京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13364号 / 論医博第2206号 / 新制||医||1045(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 高橋 淳, 教授 髙橋 良輔, 教授 斎藤 通紀 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

La maladie de Charcot-Marie-Tooth (CMT) est une maladie neurologique héréditaire du système nerveux périphérique. A ce jour, près de 80 gènes sont décrits comme étant à l’origine d’une forme de CMT dont tous les modes de transmission sont connus. AR-CMT2A est due à une mutation faux-sens homozygote, c.892C>T, dans l’exon 5 du gène LMNA et conduit à la substitution d’une Arginine par une Cystéine (p.Arg298Cys) au sein d’un motif conservé du domaine central coil des Lamines de type A. L’étude présentée ici fait suite à un certain nombre d’observations ayant démontré la diminution de l’expression du gène dans les cellules de patients, et la perte d’interaction entre les Lamines A/C mutées et le facteur de transcription c-Jun. Or celui-ci participe au complexe régulateur AP-1 pour lequel le promoteur du gène LMNA possède deux éléments de fixation. L’ensemble du travail exposé dans ce manuscrit s’est donc basé sur l’hypothèse selon laquelle les Lamines de type A auraient la capacité de réguler leur propre expression et seraient capables, dans le nerf périphérique, d’établir des interactions avec des partenaires spécifiques du nerf périphérique. / Charcot-Marie-Tooth (CMT) disorders constitute a complex and heterogeneous group of hereditary motor and sensory neuropathies characterized by muscle weakness and wasting, foot and hand deformities and electrophysiological changes. Genetically, CMT is characterized by a great heterogeneity, with all modes of inheritance and more than 50 genes described to date. My PhD work focuses on AR-CMT2A, a rare autosomal recessive axonal form of CMT, due to a unique homozygous missense mutation c.892C>T in LMNA exon 5, which leads to the substitution of an arginine by a cysteine (p.Arg298Cys) within a conserved motif in the central rod domain of A-type Lamins. My work aimed at providing clues toward a better understanding of the physiopathological mechanisms underlying AR-CMT2A and is based on previous results for my research team, showing a decrease in the expression of LMNA in patients’ cells, and a loss of interaction between A-type Lamins and the transcription factor c-Jun in patients’ cells. c-Jun is a member of the AP-1 complex, a well-known dimeric transcription factor, and for which interestingly, the LMNA promoter has two binding sites. All the work outlined in this manuscript is based on the hypothesis that A-type Lamins, have the capacity to regulate their own expression and therefore, are also most probably involved in interactions with partners involved in gene regulation, in particular in the Peripheral Nerve System.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20756号 / 医博第4286号 / 新制||医||1024(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邉 大, 教授 伊佐 正, 教授 髙橋 良輔 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・論文博士 / 博士(医学) / 乙第13213号 / 論医博第2163号 / 京都大学大学院医学研究科脳統御医科学系専攻 / (主査)教授 山下 潤, 教授 髙橋 良輔, 教授 木村 剛 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

The cerebral cortex is one of the most complex and divergent of all biological structures and is composed of hundreds of different types of highly interconnected neurons. This complexity underlies its ability to perform exceedingly complex neural processes. One of the most important questions in developmental neurobiology is how such a vast degree of diversity and specificity is achieved during embryogenesis. Furthermore, understanding the cellular and genetic basis of cortical development may yield insights into the mechanisms underlying human disorders such as mental retardation, autism, epilepsies and brain tumors. <p>During this Phd-project, we set out to identify novel transcription factors involved in cortical neurogenesis. Therefore, we initially took advantage of a model of in vitro embryonic stem cell (ESC)-derived corticogenesis that was previously established in the lab (Gaspard et al. 2008) and from several previously generated ESC lines that allow overexpression of specific transcription factors potentially involved in corticogenesis (van den Ameele et al. 2012). <p>Among the genes tested, Bcl6, a B-cell lymphoma oncogene known to be expressed during cortical development but without well-characterized function in this context, displayed a strong proneurogenic activity and thus became the main focus of this thesis. <p><p>During neurogenesis, neural stem/progenitor cells (NPCs) undergo an irreversible fate transition to become neurons. The Notch pathway is well known to be important for this process, and repression of Notch-dependent Hes genes is essential for triggering differentiation. However, Notch signalling often remains active throughout neuronal differentiation, implying a change in the transcriptional responsiveness to Notch during the neurogenic transition.<p>We showed that Bcl6 starts to be expressed specifically during the transition from progenitors to postmitotic neurons and is required for proper neurogenesis of the mouse cerebral cortex. Bcl6 promotes this neurogenic conversion by switching the composition of Notch-dependent transcriptional complexes at the Hes5 promoter. Bcl6 triggers exclusion of the co-activator Mastermind-like 1 and recruitment of the NAD+-dependent deacetylase Sirt1, which we showed to be required for Bcl6-dependent neurogenesis in vitro. The resulting epigenetic silencing of Hes5 leads to neuronal differentiation despite active Notch signalling. These findings thus suggest a role for Bcl6 as a novel proneurogenic factor and uncover Notch-Bcl6-Sirt1 interactions that may affect other aspects of physiology and disease (Tiberi et al. 2012a). <p><p>A subsequent yet unpublished part of this Phd-project focused on unraveling roles for Bcl6 in regionalization of the cerebral cortex. In all mammals, the three major areas of the neocortex are the motor, somatosensory and visual areas, each subdivided in secondary domains and complemented with species-specific additional areas. All these domains comprise of neurons with different functionality, molecular profiles, electrical activity and connectivity. Spatial patterning of the cortex is mainly under the control of diffusible molecules produced by organizing centers, but is also regulated by intrinsic, cell-autonomous programs (Tiberi et al. 2012b). <p>Since Bcl6 expression is confined to frontal and parietal regions of the developing cerebral cortex and remains high in postmitotic neurons, also after completion of neurogenesis, we hypothesized it would be involved in acquisition of motor and somatosensory identity. As expected from the neurogenesis defect in these regions, we observed a trend towards a reduced size of the frontal areas in the Bcl6 mutant cortex. Preliminary data from cDNA microarray profiling after gain- and loss-of-function of Bcl6 and from in situ hybridization on mouse cortex however do not show dramatic changes in molecular markers of different cortical areas. Similarly, the coarse-grained pattern of thalamocortical and efferent projections of motor and somatosensory neurons appears to be spared. These preliminary findings thus suggest that Bcl6 is not strictly required for proper acquisition of motor and somatosensory areal identity. / Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished