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WNT/β-Catenin Signalling and Epithelial Patterning in the Homoscleromorph Sponge Oscarella  [PDF]
Pascal Lapébie, Eve Gazave, Alexander Ereskovsky, Romain Derelle, Chantal Bézac, Emmanuelle Renard, Evelyn Houliston, Carole Borchiellini
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0005823
Abstract: Sponges branch basally in the metazoan phylogenetic tree and are thus well positioned to provide insights into the evolution of mechanisms controlling animal development, likely to remain active in adult sponges. Of the four sponge clades, the Homoscleromorpha are of particular interest as they alone show the “true” epithelial organization seen in other metazoan phyla (the Eumetazoa). We have examined the deployment in sponges of Wnt signalling pathway components, since this pathway is an important regulator of many developmental patterning processes. We identified a reduced repertoire of three divergent Wnt ligand genes in the recently-sequenced Amphimedon queenslandica (demosponge) genome and two Wnts from our EST collection from the homoscleromorph Oscarella lobularis, along with well-conserved genes for intracellular pathway components (β-catenin, GSK3β). Remarkably, the two O. lobularis Wnt genes showed complementary expression patterns in relation to the evenly spaced ostia (canal openings) of the exopinacoderm (ectoderm), highly reminiscent of Wnt expression during skin appendage formation in vertebrates. Furthermore, experimental activation of the Wnt/β-catenin pathway using GSK3β inhibitors provoked formation of ectopic ostia, as has been shown for epithelial appendages in Eumetazoa. We thus suggest that deployment of Wnt signalling is a common and perhaps ancient feature of metazoan epithelial patterning and morphogenesis.
Localised JAK/STAT Pathway Activation Is Required for Drosophila Wing Hinge Development  [PDF]
Kirsty Johnstone, Richard E. Wells, David Strutt, Martin P. Zeidler
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0065076
Abstract: Extensive morphogenetic remodelling takes place during metamorphosis from a larval to an adult insect body plan. These changes are particularly intricate in the generation of the dipteran wing hinge, a complex structure that is derived from an apparently simple region of the wing imaginal disc. Using the characterisation of original outstretched alleles of the unpaired locus as a starting point, we demonstrate the role of JAK/STAT pathway signalling in the process of wing hinge development. We show that differences in JAK/STAT signalling within the proximal most of three lateral folds present in the wing imaginal disc is required for fold morphology and the subsequent differentiation of the first and second auxiliary sclerites as well as the posterior notal wing process. Changes in these domains are consistent with the established fate map of the wing disc. We show that outstretched wing posture phenotypes arise from the loss of a region of Unpaired expression in the proximal wing fold and demonstrate that this results in a decrease in JAK/STAT pathway activity. Finally we show that reduction of JAK/STAT pathway activity within the proximal wing fold is sufficient to phenocopy the outstretched phenotype. Taken together, we suggest that localised Unpaired expression and hence JAK/STAT pathway activity, is required for the morphogenesis of the adult wing hinge, providing new insights into the link between signal transduction pathways, patterning and development.
Plasmonic modulator optimized by patterning of active layer and tuning permittivity  [PDF]
Viktoriia E. Babicheva,Andrei V. Lavrinenko
Physics , 2012, DOI: 10.1016/j.optcom.2012.07.117
Abstract: We study an ultra-compact plasmonic modulator that can be applied in photonic integrated circuits. The modulator is a metal-insulator-metal waveguide with an additional ultra-thin layer of indium tin oxide (ITO). Bias is applied to the multilayer core by means of metal plates that serve as electrodes. External field changes carrier density in the ultra-thin ITO layer, which influences the permittivity. The metal-insulator-metal system possesses a plasmon resonance, and it is strongly affected by changes in the permittivity of the active layer. To improve performance of the structure we propose several optimizations. We examine influence of the ITO permittivity on the modulator's performance and point out appropriate values. We analyze eigenmodes of the waveguide structure and specify the range for its efficient operation. We show that substituting the continuous active layer by a one-dimension periodic stripes increases transmittance through the device and keeps the modulator's performance at the same level. The dependence on the pattern size and filling factor of the active material is analyzed and optimum parameters are found. Patterned ITO layers allow us to design a Bragg grating inside the waveguide. The grating can be turned on and off, thus modulating reflection from the structure. The considered structure with electrical control possesses a high performance and can efficiently work as a plasmonic component in nanophotonic architectures.
Structural Variations in Wing Patterning of Seasonal Polyphenic Melanitis leda (Satyrinae)  [PDF]
Eram Sultan, Debabrat Sabat, Binod Bihari Sahu, Monalisa Mishra
Microscopy Research (MR) , 2016, DOI: 10.4236/mr.2016.44006
Abstract: Seasonal polyphenism is a common phenomenon observed among members of the Lepidopteran subfamily Satyrinae. Melanitis leda, being a member of that subfamily, exhibits seasonal variation in terms of wing patterning. In butterflies, wing patterning is due to the nanostructural architecture of the scales, which reflects and refracts incident light, with or without the combination of pigments. The current scanning electron, fluorescence and optical microscope study divulge fine structural and signal changes that occur with different season in the scales of M. leda and give rise to the different wing pattern in butterfly. The structural and consequent signal changes are likely to be correlated with behavioural processes such as mate selection and escape from predation.
Mad Is Required for Wingless Signaling in Wing Development and Segment Patterning in Drosophila  [PDF]
Edward Eivers, Luis C. Fuentealba, Veronika Sander, James C. Clemens, Lori Hartnett, E. M. De Robertis
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006543
Abstract: A key question in developmental biology is how growth factor signals are integrated to generate pattern. In this study we investigated the integration of the Drosophila BMP and Wingless/GSK3 signaling pathways via phosphorylations of the transcription factor Mad. Wingless was found to regulate the phosphorylation of Mad by GSK3 in vivo. In epistatic experiments, the effects of Wingless on wing disc molecular markers (senseless, distalless and vestigial) were suppressed by depletion of Mad with RNAi. Wingless overexpression phenotypes, such as formation of ectopic wing margins, were induced by Mad GSK3 phosphorylation-resistant mutant protein. Unexpectedly, we found that Mad phosphorylation by GSK3 and MAPK occurred in segmental patterns. Mad depletion or overexpression produced Wingless-like embryonic segmentation phenotypes. In Xenopus embryos, segmental border formation was disrupted by Smad8 depletion. The results show that Mad is required for Wingless signaling and for the integration of gradients of positional information.
Early Embryonic Vascular Patterning by Matrix-Mediated Paracrine Signalling: A Mathematical Model Study  [PDF]
Alvaro K?hn-Luque, Walter de Back, J?rn Starru?, Andrea Mattiotti, Andreas Deutsch, José María Pérez-Pomares, Miguel A. Herrero
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0024175
Abstract: During embryonic vasculogenesis, endothelial precursor cells of mesodermal origin known as angioblasts assemble into a characteristic network pattern. Although a considerable amount of markers and signals involved in this process have been identified, the mechanisms underlying the coalescence of angioblasts into this reticular pattern remain unclear. Various recent studies hypothesize that autocrine regulation of the chemoattractant vascular endothelial growth factor (VEGF) is responsible for the formation of vascular networks in vitro. However, the autocrine regulation hypothesis does not fit well with reported data on in vivo early vascular development. In this study, we propose a mathematical model based on the alternative assumption that endodermal VEGF signalling activity, having a paracrine effect on adjacent angioblasts, is mediated by its binding to the extracellular matrix (ECM). Detailed morphometric analysis of simulated networks and images obtained from in vivo quail embryos reveals the model mimics the vascular patterns with high accuracy. These results show that paracrine signalling can result in the formation of fine-grained cellular networks when mediated by angioblast-produced ECM. This lends additional support to the theory that patterning during early vascular development in the vertebrate embryo is regulated by paracrine signalling.
Tay Bridge Is a Negative Regulator of EGFR Signalling and Interacts with Erk and Mkp3 in the Drosophila melanogaster Wing  [PDF]
Cristina Molnar,Jose F. de Celis
PLOS Genetics , 2013, DOI: 10.1371/journal.pgen.1003982
Abstract: The regulation of Extracellular regulated kinase (Erk) activity is a key aspect of signalling by pathways activated by extracellular ligands acting through tyrosine kinase transmembrane receptors. In this process, participate proteins with kinase activity that phosphorylate and activate Erk, as well as different phosphatases that inactivate Erk by de-phosphorylation. The state of Erk phosphorylation affects not only its activity, but also its subcellular localization, defining the repertoire of Erk target proteins, and consequently, the cellular response to Erk. In this work, we characterise Tay bridge as a novel component of the EGFR/Erk signalling pathway. Tay bridge is a large nuclear protein with a domain of homology with human AUTS2, and was previously identified due to the neuronal phenotypes displayed by loss-of-function mutations. We show that Tay bridge antagonizes EGFR signalling in the Drosophila melanogaster wing disc and other tissues, and that the protein interacts with both Erk and Mkp3. We suggest that Tay bridge constitutes a novel element involved in the regulation of Erk activity, acting as a nuclear docking for Erk that retains this protein in an inactive form in the nucleus.
Drosophila Hephaestus/Polypyrimidine Tract Binding Protein Is Required for Dorso-Ventral Patterning and Regulation of Signalling between the Germline and Soma  [PDF]
Suzanne M. McDermott, Ilan Davis
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0069978
Abstract: In the Drosophila oocyte, gurken (grk) mRNA encodes a secreted TGF-α signal that specifies the future embryonic dorso-ventral axes by altering the fate of the surrounding epithelial follicle cells. We previously identified a number of RNA binding proteins that associate specifically with the 64 nucleotide grk localization signal, including the Drosophila orthologue of polypyrimidine tract-binding protein (PTB), Hephaestus (Heph). To test whether Heph is required for correct grk mRNA or protein function, we used immunoprecipitation to validate the association of Heph with grk mRNA and characterized the heph mutant phenotype. We found that Heph is a component of grk mRNP complexes but heph germline clones show that Heph is not required for grk mRNA localization. Instead, we identify a novel function for Heph in the germline and show that it is required for proper Grk protein localization. Furthermore, we show that Heph is required in the oocyte for the correct organization of the actin cytoskeleton and dorsal appendage morphogenesis. Our results highlight a requirement for an mRNA binding protein in the localization of Grk protein, which is independent of mRNA localization, and we propose that Heph is required in the germline for efficient Grk signalling to the somatic follicle cells during dorso-ventral patterning.
Genetic basis of wing morphogenesis in Drosophila: sexual dimorphism and non-allometric effects of shape variation
Valeria P Carreira, Ignacio M Soto, Julián Mensch, Juan J Fanara
BMC Developmental Biology , 2011, DOI: 10.1186/1471-213x-11-32
Abstract: Our results indicate that more than 63% of induced mutations affected wing shape in one or both sexes, although only 33% showed significant differences in both males and females. The joint analysis of wing size and shape revealed that only 19% of the P-element insertions caused coincident effects on both components of wing form in one or both sexes. Further morphometrical analyses revealed that the intersection between veins showed the smallest displacements in the proximal region of the wing. Finally, we observed that mutations causing general deformations were more common than expected in both sexes whereas the opposite occurred with those generating local changes. For most of the 94 candidate genes identified, this seems to be the first record relating them with wing shape variation.Our results support the idea that the genetic architecture of wing shape is complex with many different genes contributing to the trait in a sexually dimorphic manner. This polygenic basis, which is relatively independent from that of wing size, is composed of genes generally involved in development and/or metabolic functions, especially related to the regulation of different cellular processes such as motility, adhesion, communication and signal transduction. This study suggests that understanding the genetic basis of wing shape requires merging the regulation of vein patterning by signalling pathways with processes that occur during wing development at the cellular level.In general, organ development is organized in two parts; the first is related to the generation of positional information across a field of cells and the second to the refinement of mature form (i.e. organ's size and shape) [1]. The Drosophila wing represents a particularly appropriate model to investigate the developmental control of phenotypic variation. It is involved in several functions of ecological and evolutionary importance (e.g., flight and male courtship song) and its developmental genetics is extensively
Wingless Signalling Alters the Levels, Subcellular Distribution and Dynamics of Armadillo and E-Cadherin in Third Instar Larval Wing Imaginal Discs  [PDF]
Ildiko M. L. Somorjai, Alfonso Martinez-Arias
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002893
Abstract: Background Armadillo, the Drosophila orthologue of vertebrate ?-catenin, plays a dual role as the key effector of Wingless/Wnt1 signalling, and as a bridge between E-Cadherin and the actin cytoskeleton. In the absence of ligand, Armadillo is phosphorylated and targeted to the proteasome. Upon binding of Wg to its receptors, the “degradation complex” is inhibited; Armadillo is stabilised and enters the nucleus to transcribe targets. Methodology/Principal Findings Although the relationship between signalling and adhesion has been extensively studied, few in vivo data exist concerning how the “transcriptional” and “adhesive” pools of Armadillo are regulated to orchestrate development. We have therefore addressed how the subcellular distribution of Armadillo and its association with E-Cadherin change in larval wing imaginal discs, under wild type conditions and upon signalling. Using confocal microscopy, we show that Armadillo and E-Cadherin are spatio-temporally regulated during development, and that a punctate species becomes concentrated in a subapical compartment in response to Wingless. In order to further dissect this phenomenon, we overexpressed Armadillo mutants exhibiting different levels of activity and stability, but retaining E-Cadherin binding. ArmS10 displaces endogenous Armadillo from the AJ and the basolateral membrane, while leaving E-Cadherin relatively undisturbed. Surprisingly, ΔNArm1–155 caused displacement of both Armadillo and E-Cadherin, results supported by our novel method of quantification. However, only membrane-targeted Myr-ΔNArm1–155 produced comparable nuclear accumulation of Armadillo and signalling to ArmS10. These experiments also highlighted a row of cells at the A/P boundary depleted of E-Cadherin at the AJ, but containing actin. Conclusions/Significance Taken together, our results provide in vivo evidence for a complex non-linear relationship between Armadillo levels, subcellular distribution and Wingless signalling. Moreover, this study highlights the importance of Armadillo in regulating the subcellular distribution of E-Cadherin
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