Studying a contractile actomyosin network underlying larval epithelial cell behaviour coordination during Drosophila abdominal morphogenesis
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During animal development, cells undergo various behaviours, such as migration and shape change, which need to be coordinated. How this coordination is achieved is still elusive. During morphogenesis of the adult abdominal epidermis of Drosophila, the larval epithelial cells (LECs) are replaced by the adult histoblasts. The LECs migrate directedly and, subsequently, cease migration, constrict apically and die. Here, I use in vivo 4D microscopy to study the spatial and temporal organisation of the actomyosin cytoskeleton of LECs as a potential mechanism to coordinate migration and apical constriction. The analysis of LECs apical actomyosin network shows that are planar polarized during migration, undergoing pulsed contractions in the back of the cell, while protruding at the front. During constriction, the cytoskeleton of LECs displays radial polarity with contractions localising in the centre of the cell. Behavioural change, thus, involves a change in the polarity of the contractile network. The properties of the contractile network are further studied manipulating actomyosin contractility by interfering with Rho kinase and Myosin phosphatase. The results show that the regulation of Myosin activation not only impacts on the contractility of the network but also on the network’s dynamics and the cell’s behaviour. A loss-of-function analysis of several Rho-GEFs, the activators of the Rho GTPases, is performed to study the molecular mechanisms that underlie the behavioural change. The depletion of individual RhoGEFs identifies 5 genes involved in the regulation of specific aspects of cell migration and the apical constriction of LECs. Altogether, the results suggest that cytoskeletal architecture and autonomous network dynamics underlie the behaviour of the contractile network. The results furthermore suggest that pulsed contractions, along with the cortical actomyosin network, underlie behavioural change, being one of the force generation mechanisms that orchestrate abdominal morphogenesis.
Thesis, PhD Doctor of Philosophy
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