Highlights d Drosophila DN1p clock neurons innervate the anterior optic tubercle (AOTU) d A subset of tubercular-bulbar (TuBu) neurons in the AOTU is inhibited by DN1p neurons d These TuBu neurons promote consolidated sleep during the day d Ellipsoid body ring neurons are downstream of sleepregulatory TuBu neurons

Sleep is a highly conserved and essential behaviour in many species, including the fruit fly Drosophila melanogaster. In the wild, sensory signalling encoding environmental information must be integrated with sleep drive to ensure that sleep is not initiated during detrimental conditions. However, the molecular and circuit mechanisms by which sleep timing is modulated by the environment are unclear. Here we introduce a novel behavioural paradigm to study this issue. We show that in male fruit flies, onset of the daytime siesta is delayed by ambient temperatures above 29 °C. We term this effect Prolonged Morning Wakefulness (PMW). We show that signalling through the TrpA1 thermo-sensor is required for PMW, and that TrpA1 specifically impacts siesta onset, but not night sleep onset, in response to elevated temperatures. We identify two critical TrpA1-expressing circuits and show that both contact DN1p clock neurons, the output of which is also required for PMW. Finally, we identify the circadian blue-light photoreceptor CRYPTOCHROME as a molecular regulator of PMW, and propose a model in which the Drosophila nervous system integrates information encoding temperature, light, and time to dynamically control when sleep is initiated. Our results provide a platform to investigate how environmental inputs co-ordinately regulate sleep plasticity.

Riboflavin metabolites are critical components of the mitochondrial electron transport chain. Manole et al. describe the genetics, phenotypes and neuropathology of a large patient series with riboflavin-responsive neuropathy. Using in-vitro and in-vivo models, they reveal mitochondrial dysfunction in the disorder, and validate riboflavin esters as a potential therapeutic strategy.

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Loss of FMR1 gene function results in fragile X syndrome (FXS), the most common heritable form of intellectual disability. The protein encoded from this locus (FMRP) is an RNA binding protein thought to primarily act as a translational regulator, however recent studies implicate FMRP in other mechanisms of gene regulation. Here, we demonstrate that the Drosophila fragile X homolog (dFMR1) biochemically interacts with the A-to-I RNA editing enzyme, dADAR. We found that dAdar and dfmr1 mutant larvae exhibit distinct morphological neuromuscular junction (NMJ) defects. Epistasis experiments based on these phenotypic differences suggest that dAdar acts downstream of dfmr1 and that dFMR1 modulates dADAR activity. Furthermore, sequence analyses revealed that loss or overexpression of dFMR1 affects editing efficiency on certain dADAR targets with defined roles in synaptic transmission. These results link dFMR1 with the RNA editing pathway and suggest that proper NMJ synaptic architecture requires modulation of dADAR activity by dFMR1.

Auto-regulatory feedback loops are a common molecular strategy used to optimize protein function. In Drosophila many mRNAs involved in neuro-transmission are re-coded at the RNA level by the RNA editing enzyme dADAR, leading to the incorporation of amino acids that are not directly encoded by the genome. dADAR also re-codes its own transcript, but the consequences of this auto-regulation in vivo are unclear. Here we show that hard-wiring or abolishing endogenous dADAR auto-regulation dramatically remodels the landscape of re-coding events in a site-specific manner. These molecular phenotypes correlate with altered localization of dADAR within the nuclear compartment. Furthermore, auto-editing exhibits sexually dimorphic patterns of spatial regulation and can be modified by abiotic environmental factors. Finally, we demonstrate that modifying dAdar auto-editing affects adaptive complex behaviors. Our results reveal the in vivo relevance of auto-regulatory control over post-transcriptional mRNA re-coding events in fine-tuning brain function and organismal behavior.

Heterochromatin formation drives epigenetic mechanisms associated with silenced gene expression. Repressive heterochromatin is established through the RNA interference pathway, triggered by double-stranded RNAs that can be modified via RNA editing. However, the biological consequences of such modifications remain enigmatic. Here we show that RNA editing regulates heterochromatic gene silencing in Drosophila. We utilize the binding activity of an RNA editing enzyme to visualize the in vivo production of a long double-stranded RNA trigger mediated by Hoppel transposable elements. Using homologous recombination, we delete this trigger, dramatically altering heterochromatic gene silencing and chromatin architecture. Furthermore, we show that the trigger RNA is edited, serves as a key regulator of chromatin state, and that dADAR auto-editing generates a natural suppressor of gene silencing. Lastly, systemic differences in RNA editing activity generates inter-individual variation in silencing state within a population. Our data reveal a global role for RNA editing in regulating gene expression.

Select proteins involved in electrical and chemical neurotransmission are re-coded at the RNA level via the deamination of particular adenosines to inosine by adenosine deaminases acting on RNA (ADARs). It has been hypothesized that this process, termed RNA editing, acts to "fine-tune" neurophysiological properties in animals and potentially downstream behavioral outputs. However, the extreme phenotypes resulting from deletions of adar loci have precluded investigations into the relationship between ADAR levels, target transcripts, and complex behaviors. Here, we engineer Drosophila hypomorphic for ADAR expression using homologous recombination. A substantial reduction in ADAR activity (>80%) leads to altered circadian motor patterns and abnormal male courtship, although surprisingly, general locomotor coordination is spared. The altered phenotypic landscape in our adar hypomorph is paralleled by an unexpected dichotomous response of ADAR target transcripts, i.e. certain adenosines are minimally affected by dramatic ADAR reduction, whereas editing of others is severely curtailed. Furthermore, we use a novel reporter to map RNA editing activity across the nervous system, and we demonstrate that knockdown of editing in fruitless-expressing neurons is sufficient to modify the male courtship song. Our data demonstrate that network-wide temporal and spatial regulation of ADAR activity can tune the complex system of RNA-editing sites and modulate multiple ethologically relevant behavioral modalities.Informational recoding of RNA by the catalytic deamination of adenosine to inosine proceeds through the action of ADARs 3 (1). Long double strand RNA duplexes exhibiting perfect complementarity can be modified extensively by promiscuous ADAR activity. However, mRNAs may also serve as site-specific substrates for ADARs via base pairing interactions that generate short imperfect duplexes that generally include the exon destined for editing and a cis-acting complementary sequence, usually found in a neighboring intron (2, 3). Because inosine is recognized by the translation machinery as guanosine (4), A-to-I editing in mRNAs can lead to the incorporation of amino acids differing from those specified by the literal genome.In Drosophila, the spectrum of ADAR substrates is peculiarly specific, consisting primarily of mRNAs encoding an array of voltage-and ligand-gated ion channels, as well as numerous pre-synaptic proteins involved in exo-and endocytosis of synaptic vesicles (5-8). Similarly, several mammalian ion channels and G-protein-coupled receptors are also subject to RNA editing (2, 7, 9 -11). In light of the ontological class and high sequence conservation of ADAR target genes, RNA editing has been invoked as an essential function in controlling synaptic transmission and neurophysiology. Correspondingly, deletion of the single Drosophila adar locus (dAdar) results in severe adult-stage behavioral abnormalities, including extreme uncoordination, seizures and a complete lack of courtship in dAdar null (dAdar 5g1 ) males (1...