Thesis (Ph. D.)--Case Western Reserve University, 2005. / [School of Medicine] Department of Genetics. Includes bibliographical references. Available online via OhioLINK's ETD Center.

Thesis (Ph. D. in Neuroscience)--Vanderbilt University, Aug. 2007. / Title from title screen. Includes bibliographical references.

No description available.

NEDD8, molécule de la famille de l’ubiquitine est essentielle au développement, à la croissance et à la viabilité d’un organisme, de plus c’est une cible prometteuse en thérapeutique. Nous avons découvert que l’inhibiteur spécifique de la NEDDylation, MLN4924 altère la morphologie sans fragmentation et augmente la surface du nucléole de cellules humaines et de noyaux de la lignée germinale de Caenorhabditis elegans. Une approche de protéomique quantitative (SILAC) combiné à l’analyse de la production des ARNr et des ribosomes montrent que MLN4924 change la composition protéique du nucléole sans affecter l’activité transcriptionnelle de l’ARN pol I. Notre analyse montre que MLN4924 active p53 par la voie RPL11/RPL5-Mdm2 caractéristique d’un stress du nucléole. Cette étude identifie le nucléole comme une cible intéressante dans l’utilisation d’inhibiteurs de la NEDDylation et apporte un nouveau mécanisme d’activation de p53 par inhibition de la voie NEDD8.Dans une seconde étude nous avons adapté la méthode de FLIM-FRET (« Fluorescence Lifetime Imaging Microscopy – Förster Resonance Energy Transfer ») à l’étude de la compaction de la chromatine à l’échelle du nanomètre dans un organisme vivant. Le nématode Caenorhabditis elegans s’est révélé être un modèle de choix. Au sein des chromosomes méiotiques, nous avons identifié différentes régions de compaction, de niveau variable par mesure du FRET entre histones fusionnées à des protéines fluorescentes. Par une approche originale d’ARN interférence et injection d’un « extra-chromosome » nous avons défini l’architecture à une nano-échelle de différents états de l’hétérochromatine et montré que cette organisation est contrôlée par les protéines HP1 « Heterochromatin Protein 1 » et SETDB1, une protéine « H3-Lysine 9 methyl transferase ». Nous avons également montré que la compaction de l’hétérochromatine est dépendante des condensines I et II et plus particulièrement la condensine I contrôle l’état faiblement compacté de la chromatine.Nos travaux ont confirmé que C. elegans est un modèle d’intérêt majeur pour l’étude des compartiments nucléaires et parfaitement adapté pour des études pré-clinique. / The ubiquitin-like molecule NEDD8 is conserved and essential for viability, growth and development; its activation pathway is a promising target for therapeutic intervention. We found that the small molecule inhibitor of NEDDylation, MLN4924, alters the morphology and increases the surface size of the nucleolus in human cells and Caenorhabditis elegans germ cells in the absence of nucleolar fragmentation. Through SILAC proteomic analysis and rRNA production, processing and ribosome profiling, we show that MLN4924 changes the composition of the nucleolar proteome but does not inhibit RNA Pol I transcription. Further analysis demonstrates that MLN4924 activates the p53 tumour suppressor through the RPL11/RPL5-Mdm2 pathway, with characteristics of nucleolar stress. The study identifies the nucleolus as a target of the NEDDylation pathway and provides a mechanism for p53 activation upon NEDD8 inhibition.Then we adapted a quantitative FRET (Förster resonance energy transfer)-based fluorescence lifetime imaging microscopy (FLIM) approach to assay the nano-scale chromatin compaction in a living organism, the nematode Caenorhabditis elegans. By measuring FRET between histone-tagged fluorescent proteins, we visualized distinct chromosomal regions and quantified the different levels of nanoscale compaction in meiotic cells. Using RNAi and repetitive extrachromosomal array approaches, we defined the heterochromatin state and showed that its architecture presents a nanoscale-compacted organization controlled by Heterochromatin Protein-1 (HP1) and SETDB1 H3-lysine-9 methyl-transferase homologs in vivo. Next, we functionally explored condensin complexes. We found that condensin I and condensin II are essential for heterochromatin compaction and that condensin I additionally controls lowly compacted regions. Our data show that, in living animals, nanoscale chromatin compaction is controlled not only by histone modifiers and readers but also by condensin complexes.We confirm that C. elegans is an interesting model to study nuclear signalling and perfectly adapt to be a platform for pre-clinical studies.

De acordo com dados da Organização Mundial da Saúde (OMS) estimam-se que os agrotóxicos causam anualmente 70 mil intoxicações agudas e crônicas que evoluem para óbito. Dentre eles, o paraquat (PQ) é o que apresenta maior taxa de mortalidade, sendo responsável por cerca de 13% de todos os casos registrados, principalmente devido a falta de um tratamento efetivo. O principal mecanismo de toxicidade proposto está associado ao ciclo redox do PQ, onde ocorre a formação de espécies reativas (ERs) de oxigênio e nitrogênio, levando ao estresse oxidativo (EO). Na literatura há relatos do uso de antioxidantes para casos de intoxicação do PQ. Dessa maneira, nesse trabalho avaliou-se o uso de melatonina associada a nanocápsulas de núcleo lipídico (Mel-LNC) na proteção contra os danos causados pelo PQ, uma vez que o uso da nanotecnologia melhorou a atividade antioxidante dessa molécula. Para tal utilizou-se o sistema in vitro, linhagem celular de adenocarcinoma pulmonar (A549), e o modelo alternativo in vivo, Caenorhabditis elegans. Mel-LNC e nanocápsulas de núcleo lipídico (LNC) foram preparadas de acordo com o método de deposição do polímero pré-formado. Ambas as formulações foram caracterizadas avaliando tamanho de partícula, potencial zeta e pH, e para Mel-LNC foram determinadas a concentração de melatonina e porcentagem de encapsulação. Os resultados encontrados estão de acordo com os parâmetros já validados para essas formulações. Foi possível verificar que as formulações MEL-LNC e LNC se mantiveram estáveis nos meios de cultura utilizados nos ensaios in vitro e in vivo. No estudo in vitro foi observado que o tratamento com ambas as formulações não causaram diminuição da viabilidade nem dano de DNA na linhagem celular utilizada. Além disso, foi verificado a internalização da Mel-LNC utilizando-se a formulação marcada com rodamina B, sendo possível verificar uma intensa fluorescência vermelha ao redor do núcleo da célula. O pré-tratamento com Mel-LNC foi capaz de aumentar a viabilidade celular e diminuir o dano oxidativo de DNA causado pelo paraquat após 24 horas de exposição, porém isso não ocorreu quando as células foram pré-tratadas com melatonina livre. No estudo com o modelo alternativo C. elegans, foi utilizada uma formulação de Mel-LNC marcada com rodamina B (Mel-LNC-RoB), a fim de verificar a absorção dessa formulação pelo nematoide. Foi possível observar que a internalização da Mel-LNC no C. elegans ocorre principalmente pela via oral, uma vez que se verificou uma intensa fluorescência no intestino do nematoide após o tratamento com a Mel-LNC-RoB e após três horas, essa fluorescência se distribuiu pelo restante do corpo, apresentando inúmeros pontos de fluorescência fora do intestino. Com relação à avaliação do efeito protetor nesse modelo alternativo in vivo, pode-se inferir que o pré-tratamento com Mel-LNC aumentou a sobrevida, diminuiu a produção de espécies reativas (ERs) e manteve o desenvolvimento normal dos nematoides após a exposição ao PQ, sendo que isso não foi verificado quando os mesmos foram pré-tratados com melatonina livre. Além disso, verificou-se que as nanocápsulas de núcleo lipídico (LNC) são seguras para o uso no modelo C. elegans, uma vez que apresentou alto valor para a dose letal 50 (DL50), e alterações no desenvolvimento e produção de ERs somente ocorreram em doses mais elevadas que as utilizadas em nossos experimentos. Dessa maneira, a formulação de Mel-LNC mostrou-se um promissor candidato para estudos futuros nos casos de intoxicação por paraquat. / According to estimations by World Health Organization (WHO), pesticides are responsible for 70 thousand acute intoxication cases that lead to death per year. Among these compounds, paraquat (PQ) presents the highest mortality rate, about 13% of all registered cases, especially for the lack of effective treatment. The major mechanism of toxicity proposed is associated to its redox cycle, in which oxygen and nitrogen reactive species (RS) are generated culminating in oxidative stress (OS). Some reports in the literature support the use of antioxidants for PQ intoxication cases. The present study aimed to evaluate the use of melatonin-loaded lipid-core nanocapsules (Mel-LNC) in the protection against PQ-induced damages, considering that nanotechnology has improved the antioxidant activity of this molecule. For this purpose, an in vitro system composed by lung adenocarcinoma (A549) cell line, and the in vivo alternative model of Caenorhabditis elegans have been utilized. Mel-LNC and unloaded lipid-core nanocapsules were prepared by self-assembly and characterized by particle sizing, zeta potential and pH, and for Mel-LNC formulation it was determined the drug content and encapsulation efficiency. The results are in agreement with the parameters already validated for these formulations. It was possible verify that Mel-LNC and LNC formulations remained stable in the culture medium utilized in in vitro and in vivo experiments. Results from in vitro studies showed that none of the formulations induced reduction in cell viability or DNA damage in treated cells. Besides, it was observed the internalization of Mel-LNC marked with rhodamine B, showing an intense red fluorescence around the cell nucleus. Pretreatment with Mel-LNC was able to enhance cell viability and diminish DNA oxidative damage caused by paraquat after 24h exposure, which could not be observed when cells were pretreated with Mel. In the study with the alternative model C. elegans, a rhodamine (Ro)-linked Mel-LNC formulation was prepared in order to assess the absorption of the formulation by the nematode. Mel-LNC uptake in C. elegans was found to occur mainly by the oral route, once an intense fluorescence was observed in the intestine after treatment with Mel-LNC-RoB, which after 3h distributed to the rest of the body, presenting numerous fluorescence dots outside the intestine. In relation to the evaluation of protection with the in vivo alternative model, results indicate that pretreatment with Mel-LNC increased survival rate, reduced the production of reactive species and maintained the normal development of nematodes after paraquat exposure, while the same observations were not found after pretreatment with free melatonin. In addition, the lipid-core nanocapsules (LNC) were found to be safe in the C. elegans model, due to its high lethal dose (LD50) value, and development alterations and RS production only occurred in the higher doses than those utilized in our experiments. Therefore, the Mel-LNC formulation demonstrated to be a promising candidate for future studies aiming treatment of paraquat intoxication cases.

De acordo com dados da Organização Mundial da Saúde (OMS) estimam-se que os agrotóxicos causam anualmente 70 mil intoxicações agudas e crônicas que evoluem para óbito. Dentre eles, o paraquat (PQ) é o que apresenta maior taxa de mortalidade, sendo responsável por cerca de 13% de todos os casos registrados, principalmente devido a falta de um tratamento efetivo. O principal mecanismo de toxicidade proposto está associado ao ciclo redox do PQ, onde ocorre a formação de espécies reativas (ERs) de oxigênio e nitrogênio, levando ao estresse oxidativo (EO). Na literatura há relatos do uso de antioxidantes para casos de intoxicação do PQ. Dessa maneira, nesse trabalho avaliou-se o uso de melatonina associada a nanocápsulas de núcleo lipídico (Mel-LNC) na proteção contra os danos causados pelo PQ, uma vez que o uso da nanotecnologia melhorou a atividade antioxidante dessa molécula. Para tal utilizou-se o sistema in vitro, linhagem celular de adenocarcinoma pulmonar (A549), e o modelo alternativo in vivo, Caenorhabditis elegans. Mel-LNC e nanocápsulas de núcleo lipídico (LNC) foram preparadas de acordo com o método de deposição do polímero pré-formado. Ambas as formulações foram caracterizadas avaliando tamanho de partícula, potencial zeta e pH, e para Mel-LNC foram determinadas a concentração de melatonina e porcentagem de encapsulação. Os resultados encontrados estão de acordo com os parâmetros já validados para essas formulações. Foi possível verificar que as formulações MEL-LNC e LNC se mantiveram estáveis nos meios de cultura utilizados nos ensaios in vitro e in vivo. No estudo in vitro foi observado que o tratamento com ambas as formulações não causaram diminuição da viabilidade nem dano de DNA na linhagem celular utilizada. Além disso, foi verificado a internalização da Mel-LNC utilizando-se a formulação marcada com rodamina B, sendo possível verificar uma intensa fluorescência vermelha ao redor do núcleo da célula. O pré-tratamento com Mel-LNC foi capaz de aumentar a viabilidade celular e diminuir o dano oxidativo de DNA causado pelo paraquat após 24 horas de exposição, porém isso não ocorreu quando as células foram pré-tratadas com melatonina livre. No estudo com o modelo alternativo C. elegans, foi utilizada uma formulação de Mel-LNC marcada com rodamina B (Mel-LNC-RoB), a fim de verificar a absorção dessa formulação pelo nematoide. Foi possível observar que a internalização da Mel-LNC no C. elegans ocorre principalmente pela via oral, uma vez que se verificou uma intensa fluorescência no intestino do nematoide após o tratamento com a Mel-LNC-RoB e após três horas, essa fluorescência se distribuiu pelo restante do corpo, apresentando inúmeros pontos de fluorescência fora do intestino. Com relação à avaliação do efeito protetor nesse modelo alternativo in vivo, pode-se inferir que o pré-tratamento com Mel-LNC aumentou a sobrevida, diminuiu a produção de espécies reativas (ERs) e manteve o desenvolvimento normal dos nematoides após a exposição ao PQ, sendo que isso não foi verificado quando os mesmos foram pré-tratados com melatonina livre. Além disso, verificou-se que as nanocápsulas de núcleo lipídico (LNC) são seguras para o uso no modelo C. elegans, uma vez que apresentou alto valor para a dose letal 50 (DL50), e alterações no desenvolvimento e produção de ERs somente ocorreram em doses mais elevadas que as utilizadas em nossos experimentos. Dessa maneira, a formulação de Mel-LNC mostrou-se um promissor candidato para estudos futuros nos casos de intoxicação por paraquat. / According to estimations by World Health Organization (WHO), pesticides are responsible for 70 thousand acute intoxication cases that lead to death per year. Among these compounds, paraquat (PQ) presents the highest mortality rate, about 13% of all registered cases, especially for the lack of effective treatment. The major mechanism of toxicity proposed is associated to its redox cycle, in which oxygen and nitrogen reactive species (RS) are generated culminating in oxidative stress (OS). Some reports in the literature support the use of antioxidants for PQ intoxication cases. The present study aimed to evaluate the use of melatonin-loaded lipid-core nanocapsules (Mel-LNC) in the protection against PQ-induced damages, considering that nanotechnology has improved the antioxidant activity of this molecule. For this purpose, an in vitro system composed by lung adenocarcinoma (A549) cell line, and the in vivo alternative model of Caenorhabditis elegans have been utilized. Mel-LNC and unloaded lipid-core nanocapsules were prepared by self-assembly and characterized by particle sizing, zeta potential and pH, and for Mel-LNC formulation it was determined the drug content and encapsulation efficiency. The results are in agreement with the parameters already validated for these formulations. It was possible verify that Mel-LNC and LNC formulations remained stable in the culture medium utilized in in vitro and in vivo experiments. Results from in vitro studies showed that none of the formulations induced reduction in cell viability or DNA damage in treated cells. Besides, it was observed the internalization of Mel-LNC marked with rhodamine B, showing an intense red fluorescence around the cell nucleus. Pretreatment with Mel-LNC was able to enhance cell viability and diminish DNA oxidative damage caused by paraquat after 24h exposure, which could not be observed when cells were pretreated with Mel. In the study with the alternative model C. elegans, a rhodamine (Ro)-linked Mel-LNC formulation was prepared in order to assess the absorption of the formulation by the nematode. Mel-LNC uptake in C. elegans was found to occur mainly by the oral route, once an intense fluorescence was observed in the intestine after treatment with Mel-LNC-RoB, which after 3h distributed to the rest of the body, presenting numerous fluorescence dots outside the intestine. In relation to the evaluation of protection with the in vivo alternative model, results indicate that pretreatment with Mel-LNC increased survival rate, reduced the production of reactive species and maintained the normal development of nematodes after paraquat exposure, while the same observations were not found after pretreatment with free melatonin. In addition, the lipid-core nanocapsules (LNC) were found to be safe in the C. elegans model, due to its high lethal dose (LD50) value, and development alterations and RS production only occurred in the higher doses than those utilized in our experiments. Therefore, the Mel-LNC formulation demonstrated to be a promising candidate for future studies aiming treatment of paraquat intoxication cases.

L’acquisition d'une identité cellulaire différenciée est souvent considérée comme définitive et figée dans le temps; or un nombre croissant d’études démontre que les cellules différenciées peuvent faire preuve de plasticité sous certaines conditions. Afin de mieux comprendre ces phénomènes, notre laboratoire a établi un modèle unique chez Caenorhabditis elegans (C. elegans) permettant l’étude d’un événement de transdifférenciation dans un contexte physiologique à l'échelle de cellules uniques. Au cours du développement, une cellule épithéliale du rectum de C. elegans, nommé Y, va migrer antérieurement puis changer d’identité pour devenir un motoneurone nommé PDA. Les travaux préliminaires du laboratoire ont montré que la voie de signalisation LIN-12/Notch est le signal le plus précoce nécessaire pour le bon déroulement de la transdifférenciation de Y en PDA. Nous avons pu mettre en évidence : i) que lors de l’embryogénèse, deux ligands canoniques (apx-1 et lag-2) semblent agir de façon redondante afin d’activer la voie Notch. ii) l’activation ectopique et contrôlée de la voie Notch est suffisante pour induire la formation d’un second neurone PDA. iii) Les facteurs nucléaires que le laboratoire a identifiés comme cruciaux pour l'initiation de cet évènement de TD sont également importants pour la reprogrammation induite de cette deuxième cellule en neurone PDA par l'activation ectopique de Notch. iv) La suractivation prolongée de la voie Notch dans la cellule Y maintien l’identité épithéliale de cette dernière, ayant pour conséquence le blocage de la transdifférenciation de Y en PDA. L’ensemble de nos résultats montrent que la voie Notch est nécessaire et suffisante afin d’établir la compétence à transdifférencier et que cela ne peut être réalisé que si la voie Notch est régulée de façon très précise dans la cellule Y. / The acquisition of a differentiated cell identity is often considered as final and frozen in time. However, a growing number of studies showed that differentiated cells can exhibit plasticity under certain conditions. To better understand these cell plasticity phenomena, our laboratory has developed a unique model in Caenorhabditis elegans (C. elegans) to study a transdifferentiation event in a physiological context and at the single-cell level. During the worm development, an epithelial rectal cell, named Y, will migrate anteriorly and change its identity to become a neuron named PDA. Preliminary work performed by our laboratory showed that the LIN-12/Notch signalling pathway is the earliest signal necessary for the proper conduct of the transdifferentiation of Y into PDA. In our study, we showed that: i) during embryogenesis, two canonical ligands (apx-1 and lag-2) appear to act redundantly to activate the Notch pathway in Y. ii) ectopic and controlled activation of the Notch pathway is sufficient to induce formation of a second PDA neuron. iii) Nuclear factors indentified in our laboratory as crucial for the initiation of this event are also important for transdifferentiation of the second PDA obtained by ectopic activation of Notch. iv) A prolonged activation of the Notch pathway in the Y cell maintains its epithelial identity, which results in the inhibition of the transdifferentiation of Y into PDA. Together, our results showed that the Notch pathway is necessary and sufficient to establish the competence to transdifferentiate. This can only be achieved if the Notch pathway is regulated very precisely in the Y cell.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Sementes de Platypodium elegans Vogel, pertencente à FamÃlia Fabaceae, subfamÃlia Papilionoideae, Tribo Dalbergiae possui uma lectina Manose/Glicose ligante. Na purificaÃÃo da lectina em estudo, o extrato total de sementes de P. elegans preparado em NaCl 0,15M teve sua fraÃÃo hemaglutinante isolada por cromatografia de afinidade em quitina, trocas iÃnica em DEAE-Sephacel e em HiTrap SP, essa Ãltima acoplada a HPLC. As fraÃÃes ativas para atividade hemaglutinante obtidas sequencialmente nesses procedimentos foram avaliados quanto à sua atividade especÃfica e homogeneidade em SDS-PAGE. A lectina em seu Ãltimo passo de purificaÃÃo apresentou massa molecular aparente de 55 kDa. A fraÃÃo prÃ-purificada ativa obtida em DEAE-Sephacel foi caracterizada quanto ao seu potencial termiticida e fungicida. A atividade termiticida contra operÃrios e soldados de Nasutitermes corniger, induzindo 100% de mortalidade em ambas as classes, foram melhor visualizadas com as concentraÃÃes 1,0 e 0,8mg/mL, entre 8 e 9 dias para operÃrios e 7 e 8 dias para soldados, onde ainda nÃo se havia registrado menos que 50% de mortalidade no controle negativo. A fraÃÃo testada nÃo apresentou efeito repelente. Em relaÃÃo à atividade fungicida, 20 ug da fraÃÃo chegou a inibir consideravelmente Fusarium lateritium (33%), F. oxysporum (19,4%) e F. solani (14,3%). F. decemcellulare teve uma inibiÃÃo de 4,8% e F. moniliforme, 3,3%. Essas duas atividades reforÃam a participaÃÃo dessa lectina na defesa vegetal, fazendo-a uma potente ferramenta biotecnolÃgica a ser mais profundamente investigada e estudada em relaÃÃo a seu papel na defesa vegetal e na potencial utilizaÃÃo na resistÃncia de madeiras susceptÃveis a cupins. / Seeds of Platypodium elegans Vogel, belonging to the Fabaceae family, Papilionoideae sub-family, Dalbergiae Tribe, posses a specific mannose/glucose lectin. In the purification of the lectin in study, the total extract of seeds of P. elegans prepared in NaCl 0,15M had its active fraction isolated for affinity chromatography in chitin and exchange ionic chromatography in DEAE-Sephacel and HiTrap SP, this last one connected to the HPLC.The active fractions for hemmagutinant activity gotten in these procedures had been sequentially about its specific activity and homogeneity in SDS-PAGE. The lectin in the last step of purification presented apparent molecular mass of 55 kDa. The active fraction from DEAE-Sephacel was characterized about its termiticidal and fungicidal potential. The termiticidal activity against laborers and soldiers of Nasutitermes corniger, inducing 100% of mortality in both the classrooms, was better visualized with the concentrations of 1,0 and 0,8mg/mL, between 8 and 9 days for laborers and 7 and 8 days for soldiers, where it had not been registered mortality less than 50% in the negative control. The tested fraction did not present repellent effect. In relation to the fungicidal activity, 20 ug of the fraction arrived to inhibit considerably Fusarium lateritium (33%), F. oxysporum (19.4%) and F. solani (14.3%). F. decemcellulare had a inhibition of 4,8% and F. moniliforme, 3.3%. These two activities strengthen the participation of this lectin in the vegetal defense, making it a powerful biotechnological tool to be more deeply investigated and studied about its paper in the vegetal defense and the potential use in the resistance of susceptible wood to termites.

No presente trabalho o gênero fóssil Bauruemys elegans é redescrito. Sua anatomia craniana e pós-craniana foi analisada em detalhes com base em novos exemplares coletados deste fóssil. Bauruemys elegans é um quelônio do Cretáceo Superior da Bacia Bauru, encontrado no Município de Pirapozinho, interior do estado de São Paulo e descrito originalmente por Suárez em 1969 como “Podocnemis elegans”. Os materiais analisados foram comparados com a osteologia de representantes atuais dos clados Chelidae, Pelomedusidae e Podocnemididae, bem como com descrições de outros táxons disponíveis na literatura. As relações filogenéticas de Bauruemys elegans dentro do clado Podocnemidinura foram analisadas através da análise de parcimônia envolvendo 19 táxons e 56 caracteres. Nesta análise Bauruemys elegans constitui, de fato, um gênero distinto entre os podocnemidídeos, corroborando propostas já descritas na literatura. A análise também revelou que, através dos caracteres osteológicos, Bauruemys elegans possui afinidades filogenéticas próximas aos podocnemidídeos atuais, posicionando-se como grupo-irmão do clado formado pelo fóssil Cambaremys langertoni e pela Família Podocnemididae. / In this study, the fossil Bauruemys elegans is redescribed. Its cranial and postcranial anatomy was analysed in detail based on new specimens collected. Bauruemys elegans is a chelonian from Upper Cretaceous of the Bauru Basin founded in the municipality of Pirapozinho, São Paulo state and was originally described by Suarez (1969) as Podocnemis elegans. The specimens analysed was compared with some extant representatives of Chelidae, Pelomedusidae and Podocnemididae families and descriptions avaliable on the literature. The phylogenetic affinities of the Bauruemys elegans within Podocnemidinura was evaluated through a parsimony analysis envolving 19 taxa and 56 characters. The results of phylogenetic analysis shows that Bauruemys elegans is, in fact, a distinct genus within the clade Podocnemididae. This corroborated anterior hypothesis proposed. Adittionally, this analysis using osteological characters, indicate Bauruemys elegans as the sister group of Cambaremys langertoni and Podocnemididae.

La transmission de l’information au niveau des synapses chimiques requiert la concentration de récepteurs appropriés face aux sites de libération des neurotransmetteurs. Afin d'identifier de nouveaux gènes impliqués dans la localisation synaptique des récepteurs de l’acétylcholine (RAChs), un crible génétique basé sur l'observation in vivo de ces récepteurs à la jonction neuromusculaire (JNM) de C. elegans a été conduit et a permis d’isoler 29 mutants. J’ai identifié des gènes candidats dans cinq lignées et la mutation causale dans trois autres en caractérisant 9 de ces mutants par séquençage de leur génome. Par ailleurs, l’analyse fonctionnelle de 2 autres des mutants nous a permis de mettre en évidence deux activités mobilisatrices des récepteurs très différentes. D’une part, nous avons mis en évidence le rôle déterminant d’isoformes de Ce-Punctine/MADD-4, sécrétées spécifiquement par les motoneurones cholinergiques et GABAergiques, dans le recrutement local des récepteurs appropriés à la membrane de la cellule musculaire. Chef d’orchestre de la transmission neuronale, la Punctine définit ainsi l’identité excitatrice ou inhibitrice des JNMs. D’autre part, nous avons montré que les RAChs extrasynaptiques normalement diffus à la membrane de la cellule musculaire s’agrègent en amas ectopiques dans un mutant du gène suppresseur de tumeurs rsu-1 (ras suppresseur 1). L’absence de RSU-1, protéine localisée aux sites d’adhésion focale en aval des intégrines, engendre une diminution des récepteurs synaptiques, ce qui met à jour un mécanisme actif prévenant l’agrégation illégitime des récepteurs extrasynaptiques et permettant d’assurer leur recrutement effectif à la synapse. / Chemical neurotransmission relies on the concentration of receptors in front of neurotransmitter release sites. To identify new genes involved in the synaptic localization of receptors, a genetic screen based on the in vivo visualization of acetylcholine receptors (AChRs) at the C. elegans neuromuscular junction (NMJ) was performed and twenty-nine mutants were retrieved. By whole genome sequencing of nine mutated lines, I identified candidate genes for five mutants and the causal mutation for three others. The functional analysis performed in parallel of two other mutants from the same screen revealed two novel and distinct activities that are required for the synaptic localization of AChRs. We evidenced the fundamental role of Ce Punctin/MADD-4 isoforms, which are specifically secreted by cholinergic and GABAergic motoneurons, in recruiting locally appropriate receptors at the muscle cell membrane. This showed that Punctin is a key factor specifying the excitatory or the inhibitory identity of NMJs and defined a new paradigm with isoforms from the same gene that promote specific post-synaptic domains assembly. The tumor suppressor gene rsu-1 (ras suppressor 1) is evolutionary conserved and encodes a protein localized at focal adhesion sites. In the absence of RSU-1, normally diffused extrasynaptic AChRs are found aggregated and the synaptic receptor content is diminished. This reveals that an RSU-1 dependent mechanism is required to maintain receptors dispersed in the extrasynaptic membrane, allowing for their proper recruitment at the synapse.