Figure 4.

Emerging force measurement tools may allow mechanotransduction studies in 3D in vitro cell culture models. A) FRET complexes are inserted between the transmembrane domain and the cytoplasmic β-catenin binding domain of the cadherin molecule. The FRET signal is observable when the molecule is not under tension. Signal is absent when the FRET-containing cadherin is under tension. B) FRET index of MDCK epithelial cells expressing the tension sensitive FRET-cadherin (EcadTSMod) indicates cadherin molecules are under tension both at cell-cell junctions and in the free plasma membrane. This tension is lost when cells are treated with actin polymerization inhibitor, Cytochalasin B (Borghi et al., 2012). C) In vitro 3D cardiac microtissues. Immunofluorescence stainings of cytoskeletal and ECM proteins demonstrate cell alignment and cell-cell and cell-ECM adhesions (i) F-actin (green), Fibronectin (Red), Tenascin-C (Yellow) (Legant et al., 2009). (ii) Troponin-T (red) and nuclei (blue). Scale bar: 10μm (Boudou et al., 2012). (iii) N-cadherin (red), α-actinin (green) and nuclei (blue). Scale bar: 20μm. D) (i) Histochemistry and (ii) immunofluorescence staining of a 3D in vitro skin model adapted to explore tumor cells migration. β-Gal expressing tumor cells line the top of an epithelium of human epidermal keratinocytes, which lies above a collagen matrix that contains dermal fibroblasts. β-catenin (red), β-gal (green) and nuclei (blue). E) (i) Bead displacement trajectories around a volume rendering of a 3T3 fibroblast spreading in a 3D hydrogel are color-coded by magnitude. Scale bar: 50 μm. (ii) Contour plot of the magnitude of traction forces exerted by the cell in one protrusion. Range of approximately 0 kPa (blue) to 2 kPa (red) of force (Legant et al., 2010).