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Genes Hox e a padronização do esqueleto axial
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Os genes Hox são considerados os “motores” da padronização antero-posterior nos Bilatéria. Nos Vertebrados, estes factores de transcrição desempenham um papel essencial no desenvolvimento do esqueleto axial. As proteínas Hox dos grupos parálogos 6 e 10 encontram-se envolvidas no desenvolvimento da região torácica e lombar, respectivamente, através da ligação ao enhancer H1 dos genes Myf5 e MYf6 que permite regular a expressão destes no miótomo hipaxial. Apesar de os genes Hox apresentarem elevada especificidade funcional in -vivo, as análises da sequência do homeodomínio revelaram-se insuficientes para explicar esta especificidade. Este trabalho teve como um dos seus objectivos, avaliar o impacto de uma variação nucleotídica nas sequências alvo das proteínas Hox dos enhancers H1 da cobra e do elefante na padronização do esqueleto destes animais. Os dados obtidos fornecem indicações de que esta variação é importante para a padronização dos esqueletos da cobra e do elefante, dado que as proteínas Hoxa10 têm reduzida afinidade para o enhancer H1 da cobra e do elefante. Os nossos resultados mostram também que Hoxb6 forma um complexo com Pax3 com capacidade de ligação ao enhancer H1 de ratinho, uma capacidade não partilhada por Hoxa10. Surpreendentemente, apesar de Hoxb6 não ser capaz de ligar-se individualmente ao enhancer H1 da cobra e do elefante, é capaz de ligar-se a este enhancer em forma de complexo com Pax3. À semelhança de Hoxb6, Hoxb9 apresenta também capacidade de ligação ao enhancer H1 em complexo com Pax3. O segundo objectivo deste trabalho consistiu no estudo de possíveis assinaturas moleculares das proteínas Hox10 e Hox6. Os dados obtidos demonstraram que os resíduos treonina e serina do motivo NWLTAKSG de Hoxa10 são necessários para a ligação destas proteínas ao enhancer H1. Ainda não foram obtidos dados acerca da relevância do motivo YPWM e da linker region para a função das proteínas Hox6.
Hox genes are considered the main “engines” of bilaterian anterior-posterior patterning. In vertebrates, these transcription factors play a central role in axial skeleton development. Hox proteins of the groups 6 and 10 are involved in the development of the thoracic and lumbar regions, respectively, through their binding to the H1 enhancer which regulates Myf5 and Myf6 expression in the hypaxial myotome. Although Hox genes have a high functional specificity in -vivo, sequence analysis of the homeodomain fail to explain this specificity. In this work, one of the main goals was to study the possible relevance of a nucleotide variation in the Hox binding site present in the H1 enhancer of snakes and elephants for skeletal patterning in these animals. We show that this might indeed be the case, as Hoxa10 binds with very low affinity to H1 enhancer of snake and elephant. We also show that Hoxb6, but not Hoxa10, binds to the mouse H1 enhancer as a complex with Pax3. On its own, Hoxb6 also presented low affinity for the H1 enhancer of snake and elephant, but it was able to bind this enhancer as a complex with Pax3. Similar to Hoxb6, Hoxb9 also forms a complex with Pax3 able to bind to the mouse H1 enhancer. The second objective of this work was to study possible molecular signatures of Hox10 and Hox6 proteins. The analysis of Hoxa10 proteins with mutations in their NWLTAKSG motif showed that the threonine and serine residues of this motif are necessary for high affinity binding of Hoxa10 to the H1 enhancer. Until now, there’s no data concerning the importance of the YPWM and linker region of Hoxb6 for its patterning function.
Hox genes are considered the main “engines” of bilaterian anterior-posterior patterning. In vertebrates, these transcription factors play a central role in axial skeleton development. Hox proteins of the groups 6 and 10 are involved in the development of the thoracic and lumbar regions, respectively, through their binding to the H1 enhancer which regulates Myf5 and Myf6 expression in the hypaxial myotome. Although Hox genes have a high functional specificity in -vivo, sequence analysis of the homeodomain fail to explain this specificity. In this work, one of the main goals was to study the possible relevance of a nucleotide variation in the Hox binding site present in the H1 enhancer of snakes and elephants for skeletal patterning in these animals. We show that this might indeed be the case, as Hoxa10 binds with very low affinity to H1 enhancer of snake and elephant. We also show that Hoxb6, but not Hoxa10, binds to the mouse H1 enhancer as a complex with Pax3. On its own, Hoxb6 also presented low affinity for the H1 enhancer of snake and elephant, but it was able to bind this enhancer as a complex with Pax3. Similar to Hoxb6, Hoxb9 also forms a complex with Pax3 able to bind to the mouse H1 enhancer. The second objective of this work was to study possible molecular signatures of Hox10 and Hox6 proteins. The analysis of Hoxa10 proteins with mutations in their NWLTAKSG motif showed that the threonine and serine residues of this motif are necessary for high affinity binding of Hoxa10 to the H1 enhancer. Until now, there’s no data concerning the importance of the YPWM and linker region of Hoxb6 for its patterning function.
Descrição
Tese de mestrado. Biologia (Biologia Evolutiva e do Desenvolbimento). Universidade de Lisboa, Faculdade de Ciências, 2011
Palavras-chave
Biologia molecular Genes Hox Esqueleto Teses de mestrado - 2011