Étude de la signalisation Sonic Hedgehog dans le guidage des axones de la rétine lors de l’établissement de la vision binoculaire

Chez les animaux à vision binoculaire, la vision tridimensionnelle permet la perception de la profondeur grâce à l'intégration de l'information visuelle en provenance des deux yeux. La première étape de cette intégration est rendue possible anatomiquement par la ségrégation des axones controlatéraux et ipsilatéraux des cellules ganglionnaires de la rétine (CGR) au niveau du chiasma optique. Les axones controlatéraux croisent la ligne médiane au chiasma en route du nerf optique vers le cerveau. À l’inverse, les axones ipsilatéraux s'écartent du chiasma et continuent dans le tractus optique ipsilatéral, en évitant la ligne médiane vers leurs cibles cérébrales. Les mécanismes moléculaires à la base de ce phénomène ne sont pas complètement compris. Les études présentées dans cette thèse montrent que Boc, le récepteur de Sonic Hedgehog (Shh) dans le guidage axonal, est enrichi dans les CGRs ipsilatérales de la rétine en développement. La présence de Shh sur la ligne médiane, et le mode d'expression complémentaire du récepteur nous ont conduit à émettre l'hypothèse que Shh pourrait repousser les axones ipsilatéraux au niveau du chiasma en activant le récepteur Boc. Conformément à cette hypothèse, nous avons constaté que seulement les CGR exprimant Boc se rétractent in vitro en réponse à Shh et que cette réponse est perdue dans les CGR mutantes pour Boc. In vivo, nous démontrons que Boc est requis pour la ségrégation normale des axones ipsilatéraux au niveau du chiasma optique et, inversement, que l'expression ectopique de Boc dans les CGR contralatérales empêche leurs axones de traverser le chiasma optique. Dans l’ensemble, ces résultats suggèrent que Shh repousse les axones ipsilatéraux au niveau du chiasma optique par son récepteur Boc. Cette première partie de notre travail identifie un nouveau couple ligand-récepteur requis pour la ségrégation des axones au niveau du chiasma optique. Une interaction moléculaire impliquée dans cette ségrégation implique l’éphrine-B2 et ses récepteurs EphB (EphB1). Dans la deuxième partie de notre travail, nous montrons, in vivo, en utilisant des souris doubles et quadruples mutantes pour les récepteurs Boc, EphB1 ou les trois récepteurs EphB, que l’abrogation des deux voies de signalisation Shh et éphrine-B2 conduit à l'absence de projections ipsilatérales. Ceci indique que les deux signalisations agissent de façon indépendante dans des voies parallèles. De manière intéressante, ces souris mutantes ont été utilisées comme modèle génétique pour démontrer des défauts dans la perception de la profondeur de champs chez des animaux dépourvus de projections visuelles ipsilatérales. Ainsi, les travaux présentés dans cette thèse démontrent pour la première fois que la formation des projections rétiniennes ipsilatérales est essentielle à l’établissement de la vision binoculaire et dépend des voies induites par les récepteurs d’éphrine-B2 et Shh.In animals with binocular vision, three dimensional vision allows perception of depth through the integration of visual information from both eyes. The first step of this integration is possible anatomically with the segregation of contralateral and ipsilateral axons at the optic chiasm. Contralateral axons cross the chiasm midline as they progress from the optic nerve to the optic tract. In contrast, ipsilateral axons deviate from the chiasm and continue in the ipsilateral optic tract. The molecular mechanism underlying this phenomenon is not completely understood. The studies presented in this thesis show that the Sonic Hedgehog (Shh) receptor Boc is enriched in ipsilateral RGCs of the developing retina. Together with the presence of Shh at the midline, this complementary expression pattern led us to hypothesize that Shh might repel ipsilateral RGC axons at the chiasm. Consistent with this hypothesis, we found that only Boc positive RGC axons retract in vitro in response to Shh and that this response is lost in Boc mutant RGCs. In vivo, we show that Boc is required for the normal segregation of ipsilateral axons at the optic chiasm and, conversely, that Boc expression in contralateral RGCs prevents their axons from crossing the optic chiasm. Taken together, these results suggest that Shh repels ipsilateral RGC axons at the optic chiasm via its receptor Boc. This first part of this thesis identifies a novel receptor required for the segregation of axons at the optic chiasm. The other couple ligand-receptor involved in this segregation is the Ephrin-B2/EphB signalling. In the second part of this thesis, I show that in vivo, the abrogation of both signalling pathways using quadruple knockout mice of the receptor Boc and three EphB receptors led to the absence of ipsilateral projections, indicating that Shh and ephrinB2 signalling act independently in two parallel pathways. More importantly, these animals, used as a new genetic model to perform visual tests, had a diminished ability to perceive depth. Thus, this thesis demonstrates for the first time that the establishment of ipsilateral retinal projections, essential for accurate binocular vision and perception of depth, is made possible by the combination of EphB and Shh signalling

A glimpse on the pattern of rodent diversification:a phylogenetic approach

RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are.Abstract Background Development of phylogenetic methods that do not rely on fossils for the study of evolutionary processes through time have revolutionized the field of evolutionary biology and resulted in an unprecedented expansion of our knowledge about the tree of life. These methods have helped to shed light on the macroevolution of many taxonomic groups such as the placentals (Mammalia). However, despite the increase of studies addressing the diversification patterns of organisms, no synthesis has addressed the case of the most diversified mammalian clade: the Rodentia. Results Here we present a rodent maximum likelihood phylogeny inferred from a molecular supermatrix. It is based on 11 mitochondrial and nuclear genes that covers 1,265 species, i.e., respectively 56% and 81% of the known specific and generic rodent diversity. The inferred topology recovered all Rodentia clades proposed by recent molecular works. A relaxed molecular clock dating approach provided a time framework for speciation events. We found that the Myomorpha clade shows a greater degree of variation in diversification rates than Sciuroidea, Caviomorpha, Castorimorpha and Anomaluromorpha. We identified a number of shifts in diversification rates within the major clades: two in Castorimorpha, three in Ctenohystrica, 6 within the squirrel-related clade and 24 in the Myomorpha clade. The majority of these shifts occurred within the most recent familial rodent radiations: the Cricetidae and Muridae clades. Using the topological imbalances and the time line we discuss the potential role of different diversification factors that might have shaped the rodents radiation. Conclusions The present glimpse on the diversification pattern of rodents can be used for further comparative meta-analyses. Muroid lineages have a greater degree of variation in their diversification rates than any other rodent group. Different topological signatures suggest distinct diversification processes among rodent lineages. In particular, Muroidea and Sciuroidea display widespread distribution and have undergone evolutionary and adaptive radiation on most of the continents. Our results show that rodents experienced shifts in diversification rate regularly through the Tertiary, but at different periods for each clade. A comparison between the rodent fossil record and our results suggest that extinction led to the loss of diversification signal for most of the Paleogene nodes

Власні назви як елемент інтертекстуальності в поетичних творах XX століття

У роботі розглядаються проблеми інтертекстуальності та аналізуються власні назви як самостійні елементи інтертекстуальних зв’язків на матеріалі поетичних творів ХХ століття. Досліджуються особливості інтерпретації онімів як конденсованих символів, індивідуально- авторського переосмислення контексту світової і національної культури та історії у творах “неокласиків”. Розглядаються семантичні особливості художнього мовлення, визначаються функції, семантико-стилістичні та структурні особливості мовних засобів, простежуються тенденції своєрідного вживання власних назв у творчості “неокласиків”.В работе рассматриваются проблемы интертекстуальности и анализируются имена собственные как самостоятельные элементы интертекстуальных связей на материале поэзии ХХ столетия. Исследуются особенности интерпретации онимов как конденсированных символов, индивидуально-авторского переосмысления контекста мировой и национальной культуры и истории в творчестве “неоклассиков”. Рассматриваются семантические особенности художественной речи, семантико-стилистические и структурные особенности языковых средств, прослеживаются тенденции своеобразного использования имен собственных в творчестве “неоклассиков”.In work deals with the problems of intertextuality and analyzed their own names as separate elements intertextual connections on the material of poetry of the twentieth century. Investigates the features of the interpretation onyms as condensed symbols of author individual rethinking the context of global and national culture and history in the work of "neoclassicists". Lexical variety and semantic peculiarities of artistic language are examined. The functions, semantic-stylistic and structural peculiarities of language means are defined. The tendencies of distinctive word usage in language creativity of “neoclassics” are revealed and scientifically grounded

The HoxD cluster is a dynamic and resilient TAD boundary controlling the segregation of antagonistic regulatory landscapes

The mammalian HoxD cluster lies between two topologically associating domains (TADs) matching distinct enhancer-rich regulatory landscapes. During limb development, the telomeric TAD controls the early transcription of Hoxd genes in forearm cells, whereas the centromeric TAD subsequently regulates more posterior Hoxd genes in digit cells. Therefore, the TAD boundary prevents the terminal Hoxd13 gene from responding to forearm enhancers, thereby allowing proper limb patterning. To assess the nature and function of this CTCF-rich DNA region in embryos, we compared chromatin interaction profiles between proximal and distal limb bud cells isolated from mutant stocks where various parts of this boundary region were removed. The resulting progressive release in boundary effect triggered inter-TAD contacts, favored by the activity of the newly accessed enhancers. However, the boundary was highly resilient, and only a 400-kb deletion, including the whole-gene cluster, was eventually able to merge the neighboring TADs into a single structure. In this unified TAD, both proximal and distal limb enhancers nevertheless continued to work independently over a targeted transgenic reporter construct. We propose that the whole HoxD cluster is a dynamic TAD border and that the exact boundary position varies depending on both the transcriptional status and the developmental context. Press

The P2Y1 receptor is involved in the maintenance of glucose homeostasis and in insulin secretion in mice

Pancreatic β cells express several P2 receptors including P2Y1 and the modulation of insulin secretion by extracellular nucleotides has suggested that these receptors may contribute to the regulation of glucose homeostasis. To determine whether the P2Y1 receptor is involved in this process, we performed studies in P2Y1 mice. In baseline conditions, P2Y1-mice exhibited a 15% increase in glycemia and a 40% increase in insulinemia, associated with a 10% increase in body weight, pointing to a role of the P2Y1 receptor in the control of glucose metabolism. Dynamic experiments further showed that P2Y1-mice exhibited a tendency to glucose intolerance. These features were associated with a decrease in the plasma levels of free fatty acid and triglycerides. When fed a lipids and sucrose enriched diet for 15 weeks, the two genotypes no longer displayed any significant differences. To determine whether the P2Y1 receptor was directly involved in the control of insulin secretion, experiments were carried out in isolated Langerhans islets. In the presence of high concentrations of glucose, insulin secretion was significantly greater in islets from P2Y1-mice. Altogether, these results show that the P2Y1 receptor plays a physiological role in the maintenance of glucose homeostasis at least in part by regulating insulin secretion

TWIST1 a New Determinant of Epithelial to Mesenchymal Transition in EGFR Mutated Lung Adenocarcinoma

Metastasis is a multistep process and the main cause of mortality in lung cancer patients. We previously showed that EGFR mutations were associated with a copy number gain at a locus encompassing the TWIST1 gene on chromosome 7. TWIST1 is a highly conserved developmental gene involved in embryogenesis that may be reactivated in cancers promoting both malignant conversion and cancer progression through an epithelial to mesenchymal transition (EMT). The aim of this study was to investigate the possible implication of TWIST1 reactivation on the acquisition of a mesenchymal phenotype in EGFR mutated lung cancer. We studied a series of consecutive lung adenocarcinoma from Caucasian non-smokers for which surgical frozen samples were available (n = 33) and showed that TWIST1 expression was linked to EGFR mutations (P<0.001), to low CDH1 expression (P<0.05) and low disease free survival (P = 0.044). To validate that TWIST1 is a driver of EMT in EGFR mutated lung cancer, we used five human lung cancer cell lines and demonstrated that EMT and the associated cell mobility were dependent upon TWIST1 expression in cells with EGFR mutation. Moreover a decrease of EGFR pathway stimulation through EGF retrieval or an inhibition of TWIST1 expression by small RNA technology reversed the phenomenon. Collectively, our in vivo and in vitro findings support that TWIST1 collaborates with the EGF pathway in promoting EMT in EGFR mutated lung adenocarcinoma and that large series of EGFR mutated lung cancer patients are needed to further define the prognostic role of TWIST1 reactivation in this subgroup

Kelvin-Helmholtz instability in the presence of variable viscosity for mudflow resuspension in estuaries

The temporal stability of a parallel shear flow of miscible fluid layers of dif- ferent density and viscosity is investigated through a linear stability analysis and direct numerical simulations. The geometry and rheology of this Newto- nian fluid mixing can be viewed as a simplified model of the behavior of mud- flow at the bottom of estuaries for suspension studies. In this study, focus is on the stability and transition to turbulence of an initially laminar configuration. A parametric analysis is performed by varying the values of three control pa- rameters, namely the viscosity ratio, the Richardson and Reynolds numbers, in the case of initially identical thickness of the velocity, density and viscosity profiles. The range of parameters has been chosen so as to mimic a wide variety of real configurations. This study shows that the Kelvin-Helmholtz instability is controlled by the local Reynolds and Richardson numbers of the inflection point. In addition, at moderate Reynolds number, viscosity strat- ification has a strong influence on the onset of instability, the latter being enhanced at high viscosity ratio, while at high Reynolds number, the influ- ence is less pronounced. In all cases, we show that the thickness of the mixing layer (and thus resuspension) is increased by high viscosity stratification, in particular during the non-linear development of the instability and especially pairing processes. This study suggests that mud viscosity has to be taken into account for resuspension parameterizations because of its impact on the inflec- tion point Reynolds number and the viscosity ratio, which are key parameters for shear instabilities

Genome wide SNP comparative analysis between EGFR and KRAS mutated NSCLC and characterization of two models of oncogenic cooperation in non-small cell lung carcinoma

<p>Abstract</p> <p>Background</p> <p>Lung cancer with EGFR mutation was shown to be a specific clinical entity. In order to better understand the biology behind this disease we used a genome wide characterization of loss of heterozygosity and amplification by Single Nucleotide Polymorphism (SNP) Array analysis to point out chromosome segments linked to <it>EGFR </it>mutations. To do so, we compared genetic profiles between <it>EGFR </it>mutated adenocarcinomas (ADC) and <it>KRAS </it>mutated ADC from 24 women with localized lung cancer.</p> <p>Results</p> <p>Patterns of alterations were different between <it>EGFR </it>and <it>KRAS </it>mutated tumors and specific chromosomes alterations were linked to the <it>EGFR </it>mutated group. Indeed chromosome regions 14q21.3 (p = 0.027), 7p21.3-p21.2 (p = 0.032), 7p21.3 (p = 0.042) and 7p21.2-7p15.3 (p = 0.043) were found significantly amplified in EGFR mutated tumors. Within those regions 3 genes are of special interest <it>ITGB8</it>, <it>HDAC9 </it>and <it>TWIST1</it>. Moreover, homozygous deletions at <it>CDKN2A </it>and LOH at <it>RB1 </it>were identified in <it>EGFR </it>mutated tumors. We therefore tested the existence of a link between EGFR mutation, CDKN2A homozygous deletion and cyclin amplification in a larger series of tumors. Indeed, in a series of non-small-cell lung carcinoma (n = 98) we showed that homozygous deletions at <it>CDKN2A </it>were linked to <it>EGFR </it>mutations and absence of smoking whereas cyclin amplifications (<it>CCNE1 </it>and <it>CCND1</it>) were associated to <it>TP53 </it>mutations and smoking habit.</p> <p>Conclusion</p> <p>All together, our results show that genome wide patterns of alteration differ between <it>EGFR </it>and <it>KRAS </it>mutated lung ADC, describe two models of oncogenic cooperation involving either <it>EGFR </it>mutation and <it>CDKN2A </it>deletion or cyclin amplification and <it>TP53 </it>inactivating mutations and identified new chromosome regions at 7p and 14q associated to EGFR mutations in lung cancer.</p