Cell Cortex and germlayer formation in zebrafishgastrulation

Differences in tissue surface tension influence germ layer formation during zebrafish gastrulation (Schötz et al., 2008). We have previously shown that differential actomyosin-mediated tension of the cell cortex plays a critical role in the establishment of differential germ layer tissue surface tension, and consequently progenitor cell segregation and germ layer formation (Krieg et al., 2008). However, the molecular and cellular mechanisms by which cell cortex tension is regulated in the different germ layer progenitor cell types during cell aggregation, and the specific contribution of cortex tension to tissue surface tension and ultimately germ layer formation is still unclear. Using a combination of cell biological, genetic, and biophysical experiments, we will analyze how different components of the cytoskeletal and adhesion apparatus control progenitor cell cortex tension, how cortex tension is remodeled during cell-cell contact formation, and how contact formation affects progenitor cell-cell contact strength and germ layer tissue surface tension. We expect that these experiments will provide novel insight into the molecular and cellular mechanisms by which cell cortex tension controls germ layer formation during gastrulation.

In this project we have investigated to role of the cell cortex in germ layer progenitor cell segregation, migration and germ layer formation. To analyse these processes, we undertook a interdisciplinary approach using techniques and methods from developmental biology, cell biology and biophysics. In addition, we collaborated with physicists to develop mathematical models of key aspects of our work. The results of our work provided novel insight into the role of the cell cytoskeleton in controlling cell sorting and cell migration in the early zebrafish embryo. Specifically, we showed that cell sorting is driven by differences in the ability of cells to modulate the cell cytoskeleton at cell-cell contact sites (Maitre et al., Science, 2012). Furthermore, we demonstrated that enhancing cell contractility transforms cells within the early embryo into extremely fast migrating amoeboid cells, which we named stable-bleb cells (Ruprecht at al., Cell, 2015). These findings point at a critical role of the cell cytoskeleton, and in particular the actin-myosin cell cortex, for determining the ability of early embryonic cells to undergo efficient sorting and migration, two key processes by which the embryo takes shape.