Fatty-acid binding proteins modulate sleep and enhance long-term memory consolidation in Drosophila

A neuron-glia lipid metabolic cycle couples daily sleep to mitochondrial homeostasis

Sleep is thought to be restorative to brain energy homeostasis, but it is not clear how this is achieved. We show here that Drosophila glia exhibit a daily cycle of glial mitochondrial oxidation and lipid accumulation that is dependent on prior wake and requires the Drosophila APOE orthologs NLaz and GLaz, which mediate neuron-glia lipid transfer. In turn, a full night of sleep is required for glial lipid clearance, mitochondrial oxidative recovery and maximal neuronal mitophagy. Knockdown of neuronal NLaz causes oxidative stress to accumulate in neurons, and the neuronal mitochondrial integrity protein, Drp1, is required for daily glial lipid accumulation. These data suggest that neurons avoid accumulation of oxidative mitochondrial damage during wake by using mitophagy and passing damage to glia in the form of lipids. We propose that a mitochondrial lipid metabolic cycle between neurons and glia reflects a fundamental function of sleep relevant for brain energy homeostasis.

Importance of fatty acid binding proteins in cellular function and organismal metabolism

Fatty acid binding proteins (Fabps) are small soluble proteins that are abundant in the cytosol. These proteins are known to bind a myriad of small hydrophobic molecules and have been postulated to serve a variety of roles, yet their precise functions have remained an enigma over half a century of study. Here, we consider recent findings, along with the cumulative findings contributed by many laboratories working on Fabps over the last half century, to synthesize a new outlook for what functions Fabps serve in cells and organisms. Collectively, the findings illustrate that Fabps function as versatile multi-purpose devices serving as sensors, conveyors and modulators to enable cells to detect and handle a specific class of metabolites, and to adjust their metabolic capacity and efficiency.

FABP7: a glial integrator of sleep, circadian rhythms, plasticity, and metabolic function

Sleep and circadian rhythms are observed broadly throughout animal phyla and influence neural plasticity and cognitive function. However, the few phylogenetically conserved cellular and molecular pathways that are implicated in these processes are largely focused on neuronal cells. Research on these topics has traditionally segregated sleep homeostatic behavior from circadian rest-activity rhythms. Here we posit an alternative perspective, whereby mechanisms underlying the integration of sleep and circadian rhythms that affect behavioral state, plasticity, and cognition reside within glial cells. The brain-type fatty acid binding protein, FABP7, is part of a larger family of lipid chaperone proteins that regulate the subcellular trafficking of fatty acids for a wide range of cellular functions, including gene expression, growth, survival, inflammation, and metabolism. FABP7 is enriched in glial cells of the central nervous system and has been shown to be a clock-controlled gene implicated in sleep/wake regulation and cognitive processing. FABP7 is known to affect gene transcription, cellular outgrowth, and its subcellular localization in the fine perisynaptic astrocytic processes (PAPs) varies based on time-of-day. Future studies determining the effects of FABP7 on behavioral state- and circadian-dependent plasticity and cognitive processes, in addition to functional consequences on cellular and molecular mechanisms related to neural-glial interactions, lipid storage, and blood brain barrier integrity will be important for our knowledge of basic sleep function. Given the comorbidity of sleep disturbance with neurological disorders, these studies will also be important for our understanding of the etiology and pathophysiology of how these diseases affect or are affected by sleep.

Ecdysone acts through cortex glia to regulate sleep in Drosophila

Steroid hormones are attractive candidates for transmitting long-range signals to affect behavior. These lipid-soluble molecules derived from dietary cholesterol easily penetrate the brain and act through nuclear hormone receptors (NHRs) that function as transcription factors. To determine the extent to which NHRs affect sleep:wake cycles, we knocked down each of the 18 highly conserved NHRs found in Drosophila adults and report that the ecdysone receptor (EcR) and its direct downstream NHR Eip75B (E75) act in glia to regulate the rhythm and amount of sleep. Given that ecdysone synthesis genes have little to no expression in the fly brain, ecdysone appears to act as a long-distance signal and our data suggest that it enters the brain more at night. Anti-EcR staining localizes to the cortex glia in the brain and functional screening of glial subtypes revealed that EcR functions in adult cortex glia to affect sleep. Cortex glia are implicated in lipid metabolism, which appears to be relevant for actions of ecdysone as ecdysone treatment mobilizes lipid droplets (LDs), and knockdown of glial EcR results in more LDs. In addition, sleep-promoting effects of exogenous ecdysone are diminished in lsd-2 mutant flies, which are lean and deficient in lipid accumulation. We propose that ecdysone is a systemic secreted factor that modulates sleep by stimulating lipid metabolism in cortex glia.

Circadian disruption of memory consolidation in Drosophila

The role of the circadian system in memory formation is an important question in neurobiology. Despite this hypothesis being intuitively appealing, the existing data is confusing. Recent work in Drosophila has helped to clarify certain aspects of the problem, but the emerging sense is that the likely mechanisms are more complex than originally conceptualized. In this report, we identify a post-training window of time (during consolidation) when the circadian clock and its components are involved in memory formation. In the broader context, our data suggest that circadian biology might have multiple roles during memory formation. Testing for its roles at multiple timepoints, and in different cells, will be necessary to resolve some of the conflicting data.

Fatty acid binding protein is required for chitin biosynthesis in the wing of Drosophila melanogaster

Chitin, the major structural polysaccharide in arthropods such as insects and mites, is a linear polymer of N-acetylglucosamine units. The growth and development of insects are intimately coupled with chitin biosynthesis. The membrane-bound β-glycosyltransferase chitin synthase is known to catalyze the key polymerization step of N-acetylglucosamine. However, the additional proteins that might assist chitin synthase during chitin biosynthesis are not well understood. Recently, fatty acid binding protein (Fabp) has been suggested as a candidate that interacts with the chitin synthase Krotzkopf verkehrt (Kkv) in Drosophila melanogaster. Here, using split-ubiquitin membrane yeast two-hybrid and pull-down assays, we have demonstrated that the Fabp-B splice variant physically interacts with Kkv in vitro. The global knockdown of Fabp in D. melanogaster using RNA interference (RNAi) induced lethality at the larval stage. Moreover, in tissue-specific RNAi experiments, silenced Fabp expression in the epidermis and tracheal system caused a lethal larval phenotype. Fabp knockdown in the wings resulted in an abnormal wing development and uneven cuticular surface. In addition to reducing the chitin content in the first longitudinal vein of wings, Fabp silencing also caused the loss of procuticle laminate structures. This study revealed that Fabp plays an important role in chitin synthesis and contributes to a comprehensive understanding of the complex insect chitin biosynthesis.

Sleep-promoting neurons remodel their response properties to calibrate sleep drive with environmental demands

Falling asleep at the wrong time can place an individual at risk of immediate physical harm. However, not sleeping degrades cognition and adaptive behavior. To understand how animals match sleep need with environmental demands, we used live-brain imaging to examine the physiological response properties of the dorsal fan-shaped body (dFB) following interventions that modify sleep (sleep deprivation, starvation, time-restricted feeding, memory consolidation) in Drosophila. We report that dFB neurons change their physiological response-properties to dopamine (DA) and allatostatin-A (AstA) in response to different types of waking. That is, dFB neurons are not simply passive components of a hard-wired circuit. Rather, the dFB neurons intrinsically regulate their response to the activity from upstream circuits. Finally, we show that the dFB appears to contain a memory trace of prior exposure to metabolic challenges induced by starvation or time-restricted feeding. Together, these data highlight that the sleep homeostat is plastic and suggests an underlying mechanism.

The Role of Glia Clocks in the Regulation of Sleep in Drosophila melanogaster

In Drosophila melanogaster, the pacemaker located in the brain plays the main role in maintaining circadian rhythms; however, peripheral oscillators including glial cells, are also crucial components of the circadian network. In the present study, we investigated an impact of oscillators located in astrocyte-like glia, the chiasm giant glia of the optic lobe, epithelial and subperineurial glia on sleep of Drosophila males. We described that oscillators located in astrocyte-like glia and chiasm giant glia are necessary to maintain daily changes in clock neurons arborizations, while those located in epithelial glia regulate amplitude of these changes. Finally, we showed that communication between glia and neurons through tripartite synapses formed by epithelial glia and, in effect, neurotransmission regulation plays important role in wake-promoting during the day.SIGNIFICANCE STATEMENT Circadian clock or pacemaker regulates many aspects of animals' physiology and behavior. The pacemaker is located in the brain and is composed of neurons. However, there are also additional oscillators, called peripheral clocks, which synchronize the main clock. Despite the critical role of glia in the clock machinery, little is known which type of glia houses peripheral oscillators and how they affect neuronal clocks. This study using Drosophila shows that oscillators in specific glia types maintain awakeness during the day by regulating the daily plasticity of clock neurons.

A Dichotomous Role for FABP7 in Sleep and Alzheimer's Disease Pathogenesis: A Hypothesis

Fatty acid binding proteins (FABPs) are a family of intracellular lipid chaperone proteins known to play critical roles in the regulation of fatty acid uptake and transport as well as gene expression. Brain-type fatty acid binding protein (FABP7) is enriched in astrocytes and has been implicated in sleep/wake regulation and neurodegenerative diseases; however, the precise mechanisms underlying the role of FABP7 in these biological processes remain unclear. FABP7 binds to both arachidonic acid (AA) and docosahexaenoic acid (DHA), resulting in discrete physiological responses. Here, we propose a dichotomous role for FABP7 in which ligand type determines the subcellular translocation of fatty acids, either promoting wakefulness aligned with Alzheimer's pathogenesis or promoting sleep with concomitant activation of anti-inflammatory pathways and neuroprotection. We hypothesize that FABP7-mediated translocation of AA to the endoplasmic reticulum of astrocytes increases astrogliosis, impedes glutamatergic uptake, and enhances wakefulness and inflammatory pathways via COX-2 dependent generation of pro-inflammatory prostaglandins. Conversely, we propose that FABP7-mediated translocation of DHA to the nucleus stabilizes astrocyte-neuron lactate shuttle dynamics, preserves glutamatergic uptake, and promotes sleep by activating anti-inflammatory pathways through the peroxisome proliferator-activated receptor-γ transcriptional cascade. Importantly, this model generates several testable hypotheses applicable to other neurodegenerative diseases, including amyotrophic lateral sclerosis and Parkinson's disease.

Fabp7 Is Required for Normal Sleep Suppression and Anxiety-Associated Phenotype following Single-Prolonged Stress in Mice

Humans with post-traumatic stress disorder (PTSD) exhibit sleep disturbances that include insomnia, nightmares, and enhanced daytime sleepiness. Sleep disturbances are considered a hallmark feature of PTSD; however, little is known about the cellular and molecular mechanisms regulating trauma-induced sleep disorders. Using a rodent model of PTSD called "Single Prolonged Stress" (SPS) we examined the requirement of the brain-type fatty acid binding protein Fabp7, an astrocyte expressed lipid-signaling molecule, in mediating trauma-induced sleep disturbances. We measured baseline sleep/wake parameters and then exposed Fabp7 knock-out (KO) and wild-type (WT) C57BL/6N genetic background control animals to SPS. Sleep and wake measurements were obtained immediately following the initial trauma exposure of SPS, and again 7 days later. We found that active-phase (dark period) wakefulness was similar in KO and WT at baseline and immediately following SPS; however, it was significantly increased after 7 days. These effects were opposite in the inactive-phase (light period), where KOs exhibited increased wake in baseline and following SPS, but returned to WT levels after 7 days. To examine the effects of Fabp7 on unconditioned anxiety following trauma, we exposed KO and WT mice to the light-dark box test before and after SPS. Prior to SPS, KO and WT mice spent similar amounts of time in the lit compartment. Following SPS, KO mice spent significantly more time in the lit compartment compared to WT mice. These results demonstrate that mutations in an astrocyte-expressed gene (Fabp7) influence changes in stress-dependent sleep disturbances and associated anxiety behavior.

LKB1 Is Physiologically Required for Sleep from Drosophila melanogaster to the Mus musculus

Liver Kinase B1 (LKB1) is known as a master kinase for 14 kinases related to the adenosine monophosphate (AMP)-activated protein kinase (AMPK). Two of them salt inducible kinase 3 (SIK3) and AMPKα have previously been implicated in sleep regulation. We generated loss-of-function (LOF) mutants for Lkb1 in both Drosophila and mice. Sleep, but not circadian rhythms, was reduced in Lkb1-mutant flies and in flies with neuronal deletion of Lkb1. Genetic interactions between Lkb1 and Threonine to Alanine mutation at residue 184 of AMPK in Drosophila sleep or those between Lkb1 and Threonine to Glutamic Acid mutation at residue 196 of SIK3 in Drosophila viability have been observed. Sleep was reduced in mice after virally mediated reduction of Lkb1 in the brain. Electroencephalography (EEG) analysis showed that non-rapid eye movement (NREM) sleep and sleep need were both reduced in Lkb1-mutant mice. These results indicate that LKB1 plays a physiological role in sleep regulation conserved from flies to mice.

Roles of Drosophila fatty acid-binding protein in development and behavior

Fatty acid-binding proteins (FABPs) are lipid chaperones that mediate the intracellular dynamics of the hydrophobic molecules that they physically bind to. FABPs are implicated in sleep and psychiatric disorders, as well as in various cellular processes, such as cell proliferation and survival. FABP is well conserved in insects, and Drosophila has one FABP ortholog, dFabp, in its genome. Although dFabp appears to be evolutionarily conserved in some brain functions, little is known about its development and physiological function. In the present study, we investigated the function of dFabp in Drosophila development and behavior. Knockdown or overexpression of dFabp in the developing brain, wing, and eye resulted in developmental defects, such as decreased survival, altered cell proliferation, and increased apoptosis. Glia-specific knockdown of dFabp affected neuronal development, and neuronal regulation of dFabp affected glial cell proliferation. Moreover, the behavioral phenotypes (circadian rhythm and locomotor activity) of flies with regulated dFabp expression in glia and flies with regulated dFabp expression in neurons were very similar. Collectively, our results suggest that dFabp is involved in the development of various tissues and brain functions to control behavior and is a mediator of neuron-glia interactions in the Drosophila nervous system.

Astrocytes deficient in circadian clock gene Bmal1 show enhanced activation responses to amyloid-beta pathology without changing plaque burden

An emerging link between circadian clock function and neurodegeneration has indicated a critical role for the molecular clock in brain health. We previously reported that deletion of the core circadian clock gene Bmal1 abrogates clock function and induces cell-autonomous astrocyte activation. Regulation of astrocyte activation has important implications for protein aggregation, inflammation, and neuronal survival in neurodegenerative conditions such as Alzheimer's disease (AD). Here, we investigated how astrocyte activation induced by Bmal1 deletion regulates astrocyte gene expression, amyloid-beta (Aβ) plaque-associated activation, and plaque deposition. To address these questions, we crossed astrocyte-specific Bmal1 knockout mice (Aldh1l1-CreERT2;Bmal1fl/fl, termed BMAL1 aKO), to the APP/PS1-21 and the APPNL-G-F models of Aβ accumulation. Transcriptomic profiling showed that BMAL1 aKO induced a unique transcriptional profile affecting genes involved in both the generation and elimination of Aβ. BMAL1 aKO mice showed exacerbated astrocyte activation around Aβ plaques and altered gene expression. However, this astrogliosis did not affect plaque accumulation or neuronal dystrophy in either model. Our results demonstrate that the striking astrocyte activation induced by Bmal1 knockout does not influence Aβ deposition, which indicates that the effect of astrocyte activation on plaque pathology in general is highly dependent on the molecular mechanism of activation.

The metabolism and role of free fatty acids in key physiological processes in insects of medical, veterinary and forensic importance

Insects are the most widespread group of organisms and more than one million species have been described. These animals have significant ecological functions, for example they are pollinators of many types of plants. However, they also have direct influence on human life in different manners. They have high medical and veterinary significance, stemming from their role as vectors of disease and infection of wounds and necrotic tissue; they are also plant pests, parasitoids and predators whose activities can influence agriculture. In addition, their use in medical treatments, such as maggot therapy of gangrene and wounds, has grown considerably. They also have many uses in forensic science to determine the minimum post-mortem interval and provide valuable information about the movement of the body, cause of the death, drug use, or poisoning. It has also been proposed that they may be used as model organisms to replace mammal systems in research. The present review describes the role of free fatty acids (FFAs) in key physiological processes in insects. By focusing on insects of medical, veterinary significance, we have limited our description of the physiological processes to those most important from the point of view of insect control; the study examines their effects on insect reproduction and resistance to the adverse effects of abiotic (low temperature) and biotic (pathogens) factors.

Glitazone Treatment Rescues Phenotypic Deficits in a Fly Model of Gaucher/Parkinson's Disease

Parkinson’s Disease (PD) is the most common movement disorder, and the strongest genetic risk factor for PD is mutations in the glucocerebrosidase gene (GBA). Mutations in GBA also lead to the development of Gaucher Disease (GD), the most common type of lysosomal storage disorder. Current therapeutic approaches fail to address neurological GD symptoms. Therefore, identifying therapeutic strategies that improve the phenotypic traits associated with GD/PD in animal models may provide an opportunity for treating neurological manifestations of GD/PD. Thiazolidinediones (TZDs, also called glitazones) are a class of compounds targeted for the treatment of type 2 diabetes, and have also shown promise for the treatment of neurodegenerative disease, including PD. Here, we tested the efficacy of glitazone administration during development in a fly GD model with deletions in the GBA homolog, dGBA1b (GBA1^ΔTT/ΔTT). We observed an optimal dose of pioglitazone (PGZ) at a concentration of 1 μM that reduced sleep deficits, locomotor impairments, climbing defects, and restoration of normal protein levels of Ref(2)P, a marker of autophagic flux, in GBA1^ΔTT/ΔTT mutant flies, compared to GBA1^+/+ control flies. These data suggest that PGZ may represent a potential compound with which to treat GD/PD by improving function of lysosomal-autophagy pathways, a cellular process that removes misfolded or aggregated proteins.

Drosophila fabp is required for light-dependent Rhodopsin-1 clearance and photoreceptor survival

Rhodopsins are light-detecting proteins coupled with retinal chromophores essential for visual function. Coincidentally, dysfunctional Rhodopsin homeostasis underlies retinal degeneration in humans and model organisms. Drosophila ninaEG69D mutant is one such example, where the encoded Rh1 protein imposes endoplasmic reticulum (ER) stress and causes light-dependent retinal degeneration. The underlying reason for such light-dependency remains unknown. Here, we report that Drosophila fatty acid binding protein (fabp) is a gene induced in ninaEG69D/+ photoreceptors, and regulates light-dependent Rhodopsin-1 (Rh1) protein clearance and photoreceptor survival. Specifically, our photoreceptor-specific gene expression profiling study in ninaEG69D/+ flies revealed increased expression of fabp together with other genes that control light-dependent Rh1 protein degradation. fabp induction in ninaEG69D photoreceptors required vitamin A and its transporter genes. In flies reared under light, loss of fabp caused an accumulation of Rh1 proteins in cytoplasmic vesicles. The increase in Rh1 levels under these conditions was dependent on Arrestin2 that mediates feedback inhibition of light-activated Rh1. fabp mutants exhibited light-dependent retinal degeneration, a phenotype also found in other mutants that block light-induced Rh1 degradation. These observations reveal a previously unrecognized link between light-dependent Rh1 proteostasis and the ER-stress imposing ninaEG69D mutant that cause retinal degeneration.

Developmental Alcohol Exposure in Drosophila: Effects on Adult Phenotypes and Gene Expression in the Brain

Fetal alcohol exposure can lead to developmental abnormalities, intellectual disability, and behavioral changes, collectively termed fetal alcohol spectrum disorder (FASD). In 2015, the Centers for Disease Control found that 1 in 10 pregnant women report alcohol use and more than 3 million women in the USA are at risk of exposing their developing fetus to alcohol. Drosophila melanogaster is an excellent genetic model to study developmental effects of alcohol exposure because many individuals of the same genotype can be reared rapidly and economically under controlled environmental conditions. Flies exposed to alcohol undergo physiological and behavioral changes that resemble human alcohol-related phenotypes. Here, we show that adult flies that developed on ethanol-supplemented medium have decreased viability, reduced sensitivity to ethanol, and disrupted sleep and activity patterns. To assess the effects of exposure to alcohol during development on brain gene expression, we performed single cell RNA sequencing and resolved cell clusters with differentially expressed genes which represent distinct neuronal and glial populations. Differential gene expression showed extensive sexual dimorphism with little overlap between males and females. Gene expression differences following developmental alcohol exposure were similar to previously reported differential gene expression following cocaine consumption, suggesting that common neural substrates respond to both drugs. Genes associated with glutathione metabolism, lipid transport, glutamate and GABA metabolism, and vision feature in sexually dimorphic global multi-cluster interaction networks. Our results provide a blueprint for translational studies on alcohol-induced effects on gene expression in the brain that may contribute to or result from FASD in human populations.

Transcriptomic and proteomic analysis of the underlying mechanisms of digestion of triacylglycerols and phosphatides and absorption and fate of fatty acids along the midgut of Musca domestica

Most dietary lipids are triacylglycerols (TAGs) and phosphatides that are digested by TAG lipases and phospholipases (PLIPs), respectively, originating fatty acids (FA). The genome of Musca domestica has genes coding for phospholipases A1 (1PLIP), A2 (2PLIP), B (BPLIP), and acid lipases (ALIP), as for proteins involved in activation, binding, and metabolism of FA, which expression in the larval midgut was evaluated by RNA-seq. Some of the codified proteins were identified in midgut microvillar-enriched membrane by proteomics. 1PLIPs are the most expressed PLIPs, mainly in anterior midgut whereas 2PLIPs, and BPLIP in middle and posterior midgut, and ALIPs between middle and posterior regions. Absorption of FAs is putatively accomplished by proteins involved in FA activation (acyl-CoA synthetases) found in microvillar-enriched membrane preparations. Furthermore, FA uptake could be enhanced by proteins that bind FAs (FA-binding proteins) and its activated form (acyl-CoA binding proteins) mainly expressed in posterior midgut. Activated FAs could have different fates: synthesis of diacylglycerol (DAG) and TAG through monoacylglycerol and glycerol-3-phosphate pathways; synthesis of phosphatides; energy source by β-oxidation. Most genes coding for enzymes of those routes is expressed mainly at the end of posterior midgut. Data suggest that phosphatides are digested in anterior midgut by Md1PLIPs, releasing lysophosphatides that emulsify fats to be digested by MdALIPs in the middle and posterior midgut. Most resulting FAs is absorbed in the posterior midgut, where they follow the synthesis of DAG, TAG, and phosphatides or are oxidized along the midgut, mainly in highly metabolic middle and posterior midgut regions.

Cannabinoids modulate food preference and consumption in Drosophila melanogaster

Cannabinoids have an important role in regulating feeding behaviors via cannabinoid receptors in mammals. Cannabinoids also exhibit potential therapeutic functions in Drosophila melanogaster, or fruit fly that lacks cannabinoid receptors. However, it remains unclear whether cannabinoids affect food consumption and metabolism in a cannabinoid receptors-independent manner in flies. In this study, we systematically investigated pharmacological functions of various cannabinoids in modulating food preference and consumption in flies. We show that flies display preferences for consuming cannabinoids, independent of two important sensory regulators Poxn and Orco. Interestingly, phyto- and endo- cannabinoids exhibit an inhibitory effect on food intake. Unexpectedly, the non-selective CB1 receptor antagonist AM251 attenuates the suppression of food intake by endocannabinoids. Moreover, the endocannabinoid anandamide (AEA) and its metabolite inhibit food intake and promote resistance to starvation, possibly through reduced lipid metabolism. Thus, this study has provided insights into a pharmacological role of cannabinoids in feeding behaviors using an adult Drosophila model.

The Sleep Nullifying Apparatus: A Highly Efficient Method of Sleep Depriving Drosophila

Sleep homeostasis, the increase in sleep observed following sleep loss, is one of the defining criteria used to identify sleep throughout the animal kingdom. As a consequence, sleep deprivation and sleep restriction are powerful tools that are commonly used to provide insight into sleep function. Nonetheless, sleep deprivation experiments are inherently problematic in that the deprivation stimulus itself may be the cause of observed changes in physiology and behavior. Accordingly, successful sleep deprivation techniques should keep animals awake and, ideally, result in a robust sleep rebound without also inducing a large number of unintended consequences. Here, we describe a sleep deprivation technique for Drosophila melanogaster. The Sleep Nullifying Apparatus (SNAP) administers a stimulus every 10s to induce negative geotaxis. Although the stimulus is predictable, the SNAP effectively prevents >95% of nighttime sleep even in flies with high sleep drive. Importantly, the subsequent homeostatic response is very similar to that achieved using hand-deprivation. The timing and spacing of the stimuli can be modified to minimize sleep loss and thus examine non-specific effects of the stimulus on physiology and behavior. The SNAP can also be used for sleep restriction and to assess arousal thresholds. The SNAP is a powerful sleep disruption technique that can be used to better understand sleep function.

The Glial Perspective on Sleep and Circadian Rhythms

While neurons and circuits are almost unequivocally considered to be the computational units and actuators of behavior, a complete understanding of the nervous system must incorporate glial cells. Far beyond a copious but passive substrate, glial influence is inextricable from neuronal physiology, whether during developmental guidance and synaptic shaping or through the trophic support, neurotransmitter and ion homeostasis, cytokine signaling and immune function, and debris engulfment contributions that this class provides throughout an organism's life. With such essential functions, among a growing literature of nuanced roles, it follows that glia are consequential to behavior in adult animals, with novel genetic tools allowing for the investigation of these phenomena in living organisms. We discuss here the relevance of glia for maintaining circadian rhythms and also for serving functions of sleep.

The Molecular Genetic Interaction Between Circadian Rhythms and Susceptibility to Seizures and Epilepsy

Seizure patterns observed in patients with epilepsy suggest that circadian rhythms and sleep/wake mechanisms play some role in the disease. This review addresses key topics in the relationship between circadian rhythms and seizures in epilepsy. We present basic information on circadian biology, but focus on research studying the influence of both the time of day and the sleep/wake cycle as independent but related factors on the expression of seizures in epilepsy. We review studies investigating how seizures and epilepsy disrupt expression of core clock genes, and how disruption of clock mechanisms impacts seizures and the development of epilepsy. We focus on the overlap between mechanisms of circadian-associated changes in SCN neuronal excitability and mechanisms of epileptogenesis as a means of identifying key pathways and molecules that could represent new targets or strategies for epilepsy therapy. Finally, we review the concept of chronotherapy and provide a perspective regarding its application to patients with epilepsy based on their individual characteristics (i.e., being a “morning person” or a “night owl”). We conclude that better understanding of the relationship between circadian rhythms, neuronal excitability, and seizures will allow both the identification of new therapeutic targets for treating epilepsy as well as more effective treatment regimens using currently available pharmacological and non-pharmacological strategies.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

Modulation of KDM1A with vafidemstat rescues memory deficit and behavioral alterations

Transcription disequilibria are characteristic of many neurodegenerative diseases. The activity-evoked transcription of immediate early genes (IEGs), important for neuronal plasticity, memory and behavior, is altered in CNS diseases and governed by epigenetic modulation. KDM1A, a histone 3 lysine 4 demethylase that forms part of transcription regulation complexes, has been implicated in the control of IEG transcription. Here we report the development of vafidemstat (ORY-2001), a brain penetrant inhibitor of KDM1A and MAOB. ORY-2001 efficiently inhibits brain KDM1A at doses suitable for long term treatment, and corrects memory deficit as assessed in the novel object recognition testing in the Senescence Accelerated Mouse Prone 8 (SAMP8) model for accelerated aging and Alzheimer's disease. Comparison with a selective KDM1A or MAOB inhibitor reveals that KDM1A inhibition is key for efficacy. ORY-2001 further corrects behavior alterations including aggression and social interaction deficits in SAMP8 mice and social avoidance in the rat rearing isolation model. ORY-2001 increases the responsiveness of IEGs, induces genes required for cognitive function and reduces a neuroinflammatory signature in SAMP8 mice. Multiple genes modulated by ORY-2001 are differentially expressed in Late Onset Alzheimer's Disease. Most strikingly, the amplifier of inflammation S100A9 is highly expressed in LOAD and in the hippocampus of SAMP8 mice, and down-regulated by ORY-2001. ORY-2001 is currently in multiple Phase IIa studies.

Disrupting flight increases sleep and identifies a novel sleep-promoting pathway in Drosophila

Sleep is plastic and is influenced by ecological factors and environmental changes. The mechanisms underlying sleep plasticity are not well understood. We show that manipulations that impair flight in Drosophila increase sleep as a form of sleep plasticity. We disrupted flight by blocking the wing-expansion program, genetically disrupting flight, and by mechanical wing perturbations. We defined a new sleep regulatory circuit starting with specific wing sensory neurons, their target projection neurons in the ventral nerve cord, and the neurons they connect to in the central brain. In addition, we identified a critical neuropeptide (burs) and its receptor (rickets) that link wing expansion and sleep. Disrupting flight activates these sleep-promoting projection neurons, as indicated by increased cytosolic calcium levels, and stably increases the number of synapses in their axonal projections. These data reveal an unexpected role for flight in regulating sleep and provide new insight into how sensory processing controls sleep need.

Sleep restores place learning to the adenylyl cyclase mutant rutabaga

Sleep plays an important role in regulating plasticity. In Drosophila, the relationship between sleep and learning and memory has primarily focused on mushroom body dependent operant-learning assays such as aversive phototaxic suppression and courtship conditioning. In this study, sleep was increased in the classic mutant rutabaga (rut2080) and dunce (dnc1) by feeding them the GABA-A agonist gaboxadol (Gab). Performance was evaluated in each mutant in response to social enrichment and place learning, tasks that do not require the mushroom body. Gab-induced sleep did not restore behavioral plasticity to either rut2080 or dnc1 mutants following social enrichment. However, increased sleep restored place learning to rut2080 mutants. These data extend the positive effects of enhanced sleep to place learning and highlight the utility of Gab for elucidating the beneficial effects of sleep on brain functioning.

Molecular mechanism with regard to the binding selectivity of inhibitors toward FABP5 and FABP7 explored by multiple short molecular dynamics simulations and free energy analyses

Recently, fatty acid binding proteins 5 and 7 (FABP5 and FABP7) have been regarded as the prospective targets for clinically treating multiple diseases related to FABPs.

Circadian clock genes link photoperiodic signals to lipid accumulation during diapause preparation in the diapause-destined female cabbage beetles Colaphellus bowringi

Many organisms have evolved a series of adaptions, such as dormancy or diapause in insects that enable them to withstand seasonally adverse conditions. In insects, photoperiodic signals received during the diapause induction phase have irreversible effect on diapause initiation. Insects continue to be exposed to diapause-inducing photoperiod after the diapause induction phase during diapause preparation before they enter diapause. However, how photoperiodic signals experienced during the diapause preparation phase (DPP) regulate diapause remains largely unclear. In this paper, we investigate this in the cabbage beetle Colaphellus bowringi. The cabbage beetle is in many respects an ideal experimental model in which to investigate the effect of photoperiodic signals on the DPP because it has facultative reproductive diapause induced by long-day length and has differentiable diapause induction and preparation phases. We found that the lipid content of female cabbage beetles decreased after diapause-destined (DD) individuals were exposed to a diapause-inhibiting photoperiod during the DPP. Two circadian clock negative regulators, per and tim, were probably involved in the photoperiodic response of beetles during the DPP. Per and tim presented obvious oscillation of circadian rhythm and photoperiodic response during the DPP in DD females and knock-down of these genes in DD females caused their lipid content to decrease. Per and tim probably promote lipid accumulation by regulating the expression of genes that regulate lipogenesis and lipolysis. Moreover, decreased lipid accumulation caused by exposure to different photoperiods during the DPP was independent of juvenile hormone. In summary, these results suggest that photoperiodic signals received during the DPP influence lipid accumulation in DD insects. DD insects still have some ability to monitor photoperiodic changes during the DPP and per and tim are probably involved in regulating physiological responses to photoperiodic signals during diapause preparation. These results shed light on the relationship between photoperiodic signals and diapause preparation, and may provide new insights on both how to better utilize insects as resources and for pest management.

Regulators of Long-Term Memory Revealed by Mushroom Body-Specific Gene Expression Profiling in Drosophila melanogaster

Memory formation is achieved by genetically tightly controlled molecular pathways that result in a change of synaptic strength and synapse organization. While for short-term memory traces, rapidly acting biochemical pathways are in place, the formation of long-lasting memories requires changes in the transcriptional program of a cell. Although many genes involved in learning and memory formation have been identified, little is known about the genetic mechanisms required for changing the transcriptional program during different phases of long-term memory (LTM) formation. With Drosophila melanogaster as a model system, we profiled transcriptomic changes in the mushroom body—a memory center in the fly brain—at distinct time intervals during appetitive olfactory LTM formation using the targeted DamID technique. We describe the gene expression profiles during these phases and tested 33 selected candidate genes for deficits in LTM formation using RNAi knockdown. We identified 10 genes that enhance or decrease memory when knocked-down in the mushroom body. For vajk-1 and hacd1—the two strongest hits—we gained further support for their crucial role in appetitive learning and forgetting. These findings show that profiling gene expression changes in specific cell-types harboring memory traces provides a powerful entry point to identify new genes involved in learning and memory. The presented transcriptomic data may further be used as resource to study genes acting at different memory phases.

Adaptations in energy metabolism and gene family expansions revealed by comparative transcriptomics of three Chagas disease triatomine vectors

Background

Chagas disease is a parasitic infection caused by Trypanosoma cruzi. It is an important public health problem affecting around seven to eight million people in the Americas. A large number of hematophagous triatomine insect species, occupying diverse natural and human-modified ecological niches transmit this disease. Triatomines are long-living hemipterans that have evolved to explode different habitats to associate with their vertebrate hosts. Understanding the molecular basis of the extreme physiological conditions including starvation tolerance and longevity could provide insights for developing novel control strategies. We describe the normalized cDNA, full body transcriptome analysis of three main vectors in North, Central and South America, Triatoma pallidipennis, T. dimidiata and T. infestans.

Results

Two-thirds of the de novo assembled transcriptomes map to the Rhodnius prolixus genome and proteome. A Triatoma expansion of the calycin family and two types of protease inhibitors, pacifastins and cystatins were identified. A high number of transcriptionally active class I transposable elements was documented in T. infestans, compared with T. dimidiata and T. pallidipennis. Sequence identity in Triatoma-R. prolixus 1:1 orthologs revealed high sequence divergence in four enzymes participating in gluconeogenesis, glycogen synthesis and the pentose phosphate pathway, indicating high evolutionary rates of these genes. Also, molecular evidence suggesting positive selection was found for several genes of the oxidative phosphorylation I, III and V complexes.

Conclusions

Protease inhibitors and calycin-coding gene expansions provide insights into rapidly evolving processes of protease regulation and haematophagy. Higher evolutionary rates in enzymes that exert metabolic flux control towards anabolism and evidence for positive selection in oxidative phosphorylation complexes might represent genetic adaptations, possibly related to prolonged starvation, oxidative stress tolerance, longevity, and hematophagy and flight reduction. Overall, this work generated novel hypothesis related to biological adaptations to extreme physiological conditions and diverse ecological niches that sustain Chagas disease transmission.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4696-8) contains supplementary material, which is available to authorized users.

The acyl-CoA Synthetase, pudgy, Promotes Sleep and Is Required for the Homeostatic Response to Sleep Deprivation

The regulation of sleep and the response to sleep deprivation rely on multiple biochemical pathways. A critical connection is the link between sleep and metabolism. Metabolic changes can disrupt sleep, and conversely decreased sleep can alter the metabolic environment. There is building evidence that lipid metabolism, in particular, is a critical part of mounting the homeostatic response to sleep deprivation. We have evaluated an acyl-CoA synthetase, pudgy (pdgy), for its role in sleep and response to sleep deprivation. When pdgy transcript levels are decreased through transposable element disruption of the gene, mutant flies showed lower total sleep times and increased sleep fragmentation at night compared to genetic controls. Consistent with disrupted sleep, mutant flies had a decreased lifespan compared to controls. pdgy disrupted fatty acid handling as pdgy mutants showed increased sensitivity to starvation and exhibited lower fat stores. Moreover, the response to sleep deprivation is reduced when compared to a control flies. When we decreased the transcript levels for pdgy using RNAi, the response to sleep deprivation was decreased compared to background controls. In addition, when the pdgy transcription is rescued throughout the fly, the response to sleep deprivation is restored. These data demonstrate that the regulation and function of acyl-CoA synthetase plays a critical role in regulating sleep and the response to sleep deprivation. Endocrine and metabolic signals that alter transcript levels of pdgy impact sleep regulation or interfere with the homeostatic response to sleep deprivation.

Molecular Mechanisms of Sleep Homeostasis in Flies and Mammals

Sleep is homeostatically regulated with sleep pressure accumulating with the increasing duration of prior wakefulness. Yet, a clear understanding of the molecular components of the homeostat, as well as the molecular and cellular processes they sense and control to regulate sleep intensity and duration, remain a mystery. Here, we will discuss the cellular and molecular basis of sleep homeostasis, first focusing on the best homeostatic sleep marker in vertebrates, slow wave activity; second, moving to the molecular genetic analysis of sleep homeostasis in the fruit fly Drosophila; and, finally, discussing more systemic aspects of sleep homeostasis.

Amyloid-β induces sleep fragmentation that is rescued by fatty acid binding proteins in Drosophila

Disruption of sleep/wake activity in Alzheimer's disease (AD) patients significantly affects their quality of life and that of their caretakers and is a major contributing factor for institutionalization. Levels of amyloid-β (Aβ) have been shown to be regulated by neuronal activity and to correlate with the sleep/wake cycle. Whether consolidated sleep can be disrupted by Aβ alone is not well understood. We hypothesize that Aβ42 can increase wakefulness and disrupt consolidated sleep. Here we report that flies expressing the human Aβ42 transgene in neurons have significantly reduced consolidated sleep compared with control flies. Fatty acid binding proteins (Fabp) are small hydrophobic ligand carriers that have been clinically implicated in AD. Aβ42 flies that carry a transgene of either the Drosophila Fabp or the mammalian brain-type Fabp show a significant increase in nighttime sleep and long consolidated sleep bouts, rescuing the Aβ42-induced sleep disruption. These studies suggest that alterations in Fabp levels and/or activity may be associated with sleep disturbances in AD. Future work to determine the molecular mechanisms that contribute to Fabp-mediated rescue of Aβ42-induced sleep loss will be important for the development of therapeutics in the treatment of AD. © 2016 Wiley Periodicals, Inc.

The Antinociceptive Agent SBFI-26 Binds to Anandamide Transporters FABP5 and FABP7 at Two Different Sites

Human FABP5 and FABP7 are intracellular endocannabinoid transporters. SBFI-26 is an α-truxillic acid 1-naphthyl monoester that competitively inhibits the activities of FABP5 and FABP7 and produces antinociceptive and anti-inflammatory effects in mice. The synthesis of SBFI-26 yields several stereoisomers, and it is not known how the inhibitor binds the transporters. Here we report co-crystal structures of SBFI-26 in complex with human FABP5 and FABP7 at 2.2 and 1.9 Å resolution, respectively. We found that only (S)-SBFI-26 was present in the crystal structures. The inhibitor largely mimics the fatty acid binding pattern, but it also has several unique interactions. Notably, the FABP7 complex corroborates key aspects of the ligand binding pose at the canonical site previously predicted by virtual screening. In FABP5, SBFI-26 was unexpectedly found to bind at the substrate entry portal region in addition to binding at the canonical ligand-binding pocket. Our structural and binding energy analyses indicate that both R and S forms appear to bind the transporter equally well. We suggest that the S enantiomer observed in the crystal structures may be a result of the crystallization process selectively incorporating the (S)-SBFI-26-FABP complexes into the growing lattice, or that the S enantiomer may bind to the portal site more rapidly than to the canonical site, leading to an increased local concentration of the S enantiomer for binding to the canonical site. Our work reveals two binding poses of SBFI-26 in its target transporters. This knowledge will guide the development of more potent FABP inhibitors based upon the SBFI-26 scaffold.

Describing the Diapause-Preparatory Proteome of the Beetle Colaphellus bowringi and Identifying Candidates Affecting Lipid Accumulation Using Isobaric Tags for Mass Spectrometry-Based Proteome Quantification (iTRAQ)

Prior to entering diapause, insects must prepare themselves physiologically to withstand the stresses of arresting their development for a lengthy period. While studies describing the biochemical and cellular milieu of the maintenance phase of diapause are accumulating, few studies have taken an “omics” approach to describing molecular events during the diapause preparatory phase. We used isobaric tags and mass spectrometry (iTRAQ) to quantitatively compare the expression profiles of proteins identified during the onset of diapause preparation phase in the heads of adult female cabbage beetles, Colaphellus bowringi. A total of 3,175 proteins were identified, 297 of which were differentially expressed between diapause-destined and non-diapause-destined female adults and could therefore be involved in diapause preparation in this species. Comparison of identified proteins with protein function databases shows that many of these differentially expressed proteins enhanced in diapause destined beetles are involved in energy production and conversion, carbohydrate metabolism and transport, and lipid metabolism. Further hand annotation of differentially abundant peptides nominates several associated with stress hardiness, including HSPs and antioxidants, as well as neural development. In contrast, non-diapause destined beetles show substantial increases in cuticle proteins, suggesting additional post-emergence growth. Using RNA interference to silence a fatty acid-binding protein (FABP) that was highly abundant in the head of diapause-destined females prevented the accumulation of lipids in the fat body, a common product of diapause preparation in this species and others. Surprisingly, RNAi against the FABP also affected the transcript abundance of several heat shock proteins. These results suggest that the identified differentially expressed proteins that play vital roles in lipid metabolism may also contribute somehow to enhanced hardiness to environmental stress that is characteristic of diapause.

Normal sleep requires the astrocyte brain-type fatty acid binding protein FABP7

Sleep is found widely in the animal kingdom. Despite this, few conserved molecular pathways that govern sleep across phyla have been described. The mammalian brain-type fatty acid binding protein (Fabp7) is expressed in astrocytes, and its mRNA oscillates in tandem with the sleep-wake cycle. However, the role of FABP7 in regulating sleep remains poorly understood. We found that the missense mutation FABP7.T61M is associated with fragmented sleep in humans. This phenotype was recapitulated in mice and fruitflies bearing similar mutations: Fabp7-deficient mice and transgenic flies that express the FABP7.T61M missense mutation in astrocytes also show fragmented sleep. These results provide novel evidence for a distinct molecular pathway linking lipid-signaling cascades within astrocytes in sleep regulation among phylogenetically disparate species.

Control of sleep by a network of cell cycle genes

Sleep is essential for health and cognition, but the molecular and neural mechanisms of sleep regulation are not well understood. We recently reported the identification of TARANIS (TARA) as a sleep-promoting factor that acts in a previously unknown arousal center in Drosophila. tara mutants exhibit a dose-dependent reduction in sleep amount of up to ∼60%. TARA and its mammalian homologs, the Trip-Br (Transcriptional Regulators Interacting with PHD zinc fingers and/or Bromodomains) family of proteins, are primarily known as transcriptional coregulators involved in cell cycle progression, and contain a conserved Cyclin-A (CycA) binding homology domain. We found that tara and CycA synergistically promote sleep, and CycA levels are reduced in tara mutants. Additional data demonstrated that Cyclin-dependent kinase 1 (Cdk1) antagonizes tara and CycA to promote wakefulness. Moreover, we identified a subset of CycA expressing neurons in the pars lateralis, a brain region proposed to be analogous to the mammalian hypothalamus, as an arousal center. In this Extra View article, we report further characterization of tara mutants and provide an extended discussion of our findings and future directions within the framework of a working model, in which a network of cell cycle genes, tara, CycA, and Cdk1, interact in an arousal center to regulate sleep.

1H, 15N and 13C resonance assignments of light organ-associated fatty acid-binding protein of Taiwanese fireflies

Fatty acid-binding proteins (FABPs) are a family of proteins that modulate the transfer of various fatty acids in the cytosol and constitute a significant portion in many energy-consuming cells. The ligand binding properties and specific functions of a particular type of FABP seem to be diverse and depend on the respective binding cavity as well as the cell type from which this protein is derived. Previously, a novel FABP (lcFABP; lc: Luciola cerata) was identified in the light organ of Taiwanese fireflies. The lcFABP was proved to possess fatty acids binding capabilities, especially for fatty acids of length C14-C18. However, the structural details are unknown, and the structure-function relationship has remained to be further investigated. In this study, we finished the (1)H, (15)N and (13)C chemical shift assignments of (15)N/(13)C-enriched lcFABP by solution NMR spectroscopy. In addition, the secondary structure distribution was revealed based on the backbone N, H, Cα, Hα, C and side chain Cβ assignments. These results can provide the basis for further structural exploration of lcFABP.

Altered Sleep Homeostasis in Rev-erbα Knockout Mice

STUDY OBJECTIVES

The nuclear receptor REV-ERBα is a potent, constitutive transcriptional repressor critical for the regulation of key circadian and metabolic genes. Recently, REV-ERBα's involvement in learning, neurogenesis, mood, and dopamine turnover was demonstrated suggesting a specific role in central nervous system functioning. We have previously shown that the brain expression of several core clock genes, including Rev-erbα, is modulated by sleep loss. We here test the consequences of a loss of REV-ERBα on the homeostatic regulation of sleep.

METHODS

EEG/EMG signals were recorded in Rev-erbα knockout (KO) mice and their wild type (WT) littermates during baseline, sleep deprivation, and recovery. Cortical gene expression measurements after sleep deprivation were contrasted to baseline.

RESULTS

Although baseline sleep/wake duration was remarkably similar, KO mice showed an advance of the sleep/wake distribution relative to the light-dark cycle. After sleep onset in baseline and after sleep deprivation, both EEG delta power (1-4 Hz) and sleep consolidation were reduced in KO mice indicating a slower increase of homeostatic sleep need during wakefulness. This slower increase might relate to the smaller increase in theta and gamma power observed in the waking EEG prior to sleep onset under both conditions. Indeed, the increased theta activity during wakefulness predicted delta power in subsequent NREM sleep. Lack of Rev-erbα increased Bmal1, Npas2, Clock, and Fabp7 expression, confirming the direct regulation of these genes by REV-ERBα also in the brain.

CONCLUSIONS

Our results add further proof to the notion that clock genes are involved in sleep homeostasis. Because accumulating evidence directly links REV-ERBα to dopamine signaling the altered homeostatic regulation of sleep reported here are discussed in that context.

Learning and memory: do bees dream?

In mammals, evidence for memory reactivation during sleep highlighted the important role that sleep plays in memory consolidation. A new study reports that memory reactivation is evolutionarily conserved and can also be found in the honeybee.

Identification of genes associated with resilience/vulnerability to sleep deprivation and starvation in Drosophila

BACKGROUND AND STUDY OBJECTIVES

Flies mutant for the canonical clock protein cycle (cyc(01)) exhibit a sleep rebound that is ∼10 times larger than wild-type flies and die after only 10 h of sleep deprivation. Surprisingly, when starved, cyc(01) mutants can remain awake for 28 h without demonstrating negative outcomes. Thus, we hypothesized that identifying transcripts that are differentially regulated between waking induced by sleep deprivation and waking induced by starvation would identify genes that underlie the deleterious effects of sleep deprivation and/or protect flies from the negative consequences of waking.

DESIGN

We used partial complementary DNA microarrays to identify transcripts that are differentially expressed between cyc(01) mutants that had been sleep deprived or starved for 7 h. We then used genetics to determine whether disrupting genes involved in lipid metabolism would exhibit alterations in their response to sleep deprivation.

SETTING

Laboratory.

PATIENTS OR PARTICIPANTS

Drosophila melanogaster.

INTERVENTIONS

Sleep deprivation and starvation.

MEASUREMENTS AND RESULTS

We identified 84 genes with transcript levels that were differentially modulated by 7 h of sleep deprivation and starvation in cyc(01) mutants and were confirmed in independent samples using quantitative polymerase chain reaction. Several of these genes were predicted to be lipid metabolism genes, including bubblegum, cueball, and CG4500, which based on our data we have renamed heimdall (hll). Using lipidomics we confirmed that knockdown of hll using RNA interference significantly decreased lipid stores. Importantly, genetically modifying bubblegum, cueball, or hll resulted in sleep rebound alterations following sleep deprivation compared to genetic background controls.

CONCLUSIONS

We have identified a set of genes that may confer resilience/vulnerability to sleep deprivation and demonstrate that genes involved in lipid metabolism modulate sleep homeostasis.

Sleep restores behavioral plasticity to Drosophila mutants

Given the role that sleep plays in modulating plasticity, we hypothesized that increasing sleep would restore memory to canonical memory mutants without specifically rescuing the causal molecular lesion. Sleep was increased using three independent strategies: activating the dorsal fan-shaped body, increasing the expression of Fatty acid binding protein (dFabp), or by administering the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Short-term memory (STM) or long-term memory (LTM) was evaluated in rutabaga (rut) and dunce (dnc) mutants using aversive phototaxic suppression and courtship conditioning. Each of the three independent strategies increased sleep and restored memory to rut and dnc mutants. Importantly, inducing sleep also reverses memory defects in a Drosophila model of Alzheimer's disease. Together, these data demonstrate that sleep plays a more fundamental role in modulating behavioral plasticity than previously appreciated and suggest that increasing sleep may benefit patients with certain neurological disorders.

Sleep, Performance, and Memory in Flies

Drosophila has proven to be a powerful model to identify genes and circuits that impact sleep. While the majority of studies have primarily been interested in identifying manipulations that alter sleep time, a growing body of work has begun to focus on how changing sleep influences functional outcomes such as cognitive performance, structural plasticity, and metabolism to name a few. Evaluating sleep time provides an appropriate entry point into elucidating sleep function. However, it is not possible to fully understand how a manipulation has impacted sleep regulation without first establishing how it has affected the animals’ well-being. Synaptic plasticity and memory are important functional outcomes that can be used to asses an animal’s status. In this manuscript, we review recent advances in studies examining sleep, memory, and performance. We conclude that as Drosophila sleep researchers expand their analysis beyond sleep time, the opportunities to discover the function of sleep will be enhanced.

Modulation of innate and learned sexual behaviors by the TRP channel Painless expressed in the fruit fly brain: behavioral genetic analysis and its implications

Transient receptor potential (TRP) channels have attracted considerable attention because of their vital roles in primary sensory neurons, mediating responses to a wide variety of external environmental stimuli. However, much less is known about how TRP channels in the brain respond to intrinsic signals and are involved in neurophysiological processes that control complex behaviors. Painless (Pain) is the Drosophila TRP channel that was initially identified as a molecular sensor responsible for detecting noxious thermal and mechanical stimuli. Here, we review recent behavioral genetic studies demonstrating that Pain expressed in the brain plays a critical role in both innate and learned aspects of sexual behaviors. Several members of the TRP channel superfamily play evolutionarily conserved roles in sensory neurons as well as in other peripheral tissues. It is thus expected that brain TRP channels in vertebrates and invertebrates would have some common physiological functions. Studies of Pain in the Drosophila brain using a unique combination of genetics and physiological techniques should provide valuable insights into the fundamental principles concerning TRP channels expressed in the vertebrate and invertebrate brains.

New insights in the clockwork mechanism regulating lineage specification: Lessons from the Drosophila nervous system

BACKGROUND

Powerful transcription factors called fate determinants induce robust differentiation programs in multipotent cells and trigger lineage specification. These factors guarantee the differentiation of specific tissues/organs/cells at the right place and the right moment to form a fully functional organism. Fate determinants are activated by temporal, positional, epigenetic, and post-transcriptional cues, hence integrating complex and dynamic developmental networks. In turn, they activate specific transcriptional/epigenetic programs that secure novel molecular landscapes.

RESULTS

In this review, we use the Drosophila Gcm glial determinant as a model to discuss the mechanisms that allow lineage specification in the nervous system. The dynamic regulation of Gcm via interlocked loops has recently emerged as a key event in the establishment of stable identity. Gcm induces gliogenesis while triggering its own extinction, thus preventing the appearance of metastable states and neoplastic processes.

CONCLUSIONS

Using simple animal models that allow in vivo manipulations provides a key tool to disentangle the complex regulation of cell fate determinants.

Inhibition of fatty acid binding proteins elevates brain anandamide levels and produces analgesia

The endocannabinoid anandamide (AEA) is an antinociceptive lipid that is inactivated through cellular uptake and subsequent catabolism by fatty acid amide hydrolase (FAAH). Fatty acid binding proteins (FABPs) are intracellular carriers that deliver AEA and related N-acylethanolamines (NAEs) to FAAH for hydrolysis. The mammalian brain expresses three FABP subtypes: FABP3, FABP5, and FABP7. Recent work from our group has revealed that pharmacological inhibition of FABPs reduces inflammatory pain in mice. The goal of the current work was to explore the effects of FABP inhibition upon nociception in diverse models of pain. We developed inhibitors with differential affinities for FABPs to elucidate the subtype(s) that contributes to the antinociceptive effects of FABP inhibitors.

Inhibition of FABPs reduced nociception associated with inflammatory, visceral, and neuropathic pain. The antinociceptive effects of FABP inhibitors mirrored their affinities for FABP5, while binding to FABP3 and FABP7 was not a predictor of in vivo efficacy. The antinociceptive effects of FABP inhibitors were mediated by cannabinoid receptor 1 (CB₁) and peroxisome proliferator-activated receptor alpha (PPARα) and FABP inhibition elevated brain levels of AEA, providing the first direct evidence that FABPs regulate brain endocannabinoid tone. These results highlight FABPs as novel targets for the development of analgesic and anti-inflammatory therapeutics.

Modeling the genetic basis for human sleep disorders in Drosophila

Sleep research in Drosophila is not only here to stay, but is making impressive strides towards helping us understand the biological basis for and the purpose of sleep—perhaps one of the most complex and enigmatic of behaviors. Thanks to over a decade of sleep-related studies in flies, more molecular methods are being applied than ever before towards understanding the genetic basis of sleep disorders. The advent of high-throughput technologies that can rapidly interrogate whole genomes, epigenomes and proteomes, has also revolutionized our ability to detect genetic variants that might be causal for a number of sleep disorders. In the coming years, mutational studies in model organisms such as Drosophila will need to be functionally connected to information being generated from these whole-genome approaches in humans. This will necessitate the development of appropriate methods for interpolating data and increased analytical power to synthesize useful network(s) of sleep regulatory pathways—including appropriate discriminatory and predictive capabilities. Ultimately, such networks will also need to be interpreted in the context of fundamental neurobiological substrates for sleep in any given species. In this review, we highlight some emerging approaches, such as network analysis and mathematical modeling of sleep distributions, which can be applied to contemporary sleep research as a first step to achieving these aims. These methodologies should favorably impact not only a mechanistic understanding of sleep, but also future pharmacological intervention strategies to manage and treat sleep disorders in humans.