Remodelling of the extracellular matrix (ECM) occurs during embryonic development, asexual reproduction and tissue regeneration. However, the processes by which ECM dynamics contribute to the establishment of tissue shape and function are poorly understood. Roland Aufschnaiter, Xiaoming Zhang and colleagues (p. 4027) now show that, instead of simply providing a static substrate for cell movement, the ECM acts as a dynamic tissue component that influences growth and morphogenesis in epithelial tissues. They employ the freshwater polyp Hydra – a simple metazoan that consists of an epithelial double layer separated by an intervening ECM, the mesoglea – to track the fate of the ECM throughout the organism. By labelling collagen-1 and laminin with fluorescently tagged antibodies they show that the mesoglea is stable in the head region. By contrast, it is continuously displaced along the body column and towards the tips of tentacles in a movement that largely overlaps with that of epithelial cells. At the sites of bud evagination, however, the mesoglea is stretched and remodelled, which involves the site-specific degradation of laminin. In addition, during bud formation the cells move at different rates than the mesoglea. Taken together, these data highlight that the ECM carries out more dynamic functions than previously thought and can have different biological functions depending on its location.

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