Genetic and molecular analysis of biological rhythms

Investigation of natural genetic variation in the circadian system of Drosophila melanogaster. II. Biometrical analyses of locomotor activity rhythms recorded in constant darkness

The locomotor activity rhythms of 24 isochromosomal strains of Drosophila melanogaster were recorded in constant conditions, using an experimental design suitable for the serial screening with so many strains using limited equipment. The data obtained were subjected to biometrical genetic analysis. The results show that four characteristics of the rhythms (period, phase, definition, and waveform) display genetically based variation in expression and that each appears to be affected by a range of genes.

Genetic control of biological rhythms: independent expression of each rhythm parameter

Biological rhythm whose pattern approaches a sinusoidal curve can be characterized by four parameters: Period, Mesor, Acrophase and Amplitude. Inheritance patterns of these parameters were assessed by monitoring White Blood Cell (WBC) count rhythms of C57BL/6J mice, BALB/c mice and the F1 progeny prior and after injection of Cisplatinum at either 0900, 1500, 2100, or 0300. All untreated mice exhibited similar WBC rhythms while a variety of rhythm phenotypes was revealed among the injected mice. Analyses of the variety in the parental strains and F1 progeny suggested that each of the rhythm parameters is independently controlled.

A circadian clock of Drosophila: effects of deuterium oxide and mutations at the period locus

Mutations at the period (per) locus (1:1.3; 3B1-2) in Drosophila melanogaster lengthen (perL), shorten (pers), or abolish (per0) overt circadian rhythmicity. Deuterium oxide lengthens the free-running circadian period. We tested the effects of deuterium on three mutants of the per gene (pers, perL, and per0) and wild-type Drosophila melanogaster (per+) to assess interactions. With increasing concentrations of deuterium, the free-running circadian period of locomotor activity rhythms increased. The dose-response was linear in all genotypes tested. With increasing dosages of deuterium, circadian rhythms became weaker as evidenced by the signal-to-noise ratio (SNR). Genotype and deuterium changed circadian period length independently and additively, showing no interaction. SNRs for all genotypes converged on a low level as deuterium concentration increased. Deuterium increased life span, except at high concentrations (40 and 50%).

The Drosophila per gene homologs are expressed in mammalian suprachiasmatic nucleus and heart as well as in molluscan eyes

This study presents evidence for the conservation of Drosophila per gene homologs in mammalian DNA and for their expression in a number of tissues which are involved in various aspects of circadian timekeeping. Distinct 5 kb sequences, which hybridized to a non repetitive fragment of the Drosophila per gene under stringent conditions, were detected by Southern blotting. Sequences homologous to per gene of Drosophila were also amplified from rat and mouse brain cDNA libraries and from a mouse anterior hypothalamus and human hypothalamus libraries. Degenerate PCR primer design was based on conserved segments of the per protein. The per homologs were shown directly (by RT-PCR) to be expressed in hamster and mouse SCN, in hamster heart and in Aplysia and Bulla eyes.

Effects of deuterium oxide and temperature on heart rate in Drosophila melanogaster

A non-intrusive optical technique has been developed to monitor heartbeat in late third-instar Drosophila larvae. Heartbeat in this insect is an oscillation that is not temperature compensated. Deuterium oxide lengthens the period of a number of high and low frequency oscillators and clocks in a variety of organisms. To determine whether deuterium affects heart rate, flies were raised on proteated and deuterated media and their heartbeat was monitored at four temperatures ranging from 18 to 33 degrees C. The rate of heartbeat increased linearly with increasing temperature, and decreased with increasing concentrations of deuterium. There was a significant interaction between temperature and deuterium: the higher the concentration of deuterium oxide the less temperature-sensitive was the heart rate. Raising temperatures also increased the amount of "noise" in the rhythm: signal-to-noise ratio, which characterizes the amount of power in a rhythmic signal, decreased with increasing temperatures. Deuterium oxide had no effect on signal-to-noise ratio.

An antibody to the Drosophila period protein labels antigens in the suprachiasmatic nucleus of the rat

Cell bodies in the rat suprachiasmatic nucleus (SCN) were labeled with an antibody against a small domain of the period (per) protein, the product of a gene in Drosophila that regulates circadian rhythms. In immunoblots of SCN protein extracts, the antibody recognized a band of approximately 115 kD, as well as a heterogeneous antigen ranging from 160 kD to 170 kD. The antibody was found in previous studies to label putative circadian pacemaker neurons in Aplysia and Bulla, as well as the cellular sites of per expression in flies. Taken together, these results suggest that the region of the per protein recognized by this antibody may be widely conserved in neuronal circadian pacemakers.

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.

Drosophila courtship song cycles in normal and period mutant males revisited

Courtship songs of normal males and those expressing short-period, long-period, and arrhythmic mutations at the period (per) locus of Drosophila melanogaster have been reanalyzed for rhythmic components, using spectral treatments of the fluctuating rates of tone pulse production that occur during courtship. It was concluded, as in previous studies, that such songs are strongly rhythmic, except for courtships performed by per01 males. Songs produced by males expressing this and other per alleles were compared to computer-generated "random" ones. Interpulse interval variations influenced by per01 and songs stimulated to be arrhythmic both were found to be associated with cryptic rhythmicities; several such period values, extracted by the spectral analyses, defined very short cycle durations. We discuss the implications of these findings and of some recently reported results that have challenged the existence of rhythmicity in Drosophila songs.

Reciprocal behaviour associated with altered homeostasis and photosensitivity of Drosophila clock mutants

The circadian oscillators of genetically short-period and long-period Drosophila exhibit reciprocal behaviour in four distinct ways: (1) with respect to the dependence of period on temperature, (2) in the change of period during constant darkness after ten days of constant light, (3) in the change of period during the second ten days of darkness as compared with the period during the first ten days, and (4) in the period change resulting from exposure to low-intensity constant light. The homeostatic control of the dependence of period length on temperature is impaired in the mutants as compared with wild-type flies. The normal Drosophila pacemaker may comprise two mutually coupled oscillators, whereas the mutants may represent a reduction in activity of one or the other constituent oscillator.

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

A new period mutation has been induced and characterized in D. melanogaster. It causes flies to be apparently arrhythmic in tests of locomotor activity and thus is superficially similar to the original per01 mutant. Yet, the new "zero" allele, per04, has some novel properties and effects: Behaviorally, per04 adults often exhibit weak, long-period rhythms of locomotor activity in constant darkness; this low-frequency rhythmicity usually was not obvious in the analog behavioral records but was readily revealed by spectral analyses. These treatments of the data also extracted hidden high-frequency (ultradian) rhythms in many of the behavioral records, of the type associated with per01 and other per-nulls. The wide range of periodicities exhibited by different per04-expressing flies implies the expression of multiple oscillatory modes by this mutant. The new mutation also leads to a tendency for flies to be hyperactive during activity monitoring and is thus dissimilar to the other arrhythmic variants in the per gene but similar to the effects of a deletion of the locus. During light:dark cycling, per04 adults once more behave differently from other per0's and in fact tend to resemble wild-type flies in these conditions. The new mutation is not caused by the same nucleotide substitution that created a stop codon in the original arrhythmic per mutant and, as it turns out, per02 and per03 as well. per04 is also not a null variant at the transcriptional level; but it leads to an anomalous form of per mRNA, which is smaller than the normal 4.5 kb species encoded by this clock gene.

High-resolution analysis of locomotor activity rhythms in disconnected, a visual-system mutant of Drosophila melanogaster

Free-running locomotor activity and eclosion rhythms of Drosophila melanogaster, mutant at the disconnected (disco) locus, are substantially different from the wild-type phenotype. Initial periodogram analysis revealed little or no rhythmicity (Dushay et al., 1989). We have reanalyzed the locomotor activity data using high-resolution signal analysis (maximum-entropy spectral analysis, or MESA). These analyses, corroborated by autocorrelograms, uncovered significant residual circadian rhythmicity and strong ultradian rhythms in most of the animals tested. In this regard the disco mutants are much like flies expressing mutant alleles of the period gene, as well as wild-type flies reared throughout life in constant darkness. We hypothesize that light normally triggers the coupling of multiple ultradian oscillators into a functional circadian clock and that this process is disrupted in disco flies as a result of the neural lesion.

In situ localization of the per clock protein during development of Drosophila melanogaster

The per locus influences biological rhythms in Drosophila melanogaster. In this study, per transcripts and proteins were localized in situ in pupae and adults. Earlier genetic studies have demonstrated that per expression is required in the brain for circadian locomotor activity rhythms and in the thorax for ultradian rhythmicity of the Drosophila courtship song. per RNA and proteins were detected in a restricted group of cells in the eyes and optic lobes of the adult brain and in many cell bodies in the adult and pupal thoracic ganglia. per products were also found in the pupal ring gland complex, a tissue involved in rhythmic aspects of Drosophila development. Abundant expression was seen in gonadal tissue. No biological clock phenotypes have been reported for this tissue in any of the per mutants, per protein mapped to different subcellular locations in different tissues. The protein accumulated in or around nuclei in some cells and appeared to be cytoplasmic in others.

Induction of diapause in Drosophila melanogaster: photoperiodic regulation and the impact of arrhythmic clock mutations on time measurement

The fruit fly Drosophila melanogaster displays an ovarian diapause that is regulated by photoperiod. Newly eclosed female flies (Canton-S wild type) exposed to short days (less than 14 hr of light per day) at 12 degrees C (or 10 degrees C) enter a fairly shallow reproductive diapause. Females exposed to long days (16 hr of light per day) at the same low temperature undergo ovarian maturation. The short day induced diapause continues for 6-7 weeks under a 10:14 light/dark cycle at 12 degrees C but is terminated rapidly after a transfer to higher temperature (18 or 25 degrees C) or to long days (18:6 light/dark cycle). Females from three strains homozygous for alleles of the period (per) locus, reportedly arrhythmic for behavioral circadian rhythms, and females that possessed two overlapping deletions of per were also capable of discriminating between long and short days, although, when compared with the wild-type flies, the critical day length was shifted to shorter values by approximately 2 hr. It is concluded that the period locus is not causally involved in photoperiod time measurement.

The disconnected visual system mutations in Drosophila melanogaster drastically disrupt circadian rhythms

Mutations at the disconnected (disco) locus in Drosophila melanogaster cause cultures of this insect to eclose in an essentially arrhythmic manner and also nearly eliminate free-running circadian rhythms of locomotor activity. Yet disco mutants are not totally light-insensitive: Whereas they performed very poorly in tests of certain behavioral responses to visual stimuli, they were able to exhibit "forced" periodic locomotor activity under conditions of light-dark cycling. We discuss these results in the context of (1) the dispensability of this insect's external photoreceptors for entrainment of its circadian pacemaker, and (2) possible disco-induced abnormalities in the connections of extraocular photoreceptors to their targets in the central nervous system and/or abnormalities in the targets themselves--which presumably include elements of the fly's circadian clock.

Circadian control of heat tolerance in stationary phase cultures of Schizosaccharomyces pombe

The capacity of stationary phase cultures of Schizosaccharomyces pombe to survive a heat treatment at 55 degrees C is controlled by a circadian rhythm. In a synchronizing light-dark-cycle this rhythm shows a stable phase relationship to the onset of light. In continuous darkness it persists for several cycles without marked damping. The free-running period of about 27 h at 30 degrees C is only slightly longer at 20 degrees C, hence temperature-compensated. These results indicate that S. pombe is a suitable experimental organism for further research into both heat tolerance and circadian rhythms.

In situ localization of the per clock protein during development of Drosophila melanogaster

The per locus influences biological rhythms in Drosophila melanogaster. In this study, per transcripts and proteins were localized in situ in pupae and adults. Earlier genetic studies have demonstrated that per expression is required in the brain for circadian locomotor activity rhythms and in the thorax for ultradian rhythmicity of the Drosophila courtship song. per RNA and proteins were detected in a restricted group of cells in the eyes and optic lobes of the adult brain and in many cell bodies in the adult and pupal thoracic ganglia. per products were also found in the pupal ring gland complex, a tissue involved in rhythmic aspects of Drosophila development. Abundant expression was seen in gonadal tissue. No biological clock phenotypes have been reported for this tissue in any of the per mutants, per protein mapped to different subcellular locations in different tissues. The protein accumulated in or around nuclei in some cells and appeared to be cytoplasmic in others.

A mutation of the circadian system in golden hamsters

A mutation has been found that dramatically shortens the period of the circadian locomotor rhythm of golden hamsters. The pattern of inheritance of this mutation suggests that it occurred at a single, autosomal locus (tau). Wild-type animals have rhythms with free-running periods averaging about 24 hours; animals heterozygous for the mutation have periods of about 22 hours, whereas homozygous animals have rhythms with periods close to 20 hours. Animals that carry the mutant alleles exhibit abnormal entrainment to 24-hour light:dark cycles or are unable to entrain.

Vasopressin mRNA in the suprachiasmatic nuclei: daily regulation of polyadenylate tail length

Daily variation has been found in the length of the polyadenylate tail attached to vasopressin messenger RNA in the suprachiasmatic nuclei, which is the location of an endogenous circadian pacemaker in mammals. No such variation was found in the supraoptic or paraventricular nuclei. This variation in the length of the polyadenylate tail may underlie the circadian rhythm of vasopressin peptide levels in cerebrospinal fluid and is a unique example of a daily rhythm in messenger RNA structure.

An inducible promoter fused to the period gene in Drosophila conditionally rescues adult per-mutant arrhythmicity

The period (per) gene of Drosophila melanogaster is involved in the expression of circadian rhythms of locomotor activity in adult flies. Molecular studies of per (reviewed in ref. 2) have shown that the transcribed and translated products of this gene are present primarily at the embryonic, pupal and adult stages. Here we describe experiments with arrhythmic per mutants bearing an inducible form of this gene which indicate that strongly rhythmic adult behaviour can be obtained only if per expression is induced in the adult, independent of its history of expression earlier in development. Thus per-mutant locomotor-activity phenotypes seem not to result from abnormalities in the development of neural structures or in physiological processes that may be required at pre-adult stages for the expression of this circadian rhythm. Moreover, the action of per after light:dark cycle entrainment seems to be sufficient for activity rhythms to be exhibited in constant darkness; this suggests further that the per product is required only during the time that the rhythmic behaviour is being manifested. Our strategy used a heat-shock gene promotor fused to per coding sequences to obtain conditional gene expression. Heat-shock promoter-driven genes have previously been used to study the mode of action and tissue specificity of a variety of Drosophila genes; our experiments on circadian rhythms demonstrate the use of such gene constructions for the temporal manipulation of genes whose phenotypes, behavioural and otherwise, affect whole organisms.

Antibodies to the period gene product of Drosophila reveal diverse tissue distribution and rhythmic changes in the visual system

Polyclonal antibodies were prepared against the period gene product, which influences biological rhythms in D. melanogaster, by using small synthetic peptides from the per sequence as immunogens. The peptide that elicited the best antibody reagent was a small domain near the site of the pers (short period) mutation. Specific immunohistochemical staining was detected in a variety of tissue types: the embryonic CNS; a few cell bodies in the central brain of pupae; these and other cells in the central brain of adults, as well as imaginal cells in the eyes, optic lobes, and the gut. The intensity of per-specific staining in the visual system was found to oscillate, defining a free-running circadian rhythm with a peak in the middle of the night.

Spatial and temporal expression of the period gene in Drosophila melanogaster

The temporal and spatial expression of the period gene of Drosophila melanogaster has been analyzed by examining the expression of a per beta-galactosidase fusion gene in transformants and by in situ hybridization experiments with wild-type flies. Several strains of Drosophila melanogaster, transformed with the fusion gene, have been generated. The gene is active in mid-late embryos in the midline of the nervous system. Thereafter, beta-galactosidase activity is undetectable until the pupal stage when the prothoracic gland-corpora allata and the optic lobes are beta-galactosidase positive. In adults a surprisingly large number of tissues stain positively, including antennae, proboscis, eyes, optic lobes, cells of the central brain, cells of the thoracic ganglia, gut, Malpighian tubules, and ovarian follicle cells. The temporal pattern of expression agrees well with previous estimates made from developmental Northern blots with RNA extracted from wild-type animals. We suggest that many of the tissues that express the per gene contain their own intrinsic oscillator activity.