Autor(es):
Marques, Luís Fernando Rosa Portela 
Data: 2007
Identificador Persistente: http://hdl.handle.net/10451/1178
Origem: Repositório da Universidade de Lisboa
Assunto(s): Embriologia animal; Histologia; Teses de mestrado
Descrição
Tese de mestrado em Biologia (Biologia Evolutiva e do Desenvolvimento), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2007 We have previously shown (Bajanca, et al. 2006) that disrupting the binding of the α6ß1 integrin from the laminin extracellular matrix in the mouse epaxial dermomyotome using a blocking antibody (GoH3) causes ectopic activation of the myogenic regulatory factor Myf5. It was proposed that, under normal circumstances, this integrin - extracellular matrix disengagement activates Myf5 during myogenesis in vivo as myogenic precursor cells delaminate from the epaxial lip of the dermomyotome to the myotomal space. The process by which this occurs is still unknown. In this work, we test the hypothesis that it may be mediated by the PI3K/Akt pathway, previously shown to transduce α6ß1 signaling (Nho, et al. 2005, Xia, et al. 2004). The PI3K/Akt pathway converges with canonical Wnt signaling, enabling ß-catenin mobilization to the nucleus, where it promotes transcription. Using C2C12 myoblasts and E9.5 and E10.5 mouse embryo explants in conditions in which we activated or inhibited the PI3K/Akt pathway, we addressed whether this pathway effectively regulates Myf5 expression downstream of α6ß1 signaling. We discovered that in C2C12 cells in which we artificially activated the PI3K/Akt pathway, Myf5 was upregulated; in embryo explant cultures, Myf5 was not upregulated, but was ectopically expressed in the dermomyotome, an effect similar to the one observed when α6ß1 laminin binding was blocked. Inhibition of PI3K/Akt both in C2C12 cells and in explants caused severe downregulation of Myf5 expression. We also discovered that PI3K/Akt inhibition increases proliferation in embryo explants cultures, possibly caused by a blockade of the myogenic program, as cells are kept in a proliferative, undifferentiated state. We propose that the PI3K/Akt pathway specifically transducing differentiation promoting signals downstream of α6ß1 integrin-ECM disengagement, which enables the onset of Myf5 expression and the first steps of the myogenic program during mouse epaxial Resumo alargado disponível em português
