Resumen de Expression and functional analysis of notch signalling during cardiac development with special focus on the epicardium and coronary vasculature
Gonzalo del Monte Nieto
The Notch pathway is a cell-to-cell signalling pathway conserved from invertebrates to humans. The pattern of Notch1 transcription during mouse embryonic development has been extensively characterized (Del Amo et al., 1992; Reaume et al., 1992; Weinmaster et al., 1991). However, Notch receptor activation depends on where the ligands are expressed and on the expression of proteins that modify the receptor, such as Fringe. In the first part of this PhD project we have shown that our staining method to detect the active Notch1 receptor (N1ICD) using the V1744 antibody is a useful tool for the comparative analysis of Notch1 activity and function during mouse development. We described in detail the expression pattern of N1ICD focusing our attention on the cardiovascular system. Even more, 3D reconstruction analysis confirmed the pattern described in 2D.
Trying to understand the restriction pattern showed by N1ICD in the endocardium, we carried out expression analysis of the Delta4 and Jagged1 ligands as well as Fringe genes during the early stages of cardiovascular development in order to determine which of them were responsible for the restriction of Notch1 activation. Our results show that the complex balance between these signalling and modifying elements regulate Notch1 activation.
Our expression analysis also showed that N1ICD is expressed in the coronary vessels, prompting us to study the expression and function of Notch in epicardial and coronary vessel development. The expression analysis of Notch elements determined that the pathway is present in all steps and cell types during epicardial linage development. Functional analysis using RBPJk standard mutants conclude that the Notch pathway inhibits cardiogenesis in the pericardial mesoderm region. Later in development, Notch ablation in the epicardial cell lineage disrupts coronary vessel development, specifically affecting the differentiation of arterial coronary endothelium and muscularization of the vessel wall. Loss of epicardial Notch signalling also impairs compact myocardium growth. Ectopic N1ICD expression impairs epicardium development affecting normal compact myocardium growth.
