Notch signalling dynamics during mouse development and homeostasis

Abstract

In this thesis we investigate the Notch signalling pathway, which is known to play a crucial role in embryonic development and tissue homeostasis. A key component of this pathway is the Hes1 protein, regulating cell proliferation and differentiation. By studying the dynamics of Hes1 expression, the role of the Notch pathway in tissue formation across different contexts can be uncovered. To do this, a new Hes1-Achilles mouse model was created, in which the Hes1 protein is endogenously coupled with a fluorescent protein. This enables real-time visualization of Hes1 expression at single-cell resolution, which was not possible before. Thus, by generating this model, the study of Hes1 dynamics in living tissues is made possible, offering insights into how cells behave during development and homeostasis. We first examined Hes1 dynamics in the presomitic mesoderm (PSM) and preneural tube (pre-NT) of the mouse embryonic tail, where single-cell resolution enabled detailed analysis of cell-specific behaviour. We wanted to do this, because each cell type may respond differently to signalling cues, revealing diverse regulatory mechanisms. Indeed, our results showed synchronized oscillations in PSM cells and irregular differentiation-linked oscillations in pre-NT cells. Furthermore, Notch inhibition significantly altered Hes1 expression patterns in a cell-type-dependent manner. The role of the Notch pathway was also studied in the small intestine, where a gradient of Hes1 expression was uncovered in the crypts. In addition, oscillations with periods of 90, 130, and 170 minutes suggest that Hes1 dynamics contribute to tissue patterning and homeostasis. How these dynamics regulate stem cell behaviour, can now be explored in further studies.