Figure 3. The extracellular matrix and tensional homeostasis in development.

In tissue and organ morphogenesis, mechanical forces generated by morphogenetic movements play an important part in gene expression by activating developmental biochemical signalling cascades⁴⁷. Embryogenesis provides an example of a multistage process that requires mechanical force, the subsequent localization of proteins, and biochemical signalling to work together. In this process, the cytoskeleton of the cells themselves has a key role in generating the contractile forces required for invagination, gastrulation, proliferation and differentiation^44,106. During the onset of gastrulation, an early phase of embryonic development in Drosophila melanogaster, actin filaments are contracted by non-muscle myosins. Compressive forces result in the ectopic expression of the transcription factor Twist (TWI)^54,107, which then directs significant changes in the shape of the developing embryo. When compressive forces (depicted by arrows in the schematic) are disrupted through the laser-ablation of dorsal cells (red region), there is a corresponding reduction in the level of mechanically induced TWI expression in the stomodeal primordium (white arrows) (ablated). Cell nuclei are visualized with a nuclear localization signal-tagged green fluorescent protein (NLS GFP) and immunofluorescence shows the distribution of TWI. Upon gentle compression of the stomodeal cells using a needle, TWI expression is restored in a mechanically induced mechanism (ablated, indented). Figure is modified, with permission, from REF. 54 (2008) Elsevier.