used to analyze and compare behavioral and molecular rhythms. These methods are shown to be versatile and will also be adaptable to further experiments, owing in part to the non-proprietary nature of the code we have developed.

The discovery of circadian clock genes and the use of similar strategies to discover unknown genes underlying complex behaviors and brain disorders

Over just the past few years, tremendous progress has been made in unraveling the molecular basis of the circadian clock in mammals. This success has been primarily due to an approach whereby mutations are induced randomly in the germ line and the offspring of the mutagenized animals are tested for abnormal circadian phenotype. Circadian clock genes have been discovered this way in both fruit flies and mice and it is now clear that most, if not all clock genes show homology between flies and mammals, including humans. This 'forward genetics' approach is a powerful tool for uncovering genes which underline complex behaviors and brain disorders. Even when a complex neural function involves many, many genes, mutating just one of these genes can have pronounced effects on the expressed behavior and can lead to the discovery of other genes, and their protein products, that interact directly or indirectly with the mutated gene.

Multiple amidated neuropeptides are required for normal circadian locomotor rhythms in Drosophila

In Drosophila, the amidated neuropeptide pigment dispersing factor (PDF) is expressed by the ventral subset of lateral pacemaker neurons and is required for circadian locomotor rhythms. Residual rhythmicity in pdf mutants likely reflects the activity of other neurotransmitters. We asked whether other neuropeptides contribute to such auxiliary mechanisms. We used the gal4/UAS system to create mosaics for the neuropeptide amidating enzyme PHM; amidation is a highly specific and widespread modification of secretory peptides in Drosophila. Three different gal4 drivers restricted PHM expression to different numbers of peptidergic neurons. These mosaics displayed aberrant locomotor rhythms to degrees that paralleled the apparent complexity of the spatial patterns. Certain PHM mosaics were less rhythmic than pdf mutants and as severe as per mutants. Additional gal4 elements were added to the weakly rhythmic PHM mosaics. Although adding pdf-gal4 provided only partial improvement, adding the widely expressed tim-gal4 largely restored rhythmicity. These results indicate that, in Drosophila, peptide amidation is required for neuropeptide regulation of behavior. They also support the hypothesis that multiple amidated neuropeptides, acting upstream, downstream, or in parallel to PDF, help organize daily locomotor rhythms.

Disruption of synaptic transmission or clock-gene-product oscillations in circadian pacemaker cells of Drosophila cause abnormal behavioral rhythms

To study the function of clock-gene-expressing neurons, the tetanus-toxin light chain (TeTxLC), which blocks chemical synaptic transmission, was expressed under the control of promoters of the clock genes period (per) and timeless (tim), each fused to GAL4-encoding sequences. Although TeTxLC did not affect cycling of a clock-gene product at the gross level, it disrupted the rhythmic behavior of adult Drosophila. In constant darkness, the proportion of rhythmic flies was reduced in flies expressing active TeTxLC compared to controls, including those expressing inactive toxin. The behavior of TeTxLC-expressing flies was less synchronized to light:dark cycles than that of controls. To determine which neurons are responsible for these effects on behavior, the toxin was also expressed in restricted subsets of per/tim-expressing, laterally located pacemaker neurons by expressing TeTxLC under the control of a driver in which GAL4-encoding sequences are fused to the promoter of the pigment dispersing factor (pdf) gene. pdf-gal4-driven TeTxLC expression had relatively little effect on behavioral rhythms, implying that per/tim neurons other than pdf-expressing lateral neurons participate in the generation of rhythmic behavior. In another set of experiments, period gene products were expressed under the control of per-gal4 or tim-gal4. This resulted in an increased level of PER protein in many brain cells and reduction of bioluminescence cycling reported by a per-luciferase transgene, especially in the case of per expression affected by tim-gal4. This indicates a disruption of the transcriptional feedback loop that is a part of the oscillatory mechanism underlying Drosophila's circadian rhythms. Consistent with this molecular defect, the proportion of rhythmic individuals in constant darkness was subnormal in flies expressing PER under the control of tim-gal4, and their behavior in light:dark cycles was abnormal.

The search for circadian clock and sleep genes

In recent years, there has been extraordinary progress in elucidating the molecular components of the mammalian circadian clock system. The discovery of circadian clock genes in lower organisms (such as fruit flies and fungi), which show many similarities with clock genes in mammals, together with advances in mouse molecular genetics have led to major new discoveries on the molecular and genetic basis of mammalian circadian rhythms. This article reviews both of these lines of research from an historical perspective and discusses how these lines have merged to provide unique insights into the molecular mechanisms of circadian function. The review also speculates on how the discovery of circadian clock genes may lead directly or indirectly to the discovery of mammalian sleep genes. The determination of the molecular mechanisms via which circadian clock genes (and their protein products) regulate the timing and the need for sleep, and the identification of new genes involved in sleep regulation, may produce new information on the genetic and molecular control of sleep which could ultimately lead to the development of new treatments for sleep disorders.

Involvement of the period gene in developmental time-memory: effect of the perShort mutation on phase shifts induced by light pulses delivered to Drosophila larvae

Phases of circadian locomotor activity rhythms of adult Drosophila reared in constant darkness have been shown to be set by a light stimulus delivered as early as the first-instar larval stage. This implies that a circadian clock functions continuously throughout postembryonic development. The clock genes period (per) and timeless (tim) are expressed cyclically in the larval central nervous system of Drosophila, and daily oscillations of per expression persist throughout metamorphosis in a group of cells, which gives rise to the pacemaker cells underlying locomotor activity rhythms of adults. Therefore, PER and TIM cyclings in these neurons may be responsible for the phenomenon of "larval time-memory." In the absence of any evidence for the involvement of these genes in such a developmental clock, and because circadian-pacemaker functions are underanalyzed in terms of the functions during development, the authors tested the time-memory of a fast-clock period mutant. They show that dark-reared perS mutant individuals as well as wild-type flies can be entrained as larvae and that a brief light pulse given to such entrained larvae can induce phase shifts in animals of either genotype. However, the direction and magnitude of phase shifts were different between wild type and perS, suggesting that a clock under the control of period gene participates in the regulation of developmental time-memory. The authors show that the relevant clock can be entrained by two light input pathways, one involving the phospholipase C encoded by the norpA gene, the other mediated by the blue-light receptor cryptochrome. Phase shifts of molecular oscillations during the larval stage were smaller than those measured by adult behavior, suggesting molecularly transient responses during development.

A pdf neuropeptide gene mutation and ablation of PDF neurons each cause severe abnormalities of behavioral circadian rhythms in Drosophila

The mechanisms by which circadian pacemaker systems transmit timing information to control behavior are largely unknown. Here, we define two critical features of that mechanism in Drosophila. We first describe animals mutant for the pdf neuropeptide gene, which is expressed by most of the candidate pacemakers (LNv neurons). Next, we describe animals in which pdf neurons were selectively ablated. Both sets of animals produced similar behavioral phenotypes. Both sets entrained to light, but both were largely arrhythmic under constant conditions. A minority of each pdf variant exhibited weak to moderate free-running rhythmicity. These results confirm the assignment of LNv neurons as the principal circadian pacemakers controlling daily locomotion in Drosophila. They also implicate PDF as the principal circadian transmitter.

Aging alters properties of the circadian pacemaker controlling the locomotor activity rhythm in males of Drosophila nasuta

Effects of aging on the circadian rhythm of locomotor activity in males of Drosophila nasuta were investigated. The adult life of males was divided in 1-3 stages according to spontaneous changes in free-running period tau in constant darkness (DD): stage 1, days 1-19; stage 2, days 20-36; stage 3, days 37-43. Stage 1 was characterized by a bimodal activity pattern with a short light-induced morning peak and a prolonged evening peak when the flies were entrained to light-dark cycles of 12 hours of light, 12 hours of darkness (LD 12:12). The morning peak had a phase angle difference psi m (psi, the time from lights on in LD 12:12 cycles to the onset of morning peak) of about 0.1 h, while psi e (psi of evening peak) was about 9 h at stage 1. The transient morning peak was curtailed at the end of stage 1. At stage 2, the psi e was about 10 h, and the activity end was delayed by an addition of about 3 h of activity in the scotophase. The changes in tau during DD free runs were determined in two groups of flies: flies reared in LD 12:12 and flies reared in DD. In both groups, tau increased from about 23 h at stage 1 to about 25 h at stage 2. Stage 3 was characterized by arrhythmicity associated with highest mean activity level (total number of passes/fly/day) in the entrained and both free-running groups. The mean activity level increased significantly from stage 1 to stage 3 in all three groups of flies.

The cryb mutation identifies cryptochrome as a circadian photoreceptor in Drosophila

A new rhythm mutation was isolated based on its elimination of per-controlled luciferase cycling. Levels of period or timeless clock gene products in the mutant are flat in daily light-dark cycles or constant darkness (although PER and TIM oscillate normally in temperature cycles). Consistent with the fact that light normally suppresses TIM, cryb is an apparent null mutation in a gene encoding Drosophila's version of the blue light receptor cryptochrome. Behaviorally, cryb exhibits poor synchronization to light-dark cycles in genetic backgrounds that cause external blindness or demand several hours of daily rhythm resets, and it shows no response to brief light pulses. cryb flies are rhythmic in constant darkness, correlating with robust PER and TIM cycling in certain pacemaker neurons.

The timSL mutant affects a restricted portion of the Drosophila melanogaster circadian cycle

The circadian rhythm genes period (per) and timeless (tim) are central to contemporary studies on Drosophila circadian rhythms. Mutations in these genes give rise to arrhythmic or period-altered phenotypes, and per and tim gene expression is under clock control. per and tim proteins (PER and TIM) also undergo circadian changes in level and phosphorylation state. The authors previously described a period-altering tim mutation, timSL, with allele-specific effects in different per backgrounds. This mutation also affected the TIM phosphorylation profile during the mid-late night. The authors show here that the single amino acid alteration in TIM-SL is indeed responsible for the phenotype, as a timSL transgene recapitulates the original mutant phenotype and shortens the period of perL flies by 3 h. The authors also show that this mutation has comparable effects in a light-dark cycle, as timSL also accelerates the activity offset during the mid-late night of perL flies. Importantly, timSL advances predominantly the mid-late night region of the perL phase response curve, consistent with the notion that this portion of the cycle is governed by unique rate-limiting steps. The authors propose that TIM and PER phosphorylation are normally rate determining during the mid-late night region of the circadian cycle.

A mutant Drosophila homolog of mammalian Clock disrupts circadian rhythms and transcription of period and timeless

We report the identification, characterization, and cloning of a novel Drosophila circadian rhythm gene, dClock. The mutant, initially called Jrk, manifests dominant effects: heterozygous flies have a period alteration and half are arrhythmic, while homozygous flies are uniformly arrhythmic. Furthermore, these flies express low levels of the two clock proteins, PERIOD (PER) and TIMELESS (TIM), due to low per and tim transcription. Mapping and cloning of the Jrk gene indicates that it encodes the Drosophila homolog of mouse Clock. The mutant phenotype results from a premature stop codon that eliminates much of the putative activation domain of this bHLH-PAS transcription factor, thus explaining the dominant features of Jrk. The remarkable sequence conservation strongly supports common clock components present in the common ancestor of Drosophila and mammals.

Molecular and behavioral analysis of four period mutants in Drosophila melanogaster encompassing extreme short, novel long, and unorthodox arrhythmic types

Of the mutationally defined rhythm genes in Drosophila melanogaster, period (per) has been studied the most. We have molecularly characterized three older per mutants-perT, perClk, and per04-along with a novel long-period one (perSLIH). Each mutant is the result of a single nucleotide change. perT, perClk, and perSLIH are accounted for by amino acid substitutions; per04 is altered at a splice site acceptor and causes aberrant splicing. perSLIH exhibits a long period of 27 hr in constant darkness and entrains to light/dark (L/D) cycles with a later-than-normal evening peak of locomotion. perSLIH males are more rhythmic than females. perSLIH's clock runs faster at higher temperatures and slower at lower ones, exhibiting a temperature-compensation defect opposite to that of perLong. The per-encoded protein (PER) in the perT mutant cycles in L/D with an earlier-than-normal peak; this peak in perSLIH is later than normal, and there was a slight difference in the PER timecourse of males vs. females. PER in per04 was undetectable. Two of these mutations, perSLIH and perClk, lie within regions of PER that have not been studied previously and may define important functional domains of this clock protein.

Temporal and spatial expression patterns of transgenes containing increasing amounts of the Drosophila clock gene period and a lacZ reporter: mapping elements of the PER protein involved in circadian cycling

Rhythmic oscillations of the PER protein, the product of the Drosophila period (per) gene, in brain neurons of the adult fly are strongly involved in the control of circadian rhythms. We analyzed temporal and spatial expression patterns of three per-reporter fusion genes, which share the same 4 kb regulatory upstream region but contain increasing amounts of per's coding region fused in frame to the bacterial lacZ gene. The fusion proteins contained either the N-terminal half (SG), the N-terminal-two-thirds (BG), or nearly all (XLG) of the PER protein. All constructs led to reporter signals only in the known per-expressing cell types within the anterior CNS and PNS. Whereas the staining intensity of SG files was constantly high at different Zeitgeber times, the in situ signals in BG and XLG files cycled with approximately 24 hr periodicity in the PER-expressing brain cells in wild-type and per01 loss of function files. Despite the rhythmic fusion-gene expression within the relevant neurons of per01 BG files, their locomotor activity in light/dark cycling conditions and in constant darkness was identical to that of per01 controls, uncoupling protein cycling from rhythmic behavior. The XLG construct restored weak behavioral rhythmicity to (otherwise) per01 files, indicating that the C-terminal third of PER (missing in BG) is necessary to fulfill the biological function of this clock protein.

Control of male sexual behavior and sexual orientation in Drosophila by the fruitless gene

Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 10(5) neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

per mRNA cycling is locked to lights-off under photoperiodic conditions that support circadian feedback loop function

Circadian fluctuations in per mRNA and protein are central to the operation of a negative feedback loop that is necessary for setting the free-running period and for entraining the circadian oscillator to light-dark cycles. In this study, per mRNA cycling and locomotor activity rhythms were measured under different light and dark cycling regimes to determine how photoperiods affect the molecular feedback loop and circadian behavior, respectively. These experiments reveal that per mRNA peaks in abundance 4 h after lights-off in photoperiods of < or = 16 h, that, phase shifts in per mRNA cycling and behavioral rhythmicity occur rapidly after flies are transferred from one photoperiod to another, and that photoperiods longer than 20 h abolish locomotor activity rhythms and leave per mRNA at a median constitutive level. These results indicate that the per feedback loop uses lights-off as a phase reference point and suggest (along with previous findings for per01 and tim01) that per mRNA cycling is not regulated via simple negative feedback from the per protein.

Tripping along the trail to the molecular mechanisms of biological clocks

Solving the mechanism of circadian clocks has become an important goal, in part because daily rhythms are running in such a wide variety of organisms, and contribute to many aspects of their well being. Systematic genetic approaches to studying 'the clock' were initiated in fruitflies more than 20 years ago as a novel means by which neural-pacemaking mysteries might be solved. Such chronogenetic investigations gained momentum when they spread to other species, and became molecular. However, the molecular studies were misleading, that is, until some elementary neuro-anatomical observations, involving the expression of a 'clock gene' in Drosophila, gave the experiments in this molecular-neurogenetic area of chronobiology a new direction. The initially neuro-descriptive studies led to the current investigations that involve negatively acting transcription factors and other clock molecules that are presumed to interact with them. In addition, new mutants and clones have been isolated in a timely manner. These mutations and molecules should permit chronogeneticists, working on a wide variety of organisms, to unravel further details of how the clock works, how environmental information finds its way to it, and how it sends information out into the organism's physiology, biochemistry and behavior.

Developmental and genetic mosaic analysis of Drosophila m-dy mutants: tissue foci for behavioral and morphogenetic defects

Mutants of the Drosophila miniature-dusky (m-dy) gene complex display morphogenetic phenotypes (miniature or dusky) caused by a change in the size and/or shape of the epidermal cells comprising the adult wing. In addition to a dusky phenotype, certain Andante-type mutants also exhibit lengthened circadian periods for two different behavioral rhythms. If the latter phenotype results from a direct effect on the circadian pacemaker, the Andante function should be required within the brain. In order to define the tissues that require the morphogenetic and behavioral functions, we have carried out a genetic mosaic analysis. This study demonstrates that normal wing morphogenesis is entirely dependent on the genotype of wing cells. Furthermore, temperature-shift experiments with a temperature-sensitive dy mutant indicate that the morphogenetic function is required during adult development, and after the cessation of wing epidermal cell proliferation. At this time in development, a columnar epithelium in the developing wing becomes flattened into the mature wing blade, and we postulate that the cell-size defect of m-dy mutants results from an alteration of this morphogenetic process. In contrast to the wing morphogenesis phenotype, the characterization of locomotor activity in mosaic adults revealed a strong correlation between the head genotype and the Andante circadian-period phenotype. This result indicates that neural tissues mediate the rhythm function. Thus, the behavioral and morphogenetic functions require gene expression in distinct tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

An ultrashort clock mutation at the period locus of Drosophila melanogaster that reveals some new features of the fly's circadian system

A rhythm mutant of Drosophila melanogaster was induced by chemical mutagenesis and isolated by testing for locomotor activity rhythms, which in the new variant had periods of approximately 16 hr. The sex-linked mutation responsible for this ultrashort period causes 20-hr rhythms when heterozygous with a normal X. This semidominance notwithstanding, the new mutation was revealed to be an allele of the period (per) gene by noncomplementation with per-null variants, in the sense that females heterozygous for perT (as the ultrafast-clock allele is called) and per- exhibited periods that were much shorter than in the case of perT/+. These tests also revealed in a clearer manner than in previous cases that two "doses" of a fast-clock per mutation lead to appreciably shorter periods than those exhibited by one-dose females whose other per allele is a loss-of-function variant. In light-dark cycles (LD 12:12), flies carrying perT in a genotypic condition leading to free-running periods that are 8 hr faster than normal nevertheless entrained, by phase-shifting that large number of hours each day; the evening peak of locomotor activity was, however, many hours earlier than normal. The use of a newly developed device for monitoring Drosophila eclosion automatically showed that perT exhibits a very marginal emergence rhythm at 25 degrees C, but periodicity of ca. 17-18 hr at 19 degrees. Staining of the per-encoded protein (PER) in sections of perT versus normal pharate adults revealed for the first time that the immunohistochemically detected signal cycles in its intensity in wild-type, in a manner that is similar to the PER rhythm previously demonstrated in adults. The staining cycle in pharate adults expressing perT differed from that of wild-type. Temperature compensation of the adult activity rhythm of perT was found to be faulty, in that periods became appreciably shorter as the flies were heated. However, the mutant exhibited a normal degree of period lengthening when its locomotor activity was monitored in the presence of heavy water. The perT mutation interacted with the long-period Andante allele of the dusky locus in a manner that was anomalous (in comparison to dyAnd interactions with per+ or another short-period per mutation). This and other unique features of perT are discussed from the standpoint of the new mutation's heuristic value, including that which may stimulate a deeper understanding of the period gene's action at the molecular level.

The GTS1 gene, which contains a Gly-Thr repeat, affects the timing of budding and cell size of the yeast Saccharomyces cerevisiae

A gene with an open reading frame encoding a protein of 417 amino acid residues with a Gly-Thr repeat was isolated from the yeast Saccharomyces cerevisiae by using synthetic oligonucleotides encoding three Gly-Thr dimers as probes. The deduced amino acid sequence showed partial homology to the clock-affecting gene, per, of Drosophila melanogaster in the regions including the GT repeat. The function of the gene, named GTS1, was examined by characterizing the phenotypes of transformants with different copy numbers of the GTS1 gene produced either by inactivating the GTS1 gene by gene disruption (TM delta gts1) or by transformation with multicopy plasmid pPER119 (TMpGTS1). They grew at similar rates during the exponential growth phase, but the lag phases were shorter for TM delta gts1 and longer for TMpGTS1 cells than that for the wild type. Analyses of their cell cycle parameters using synchronized cells revealed that the unbudding period changed as a function of gene dosage; that is, the periods of TM delta gts1 and TMpGTS1 were about 20% shorter and longer, respectively, than that of the wild-type. Another significant change in the transformants was detected in the distribution of the cell size. The mean cell volume of the TM delta gts1 cells in the unbudded period (single cells) was 27% smaller than that of single wild-type cells, whereas that of single TMpGTS1 cells was 48% larger. Furthermore, in the temperature-sensitive cdc4 mutant, the GTS1 gene affected the timing of budding at the restrictive temperature. Thus, the GTS1 gene product appears to modulate the timing of budding to obtain an appropriate cell size independent of the DNA replication cycle.

The GTS1 gene, which contains a Gly-Thr repeat, affects the timing of budding and cell size of the yeast Saccharomyces cerevisiae

A gene with an open reading frame encoding a protein of 417 amino acid residues with a Gly-Thr repeat was isolated from the yeast Saccharomyces cerevisiae by using synthetic oligonucleotides encoding three Gly-Thr dimers as probes. The deduced amino acid sequence showed partial homology to the clock-affecting gene, per, of Drosophila melanogaster in the regions including the GT repeat. The function of the gene, named GTS1, was examined by characterizing the phenotypes of transformants with different copy numbers of the GTS1 gene produced either by inactivating the GTS1 gene by gene disruption (TM delta gts1) or by transformation with multicopy plasmid pPER119 (TMpGTS1). They grew at similar rates during the exponential growth phase, but the lag phases were shorter for TM delta gts1 and longer for TMpGTS1 cells than that for the wild type. Analyses of their cell cycle parameters using synchronized cells revealed that the unbudding period changed as a function of gene dosage; that is, the periods of TM delta gts1 and TMpGTS1 were about 20% shorter and longer, respectively, than that of the wild-type. Another significant change in the transformants was detected in the distribution of the cell size. The mean cell volume of the TM delta gts1 cells in the unbudded period (single cells) was 27% smaller than that of single wild-type cells, whereas that of single TMpGTS1 cells was 48% larger. Furthermore, in the temperature-sensitive cdc4 mutant, the GTS1 gene affected the timing of budding at the restrictive temperature. Thus, the GTS1 gene product appears to modulate the timing of budding to obtain an appropriate cell size independent of the DNA replication cycle.

A promoterless period gene mediates behavioral rhythmicity and cyclical per expression in a restricted subset of the Drosophila nervous system

Transgenic flies carrying a 7.2 kb piece of DNA from the period (per) gene were analyzed for the presence of circadian locomotor activity rhythms and fluctuations of per-encoded mRNA and protein. The 5' end of this genomic fragment is within the first intron, which precedes the coding region. This promotorless fragment could rescue circadian behavioral rhythms and mediate spatial expression of PER in a subset of wild-type per cells within the CNS and PNS. In one behaviorally rhythmic line, PER protein was found in only "per lateral neurons." In the rhythmic transgenics, per mRNA and protein levels undergo circadian cycling, as previously described for wild type. Cycling of PER in brain cells of flies carrying the same 7.2 kb piece of per DNA under the control of a heat shock promoter corroborated the hypothesis that per's molecular cyclings and behavioral rhythmicity are causally related.

On the molecular mechanism of the circadian clock. The 41,000 M(r) clock protein of Chlorella was identified as 3-phosphoglycerate kinase

A 41,000 M(r) polypeptide of Chlorella exhibits a circadian rhythm in its synthesis and possesses characteristic features of a putative essential clock protein as was proposed by the coupled translation-membrane model. Purification of this polypeptide and a microsequencing analysis yielded a N-terminal sequence of 35 amino acids that showed no homology to known sequences that were thought to be involved in circadian rhythm such as the per gene of Drosophila and the frq gene of Neurospora. However, strong homology was observed to 3-phosphoglycerate kinase (PGK) of different organisms. The highest homology (83%) of this Chlorella sequence was found with the PGK of wheat chloroplast. PGK activity and the 41,000 M(r) polypeptide co-purified through differential centrifugation and gel filtration. These data, and comparison with the physical properties of other known PGK molecules, support the conclusion that the 41,000 M(r) polypeptide of Chlorella, a candidate for a putative essential clock protein, is 3-phosphoglycerate kinase.

Behavior in light-dark cycles of Drosophila mutants that are arrhythmic, blind, or both

Certain of the rhythm mutations in Drosophila melanogaster lead to arrhythmic locomotor activity (and aperiodic eclosion) in constant conditions. In light-dark (LD) cycles, however, such mutants exhibit clear fluctuations between high levels of activity when the lights are on and much lower ones when they are off. Our data, in contrast to some previous conclusions, strongly suggest that period0 (per0) adults are, in LD conditions, merely being "forced" into exhibiting periodic behavior. These experiments involved application of 8-, 12-, 16-, and 24-hr LD cycles, in which the arrhythmic mutant could have any of these periodicities imposed upon it, whereas wild-type flies tended to exhibit periods of about 24 hr in cycling conditions whose T values were > 8 hr different from 24. In phase-shift experiments, it was found that Drosophila expressing genotypes associated with rhythmicity achieved a 5-hr advance over a 2-day period following an advanced lights-on; per0 adults altered the phase of their locomotor peaks more rapidly. Against a background of the fact that eyeless or blind flies exhibit normal entrainment, it was hypothesized that double-mutant flies--carrying such visual mutations and per0 as well--should not synchronize to LD cycles, if the forced rhythms seen in the latter single-mutant type are mediated solely by light input through the external photoreceptors. Since an appreciable proportion of the double mutants did synchronize (to LD 12:12), it is thus suggested that the visual cues involved in forcing rhythmicity could be input through the same extraocular photoreceptors that, in general, subserve the fly's rhythm system.

Mapping the clock rhythm mutation to the period locus of Drosophila melanogaster by germline transformation

The Clock (Clk) mutation shortens circadian rhythms of locomotor activity and eclosion from ca. 24 h to 22.5-23 h. Clk was previously mapped, by meiotic recombination, very close to the period(per) locus on the X chromosome. To determine whether Clk is a mutation within the per gene or if the former is separate from the latter, two overlapping genomic fragments were cloned from Clk flies to produce a per-containing 13.2 kb construct, per01 flies (which by themselves are arrhythmic)--when transformed with this construct--expressed short-period rhythms. This indicates that the Clk mutation is contained within this 13.2 kb region and is almost certainly a new "fast-clock" allele of per.

Reassessment of the effect of biological rhythm mutations on learning in Drosophila melanogaster

A link between learning deficits and circadian period-lengthening mutations in Drosophila melanogaster previously has been reported. Mutant long-period males performed poorly in two learning assays involving experience-dependent courtship inhibition. In one, normal males that have courted fertilized females subsequently show courtship inhibition with virgin females. In the other, normal males that have courted sexually immature males subsequently fail to court other immature males. Those results have been reassessed in an extended study of genetic variants involving the period gene. 1. Long-period perL1 males demonstrated poor conditioned courtship inhibition when exposed to fertilized females; they showed normal courtship conditioning when exposed to immature males. This could be due to a perL1-associated olfactory deficit with fertilized females, since perL1 males were unable to discriminate behaviorally between fertilized and virgin females. 2. Other long-period males, including perL2 males and transgenic perL1 males bearing a truncated form of the per+ gene, were conditioned normally by fertilized females. Thus, the courtship inhibition defect is specific to the perL1 mutant strain. 3. perL1 (and other per mutant) flies showed normal acquisition and retention of a classically conditioned olfactory avoidance response. 4. Results from a new conditioned courtship inhibition experiment are presented; males exposed to fertilized females during training showed further courtship inhibition during subsequent exposure to fertilized females. From the perspective of learning theory, this can be viewed as a savings experiment.

Molecular transfer of a species-specific behavior from Drosophila simulans to Drosophila melanogaster

Drosophila males modulate the interpulse intervals produced during their courtship songs. These song cycles, which are altered by mutations in the clock gene period, exhibit a species-specific variation that facilitates mating. We have used chimeric period gene constructs from Drosophila melanogaster and Drosophila simulans in germline transformation experiments to map the genetic control of their song rhythm difference to a small segment of the amino acid encoding information within this gene.

Drosophila ebony mutants have altered circadian activity rhythms but normal eclosion rhythms

Drosophila ebony mutants exhibit a syndrome of morphological and behavioral phenotypes that include an abnormally dark body color and defects in visual and courtship responses. We now show that mutants carrying any one of five ebony alleles display complex and variable locomotor activity rhythms. Although in the most extreme cases activity is essentially aperiodic, many individuals express short- and/or long-period activity components. Three different ebony mutants (e, e1, and e11) express free-running rhythmicity in a temperature-dependent manner; activity rhythms are robust at 28 degrees C, but weak or absent at 20 degrees C. Even while maintained in a light-dark (LD) cycle, ebony homozygotes characteristically display extremely disorganized patterns of activity; some individuals entrain with an apparently abnormal phase and/or express multiple rhythmic components. Interestingly, the visual system mutation norpA partially suppresses effects of the e1 allele, which suggests that aberrant visual system inputs might contribute to the rhythm deficits of ebony mutants. In contrast to their effects on the locomotor activity rhythm, ebony mutations have no apparent impact on the circadian rhythm of adult eclosion, and thus exert rhythm-specific effects on circadian periodicity.

The circadian basis of ovarian diapause regulation in Drosophila melanogaster: is the period gene causally involved in photoperiodic time measurement?

Females of a wild-type strain of Drosophila melanogaster (Canton-S), and of several clock mutants (period), were able to discriminate between diapause-inducing short days and diapause-averting long days with a well-defined critical daylength. The critical daylengths of a short-period mutant (pers) and a long-period mutant (perL2) were almost identical, both to each other and to that of Canton-S. The critical daylength of an arrhythmic mutant (perol), however, was about 3 hr shorter than that of Canton-S, and that of per- was about 5 hr shorter. Exposure of Canton-S females to Nanda-Hamner experiments, consisting of a 10-hr photophase coupled to a dark phase varying between 4 and 74 hr, showed (1) that the photoperiodic clock in D. melanogaster measures nightlength rather than daylength, and (2) that photoperiodic time measurement is somehow based on (or affected by) constituent oscillators in the circadian system. Nanda-Hamner results for the period mutants all showed similar profiles regardless of genotype, or the presence or absence of per locus DNA. These results suggest that photoperiodic induction and locomotor activity do not share a common pacemaker in D. melanogaster, and that the per gene is not causally involved in nightlength measurement by the photoperiodic clock, although flies in which the per locus is missing (per-) or defective (perol) show an altered critical value.