Short-period Mutation Research Articles

Natural selection against a circadian clock gene mutation in mice

Circadian rhythms with an endogenous period close to or equal to the natural light-dark cycle are considered evolutionarily adaptive ("circadian resonance hypothesis"). Despite remarkable insight into the molecular mechanisms driving circadian cycles, this hypothesis has not been tested under natural conditions for any eukaryotic organism. We tested this hypothesis in mice bearing a short-period mutation in the enzyme casein kinase 1ε (tau mutation), which accelerates free-running circadian cycles. We compared daily activity (feeding) rhythms, survivorship, and reproduction in six replicate populations in outdoor experimental enclosures, established with wild-type, heterozygous, and homozygous mice in a Mendelian ratio. In the release cohort, survival was reduced in the homozygote mutant mice, revealing strong selection against short-period genotypes. Over the course of 14 mo, the relative frequency of the tau allele dropped from initial parity to 20%. Adult survival and recruitment of juveniles into the population contributed approximately equally to the selection for wild-type alleles. The expression of activity during daytime varied throughout the experiment and was significantly increased by the tau mutation. The strong selection against the short-period tau allele observed here contrasts with earlier studies showing absence of selection against a Period 2 (Per2) mutation, which disrupts internal clock function, but does not change period length. These findings are consistent with, and predicted by the theory that resonance of the circadian system plays an important role in individual fitness.

Retention of a 24-hour time memory in Syrian hamsters carrying the 20-hour short circadian period mutation in casein kinase-1ε (ck1εtau/tau)

Circadian rhythmic expression of conditioned place avoidance (CPA) was produced in Syrian hamsters homozygous for the circadian short period mutation, tau. In constant dim red light neither the 20h endogenous period, nor a 20h place conditioning schedule eliminated the 24h modulation of CPA behavior described previously for wild type (wt) hamsters and other species. Tau mutants exhibited a 20h rhythm superimposed on the 24h modulation. The 20h component was removed selectively with lesions of the suprachiasmatic nucleus. Wt animals conditioned on a 20h schedule did not produce a 20h rhythm, but still expressed the 24h modulation. The results show that the context entrainable oscillator (CEO) underlying memory for the timing of an unconditioned stimulus, retains a period of about 24h regardless of clock gene background (tau mutation) and/or the conditioning schedule (24 vs 20h). Therefore the CEO responsible for time memory is distinct from the biological clock controlling activity; the underlying circadian molecular mechanisms may differ from the ubiquitous transcription–translation feedback oscillator; and time memory itself is not classically conditioned.

Circadian rhythm disorganization produces profound cardiovascular and renal disease in hamsters

Sleep deprivation, shift work, and jet lag all disrupt normal biological rhythms and have major impacts on health; however, circadian disorganization has never been shown as a causal risk factor in organ disease. We now demonstrate devastating effects of rhythm disorganization on cardiovascular and renal integrity and that interventions based on circadian principles prevent disease pathology caused by a short-period mutation (tau) of the circadian system in hamsters. The point mutation in the circadian regulatory gene, casein kinase-1epsilon, produces early onset circadian entrainment with fragmented patterns of behavior in +/tau heterozygotes. Animals die at a younger age with cardiomyopathy, extensive fibrosis, and severely impaired contractility; they also have severe renal disease with proteinuria, tubular dilation, and cellular apoptosis. On light cycles appropriate for their genotype (22 h), cyclic behavioral patterns are normalized, cardiorenal phenotype is reversed, and hearts and kidneys show normal structure and function. Moreover, hypertrophy does not develop in animals whose suprachiasmatic nucleus was ablated as young adults. Circadian organization therefore is critical for normal health and longevity, whereas chronic global asynchrony is implicated in the etiology of cardiac and renal disease.

Short-period mutations of per affect a double-time-dependent step in the Drosophila circadian clock.

Circadian (24 hour) PERIOD (PER) protein oscillation is dependent on the double-time (dbt) gene, a casein kinase Ivarepsilon homolog [1-3]. Without dbt activity, hypophosphorylated PER proteins over-accumulate, indicating that dbt is required for PER phosphorylation and turnover [3,4]. There is evidence of a similar role for casein kinase Ivarepsilon in the mammalian circadian clock [5,6]. We have isolated a new dbt allele, dbt(ar), which causes arrhythmic locomotor activity in homozygous viable adults, as well as molecular arrhythmicity, with constitutively high levels of PER proteins, and low levels of TIMELESS (TIM) proteins. Short-period mutations of per, but not of tim, restore rhythmicity to dbt(ar) flies. This suppression is accompanied by a restoration of PER protein oscillations. Our results suggest that short-period per mutations, and mutations of dbt, affect the same molecular step that controls nuclear PER turnover. We conclude that, in wild-type flies, the previously defined PER'short domain' [7,8] may regulate the activity of DBT on PER.

Chapter 3 The Drosophila genes timeless and period collaborate to promote cycles of gene expression composing a circadian pacemaker

Publisher Summary This chapter focuses on the genes and proteins controlling circadian rhythms in drosophila . Thus far, two genes, timeless ( tim ) and period ( per) have been identified that are essential for production of all known behavioral and molecular circadian rhythms. Therefore, the molecular changes associated with the arrhythmic and certain long-period and short-period mutations are known. For per , mutations changing period length thus far have been associated with single amino acid substitutions in the encoded protein. As might be expected from these effects of gene dosage on period length, transient increases in the titer of per RNA can shift the phase of the circadian rhythm. As comparable shifts in phase can be induced by Zeitgeber, such as entraining light pulses, the results suggest that the changes in the abundance or activities of PER proteins may be a part of the normal mechanism by which circadian behavioral rhythms are endogenously generated and reset by environmental stimuli. In the absence of such a delay, constitutive application of feedback regulation will specify an equilibrium state associated with constant levels of per and tim RNA and proteins. In contrast, by separating the phases of RNA and protein accumulation through a requirement for PER–TIM interaction, feedback control is applied at only some times of day. Sustained cycling of RNA and protein levels is expected if nuclear PER inhibits per and tim RNA synthesis.

Circadian Clock Mutants in Arabidopsis Identified by Luciferase Imaging

The cycling bioluminescence of Arabidopsis plants carrying a firefly luciferase fusion construct was used to identify mutant individuals with aberrant cycling patterns. Both long- and short-period mutants were recovered. A semidominant short-period mutation, timing of CAB expression (toc1), was mapped to chromosome 5. The toc1 mutation shortens the period of two distinct circadian rhythms, the expression of chlorophyll a/b-binding protein (CAB) genes and the movements of primary leaves, although toc1 mutants do not show extensive pleiotropy for other phenotypes.

New short period mutations of the Drosophila clock gene per

Earlier work has indicated that the period length of Drosophila circadian behavioral rhythms is dependent on the abundance of the period ( per) gene product. Increased expression of this gene has been associated with period shortening for both the circadian eclosion (pupal hatching) rhythm and circadian locomotor activity rhythms of adult Drosophila. In this study it is shown that a wide variety of missense mutations, affecting a region of the per protein consisting of ∼ 20 aa, predominantly generate short period phenotypes. The prevalence of such mutations suggests that short period phenotypes may result from loss or depression of function in this domain of the per protein. Possibly mutations in the region eliminate a regulatory function provided by this segment, or substantially increase stability of the mutant protein.

Effects of dosage alterations at the per locus on the period of the circadian clock of Drosophila

The normal 24-h period of the circadian rhythms of locomotor activity and eclosion of Drosophila melanogaster is altered by changes in per gene dosage. Females with only one dose of per+ or pers (the 19-h short-period mutant allele) or per1 (the 29-h long-period mutant allele) have periods which are about 1–2 h longer than the corresponding females with 2 doses. Females with 3 doses of per+ and males with 2 doses of per+ or pers have periods which are 1/2 to 1 h shorter than the corresponding individuals without the extra dose. Males with three per+ doses have periods which are about 1.5 h shorter than wild-type males; additional per+ doses do not shorten period further. The observation that decreased per dosage lengthens period while increased dosage shortens period suggests that the long- and short-period mutations alter period by respectively decreasing and increasing per gene or gene product activity. The per+ dosage results and the complementation behavior of pers indicate that the hypermorphic phenotype of pers results from increased activity of the pers gene product rather than an overproduction of per+ product. This is the first report of such a mutant action in Drosophila.