Participation of paraxis gene in Xenopus laevis somite development

SANCHEZ R.S.; SANCHEZ S.S.

Montevideo

Congreso; VI International Meeting of the Latin American of Developmental Biology; 2012

LASDB

In most vertebrates, the segmentation of the paraxial mesoderm involves the formation of metameric units called somites through a Mesenchymal-Epithelial Transition. However this morphogenetic process is different in the amphibian Xenopus laevis because it does not form an epithelial somite, it rather undergoes a complex cell rearrangement. The molecular mechanisms that control these cell behaviours underlying somite formation remain elusive. Paraxis is a bHLH transcription factor expressed in vertebrate paraxial mesoderm and in the somite. Studies in birds and mice demonstrate that this gene is required for the formation of epithelial somites. In the absence of paraxis, the axial skeleton and skeletal muscle form but are improperly patterned. To establish the role of paraxis in the Xenopus development, we carried out experiments of gain- and loss- of function by using a hormone-inducible construct and morpholino oligonucleotide respectively. In the analysis by Scanning Electron Microscope, we observed that both gain- and loss- of function approaches caused a disorganization of the somitic territory, with little compacted cells. The paraxial mesoderm was segmented but it was not as sharply demarcated as the intersomitic clefts seen in control side. We found that alterations in the expression levels of paraxis caused a decrease in the expression of molecular markers of cell adhesion and somitic differentiation. The defects in cell adhesion were confirmed by mesoderm explants experiments, in which the loss- of function of paraxis led to a decrease in the cell adhesion. These results suggest that paraxis plays an important role in the cell rearrangement during Presomitic to Somitic Transition in Xenopus laevis, possibly through the regulation of the cell adhesion.