Squelette membranaire chez Paramecium Tetraurelia : analyse structurale et fonctionnelle de la famille multigénique des épiplasmines

Abstract : Cortex in most ciliate protozoan contains a membrane skeleton mainly composed of epiplasm, a layer closely apposed to the inner alveolar membrane. In Paramecium, this layer is segmented into independent scales centered on each ciliary apparatus; the epiplasm is composed by a multigenic family of protein called epiplasmins. We performed a structural analysis of this multigenic family. Phylogenic analysis supports a clustering of epiplasmins in 5 groups, each of them subdivided in 2 sub-groups a and b. Using HCA method, we show that these proteins are modular, and that they present various arrangements of their structural domains. Epiplasmins can be regrouped into three classes symmetrical, asymmetrical, and atypical. Analysis of the 5'UTR sequences shows that putative expression regulative elements are present in most of the members of this multigenic family. Comparison of Paramecium epiplasmins with their orthologs in Tetrahymena shows a structural relationship between groups 1, 2, 3, and 5 and EpiT1, 2, 3, and 5, respectively, suggesting that both epiplasms evolved from a common ancestor. We present a functional analysis of epiplasmins, using RNA interference and GFP-labeled epiplasmins. Decreasing the expression of symmetrical and asymmetrical epiplasmins induces a common cellular response: change in rounded pear-shaped cells and cytokinesis blockage leading to a 'Boomerang' cell shape, later followed by plasmodial forms. Analysis of cortex by fluorescence microscopy shows that the alteration of cortical units using various RNAi conditions depends on the epiplasmin structural type. Expression of GFP-epiplasmins shows that these proteins are differentially localized around the basal body, defining a territory which conforms to a centrifugal organization model. Epiplasmins are thus defined as kinetosomal, peri-kinetosomal, core, and peripheral. We discuss this model in relation to the phenotypes we obtained from functional analysis. This model provides a way to integrate the different levels of relationship between the basal body, its territory, and the epiplasm in its entirety.
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Raghida Damaj. Squelette membranaire chez Paramecium Tetraurelia : analyse structurale et fonctionnelle de la famille multigénique des épiplasmines. Biologie cellulaire. Université Blaise Pascal - Clermont-Ferrand II, 2008. Français. ⟨NNT : 2008CLF21869⟩. ⟨tel-00731002⟩

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