Figure 2.

Experimental examples of cyclic motility processes that are tied to mechanosensing. In panels a–c, the cyclic apical contractions of Drosophila epithelial cells are shown as adapted from Martin et al. (2009). In panel a, the rates of change in the apical areas of 40 cells are color coded and show seemingly stochastic contractions. The rate of change in the area of one cell (marked by the red arrow in panel a) is plotted versus time to show that the contractions are brief and are followed by periods of stasis during which time mechanosensing as well as consolidation of the contraction occurs (panel b). The outlines of the cells also show that the contraction of one cell is not correlated with the motility of its neighbors (panel c). Since the transient contractions continue until the epithelium has achieved the proper curvature, there must be a sensory process that will signal the cell to activate further contractions (C) or stop (S) contractions and to go on to the next phase in development. In panels d and e, the spreading of a fibroblast on glass is documented. In panel d, the rate of edge movement is noted by the color code for the whole edge of a mouse embryo fibroblast spreading on fibronectin (FN)-coated glass. The kymographs in panel e show that the designated area of the edge moves in an oscillatory fashion while undergoing net spreading, shown in the bottom-left and bottom-right images of panel e, along with the boxed area that was used for the kymograph. Panel e adapted from Giannone et al. (2007).