Autonomous epithelial folding induced by an intracellular mechano–polarity feedback loop

Epithelial tissues form folded structures during embryonic development and organogenesis. Whereas substantial efforts have been devoted to identifying mechanical and biochemical mechanisms that induce folding, whether and how their interplay synergistically shapes epithelial folds remains poorly understood. Here we propose a mechano–biochemical model for dorsal fold formation in the early Drosophila embryo, an epithelial folding event induced by shifts of cell polarity. Based on experimentally observed apical domain homeostasis, we couple cell mechanics to polarity and find that mechanical changes following the initial polarity shifts alter cell geometry, which in turn influences the reaction-diffusion of polarity proteins, thus forming a feedback loop between cell mechanics and polarity. This model can induce spontaneous fold formation in silico, recapitulate polarity and shape changes observed in vivo, and confer robustness to tissue shape change against small fluctuations in mechanics and polarity. These findings reveal emergent properties of a developing epithelium under control of intracellular mechano–polarity coupling.

A Three-Dimensional Numerical Model of an Active Cell Cortex in the Viscous Limit

The cell cortex is a highly dynamic network of cytoskeletal filaments in which motor proteins induce active cortical stresses which in turn drive dynamic cellular processes such as cell motility, furrow formation or cytokinesis during cell division. Here, we develop a three-dimensional computational model of a cell cortex in the viscous limit including active cortical flows. Combining active gel and thin shell theory, we base our computational tool directly on the force balance equations for the velocity field on a discretized and arbitrarily deforming cortex. Since our method is based on the general force balance equations, it can easily be extended to more complex biological dependencies in terms of the constitutive laws or a dynamic coupling to a suspending fluid. We validate our algorithm by investigating the formation of a cleavage furrow on a biological cell immersed in a passive outer fluid, where we successfully compare our results to axi-symmetric simulations. We then apply our fully three-dimensional algorithm to fold formation and to study furrow formation under the influence of non-axisymmetric disturbances such as external shear. We report a reorientation mechanism by which the cell autonomously realigns its axis perpendicular to the furrow plane thus contributing to the robustness of cell division under realistic environmental conditions.

The Mechanics of Initiation and Development of Thrust Ramps

We examine the mechanics of thrust fault initiation and development in sedimentary rocks which accounts for vertical variation in mechanical strength of the rocks. We use numerical mechanical models of mechanically layered rocks to examine thrust ramp nucleation in competent units, and fault propagation upward and downward into weaker units forming folds at both fault tips. We investigate the effects of mechanical stratigraphy on stress heterogeneity, rupture direction, fold formation, and fault geometry motivated by the geometry of the Ketobe Knob thrust fault in central Utah. The study incorporates finite element models to examine how mechanical stratigraphy, loading conditions, and fault configurations determine temporal and spatial variation in stress and strain. We model the predicted deformation and stress distributions in four model domains: (1) an intact, mechanically stratified rock sequence, (2) a mechanically stratified section with a range of interlayer frictional strengths, and two faulted models, (3) one with a stress boundary condition, and (4) one with a displacement boundary condition. The models show that a dramatic increase in stress develops in the competent rock layers whereas the stresses are lower in the weaker rocks. The frictional models reveal that the heterogeneous stress variations increase contact frictional strength. Faulted models contain a 20° dipping fault in the most competent unit. The models show an increase in stress in areas above and below fault tips, with extremely high stresses predicted in a ‘back thrust’ location at the lower fault tip. These findings support the hypothesis that thrust faults and associated folds at the Ketobe Knob developed in accordance with the ramp-first kinematic model and development of structures was significantly influenced by the nature of the mechanical stratigraphy.

Sukil River valley — a natural geological laboratory

<p>We present a number of geological objects located along the valley of the Sukil River, which flows within the Ivano-Frankivsk Region in the west of Ukraine. The river crosses a number of structures of the Skyba nappe and the Inner unit of the Ukrainian Carpathian foredeep, which belong to the orogen of the Outer Ukrainian Carpathians. The Outer Ukrainian Carpathians were formed as a result of alpine tectogenesis. They are composed mainly of flysch deposited in Cretaceous-Neogene basins. The foredeep is filled with sediments known as molasses.</p><p>The research objects allow to study many aspects of geology —sedimentation, fold formation, fault formation, formation of mountain systems.</p><p>Many objects in the Sukil River valley are currently being studied using the latest technologies — digital photogrammetry and terrestrial laser scanning  to create virtual geological outcrops.</p><p>Unique samples of Oligocene fish remnants collected during field research are stored in the Natural History Museum of the Precarpathian Professional College of Forestry and Tourism in Bolekhiv which is located on the Sukil River. Here there are also great druses of gypsum from a local quarry. In the same town are the remains of a saltworks which was one of the oldest in the region.</p><p>Objects located in the Sukil River valley have not only scientific but also aesthetic significance. The folds from Bukivets are the object of the international geotourism route "Geocarpathians".</p>

Autonomous epithelial folding induced by an intracellular mechano–polarity feedback loop

Epithelial tissues form folded structures during embryonic development and organogenesis. Whereas substantial efforts have been devoted to identifying mechanical and biochemical mechanisms that induce folding, how they interact remains poorly understood. Here we propose a mechano–biochemical model for dorsal fold formation in the early Drosophila embryo, an epithelial folding event induced by shifts of cell polarity. Based on experimentally observed apical domain homeostasis, we couple cell mechanics to polarity and find that mechanical changes following the initial polarity shifts alter cell geometry, which in turn influences the reaction-diffusion of polarity proteins, thus forming a feedback loop between mechanics and polarity. This model can induce spontaneous fold formation in silico, recapitulate polarity and shape changes observed in vivo, and confer robustness to tissue shape change against small fluctuations in mechanics and polarity. These findings reveal emergent properties of a developing epithelium under control of intracellular mechano–polarity coupling.

Hallmarks of primary neurulation are conserved in the zebrafish forebrain

Primary neurulation is the process by which the neural tube, the central nervous system precursor, is formed from the neural plate. Incomplete neural tube closure occurs frequently, yet underlying causes remain poorly understood. Developmental studies in amniotes and amphibians have identified hingepoint and neural fold formation as key morphogenetic events and hallmarks of primary neurulation, the disruption of which causes neural tube defects. In contrast, the mode of neurulation in teleosts has remained highly debated. Teleosts are thought to have evolved a unique mode of neurulation, whereby the neural plate infolds in absence of hingepoints and neural folds, at least in the hindbrain/trunk where it has been studied. Using high-resolution imaging and time-lapse microscopy, we show here the presence of these morphological landmarks in the zebrafish anterior neural plate. These results reveal similarities between neurulation in teleosts and other vertebrates and hence the suitability of zebrafish to understand human neurulation.

Increased lateral tension is sufficient for epithelial folding in Drosophila

ABSTRACTThe folding of epithelial sheets is important for tissues, organs and embryos to attain their proper shapes. Epithelial folding requires subcellular modulations of mechanical forces in cells. Fold formation has mainly been attributed to mechanical force generation at apical cell sides, but several studies indicate a role of mechanical tension at lateral cell sides in this process. However, whether lateral tension increase is sufficient to drive epithelial folding remains unclear. Here, we have used optogenetics to locally increase mechanical force generation at apical, lateral or basal sides of epithelial Drosophila wing disc cells, an important model for studying morphogenesis. We show that optogenetic recruitment of RhoGEF2 to apical, lateral or basal cell sides leads to local accumulation of F-actin and increase in mechanical tension. Increased lateral tension, but not increased apical or basal tension, results in sizeable fold formation. Our results stress the diversification of folding mechanisms between different tissues and highlight the importance of lateral tension increase for epithelial folding.

Evaluation of oil-gas bearing potential associated with fold formation properties of Lower Kur depression and Baku archipelago

The article explores the oil and gas generation properties and hydrocarbon content of Lower Kur depression and Baku archipelago based on the studies of morphology, space position of local uplifts, types of faults, evolution of mud volcanoes, distribution properties of compressive stresses and earth temperature environment. It was defined that as a result of action of longitudinal and lateral folding mechanisms predominantly brachy-form structures had been formed, the anticline zones and trends of which show that their space position is controlled by compressive stresses arising within the narrow north-western part of the Iranian-Afghani plate. The folding process in Oligocene-Pliocene series of the South-Caspian depression basically takes place due to the dynamics of active Maikop clays. Local uplifts of reviewed area are originated no later than the end of the Miocene. Carried out analysis justifies that the intensity of folding processes within Lower Kur depression and Baku archipelago rises both in time and from the south-east towards the north-west. A diagram of vertical oil generation zoning for Lower Kur depression and Baku archipelago has been developed based on the earth temperature data, according to which it was established that the Upper Cretaceous, Paleogene-Miocene sediments and the Productive Series represent strata generating commercial oil and gas.

Basidiospores from Wood-Decay Fungi Transform Laccase Substrates in the Absence of Glucose and Nitrogen Supplements

Preparations of bacterial endospores and fungal conidia are applied in biocontrols, biocatalyses, and lignocellulose fermentations. The biocatalytic abilities of basidiospores from mushrooms of the order Agaricales are unknown. To assess their potential in colonizing recalcitrant substrates solely with their inherent resources, spores of the white-rot fungi Stropharia rugoso-annulata (Stru) and Kuehneromyces mutabilis (Kmt, Strophariaceae) were analyzed for surface-bound and internal total carbohydrates, phenols, proteins, minerals, and oxidoreductases to estimate their chemistry and the preconditions to transform the laccase substrates guaiacol and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) independent of external glucose and nitrogen. Surfaces of Stru/Kmt spores released (mg kg−1) hexoses, 7300/9700; phenols, >62/220; proteins, 21/168; and laccases, 42/0–0.15 µmol ABTS•+ kg−1 min−1 that mimicked oxidative activities of the resting spores. Milled-spore extracts contained pentoses, 96,600/6750; hexoses, 160,000/15,130; phenols, 452/767; protein, 12,600/924; true laccase, 688/0.30; and enzyme-protein-activating transition metals such as Cu in concentrations typical of wheat grains. Independent of external N and C supply, spores (<1‰) germinated in bideionized water, supported by their surface resources. Kmt spores germinated, too, at comparable rates in N-free solutions of glucose and the not immediately metabolizable ABTS and guaiacol. The release of proteins and oxidoreductase(s) by Kmt spores starting upon germination was higher in guaiacol-incubated idiophase- than in glucose-incubated trophophase-spores and led to the 3–4-fold formation of guaiacol polymerizates and ABTS•+. Constitutive aromatic ring-cleaving dioxygenases in the dormant spore that could be involved in the intrinsic metabolization of guaiacol were not detected. It is concluded that intrinsic resources enable (germinating) spores to release the highly efficient laccases of basidiomycetes and to transform aromatic compounds in the absence of sugar amendments. Spores show therefore plant seed-like autonomy in nutrient modification and acquisition during the early stages of the colonization of inert substrates.