Fig. 4. Increase in proliferation with cell-cell contact is mediated by intracellular, not intercellular, tension.

(A) Fluorescence image of actin stress fibers and inset illustration of a “mixed” pair of cells containing an untreated cell (top) and a cell expressing RhoN19 (bottom). The “X” in the inset indicates expression of RhoN19. (B) Graph of the percentage of cells within mixed pairs that exhibited more stress fibers than their paired neighbor. Darker shading (inset illustrations) indicates the cell that was counted for each bar. (C) Graph of BrdU incorporation in single cells, in pairs of cells, and in mixed pairs of cells containing one untreated and one RhoN19 expressing cell. For mixed pairs, untreated and RhoN19 expressing cells were counted separately. Darker shading (inset illustrations) indicates the cell that was counted for each bar. (D) Immunofluorescence images of β-catenin in single and paired cells. As indicated, cells were either untreated, transfected with RhoN19, or mixed pairs containing one untreated and one RhoN19 expressing cell. In the mixed pair, the upper and lower cells are untreated and RhoN19 expressing, respectively. Dotted white lines indicate the borders of the wells. Error bars are standard error with (*) p<0.05 and (**) p<0.001 versus untreated control by t-test. Scale bars are 10 µm.