Os problemas da poluição atmosférica atingem todos os grandes centros urbanos, em particular as megacidades com população maior do que 10 milhões de habitantes. Emissões veiculares e industriais destacam-se entre as principais responsáveis pelas altas concentrações de poluentes do ar nesses centros urbanos. Os diferentes componentes da poluição atmosférica, a dose e o tempo de exposição, podem levar a diversos impactos na saúde humana. Esse estudo teve por objetivo avaliar a genotoxicidade da poluição atmosférica (PM2,5 e NO2) e sua correlação com modificações no perfil de metilação das citocinas IL-10 e TNF-alfa, em trabalhadores da cidade de São Paulo/SP ocupacionalmente expostos. Participaram deste estudo 57 indivíduos do gênero masculino, com idades variando entre 28 e 66 anos de idade, trabalhadores em turnos diários de atividades externas na cidade de São Paulo e, portanto, ocupacionalmente expostos à poluição atmosférica. Foram recrutadas 3 categorias de profissionais: 1) controladores de tráfego (n=18); 2) taxistas (n=21) e profissionais do Instituto Florestal (n=18). Esses trabalhadores foram divididos em dois grupos em função dos locais de trabalho e exposição: 1) grupo área urbana (AU), composto pelos controladores de tráfego e taxistas e 2) grupo área periurbana (APU), composto pelos profissionais do Instituto Florestal. Amostradores individuais de poluição atmosférica foram utilizados para a coleta dos poluentes PM2,5 e NO2. A análise da genotoxicidade foi realizada pelo teste de micronúcleos nas células epiteliais da mucosa oral e em linfócitos do sangue periférico. O perfil de metilação das citocinas IL-10 e TNFalfa foi realizado por sequenciamento de nova geração. Nossos resultados mostraram uma diferença na concentração do PM2,5 entre os grupos (AU=32,92?g.m-3, APU=25,77ug.m-3; p=0,0311). Não foi encontrada diferença na concentração de NO2 entre os grupos. Foram encontradas diferenças nas frequências de micronúcleos, tanto em mucosa oral (AU=2,78%, APU=1,16%; p < 0,0001) quanto em linfócitos periféricos (AU=1,51%, APU=0,73%; p < 0,0001). Também foi encontrada diferença na metilação média do gene IL-10 entre os grupos (AU=25%, APU=30%; p=0,0120). Não foi encontrada diferença na metilação média do gene TNF-alfa entre os grupos. Concluímos que os trabalhadores da área urbana da cidade estão expostos a maiores concentrações de PM2,5, possuem maiores frequências de micronúcleos tanto em células da mucosa oral quanto em linfócitos periféricos e apresentam um perfil de hipometilação do gene IL-10 em comparação com os trabalhadores da área periurbana da cidade / The problems of air pollution affect all major urban centers, particularly megacities with populations greater than 10 million. Vehicular and industrial emissions stand out among the main responsible for the high concentrations of air pollutants in these urban centers. The different components of air pollution, the dose and time of exposure, can lead to different impacts on human health. This study aimed to evaluate the genotoxicity of air pollution (PM2,5 and NO2) and its correlation with changes in the methylation profile of the cytokines IL-10 and TNF-alpha in workers of São Paulo/SP occupationally exposed. The study included 57 male individuals, with age range between 28 and 66 years old, workers in daily shifts of outdoor activities in the São Paulo city and therefore occupationally exposed to air pollution. Were recruited professional of three categories: 1) traffic controllers (n=18); 2) taxi drivers (n=21) and professionals from the Forestry Institute (n=18). These workers were divided into two groups according to workplaces and exposure: 1) urban area group (UA), composed of traffic controllers and taxi drivers and 2) peri-urban area group (PUA), composed of professionals from the Forestry Institute. Individual samplers of air pollution were used for the collection of PM2,5 and NO2 pollutants. The analysis was performed by genotoxicity micronucleus test in the buccal mucosa epithelial cells and in peripheral blood lymphocytes. The methylation profile of the cytokines IL-10 and TNF-alpha was done by next generation sequencing. Our results showed a difference in PM2,5 concentration between the groups (UA=32,92ug.m-3, PUA=25,77ug.m-3; p=0,0311). No difference was found in NO2 concentrations between groups. Differences were found in the frequency of micronuclei in both buccal mucosa (UA=2,78%, PUA=1,16%; p < 0,0001) and in peripheral lymphocytes (UA=1,51%, PUA=0,73%; p < 0.0001). Difference was also found in average methylation of the IL-10 gene between the groups (UA=25%, PUA=30%; p=0,0120). There was no difference in the average methylation of TNF-alpha gene between the groups. We conclude that the workers of the urban area of the city are exposed to higher concentrations of PM2,5, have higher frequencies of micronuclei in both the buccal mucosa cells and in peripheral lymphocytes and have a hypomethylation profile of IL-10 gene in comparison with workers the peri-urban area of the city

Le mélanome est un cancer très agressif en raison de sa capacité rapide à former des métastases et de développer une résistance aux traitements existants.
 MITF (Micropthalmia-associated Transcription Factor) est un facteur de transcription clé à toutes les étapes de développement du lignage mélanocytaire et dans la physiopathologie du mélanome. Afin de comprendre les mécanismes impliqués dans la régulation de l’activité et de la stabilité de MITF, nous avons identifié ses partenaires protéiques parmi lesquels figurent de nombreuses sous-unités des complexes de remodelage de la chromatine ATP-dépendant PBAF et NURF. Ce travail caractérise le rôle et l’étendue de la coopération entre BRG1/PBAF et plusieurs facteurs de transcription clés tels que MITF et SOX10 dans le fonctionnement des cellules de mélanome, qui recrutent activement de BRG1 à la chromatine et contribuent ainsi à la mise en place de la signature épigénétique caractéristique des cellules de mélanome prolifératives. Par ailleurs, l’utilisation de différents modèles murins a permis de révéler in vivo la contribution fonctionnelle distincte mais complémentaire de ces deux complexes de remodelage associé à MITF aux cours de trois stades majeurs du lignage mélanocytaire : le développement embryonnaire des mélanocytes, leur différentiation ainsi que lors de l’initiation et la progression du mélanome. Ce travail contribue ainsi à une meilleure compréhension du fonctionnement biologique des mélanocytes, du mélanome et du remodelage de la chromatine chez les eucaryotes. / Malignant melanoma is the most deadly form of skin cancer due to its quick metastatic spread and the development of resistance to available treatments.
MITF (Micropthalmia-associated Transcription Factor) is a transcription factor and master regulator of melanocyte lineage development and melanoma physiopathology. In order to investigate the mechanisms involved in the regulation of MITF activity and stability, we identified its numerous partners by tandem affinity purification coupled to mass spectrometry, which include several subunits of the PBAF and NURF ATP-dependant chromatin remodelling complexes. The present work characterizes the role and extent of cooperation between BRG1/PBAF and several key transcription factors including MITF and SOX10 in melanoma cell function, that actively recruit BRG1 to chromatin to establish the epigenetic landscape of proliferative melanoma cells. Furthermore, using different mouse models we revealed the distinct but complementary functional contribution of these two MITF-associated chromatin remodelers in vivo at three majors stages of melanocyte lineage development: embryonic development of melanocytes, their differentiation and during melanomagenesis. Thus, this work contributes to a better understanding of processes regulating the biological function of melanocytes, melanoma and more widely chromatin remodelling events in eukaryotes.

Os problemas da poluição atmosférica atingem todos os grandes centros urbanos, em particular as megacidades com população maior do que 10 milhões de habitantes. Emissões veiculares e industriais destacam-se entre as principais responsáveis pelas altas concentrações de poluentes do ar nesses centros urbanos. Os diferentes componentes da poluição atmosférica, a dose e o tempo de exposição, podem levar a diversos impactos na saúde humana. Esse estudo teve por objetivo avaliar a genotoxicidade da poluição atmosférica (PM2,5 e NO2) e sua correlação com modificações no perfil de metilação das citocinas IL-10 e TNF-alfa, em trabalhadores da cidade de São Paulo/SP ocupacionalmente expostos. Participaram deste estudo 57 indivíduos do gênero masculino, com idades variando entre 28 e 66 anos de idade, trabalhadores em turnos diários de atividades externas na cidade de São Paulo e, portanto, ocupacionalmente expostos à poluição atmosférica. Foram recrutadas 3 categorias de profissionais: 1) controladores de tráfego (n=18); 2) taxistas (n=21) e profissionais do Instituto Florestal (n=18). Esses trabalhadores foram divididos em dois grupos em função dos locais de trabalho e exposição: 1) grupo área urbana (AU), composto pelos controladores de tráfego e taxistas e 2) grupo área periurbana (APU), composto pelos profissionais do Instituto Florestal. Amostradores individuais de poluição atmosférica foram utilizados para a coleta dos poluentes PM2,5 e NO2. A análise da genotoxicidade foi realizada pelo teste de micronúcleos nas células epiteliais da mucosa oral e em linfócitos do sangue periférico. O perfil de metilação das citocinas IL-10 e TNFalfa foi realizado por sequenciamento de nova geração. Nossos resultados mostraram uma diferença na concentração do PM2,5 entre os grupos (AU=32,92?g.m-3, APU=25,77ug.m-3; p=0,0311). Não foi encontrada diferença na concentração de NO2 entre os grupos. Foram encontradas diferenças nas frequências de micronúcleos, tanto em mucosa oral (AU=2,78%, APU=1,16%; p < 0,0001) quanto em linfócitos periféricos (AU=1,51%, APU=0,73%; p < 0,0001). Também foi encontrada diferença na metilação média do gene IL-10 entre os grupos (AU=25%, APU=30%; p=0,0120). Não foi encontrada diferença na metilação média do gene TNF-alfa entre os grupos. Concluímos que os trabalhadores da área urbana da cidade estão expostos a maiores concentrações de PM2,5, possuem maiores frequências de micronúcleos tanto em células da mucosa oral quanto em linfócitos periféricos e apresentam um perfil de hipometilação do gene IL-10 em comparação com os trabalhadores da área periurbana da cidade / The problems of air pollution affect all major urban centers, particularly megacities with populations greater than 10 million. Vehicular and industrial emissions stand out among the main responsible for the high concentrations of air pollutants in these urban centers. The different components of air pollution, the dose and time of exposure, can lead to different impacts on human health. This study aimed to evaluate the genotoxicity of air pollution (PM2,5 and NO2) and its correlation with changes in the methylation profile of the cytokines IL-10 and TNF-alpha in workers of São Paulo/SP occupationally exposed. The study included 57 male individuals, with age range between 28 and 66 years old, workers in daily shifts of outdoor activities in the São Paulo city and therefore occupationally exposed to air pollution. Were recruited professional of three categories: 1) traffic controllers (n=18); 2) taxi drivers (n=21) and professionals from the Forestry Institute (n=18). These workers were divided into two groups according to workplaces and exposure: 1) urban area group (UA), composed of traffic controllers and taxi drivers and 2) peri-urban area group (PUA), composed of professionals from the Forestry Institute. Individual samplers of air pollution were used for the collection of PM2,5 and NO2 pollutants. The analysis was performed by genotoxicity micronucleus test in the buccal mucosa epithelial cells and in peripheral blood lymphocytes. The methylation profile of the cytokines IL-10 and TNF-alpha was done by next generation sequencing. Our results showed a difference in PM2,5 concentration between the groups (UA=32,92ug.m-3, PUA=25,77ug.m-3; p=0,0311). No difference was found in NO2 concentrations between groups. Differences were found in the frequency of micronuclei in both buccal mucosa (UA=2,78%, PUA=1,16%; p < 0,0001) and in peripheral lymphocytes (UA=1,51%, PUA=0,73%; p < 0.0001). Difference was also found in average methylation of the IL-10 gene between the groups (UA=25%, PUA=30%; p=0,0120). There was no difference in the average methylation of TNF-alpha gene between the groups. We conclude that the workers of the urban area of the city are exposed to higher concentrations of PM2,5, have higher frequencies of micronuclei in both the buccal mucosa cells and in peripheral lymphocytes and have a hypomethylation profile of IL-10 gene in comparison with workers the peri-urban area of the city

Comme tous les ciliés, P. tetraurelia réarrange son génome à chaque génération sexuelle pendant le développement de son macronoyau somatique ¿ partir du micronoyau germinal. Les réarrangements incluent l’excision précise de courtes séquences dérivant de transposons et appelés IES (Internal Eliminated Sequences) dont la majorité sont intragéniques. L’excision d’une fraction d’entre elles dépend de petits ARN maternels (appelés scnARN) qui sont produits à partir de tout le génome germinal pendant la méiose. Ce mécanisme pose un problème lors d’une conjugaison entre deux souches présentant des polymorphismes d’insertion : une cellule sera théoriquement incapable d’exciser une IES portée par l’allèle paternel reçu si cette IES est absente de l’allèle maternel ou si la séquence est trop divergente. Mes résultats montrent cependant que les allèles paternels divergents sont correctement excisés en utilisant les scnARN produit par la cellule paternelle. Dans le cas d’un polymorphisme absence/présence, l’IES que j’ai étudié est excisée chez 70 % des hétérozygotes F1, également via les scnARN paternels. Nous avons exploré deux hypothèses pour expliquer comment ils pouvaient agir. Il pourrait s’agir d’une programmation précoce des noyaux gamétiques ou alors d’un échange cytoplasmique des scnARN. Finalement, j’ai montré qu’un défaut de scnARN maternels n’est pas une cause possible de dysgénésie hybride. Cependant, 30 % des hétérozygotes F1 présentent une rétention variable de l’IES étudié via un mécanisme inconnu. Si cela est généralisable à toutes les IES homozygotes, alors ce mécanisme aurait un effet délétère sérieux sur les F1 et pourrait contribuer à l’isolement reproductif. / Like all ciliates, P. tetraurelia entirely rearranges its genome during development of the somatic macronucleus from the germline micronucleus, in each sexual generation. Rearrangements include the precise excision of IESs (Internal Eliminated Sequences), single-copy intervening sequences likely derived from transposon insertions. At least for a fraction of IESs, correct excision, which is required to reconstitute functional genes in the macronucleus, is thought to depend on their recognition by Piwi-bound small RNAs (called scnRNAs) produced from the maternal germline genome during meiosis. This raises a problem during conjugation between strains presenting insertion polymorphisms: a cell will be theoretically unable to excise an IES from the incoming (paternal) allele if that IES is absent from the maternal allele, or if its sequence is too divergent. Our results, however, indicate that divergent paternal alleles are correctly rearranged, using scnRNAs produced by the paternal cell. In the case of an absence/presence polymorphism, the IES we studied is excised in 70% of heterozygotes, also using paternal scnRNAs. We explored two hypotheses to explain how they can act. It could be either an early programming of the gametic nuclei or through cytoplasmic exchange of scnRNAs. My results seem to favor the latter. Overall, I showed that the lack of maternal scnRNAs is not a possible cause of hybrid dysgenesis. However, 30% of heterozygous F1 display a variable retention of the IES through an unknown mechanism. If this is true for all hemizygous IESs then it will have a strong deleterious effect on hybrid F1s and may contribute to reproductive isolation.

Orientador: Doris Hissako Matsushita / Banca: Maria Aparecida Visconti / Banca: Flávia Lombardi Lopes / Banca: Joel Claudio Heimann / Banca: Fernando Yamamoto Chiba / Resumo: Atualmente, está bem estabelecido que o ambiente fetal está ligado à saúde materna, e estímulos ou agressões anormais durante a vida intra-uterina podem resultar em mudanças na fisiologia e metabolismo da prole, aumentando o risco de doenças na vida adulta, este fenômeno é conhecido como programação fetal. Alterações na metilação do DNA e expressão gênica são consideradas mecanismos moleculares responsáveis por esta programação. Estudos anteriores demonstraram que a doença periodontal (DP) materna promove resistência insulínica, aumento nas concentrações plasmáticas de citocinas, redução do conteúdo de GLUT4 e do seu índice de translocação para membrana plasmática em sua prole adulta. E citocinas, como por exemplo, o TNF-α, têm sido relacionadas com a redução da expressão de GLUT4 por meio da ativação do fator de transcrição nuclear κappa B (NF-κB). Além disso, esta citocina pode estimular algumas serinas quinases, incluindo IκB quinase (IKK), c-Jun amino-terminal kinase (JNK) e quinases reguladas por sinais extracelulares (ERKs) que estão envolvidas na resistência insulínica. Tais achados evidenciam a necessidade de realizar mais estudos para verificar os mecanismos envolvidos nestas alterações. Portanto, os objetivos do presente estudo foram avaliar em ratos adultos, proles de ratas com DP: 1) glicemia e insulinemia; 2) expressão do RNAm da proteína transportadora de glicose GLUT4 e do IRS1 em muscular esquelético gastrocnêmio (MG); 3) o grau de metilação do DNA na região p... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: It is well establishedthat the fetal environment is linked to maternal health, and abnormal stimuli or aggressions during intrauterine life can result in changes in the physiology and metabolism of offspring, increasing the risk of disease in adult life, this phenomenon is known as fetal programming. Changes in DNA methylation and gene expression are considered molecular mechanisms responsible for this programming. Previous studies have demonstrated that maternal periodontaldisease (PD) promotes insulin resistance, increased plasma concentrations of cytokines, reduced GLUT4 content and its plasma membrane translocation index in its adult offspring. And cytokines, such as TNF-α, have been linked to reduced GLUT4 expressionthrough the activation of nuclear transcription factor kappa B (NF-κB). In addition, this cytokine can stimulate some serine kinases including IκB kinase (IKK), c-Jun amino-terminal kinase (JNK) and extracellular signal-regulated kinases (ERKs)that are involved in insulin resistance. These findings evidenced the need for further studies to verify the mechanisms involved in these changes. Therefore, the objectives of the present study were to evaluate in adult rats, offspring of rats with PD: 1) birth weight and during the75 days of age;2) glycemia and insulinemia; 3) GLUT4 and IRS1mRNA expression in skeletal muscle gastrocnemius (MG); 4) the degree of DNA methylation in the promoter region of the GLUT4 gene in MG; 5) phosphorylation of JNK, IKKα/β, ERK 1/2, N... (Complete abstract click electronic access below) / Doutor

<p>Pancreatic endocrine tumors (PETs) may cause typical syndromes of hormone excess, or appear clinically non-functioning without hormonal symptoms. PETs occur sporadically, in association with the multiple endocrine neoplasia type 1 (MEN1) syndrome, or rarely the von Hippel-Lindau syndrome. Molecular genetic investigations may reveal pathways important for tumor development, and be of clinical use.</p><p>The aim of this thesis was to investigate regulation of different genes involved in cell proliferation, and relate findings to signs of malignancy in PETs.</p><p>The MEN1 gene on chromosome 11q13 was mutated in three out of eleven sporadic malignant PETs. Two nonsense mutations, causing truncation of the protein, and one missense mutation were found.</p><p>Relation of allelic loss at 11q13 and 3p25 to malignant behavior was observed in sporadic PETs. Allelic loss at 18q21 was found in a subset of sporadic and MEN1-associated PETs, and mutation analysis of Smad4 excluded a tumor suppressor gene function.</p><p>In PETs with allelic loss on chromosome 3p25, mutation analysis of WNT7A and HDAC11 excluded function as tumor suppressor genes.</p><p>Menin, encoded by the MEN1 gene, was reported to regulate expression of the cyclin-dependent kinase inhibitors CDKN2C/p18, CDKN1B/p27, and CDKN2B/p15 in mouse pancreatic islet tumor models. Here, the mRNA expression of these genes was not related to MEN1 gene mutations in human PETs.</p><p>Cyclin-dependent kinase 4 (CDK4) and the protooncogene c-Myc were found to be overexpressed regardless of MEN1 gene mutational status of the PETs. The CDK4 gene was neither amplified nor mutated. Targeting of CDK4 may present an alternative to traditional chemotherapy of PETs in the future.</p>

Pancreatic endocrine tumors (PETs) may cause typical syndromes of hormone excess, or appear clinically non-functioning without hormonal symptoms. PETs occur sporadically, in association with the multiple endocrine neoplasia type 1 (MEN1) syndrome, or rarely the von Hippel-Lindau syndrome. Molecular genetic investigations may reveal pathways important for tumor development, and be of clinical use. The aim of this thesis was to investigate regulation of different genes involved in cell proliferation, and relate findings to signs of malignancy in PETs. The MEN1 gene on chromosome 11q13 was mutated in three out of eleven sporadic malignant PETs. Two nonsense mutations, causing truncation of the protein, and one missense mutation were found. Relation of allelic loss at 11q13 and 3p25 to malignant behavior was observed in sporadic PETs. Allelic loss at 18q21 was found in a subset of sporadic and MEN1-associated PETs, and mutation analysis of Smad4 excluded a tumor suppressor gene function. In PETs with allelic loss on chromosome 3p25, mutation analysis of WNT7A and HDAC11 excluded function as tumor suppressor genes. Menin, encoded by the MEN1 gene, was reported to regulate expression of the cyclin-dependent kinase inhibitors CDKN2C/p18, CDKN1B/p27, and CDKN2B/p15 in mouse pancreatic islet tumor models. Here, the mRNA expression of these genes was not related to MEN1 gene mutations in human PETs. Cyclin-dependent kinase 4 (CDK4) and the protooncogene c-Myc were found to be overexpressed regardless of MEN1 gene mutational status of the PETs. The CDK4 gene was neither amplified nor mutated. Targeting of CDK4 may present an alternative to traditional chemotherapy of PETs in the future.

Major Histocompatibility Complex Class-II (MHC-II) molecules are critical regulators of adaptive immunity that present extracellular antigens required to activate CD4+ T cells. MHC-II are regulated at the level of transcription by master regulator, the Class II Transactivator (CIITA), whose association with the MHC-II promoter is necessary to initiate transcription. Recently, much research focused on novel mechanisms of transcriptional regulation of critical genes like MHC-II and CIITA; findings that the macromolecular complex of the 26S-proteasome is involved in transcription have been perhaps the most exciting as they impart novel functions to a well studied system. Proteasome is a multi-subunit complex composed of a 20S-core particle capped by a 19S-regulatory particle. The 19S contains six ATPases which are required for transcription initiation and elongation. We demonstrate that 19S ATPase-S6a inducibly associates with CIITA promoters. Decreased expression of S6a negatively impacts recruitment of the transcription factors STAT-1 and IRF-1 to the CIITA due to significant loss in histone H3 and H4 acetylation. S6a is robustly recruited to CIITA coding regions, where S6a binding coordinates with that of RNA polymerase II. RNAi mediated S6a knockdown significantly diminishes recruitment of Pol II and P-TEF-b components to CIITA coding regions, indicating S6a plays important roles in transcriptional elongation. Our research is focused on the ways in which accessibility to and transcription of DNA is regulated. While cancers are frequently linked to dysregulated gene expression, contribution of epigenetics to cancers remains unknown. To achieve metastatic ability, tumors alter gene expression to escape host immunosurveilance. MHC-II and CIITA expression are significantly downregulated in highly metastatic MDA-MB-435 breast cancer cells. This suppression correlates with elevated levels of the silencing modification H3K27me3 at CIITA and a significant reduction in Pol II recruitment. We observe elevated binding of the histone methyltransferase to CIITApIV and demonstrate this enzyme is a master regulator of CIITA gene expression. EZH2 knockdown results in significant increases in CIITA and MHC-II transcript levels in metastatic cells. In sum, transcriptional regulation by the 19S-proteasome and histone modifying enzymes represents novel mechanisms of control of mammalian gene expression and present novel therapeutic targets for manipulating MHC expression in disease.

Le fonctionnement du cortex cérébral nécessite l’action coordonnée de deux des sous-types majeurs de neurones, soient les neurones à projections glutamatergiques et les interneurones GABAergiques. Les interneurones GABAergiques ne constituent que 20 à 30% des cellules corticales par rapport au grand nombre de neurones glutamatergiques. Leur rôle est toutefois prépondérant puisqu’ils modulent fortement la dynamique et la plasticité des réseaux néocorticaux. Il n’est donc pas surprenant que les altérations de développement des circuits GABAergiques soient associées à plusieurs maladies du cerveau, incluant l’épilepsie, le syndrome de Rett et la schizophrénie. La compréhension des mécanismes moléculaires régissant le développement des circuits GABAergiques est une étape essentielle menant vers une meilleure compréhension de la façon dont les anormalités se produisent. Conséquemment, nous nous intéressons au rôle de l’acide polysialique (PSA) dans le développement des synapses GABAergiques. PSA est un homopolymère de chaînons polysialylés en α-2,8, et est exclusivement lié à la molécule d’adhésion aux cellules neuronales (NCAM) dans les cerveaux de mammifères. PSA est impliqué dans plusieurs processus développementaux, y compris la formation et la plasticité des synapses glutamatergiques, mais son rôle dans les réseaux GABAergiques reste à préciser. Les données générées dans le laboratoire du Dr. Di Cristo démontrent que PSA est fortement exprimé post- natalement dans le néocortex des rongeurs, que son abondance diminue au cours du développement, et, faits importants, que son expression dépend de l’activité visuelle i et est inversement corrélée à la maturation des synapses GABAergiques. La présente propose de caractériser les mécanismes moléculaires régulant l’expression de PSA dans le néocortex visuel de la souris. Les enzymes polysialyltransférases ST8SiaII (STX) et ST8SiaIV (PST) sont responsables de la formation de la chaîne de PSA sur NCAM. En contrôlant ainsi la quantité de PSA sur NCAM, ils influenceraient le développement des synapses GABAergiques. Mon projet consiste à déterminer comment l’expression des polysialyltransférases est régulée dans le néocortex visuel des souris durant la période post-natale; ces données sont à la fois inconnues, et cruciales. Nous utilisons un système de cultures organotypiques dont la maturation des synapses GABAergiques est comparable au modèle in vivo. L’analyse de l’expression génique par qPCR a démontré que l’expression des polysialyltransférases diminue au cours du développement; une baisse majeure corrélant avec l’ouverture des yeux chez la souris. Nous avons de plus illustré pour la première fois que l’expression de STX, et non celle de PST, est activité-dépendante, et que ce processus requiert l’activation du récepteur NMDA, une augmentation du niveau de calcium intracellulaire et la protéine kinase C (PKC). Ces données démontrent que STX est l’enzyme régulant préférentiellement le niveau de PSA sur NCAM au cours de la période post-natale dans le cortex visuel des souris. Des données préliminaires d’un second volet de notre investigation suggèrent que l’acétylation des histones et la méthylation de l’ADN pourraient également contribuer à la régulation de la transcription de cette enzyme durant le développement. Plus d’investigations seront toutefois nécessaires afin de confirmer cette hypothèse. En somme, la connaissance des mécanismes par lesquels l’expression des ii polysialyltransférases est modulée est essentielle à la compréhension du processus de maturation des synapses GABAergiques. Ceci permettrait de moduler pharmacologiquement l’expression de ces enzymes; la sur-expression de STX et/ou PST pourrait produire une plus grande quantité de PSA, déstabiliser les synapses GABAergiques, et conséquemment, ré-induire la plasticité cérébrale. / The functioning of the cerebral cortex requires coordinated action of two major neuronal subtypes - the glutamatergic projection neurons and the GABAergic interneurons. GABAergic interneurons represent 20 to 30% of all cortical cells. Even though they are a minor cell population in the cerebral cortex compared to glutamatergic neurons, they are key modulators of network dynamics and plasticity of neocortical circuits. It is therefore not surprising that aberrant development of GABAergic circuits is implicated in many neurodevelopmental disorders including epilepsy, Rett syndrome and schizophrenia. Understanding the molecular mechanisms governing the development of GABAergic inhibitory synapses in neocortex is important towards a better comprehension of how abnormalities in this developmental process can occur. Therefore, we focus specifically on the role of polysialic acid (PSA) in the development of GABAergic synapses. PSA is a α-2,8 polysialylated homopolymer, which is exclusively linked to the Neural Cell Adhesion Molecule (NCAM) in the mammalian brain. It is involved in several developmental processes including formation and plasticity of glutamatergic synapses; however its role in GABAergic circuit formation has not been explored so far. Previously in Dr Di Cristo’s lab, we showed that PSA is strongly expressed post-natally and its expression steadily declines during development in mice neocortex. We also showed that the developmental and activity-dependant regulation of PSA expression is inversely correlated with the maturation of perisomatic GABAergic innervation. Our aim is to characterize the molecular mechanisms regulating PSA expression in mouse iv visual cortex during post-natal development. Two polysialyltransferases, ST8SiaII (STX) and ST8SiaIV (PST), are responsible for PSA attachment to NCAM. By controlling the amount of PSA on NCAM, they can influence GABAergic synapses development. The mechanisms regulating STX and PST expression is crucial but remain still unknown. My research project focused on the mechanisms regulating STX and PST transcription in the mouse postnatal cortex. We used an organotypic culture system, which recapitulates many aspects of GABAergic synapse maturation as observed in vivo. Polysialyltransferases transcript levels were measured by qPCR and showed that STX and PST mRNA levels steadily decline during post-natal development in the mouse cortex; the sharpest reduction in the expression of both enzymes correlate with eye opening. We further demonstrate for the first time that STX mRNA levels is activity-dependant, requires the activation of NMDA receptors, an increase in intracellular Calcium levels and is PKC-dependent. Altogether, we show that the regulation of the expression of STX is the main mechanism responsible for PSA expression levels in the cortex around eyes opening. We next investigated whether epigenetic mechanisms regulate STX transcription and preliminary data suggest that histone acetylation and DNA methylation may contribute to STX expression during development. However, further experiments are required to confirm this hypothesis. In summary, understanding the mechanisms modulating STX and PST expression in the neocortex is essential for the comprehension of their precise role in GABAergic synapse maturation. This knowledge could allow us to modulate pharmacologically the expression of these enzymes; in turn overexpression of STX and PST may re-induce PSA expression, thereby destabilizing GABAergic synapses, and ultimately facilitating cortical plasticity in the adult.

In this thesis, I first focused on the testing of the hypothesis of the mechanotransductive activation of the apical accumulation of Myosin-II (Myo-II) that leads to Drosophila embryos mesoderm invagination, in response to the active cell apex pulsations preceding gastrulation in the mesoderm. This hypothesis was proposed on the basis of previous experiments realized in my host lab, having consisted in the rescue of mesoderm invagination in pulsation and invagination defective mutants, in response to a simple mechanical indent of the mesoderm. Here I demonstrated quantitatively the plausibility of such mechanical trigger of the active apical accumulation of Myo-II leading to subsequent mesoderm invagination, in response to the mechanical strains developed by the endogenous pulsative movements of mesoderm cell apexes, in silico. In a second part, I tested experimentally the role of the mechanical strains developed by the very first morphogenetic movements of zebrafish (Danio rerio) and Drosophila embryos, in the early specification of mesoderm cells identity. Specifically, to test this hypothesis, I developed magnetic biophysical tools to mimic the epiboly morphogenetic movements in epiboly defective zebrafish embryos. We found the beta-catenin (B-cat) Y667 phosphorylation as the common mechano-transductive pathway involved in earliest mesoderm genes expression notail and twist respectively, in response to the very first morphogenetic movements of embryogenesis in both species, epiboly and mesoderm invagination, respectively. This allowed to suggest such mechanotransduction pathway as conserved from the last common ancestor of both species, namely the last common ancestor of bilaterians, therefore possibly involved in the origins of mesoderm emergence in the ancestor, which represents a currently important opened question of evo-devo. In a third part, I developed experiments of mechanical indent of Drosophila embryos germ cells, and demonstrated the production of generational heritable developmental defects induced on at least 3 generations. These experiments suggest accidental mechanical perturbation of germ cells as a putative new motor mode of heritable modulations in the genetic developmental program of embryogenesis, with the molecular mechanism underlying such transmission being currently in progress.