Figure 3.

How cell growth impacts on tissue mechanics. (A) If a cell grows (red arrows) more than its neighbors, a mechanical stress is generated that results in increased pressure in the growing cell and the stretching of its neighbors (top). The stress disappears when the neighbors also grow until growth is spatially homogeneous (left). Other mechanisms that can dissipate the mechanical stress are cell exchange (see the green cells in the middle), and oriented divisions along the axis of stress (see the orange cells on the right). (B) Patterns of growth, such as growth heterogeneities or polarized growth, induce mechanical stresses in a tissue. Regional differences in tissue growth (left) may lead to mechanical stress in the tissue. Here, growth was symbolized by cell division, but it is indeed the volume increase that matters, not cell divisions. If more growth proceeds in the center of the tissue, and provided tissue is sufficiently elastic to prevent stress dissipation, this will result in a stretch of the periphery of the tissue. Oriented cell division (right) can lead to similar patterns of mechanical stress, provided they are accompanied by volume increase. (C) In a tissue with no preferred direction, cells are isotropic, and the average fit to an ellipse yields a circle (right). (C′) An external uniaxial mechanical stress (which may originate from neighboring regions) deforms cells along its axis (right: average fit to an ellipse is elongated). This stretch promotes orientation of cell divisions (red dividing cells on the schematic). (C″) As a result of the polarized growth, cells will at least partially lose their stretch (averaged fit to an ellipse is a circle). Thus, oriented cell divisions contribute to the dissipation of the mechanical stress that was imposed on the tissue.