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

Flies as models for circadian clock adaptation to environmental challenges

Life on earth is assumed to have developed in tropical regions that are characterized by regular 24 hr cycles in irradiance and temperature that remain the same throughout the seasons. All organisms developed circadian clocks that predict these environmental cycles and prepare the organisms in advance for them. A central question in chronobiology is how endogenous clocks changed in order to anticipate very different cyclical environmental conditions such as extremely short and long photoperiods existing close to the poles. Flies of the family Drosophilidae can be found all over the world-from the tropics to subarctic regions-making them unprecedented models for studying the evolutionary processes that underlie the adaptation of circadian clocks to different latitudes. This review summarizes our current understanding of these processes. We discuss evolutionary changes in the clock genes and in the clock network in the brain of different Drosophilids that may have caused behavioural adaptations to high latitudes.

Expression of human Gaucher disease gene GBA generates neurodevelopmental defects and ER stress in Drosophila eye

Gaucher disease (GD) is the most common of the lysosomal storage disorders and is caused by defects in the GBA gene encoding glucocerebrosidase (GlcCerase). The accumulation of its substrate, glucocylceramide (GlcCer) is considered the main cause of GD. We found here that the expression of human mutated GlcCerase gene (hGBA) that is associated with neuronopathy in GD patients causes neurodevelopmental defects in Drosophila eyes. The data indicate that endoplasmic reticulum (ER) stress was elevated in Drosophila eye carrying mutated hGBAs by using of the ER stress markers dXBP1 and dBiP. We also found that Ambroxol, a potential pharmacological chaperone for mutated hGBAs, can alleviate the neuronopathic phenotype through reducing ER stress. We demonstrate a novel mechanism of neurodevelopmental defects mediated by ER stress through expression of mutants of human GBA gene in the eye of Drosophila.

Identification of representative genes of the central nervous system of the locust, Locusta migratoria manilensis by deep sequencing

The shortage of available genomic and transcriptomic data hampers the molecular study on the migratory locust, Locusta migratoria manilensis (L.) (Orthoptera: Acrididae) central nervous system (CNS). In this study, locust CNS RNA was sequenced by deep sequencing. 41,179 unigenes were obtained with an average length of 570 bp, and 5,519 unigenes were longer than 1,000 bp. Compared with an EST database of another locust species Schistocerca gregaria Forsskåi, 9,069 unigenes were found conserved, while 32,110 unigenes were differentially expressed. A total of 15,895 unigenes were identified, including 644 nervous system relevant unigenes. Among the 25,284 unknown unigenes, 9,482 were found to be specific to the CNS by filtering out the previous ESTs acquired from locust organs without CNS's. The locust CNS showed the most matches (18%) with Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) sequences. Comprehensive assessment reveals that the database generated in this study is broadly representative of the CNS of adult locust, providing comprehensive gene information at the transcriptional level that could facilitate research of the locust CNS, including various physiological aspects and pesticide target finding.

Circadian phenotypes of Drosophila fragile x mutants in alternative genetic backgrounds

Drosophila FMR1 mutants are models of human fragile X syndrome. They show a loss of locomotor activity rhythm and severe degradation of eclosion timing. We analyzed the circadian behavior of FMR1 mutants (dfmr1B55) in two genetic backgrounds, yellow white (yw) and Canton S (CS). The arrhythmic phenotype of circadian locomotor activity in constant darkness (DD) did not significantly change in either genetic background. Surprisingly, eclosion timing was completely restored by backcrossing dfmr1B55 with yw or CS flies. Morphological analysis of the small ventrally located lateral neurons of FMR1 mutants revealed that the dorsal-projection area was significantly larger in arrhythmic than rhythmic flies. In addition, dfmr1B55 mutants in both genetic backgrounds had a significantly lower evening peak in the light-dark (LD) cycle. These results indicate that lack of FMR1 does not affect eclosion timing, but alters locomotor activity patterns in both LD and DD conditions by affecting the arborization of small ventrally located lateral neurons. Thus, the FMR1 gene may regulate the circadian-related locomotor activity of Drosophila.

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

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

Cloning and daily expression of the timeless gene in Aedes aegypti (Diptera:Culicidae)

Molecular approaches for studying biological rhythms in insects have been well investigated in the model Drosophila melanogaster, in which a number of genes have been characterized in terms of sequence, expression, protein interactions and involvement in the control of locomotor activity and eclosion rhythms. However, only scattered information is available for insect vectors of diseases. In this paper, we report the cloning and expression analysis of the clock gene timeless in the mosquito Aedes aegypti, vector of Dengue and Yellow Fever viruses. In Drosophila, timeless has a crucial role in the control of the central pacemaker and the resetting mechanism that allows the clock to synchronize with the environment light-dark cycles. Comparison of the predicted protein sequence encoded by timeless in Ae. aegypti and D. melanogaster demonstrated high similarity in some important domains, suggesting functional conservation. Analysis of the daily expression of timeless in Ae. aegypti shows a peak in mRNA abundance around the light-dark transition.

Mating rhythms of Drosophila: rescue of tim01 mutants by D. ananassae timeless

Background

It is reported that the circadian rhythms of female mating activity differ among Drosophila species and are controlled by an endogenous circadian clock. Here, we found that the mating rhythm of D. ananassae differed from that of D. melanogaster. Moreover, to evaluate the effect of clock gene products on mating activities, we examined the mating activity of D. melanogaster timeless (tim⁰¹) transgenic fly harboring heat-shock promotor driven-D. ananassae timeless (tim) gene (hs-AT tim⁰¹).

Methods

Flies were maintained under light/dark (LD) cycles for several days and then they were transferred to constant dark (DD) conditions at 25°C. Transformant flies were heat-shocked for 30 min (PZT 10.5–11.0 or PZT 22.5–23.0; PZT means Projected Zeitgeber Time) at 37°C every day. Daily expressions of D. ananassae TIMELESS (TIM) protein in transgenic flies were measured by western blotting. To examine whether the timing of D. ananassae TIM protein induction by heat shock can change the patterns of the behavior activities of D. melanogaster tim⁰¹ flies, we measured locomotor and mating activity rhythms under DD at 25°C ± 0.5°C except when heat shock was applied.

Results

Heat shock applied at PZT 10.5–11.0 and at PZT 22.5–23.0 induced high TIM levels during subjective night and day, respectively, in hs-AT tim⁰¹ flies. The locomotor rhythm of these flies was changed from diurnal to nocturnal by the timing of D. ananassae TIM induction. However, the mating rhythm of these flies could not be entrained by the timing of D. ananassae TIM induction.

Conclusion

The pattern of mating activity rhythms of D. ananassae and of D. melanogaster differed. The mating activity rhythms of D. melanogaster tim⁰¹ flies harboring hs-AT tim appeared after heat-shock but the pattern and phase differed from those of wild-type D. ananassae and D. melanogaster. Moreover, the mating rhythm of these flies could not be entrained by the timing of D. ananassae TIM induction although the locomotor rhythm of hs-AT tim⁰¹ was changed from diurnal to nocturnal according to the timing of D. ananassae TIM induction. These data suggest that species-specific mating activities require output pathways different from those responsible for locomotor rhythms.

Bio-Object, a stochastic simulator for post-transcriptional regulation

MOTIVATION

Recently, biologists learnt that the transport and degradation of transcribed mRNA and protein present critically important steps for the regulation of gene expression through extensive studies of RNA interference, none-sense mediated decay and ubiquitination. However, adequate consideration of these factors has not been done in the past in in silico analysis compared with transcriptional regulations.

RESULTS

We have developed a bio-system simulator 'Bio-Object' and assessed the contribution of numerous factors including movements, stability and interactions of both mRNAs and proteins in the virtual cell space to the Drosophila circadian rhythm. The oscillations of period (per), timeless (tim) and Drosophila Clock (dClk) mRNAs and proteins predicted by the simulations agreed with the observed data in Drosophila and were lost with the knock-out of either the per or the dClk gene as observed experimentally. Bio-Object predicts that (1) the stability of dClk mRNA, (2) the stability of dCLK and (3) the affinity of the PER-TIM complex are determinants of the circadian duration.

AVAILABILITY

The source code is available for download from http://www.tmd.ac.jp/mri/mri-end/bio-object/download/