Cell-Substrate Dynamics of the Epithelial-to-Mesenchymal Transition.

The biological process of the epithelial-to-mesenchymal transition (EMT) allows epithelial cells to enhance their migratory and invasive behavior and plays a key role in embryogenesis, fibrosis, wound healing, and metastasis. Among the multiple biochemical changes from an epithelial to a mesenchymal phenotype, the alteration of cellular dynamics in cell-cell as well as cell-substrate contacts is crucial. To determine these variations over the whole time scale of the EMT, we measure the cell-substrate distance of epithelial NMuMG cells during EMT using our newly established metal-induced energy transfer (MIET) microscopy, which allows one to achieve nanometer axial resolution. We show that, in the very first hours of the transition, the cell-substrate distance increases substantially, but later in the process after reaching the mesenchymal state, this distance is reduced again to the level of untreated cells. These findings relate to a change in the number of adhesion points and will help to better understand remodeling processes associated with wound healing, embryonic development, cancer progression, or tissue regeneration.

Reduction in E-cadherin expression fosters migration of Xenopus laevis primordial germ cells.

The transition from passive to active migration of primordial germ cells in Xenopus embryos correlates with a reduction in overall adhesion to surrounding endodermal cells as well as with reduced E-cadherin expression. Single cell force spectroscopy, in which cells are brought into brief contact with a gold surface functionalized with E-cadherin constructs, allows for a quantitative estimate of functional E-cadherin molecules on the cell surface. The adhesion force between migratory PGCs and the cadherin-coated surface was almost identical to cells where E-cadherin was knocked down by morpholino oligonucleotides (180 pN). In contrast, non-migratory PGCs display significantly higher adhesion forces (270 pN) on E-cadherin functionalised surfaces. On the basis of these observations, we propose that migration of PGCs in Xenopus embryos is regulated via modulation of E-cadherin expression levels, allowing these cells to move more freely if the level of E-cadherin is reduced.

Tension monitoring during epithelial-to-mesenchymal transition links the switch of phenotype to expression of moesin and cadherins in NMuMG cells.

Structural alterations during epithelial-to-mesenchymal transition (EMT) pose a substantial challenge to the mechanical response of cells and are supposed to be key parameters for an increased malignancy during metastasis. Herein, we report that during EMT, apical tension of the epithelial cell line NMuMG is controlled by cell-cell contacts and the architecture of the underlying actin structures reflecting the mechanistic interplay between cellular structure and mechanics. Using force spectroscopy we find that tension in NMuMG cells slightly increases 24 h after EMT induction, whereas upon reaching the final mesenchymal-like state characterized by a complete loss of intercellular junctions and a concerted down-regulation of the adherens junction protein E-cadherin, the overall tension becomes similar to that of solitary adherent cells and fibroblasts. Interestingly, the contribution of the actin cytoskeleton on apical tension increases significantly upon EMT induction, most likely due to the formation of stable and highly contractile stress fibers which dominate the elastic properties of the cells after the transition. The structural alterations lead to the formation of single, highly motile cells rendering apical tension a good indicator for the cellular state during phenotype switching. In summary, our study paves the way towards a more profound understanding of cellular mechanics governing fundamental morphological programs such as the EMT.