Biodiversité et approche bioécologique de la faune des Monts des Traras Occidentaux (Nord-Ouest Algérien)

La région des Traras Occidentaux, important massif du littoral Oranais (Nord-Ouest Algérien), offre des conditions assez particulièrement favorables pour le développement d’une faune diversifiée. Elle se caractérise par un bioclimat semi-aride. Notre objectif de cette étude est de faire un inventaire faunistique au niveau de trois stations différentes de point de vue cortège floristique (Tamarchalet, Tarasmouth, El Mahsar). Les échantillonnages sont effectués du mars 2009 à décembre 2009, soit 18 prélèvements. L’analyse de la faune a révélé l’existence de 120 espèces. L’entomofaune est diversifiée (10 ordres systématiques), elle contient 77 espèces. Les Gastéropodes et les Oiseaux sont représentés par 10 espèces pour chacun. Ensuite viennent les Arachnides (8 espèces), les Mammifères (6 espèces). Les Crustacés et les Amphibiens viennent en dernier rang avec 2 espèces pour les premiers et 1 espèce pour les seconds. Une étude analytique avec la répartition des groupes faunistiques selon la saison, le mois et la strate est définie.Mots-clés : traras occidentaux, nord-ouest Algérien, faune, biodiversité.Biodiversity and bioecological approach fauna of the Traras mounts west (North Western Algerian). The Western Region Traras, important coastal massif Oran (North West Algeria), offers particularly favorable conditions enough for the development of a variety of wildlife. It is characterized by a semi-arid bioclimate. Our objective of this study is to make an inventory of fauna at three different stations of floristic point of view (Tamarchalet, Tarasmouth El Mahsar). Sampling is conducted from March 2009 to December 2009, 18 specimens. The analysis of the fauna revealed 120 species. The insect fauna is diverse (10 systematic orders), it contains 77 species. Gastropods and birds are represented by 10 species each. Then come the Arachnida (8 species), mammals (6 species). Crustaceans and amphibians come in last place with 2 species and 1 for the first case to the second. An analytical study with the distribution of faunal groups according to the season, month and stratum is defined.Keywords : traras west, north western Algerian, fauna, biodiversity

Collective Cell Migration Drives Morphogenesis of the Kidney Nephron

Tissue organization in epithelial organs is achieved during development by the combined processes of cell differentiation and morphogenetic cell movements. In the kidney, the nephron is the functional organ unit. Each nephron is an epithelial tubule that is subdivided into discrete segments with specific transport functions. Little is known about how nephron segments are defined or how segments acquire their distinctive morphology and cell shape. Using live, in vivo cell imaging of the forming zebrafish pronephric nephron, we found that the migration of fully differentiated epithelial cells accounts for both the final position of nephron segment boundaries and the characteristic convolution of the proximal tubule. Pronephric cells maintain adherens junctions and polarized apical brush border membranes while they migrate collectively. Individual tubule cells exhibit basal membrane protrusions in the direction of movement and appear to establish transient, phosphorylated Focal Adhesion Kinase–positive adhesions to the basement membrane. Cell migration continued in the presence of camptothecin, indicating that cell division does not drive migration. Lengthening of the nephron was, however, accompanied by an increase in tubule cell number, specifically in the most distal, ret1-positive nephron segment. The initiation of cell migration coincided with the onset of fluid flow in the pronephros. Complete blockade of pronephric fluid flow prevented cell migration and proximal nephron convolution. Selective blockade of proximal, filtration-driven fluid flow shifted the position of tubule convolution distally and revealed a role for cilia-driven fluid flow in persistent migration of distal nephron cells. We conclude that nephron morphogenesis is driven by fluid flow–dependent, collective epithelial cell migration within the confines of the tubule basement membrane. Our results establish intimate links between nephron function, fluid flow, and morphogenesis

Endothelin-1 supports clonal derivation and expansion of cardiovascular progenitors derived from human embryonic stem cells

Coronary arteriogenesis is a central step in cardiogenesis, requiring coordinated generation and integration of endothelial cell and vascular smooth muscle cells. At present, it is unclear whether the cell fate programme of cardiac progenitors to generate complex muscular or vascular structures is entirely cell autonomous. Here we demonstrate the intrinsic ability of vascular progenitors to develop and self-organize into cardiac tissues by clonally isolating and expanding second heart field cardiovascular progenitors using WNT3A and endothelin-1 (EDN1) human recombinant proteins. Progenitor clones undergo long-term expansion and differentiate primarily into endothelial and smooth muscle cell lineages in vitro, and contribute extensively to coronary-like vessels in vivo, forming a functional human–mouse chimeric circulatory system. Our study identifies EDN1 as a key factor towards the generation and clonal derivation of ISL1+ vascular intermediates, and demonstrates the intrinsic cell-autonomous nature of these progenitors to differentiate and self-organize into functional vasculatures in vivo

LIF-Dependent Signaling: New Pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine

Current perspectives of the signaling pathways directing neural crest induction

The neural crest is a migratory population of embryonic cells with a tremendous potential to differentiate and contribute to nearly every organ system in the adult body. Over the past two decades, an incredible amount of research has given us a reasonable understanding of how these cells are generated. Neural crest induction involves the combinatorial input of multiple signaling pathways and transcription factors, and is thought to occur in two phases from gastrulation to neurulation. In the first phase, FGF and Wnt signaling induce NC progenitors at the border of the neural plate, activating the expression of members of the Msx, Pax, and Zic families, among others. In the second phase, BMP, Wnt, and Notch signaling maintain these progenitors and bring about the expression of definitive NC markers including Snail2, FoxD3, and Sox9/10. In recent years, additional signaling molecules and modulators of these pathways have been uncovered, creating an increasingly complex regulatory network. In this work, we provide a comprehensive review of the major signaling pathways that participate in neural crest induction, with a focus on recent developments and current perspectives. We provide a simplified model of early neural crest development and stress similarities and differences between four major model organisms: Xenopus, chick, zebrafish, and mouse

Study of the molecular mechanisms controlling neural crest cells proliferation in xenopus

La crête neurale (CN) est une structure transitoire apparaissant en bordure de la plaque neurale chez les embryons de vertébrés. Au cours du développement embryonnaire, les cellules de la CN prolifèrent, subissent une transition épithélio-mésenchymateuse, migrent et se différencient en de nombreux types cellulaires tels que des neurones et cellules gliales du système nerveux périphérique, des mélanocytes, des cellules musculaires lisses ou des élements du squelette cranio-facial. Afin de mieux comprendre les mécanismes moléculaires contrôlant la prolifération et la spécification des cellules de la CN, nous avons étudié le rôle de deux facteurs de transcription, Hairy2 et Stat3, via des expériences de perte et gain de fonction chez l’embryon de xénope. Le gène Hairy2 code pour un facteur de transcription bHLH-O répresseur. Il est exprimé précocement au niveau de la bordure de la plaque neurale incluant la CN présomptive. Nous avons montré que Hairy2 est requis pour la prolifération des cellules de la CN en aval de signaux FGFs et qu’il maintient les cellules dans un état indifférencié en réprimant l’expression précoce des gènes spécifiques de la CN. Hairy2 réprime aussi la transcription du gène Id3 codant pour un facteur HLH essentiel à la prolifération des cellules de la CN. Id3 affecte également Hairy2. Nous avons observé que la protéine Id3 interagit physiquement avec Hairy2 et bloque son activité, démontrant que les interactions entre Hairy2 et Id3 jouent un rôle important dans la prolifération et la spécification des cellules de la CN. \Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe

An architect gene at word : identification of potential target genes of Hoxa2

Hox genes encode evolutionarily conserved transcription factors which control important pathways during embryo development and adult lifetime. The Hoxa2 gene plays crucial conserved functions in craniofacial and hindbrain patterning and morphogenesis. While its biological roles are well documented, very little is known about the precise way of action of this transcription factor. The aim of this study was to identify potential primary target genes of Hoxa2 among a subset of thirty two candidate genes previously revealed by a screen in a cellular model. The first step of the strategy we adopted was to validate candidate target genes and to quantify the modulation of their activity upon expression of Hoxa2 and its Pbx cofactor. The second step was to establish whether these target genes could define direct targets of Hoxa2. This consisted in identifying Hoxa2/Pbx binding sites in the vicinity of the validated targets and in assaying their functionality. The last step was to correlate the expression profile of target genes with what is known for Hoxa2. As a result, we demonstrated that Adamts1, Frg1, Lmo1 and Plekha6 are potential primary target genes of Hoxa2. We mapped Hoxa2/Pbx binding sites (Hox Response Element or HRE) corresponding to the designed TGATDBAWKD consensus in the vicinity of each target gene. One HRE was identified upstream Frg1, three upstream Lmo1and two upstream Plekha6. We then confirmed that these elements display Hoxa2-dependent transcriptional activity by a reporter gene assay. Finally, we provided evidence that Adamts1 is up-regulated in the spine of mouse embryos ectopically expressing Hoxa2 in cells entering chondrogenesis, that Hoxa2 and Phox2b, a neuronal specification factor, probably act together to regulate Lmo1 in the developing hindbrain, and that Plekha6 is expressed in discrete territories of the developing hindbrain. These expression data therefore support that Hoxa2 may specify neuronal subtypes in the developing hindbrain through Lmo1 and Plekha6 regulation, and could control morphogenesis through Adamts1 and Frg1. In conclusion, our work provides new insights into the mode of action of the architect gene Hoxa2 by the identification of Adamts1, Frg1, Lmo1 and Plekha6 as potential primary target genes.(BIOL 3) -- UCL, 201

An engineering model for ignition and extinction of wood flames using bench-scale data

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Self-regulation of Stat3 activity coordinates cell-cycle progression and neural crest specification

A complex set of extracellular signals is required for neural crest (NC) specification. However, how these signals function to coordinate cell-cycle progression and differentiation remains poorly understood. Here, we report in Xenopus a role for the transcription factor signal transducers and activators of transcription-3 (Stat3) in this process downstream of FGF signalling. Depletion of Stat3 inhibits NC gene expression and cell proliferation, whereas overexpression expands the NC domain and promotes cell proliferation. Stat3 is phosphorylated and activated in ectodermal cells by FGFs through binding with FGFR4. Stat3 activation is also modulated by Hairy2 and Id3 proteins that, respectively, facilitate and disrupt Stat3-FGFR4 complex formation. Furthermore, distinct levels of Stat3 activity control Hairy2 and Id3 transcription, leading to Stat3 self-regulation. Finally, high Stat3 activity maintains cells in an undifferentiated state, whereas low activity promotes cell proliferation and NC differentiation. Together, our data suggest that Stat3, downstream of FGFs and under the positive and negative feedback regulation of Hairy2 and Id3, plays an essential role in the coordination of cell-cycle progression and differentiation during NC specification