The microRNA bantam functions in epithelial cells to regulate scaling growth of dendrite arbors in drosophila sensory neurons

Amyloid β42 peptide is toxic to non-neural cells in Drosophila yielding a characteristic metabolite profile and the effect can be suppressed by PI3K

The human Aβ42 peptide is associated with Alzheimer's disease through its deleterious effects in neurons. Expressing the human peptide in adult Drosophila in a tissue- and time-controlled manner, we show that Aβ42 is also toxic in non-neural cells, neurosecretory and epithelial cell types in particular. This form of toxicity includes the aberrant signaling by Wingless morphogen leading to the eventual activation of Caspase 3. Preventing Caspase 3 activation by means of p53 keeps epithelial cells from elimination but maintains the Aβ42 toxicity yielding more severe deleterious effects to the organism. Metabolic profiling by nuclear magnetic resonance (NMR) of adult flies at selected ages post Aβ42 expression onset reveals characteristic changes in metabolites as early markers of the pathological process. All morphological and most metabolic features of Aβ42 toxicity can be suppressed by the joint overexpression of PI3K.

Summary: The Alzheimer's disease-related Aβ42 peptide is toxic for non-neural cells. This toxicity can be detected by specific metabolite changes and suppressed by the overexpression of the enzyme PI3K.

Effects of mutating α-tubulin lysine 40 on sensory dendrite development

Microtubules are essential for neuronal structure and function. Axonal and dendritic microtubules are enriched in post-translational modifications that impact microtubule dynamics, transport and microtubule-associated proteins. Acetylation of α-tubulin lysine 40 (K40) is a prominent and conserved modification of neuronal microtubules. However, the cellular role of microtubule acetylation remains controversial. To resolve how microtubule acetylation might affect neuronal morphogenesis, we mutated endogenous α-tubulin in vivo using a new Drosophila strain that facilitates the rapid knock-in of designer αTub84B alleles (the predominant α-tubulin-encoding gene in flies). Leveraging our new strain, we found that microtubule acetylation, as well as polyglutamylation and (de)tyrosination, is not essential for survival. However, we found that dendrite branch refinement in sensory neurons relies on α-tubulin K40. Mutagenesis of K40 reveals moderate yet significant changes in dendritic lysosome transport, microtubule polymerization and Futsch protein distribution in dendrites but not in axons. Our studies point to an unappreciated role for α-tubulin K40 and acetylation in dendrite morphogenesis. While our results are consistent with the idea that acetylation tunes microtubule function within neurons, they also suggest there may be an acetylation-independent requirement for α-tubulin K40.

This article has an associated First Person interview with the first author of the paper.

Highlighted Article: Neurons are enriched in post-translationally modified microtubules. Targeted mutagenesis of endogenous α-tubulin in flies reveals that dendrite branch refinement is altered by acetylation-blocking mutations.

Dendritic space-filling requires a neuronal type-specific extracellular permissive signal in Drosophila

Neurons sometimes completely fill available space in their receptive fields with evenly spaced dendrites to uniformly sample sensory or synaptic information. The mechanisms that enable neurons to sense and innervate all space in their target tissues are poorly understood. Using Drosophila somatosensory neurons as a model, we show that heparan sulfate proteoglycans (HSPGs) Dally and Syndecan on the surface of epidermal cells act as local permissive signals for the dendritic growth and maintenance of space-filling nociceptive C4da neurons, allowing them to innervate the entire skin. Using long-term time-lapse imaging with intact Drosophila larvae, we found that dendrites grow into HSPG-deficient areas but fail to stay there. HSPGs are necessary to stabilize microtubules in newly formed high-order dendrites. In contrast to C4da neurons, non-space-filling sensory neurons that develop in the same microenvironment do not rely on HSPGs for their dendritic growth. Furthermore, HSPGs do not act by transporting extracellular diffusible ligands or require leukocyte antigen-related (Lar), a receptor protein tyrosine phosphatase (RPTP) and the only known Drosophila HSPG receptor, for promoting dendritic growth of space-filling neurons. Interestingly, another RPTP, Ptp69D, promotes dendritic growth of C4da neurons in parallel to HSPGs. Together, our data reveal an HSPG-dependent pathway that specifically allows dendrites of space-filling neurons to innervate all target tissues in Drosophila.

In vivo dendrite regeneration after injury is different from dendrite development

Thompson-Peer et al. show that, in intact Drosophila larvae, a discrete injury that removes all dendrites induces robust dendritic growth that recreates many features of uninjured dendrites. However, the growth and patterning of injury-induced dendrites is significantly different from uninjured dendrites.

Neurons receive information along dendrites and send signals along axons to synaptic contacts. The factors that control axon regeneration have been examined in many systems, but dendrite regeneration has been largely unexplored. Here we report that, in intact Drosophila larvae, a discrete injury that removes all dendrites induces robust dendritic growth that recreates many features of uninjured dendrites, including the number of dendrite branches that regenerate and responsiveness to sensory stimuli. However, the growth and patterning of injury-induced dendrites is significantly different from uninjured dendrites. We found that regenerated arbors cover much less territory than uninjured neurons, fail to avoid crossing over other branches from the same neuron, respond less strongly to mechanical stimuli, and are pruned precociously. Finally, silencing the electrical activity of the neurons specifically blocks injury-induced, but not developmental, dendrite growth. By elucidating the essential features of dendrites grown in response to acute injury, our work builds a framework for exploring dendrite regeneration in physiological and pathological conditions.

Removal of Drosophila Muscle Tissue from Larval Fillets for Immunofluorescence Analysis of Sensory Neurons and Epidermal Cells

Drosophila larval dendritic arborization (da) neurons are a popular model for investigating mechanisms of neuronal morphogenesis. Da neurons develop in communication with the epidermal cells they innervate and thus their analysis benefits from in situ visualization of both neuronally and epidermally expressed proteins by immunofluorescence. Traditional methods of preparing larval fillets for immunofluorescence experiments leave intact the muscle tissue that covers most of the body wall, presenting several challenges to imaging neuronal and epidermal proteins. Here we describe a method for removing muscle tissue from Drosophila larval fillets. This protocol enables imaging of proteins that are otherwise obscured by muscle tissue, improves signal to noise ratio, and facilitates the use of super-resolution microscopy to study da neuron development.

Intrinsic Axonal Growth and the Drive for Regeneration

Following damage to the adult nervous system in conditions like stroke, spinal cord injury, or traumatic brain injury, many neurons die and most of the remaining spared neurons fail to regenerate. Injured neurons fail to regrow both because of the inhibitory milieu in which they reside as well as a loss of the intrinsic growth capacity of the neurons. If we are to develop effective therapeutic interventions that promote functional recovery for the devastating injuries described above, we must not only better understand the molecular mechanisms of developmental axonal growth in hopes of re-activating these pathways in the adult, but at the same time be aware that re-activation of adult axonal growth may proceed via distinct mechanisms. With this knowledge in hand, promoting adult regeneration of central nervous system neurons can become a more tractable and realistic therapeutic endeavor.

FoxO regulates microtubule dynamics and polarity to promote dendrite branching in Drosophila sensory neurons

The size and shape of dendrite arbors are defining features of neurons and critical determinants of neuronal function. The molecular mechanisms establishing arborization patterns during development are not well understood, though properly regulated microtubule (MT) dynamics and polarity are essential. We previously found that FoxO regulates axonal MTs, raising the question of whether it also regulates dendritic MTs and morphology. Here we demonstrate that FoxO promotes dendrite branching in all classes of Drosophila dendritic arborization (da) neurons. FoxO is required both for initiating growth of new branches and for maintaining existing branches. To elucidate FoxO function, we characterized MT organization in both foxO null and overexpressing neurons. We find that FoxO directs MT organization and dynamics in dendrites. Moreover, it is both necessary and sufficient for anterograde MT polymerization, which is known to promote dendrite branching. Lastly, FoxO promotes proper larval nociception, indicating a functional consequence of impaired da neuron morphology in foxO mutants. Together, our results indicate that FoxO regulates dendrite structure and function and suggest that FoxO-mediated pathways control MT dynamics and polarity.

Duplication of a Single Neuron in C. elegans Reveals a Pathway for Dendrite Tiling by Mutual Repulsion

Simple cell-cell interactions can give rise to complex cellular patterns. For example, neurons of the same type can interact to create a complex patchwork of non-overlapping dendrite arbors, a pattern known as dendrite tiling. Dendrite tiling often involves mutual repulsion between neighboring neurons. While dendrite tiling is found across nervous systems, the nematode Caenorhabditis elegans has a relatively simple nervous system with few opportunities for tiling. Here, we show that genetic duplication of a single neuron, PVD, is sufficient to create dendrite tiling among the resulting ectopic neurons. We use laser ablation to show that this tiling is mediated by mutual repulsion between neighbors. Furthermore, we find that tiling requires a repulsion signal (UNC-6/Netrin and its receptors UNC-40/DCC and UNC-5) that normally patterns the PVD dendrite arbor. These results demonstrate that an apparently complex cellular pattern can emerge in a simple nervous system merely by increasing neuron number.

Nanos-mediated repression of hid protects larval sensory neurons after a global switch in sensitivity to apoptotic signals

Dendritic arbor morphology is a key determinant of neuronal function. Once established, dendrite branching patterns must be maintained as the animal develops to ensure receptive field coverage. The translational repressors Nanos (Nos) and Pumilio (Pum) are required to maintain dendrite growth and branching of Drosophila larval class IV dendritic arborization (da) neurons, but their specific regulatory role remains unknown. We show that Nos-Pum-mediated repression of the pro-apoptotic gene head involution defective (hid) is required to maintain a balance of dendritic growth and retraction in class IV da neurons and that upregulation of hid results in decreased branching because of an increase in caspase activity. The temporal requirement for nos correlates with an ecdysone-triggered switch in sensitivity to apoptotic stimuli that occurs during the mid-L3 transition. We find that hid is required during pupariation for caspase-dependent pruning of class IV da neurons and that Nos and Pum delay pruning. Together, these results suggest that Nos and Pum provide a crucial neuroprotective regulatory layer to ensure that neurons behave appropriately in response to developmental cues.

Epithelia-derived wingless regulates dendrite directional growth of drosophila ddaE neuron through the Fz-Fmi-Dsh-Rac1 pathway

Background

Proper dendrite patterning is critical for the receiving and processing of information in the nervous system. Cell-autonomous molecules have been extensively studied in dendrite morphogenesis; however, the regulatory mechanisms of environmental factors in dendrite growth remain to be elucidated.

Results

By evaluating the angle between two primary dendrites (PD-Angle), we found that the directional growth of the primary dendrites of a Drosophila periphery sensory neuron ddaE is regulated by the morphogen molecule Wingless (Wg). During the early stage of dendrite growth, Wg is expressed in a group of epithelial cells posteriorly adjacent to ddaE. When Wg expression is reduced or shifted anteriorly, the PD-Angle is markedly decreased. Furthermore, Wg receptor Frizzled functions together with Flamingo and Dishevelled in transducing the Wg signal into ddaE neuron, and the downstream signal is mediated by non-canonical Wnt pathway through Rac1.

Conclusions

In conclusion, we reveal that epithelia-derived Wg plays a repulsive role in regulating the directional growth of dendrites through the non-canonical Wnt pathway. Thus, our findings provide strong in vivo evidence on how environmental signals serve as spatial cues for dendrite patterning.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0228-0) contains supplementary material, which is available to authorized users.

MicroRNA function in Drosophila melanogaster

Over the last decade, microRNAs have emerged as critical regulators in the expression and function of animal genomes. This review article discusses the relationship between microRNA-mediated regulation and the biology of the fruit fly Drosophila melanogaster. We focus on the roles that microRNAs play in tissue growth, germ cell development, hormone action, and the development and activity of the central nervous system. We also discuss the ways in which microRNAs affect robustness. Many gene regulatory networks are robust; they are relatively insensitive to the precise values of reaction constants and concentrations of molecules acting within the networks. MicroRNAs involved in robustness appear to be nonessential under uniform conditions used in conventional laboratory experiments. However, the robust functions of microRNAs can be revealed when environmental or genetic variation otherwise has an impact on developmental outcomes.

MicroRNAs: Not "Fine-Tuners" but Key Regulators of Neuronal Development and Function

MicroRNAs (miRNAs) are a class of short non-coding RNAs that operate as prominent post-transcriptional regulators of eukaryotic gene expression. miRNAs are abundantly expressed in the brain of most animals and exert diverse roles. The anatomical and functional complexity of the brain requires the precise coordination of multilayered gene regulatory networks. The flexibility, speed, and reversibility of miRNA function provide precise temporal and spatial gene regulatory capabilities that are crucial for the correct functioning of the brain. Studies have shown that the underlying molecular mechanisms controlled by miRNAs in the nervous systems of invertebrate and vertebrate models are remarkably conserved in humans. We endeavor to provide insight into the roles of miRNAs in the nervous systems of these model organisms and discuss how such information may be used to inform regarding diseases of the human brain.

High-Throughput Profiling of Caenorhabditis elegans Starvation-Responsive microRNAs

MicroRNAs (miRNAs) are non-coding RNAs of ~22 nucleotides in length that regulate gene expression by interfering with the stability and translation of mRNAs. Their expression is regulated during development, under a wide variety of stress conditions and in several pathological processes. In nature, animals often face feast or famine conditions. We observed that subjecting early L4 larvae from Caenorhabditis elegans to a 12-hr starvation period produced worms that are thinner and shorter than well-fed animals, with a decreased lipid accumulation, diminished progeny, reduced gonad size, and an increased lifespan. Our objective was to identify which of the 302 known miRNAs of C. elegans changed their expression under starvation conditions as compared to well-fed worms by means of deep sequencing in early L4 larvae. Our results indicate that 13 miRNAs (miR-34-3p, the family of miR-35-3p to miR-41-3p, miR-39-5p, miR-41-5p, miR-240-5p, miR-246-3p and miR-4813-5p) were upregulated, while 2 miRNAs (let-7-3p and miR-85-5p) were downregulated in 12-hr starved vs. well-fed early L4 larvae. Some of the predicted targets of the miRNAs that changed their expression in starvation conditions are involved in metabolic or developmental process. In particular, miRNAs of the miR-35 family were upregulated 6–20 fold upon starvation. Additionally, we showed that the expression of gld-1, important in oogenesis, a validated target of miR-35-3p, was downregulated when the expression of miR-35-3p was upregulated. The expression of another reported target, the cell cycle regulator lin-23, was unchanged during starvation. This study represents a starting point for a more comprehensive understanding of the role of miRNAs during starvation in C. elegans.

Regulation of dendrite growth and maintenance by exocytosis

Dendrites lengthen by several orders of magnitude during neuronal development, but how membrane is allocated in dendrites to facilitate this growth remains unclear. Here, we report that Ras opposite (Rop), the Drosophila ortholog of the key exocytosis regulator Munc18-1 (also known as STXBP1), is an essential factor mediating dendrite growth. Neurons with depleted Rop function exhibit reduced terminal dendrite outgrowth followed by primary dendrite degeneration, suggestive of differential requirements for exocytosis in the growth and maintenance of different dendritic compartments. Rop promotes dendrite growth together with the exocyst, an octameric protein complex involved in tethering vesicles to the plasma membrane, with Rop-exocyst complexes and exocytosis predominating in primary dendrites over terminal dendrites. By contrast, membrane-associated proteins readily diffuse from primary dendrites into terminals, but not in the reverse direction, suggesting that diffusion, rather than targeted exocytosis, supplies membranous material for terminal dendritic growth, revealing key differences in the distribution of materials to these expanding dendritic compartments.

Development of dendritic form and function

The nervous system is populated by numerous types of neurons, each bearing a dendritic arbor with a characteristic morphology. These type-specific features influence many aspects of a neuron's function, including the number and identity of presynaptic inputs and how inputs are integrated to determine firing properties. Here, we review the mechanisms that regulate the construction of cell type-specific dendrite patterns during development. We focus on four aspects of dendrite patterning that are particularly important in determining the function of the mature neuron: (a) dendrite shape, including branching pattern and geometry of the arbor; (b) dendritic arbor size;

Centrosomin represses dendrite branching by orienting microtubule nucleation

Neuronal dendrite branching is fundamental for building nervous systems. Branch formation is genetically encoded by transcriptional programs to create dendrite arbor morphological diversity for complex neuronal functions. In Drosophila sensory neurons, the transcription factor Abrupt represses branching via an unknown effector pathway. Targeted screening for branching-control effectors identified Centrosomin, the primary centrosome-associated protein for mitotic spindle maturation. Centrosomin repressed dendrite branch formation and was used by Abrupt to simplify arbor branching. Live imaging revealed that Centrosomin localized to the Golgi cis face and that it recruited microtubule nucleation to Golgi outposts for net retrograde microtubule polymerization away from nascent dendrite branches. Removal of Centrosomin enabled the engagement of wee Augmin activity to promote anterograde microtubule growth into the nascent branches, leading to increased branching. The findings reveal that polarized targeting of Centrosomin to Golgi outposts during elaboration of the dendrite arbor creates a local system for guiding microtubule polymerization.

The SLC36 transporter Pathetic is required for extreme dendrite growth in Drosophila sensory neurons

Lin et al. identified a mutant that selectively affects dendrite growth in neurons with large dendrite arbors without affecting dendrite growth in neurons with small dendrite arbors or the animal overall. This mutant disrupts a putative amino acid transporter, Pathetic (Path), that localizes to the cell surface and endolysosomal compartments in neurons.

Dendrites exhibit enormous diversity in form and can differ in size by several orders of magnitude even in a single animal. However, whether neurons with large dendrite arbors have specialized mechanisms to support their growth demands is unknown. To address this question, we conducted a genetic screen for mutations that differentially affected growth in neurons with different-sized dendrite arbors. From this screen, we identified a mutant that selectively affects dendrite growth in neurons with large dendrite arbors without affecting dendrite growth in neurons with small dendrite arbors or the animal overall. This mutant disrupts a putative amino acid transporter, Pathetic (Path), that localizes to the cell surface and endolysosomal compartments in neurons. Although Path is broadly expressed in neurons and nonneuronal cells, mutation of path impinges on nutrient responses and protein homeostasis specifically in neurons with large dendrite arbors but not in other cells. Altogether, our results demonstrate that specialized molecular mechanisms exist to support growth demands in neurons with large dendrite arbors and define Path as a founding member of this growth program.

Importance of gene dosage in controlling dendritic arbor formation during development

Proper dendrite morphology is crucial for normal nervous system functioning. While a number of genes have been implicated in dendrite morphogenesis in both invertebrates and mammals, it remains unclear how developing dendrites respond to changes in gene dosage and what type of patterns their responses may follow. To understand this, I review here evidence from the recent literature, focusing on the genetic studies performed in the Drosophila larval dendritic arborization class IV neuron, an excellent cell type to understand dendrite morphogenesis. I summarize how class IV arbors change morphology in response to developmental fluctuations in the expression levels of 47 genes, studied by means of genetic manipulations such as loss-of-function and gain-of-function, and for which sufficient information is available. I find that arbors can respond to changing gene dosage in several distinct ways, each characterized by a singular dose-response curve. Interestingly, in 72% of cases arbors are sensitive, and thus adjust their morphology, in response to both decreases and increases in the expression of a given gene, indicating that dendrite morphogenesis is a process particularly sensitive to gene dosage. By summarizing the parallels between Drosophila and mammals, I show that many Drosophila dendrite morphogenesis genes have orthologs in mammals, and that some of these are associated with mammalian dendrite outgrowth and human neurodevelopmental disorders. One notable disease-related molecule is kinase Dyrk1A, thought to be a causative factor in Down syndrome. Both increases and decreases in Dyrk1A gene dosage lead to impaired dendrite morphogenesis, which may contribute to Down syndrome pathoetiology.

The Ret receptor regulates sensory neuron dendrite growth and integrin mediated adhesion

Neurons develop highly stereotyped receptive fields by coordinated growth of their dendrites. Although cell surface cues play a major role in this process, few dendrite specific signals have been identified to date. We conducted an in vivo RNAi screen in Drosophila class IV dendritic arborization (C4da) neurons and identified the conserved Ret receptor, known to play a role in axon guidance, as an important regulator of dendrite development. The loss of Ret results in severe dendrite defects due to loss of extracellular matrix adhesion, thus impairing growth within a 2D plane. We provide evidence that Ret interacts with integrins to regulate dendrite adhesion via rac1. In addition, Ret is required for dendrite stability and normal F-actin distribution suggesting it has an essential role in dendrite maintenance. We propose novel functions for Ret as a regulator in dendrite patterning and adhesion distinct from its role in axon guidance.

Conserved RNA-binding proteins required for dendrite morphogenesis in Caenorhabditis elegans sensory neurons

The regulation of dendritic branching is critical for sensory reception, cell-cell communication within the nervous system, learning, memory, and behavior. Defects in dendrite morphology are associated with several neurologic disorders; thus, an understanding of the molecular mechanisms that govern dendrite morphogenesis is important. Recent investigations of dendrite morphogenesis have highlighted the importance of gene regulation at the posttranscriptional level. Because RNA-binding proteins mediate many posttranscriptional mechanisms, we decided to investigate the extent to which conserved RNA-binding proteins contribute to dendrite morphogenesis across phyla. Here we identify a core set of RNA-binding proteins that are important for dendrite morphogenesis in the PVD multidendritic sensory neuron in Caenorhabditis elegans. Homologs of each of these genes were previously identified as important in the Drosophila melanogaster dendritic arborization sensory neurons. Our results suggest that RNA processing, mRNA localization, mRNA stability, and translational control are all important mechanisms that contribute to dendrite morphogenesis, and we present a conserved set of RNA-binding proteins that regulate these processes in diverse animal species. Furthermore, homologs of these genes are expressed in the human brain, suggesting that these RNA-binding proteins are candidate regulators of dendrite development in humans.

Coordinate control of terminal dendrite patterning and dynamics by the membrane protein Raw

The directional flow of information in neurons depends on compartmentalization: dendrites receive inputs whereas axons transmit them. Axons and dendrites likewise contain structurally and functionally distinct subcompartments. Axon/dendrite compartmentalization can be attributed to neuronal polarization, but the developmental origin of subcompartments in axons and dendrites is less well understood. To identify the developmental bases for compartment-specific patterning in dendrites, we screened for mutations that affect discrete dendritic domains in Drosophila sensory neurons. From this screen, we identified mutations that affected distinct aspects of terminal dendrite development with little or no effect on major dendrite patterning. Mutation of one gene, raw, affected multiple aspects of terminal dendrite patterning, suggesting that Raw might coordinate multiple signaling pathways to shape terminal dendrite growth. Consistent with this notion, Raw localizes to branch-points and promotes dendrite stabilization together with the Tricornered (Trc) kinase via effects on cell adhesion. Raw independently influences terminal dendrite elongation through a mechanism that involves modulation of the cytoskeleton, and this pathway is likely to involve the RNA-binding protein Argonaute 1 (AGO1), as raw and AGO1 genetically interact to promote terminal dendrite growth but not adhesion. Thus, Raw defines a potential point of convergence in distinct pathways shaping terminal dendrite patterning.

MicroRNA-9 controls dendritic development by targeting REST

MicroRNAs (miRNAs) are conserved noncoding RNAs that function as posttranscriptional regulators of gene expression. miR-9 is one of the most abundant miRNAs in the brain. Although the function of miR-9 has been well characterized in neural progenitors, its role in dendritic and synaptic development remains largely unknown. In order to target miR-9 in vivo, we developed a transgenic miRNA sponge mouse line allowing conditional inactivation of the miR-9 family in a spatio-temporal-controlled manner. Using this novel approach, we found that miR-9 controls dendritic growth and synaptic transmission in vivo. Furthermore, we demonstrate that miR-9-mediated downregulation of the transcriptional repressor REST is essential for proper dendritic growth.

DOI:http://dx.doi.org/10.7554/eLife.02755.001

Messages are sent back and forth in our brains by cells called neurons that connect to each other in complex networks. Neurons develop from stem cells in a complicated process that involves a number of different stages. In one of the final stages, tree-like structures called dendrites emerge from the neurons and connect with neighboring neurons via special junctions called synapses.

A group of small RNA molecules called microRNAs have roles in controlling the development of neurons. One microRNA, called miR-9, is abundant in the brain and is known to be involved in the early stages of neuron development. However, its role in the formation of dendrites and synapses remains unclear.

Giusti et al. studied this microRNA in mice. A length of DNA, coding for an RNA molecule that binds to miR-9 molecules and stops them performing their normal function, was inserted into the mice. These experiments showed that miR-9 is involved in controlling dendrite growth and synaptic function.

To enable a neuron to produce dendrites, miR-9 binds to and interferes with the RNA molecules that are needed to make a protein called REST. This protein is a transcription factor that switches off the expression of other genes so, in effect, miR-9 allows a set of genes that are needed for dendrite growth to be switched on.

The methodology developed by Giusti et al. could be used to study the functions of other microRNAs.

DOI:http://dx.doi.org/10.7554/eLife.02755.002

Intrinsic and extrinsic mechanisms of dendritic morphogenesis

The complex, branched morphology of dendrites is a cardinal feature of neurons and has been used as a criterion for cell type identification since the beginning of neurobiology. Regulated dendritic outgrowth and branching during development form the basis of receptive fields for neurons and are essential for the wiring of the nervous system. The cellular and molecular mechanisms of dendritic morphogenesis have been an intensely studied area. In this review, we summarize the major experimental systems that have contributed to our understandings of dendritic development as well as the intrinsic and extrinsic mechanisms that instruct the neurons to form cell type-specific dendritic arbors.

Double-bromo and extraterminal (BET) domain proteins regulate dendrite morphology and mechanosensory function

A complex array of genetic factors regulates neuronal dendrite morphology. Epigenetic regulation of gene expression represents a plausible mechanism to control pathways responsible for specific dendritic arbor shapes. By studying the Drosophila dendritic arborization (da) neurons, we discovered a role of the double-bromodomain and extraterminal (BET) family proteins in regulating dendrite arbor complexity. A loss-of-function mutation in the single Drosophila BET protein encoded by female sterile 1 homeotic [fs(1)h] causes loss of fine, terminal dendritic branches. Moreover, fs(1)h is necessary for the induction of branching caused by a previously identified transcription factor, Cut (Ct), which regulates subtype-specific dendrite morphology. Finally, disrupting fs(1)h function impairs the mechanosensory response of class III da sensory neurons without compromising the expression of the ion channel NompC, which mediates the mechanosensitive response. Thus, our results identify a novel role for BET family proteins in regulating dendrite morphology and a possible separation of developmental pathways specifying neural cell morphology and ion channel expression. Since the BET proteins are known to bind acetylated histone tails, these results also suggest a role of epigenetic histone modifications and the "histone code," in regulating dendrite morphology.

A primal analysis system of brain neurons data

It is a very challenging work to classify the 86 billions of neurons in the human brain. The most important step is to get the features of these neurons. In this paper, we present a primal system to analyze and extract features from brain neurons. First, we make analysis on the original data of neurons in which one neuron contains six parameters: room type, X, Y, Z coordinate range, total number of leaf nodes, and fuzzy volume of neurons. Then, we extract three important geometry features including rooms type, number of leaf nodes, and fuzzy volume. As application, we employ the feature database to fit the basic procedure of neuron growth. The result shows that the proposed system is effective.

Developmental shaping of dendritic arbors in Drosophila relies on tightly regulated intra-neuronal activity of protein kinase A (PKA)

Dendrites develop morphologies characterized by multiple levels of complexity that involve neuron type specific dendritic length and particular spatial distribution. How this is developmentally regulated and in particular which signaling molecules are crucial in the process is still not understood. Using Drosophila class IV dendritic arborization (da) neurons we test in vivo the effects of cell-autonomous dose-dependent changes in the activity levels of the cAMP-dependent Protein Kinase A (PKA) on the formation of complex dendritic arbors. We find that genetic manipulations of the PKA activity levels affect profoundly the arbor complexity with strongest impact on distal branches. Both decreasing and increasing PKA activity result in a reduced complexity of the arbors, as reflected in decreased dendritic length and number of branching points, suggesting an inverted U-shape response to PKA. The phenotypes are accompanied by changes in organelle distribution: Golgi outposts and early endosomes in distal dendritic branches are reduced in PKA mutants. By using Rab5 dominant negative we find that PKA interacts genetically with the early endosomal pathway. We test if the possible relationship between PKA and organelles may be the result of phosphorylation of the microtubule motor dynein components or Rab5. We find that Drosophila cytoplasmic dynein components are direct PKA phosphorylation targets in vitro, but not in vivo, thus pointing to a different putative in vivo target. Our data argue that tightly controlled dose-dependent intra-neuronal PKA activity levels are critical in determining the dendritic arbor complexity, one of the possible ways being through the regulation of organelle distribution.

MiR-223 regulates the differentiation of immature neurons

BACKGROUND

Small non-coding microRNA RNA molecules can regulate stem cell function. The role of microRNAs in neural stem/progenitor cells (NS/PCs) differentiation is not entirely clear.

METHODS

MiRNA profiling, loss and gain of function studies coupled with dendritic tree development morphometric analysis and calcium influx imaging were utilized to investigate the role of micoRNA-223 in differentiating NS/PCs.

RESULTS

MiRNA profiling in human NS/PCs before and after differentiation in vitro reveals modulation of miRNAs following differentiation of NS/PCs. MiR-223, a microRNA well characterized as a hematopoietic-specific miRNA was identified. Cell-autonomous inhibition of miR-223 in the adult mouse dentate gyrus NS/PCs led to a significant increase in immature neurons soma size, dendritic tree total length, branch number per neuron and complexity, while neuronal migration in the dentate gyrus remained unaffected. Overexpression of miR-223 decreased dendritic tree total length, branch number and complexity in neurons differentiated from human embryonic stem cells (hESCs). Inhibition of miR-223 enhanced N-methyl-D-aspartate (NMDA) induced calcium influx in human neurons differentiated from NS/PCs.

CONCLUSIONS

Taken together, these findings indicate that miR-223 regulates the differentiation of neurons derived from NS/PCs.

The microRNA bantam regulates a developmental transition in epithelial cells that restricts sensory dendrite growth

As animals grow, many early born structures grow by cell expansion rather than cell addition; thus growth of distinct structures must be coordinated to maintain proportionality. This phenomenon is particularly widespread in the nervous system, with dendrite arbors of many neurons expanding in concert with their substrate to sustain connectivity and maintain receptive field coverage as animals grow. After rapidly growing to establish body wall coverage, dendrites of Drosophila class IV dendrite arborization (C4da) neurons grow synchronously with their substrate, the body wall epithelium, providing a system to study how proportionality is maintained during animal growth. Here, we show that the microRNA bantam (ban) ensures coordinated growth of C4da dendrites and the epithelium through regulation of epithelial endoreplication, a modified cell cycle that entails genome amplification without cell division. In Drosophila larvae, epithelial endoreplication leads to progressive changes in dendrite-extracellular matrix (ECM) and dendrite-epithelium contacts, coupling dendrite/substrate expansion and restricting dendrite growth beyond established boundaries. Moreover, changes in epithelial expression of cell adhesion molecules, including the beta-integrin myospheroid (mys), accompany this developmental transition. Finally, endoreplication and the accompanying changes in epithelial mys expression are required to constrain late-stage dendrite growth and structural plasticity. Hence, modulating epithelium-ECM attachment probably influences substrate permissivity for dendrite growth and contributes to the dendrite-substrate coupling that ensures proportional expansion of the two cell types.

Drosophila Valosin-Containing Protein is required for dendrite pruning through a regulatory role in mRNA metabolism

The dendritic arbors of the larval Drosophila peripheral class IV dendritic arborization neurons degenerate during metamorphosis in an ecdysone-dependent manner. This process-also known as dendrite pruning-depends on the ubiquitin-proteasome system (UPS), but the specific processes regulated by the UPS during pruning have been largely elusive. Here, we show that mutation or inhibition of Valosin-Containing Protein (VCP), a ubiquitin-dependent ATPase whose human homolog is linked to neurodegenerative disease, leads to specific defects in mRNA metabolism and that this role of VCP is linked to dendrite pruning. Specifically, we find that VCP inhibition causes an altered splicing pattern of the large pruning gene molecule interacting with CasL and mislocalization of the Drosophila homolog of the human RNA-binding protein TAR-DNA-binding protein of 43 kilo-Dalton (TDP-43). Our data suggest that VCP inactivation might lead to specific gain-of-function of TDP-43 and other RNA-binding proteins. A similar combination of defects is also seen in a mutant in the ubiquitin-conjugating enzyme ubcD1 and a mutant in the 19S regulatory particle of the proteasome, but not in a 20S proteasome mutant. Thus, our results highlight a proteolysis-independent function of the UPS during class IV dendritic arborization neuron dendrite pruning and link the UPS to the control of mRNA metabolism.

Dying cells protect survivors from radiation-induced cell death in Drosophila

We report a phenomenon wherein induction of cell death by a variety of means in wing imaginal discs of Drosophila larvae resulted in the activation of an anti-apoptotic microRNA, bantam. Cells in the vicinity of dying cells also become harder to kill by ionizing radiation (IR)-induced apoptosis. Both ban activation and increased protection from IR required receptor tyrosine kinase Tie, which we identified in a genetic screen for modifiers of ban. tie mutants were hypersensitive to radiation, and radiation sensitivity of tie mutants was rescued by increased ban gene dosage. We propose that dying cells activate ban in surviving cells through Tie to make the latter cells harder to kill, thereby preserving tissues and ensuring organism survival. The protective effect we report differs from classical radiation bystander effect in which neighbors of irradiated cells become more prone to death. The protective effect also differs from the previously described effect of dying cells that results in proliferation of nearby cells in Drosophila larval discs. If conserved in mammals, a phenomenon in which dying cells make the rest harder to kill by IR could have implications for treatments that involve the sequential use of cytotoxic agents and radiation therapy.

In multicellular organisms where cells exist in the context of other cells, the behavior of one affects the others. The consequences of such interactions include not just cell fate choices but also life and death decisions. In the wing primordia of Drosophila melanogaster larvae, dying cells release mitogenic signals that stimulate the neighbors to proliferate. Such an effect is proposed to compensate for cell loss and help regenerate the tissue. We report here that, in the same experimental system, dying cells activate a pro-survival microRNA, bantam, in surviving cells. This results in increased protection from the killing effect of ionizing radiation (IR). Activation of ban requires tie, which encodes a receptor tyrosine kinase. tie and ban mutant larvae are hypersensitive to killing by IR, suggesting that the responses described here are important for organismal survival following radiation exposure.

An evolutionarily conserved protein CHORD regulates scaling of dendritic arbors with body size

Most organs scale proportionally with body size through regulation of individual cell size and/or cell number. Here we addressed how postmitotic and morphologically complex cells such as neurons scale with the body size by using the dendritic arbor of one Drosophila sensory neuron as an assay system. In small adults eclosed under a limited-nutrition condition, the wild-type neuron preserved the branching complexity of the arbor, but scaled down the entire arbor, making a “miniature”. In contrast, mutant neurons for the Insulin/IGF signaling (IIS) or TORC1 pathway exhibited “undergrowth”, which was characterized by decreases in both the branching complexity and the arbor size, despite a normal diet. These contrasting phenotypes hinted that a novel regulatory mechanism contributes to the dendritic scaling in wild-type neurons. Indeed, we isolated a mutation in the gene CHORD/morgana that uncoupled the neuron size and the body size: CHORD mutant neurons generated miniature dendritic arbors regardless of the body size. CHORD encodes an evolutionarily conserved co-chaperone of HSP90. Our results support the notion that dendritic growth and branching are controlled by partly separate mechanisms. The IIS/TORC1 pathways control both growth and branching to avert underdevelopment, whereas CHORD together with TORC2 realizes proportional scaling of the entire arbor.

Cysteine proteinase-1 and cut protein isoform control dendritic innervation of two distinct sensory fields by a single neuron

Dendrites often exhibit structural changes in response to local inputs. Although mechanisms that pattern and maintain dendritic arbors are becoming clearer, processes regulating regrowth, during context-dependent plasticity or after injury, remain poorly understood. We found that a class of Drosophila sensory neurons, through complete pruning and regeneration, can elaborate two distinct dendritic trees, innervating independent sensory fields. An expression screen identified Cysteome proteinase-1 (Cp1) as a critical regulator of this process. Unlike known ecdysone effectors, Cp1-mutant ddaC neurons pruned larval dendrites normally but failed to regrow adult dendrites. Cp1 expression was upregulated/concentrated in the nucleus during metamorphosis, controlling production of a truncated Cut homeodomain transcription factor. This truncated Cut, but not the full-length protein, allowed Cp1-mutant ddaC neurons to regenerate higher-order adult dendrites. These results identify a molecular pathway needed for dendrite regrowth after pruning, which allows the same neuron to innervate distinct sensory fields.

Cell-intrinsic drivers of dendrite morphogenesis

The proper formation and morphogenesis of dendrites is fundamental to the establishment of neural circuits in the brain. Following cell cycle exit and migration, neurons undergo organized stages of dendrite morphogenesis, which include dendritic arbor growth and elaboration followed by retraction and pruning. Although these developmental stages were characterized over a century ago, molecular regulators of dendrite morphogenesis have only recently been defined. In particular, studies in Drosophila and mammalian neurons have identified numerous cell-intrinsic drivers of dendrite morphogenesis that include transcriptional regulators, cytoskeletal and motor proteins, secretory and endocytic pathways, cell cycle-regulated ubiquitin ligases, and components of other signaling cascades. Here, we review cell-intrinsic drivers of dendrite patterning and discuss how the characterization of such crucial regulators advances our understanding of normal brain development and pathogenesis of diverse cognitive disorders.

Insulin signaling regulates neurite growth during metamorphic neuronal remodeling

Although the growth capacity of mature neurons is often limited, some neurons can shift through largely unknown mechanisms from stable maintenance growth to dynamic, organizational growth (e.g. to repair injury, or during development transitions). During insect metamorphosis, many terminally differentiated larval neurons undergo extensive remodeling, involving elimination of larval neurites and outgrowth and elaboration of adult-specific projections. Here, we show in the fruit fly, Drosophila melanogaster (Meigen), that a metamorphosis-specific increase in insulin signaling promotes neuronal growth and axon branching after prolonged stability during the larval stages. FOXO, a negative effector in the insulin signaling pathway, blocked metamorphic growth of peptidergic neurons that secrete the neuropeptides CCAP and bursicon. RNA interference and CCAP/bursicon cell-targeted expression of dominant-negative constructs for other components of the insulin signaling pathway (InR, Pi3K92E, Akt1, S6K) also partially suppressed the growth of the CCAP/bursicon neuron somata and neurite arbor. In contrast, expression of wild-type or constitutively active forms of InR, Pi3K92E, Akt1, Rheb, and TOR, as well as RNA interference for negative regulators of insulin signaling (PTEN, FOXO), stimulated overgrowth. Interestingly, InR displayed little effect on larval CCAP/bursicon neuron growth, in contrast to its strong effects during metamorphosis. Manipulations of insulin signaling in many other peptidergic neurons revealed generalized growth stimulation during metamorphosis, but not during larval development. These findings reveal a fundamental shift in growth control mechanisms when mature, differentiated neurons enter a new phase of organizational growth. Moreover, they highlight strong evolutionarily conservation of insulin signaling in neuronal growth regulation.

Epidermal cells are the primary phagocytes in the fragmentation and clearance of degenerating dendrites in Drosophila

During developmental remodeling, neurites destined for pruning often degenerate on-site. Physical injury also induces degeneration of neurites distal to the injury site. Prompt clearance of degenerating neurites is important for maintaining tissue homeostasis and preventing inflammatory responses. Here we show that in both dendrite pruning and dendrite injury of Drosophila sensory neurons, epidermal cells rather than hemocytes are the primary phagocytes in clearing degenerating dendrites. Epidermal cells act via Draper-mediated recognition to facilitate dendrite degeneration and to engulf and degrade degenerating dendrites. Using multiple dendritic membrane markers to trace phagocytosis, we show that two members of the CD36 family, croquemort (crq) and debris buster (dsb), act at distinct stages of phagosome maturation for dendrite clearance. Our finding reveals the physiological importance of coordination between neurons and their surrounding epidermis, for both dendrite fragmentation and clearance.

MiR-223 regulates the differentiation of immature neurons

Background

Small non-coding microRNA RNA molecules can regulate stem cell function. The role of microRNAs in neural stem/progenitor cells (NS/PCs) differentiation is not entirely clear.

Methods

MiRNA profiling, loss and gain of function studies coupled with dendritic tree development morphometric analysis and calcium influx imaging were utilized to investigate the role of micoRNA-223 in differentiating NS/PCs.

Results

MiRNA profiling in human NS/PCs before and after differentiation in vitro reveals modulation of miRNAs following differentiation of NS/PCs. MiR-223, a microRNA well characterized as a hematopoietic-specific miRNA was identified. Cell-autonomous inhibition of miR-223 in the adult mouse dentate gyrus NS/PCs led to a significant increase in immature neurons soma size, dendritic tree total length, branch number per neuron and complexity, while neuronal migration in the dentate gyrus remained unaffected. Overexpression of miR-223 decreased dendritic tree total length, branch number and complexity in neurons differentiated from human embryonic stem cells (hESCs). Inhibition of miR-223 enhanced N-methyl-D-aspartate (NMDA) induced calcium influx in human neurons differentiated from NS/PCs.

Conclusions

Taken together, these findings indicate that miR-223 regulates the differentiation of neurons derived from NS/PCs.

Electronic supplementary material

The online version of this article (doi:10.1186/2052-8426-2-18) contains supplementary material, which is available to authorized users.

New roles for "old" microRNAs in nervous system function and disease

Since their discovery, microRNAs became prominent candidates providing missing links on how to explain the developmental and phenotypical variation within one species or among different species. In addition, microRNAs were implicated in diseases such as neurodegeneration and cancer. More recently, the regulation of animal behavior was shown to be influenced by microRNAs. In spite of their numerous functions, only a few microRNAs were discovered by using classic genetic approaches. Due to the very mild or redundant phenotypes of most microRNAs or their genomic location within introns of other genes many regulatory microRNAs were missed. In this review, we focus on three microRNAs first identified in a forward genetic screen in invertebrates for their essential function in animal development, namely bantam, let-7, and miR-279. All three are essential for survival, are not located in introns of other genes, and are highly conserved among species. We highlight their important functions in the nervous system and discuss their emerging roles, especially during nervous system disease and behavior.

Sensory-neuron subtype-specific transcriptional programs controlling dendrite morphogenesis: genome-wide analysis of Abrupt and Knot/Collier

The transcription factors Abrupt (Ab) and Knot (Kn) act as selectors of distinct dendritic arbor morphologies in two classes of Drosophila sensory neurons, termed class I and class IV, respectively. We performed binding-site mapping and transcriptional profiling of these isolated neurons. Their profiles were similarly enriched in cell-type-specific enhancers of genes implicated in neural development. We identified a total of 429 target genes, of which 56 were common to Ab and Kn; these targets included genes necessary to shape dendritic arbors in either or both of the two sensory subtypes. Furthermore, a common target gene, encoding the cell adhesion molecule Ten-m, was expressed more strongly in class I than class IV, and this differential was critical to the class-selective directional control of dendritic branch sprouting or extension. Our analyses illustrate how differentiating neurons employ distinct and shared repertoires of gene expression to produce class-selective morphological traits.

Larval defense against attack from parasitoid wasps requires nociceptive neurons

Parasitoid wasps are a fierce predator of Drosophila larvae. Female Leptopilina boulardi (LB) wasps use a sharp ovipositor to inject eggs into the bodies of Drosophila melanogaster larvae. The wasp then eats the Drosophila larva alive from the inside, and an adult wasp ecloses from the Drosophila pupal case instead of a fly. However, the Drosophila larvae are not defenseless as they may resist the attack of the wasps through somatosensory-triggered behavioral responses. Here we describe the full range of behaviors performed by the larval prey in immediate response to attacks by the wasps. Our results suggest that Drosophila larvae primarily sense the wasps using their mechanosensory systems. The range of behavioral responses included both “gentle touch” like responses as well as nociceptive responses. We found that the precise larval response depended on both the somatotopic location of the attack, and whether or not the larval cuticle was successfully penetrated during the course of the attack. Interestingly, nociceptive responses are more likely to be triggered by attacks in which the cuticle had been successfully penetrated by the wasp. Finally, we found that the class IV neurons, which are necessary for mechanical nociception, were also necessary for a nociceptive response to wasp attacks. Thus, the class IV neurons allow for a nociceptive behavioral response to a naturally occurring predator of Drosophila.

Deletion of microRNA-80 activates dietary restriction to extend C. elegans healthspan and lifespan

Caloric/dietary restriction (CR/DR) can promote longevity and protect against age-associated disease across species. The molecular mechanisms coordinating food intake with health-promoting metabolism are thus of significant medical interest. We report that conserved Caenorhabditis elegans microRNA-80 (mir-80) is a major regulator of the DR state. mir-80 deletion confers system-wide healthy aging, including maintained cardiac-like and skeletal muscle-like function at advanced age, reduced accumulation of lipofuscin, and extended lifespan, coincident with induction of physiological features of DR. mir-80 expression is generally high under ad lib feeding and low under food limitation, with most striking food-sensitive expression changes in posterior intestine. The acetyltransferase transcription co-factor cbp-1 and interacting transcription factors daf-16/FOXO and heat shock factor-1 hsf-1 are essential for mir-80(Δ) benefits. Candidate miR-80 target sequences within the cbp-1 transcript may confer food-dependent regulation. Under food limitation, lowered miR-80 levels directly or indirectly increase CBP-1 protein levels to engage metabolic loops that promote DR.

Akt regulates glutamate receptor trafficking and postsynaptic membrane elaboration at the Drosophila neuromuscular junction

The Akt family of serine-threonine kinases integrates a myriad of signals governing cell proliferation, apoptosis, glucose metabolism, and cytoskeletal organization. Akt affects neuronal morphology and function, influencing dendrite growth and the expression of ion channels. Akt is also an integral element of PI3Kinase-target of rapamycin (TOR)-Rheb signaling, a pathway that affects synapse assembly in both vertebrates and Drosophila. Our recent findings demonstrated that disruption of this pathway in Drosophila is responsible for a number of neurodevelopmental deficits that may also affect phenotypes associated with tuberous sclerosis complex, a disorder resulting from mutations compromising the TSC1/TSC2 complex, an inhibitor of TOR (Dimitroff et al., 2012). Therefore, we examined the role of Akt in the assembly and physiological function of the Drosophila neuromuscular junction (NMJ), a glutamatergic synapse that displays developmental and activity-dependent plasticity. The single Drosophila Akt family member, Akt1 selectively altered the postsynaptic targeting of one glutamate receptor subunit, GluRIIA, and was required for the expansion of a specialized postsynaptic membrane compartment, the subsynaptic reticulum (SSR). Several lines of evidence indicated that Akt1 influences SSR assembly by regulation of Gtaxin, a Drosophila t-SNARE protein (Gorczyca et al., 2007) in a manner independent of the mislocalization of GluRIIA. Our findings show that Akt1 governs two critical elements of synapse development, neurotransmitter receptor localization, and postsynaptic membrane elaboration.

Functional genomic analyses of two morphologically distinct classes of Drosophila sensory neurons: post-mitotic roles of transcription factors in dendritic patterning

Background

Neurons are one of the most structurally and functionally diverse cell types found in nature, owing in large part to their unique class specific dendritic architectures. Dendrites, being highly specialized in receiving and processing neuronal signals, play a key role in the formation of functional neural circuits. Hence, in order to understand the emergence and assembly of a complex nervous system, it is critical to understand the molecular mechanisms that direct class specific dendritogenesis.

Methodology/Principal Findings

We have used the Drosophila dendritic arborization (da) neurons to gain systems-level insight into dendritogenesis by a comparative study of the morphologically distinct Class-I (C-I) and Class-IV (C-IV) da neurons. We have used a combination of cell-type specific transcriptional expression profiling coupled to a targeted and systematic in vivo RNAi functional validation screen. Our comparative transcriptomic analyses have revealed a large number of differentially enriched/depleted gene-sets between C-I and C-IV neurons, including a broad range of molecular factors and biological processes such as proteolytic and metabolic pathways. Further, using this data, we have identified and validated the role of 37 transcription factors in regulating class specific dendrite development using in vivo class-specific RNAi knockdowns followed by rigorous and quantitative neurometric analysis.

Conclusions/Significance

This study reports the first global gene-expression profiles from purified Drosophila C-I and C-IV da neurons. We also report the first large-scale semi-automated reconstruction of over 4,900 da neurons, which were used to quantitatively validate the RNAi screen phenotypes. Overall, these analyses shed global and unbiased novel insights into the molecular differences that underlie the morphological diversity of distinct neuronal cell-types. Furthermore, our class-specific gene expression datasets should prove a valuable community resource in guiding further investigations designed to explore the molecular mechanisms underlying class specific neuronal patterning.

MicroRNAome of Spodoptera frugiperda cells (Sf9) and its alteration following baculovirus infection

MicroRNAs (miRNAs) as small non-coding RNAs play important roles in many biological processes such as development, cell signalling and immune response. Studies also suggest that miRNAs are important in host–virus interactions where the host limits virus infection by differentially expressing miRNAs that target essential viral genes. Here, we identified conserved and new miRNAs from Spodoptera frugiperda cells (Sf9) using a combination of deep sequencing and bioinformatics as well as experimental approaches. S. frugiperda miRNAs share common features of miRNAs in other organisms, such as uracil (U) at the 5′ end of miRNA. The 5′ ends of the miRNAs were more conserved than the 3′ ends, revealing evolutionary protection of the seed region in miRNAs. The predominant miRNAs were found to be conserved among arthropods. The majority of homologous miRNAs were found in Bombyx mori, with 76 of the 90 identified miRNAs. We found that seed shifting and arm switching have happened in this insect's miRNAs. Expression levels of the majority of miRNAs changed following baculovirus infection. Results revealed that baculovirus infection mainly led to an overall suppression of cellular miRNAs. We found four different genes being regulated by sfr-miR-184 at the post-transcriptional level. The data presented here further support conservation of miRNAs in insects and other organisms. In addition, the results reveal a differential expression of host miRNAs upon baculovirus infection, suggesting their potential roles in host–virus interactions. Seed shifting and arm switching happened during evolution of miRNAs in different insects and caused miRNA diversification, which led to changes in the target repository of miRNAs.

Live imaging of multicolor-labeled cells in Drosophila

We describe LOLLIbow, a Brainbow-based live imaging system with applications in developmental biology and neurobiology. The development of an animal, including the environmentally sensitive adaptation of its brain, is thought to proceed through continual orchestration among diverse cell types as they divide, migrate, transform and interact with one another within the body. To facilitate direct visualization of such dynamic morphogenesis by individual cells in vivo, we have modified the original Brainbow for Drosophila in which live imaging is practical during much of its development. Our system offers permanent fluorescent labels that reveal fine morphological details of individual cells without requiring dissection or fixation of the samples. It also features a non-invasive means to control the timing of stochastic tricolor cell labeling with a light pulse. We demonstrate applicability of the new system in a variety of settings that could benefit from direct imaging of the developing multicellular organism with single-cell resolution.

Characterization and comparative profiling of MicroRNAs in a sexual dimorphism insect, Eupolyphaga sinensis Walker

BACKGROUND

MicroRNAs are now recognized as key post-transcriptional regulators in animal ontogenesis and phenotypic diversity. Eupolyphaga sinensis Walker (Blattaria) is a sexually dimorphic insect, which is also an important source of material used in traditional Chinese medicine. The male E. sinensis have shorter lifecycles and go through fewer instars than the female. Furthermore, the males have forewings, while the females are totally wingless.

RESULTS

We used the Illumina/Solexa deep sequencing technology to sequence small RNA libraries prepared from the fourth-instar larvae of male and female E. sinensis. 19,097,799 raw reads were yielded in total: 7,817,445 reads from the female library and 11,280,354 from the male, respectively. As a result, we identified 168 known miRNAs belonging to 55 families as well as 204 novel miRNAs. Moreover, 45 miRNAs showed significantly different expression between the female and the male fourth-instar larvae, and we validated 10 of them by Stem-loop qRT-PCR. Some of these differentially expressed miRNAs are related to metamorphosis, development and phenotypic diversity.

CONCLUSIONS/SIGNIFICANCE

This is the first comprehensive description of miRNAs in E. sinensis. The results provide a useful resource for further in-depth study on molecular regulation and evolution of miRNAs. These findings not only enrich miRNAs for hemimetabolans but also lay the foundation for the study of post-transcriptional regulation on the phenomena of sexual dimorphism.

MicroRNA functions in insects

MicroRNAs (miRNAs) are small non-coding RNAs that are generated in all eukaryotes and viruses. Their role as master regulators of gene expression in various biological processes has only been fully appreciated over the last decade. Accumulating evidence suggests that alterations in the expression of miRNAs may lead to disorders, including developmental defects, diseases and cancer. Here, I review what is currently known about miRNA functions in insects to provide an insight into their diverse roles in insect biology.