Large-Scale Clonal Analysis Reveals Unexpected Complexity in Surface Ectoderm Morphogenesis

Background: Understanding the series of morphogenetic processes that underlie the making of embryo structures is a highly topical issue in developmental biology, essential for interpreting the massive molecular data currently available. In mouse embryo, long-term in vivo analysis of cell behaviours and movements is difficult because of the development in utero and the impossibility of long-term culture. Methodology/Principal Findings: We improved and combined two genetic methods of clonal analysis that together make practicable large-scale production of labelled clones. Using these methods we performed a clonal analysis of surface ectoderm (SE), a poorly understood structure, for a period that includes gastrulation and the establishment of the body plan. We show that SE formation starts with the definition at early gastrulation of a pool of founder cells that is already dorso-ventrally organized. This pool is then regionalized antero-posteriorly into three pools giving rise to head, trunk and tail. Each pool uses its own combination of cell rearrangements and mode of proliferation for elongation, despite a common clonal strategy that consists in disposing along the antero-posterior axis precursors of dorso-ventrally-oriented stripes of cells. Conclusions/Significance: We propose that these series of morphogenetic processes are organized temporally and spatially in a posterior zone of the embryo crucial for elongation. The variety of cell behaviours used by SE precursor cells indicates that these precursors are not equivalent, regardless of a common clonal origin and a common clonal strategy. Anothe

COUP-TFII Controls Mouse Pancreatic β-Cell Mass through GLP-1-β-Catenin Signaling Pathways

Background: The control of the functional pancreatic beta-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how beta-cell mass is determined

Stratégies cellulaires et construction de l'ectoderme de surface chez l'embryon de souris (une approche par combinaison de la méthode d'analyse clonale LaacZ et d'une méthode d'induction temporelle du marquage cellulaire)

L'étude des comportements cellulaires lors de la construction de l'ectoderme de surface (ES) a été menée en combinant la méthode d'analyse clonale rétrospective LaacZ et une nouvelle méthode ubiquitaire d'induction temporelle de clones, basée sur le système Cre/loxP/4-OHT. L'analyse des librairies de clones E14,5 montre que la construction de l'ES se fait selon trois phases de croissance. La stratégie employée consiste à disposer le long de l axe AP des précurseurs de groupes de cellules dont la croissance sera orientée DV. A E14, un dernier changement vers un mode de croissance isotrope est observé. L'ES est mis en place à partir d'un pool fermé et régionalisé selon l'axe DV, constitué au début de la gastrulation. Vers E7, ce pool se scinde en trois pools alloués à la tête, au tronc et à la queue. La construction de l'ES met en jeu une combinaison de réarrangements et de croissance cellulaires. Dans le tronc, un mode de croissance de type auto-maintien est utilisé, tandis qu'un mode régional est employé dans la tête. La similarité de mise en place de l'ectoderme et du mésoderme conduit à proposer l existence d une zone postérieure de croissance et d intercalation des cellules, essentielle pour l'élongation de l'embryon. L'individualisation précoce d'un pool spécifique à la tête et à la queue suggère un schéma d'élongation commun à l'ensemble des Bilatériens, impliquant l'intercalation du territoire du tronc entre le stomodeum et l'anus. L'étude exhaustive de l'orientation de croissance selon les régions de l'embryon montre que la croissance de l'ES est modulée lors de l'apparition de structures tardives et lors d événements comme la fermeture du tube neural. La stratégie de croissance en trois phases est reprise de façon intégrale, selon un axe orthogonal, dans la formation de l'ES de la patte et, dans une moindre mesure, dans celle de la face. L'ES est donc un épithélium constitué de cellules d'une grande plasticité, dont les propriétés d'adhésion, de prolifération et potentiellement de polarité varient en fonction des régions de l'embryon.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Methods in clonal analysis and applications

During development, embryonic cells display a large variety of behaviors that lead to the formation of embryonic structures that are frequently transient. Simultaneously, cells progress towards a specific fate. The current challenge for embryologists is to resolve how these two distinct aspects of development co-exist. As cell behaviors (including elementary cellular operations such as motility, adhesiveness, polarization, change in shape, division and death) and their control are much less well understood than the genetic aspects of cell fate determination, there is currently much interest in the study of cell behaviors. This mainly consists of labeling groups of cells or, less frequently, single cells and observing their descendants. In this review, we describe a few techniques for labeling groups of cells and we discuss prospective and retrospective clonal analysis, in particular the LaacZ system, in detail. We examine the information generated by these approaches

Modifications d'un exopolysaccharide biosynthétisé par une bactérie issue des écosystèmes hydrothermaux profonds

Le travail concerne la modification d'un exopolysaccharide (EPS) biosynthétisé par une bactérie issue des écosystèmes hydrothermaux profonds. Ce polysaccharide complexe, de haute masse molaire, est constitué d'oses neutres et d'acides uroniques. La réduction de sa masse molaire est la première étape dans la conception de molécules d'intérêts variés. Deux voies de dépolymérisation ont été envisagées : physique avec les ultrasons et chimique avec la catalyse métallique. Les facteurs influents ont été déterminés pour ces deux voies. La dernière partie du mémoire est consacrée à la faisabilité de modifications chimiques de l'EPS natif ou dépolymérisé par ajout de groupements classiques. Des résultats de caractérisation et de quantification des modifications par des techniques d'analyses adaptées à chaque manipulation sont présentés.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Chronologie de mise en place des nappes de cailloutis des rivières ardennaises au cours des 100.000 dernières années

It is generally held that, in north-western Europe, the main part of the gravel sheets under river beds were deposited during the Weichselian period in a periglacial environment. However, other parameters such as propagation of knickpoints in fluvial networks may also influence incision or aggradation. However, only few studies have dated the periods of formation of the gravel sheets and have described their properties. The first aim of this research was to determine the thickness of the gravel sheets still remaining under the river beds and to estimate the potential incision of these rivers before reaching the bedrock. Then we tried to answer a number of other questions: When did these thick gravel deposits fill the valley bottom? When were the lowest terraces abandoned? When did the rivers incise the bedrock? What is the morphology of the bedrock under the gravel layer? Numerous boreholes were made by percussion drilling in different floodplains of the Ardenne Massif and core samples were taken, down to the bedrock. Afterwards, different volcanic tephra from the Late Pleistocene were used as stratigraphic markers to date the relative periods of terrace formation and to reconstruct the past evolution of the gravel sheets. Pollen and metallurgic slag were also used to date the periods of bed level evolution. In the Ardennian massif, the thickness of the gravel sheet beneath the river beds is very variable (from 10 m in the downstream part of the Ourthe River to less than 1 m in the upper catchments). In some valleys, weathered bedrock has been observed under the gravel sheet to a thickness of several meters. Different phases of accumulation and incision over the last 100,000 years have been dated. Some evolutions can be clearly linked to climate changes but some modifications of bed levels also occurred during the Weichselian period and could be a response to the propagation of knickpoints in the fluvial networks

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Preparation and Delivery of 4-Hydroxy-Tamoxifen for Clonal and Polyclonal Labeling of Cells of the Surface Ectoderm, Skin, and Hair Follicle

International audienceTo study the cell behavior during morphogenesis of mouse surface ectoderm, skin, and hair follicles, we (1-3) have developed a new method to temporally induce clones that is based on a tamoxifen-dependent Cre recombinase. The classical protocol consisting in dissolving 4-hydroxy-tamoxifen or tamoxifen in corn oil to perform intraperitoneal (ip) injections (4) is not optimal to control the pharmacokinetic parameters of the induction as it leads to experimental variability in terms of timing and level of induction. We have developed a new protocol that consists in solubilizing 4-OHT or tamoxifen in an aqueous solvent using Cremophor(®) EL (5). This allows for intravenous (iv) and intraperitoneal injections