Complex Interactions between GSK3 and aPKC in Drosophila Embryonic Epithelial Morphogenesis

Generally, epithelial cells must organize in three dimensions to form functional tissue sheets. Here we investigate one such sheet, the Drosophila embryonic epidermis, and the morphogenetic processes organizing cells within it. We report that epidermal morphogenesis requires the proper distribution of the apical polarity determinant aPKC. Specifically, we find roles for the kinases GSK3 and aPKC in cellular alignment, asymmetric protein distribution, and adhesion during the development of this polarized tissue. Finally, we propose a model explaining how regulation of aPKC protein levels can reorganize both adhesion and the cytoskeleton

Wnt, Hedgehog and Junctional Armadillo/β-Catenin Establish Planar Polarity in the Drosophila Embryo

To generate specialized structures, cells must obtain positional and directional information. In multi-cellular organisms, cells use the non-canonical Wnt or planar cell polarity (PCP) signaling pathway to establish directionality within a cell. In vertebrates, several Wnt molecules have been proposed as permissible polarity signals, but none has been shown to provide a directional cue. While PCP signaling components are conserved from human to fly, no PCP ligands have been reported in Drosophila. Here we report that in the epidermis of the Drosophila embryo two signaling molecules, Hedgehog (Hh) and Wingless (Wg or Wnt1), provide directional cues that induce the proper orientation of Actin-rich structures in the larval cuticle. We further find that proper polarity in the late embryo also involves the asymmetric distribution and phosphorylation of Armadillo (Arm or β-catenin) at the membrane and that interference with this Arm phosphorylation leads to polarity defects. Our results suggest new roles for Hh and Wg as instructive polarizing cues that help establish directionality within a cell sheet, and a new polarity-signaling role for the membrane fraction of the oncoprotein Arm

A non-canonical Raf function is required for dorsal–ventral patterning during Drosophila embryogenesis

Proper embryonic development requires directional axes to pattern cells into embryonic structures. In Drosophila, spatially discrete expression of transcription factors determines the anterior to posterior organization of the early embryo, while the Toll and TGFβ signalling pathways determine the early dorsal to ventral pattern. Embryonic MAPK/ERK signaling contributes to both anterior to posterior patterning in the terminal regions and to dorsal to ventral patterning during oogenesis and embryonic stages. Here we describe a novel loss of function mutation in the Raf kinase gene, which leads to loss of ventral cell fates as seen through the loss of the ventral furrow, the absence of Dorsal/NFκB nuclear localization, the absence of mesoderm determinants Twist and Snail, and the expansion of TGFβ. Gene expression analysis showed cells adopting ectodermal fates much like loss of Toll signaling. Our results combine novel mutants, live imaging, optogenetics and transcriptomics to establish a novel role for Raf, that appears to be independent of the MAPK cascade, in embryonic patterning

Wingless Signalling Alters the Levels, Subcellular Distribution and Dynamics of Armadillo and E-Cadherin in Third Instar Larval Wing Imaginal Discs

Background: Armadillo, the Drosophila orthologue of vertebrate beta-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. Arm(S10) displaces endogenous Armadillo from the AJ and the basolateral membrane, while leaving E-Cadherin relatively undisturbed. Surprisingly, Delta NArm(1-155) caused displacement of both Armadillo and E-Cadherin, results supported by our novel method of quantification. However, only membrane-targeted Myr-Delta NArm(1-155) produced comparable nuclear accumulation of Armadillo and signalling to Arm(S10). 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-CadherinPublisher PDFPeer reviewe

Possible causes of data model discrepancy in the temperature history of the last Millennium

Model simulations and proxy-based reconstructions are the main tools for quantifying pre-instrumental climate variations. For some metrics such as Northern Hemisphere mean temperatures, there is remarkable agreement between models and reconstructions. For other diagnostics, such as the regional response to volcanic eruptions, or hemispheric temperature differences, substantial disagreements between data and models have been reported. Here, we assess the potential sources of these discrepancies by comparing 1000-year hemispheric temperature reconstructions based on real-world paleoclimate proxies with climate-model-based pseudoproxies. These pseudoproxy experiments (PPE) indicate that noise inherent in proxy records and the unequal spatial distribution of proxy data are the key factors in explaining the data-model differences. For example, lower inter-hemispheric correlations in reconstructions can be fully accounted for by these factors in the PPE. Noise and data sampling also partly explain the reduced amplitude of the response to external forcing in reconstructions compared to models. For other metrics, such as inter-hemispheric differences, some, although reduced, discrepancy remains. Our results suggest that improving proxy data quality and spatial coverage is the key factor to increase the quality of future climate reconstructions, while the total number of proxy records and reconstruction methodology play a smaller role

Robustness and Stability of the Gene Regulatory Network Involved in DV Boundary Formation in the Drosophila Wing

Gene regulatory networks have been conserved during evolution. The Drosophila wing and the vertebrate hindbrain share the gene network involved in the establishment of the boundary between dorsal and ventral compartments in the wing and adjacent rhombomeres in the hindbrain. A positive feedback-loop between boundary and non-boundary cells and mediated by the activities of Notch and Wingless/Wnt-1 leads to the establishment of a Notch dependent organizer at the boundary. By means of a Systems Biology approach that combines mathematical modeling and both in silico and in vivo experiments in the Drosophila wing primordium, we modeled and tested this regulatory network and present evidence that a novel property, namely refractoriness to the Wingless signaling molecule, is required in boundary cells for the formation of a stable dorsal-ventral boundary. This new property has been validated in vivo, promotes mutually exclusive domains of Notch and Wingless activities and confers stability to the dorsal-ventral boundary. A robustness analysis of the regulatory network complements our results and ensures its biological plausibility

Wnt signalling and cancer stem cells

[Abstract] Intracellular signalling mediated by secreted Wnt proteins is essential for the establishment of cell fates and proper tissue patterning during embryo development and for the regulation of tissue homeostasis and stem cell function in adult tissues. Aberrant activation of Wnt signalling pathways has been directly linked to the genesis of different tumours. Here, the components and molecular mechanisms implicated in the transduction of Wnt signal, along with important results supporting a central role for this signalling pathway in stem cell function regulation and carcinogenesis will be briefly reviewed.Ministerio de Ciencia e Innovación; SAF2008-0060