Analysis of locomotor activity rhythms in Drosophila

Effect of donepezil hydrochloride on the transgenic Drosophila expressing human Aβ-42

AIM

In the present study, the effect of donepezil hydrochloride was studied on the transgenic Drosophila expressing human amyloid beta-42 in the neurons.

METHODS

Donepezil hydrochloride at final concentration of 0.1, 1 and 10 mM was mixed in the diet and the flies expressing human amyloid beta-42 under Upstream Activation Sequence control (Alzheimer Disease [AD] flies) were allowed to feed on it for 30 days.

RESULTS

The AD flies exposed to various doses of Donepezil hydrochloride showed a dose dependent significant delay in the loss of climbing ability, increase in activity, reduction in the oxidative stress and apoptotic markers. A significant improvement was also observed in cognitive parameters. A dose dependent significant reduction in the activity of acetylcholinesterase was also observed. The docking studies suggest the positive interaction between donepezil, amyloid beta-42 and acetylcholinesterase. The results obtained from immunohistochemistry also showed a dose dependent significant reduction in the amyloid beta-42 aggregates.

CONCLUSION

The results suggest that donepezil hydrochloride is potent enough to reduce the AD symptoms being mimicked in transgenic flies.

Deciphering a Beetle Clock: Individual and Sex-Dependent Variation in Daily Activity Patterns

Circadian clocks are inherent to most organisms, including cryptozoic animals that seldom encounter direct light, and regulate their daily activity cycles. A conserved suite of clock genes underpins these rhythms. In this study, we explore the circadian behaviors of the red flour beetle Tribolium castaneum, a significant pest impacting stored grain globally. We report on how daily light and temperature cues synchronize distinct activity patterns in these beetles, characterized by reduced morning activity and increased evening activity, anticipating the respective environmental transitions. Although less robust, rhythmicity in locomotor activity is maintained in constant dark and constant light conditions. Notably, we observed more robust rhythmic behaviors in males than females with individual variation exceeding those previously reported for other insect species. RNA interference targeting the Clock gene weakened locomotor activity rhythms. Our findings demonstrate the existence of a circadian clock and of clock-controlled behaviors in T. castaneum. Furthermore, they highlight substantial individual differences in circadian activity, laying the groundwork for future research on the relevance of individual variation in circadian rhythms in an ecological and evolutionary context.

Drosophila melanogaster as an Alternative Model to Higher Organisms for In Vivo Lung Research

COPD and asthma are lung diseases that cause considerable burden to more than 800 million people worldwide. As both lung diseases are so far incurable, it is mandatory to understand the mechanisms underlying disease development and progression for developing novel therapeutic approaches. Exposures to environmental cues such as cigarette smoke in earliest life are known to increase disease risks in the individual's own future. To explore the pathomechanisms leading to later airway disease, mammalian models are instrumental. However, such in vivo experiments are time-consuming and burdensome for the animals, which applies in particular to transgenerational studies. Along this line, the fruit fly Drosophila melanogaster comes with several advantages for research in this field. The short lifespan facilitates transgenerational studies. A high number of evolutionary conserved signaling pathways, together with a large toolbox for tissue-specific gene modification, has the potential to identify novel target genes involved in disease development. A well-defined airway microbiome could help to untangle interactions between disease development and microbiome composition. In the following article, Drosophila melanogaster is therefore presented and discussed as an alternative in vivo model to investigate airway diseases that can complement and/or replace models in higher organisms.

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.

Usp14 down-regulation corrects sleep and circadian dysfunction of a Drosophila model of Parkinson's disease

PD is a complex, multifactorial neurodegenerative disease, which occurs sporadically in aged population, with some genetically linked cases. Patients develop a very obvious locomotor phenotype, with symptoms such as bradykinesia, resting tremor, muscular rigidity, and postural instability. At the cellular level, PD pathology is characterized by the presence of intracytoplasmic neurotoxic aggregates of misfolded proteins and dysfunctional organelles, resulting from failure in mechanisms of proteostasis. Nonmotor symptoms, such as constipation and olfactory deficits, are also very common in PD. They include alteration in the circadian clock, and defects in the sleep-wake cycle, which is controlled by the clock. These non-motor symptoms precede the onset of the motor symptoms by many years, offering a window of therapeutic intervention that could delay-or even prevent-the progression of the disease. The mechanistic link between aberrant circadian rhythms and neurodegeneration in PD is not fully understood, although proposed underlying mechanisms include alterations in protein homeostasis (proteostasis), which can impact protein levels of core components of the clock. Loss of proteostasis depends on the progressive pathological decline in the proteolytic activity of two major degradative systems, the ubiquitin-proteasome and the lysosome-autophagy systems, which is exacerbated in age-dependent neurodegenerative conditions like PD. Accordingly, it is known that promoting proteasome or autophagy activity increases lifespan, and rescues the pathological phenotype of animal models of neurodegeneration, presumably by enhancing the degradation of misfolded proteins and dysfunctional organelles, which are known to accumulate in these models, and to induce intracellular damage. We can enhance proteostasis by pharmacologically inhibiting or down-regulating Usp14, a proteasome-associated deubiquitinating enzyme (DUB). In a previous work, we showed that inhibition of Usp14 enhances the activity of the ubiquitin-proteasome system (UPS), autophagy and mitophagy, and abolishes motor symptoms of two well-established fly models of PD that accumulate dysfunctional mitochondria. In this work we extended the evidence on the protective effect of Usp14 down-regulation, and investigated the beneficial effect of down-regulating Usp14 in a Pink1 Drosophila model of PD that develop circadian and sleep dysfunction. We show that down-regulation of Usp14 ameliorates sleep disturbances and circadian defects that are associated to Pink1 KO flies.

Effects of lithium on locomotor activity and circadian rhythm of honey bees

Lithium has been considered a potential acaricidal agent against the honey bee (Apis mellifera) parasite Varroa. It is known that lithium suppresses elevated activity and regulates circadian rhythms and light response when administered to humans as a primary therapeutic chemical for bipolar disorder and to other bipolar syndrome model organisms, given the crucial role of timing in the bee's foraging activity and the alternating sunlight vs dark colony environment bees are exposed, we explored the influence of lithium on locomotor activity (LMA) and circadian rhythm of honey bees. We conducted acute and chronic lithium administration experiments, altering light conditions and lithium doses to assess LMA and circadian rhythm changes. We fed bees one time 10 μl sucrose solution with 0, 50, 150, and 450 mM LiCl in the acute application experiment and 0, 1, 5, and 10 mmol/kg LiCl ad libitum in bee candy in the chronic application experiment. Both acute and chronic lithium treatments significantly decreased the induced LMA under constant light. Chronic lithium treatment disrupted circadian rhythmicity in constant darkness. The circadian period was lengthened by lithium treatment under constant light. We discuss the results in the context of Varroa control and lithium's effect on bipolar disorder.

Ethoscopy and ethoscope-lab: a framework for behavioural analysis to lower entrance barrier and aid reproducibility

Summary

High-throughput analysis of behaviour is a pivotal instrument in modern neuroscience, allowing researchers to combine modern genetics breakthrough to unbiased, objective, reproducible experimental approaches. To this extent, we recently created an open-source hardware platform (ethoscope; Geissmann Q, Garcia Rodriguez L, Beckwith EJ et al. Rethomics: an R framework to analyse high-throughput behavioural data. PLoS One 2019;14:e0209331) that allows for inexpensive, accessible, high-throughput analysis of behaviour in Drosophila or other animal models. Here we equip ethoscopes with a Python framework for data analysis, ethoscopy, designed to be a user-friendly yet powerful platform, meeting the requirements of researchers with limited coding expertise as well as experienced data scientists.

Availability and implementation

Ethoscopy is best consumed in a prebaked Jupyter-based docker container, ethoscope-lab, to improve accessibility and to encourage the use of notebooks as a natural platform to share post-publication data analysis. Ethoscopy is a Python package available on GitHub and PyPi. Ethoscope-lab is a docker container available on DockerHub. A landing page aggregating all the code and documentation is available at https://lab.gilest.ro/ethoscopy.

Drosophila mutants lacking the glial neurotransmitter-modifying enzyme Ebony exhibit low neurotransmitter levels and altered behavior

Inhibitors of enzymes that inactivate amine neurotransmitters (dopamine, serotonin), such as catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), are thought to increase neurotransmitter levels and are widely used to treat Parkinson's disease and psychiatric disorders, yet the role of these enzymes in regulating behavior remains unclear. Here, we investigated the genetic loss of a similar enzyme in the model organism Drosophila melanogaster. Because the enzyme Ebony modifies and inactivates amine neurotransmitters, its loss is assumed to increase neurotransmitter levels, increasing behaviors such as aggression and courtship and decreasing sleep. Indeed, ebony mutants have been described since 1960 as "aggressive mutants," though this behavior has not been quantified. Using automated machine learning-based analyses, we quantitatively confirmed that ebony mutants exhibited increased aggressive behaviors such as boxing but also decreased courtship behaviors and increased sleep. Through tissue-specific knockdown, we found that ebony's role in these behaviors was specific to glia. Unexpectedly, direct measurement of amine neurotransmitters in ebony brains revealed that their levels were not increased but reduced. Thus, increased aggression is the anomalous behavior for this neurotransmitter profile. We further found that ebony mutants exhibited increased aggression only when fighting each other, not when fighting wild-type controls. Moreover, fights between ebony mutants were less likely to end with a clear winner than fights between controls or fights between ebony mutants and controls. In ebony vs. control fights, ebony mutants were more likely to win. Together, these results suggest that ebony mutants exhibit prolonged aggressive behavior only in a specific context, with an equally dominant opponent.

Effects of adenosine receptor overexpression and silencing in neurons and glial cells on lifespan, fitness, and sleep of Drosophila melanogaster

A single adenosine receptor gene (dAdoR) has been detected in Drosophila melanogaster. However, its function in different cell types of the nervous system is mostly unknown. Therefore, we overexpressed or silenced the dAdoR gene in eye photoreceptors, all neurons, or glial cells and examined the fitness of flies, the amount and daily pattern of sleep, and the influence of dAdoR silencing on Bruchpilot (BRP) presynaptic protein. Furthermore, we examined the dAdoR and brp gene expression in young and old flies. We found that a higher level of dAdoR in the retina photoreceptors, all neurons, and glial cells negatively influenced the survival rate and lifespan of male and female Drosophila in a cell-dependent manner and to a different extent depending on the age of the flies. In old flies, expression of both dAdoR and brp was higher than in young ones. An excess of dAdoR in neurons improved climbing in older individuals. It also influenced sleep by lengthening nighttime sleep and siesta. In turn, silencing of dAdoR decreased the lifespan of flies, although it increased the survival rate of young flies. It hindered the climbing of older males and females, but did not change sleep. Silencing also affected the daily pattern of BRP abundance, especially when dAdoR expression was decreased in glial cells. The obtained results indicate the role of adenosine and dAdoR in the regulation of fitness in flies that is based on communication between neurons and glial cells, and the effect of glial cells on synapses.

Unveiling Subtle Geographical Clines: Phenotypic Effects and Dynamics of Circadian Clock Gene Polymorphisms

Our understanding of the gene regulatory network that constitutes the circadian clock has greatly increased in recent decades, notably due to the use of Drosophila as a model system. In contrast, the analysis of natural genetic variation that enables the robust function of the clock under a broad range of environments has developed more slowly. In the current study, we analyzed comprehensive genome sequencing data from wild European populations of Drosophila, which were densely sampled through time and space. We identified hundreds of single nucleotide polymorphisms (SNPs) in nine genes associated with the clock, 276 of which exhibited a latitudinal cline in their allele frequencies. While the effect sizes of these clinal patterns were small, indicating subtle adaptations driven by natural selection, they provided important insights into the genetic dynamics of circadian rhythms in natural populations. We selected nine SNPs in different genes and assessed their impact on circadian and seasonal phenotypes by reconstructing outbred populations fixed for either of the SNP alleles, from inbred DGRP strains. The circadian free-running period of the locomotor activity rhythm was affected by an SNP in doubletime (dbt) and eyes absent (Eya). The SNPs in Clock (Clk), Shaggy (Sgg), period (per), and timeless (tim) affected the acrophase. The alleles of the SNP in Eya conferred different levels of diapause and the chill coma recovery response.

Light Pollution Disrupts Seasonal Differences in the Daily Activity and Metabolic Profiles of the Northern House Mosquito, Culex pipiens

The Northern House mosquito, Culex pipiens, is an important disease vector, and females are capable of surviving the winter in a state of overwintering diapause. This species' diapause response has been extensively studied, and recent evidence suggests that the circadian clock is involved in measuring seasonal changes in daylength to initiate the diapause response. However, differences in the circadian activity of diapausing and non-diapausing Cx. pipiens have not been thoroughly investigated. Additionally, recent findings indicate that artificial light at night (ALAN) can disrupt mosquito diapause, potentially prolonging the mosquito biting season. We compared the circadian locomotor activity of mosquitoes reared in diapause-averting, long-day conditions and diapause-inducing, short-day conditions with and without ALAN to elucidate the interplay between circadian activity, diapause, and light pollution. We also uncovered metabolic differences between mosquitoes reared under diapausing and non-diapausing photoperiods with and without ALAN by measuring the concentration of protein, fructose, glycogen, water-soluble carbohydrates, and lipids. We found that ALAN exposure altered several diapause-associated phenotypes including slightly, but not significantly, increasing activity levels in short day-reared mosquitoes; and preventing some short day-reared mosquitoes from accumulating lipids. ALAN also significantly reduced glycogen and water-soluble carbohydrate levels in long day-reared mosquitoes. Based on our findings, light pollution may decrease insect fitness by perturbing metabolism, and may also impact several phenotypes associated with insect diapause, potentially extending the mosquito biting season and preventing insects in urban environments from overwintering successfully.

Electronic recording of lifetime locomotory activity patterns of adult medflies

Age-specific and diurnal patterns of locomotory activity, can be considered as biomarkers of aging in model organisms and vary across the lifetime of individuals. Τhe Mediterranean fruit fly (medfly), Ceratitis capitata, is a commonly used model-species in studies regarding demography and aging. In the present study, we introduce a modification of the automated locomotory activity electronic device LAM25system (Locomotory Activity Monitor)-Trikinetics, commonly used in short time studies, to record the daily locomotory activity patterns of adult medflies throughout the life. Additionally, fecundity rates and survival of adult medflies were recorded. Male and female medflies were kept in the system tubes and had access to an agar-based gel diet, which provided water and nutrients. The locomotory activity was recorded at every minute by three monitors in the electronic device. The locomotory activity of females was higher than that of males across the different ages. For both sexes locomotory rates were high during the first 20 days of the adult life and decreased in older ages. The activity of males was high in the morning and late afternoon hours, while that of females was constantly high throughout the photophase. Negligible locomotory activity was recorded for both sexes during the nighttime. Males outlived females. Fecundity of females was higher in younger ages. Our results support the adoption of LAM25system in studies addressing aging of insects using medfly as a model organism.

Increased Repellent Effect of DEET on Aedes aegypti (Diptera: Culicidae) Field Population

Insecticides and repellents are routinely used in Brazil because of the high rates of arbovirus transmission and the nuisance caused by mosquitoes. However, few studies have assessed the effectiveness of repellents against mosquito populations that have been under exposure to xenobiotics, mainly insecticides and repellents. This study investigated the sensitivity of a field population of Aedes aegypti (Linnaeus, 1762) from a dengue-endemic area under high insecticide pressure to N,N-diethylmethylbenzamide (DEET), the active ingredient in common repellent products. The field (Laranjeiras, Sergipe, Brazil) and laboratory (Rockefeller) populations were characterized for the presence of the Val1016Ile kdr mutation, associated with pyrethroid resistance, and locomotor activity. Repellency bioassays were performed to assess the response of the mosquitoes to human odor by exposing them to 10% DEET applied to the skin in ethanol. Samples from the field population showed higher frequency of the kdr mutation, 21.9% homozygous and 21.9% heterozygous, greater locomotor activity and greater sensitivity to DEET than the laboratory population. These results suggest increased sensitivity to DEET in field populations and a possible interaction between insecticide exposure and sensitivity to DEET.

Nucleotide Variation in Drosophila cryptochrome Is Linked to Circadian Clock Function: An Association Analysis

Cryptochrome (CRY) is a conserved protein associated with the circadian clock in a broad range of organisms, including plants, insects, and mammals. In Drosophila, cry is a pleiotropic gene that encodes a blue light-dedicated circadian photoreceptor, as well as an electromagnetic field sensor and a geotaxis behavior regulator. We have generated a panel of nearly-isogenic strains that originated from various wild populations and which carry different natural alleles of cry. Sequencing of these alleles revealed substantial polymorphism, the functional role of which was elusive. To link this natural molecular diversity to gene function, we relied on association mapping. Such analysis revealed two major haplogroups consisting of six linked nucleotides associated with circadian phase (haplotypes All1/All2). We also generated a maximum-likelihood gene-tree that uncovered an additional pair of haplogroups (B1/B2). Behavioral analysis of the different haplotypes indicated significant effect on circadian phase and period, as well on the amount of activity and sleep. The data also suggested substantial epistasis between the All and B haplogroups. Intriguingly, circadian photosensitivity, assessed by light-pulse experiments, did not differ between the genotypes. Using CRISPR-mediated transgenic flies, we verified the effect of B1/B2 polymorphism on circadian phase. The transgenic flies also exhibited substantially different levels of cry transcription. We, moreover, analyzed the geographical distribution of the B1/B2 haplotypes, focusing on a 12 bp insertion/deletion polymorphism that differentiates the two haplotypes. Analysis of cry sequences in wild populations across Europe revealed a geographical cline of B1/B2 indel frequency, which correlated with seasonal bioclimatic variables. This spatial distribution of cry polymorphism reinforces the functional importance of these haplotypes in the circadian system and local adaptation.

A Simulated Shift Work Schedule Does Not Increase DNA Double-Strand Break Repair by NHEJ in the Drosophila Rr3 System

Long-term shift work is widely believed to increase the risk of certain cancers, but conflicting findings between studies render this association unclear. Evidence of interplay between the circadian clock, cell cycle regulation, and DNA damage detection machinery suggests the possibility that circadian rhythm disruption consequent to shift work could alter the DNA double-strand break (DSB) repair pathway usage to favor mutagenic non-homologous end-joining (NHEJ) repair. To test this hypothesis, we compared relative usage of NHEJ and single-strand annealing (SSA) repair of a complementary ended chromosomal double-stranded break using the Repair Reporter 3 (Rr3) system in Drosophila between flies reared on 12:12 and 8:8 (simulated shift work) light:dark schedules. Actimetric analysis showed that the 8:8 light:dark schedule effectively disrupted the rhythms in locomotor output. Inaccurate NHEJ repair was not a frequent outcome in this system overall, and no significant difference was seen in the usage of NHEJ or SSA repair between the control and simulated shift work schedules. We conclude that this circadian disruption regimen does not alter the usage of mutagenic NHEJ DSB repair in the Drosophila male pre-meiotic germline, in the context of the Rr3 system.

Visualization of Mutant Aggregates from Clock Neurons by Agarose Gel Electrophoresis (AGERA) in Drosophila melanogaster

The clock neurons of the fruit fly Drosophila melanogaster have become a useful model for expressing misfolded protein aggregates that accumulate in several human neurodegenerative diseases. One advantage of such an approach is that the behavioral effects can be readily quantified on circadian locomotor rhythms, sleep or activity levels via automated, highly reliable and objective procedures. Therefore, a rapid assay is required to visualize whether these neurons develop aggregates. Here we describe a modified immunoblot method, agarose gel electrophoresis (AGERA) that has been optimized for resolving aggregates from fly clock neurons.

Mesencephalic Astrocyte-Derived Neurotrophic Factor Regulates Morphology of Pigment-Dispersing Factor-Positive Clock Neurons and Circadian Neuronal Plasticity in Drosophila melanogaster

Mesencephalic Astrocyte-derived Neurotrophic Factor (MANF) is one of a few neurotrophic factors described in Drosophila melanogaster (DmMANF) but its function is still poorly characterized. In the present study we found that DmMANF is expressed in different clusters of clock neurons. In particular, the PDF-positive large (l-LNv) and small (s-LNv) ventral lateral neurons, the CRYPTOCHROME-positive dorsal lateral neurons (LNd), the group 1 dorsal neurons posterior (DN1p) and different tim-positive cells in the fly's visual system. Importantly, DmMANF expression in the ventral lateral neurons is not controlled by the clock nor it affects its molecular mechanism. However, silencing DmMANF expression in clock neurons affects the rhythm of locomotor activity in light:dark and constant darkness conditions. Such phenotypes correlate with abnormal morphology of the dorsal projections of the s-LNv and with reduced arborizations of the l-LNv in the medulla of the optic lobe. Additionally, we show that DmMANF is important for normal morphology of the L2 interneurons in the visual system and for the circadian rhythm in the topology of their dendritic tree. Our results indicate that DmMANF is important not only for the development of neurites but also for maintaining circadian plasticity of neurons.

Effects of insemination and blood-feeding on locomotor activity of wild-derived females of the malaria mosquito Anopheles coluzzii

BACKGROUND

Behavioural shifts in the canonical location and timing of biting have been reported in natural populations of anopheline malaria vectors following the implementation of insecticide-based indoor vector control interventions. These modifications increase the likelihood of human-vector contact and allow mosquitoes to avoid insecticides, both conditions being favourable to residual transmission of the malarial parasites. The biting behaviour of mosquitoes follows rhythms that are under the control of biological clocks and environmental conditions, modulated by physiological states. In this work we explore modifications of spontaneous locomotor activity expressed by mosquitoes in different physiological states to highlight phenotypic variability associated to circadian control that may contribute to explain residual transmission in the field.

METHODS

The F10 generation progeny of field-collected Anopheles coluzzii from southwestern Burkina Faso was tested using an automated recording apparatus (Locomotor Activity Monitor, TriKinetics Inc.) under LD 12:12 or DD light regimens in laboratory-controlled conditions. Activity recordings of each test were carried out for a week with 6-day-old females belonging to four experimental treatments, representing factorial combinations of two physiological variables: insemination status (virgin vs inseminated) and gonotrophic status (glucose fed vs blood fed). Chronobiological features of rhythmicity in locomotor activity were explored using periodograms, diversity indices, and generalized linear mixed modelling.

RESULTS

The average strength of activity, onset of activity, and acrophase were modulated by both nutritional and insemination status as well as by the light regimen. Inseminated females showed a significant excess of arrhythmic activity under DD. When rhythmicity was observed in DD, females displayed sustained activity also during the subjective day.

CONCLUSIONS

Insemination and gonotrophic status influence the underlying light and circadian control of chronobiological features of locomotor activity. Overrepresentation of arrhythmic chronotypes as well as the sustained activity of inseminated females during the subjective day under DD conditions suggests potential activity of natural populations of A. coluzzii during daytime under dim conditions, with implications for residual transmission of malarial parasites.

Chronobiotics KL001 and KS15 Extend Lifespan and Modify Circadian Rhythms of Drosophila melanogaster

Chronobiotics are a group of drugs, which are utilized to modify circadian rhythms targeting clock-associated molecular mechanisms. The circadian clock is known as a controller of numerous processes in connection with aging. Hypothesis: KL001 and KS15 targeting CRY, affect lifespan, locomotor activity and circadian rhythm of Drosophila melanogaster. We observed a slight (2%, p < 0.001) geroprotective effect on median lifespan (5 µM solution of KL001 in 0.1% DMSO) and a 14% increase in maximum lifespan in the same group. KS15 10 µM solution extended males’ median lifespan by 8% (p < 0.05). The statistically significant positive effects of KL001 and KS15 on lifespan were not observed in female flies. KL001 5 µM solution improved locomotor activity in young male imagoes (p < 0.05), elevated morning activity peak in aged imagoes and modified robustness of their circadian rhythms, leaving the period intact. KS15 10 µM solution decreased the locomotor activity in constant darkness and minimized the number of rhythmic flies. KL001 5 µM solution improved by 9% the mean starvation resistance in male flies (p < 0.01), while median resistance was elevated by 50% (p < 0.0001). This phenomenon may suggest the presence of the mechanism associated with improvement of fat body glucose depos’ utilization in starvation conditions which is activated by dCRY binding KL001.

Diel and Circadian Patterns of Locomotor Activity in the Adults of Diamondback Moth (Plutella xylostella)

Simple Summary

Plutella xylostell is a worldwide migratory insect pest that mainly damages cruciferous vegetables. In this study, we established a system for measuring the diel locomotor activities and used it to evaluate the locomotor circadian patterns of P. xylostella. We tested the locomotor activities of P. xylostella adults under several laboratory settings. We found that both the males and females showed nocturnal activity under a light:dark (LD) cycle, with activity peaking very early after lights off and quickly declining after lights on. Both males and females had high locomotor activity levels in constant darkness (DD) but weak in a constant light condition (LL). In addition, circadian patterns analysis showed that males exhibit much better rhythmic characteristics than females, especially in low temperature conditions. Overall, our proposed system for studying the locomotor activities in P. xylostella is reliable, which will help us to have a better understanding of the diel activity of P. xylostella and may finally be helpful in the development of an effective pest management strategy.

Abstract

The Diamondback Moth (Plutella xylostella) is a highly destructive lepidopteran pest of cruciferous crops. However, there still is relatively little known about the locomotor activities of diel and the circadian patterns in P. xylostella. Here, we present an analysis of the diel locomotion of P. xylostella under several laboratory settings. We established a system for measuring the individual locomotor activities of P. xylostella and found that both males and females showed a nocturnal pattern of activity under 26 or 20 °C LD conditions, with activity peaking immediately after lights off and quickly declining after lights on. In addition, we showed that it is difficult to assess the free-running circadian rhythms of P. xylostella under 26 °C DD conditions. However, we found that males showed a higher power, rhythm index (RI) and rhythmic ratio than females under 20 °C DD conditions, which indicated that males in low-temperature conditions are much more suitable to study the free-running circadian rhythms of P. xylostella. The findings of this study will help us to have a better understanding of the diel activity of P. xylostella and may provide a foundation for the development of an effective pest management strategy.

Locomotor activity in Aedes aegypti with different insecticide resistance profiles

OBJECTIVE:

To evaluate locomotor activity in four field populations of Ae. aegypti with different insecticide resistance profiles from the state of São Paulo for two years.

METHODS:

This study comprised the susceptible Rockefeller strain and four populations from São Paulo, Brazil: two considered populations with “reduced susceptibility” to pyrethroids (Campinas and Marília), and two “resistant populations” (Santos and Ribeirão Preto). First, 2016 and 2017 eggs from these five populations were hatched in laboratory. Virgin females underwent experiments under laboratory conditions at 25°C, with 12:12h light/dark (LD) photoperiod; 24-hour individual activity was recorded using a locomotor activity monitor (LAM).

RESULTS:

In females from 2016 field populations, both resistant populations showed significant more locomotor activity than the two reduced susceptibility populations and the Rockefeller strain (p < 0.05). As for females from 2017 field populations, reduced susceptibility populations showed a significant increased locomotor activity than the Rockefeller strain, but no significant difference when compared to Santos resistant population (p > 0.05).

CONCLUSIONS:

Our results indicate that insecticide-resistant Ae. aegypti populations show increased locomotor activity, which may affect the transmission dynamics of their arboviruses.

Early warning indicators of population collapse in a seasonal environment

Recent studies have demonstrated that generic statistical signals derived from time series of population abundance and fitness-related traits of individuals can provide reliable indicators of impending shifts in population dynamics. However, how the seasonal timing of environmental stressors influences these early warning indicators is not well understood. The goal of this study was to experimentally assess whether the timing of stressors influences the production, detection and sensitivity of abundance- and trait-based early warning indicators derived from declining populations. In a multi-generation, season-specific habitat loss experiment, we exposed replicate populations of Drosophila melanogaster to one of two rates of chronic habitat loss (10% or 20% per generation) in either the breeding or the non-breeding period. We counted population abundance at the beginning of each season, and measured body mass and activity levels in a sample of individuals at the end of each generation. When habitat was lost during the breeding period, declining populations produced signals consistent with those documented in previous studies. Inclusion of trait-based indicators generally improved the detection of impending population collapse. However, when habitat was lost during the non-breeding period, the predictive capacity of these indicators was comparatively diminished. Our results have important implications for interpreting signals in the wild because they suggest that the production and detection of early warning indicators depends on the season in which stressors occur, and that this is likely related to the capacity of populations to respond numerically the following season.

Investigating cytosolic 5'-nucleotidase II family genes as candidates for neuropsychiatric disorders in Drosophila (114/150 chr)

Cytosolic 5'-nucleotidases II (cNT5-II) are an evolutionary conserved family of 5'-nucleotidases that catalyze the intracellular hydrolysis of nucleotides. In humans, the family is encoded by five genes, namely NT5C2, NT5DC1, NT5DC2, NT5DC3, and NT5DC4. While very little is known about the role of these genes in the nervous system, several of them have been associated with neuropsychiatric disorders. Here, we tested whether manipulating neuronal expression of cNT5-II orthologues affects neuropsychiatric disorders-related phenotypes in the model organism Drosophila melanogaster. We investigated the brain expression of Drosophila orthologues of cNT5-II family (dNT5A-CG2277, dNT5B-CG32549, and dNT5C-CG1814) using quantitative real-time polymerase chain reaction (qRT-PCR). Using the UAS/Gal4 system, we also manipulated the expression of these genes specifically in neurons. The knockdown was subjected to neuropsychiatric disorder-relevant behavioral assays, namely light-off jump reflex habituation and locomotor activity, and sleep was measured. In addition, neuromuscular junction synaptic morphology was assessed. We found that dNT5A, dNT5B, and dNT5C were all expressed in the brain. dNT5C was particularly enriched in the brain, especially at pharate and adult stages. Pan-neuronal knockdown of dNT5A and dNT5C showed impaired habituation learning. Knockdown of each of the genes also consistently led to mildly reduced activity and/or increased sleep. None of the knockdown models displayed significant alterations in synaptic morphology. In conclusion, in addition to genetic associations with psychiatric disorders in humans, altered expression of cNT5-II genes in the Drosophila nervous system plays a role in disease-relevant behaviors.

Epigenetic regulator Stuxnet modulates octopamine effect on sleep through a Stuxnet-Polycomb-Octβ2R cascade

Sleep homeostasis is crucial for sleep regulation. The role of epigenetic regulation in sleep homeostasis is unestablished. Previous studies showed that octopamine is important for sleep homeostasis. However, the regulatory mechanism of octopamine reception in sleep is unknown. In this study, we identify an epigenetic regulatory cascade (Stuxnet-Polycomb-Octβ2R) that modulates the octopamine receptor in Drosophila. We demonstrate that stuxnet positively regulates Octβ2R through repression of Polycomb in the ellipsoid body of the adult fly brain and that Octβ2R is one of the major receptors mediating octopamine function in sleep homeostasis. In response to octopamine, Octβ2R transcription is inhibited as a result of stuxnet downregulation. This feedback through the Stuxnet-Polycomb-Octβ2R cascade is crucial for sleep homeostasis regulation. This study demonstrates a Stuxnet-Polycomb-Octβ2R-mediated epigenetic regulatory mechanism for octopamine reception, thus providing an example of epigenetic regulation of sleep homeostasis.

Behavioral responses of three freshwater planaria species to light, visual and olfactory stimuli: Setting the stage for further ecotoxicological studies

Planarians are freshwater flatworms commonly used as environmental bioindicator due to their sensitivity of response and their ease of culturing in lab. Nevertheless, to date, very few studies describing their behavior have been led. This work aims to fill the literature gap by providing preliminary results through six behavioral challenges (locomotion, exploration, light stress, planarian light/dark test, shoaling and foraging) conducted with three different species Dugesia tigrina, Schmidtea mediterranea and Schmidtea polychroa. The behavioral responses of every species in each of these six assays were recorded and differences between species were highlighted, depending on the assays and conditions. Schmidtea polychroa is less active than the two others and had the highest light aversion. Reactions observed in response to diverse and realistic stimuli helped us to select the most suitable tests and choose the species that seem the most appropriate for future ecotoxicological and neurophysiological tests. Four tests - out of the six tested- seem reliable in order to standardize planarian behavioral tests.

A simple and reliable method for longitudinal assessment of untethered mosquito induced flight activity

Aedes aegypti adult females are key vectors of several arboviruses and flight activity plays a central role in mosquito biology and disease transmission. Available methods to quantify mosquito flight usually require special devices and mostly assess spontaneous locomotor activity at individual level. Here, we developed a new method to determine longitudinal untethered adult A. aegypti induced flight activity: the INduced FLight Activity TEst (INFLATE). This method was an adaptation of the "rapid iterative negative geotaxis" assay to assess locomotor activity in Drosophila and explore the spontaneous behavior of mosquitoes to fly following a physical stimulus. Insects were placed on a plastic cage previously divided in four vertical quadrants and flight performance was carried out by tapping cages towards the laboratory bench. After one minute, the number of insects per quadrant was registered by visual inspection and categorized in five different scores. By using INFLATE, we observed that flight performance was not influenced by repeated testing, sex or 5% ethanol intake. However, induced flight activity was strongly affected by aging, blood meal and inhibition of mitochondrial complex I. This simple and rapid method allows the longitudinal assessment of induced flight activity of multiple untethered mosquitoes and may contribute to a better understanding of A. aegypti dispersal biology.

Effect of kaempferol on the transgenic Drosophila model of Parkinson's disease

The present study was aimed to study the effect of kaempferol, on the transgenic Drosophila model of Parkinson's disease. Kaempferol was added in the diet at final concentration of 10, 20, 30 and 40 µM and the effect was studied on various cognitive and oxidative stress markers. The results of the study showed that kaempferol, delayed the loss of climbing ability as well as the activity of PD flies in a dose dependent manner compared to unexposed PD flies. A dose-dependent reduction in oxidative stress markers was also observed. Histopathological examination of fly brains using anti-tyrosine hydroxylase immunostaining has revealed a significant dose-dependent increase in the expression of tyrosine hydroxylase in PD flies exposed to kaempferol. Molecular docking results revealed that kaempferol binds to human alpha synuclein at specific sites that might results in the inhibition of alpha synuclein aggregation and prevents the formation of Lewy bodies.

Ropinirole silver nanocomposite attenuates neurodegeneration in the transgenic Drosophila melanogaster model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease due to the degeneration of dopaminergic neurons in substantia nigra pars compacta of the mid brain. The present study investigates the neuro-protective role of synthesized ropinirole silver nanocomposite (RPAgNC) in Drosophila model of PD. α-synuclein accumulation in the brain of flies (PD flies) leads to the damage of dopaminergic neurons, dopamine depletion, impaired muscular coordination, memory decline and increase in oxidative stress. Ingestion of the RPAgNC by Drosophila significantly prevented the neuronal degeneration compared to only ropinirole. The results confirm that the RPAgNC exerts more neuro-protective effect compared to dopamine agonist i.e. ropinirole as such drug in experimental PD flies. This article is part of the special issue entitled 'The Quest for Disease-Modifying Therapies for Neurodegenerative Disorders'.

Life at High Latitudes Does Not Require Circadian Behavioral Rhythmicity under Constant Darkness

Nearly all organisms evolved endogenous self-sustained timekeeping mechanisms to track and anticipate cyclic changes in the environment. Circadian clocks, with a periodicity of about 24 h, allow animals to adapt to day-night cycles. Biological clocks are highly adaptive, but strong behavioral rhythms might be a disadvantage for adaptation to weakly rhythmic environments such as polar areas [1, 2]. Several high-latitude species, including Drosophila species, were found to be highly arrhythmic under constant conditions [3-6]. Furthermore, Drosophila species from subarctic regions can extend evening activity until dusk under long days. These traits depend on the clock network neurochemistry, and we previously proposed that high-latitude Drosophila species evolved specific clock adaptations to colonize polar regions [5, 7, 8]. We broadened our analysis to 3 species of the Chymomyza genus, which diverged circa 5 million years before the Drosophila radiation [9] and colonized both low and high latitudes [10, 11]. C. costata, pararufithorax, and procnemis, independently of their latitude of origin, possess the clock neuronal network of low-latitude Drosophila species, and their locomotor activity does not track dusk under long photoperiods. Nevertheless, the high-latitude C. costata becomes arrhythmic under constant darkness (DD), whereas the two low-latitude species remain rhythmic. Different mechanisms are behind the arrhythmicity in DD of C. costata and the high-latitude Drosophila ezoana, suggesting that the ability to maintain behavioral rhythms has been lost more than once during drosophilids' evolution and that it might indeed be an evolutionary adaptation for life at high latitudes.

Genetic Signatures of Drug Response Variability in Drosophila melanogaster

Knowledge of the genetic basis underlying variation in response to environmental exposures or treatments is important in many research areas. For example, knowing the set of causal genetic variants for drug responses could revolutionize personalized medicine. We used Drosophila melanogaster to investigate the genetic signature underlying behavioral variability in response to methylphenidate (MPH), a drug used in the treatment of attention-deficit/hyperactivity disorder. We exposed a wild-type D. melanogaster population to MPH and a control treatment, and observed an increase in locomotor activity in MPH-exposed individuals. Whole-genome transcriptomic analyses revealed that the behavioral response to MPH was associated with abundant gene expression alterations. To confirm these patterns in a different genetic background and to further advance knowledge on the genetic signature of drug response variability, we used a system of inbred lines, the Drosophila Genetic Reference Panel (DGRP). Based on the DGRP, we showed that the behavioral response to MPH was strongly genotype-dependent. Using an integrative genomic approach, we incorporated known gene interactions into the genomic analyses of the DGRP, and identified putative candidate genes for variability in drug response. We successfully validated 71% of the investigated candidate genes by gene expression knockdown. Furthermore, we showed that MPH has cross-generational behavioral and transcriptomic effects. Our findings establish a foundation for understanding the genetic mechanisms driving genotype-specific responses to medical treatment, and highlight the opportunities that integrative genomic approaches have in optimizing medical treatment of complex diseases.

Locomotor Behaviour and Clock Neurons Organisation in the Agricultural Pest Drosophila suzukii

Drosophila suzukii (Matsumara) also called Spotted Wing Drosophila (SWD), is an invasive pest species originally from Asia that has now spread widely across Europe and North America. The majority of drosophilids including the best known Drosophila melanogaster only breed on decaying fruits. On the contrary, the presence of a strong serrated ovipositor and behavioural and metabolic adaptations allow D. suzukii to lay eggs inside healthy, ripening fruits that are still on the plant. Here we present an analysis of the rhythmic locomotor activity behaviour of D. suzukii under several laboratory settings. Moreover, we identify the canonical clock neurons in this species by reporting the expression pattern of the major clock proteins in the brain. Interestingly, a fundamentally similar organisation of the clock neurons network between D. melanogaster and D. suzukii does not correspond to similar characteristics in rhythmic locomotor activity behaviour.

Attenuating the DNA damage response to double-strand breaks restores function in models of CNS neurodegeneration

DNA double-strand breaks are a feature of many acute and long-term neurological disorders, including neurodegeneration, following neurotrauma and after stroke. Persistent activation of the DNA damage response in response to double-strand breaks contributes to neural dysfunction and pathology as it can force post-mitotic neurons to re-enter the cell cycle leading to senescence or apoptosis. Mature, non-dividing neurons may tolerate low levels of DNA damage, in which case muting the DNA damage response might be neuroprotective. Here, we show that attenuating the DNA damage response by targeting the meiotic recombination 11, Rad50, Nijmegen breakage syndrome 1 complex, which is involved in double-strand break recognition, is neuroprotective in three neurodegeneration models in Drosophila and prevents Aβ_1-42-induced loss of synapses in embryonic hippocampal neurons. Attenuating the DNA damage response after optic nerve injury is also neuroprotective to retinal ganglion cells and promotes dramatic regeneration of their neurites both in vitro and in vivo. Dorsal root ganglion neurons similarly regenerate when the DNA damage response is targeted in vitro and in vivo and this strategy also induces significant restoration of lost function after spinal cord injury. We conclude that muting the DNA damage response in the nervous system is neuroprotective in multiple neurological disorders. Our results point to new therapies to maintain or repair the nervous system.

Effects of MUL1 and PARKIN on the circadian clock, brain and behaviour in Drosophila Parkinson's disease models

Background

Mutants which carry mutations in genes encoding mitochondrial ligases MUL1 and PARKIN are convenient Drosophila models of Parkinson’s disease (PD). In several studies it has been shown that in Parkinson’s disease sleep disturbance occurs, which may be the result of a disturbed circadian clock.

Results

We found that the ROS level was higher, while the anti-oxidant enzyme SOD1 level was lower in mul1^A6 and park¹ mutants than in the white mutant used as a control. Moreover, mutations of both ligases affected circadian rhythms and the clock. The expression of clock genes per, tim and clock and the level of PER protein were changed in the mutants. Moreover, expression of ATG5, an autophagy protein also involved in circadian rhythm regulation, was decreased in the brain and in PDF-immunoreactive large ventral lateral clock neurons. The observed changes in the molecular clock resulted in a longer period of locomotor activity rhythm, increased total activity and shorter sleep at night. Finally, the lack of both ligases led to decreased longevity and climbing ability of the flies.

Conclusions

All of the changes observed in the brains of these Drosophila models of PD, in which mitochondrial ligases MUL1 and PARKIN do not function, may explain the mechanisms of some neurological and behavioural symptoms of PD.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0506-8) contains supplementary material, which is available to authorized users.

Effect of Majun Baladur on life span, climbing ability, oxidative stress and dopaminergic neurons in the transgenic Drosophila model of Parkinson's disease

The effect of a poly herbal drug Majun Baladur (MB) was studied on the transgenic Drosophila melanogaster expressing human alpha synuclein in the neurons (PD flies). The equivalents of recommended dose for human were established for 20 g of fly food i.e. 0.0014, 0.0028, 0.0042 and 0.0056 g per 20 g of diet. The PD flies were allowed to feed on it for 24 days before performing the assays. The exposure to MB increased the life span and improves the activity of PD flies. The PD flies exposed to 0.0014, 0.0028, 0.042 and 0.0056 g of MB showed a dose dependent significant delay of 1.47, 1.88, 2.52 and 3.05 folds in the climbing ability compared to unexposed PD flies. A dose dependent significant decrease of 1.38, 1.45, 1.48 and 1.65 folds in TBARS; 1.08, 1.11, 1.17 and 1.20 folds in the GST activity; 1.20, 1.28, 1.39 and 1.52 folds in the PC content; 1.43, 1.53, 1.65 and 1.79 folds in the Caspase-9 activity; 1.21, 1.31, 1.53 and 1.64 folds in the activity of Caspase-3 and 1.24, 1.42, 1.50 and 1.79 folds in the activity of catalase; 1.50, 1.63, 1.88 and 2.06 folds in the activity of SOD in PD flies exposed to 0.0014, 0.0028, 0.042 and 0.0056 g of MB, respectively. A significant dose dependent increase of 1.20, 1.29, 1.33 and 1.44 folds in as NPSH content was observed in PD flies exposed to 0.0014, 0.0028, 0.042 and 0.0056 g of MB, respectively. The exposure to MB protects the loss of dopaminergic neurons as is evident by immunohistochemistry. It is concluded that MB is potent in reducing the PD symptoms being mimicked in the transgenic flies.

Loss of Prune in Circadian Cells Decreases the Amplitude of the Circadian Locomotor Rhythm in Drosophila

The circadian system, which has a period of about 24 h, is import for organismal health and fitness. The molecular circadian clock consists of feedback loops involving both transcription and translation, and proper function of the circadian system also requires communication among intracellular organelles. As important hubs for signaling in the cell, mitochondria integrate a variety of signals. Mitochondrial dysfunction and disruption of circadian rhythms are observed in neurodegenerative diseases and during aging. However, how mitochondrial dysfunction influences circadian rhythm is largely unknown. Here, we report that Drosophila prune (pn), which localizes to the mitochondrial matrix, most likely affects the function of certain clock neurons.Deletion of pn in flies caused decreased expression of mitochondrial transcription factor TFAM and reductions in levels of mitochondrial DNA, which resulted in mitochondrial dysfunction. Loss of pn decreased the amplitude of circadian rhythms.In addition, we showed that depletion of mtDNA by overexpression of a mitochondrially targeted restriction enzyme mitoXhoI also decreased the robustness of circadian rhythms. Our work demonstrates that pn is important for mitochondrial function thus involved in the regulation of circadian rhythms.

Overexpression of Mitochondrial Ligases Reverses Rotenone-Induced Effects in a Drosophila Model of Parkinson's Disease

Mul1 and Park are two major mitochondrial ligases responsible for mitophagy. Damaged mitochondria that cannot be removed are a source of an increased level of free radicals, which in turn can destructively affect other cell organelles as well as entire cells. One of the toxins that damages mitochondria is rotenone, a neurotoxin that after exposure displays symptoms typical of Parkinson’s disease. In the present study, we showed that overexpressing genes encoding mitochondrial ligases protects neurons during treatment with rotenone. Drosophila strains with overexpressed mul1 or park show a significantly reduced degeneration of dopaminergic neurons, as well as normal motor activity during exposure to rotenone. In the nervous system, rotenone affected synaptic proteins, including Synapsin, Synaptotagmin and Disk Large1, as well as the structure of synaptic vesicles, while high levels of Mul1 or Park suppressed degenerative events at synapses. We concluded that increased levels of mitochondrial ligases are neuroprotective and could be considered in developing new therapies for Parkinson’s disease.

Most sleep does not serve a vital function: Evidence from Drosophila melanogaster

Sleep appears to be a universally conserved phenomenon among the animal kingdom, but whether this notable evolutionary conservation underlies a basic vital function is still an open question. Using a machine learning-based video-tracking technology, we conducted a detailed high-throughput analysis of sleep in the fruit fly Drosophila melanogaster, coupled with a lifelong chronic and specific sleep restriction. Our results show that some wild-type flies are virtually sleepless in baseline conditions and that complete, forced sleep restriction is not necessarily a lethal treatment in wild-type D. melanogaster. We also show that circadian drive, and not homeostatic regulation, is the main contributor to sleep pressure in flies. These results offer a new perspective on the biological role of sleep in Drosophila and, potentially, in other species.

Parallel clinal variation in the mid-day siesta of Drosophila melanogaster implicates continent-specific targets of natural selection

Similar to many diurnal animals, Drosophila melanogaster exhibits a mid-day siesta that is more robust as ambient temperature rises, an adaptive response aimed at minimizing exposure to heat. Mid-day siesta levels are partly regulated by the thermosensitive splicing of a small intron (termed dmpi8) found in the 3’ untranslated region (UTR) of the circadian clock gene period (per). Using the well-studied D. melanogaster latitudinal cline along the eastern coast of Australia, we show that flies from temperate populations sleep less during the day compared to those from tropical regions. We identified combinations of four single nucleotide polymorphisms (SNPs) in the 3’ UTR of per that yield several different haplotypes. The two most abundant of these haplotypes exhibit a reciprocal tropical-temperate distribution in relative frequency. Intriguingly, transgenic flies with the major tropical isoform manifest increased daytime sleep and reduced dmpi8 splicing compared to those carrying the temperate variant. Our results strongly suggest that for a major portion of D. melanogaster in Australia, thermal adaptation of daily sleep behavior included spatially varying selection on ancestrally derived polymorphisms in the per 3’ UTR that differentially control dmpi8 splicing efficiency. Prior work showed that African flies from high altitudes manifest reduced mid-day siesta levels, indicative of parallel latitudinal and altitudinal adaptation across continents. However, geographical variation in per 3’ UTR haplotypes was not observed for African flies, providing a compelling case for inter-continental variation in factors targeted by natural selection in attaining a parallel adaptation. We propose that the ability to calibrate mid-day siesta levels to better match local temperature ranges is a key adaptation contributing to the successful colonization of D. melanogaster beyond its ancestral range in the lowlands of Sub-Saharan Africa.

In warm climates many animals, including humans, exhibit a mid-day siesta, almost certainly a behavior meant to minimize the harm from prolonged exposure to the hot mid-day sun. But what about animals that adapted to cooler more temperate climates, might they have a less pronounced siesta? Indeed, we show that in the common fruit fly, Drosophila melanogaster, those from temperate regions in Australia exhibit less mid-day siesta compared to their tropical counterparts. Prior work showed that mid-day sleep levels are partially regulated by a ‘clock’ gene called period (per), which controls the timing of wake-sleep cycles in addition to other daily rhythms. We identified several DNA differences in the per gene that show geographical variation and contribute to the daytime sleep differences in flies from tropical and temperate regions via a mechanism that involves how well a temperature-sensitive intron in per is removed. A similar reduction in mid-day sleep was previously observed in African flies that adapted to the cooler temperatures found at high altitudes. Together, our findings provide a rare example where latitude and altitude lead to a similar behavioral adaptation to temperature. Moreover, the results suggest inter-continental differences in the evolutionary solutions used to attain the same thermal adaptation to cooler climates.

Role of the circadian clock in the statistics of locomotor activity in Drosophila

In many animals the circadian rhythm of locomotor activity is controlled by an endogenous circadian clock. Using custom made housing and video tracking software in order to obtain high spatial and temporal resolution, we studied the statistical properties of the locomotor activity of wild type and two clock mutants of Drosophila melanogaster. We show here that the distributions of activity and quiescence bouts for the clock mutants in light-dark conditions (LD) are very different from the distributions obtained when there are no external cues from the environment (DD). In the wild type these distributions are very similar, showing that the clock controls this aspect of behavior in both regimes (LD and DD). Furthermore, the distributions are very similar to those reported for Wistar rats. For the timing of events we also observe important differences, quantified by how the event rate distributions scale for increasing time windows. We find that for the wild type these distributions can be rescaled by the same function in DD as in LD. Interestingly, the same function has been shown to rescale the rate distributions in Wistar rats. On the other hand, for the clock mutants it is not possible to rescale the rate distributions, which might indicate that the extent of circadian control depends on the statistical properties of activity and quiescence.

Functional Validation of Candidate Genes Detected by Genomic Feature Models

Understanding the genetic underpinnings of complex traits requires knowledge of the genetic variants that contribute to phenotypic variability. Reliable statistical approaches are needed to obtain such knowledge. In genome-wide association studies, variants are tested for association with trait variability to pinpoint loci that contribute to the quantitative trait. Because stringent genome-wide significance thresholds are applied to control the false positive rate, many true causal variants can remain undetected. To ameliorate this problem, many alternative approaches have been developed, such as genomic feature models (GFM). The GFM approach tests for association of set of genomic markers, and predicts genomic values from genomic data utilizing prior biological knowledge. We investigated to what degree the findings from GFM have biological relevance. We used the Drosophila Genetic Reference Panel to investigate locomotor activity, and applied genomic feature prediction models to identify gene ontology (GO) categories predictive of this phenotype. Next, we applied the covariance association test to partition the genomic variance of the predictive GO terms to the genes within these terms. We then functionally assessed whether the identified candidate genes affected locomotor activity by reducing gene expression using RNA interference. In five of the seven candidate genes tested, reduced gene expression altered the phenotype. The ranking of genes within the predictive GO term was highly correlated with the magnitude of the phenotypic consequence of gene knockdown. This study provides evidence for five new candidate genes for locomotor activity, and provides support for the reliability of the GFM approach.

Locomotor activity in males of Aedes aegypti can shift in response to females' presence

BACKGROUND

The study of physiological and behavioral traits of mosquito vectors has been of growing relevance for the proposition of alternative methods for controlling vector-borne diseases. Despite this, most studies focus on the female's traits, including the behavior of host seeking, the physiology of disease transmission and the site-choice for oviposition. However, understanding the factors that lead to males' reproductive success is of utmost importance, since it can help building new strategies for constraining population growth. Male behavior towards mating varies widely among species and the communication between males and females is the first aspect securing a successful encounter. Here we used an automated monitoring system to study the profile of locomotor activity of Aedes aegypti males in response to female's presence in an adapted confinement tube. We propose a new method to quantify male response to the presence of females, which can be potentially tested as an indicator of the success of one male in recognizing a female for mating.

RESULTS

Locomotor activity varies in daily cycles regulated by an endogenous clock and synchronized by external factors, such as light and temperature. Our results show the previously described startle response to light, which is displayed as a steep morning activity peak immediately when lights are on. Activity drops during the day and begins to rise again right before evening, happening about 1.5 h earlier in males than in females. Most interestingly, males' activity shows a double peak, and the second peak is very subtle when males are alone and relatively more pronounced when females are present in the confinement tubes. The switch in the peak of activity, measured by the herein suggested Peak Matching Index (PMI), was significantly different between males with and without females.

CONCLUSIONS

The adapted monitoring system used here allowed us to quantify the response of individual males to nearby females in terms of the extent of the activity peak displacement. In this direction, we created the peak matching index (PMI), a new parameter that we anticipate could be interpreted as the inclination of males to respond to females' presence, and further tested as an indicator of the potential for finding females for mating.

Interspecific studies of circadian genes period and timeless in Drosophila

The level of rescue of clock function in genetically arrhythmic Drosophila melanogaster hosts using interspecific clock gene transformation was used to study the putative intermolecular coevolution between interacting clock proteins. Among them PER and TIM are the two important negative regulators of the circadian clock feedback loop. We transformed either the D. pseudoobscura per or tim transgenes into the corresponding arrhythmic D. melanogaster mutant (per01 or tim01) and observed >50% rhythmicity but the period of activity rhythm was either longer (D. pseudoobscura-per) or shorter than 24 h (D. pseudoobscura-tim) compared to controls. By introducing both transgenes simultaneously into double mutants, we observed that the period of the activity rhythm was rescued by the pair of hemizygous transgenes (~24 h). These flies also showed a more optimal level of temperature compensation for the period. Under LD 12:12 these flies have a D. pseudoobscura like activity profile with the absence of morning anticipation as well as a very prominent earlier evening peak of activity rhythm. These observation are consistent with the view that TIM and PER form a heterospecific coevolved module at least for the circadian period of activity rhythms. However the strength of rhythmicity was reduced by having both transgenes present, so while evidence for a coevolution between PER and TIM is observed for some characters it is not for others.

Clock Gene Period in the Chagas Disease Vector Triatoma infestans (Hemiptera: Reduviidae)

To contribute to a better understanding of the molecular bases of the circadian biological rhythms in Chagas disease vectors, in this work we identified functional domains in the sequences of the clock protein PERIOD (PER) in Rhodnius prolixus and Triatoma infestans and analyzed the expression of the PER gene at mRNA level in T. infestans. The PER protein sequences comparison among these species and those from other insects revealed that the most similar regions are the PAS domains and the most variable is the COOH-terminal. On the other hand, the per gene expression in nervous tissue of adult T. infestans varies with a daily canonical rhythm in groups of individuals maintained under photoperiod (light/dark, LD) and constant dark (DD), showing a significant peak of expression at sunset. The pattern of expression detected in LD persists under the DD condition. As expected, in the group maintained in constant light (LL), no daily increase was detected in per transcript level. Besides, the presence of per transcript in different tissues of adult individuals and in nervous tissue of nymphs evidenced activity of peripheral clocks in adults and activity of the central clock in nymphs of T. infestans.

The SR protein B52/SRp55 regulates splicing of the period thermosensitive intron and mid-day siesta in Drosophila

Similar to many diurnal animals, Drosophila melanogaster exhibits a mid-day siesta that is more robust as temperature increases, an adaptive response that aims to minimize the deleterious effects from exposure to heat. This temperature-dependent plasticity in mid-day sleep levels is partly based on the thermal sensitive splicing of an intron in the 3' untranslated region (UTR) of the circadian clock gene termed period (per). In this study, we evaluated a possible role for the serine/arginine-rich (SR) splicing factors in the regulation of dmpi8 splicing efficiency and mid-day siesta. Using a Drosophila cell culture assay we show that B52/SRp55 increases dmpi8 splicing efficiency, whereas other SR proteins have little to no effect. The magnitude of the stimulatory effect of B52 on dmpi8 splicing efficiency is modulated by natural variation in single nucleotide polymorphisms (SNPs) in the per 3' UTR that correlate with B52 binding levels. Down-regulating B52 expression in clock neurons increases mid-day siesta and reduces dmpi8 splicing efficiency. Our results establish a novel role for SR proteins in sleep and suggest that polymorphisms in the per 3' UTR contribute to natural variation in sleep behavior by modulating the binding efficiencies of SR proteins.