miR-263b Controls Circadian Behavior and the Structural Plasticity of Pacemaker Neurons by Regulating the LIM-Only Protein Beadex

miR-277 regulates the phase of circadian activity-rest rhythm in Drosophila melanogaster

Circadian clocks temporally organize behaviour and physiology of organisms with a rhythmicity of about 24 h. In Drosophila, the circadian clock is composed of mainly four clock genes: period (per), timeless (tim), Clock (Clk) and cycle (cyc) which constitutes the transcription-translation feedback loop. The circadian clock is further regulated via post-transcriptional and post-translational mechanisms among which microRNAs (miRNAs) are well known post-transcriptional regulatory molecules. Here, we identified and characterized the role of miRNA-277 (miR-277) expressed in the clock neurons in regulating the circadian rhythm. Downregulation of miR-277 in the pacemaker neurons expressing circadian neuropeptide, pigment dispersing factor (PDF) advanced the phase of the morning activity peak under 12 h light: 12 h dark cycles (LD) at lower light intensities and these flies exhibited less robust rhythms compared to the controls under constant darkness. In addition, downregulation of miR-277 in the PDF expressing neurons abolished the Clk gene transcript oscillation under LD. Our study points to the potential role of miR-277 in fine tuning the Clk expression and in maintaining the phase of the circadian rhythm in Drosophila.

MicroRNA miR-263b-5p Regulates Developmental Growth and Cell Association by Suppressing Laminin A in Drosophila

Basement membranes (BMs) play important roles under various physiological conditions in animals, including ecdysozoans. During development, BMs undergo alterations through diverse intrinsic and extrinsic regulatory mechanisms; however, the full complement of pathways controlling these changes remain unclear. Here, we found that fat body-overexpression of Drosophila miR-263b, which is highly expressed during the larval-to-pupal transition, resulted in a decrease in the overall size of the larval fat body, and ultimately, in a severe growth defect accompanied by a reduction in cell proliferation and cell size. Interestingly, we further observed that a large proportion of the larval fat body cells were prematurely disassociated from each other. Moreover, we present evidence that miR-263b-5p suppresses the main component of BMs, Laminin A (LanA). Through experiments using RNA interference (RNAi) of LanA, we found that its depletion phenocopied the effects in miR-263b-overexpressing flies. Overall, our findings suggest a potential role for miR-263b in developmental growth and cell association by suppressing LanA expression in the Drosophila fat body.

MicroRNA-263b confers imidacloprid resistance in Sitobion miscanthi (Takahashi) by regulating the expression of the nAChRβ1 subunit

The Chinese wheat aphid Sitobion miscanthi (CWA) is an important harmful pest in wheat fields. Imidacloprid plays a critical role in controlling pests with sucking mouthparts. However, imidacloprid-resistant pests have been observed after insecticide overuse. Point mutations and low expression levels of the nicotinic acetylcholine receptor β1 (nAchRβ1) subunit are the main imidacloprid-resistant mechanisms. However, the regulatory mechanism underlying nAChRβ1 subunit expression is poorly understood. In this study, a target of miR-263b was isolated from the 5'UTR of the nAchRβ1 subunit in the CWA. Low expression levels were found in the imidacloprid-resistant strain CWA. Luciferase reporter assays showed that miR-263b could combine with the 5'UTR of the nAChRβ1 subunit and suppress its expression by binding to a site in the CWA. Aphids treated with the miR-263b agomir exhibited a significantly reduced abundance of the nAchRβ1 subunit and increased imidacloprid resistance. In contrast, aphids treated with the miR-263b antagomir exhibited significantly increased nAchRβ1 subunit abundance and decreased imidacloprid resistance. These results provide a basis for an improved understanding of the posttranscriptional regulatory mechanism of the nAChRβ1 subunit and further elucidate the function of miRNAs in regulating susceptibility to imidacloprid in the CWA. These results provide a better understanding of the mechanisms of posttranscriptional regulation of nAChRβ1 and will be helpful for further studies on the role of miRNAs in the regulation of nAChRβ1 subunit resistance in homopteran pests.

The Role of microRNAs in the Drosophila Melanogaster Visual System

MicroRNAs (miRNAs) are a class of small non-coding RNAs (∼22 nucleotides in length) that negatively regulate protein-coding gene expression post-transcriptionally by targeting mRNAs and triggering either translational repression or RNA degradation. MiRNA genes represent approximately 1% of the genome of different species and it has been estimated that every miRNA can interact with an average of 200 mRNA transcripts, with peaks of 1,500 mRNA targets per miRNA molecule. As a result, miRNAs potentially play a fundamental role in several biological processes including development, metabolism, proliferation, and apoptotic cell death, both in physiological and pathological conditions. Since miRNAs were discovered, Drosophila melanogaster has been used as a model organism to shed light on their functions and their molecular mechanisms in the regulation of many biological and behavioral processes. In this review we focus on the roles of miRNAs in the fruit fly brain, at the level of the visual system that is composed by the compound eyes, each containing ∼800 independent unit eyes called ommatidia, and each ommatidium is composed of eight photoreceptor neurons that project into the optic lobes. We describe the roles of a set of miRNAs in the development and in the proper function of the optic lobes (bantam, miR-7, miR-8, miR-210) and of the compound eyes (bantam, miR-7, miR-9a, miR-210, miR-263a/b, miR-279/996), summarizing also the pleiotropic effects that some miRNAs exert on circadian behavior.

MicroRNA-Dependent Control of Sensory Neuron Function Regulates Posture Behavior in Drosophila

All what we see, touch, hear, taste, or smell must first be detected by the sensory elements of our nervous system. Sensory neurons, therefore, represent a critical component in all neural circuits and their correct function is essential for the generation of behavior and adaptation to the environment. Here, we report that the evolutionarily-conserved microRNA (miRNA) miR-263b plays a key behavioral role in Drosophila melanogaster through effects on the function of larval sensory neurons. Several independent experiments (in 50:50 male:female populations) support this finding: first, miRNA expression analysis, via reporter expression and fluorescent-activated cell sorting (FACS)-quantitative PCR (qPCR) analysis, demonstrate miR-263b expression in larval sensory neurons. Second, behavioral tests in miR-263b null mutants show defects in self-righting, an innate and evolutionarily conserved posture-control behavior that allows larvae to rectify their position if turned upside-down. Third, competitive inhibition of miR-263b in sensory neurons using a miR-263b "sponge" leads to self-righting defects. Fourth, systematic analysis of sensory neurons in miR-263b mutants shows no detectable morphologic defects in their stereotypic pattern, while genetically-encoded calcium sensors expressed in the sensory domain reveal a reduction in neural activity in miR-263b mutants. Fifth, miR-263b null mutants show reduced "touch-response" behavior and a compromised response to sound, both characteristic of larval sensory deficits. Furthermore, bioinformatic miRNA target analysis, gene expression assays, and behavioral phenocopy experiments suggest that miR-263b might exert its effects, at least in part, through repression of the basic helix-loop-helix (bHLH) transcription factor Atonal Altogether, our study suggests a model in which miRNA-dependent control of transcription factor expression affects sensory function and behavior.SIGNIFICANCE STATEMENT Sensory neurons are key to neural circuit function, but how these neurons acquire their specific properties is not well understood. Here, we examine this problem, focusing on the roles played by microRNAs (miRNAs). Using Drosophila, we demonstrate that the evolutionarily-conserved miRNA miR-263b controls sensory neuron function allowing the animal to perform an adaptive, elaborate three-dimensional movement. Our work thus shows that microRNAs can control complex motor behaviors by modulating sensory neuron physiology, and suggests that similar miRNA-dependent mechanisms may operate in other species. The work contributes to advance the understanding of the molecular basis of behavior and the biological roles of microRNAs within the nervous system.

Integrative Role of 14-3-3ε in Sleep Regulation

Sleep is a crucial factor for health and survival in all animals. In this study, we found by proteomic analysis that some cancer related proteins were impacted by the circadian clock. The 14-3-3ε protein, expression of which is activated by the circadian transcription factor Clock, regulates adult sleep of Drosophila independent of circadian rhythm. Detailed analysis of the sleep regulatory mechanism shows that 14-3-3ε directly targets the Ultrabithorax (Ubx) gene to activate transcription of the pigment dispersing factor (PDF). The dopamine receptor (Dop1R1) and the octopamine receptor (Oamb), are also involved in the 14-3-3ε pathway, which in 14-3-3ε mutant flies causes increases in the dopR1 and OAMB, while downregulation of the DopR1 and Oamb can restore the sleep phenotype caused by the 14-3-3ε mutation. In conclusion, 14-3-3ε is necessary for sleep regulation in Drosophila.

Post-transcriptional modulators and mediators of the circadian clock

The endogenous circadian timekeeping system drives ~24-h rhythms in gene expression and rhythmically coordinates the physiology, metabolism and behavior in a wide range of organisms. Regulation at various levels is important for the accurate functioning of this circadian timing system. The core circadian oscillator consists of an interlocked transcriptional-translational negative feedback loop (TTFL) that imposes a substantial delay between the accumulation of clock gene mRNA and its protein to generate 24-h oscillations. This TTFL mediated daily oscillation of clock proteins is further fine-tuned by post-translational modifications that regulate the clock protein stability, interaction with other proteins and subcellular localization. Emerging evidence from various studies indicates that besides TTFL and post-translational modifications, post-transcriptional regulation plays a key role in shaping the rhythmicity of mRNAs and to delay the accumulation of clock proteins in relation to their mRNAs. In this review, we summarize the current knowledge on the importance of post-transcriptional regulatory mechanisms such as splicing, polyadenylation, the role of RNA-binding proteins, RNA methylation and microRNAs in the context of shaping the circadian rhythmicity in Drosophila and mammals. In particular, we discuss microRNAs, an important player in post-transcriptional regulation of core-clock machinery, circadian neural circuit, clock input, and output pathways. Furthermore, we provide an overview of the microRNAs that exhibit diurnal rhythm in expression and their role in mediating rhythmic physiological processes.

Translating around the clock: Multi-level regulation of post-transcriptional processes by the circadian clock

The endogenous circadian clock functions to maintain optimal physiological health through the tissue specific coordination of gene expression and synchronization between tissues of metabolic processes throughout the 24 hour day. Individuals face numerous challenges to circadian function on a daily basis resulting in significant incidences of circadian disorders in the United States and worldwide. Dysfunction of the circadian clock has been implicated in numerous diseases including cancer, diabetes, obesity, cardiovascular and hepatic abnormalities, mood disorders and neurodegenerative diseases. The circadian clock regulates molecular, metabolic and physiological processes through rhythmic gene expression via transcriptional and post-transcriptional processes. Mounting evidence indicates that post-transcriptional regulation by the circadian clock plays a crucial role in maintaining tissue specific biological rhythms. Circadian regulation affecting RNA stability and localization through RNA processing, mRNA degradation, and RNA availability for translation can result in rhythmic protein synthesis, even when the mRNA transcripts themselves do not exhibit rhythms in abundance. The circadian clock also targets the initiation and elongation steps of translation through multiple pathways. In this review, the influence of the circadian clock across the levels of post-transcriptional, translation, and post-translational modifications are examined using examples from humans to cyanobacteria demonstrating the phylogenetic conservation of circadian regulation. Lastly, we briefly discuss chronotherapies and pharmacological treatments that target circadian function. Understanding the complexity and levels through which the circadian clock regulates molecular and physiological processes is important for future advancement of therapeutic outcomes.

Regulatory mechanism of daily sleep by miR-276a

MiRNAs have attracted more attention in recent years as regulators of sleep and circadian rhythms after their roles in circadian rhythm and sleep were discovered. In this study, we explored the roles of the miR-276a on daily sleep in Drosophila melanogaster, and found a regulatory cycle for the miR-276a pathway, in which miR-276a, regulated by the core CLOCK/CYCLE (CLK/CYC) transcription factor upstream, regulates sleep via suppressing targets TIM and NPFR1. (a) Loss of miR-276a function makes the flies sleep more during both daytime and nighttime, while flies with gain of miR-276a function sleep less; (b) MiR-276a is widely expressed in the mushroom body (MB), the pars intercerebralis (PI) and some clock neurons lateral dorsal neurons (LNds), in which tim neurons is important for sleep regulation; (c) MiR-276a promoter is identified to locate in the 8th fragment (aFrag8) of the pre-miR-276a, and this fragment is directly activated and regulated by CLK/CYC; (4) MiR-276a is rhythmically oscillating in heads of the wild-type w¹¹¹⁸ , but this oscillation disappears in the loss of function mutant clk^jrk ; (5) The neuropeptide F receptor 1 (npfr1) was found to be a downstream target of miR-276a. These results clarify that the miR-276a is a very important factor for sleep regulation.

AKH-FOXO pathway regulates starvation-induced sleep loss through remodeling of the small ventral lateral neuron dorsal projections

Starvation caused by adverse feeding stresses or food shortages has been reported to result in sleep loss in animals. However, how the starvation signal interacts with the central nervous system is still unknown. Here, the adipokinetic hormone (AKH)-Fork head Box-O (FOXO) pathway is shown to respond to energy change and adjust the sleep of Drosophila through remodeling of the s-LNv (small ventral lateral neurons) dorsal projections. Our results show that starvation prevents flies from going to sleep after the first light-dark transition. The LNvs are required for starvation-induced sleep loss through extension of the pigment dispersing factor (PDF)-containing s-LNv dorsal projections. Further studies reveal that loss of AKH or AKHR (akh receptor) function blocks starvation-induced extension of s-LNv dorsal projections and rescues sleep suppression during food deprivation. FOXO, which has been reported to regulate synapse plasticity of neurons, acts as starvation response factor downstream of AKH, and down regulation of FOXO level considerably alleviates the influence of starvation on s-LNv dorsal projections and sleep. Taking together, our results outline the transduction pathways between starvation signal and sleep, and reveal a novel functional site for sleep regulation.

miRNA-10a-5p Alleviates Insulin Resistance and Maintains Diurnal Patterns of Triglycerides and Gut Microbiota in High-Fat Diet-Fed Mice

miRNA-10a is rhythmically expressed and regulates genes involved in lipid and glucose metabolism. However, the effects of miRNA-10a on obesity and glucose intolerance, as well as on the diurnal pattern of expression of circadian clock genes, remain unknown. We explored the effects of miRNA-10a-5p on insulin resistance and on the diurnal patterns of serum triglycerides and gut microbiota in high-fat diet- (HFD-) fed mice. The results showed that oral administration of miRNA-10a-5p significantly prevented body weight gain and improved glucose tolerance and insulin sensitivity in HFD-fed mice. Administration of miRNA-10a-5p also maintained the diurnal rhythm of Clock, Per2, and Cry1 expression, as well as serum glucose and triglyceride levels. Surprisingly, the diurnal oscillations of three genera of microbes, Oscillospira, Ruminococcus, and Lachnospiraceae, disrupted by HFD feeding, maintained by administration of miRNA-10a-5p. Moreover, a strong positive correlation was found between hepatic Clock expression and relative abundance of Lachnospiraceae, both in control mice (r = 0.877) and in mice administered miRNA-10a-5p (r = 0.853). Furthermore, we found that along with changes in Lachnospiraceae abundance, butyrate content in the feces maintained a diurnal rhythm after miRNA-10a-5p administration in HFD-fed mice. In conclusion, we suggest that miRNA-10a-5p may improve HFD-induced glucose intolerance and insulin resistance through the modulation of the diurnal rhythm of Lachnospiraceae and its metabolite butyrate. Therefore, miRNA-10a-5p may have preventative properties in subjects with metabolic disorders.