Figure 2.

Mechanical anisotropy and changes in BM stiffness affect tissue shape. (a,b) A spherical tissue undergoing uniform growth/expansion can elongate through different mechanisms: (a) by creating a stiffness anisotropy and/or (b) by creating a stiffness gradient. The schematic in the box shows the cross-section of the spherical tissue consisting of BM (grey), epithelia (pink) and a central region (yellow) that is either a lumen (e.g. in spheroids) or is filled by cells (e.g. in the Drosophila egg chamber). (c) A change in BM composition can occur through a change in the levels of existing BM components or synthesis of additional components (darker lines in the right panels). Two scenarios can happen: the new material can increase the density of the network and keep the thickness constant (i), or increase the thickness of the network without changing density (ii). (d) A change in BM cross-linking can affect the connectivity of the network. (e) A uniformly growing spherical tissue is sculpted into a specific shape through local BM degradation. Local protease activity (orange circle) facilitates local bud formation and expansion.