A modular cis-regulatory system controls isoform-specific pitx expression in ascidian stomodæum

AbstractPituitary homeobox (pitx) genes have been identified in vertebrates as critical molecular determinants of various craniofacial ontogenetic processes including pituitary organogenesis. Accordingly, a prominent conserved feature of pitx genes in chordates is their early expression in the anterior neural boundary (ANB) and oral ectoderm, also known as the stomodæum. Here we used the ascidian model species Ciona intestinalis to investigate pitx gene organization and cis-regulatory logic during early stages of oral development. Two distinct Ci-pitx mRNA variants were found to be expressed in mutually exclusive embryonic domains. Ci-pitx and vertebrate pitx2 genes display remarkably similar exon usage and organization, suggesting ancestry of the pitx transcriptional unit and regulation in chordates. We next combined phylogenetic footprinting, transient transgenesis, and confocal imaging methods to study the Ci-pitx cis-regulatory system, with special emphasis on the regulation of isoform-specific ANB/stomodæal expression. Among 10 conserved noncoding sequences (CNSs) interspersed in C. intestinalis and Ciona savignyi pitx loci, we identified two separate cis-regulatory modules (CRMs) that drive ANB/stomodæal expression in complementary spatiotemporal patterns. We discuss the developmental relevance of these data that provide an entry point to investigate the gene regulatory networks (GRNs) that position and shape oral structures in chordates

The homology of odontodes in gnathostomes: insights from Dlx gene expression in the dogfish, Scyliorhinus canicula

<p>Abstract</p> <p>Background</p> <p>Teeth and tooth-like structures, together named odontodes, are repeated organs thought to share a common evolutionary origin. These structures can be found in gnathostomes at different locations along the body: oral teeth in the jaws, teeth and denticles in the oral-pharyngeal cavity, and dermal denticles on elasmobranch skin. We, and other colleagues, had previously shown that teeth in any location were serially homologous because: i) pharyngeal and oral teeth develop through a common developmental module; and ii) the expression patterns of the <it>Dlx </it>genes during odontogenesis were highly divergent between species but almost identical between oral and pharyngeal dentitions within the same species. Here we examine <it>Dlx </it>gene expression in oral teeth and dermal denticles in order to test the hypothesis of serial homology between these odontodes.</p> <p>Results</p> <p>We present a detailed comparison of the first developing teeth and dermal denticles (caudal primary scales) of the dogfish (<it>Scyliorhinus canicula</it>) and show that both odontodes develop through identical stages that correspond to the common stages of oral and pharyngeal odontogenesis. We identified six <it>Dlx </it>paralogs in the dogfish and found that three showed strong transcription in teeth and dermal denticles (<it>Dlx3</it>, <it>Dlx4 </it>and <it>Dlx5</it>) whereas a weak expression was detected for <it>Dlx1 </it>in dermal denticles and teeth, and for <it>Dlx2 </it>in dermal denticles. Very few differences in <it>Dlx </it>expression patterns could be detected between tooth and dermal denticle development, except for the absence of <it>Dlx2 </it>expression in teeth.</p> <p>Conclusions</p> <p>Taken together, our histological and expression data strongly suggest that teeth and dermal denticles develop from the same developmental module and under the control of the same set of <it>Dlx </it>genes. Teeth and dermal denticles should therefore be considered as serial homologs developing through the initiation of a common gene regulatory network (GRN) at several body locations. This mechanism of heterotopy supports the 'inside and out' model that has been recently proposed for odontode evolution.</p

Ol-insm1b, a SNAG family transcription factor involved in cell cycle arrest during medaka development

AbstractThrough whole-mount in situ hybridisation screen on medaka (Oryzias latipes) brain, Ol-insm1b, a member of the Insm1/Mlt1 subfamily of SNAG-domain containing genes, has been isolated. It is strongly expressed during neurogenesis and pancreas organogenesis, with a pattern that suggests a role in cell cycle exit. Here, we describe Ol-insm1b expression pattern throughout development and in adult brain, and we report on its functional characterisation. Our data point to a previously unravelled role for Ol-insm1b as a down-regulator of cell proliferation during development, as it slows down the cycle without triggering apoptosis. Clonal analysis demonstrates that this effect is cell-autonomous, and, through molecular dissection studies, we demonstrate that it is likely to be non-transcriptional, albeit mediated by zinc-finger domains. Additionally, we report that Ol-insm1b mRNA, when injected in one cell of two-cell stage embryos, exhibits a surprising behaviour: it does not spread uniformly amongst daughter cells but remains cytoplasmically localised in the progeny of the injected blastomere. Our experiments suggest that Insm1 is a negative regulator of cell proliferation, possibly through mechanisms that do not involve modulation of transcription

New Insights into the Molecular Structures, Compositions, and Cation Distributions in Synthetic and Natural Montmorillonite Clays

International audienceWe present a detailed investigation of the molecular structure of montmorillonite, an aluminosilicate clay with important applications in materials sciences, such as for catalysis, drug delivery, or as a waste barrier. Solid-state 29Si, 27Al, 25Mg, and 1H nuclear magnetic resonance (NMR) measurements combined with density functional theory (DFT) calculations provide a comprehensive picture of the local structure and composition of a synthetic clay and its naturally-occurring analogue. A revised composition is proposed based on NMR results that allow the identification and quantification of the signatures of otherwise undetectable non-crystalline impurities, thus largely complementing the traditional elemental analyses. Solid-state 1H NMR at fast magic-angle spinning (MAS) and high magnetic field provide quantitative information on intra- and inter-layer local environments that are crucial for the determination of the amount of Mg/Al substitution within the octahedral layer. In combination with DFT calculations of energies, it suggests that pairs of adjacent Mg atoms are unfavorable, leading to a non-random cationic distribution within the layers

Combining Computational Prediction of Cis-Regulatory Elements with a New Enhancer Assay to Efficiently Label Neuronal Structures in the Medaka Fish

The developing vertebrate nervous system contains a remarkable array of neural cells organized into complex, evolutionarily conserved structures. The labeling of living cells in these structures is key for the understanding of brain development and function, yet the generation of stable lines expressing reporter genes in specific spatio-temporal patterns remains a limiting step. In this study we present a fast and reliable pipeline to efficiently generate a set of stable lines expressing a reporter gene in multiple neuronal structures in the developing nervous system in medaka. The pipeline combines both the accurate computational genome-wide prediction of neuronal specific cis-regulatory modules (CRMs) and a newly developed experimental setup to rapidly obtain transgenic lines in a cost-effective and highly reproducible manner. 95% of the CRMs tested in our experimental setup show enhancer activity in various and numerous neuronal structures belonging to all major brain subdivisions. This pipeline represents a significant step towards the dissection of embryonic neuronal development in vertebrates

Analyse moléculaire de la morphogenèse tectale chez le medaka (Oryzias latipes

Ce travail est l'analyse moléculaire de la morphogenèse du toit optique ou tectum d'un poisson, le médaka Oryzias latipes. Une étude à la bromodéoxyuridine nous a permis de montrer que le tectum se construit par l'activité continue d'une zone proliférative marginale. Ce critère a été utilisé pour le criblage par hybridations in situ systématiques. 600 clones ont été analysés : ils ont été classés en fonction de leur expression dans les zones proliférative ou post-mitotiques. Certains gènes avaient une expression à la frontière de ces deux zones. C'est le cas du clone correspondant au gène Ol-KIP (Oryzias latipes-Kinase Inhibitor Protein) qui a été analysé. Ce gène appartient à la famille KIP d'inhibiteurs des kinases dépendantes des cyclines. Ce type de crible a donc permis d'isoler des gènes impliqués dans le contrôle de la prolifération cellulaire, ainsi que des gènes de fonction inconnue mais dont l'expression suggère qu'ils sont des régulateurs potentiels de la morphogenèse nerveuseRENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Evolution du développement du système nerveux

National audienc

Arrêt de la prolifération cellulaire pendant le développement embryonnaire (étude transcriptionnelle de gènes suppresseurs de tumeurs au cours de la croissance du système nerveux central chez le poisson médaka Oryzias latipes.)

Comment la taille d'un organisme est-elle régulée au cours du développement embryonnaire ? Quels sont les mécanismes génétiques à l'origine de l'arrêt de la prolifération pendant la croissance d'un organisme pluricellulaire ? Afin d'identifier des acteurs de la sortie du cycle cellulaire au cours du développement, mon travail s est orienté sur l étude de gènes suppresseurs de tumeurs pendant la croissance du toit optique (TO) du médaka Oryzias latipes. Le TO, structure dorsale du cerveau moyen des Vertébrés, est un modèle particulièrement adapté à l étude de la régulation de la prolifération. Trois zones de la marge vers le centre du TO sont discernables : une zone périphérique de prolifération, une zone intermédiaire de cellules sortant du cycle cellulaire et une zone centrale de cellules différenciées. Un crible d'expression par hybridation In Situ a été réalisé et a permis d'identifier 28 gènes exprimés dans le TO, suggérant leur implication dans le contrôle de la sortie du cycle cellulaire au cours du développement. Dans le but de caractériser in vivo la fonction de gènes issus de ce crible, le gène BTG1 (B-cell Translocation Gene 1) et les membres de sa famille, ont été étudiés au cours du développement du médaka. J ai mené des expériences fonctionnelles sur BTG1, permettant de mettre en évidence son rôle central pour la morphogenèse du système nerveux central. De plus, une autre partie de mon travail s est penchée sur l étude de l expression des membres de la voie de signalisation Hippo, bien connue et caractérisée chez la drosophile et les Mammifères pour son rôle dans le contrôle de la taille des organes via une régulation de l arrêt de la prolifération. A l issu de notre travail, une fonction de la voie de signalisation Hippo dans la formation du TO et des somites a pu être mise en évidence au cours du développement du médaka.How is an organisms size regulated during embryonic development? What are the genetic mechanisms that control the proliferation arrest during multicellular organisms growth? In order to identify a cell cycle exit developmental actor genes, I have analysed the role of tumor suppressor genes (TSGs) in the optic tectum (OT) of the medaka Oryzias latipes. This structure is particularly suited for this kind of studies because, during its morphogenesis, there is a strict correlation between the position of a cell and its degree of differentiation. 3 zones can be easily distinguished from the border to the center: a marginal zone made of proliferative cells, an intermediate zone in which cells exit the cycle, and a central zone made of postmitotic cells. Using this criterium, I have performed an in situ hybridization expression screen on 150 TSGs on medaka embryos. The expression patterns of 28 TSGs in the OT suggest their implication in the OT proliferation arrest mechanisms. I focused my study on the BTG1 gene, implicated in many cancers, and for which few developmental data are available. A functional analysis on developing medaka embryos has been performed and permitted to highlight the essential role of BTG1 in central nervous system morphogenesis. Furthermore, I performed an expression study on Hippo signalling pathway components. Hippo pathway is well caracterised for its organ size control function in drosophila and Mammals. Our results show that this pathway could act in OT formation and somitogenesis in medaka fish.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

CARACTERISATION DE GENES A HOMEOBOITE IMPLIQUES DANS L'ONTOGENESE DU CERVEAU ANTERIEUR CHEZ LE MEDAKA (ORYZIAS LATIPES)

RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

ASSOCIATION D'UN SYNDROME DE GUILLAIN-BARRE ET D'UNE MYASTHENIE (REVUE DE LA LITTERATURE A PARTIR D'UN CAS)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF