Dissertations / Theses: 'Ovocyte de Xenopus Laevis'

1

Bourinet, Emmanuel. "Régulation des canaux calciques par les phosphorylations." Montpellier 1, 1993. http://www.theses.fr/1993MON1T015.

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Maucuer, Alexandre. "Étude de l'évolution, de la structure et de l'expression de la stathmine, une phosphoprotéine cytoplasmique associée aux régulations des cellules par les signaux extracellulaires de leur environnement." Paris 6, 1993. http://www.theses.fr/1993PA066424.

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La stathmine est une protéine cytoplasmique ubiquitaire de 19 kDa, régulée au cours du développement et phosphorylée sur différents sites en réponse aux signaux contrôlant la prolifération, la différenciation et/ou les fonctions cellulaires. Ces données ont permis de proposer, pour cette protéine, un rôle de relais intracellulaire dans la transduction des signaux. Ce rôle général est en accord avec la bonne conservation phylogénétique de la stathmine. La stathmine du rat et celle de l'homme ne diffèrent que par un seul acide aminé. Afin de mieux apprécier cette conservation et de pouvoir étudier la stathmine dans un modèle de développement précoce nous avons cloné des ADNc codant pour la stathmine du xénope. Les stathmines du rat et du xenope sont identiques à 79% en acides aminés. Par ailleurs, deux ADNc (sc15 et xb3) codant pour des protéines apparentées, spécifiques du cerveau, ont été identifiés. La conservation de la stathmine et l'existence d'une famille de protéines ayant chacune une expression et probablement une localisation intracellulaire caractéristiques étendent les notions d'importance et d'ubiquité associées au rôle propose pour la stathmine. Au cours du développement précoce du xénope la stathmine est fortement exprimée; cependant sa phosphorylation est régulée de façon très nette, notamment au cours de la maturation de l'ovocyte. Ces résultats indiquent que la stathmine est impliquée dans les régulations cellulaires associées au développement embryonnaire précoce des vertébrés.

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Cruz, Chomón Carlos, and Zúñiga Cristián Muñoz. "Estudio comparativo de corrientes totales de cloruro provenientes de membrana apical del sinciciotrofoblasto placentario humano normal y preeclámptico trasplantado a ovocitos de Xenopus laevis." Tesis, Universidad de Chile, 2004. http://www.repositorio.uchile.cl/handle/2250/110607.

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El transporte existente entre la madre y feto es vital para el desarrollo de éste. La preeclampsia (PE) es una enfermedad que afecta múltiples funciones, entre ellas la de transporte. Hasta la fecha se han realizado pocos estudios sobre las alteraciones del transporte en la placenta con PE. El objetivo del presente estudio es comparar las corrientes totales en el ovocito de Xenopus laevis transplantado con membrana apical (MVM) proveniente de Sincicitrofoblasto (STP) normal y preeclámptico, donde el responsable de estas corrientes es el maxi-canal de cloruro, para así contribuir a establecer un modelo de transporte transplacentario en el embarazo normal y sus alteraciones en la preeclampsia. Se obtuvieron corrientes superiores en ovocitos inyectados con MVM preeclámptica, seguidas por las corrientes evocadas en ovocitos inyectados con MVM normal y las más bajas corrientes fueron obtenidas por los controles, evidenciando incorporación funcional de los canales exógenos y sugiriendo una alteración en los canales provenientes de la placenta preeclámptica.

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4

Oukerro-Haouari, Fatima. "Etude des enzymes impliquées dans l'initiation de la synthèse du DNA mitochondrial dans les ovocytes de Xenopus laevis." Bordeaux 2, 1988. http://www.theses.fr/1988BOR22023.

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5

Bodart, Jean-François. "Rôle des protéines-kinases et protéines phosphatases dans la levée du blocage métaphasique des ovocytes de Xenopus laevis." Lille 1, 2000. http://www.theses.fr/2000LIL10115.

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Au cours de la deuxieme division de meiose, les ovocytes de xenope arretent naturellement leur cycle cellulaire en metaphase. Ceci est du a l'activite du facteur cytostatique (csf) qui fait intervenir plusieurs kinases (c-mos, mapk, p90 r s k, cdk2). L'arret metaphasique est associe a une activite mpf (cdk1/cycline b) elevee. Ces activites kinasiques chutent lors de la fecondation ou d'une activation parthenogenetique induite par le calcium. Nous avons utilise des inhibiteurs de kinases ou de phosphatases afin de mieux comprendre les mecanismes regulant tant le blocage metaphasique que sa levee. La 6-dimethylaminopurine (6-dmap), inhibiteur de kinases a large spectre, leve le blocage metaphasique tandis que des inhibiteurs plus specifiques de cdks, l'olomoucine et la roscovitine, en sont incapables. Les effets de la 6-dmap ont ete compares avec ceux de l'ionophore calcique a23187. La formation d'un pronucleus est observee dans les deux cas. L'ionophore induit l'inactivation de mapk, la proteolyse des cyclines b et de c-mos. Dans les ufs traites par la 6-dmap, mapk s'inactive plus rapidement, les cyclines b sont stables tandis que c-mos est degradee. Bien que la 6-dmap declenche tardivement une liberation transitoire de calcium, celle-ci n'est pas responsable de la degradation de c-mos. L'injection de molybdate d'ammonium, inhibiteur de tyrosine phosphatases, empeche la levee du blocage metaphasique induite par a23187. Les ovocytes subissent l'exocytose des granules corticaux mais cdk1 et mapk ne sont pas inactivees, c-mos et la cycline b ne sont pas degradees. La proteolyse de c-mos serait induite par une dephosphorylation consecutive a la chute de l'activite mpf. En outre, une tyrosine phosphatase serait impliquee en aval du signal calcique

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6

Marteil, Gaëlle. "Étude des mécanismes de régulation de l'entrée et de la sortie de phase M dans les ovocytes de Xenopus laevis." Rennes 1, 2010. http://www.theses.fr/2010REN1S154.

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Notre équipe de recherche s'intéresse à la régulation de la phase M en utilisant Xenopus laevis comme organisme modèle. Concernant l'entrée en phase M, mes travaux ont démontré que la protéine EP45 pour « Estrogen regulated protein 45 kDa » possède la capacité d'améliorer la maturation ovocytaire. L'analyse de l'expression d'EP45 a également mis en évidence que cette protéine est synthétisée dans le foie, sécrétée dans le sang et ensuite incorporée dans les ovocytes. Mon second projet fut d'identifier les protéines interagissant avec le MPF, facteur clé de la progression en phase. Pour cela, j'ai utilisé deux approches afin de co-précipiter CDK1, sous-unité catalytique du MPF, suivies d'une analyse par SDS-PAGE et spectrométrie de masse. Cette étude a mis en évidence de nouveaux partenaires potentiels du MPF, tels que la peroxiredoxine-2 et la Calcineurine. Ces résultats permettront d'approfondir les connaissances sur la composition et la régulation du complexe MPF
The research topics of our team are focused on the regulation of M phase using Xenopus laevis as a model organism. Concerning M phase entry, I showed that EP45 protein for "Estrogen regulated protein 45 kDa" acts as an oocyte maturation enhancer. EP45 expression analysis also showed that this protein is synthesized in liver, secreted into the blood and then incorporated into oocytes. The second objective of my thesis was to identify new interactors of the MPF complex, the major regulator of M phase progression, during M phase or M-phase exit. For this purpose, I have used two different approaches in order to perform a CDK1, the catalytic subunit of MPF, cosedimentation assay, combined with 1D SDS-PAGE and mass spectrometry. This study allowed us to identify new potential partners of MPF, such as peroxiredoxin-2, Hsp70, calcineurin. All these results will increase knowledge about the composition and regulation of MPF complex during the progression of M phase

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Ducoudret, Olivier. "Etude du changement de couplage stoechiométrique de la forme rénale du cotransporteur Na+ et de HCO3- exprimé dans les ovocytes de Xenopus laevis." Nice, 2002. http://www.theses.fr/2002NICE5785.

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Le rapport stoechiométrique (q) du flux de HCO3- par rapport au Na+ est de 3:1 in vivo mais seulement de 2:1 dans les ovocytes de Xénopus. Pour étudier les paramètres responsables du changement de q, le cotransporteur rkNBC a éte exprimé dans des ovocytes. Q a été déterminé à partir du potentiel de réversion du courant INBC mesuré sur des " patches " de membrane géants. Le tenidap à l'inverse du DIDS peut inhiber INBC de façon réversible avec moins d'activations de courants. Le DIDS active 2 types de conductances ovocytaires : une non spécifique laissant passer les cations monovalents de type SAC (stretch-activated channel) et une spécifique du sodium de type DINa (depolarisation-induced Na+ channel). Ces conductances sont sensibles de façon réversible à 1mM d'amiloride. Nos résultats confirment que dans les patches en conditions physiologiques, rkNBC fonctionne avec q=2:1. L'élévation de la température à 32ʿC ou de la [Ca2+]i à 0. 1æM laissent q invariable. Par contre, une [Ca2+]i de 0. 5æM, permet un q de 3:1. Ceci est confirmé par modification des gradients de Na+ et de HCO3-. Ces données indiquent que rkNBC peut opérer avec différents q en fonction de la [Ca2+]i
The stoichiometric ratio of HCO3- to Na+ flux may be either 3:1 in vivo or 2:1 when expressed in Xenopus laevis oocytes. To study which parameter might be responsible for the change, we expressed rkNBC in oocytes and determined q from reversal point of the cotransport current (INBC). Q was determined from the INBC reversal potential. Instead of using DIDS, we used DIDS which inhibit INBC reversibly and had less side effects. Our results confirmed that in patches bathed with near physiological solutions, rkNBC operates with q=2:1. Raising temperature from 22 to 32ʿC does not change q. Similarly, the elevation of [Ca2+]i to 0. 1æM does not affect q. However, when raising [Ca2+]i to 0. 5æM, q increases to 3:1. The latter value was also found when Na+ and HCO3- gradients were altered, provided [Ca2+]i was elevated. The data indicate that rkNBC can operate with different stoichiometric ratios and that changes in q are triggered by [Ca2+]i. The data also suggest that [Ca2+]i does not stimulate rkNBC directly but via intracellular regulatory proteins

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8

Slaby, Sylvain. "Intérêts de l’ovocyte de Xenopus laevis en écotoxicologie ? : Caractérisation des effets de contaminants environnementaux sur ce modèle alternatif." Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1R048/document.

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Les amphibiens constituent le groupe le plus menacé d’extinction parmi les vertébrés. Néanmoins, peu de travaux en toxicologie des amphibiens tiennent compte des stades précoces de leur cycle de vie. Pourtant, un individu est exposé directement aux substances présentes dans le milieu aquatique dès l’émission des gamètes. Cette thèse de doctorat a pour objectifs d’apporter de nouvelles données sur les effets d’expositions à des xénobiotiques d’ovocytes de Xenopus laevis, de rechercher des cibles au sein de ce gamète et de participer au développement d’un nouveau modèle en écotoxicologie pour évaluer la qualité de milieux aquatiques.Les avantages, que présentent ces ovocytes, nous ont permis de développer des protocoles efficaces pour appréhender la toxicité de substances. Des endpoints ont pu être définis autour de la maturation ovocytaire, de la fécondation, du développement embryonnaire et de la formation de jeunes têtards. Les effets d’expositions au cadmium, au plomb, au cuivre, à la bouillie bordelaise, au glyphosate, au RoundUp® GT Max et à la deltaméthrine ont été déterminés. Des essais ont été également conduits pour des échantillons de milieux soumis à différentes pressions anthropiques.Il est apparu que l’ovocyte de xénope est sensible aux expositions, notamment au cadmium et au glyphosate et différentes signatures d’expositions sont apparues, comme la formation de doubles structures cytologiques induites par le glyphosate.Les réponses mises en évidence prouvent que l’ovocyte de X. laevis est un modèle pertinent et permettent de recommander l’étude des premières étapes du cycle de vie de l’amphibien en toxicologie aquatique
Amphibians are one of the most imperiled group of extinction. Nevertheless, few toxicological studies are interested in the earliest steps of their life cycle, even if gamete emission, fertilization and embryogenesis are directly exposed to water pollution. In this context, this PhD thesis aims to bring new data about xenobiotic exposure effects on Xenopus laevis oocytes, to highlight targets inside this germ cells and to contribute to the elaboration of a new model in ecotoxicology to assess aquatic environment quality.As a well-known gamete, the xenopus oocyte makes possible to establish suitable experimental designs to assess toxicity. Many endpoints were defined regarding the oocyte maturation, the fertilization and also the development. The experiments were conducted in metal (cadmium, lead, copper) and in phytopharmaceutical (Bordeaux mixture, glyphosate, RoundUp® GT Max, deltamethrin) contaminated conditions, but also in environmental samples from various aquatic habitats.The xenopus oocyte appeared to be sensitive to contaminant exposures and specially to cadmium and both formulations of glyphosate. Never observed effects were reported. Pollutant signatures were also pointed up, like the double cytological structures induced by glyphosate exposures.The observed responses and results from environmental water experimentations show that X. laevis oocyte is a pertinent model in ecotoxicology and allow to recommend the first steps of the amphibian life cycle in aquatic toxicology

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9

Guedon, Gérard. "Diadenosine tetraphosphate : synthese et relations avec le choc thermique." Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13040.

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10

BLANOT, FRANCOIS. "Vers le clonage du recepteur gaba/benzodiazepine : apport de l'electrophysiologie et de la biologie moleculaire." Paris 6, 1987. http://www.theses.fr/1987PA066701.

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Le recepteur central de l'acide g-aminobutyrique et des benzodiazepines a ete etudie par deux approches complementaires: l'une electrophysiologique, l'autre faisant appel aux techniques de la biologie moleculaire. L'etude electrophysiologique a ete realisee sur des ovocytes de xenopus injecte d'arn messager extrait de cerveau de poulet. Divers parametres caracterisant le recepteur de l'acide g-amino-butyrique ainsi que l'interaction d'une -carboline avec celui-ci ont ete etudies

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11

Minshull, Jeremy Stephen. "Cynlins in Xenopus laevis." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293835.

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Pan, Tien-Chien Burggren Warren W. "Metabolic, cardiac and ventilatory regulation in early larvae of the South African clawed frog, Xenopus laevis." [Denton, Tex.] : University of North Texas, 2009. http://digital.library.unt.edu/ark:/67531/metadc12175.

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13

Tucker, Abigail Saffron. "Tail development in Xenopus laevis." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297296.

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Costa, R. "Endoderm patterning in Xenopus laevis." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598012.

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The endoderm is the inner germ layer of the vertebrate embryo from which the respiratory and digestive systems are derived. These include organs such as the liver, pancreas, stomach, lungs and intestine. Recent research has helped our understanding of early vertebrate endoderm specification and terminal differentiation of specific endodermal lineages. However, very little is known about the molecular mechanisms that control endoderm patterning and morphogenesis during vertebrate development. As a way to identify genes involved in these elusive steps of development, I performed a differential hybridisation screen in a macroarray tailbud ventral foregut cDNA library coupled with in situ hybridisation analysis. My aim was to identify and characterise new regionally expressed endodermal genes in Xenopus laevis, a classical embryologic model organism. Here, I report the identification and characterisation of a dozen novel regionally expressed endoderm genes. At tailbud stages their expression patterns fall into three re-occurring domains; anterior ventral midgut endoderm, posterior endoderm and dorsal endoderm. In addition, regional expression of some of these genes is observable at gastrula stages, endoderm specification. These are the first early stable endodermal markers for different regions of the gastrula endoderm. This suggests that the earliest steps in endoderm patterning are concurrent with endoderm specification. Furthermore I describe the identification of a mesodermal transcription factor, which appears to be expressed in ‘early embryonic macrophages’ - and a poorly characterised embryonic cell population. I present an overview of endoderm development together with the results from my screen. Overall, these results reveal an unexpected degree of early endodermal patterning and assist our understanding of the link between early and late events of vertebrate endoderm development. In addition, this work provides us with new and very useful markers for endodermal patterning, and potentially some key developmental regulators of endodermal formation.

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Marklew, Sarah. "Retinoid receptors in Xenopus laevis." Thesis, University of Warwick, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283494.

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Benites, da Costa Ricardo Manuel. "Endodermal patterning in Xenopus laevis." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616152.

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Smith, Darrin Paul. "Xenopus laevis octamer-binding proteins." Thesis, University of Warwick, 1990. http://wrap.warwick.ac.uk/108633/.

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The ubiquitous human octamer-binding transcription factor, Oct-1, is believed to regulate the expression of a number of ubiquitously expressed genes. These include genes which are expressed throughout the cell-cycle (eg. snRNA genes) and histone H2B genes, whose expression is tightly coupled to nuclear DNA synthesis at S-phase of the cell-cycle. I have isolated and completely sequenced two X. laevis homologues of Oct-1. The high degree of relatedness of the two homologues indicates that these are likely to be copies of the same gene, which arose during the theoretical genome duplication event in X. laevis evolution. X. laevis and human Oct-1 display strong evolutionary conservation (85% Identity over a stretch of 750 amino acids), which presumably means that X. laevis has a similar, if not identical function to human Oct-1. Homology between human and X. laevis does, however, break down shortly before the N terminal end, at a point where alternate splicing is known to occur in hunan Oct-1 (W. Herr, pers. comn.). The full length X. laevis cDNA clone which I have isolated may represent a novel alternately spliced form of Oct-1. Two octamer-binding proteins have been identified (in band shift assays) in X. laevis oocyte, embryo and tissue extract. Oct-1, and a second, previously unidentified octamer-binding protein which has been termed Oct-R, for octamer-related. Oct-1 does not bind to a degenerate octamer motif most often seen in X. laevis H2B promoters. Oct-R binds more strongly to this degenerate motif than the consensus motif, but only in the context of the H2B promoter, and does not bind either motif in another sequence context. This suggests that Oct-R may have a role in regulation of H2B transcription, although no direct evidence has been obtained. Since Oct-1 is believed to stimulate the S-phase specific induction of histone H2B gene transcription the possibility that Oct-1 binding activity is cell-cycle regulated is of interest. X. laevis Oct-1 (and Oct-R) binding activity does not appear to be cell-cycle regulated. Oct-1 and Oct-R are stored in the oocyte (partly in the cytoplasm), in an amount equivalent to at least 80 000 somatic cells. Histone protein and message are stored in the oocyte as part of the mechanism to provide enough histones to keep-up with the high rate of DNA synthesis in early Xenopus development. It is possible that histone gene transcription factors are stored for the same purpose. By mutation of the octamer motif in the promoter of X. laevis histone H2B gene promoter I have tentatively concluded that the octamer motif is required for the expression of a H2B gene (independently of DNA synthesis) in the oocyte. The H2B gene occurs in association with a H2A gene, as part of a divergently expressed gene pair. The octamer motif may be required for the expression of both H2B and H2A genes. The degenerate octamer motif contained in this H2B promoter does not bind efficiently to Oct-1 in vitro, but binds well to Oct-R, indirectly suggesting that Oct-R is required for the expression of the H2B gene. A polyclonal antiserum raised against the N terminal domain of X. laevis Oct-1 reacts to proteins other than Oct-1 on Western blots of oocyte and embryo extract. These proteins, which are antigenically related to the N terminal domain of Oct-1, are entirely located in the cytoplasm of the oocyte, and entirely located in the nucleus of somatic cells. These proteins are synthesised during oogenesis, and stored in the oocyte in an amount equivalent to at least 100 000 somatic cells.

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18

Cockerill, Matthew James. "D-type cyclins in Xenopus laevis." Thesis, University College London (University of London), 1996. http://discovery.ucl.ac.uk/1349605/.

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I have isolated two D-type cyclins and a putative kinase partner related to Cdk4 from the frog Xenopus laevis. Three D-type cyclins have previously been isolated from mammalian species, where they are thought to be involved in the control of cell proliferation via the regulation the GO-+G 1 and G 1--IS transitions. The RNA and protein levels of D-type cyclins and Cdk4 were followed during Xenopus early embryonic development. The two D-type cyclins and Cdk4 are absent during the early rapid cleavage phase of Xenopus development. Cyclin D1 mRNA and protein can first be detected after the mid-blastula transition (MBT), and while Cdk4 mRNA is present throughout development the protein is only detectable after MBT. I have been unable to detect cyclin D2 mRNA or protein in embryos or adult tissues, although the D2 clone was originally isolated from an oocyte cDNA library. When translated in vitro, Xenopus cyclins D1 and D2 preferentially associate with recombinant Cdk4 protein, and bind less strongly to Cdc2 and Cdk2. Cdk4 in combination with either cyclin Dl or cyclin D2 is also able to form a ternary complex with retinoblastoma protein (pRb), and cyclin D2-Cdk4 was able to phosphorylate the pRb to which it was bound. Whole-mount in situ hybridization revealed that cyclin Dl, Cdk4 and pRb mRNAs are localised to distinct regions of the developing embryo, in contrast to other cyclins which tend to be distributed rather homogeneously, if they are present at all. In particular, cyclin D1 mRNA is strongly localised to the developing eye and other neural regions of the developing embryonic head. Dominant-negative mutants of Cdk4 were constructed by mutating the essential lysine 33 amino acid residue to arginine. The mRNA encoding this kinase-dead Cdk4 was injected into fertilized eggs to look for effects resulting from lack of Cdk4 function after MBT, when Cdk4 protein is first expressed. No discernible abnormal phenotype was seen, however, in agreement with previously reported results obtained in human cultured cells.

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Torres, Monica Alexandra. "WNT signaling pathways in Xenopus laevis /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/6293.

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Cardew, Gail. "Studies on Suc1 in Xenopus laevis." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359192.

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McKenzie, Andy. "Modelling spiral waves in Xenopus laevis oocyte." Thesis, University of Canterbury. Mathematics and Statistics, 1997. http://hdl.handle.net/10092/6954.

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An investigation was made into the spiral waves solutions for the Atri et al model, a partial differential equation model for Ca²⁺ dynamics in the Xenopus laevis oocyte. Spiral wave solutions, both stable and unstable, were found to exist in the oscillatory regime for this model. The spiral wave solutions were found to have a period that decreased as the initial IP₃ bolus increased. Increasing the initial IP₃ bolus also lead to destabilisation of the spiral waves solutions. After the break up of spiral wave solutions complex spatio-temporal patterns occurred. In some cases spirals reformed after breaking up.

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22

Beckhelling, Clare. "Regulation of mitotic progression in Xenopus laevis." Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310662.

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Poorten, Thomas J. "Maternal transfer of antibodies in Xenopus laevis." Electronic thesis, 2008. http://dspace.zsr.wfu.edu/jspui/handle/10339/174.

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Porter, Nicola J. "Muscarinic actions in Xenopus laevis tadpole swimming." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4286.

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Muscarinic acetylcholine receptors (mAChRs) mediate effects of acetylcholine (ACh) in many systems, including those involved in locomotion. In the stage 37/38 Xenopus laevis tadpole, a well-understood model system of vertebrate locomotion, mAChRs have been found to be located on motor neurons with evidence suggesting that mAChRs are involved in swimming behaviour. The current study aimed to further investigate the role of mAChR-mediated cholinergic transmission by employing extracellular and whole-cell patch clamp recordings to examine the effects of mAChR activation on the properties of different types of neurons in the Xenopus laevis tadpole swimming circuit. It was found that mAChR activation can increase the threshold for initiating swimming by skin stimulation and can lead to the generation of spontaneous motor output in the absence of physical stimuli. These effects were found to be a result of direct inhibition of dorsolateral sensory interneurons of the mechanosensory pathway, direct inhibition of glycinergic inhibitory interneurons in the CPG and a decrease in CPG neuron firing reliability during swimming. The data presented here comprise the first whole-cell patch-clamp investigation into mAChR-mediated cholinergic transmission in the Xenopus laevis tadpole swimming circuit and provide novel evidence that mAChRs modulate the properties of mechanosensory pathway and CPG neurons in this model system of vertebrate locomotion.

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Cleaver, Ondine Beatrice. "Neovascularization of the Xenopus embryo /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.

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Pan, Tien-Chien. "Metabolic, cardiac and ventilatory regulation in early larvae of the South African clawed frog, Xenopus laevis." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc12175/.

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Early development of O2 chemoreception and hypoxic responses under normoxic (150 mmHg) and chronically hypoxic (110 mmHg) conditions were investigated in Xenopus laevis from hatching to 3 weeks post fertilization. Development, growth, O2 consumption, ventilatory and cardiac performance, and branchial neuroepithelial cells (NEC) density and size were determined. At 3 days post fertilization (dpf), larvae started gill ventilation at a rate of 28 ± 4 beats/min and showed increased frequency to 60 ± 2 beats/min at a PO2 of 30 mmHg. Also at 3 dpf, NECs were identified in the gill filament buds using immunohistochemical methods. Lung ventilation began at 5 dpf and exhibited a 3-fold increase in frequency from normoxia to a PO2 of 30 mmHg. Hypoxic tachycardia developed at 5 dpf, causing an increase of 20 beats/min in heart rate, which led to a 2-fold increase in mass-specific cardiac output at a PO2 of 70 mmHg. At 10 dpf, gill ventilatory sensitivity to hypoxia increased, which was associated with the increase in NEC density, from 15 ± 1 to 29 ± 2 cells/mm of filament at 5 and 10 dpf, respectively. Unlike the elevated rate, cardiac and ventilatory volumes were independent of acute hypoxia. Despite increased cardioventilatory frequency, larvae experienced an average of 80% depression in during acute hypoxia. Chronic hypoxia (PO2 of 110 mmHg) decreased mass-specific cardiac performance before 10 dpf. In older larvae (10 to 21 dpf), chronic hypoxia decreased acute branchial and pulmonary hypoxic hyperventilation and increased NEC size. Collectively, these data suggest that larvae exhibit strong O2-driven acute hypoxic responses post-hatching, yet are still O2 conformers. All acute hypoxic responses developed before 5 dpf, and then the effects of chronic hypoxia started to show between 7 and 21 dpf. Thus, the early formation of acute hypoxic responses is susceptible to the environment and can be shaped by the ambient PO2.

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Garriock, Robert J. "Mechanisms of heart field restriction in Xenopus laevis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0002/MQ42144.pdf.

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Lancaster, Jo-Ann M. "Volume-sensitive membrane transport in Xenopus laevis erythrocytes." Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298236.

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Thorburn, A. M. "Control of vitellogenin gene expression in Xenopus laevis." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355816.

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Schulze, Sabrine. "Wnt6 function in eye development in Xenopus laevis." Thesis, University of Aberdeen, 2012. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=192239.

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The eyes are the most important sensory organs for most vertebrates. Their structure and development is conserved between several vertebrate species. The development is regulated by several signalling pathways, including the Wnt/β-catenin signalling pathway. It is required for several aspects of retinal development and it is known to regulate the proliferation of neuro-epithelial stem cells. In Xenopus laevis the intracellular Wnt/β-catenin signalling pathway is activated in the retina by the Wnt receptor Fz5. Fz5 function in the eye was shown to regulate tissue specific gene expression and neuron versus Müller glial cell differentiation. However, no candidate Wnt ligand that could act through the Fz5 receptor in this tissue had been described. Wnt6 was recently found to be expressed in the developing retina, indicating that Wnt6 and Fz5 share temporal and spatial expression. Here, I tested the hypothesis that Wnt6 might function as ligand for Fz5 in the retina. In this thesis I show that a knock down of Wnt6 led to the same eye phenotype seen in Fz5 morphants, including reduced eye size, changed marker gene expression and altered neuron/Müller glia ratio. Rescue experiments show that the observed phenotype is specific and is mediated by altered Wnt/β-catenin signalling pathway function. These findings support a linear model, in which Wnt6 signal interacts with the Fz5 receptor to activate the Wnt/β-catenin pathway to regulate neural and Müller glia cell differentiation in retinal tissue. These results make Wnt6 a candidate for Fz5 ligand.

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Farley, Esme Kila. "Immunological tolerance in the amphibian Xenopus laevis (Daudin)." Thesis, University of Plymouth, 1987. http://hdl.handle.net/10026.1/2344.

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Observation of some of the phenomena of tolerance to soluble protein antigens and allogeneic tissue transplants in Xenopus laevis has formed the framework of the present study. The method of larval induction of high-zone tolerance used in this laboratory has been confirmed and further analysed. Larvae treated with high doses of Human-γ-globulin (HGG) were unable to produce anti-HGG antibody after challenge. The proliferative response demonstrated in the spleens of tolerant toadlets 21 days after challenge was, however, of similar magnitude to that in normally responding animals. Adoptive transfer of high-zone tolerance specific to HGG was demonstrated by intravenous inoculation of tolerant histocompatible splenocytes simultaneously with an antigenic challenge via the dorsal lymph sac. This is indicative of the active involvement of a suppressor T-cell population. The induction of high-zone tolerance in X. laevis results in changes in spleen cell populations as demonstrated by buoyant density gradient separation. Spleen cell sub-populations taken from the separated layers were not, however, effective in the adoptive transfer of tolerance. A normal lymphocyte transfer reaction was observed in X. laevis to show a number of characteristics seen in the mammalian reaction. The use of mitomycin-C treated donor cells and early thymectomized hosts has demonstrated that the phenomenon is composed of donor and host components which are largely distinct from each other. Implantation of allogeneic larval spleens resulted in the induction of transplantation tolerance or impaired rejection in a significant proportion of skin grafted toadlets in which both the donor and host larvae were up to and including stage 51 at the time of transplantation. The implication of these results is that immunomaturity of the donor and host is important in the induction of transplantation tolerance but that other factors must also be involved.

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32

Civill, Nicola Dawn. "Characterisation of a bagpipe homologue in Xenopus laevis." Thesis, University College London (University of London), 2000. http://discovery.ucl.ac.uk/1348859/.

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Mutations of Drosophila bagpipe, an NK3 class homeobox gene, result in failure of visceral mesoderm to differentiate into stomach tissue. Thus bagpipe, in association with other factors, is a good candidate for specification of visceral mesoderm in Drosophila. The cloning and characterisation of a Xenopus bagpipe homologue was therefore of great interest. This study describes the isolation of a full length Xenopus cDNA clone that on the basis of database analysis and sequence comparisons has been assigned as Xenopus bagpipe (XBap). Previous studies had revealed that the majority of homeoproteins recognise DNA sites with a 5'-TAAT-3' core but the NK class of homeoproteins had been shown to bind specifically to sites containing a 5'-CAAG-3' core. Experiments described here, however, show the XBap DNA binding site to be an even more divergent, 5'-TTAAGTGG-- TTAAGTGG-3'. A series of mutant oligonucleotides revealed that the `T' of the 5'- T_{1}A_{2}A_{3}G_{4}-3' core, as well as the presence of two such cores, are indeed essential for optimal XBap DNA binding. The murine NK3 class homeoproteins, Nkx-3.1 and Bapxl, are demonstrated to have the same requirements for optimal DNA binding as XBap. Drosophila Bagpipe, however, was found to have a less stringent requirement for a `T' at position one of the core, binding equally well to a 'C' in this position, but the presence of two such cores is still necessary for optimal DNA binding. Preliminary studies using site directed mutagenesis attempted to define the amino acids responsible for the differences. The effect of XBap on transcription was studied using a Xenopus oocyte assay and two cell transfection assays. XBap was not found to act as a transcriptional activator in any of these assays but evidence was obtained to suggest that a C-terminal truncation of XBap could act as a repressor of transcription.

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33

Hough, Katherine Ann. "Photodispersion and melanopsin expression in Xenopus laevis melanophores." Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416960.

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Hopwood, N. D. "Molecular markers of mesoderm induction in Xenopus laevis." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317830.

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35

Carroll, Thomas Joseph. "Specification and patterning of the Xenopus laevis pronephros /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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36

Cesare, Gargioli. "Cell lineage tracing during Xenopus laevis tail regeneration." Thesis, University of Bath, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425270.

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Chalmers, Andrew Douglas. "Development of the endodermal organs in Xenopus laevis." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302152.

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Vollmar, Friederike Lara Veronika. "Analyse der Kernhüllenbildung am Modellsystem Xenopus laevis = Studying nuclear envelope assembly in the cell-free system derived from Xenopus laevis eggs." kostenfrei, 2008. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/2929/.

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39

Hamm, Lisa. "Controlled ablation of rod photoreceptors in transgenic Xenopus laevis." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/236.

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Retinal degeneration is the progressive loss of neurons lining the posterior surface of the eye. Loss of a certain group of neurons called rod photoreceptors can occur as the result of genetic mutation. In humans, and in mammalian models of retinal degeneration, the death of these cells is permanent, and often followed by cone photoreceptor death, which leads to blindness. As a step towards understanding the implications of rod cell death in the retina, we generated transgenic X. laevis that expressed a novel form of caspase-9, with binding domains specific to the compound AP20187. We treated these transgenic animals with AP20187 and caused rod cell death by apoptosis in tadpoles and post metamorphic animals. Peak rod apoptosis occurred two days after drug exposure. We adapted an electroretinography apparatus, and protocols designed for mammals to measure functional changes in X. laevis rod and cone derived responses. We observed delayed secondary cone cell dysfunction after induced rod cell apoptosis, which was subsequently restored. These animals provide a simple and clinically relevant model of diseases like Retinitis pigmentosa, in which we will be able to probe in detail the mechanisms that govern cone cell dysfunction as a consequence of rod apoptosis. The unique ability of this species to recover from this insult will provide clues towards initiating similar recovery in humans.

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40

Feng, Jun. "A kinetic investigation of recombinant xenopus laevis amidating enzymes." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/30084.

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41

Héligon, Christophe. "Wnt/frizzled signaling during Xenopus laevis pronephric kidney organogenesis /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17287.

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42

Ishimaru, Hiroshi. "Molecular biology of novel glutamate receptors in Xenopus laevis." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309048.

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43

James, Lisa. "Initiation of motor responses in developing Xenopus Laevis tadpoles." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503893.

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44

Ali, M. "Structural studies of Xenopus laevis Quaking protein QUA1 domain." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595447.

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A recent report showed that a specific point mutation of glutamate to glycine (E48G) in the QUA1 domain affects both the oligomerisation and the RNA-binding properties of the murine Quaking homologue (QkI). The mutation has also been shown to be embryonic lethal in mice at around day 10 of gestation. The aims of this thesis were to investigate the structural features of QUA1 domain and explain why E48G mutants fail to dimerize. The first objective was pursued by expression and purification of the Xenopus laevis Quaking homologue (pXqua) QUA1 motif, followed by biophysical characterization and structural studies using solution-state nuclear magnetic resonance (NMR) spectroscopy. The second objective was addressed by biophysical characterization of an E48G mutant of the QUA1 domain, prepared using site directed mutagenesis. The QUA1 dimer was shown to comprise two α-helical hairpins assembling via an unusually small and polar protein-protein interface. Based on this structure, we proposed that the properties of the E48G mutant could be explained by disruption of salt-bridge interactions, either between E43 and R46 of the same protomer or R38 of the other protomer. This hypothesis was tested by generating a series of QUA1 mutants by site directed mutagenesis and analyzing them using analytical SEC, both as cleaved proteins and as MBP fusion proteins. Moreover, a separate mutational analysis was performed to compare the pXqua QUA1 domain with the corresponding regions in other STAR/GSG proteins. Sequence alignment of the QUA1 region showed proline residue in the predicted helix α1 of SAM68 and SF1. Corresponding mutations were made in pXqua QUA1 domain and the effect was investigated by studying their oligomerisation.

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45

Ahmed, Nadeem M. "Transgenic analysis of the endodermin promoter in Xenopus laevis." Thesis, University of Warwick, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269083.

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46

Mason, Clive S. "Transcriptional effects of retinoic acid in Xenopus laevis embryos." Thesis, University of Warwick, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307343.

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47

Firek, Simon. "The promotion of ribosomal RNA transcription in Xenopus laevis." Thesis, University of Portsmouth, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236392.

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48

August, Lisa Layne. "Characterization of the xGAT-1 Gene in Xenopus laevis." W&M ScholarWorks, 2003. https://scholarworks.wm.edu/etd/1539626405.

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Bernard, Emmanuelle Alexa. "Cloning and characterisation of the Xenopus laevis bloom's protein." Thesis, University of Sussex, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367351.

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50

Stephenson, Rachel A. "Notch signalling in Xenopus laevis haematopoietic stem cell programming." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:4a6db3d9-14ec-4ad2-ad7f-06705c49d32e.

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Multipotent haematopoietic stem cells (HSCs) originate in the dorsal aorta (DA) during vertebrate embryogenesis, and after migrating to a permanent niche, give rise to a continuous supply of mature blood cells of all lineages throughout adult life. Previous cell tracing experiments have shown that the cells of the DA migrate here from an early collection of haemangioblasts (bipotential precursors of blood and endothelial cells) which reside in the dorsolateral plate (DLP) mesoderm. Development of HSCs is tightly regulated by a number of key signalling pathways in both the DLP and the DA. In particular, notch signalling is considered an important factor in vascular, arterial and HSC development. Here, the relatively slow development and the spatial separation of definitive haematopoiesis from primitive haematopoiesis in Xenopus laevis has been exploited to reveal the first defect of reduced notch signalling in the Xenopus DA. Two notch inputs to HSC programming have been identified in Xenopus: notch4 and its target genes, esr7 and esr10, are expressed from stage 31, immediately after migrating haemangioblast cells reach the midline of the embryo to form the DA, whilst notch1 is expressed slightly later, from stage 34, and controls expression of two further notch target genes, esr1 and hesr1. Using both morpholino knockdown of these six genes, and chemical inhibition of notch signalling using a specific γ-secretase inhibitor, notch signalling has been demonstrated to be essential for HSC programming but dispensable for earlier haemangioblast and arterial programming. Furthermore, esr1, downstream of both notch1 and notch4, is shown to be responsible for repression of endothelial genes in the DA. Taken together, this demonstrates that a cascade of notch and notch effector genes are essential for the programming of Xenopus HSCs.

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Dissertations / Theses on the topic 'Ovocyte de Xenopus Laevis'

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