Although ECM mechanical properties have been measured and manipulated in vitro in order to address their role during single-cell migration ( Lo et al., 2000 Paszek and Weaver, 2004 Reinhart-King et al., 2008 Roca-Cusachs et al., 2013), it is still unknown how BM mechanical properties change during the course of development to shape cells, organs or tissues. It is therefore essential to determine how BM mechanical properties vary in vivo during organ formation and to decipher the link between these properties and morphogenesis. BM mechanical properties have been shown to control cell migration in vitro and BM structure is modified by proteases during branching morphogenesis ( Daley and Yamada, 2013 Kai et al., 2016). All these roles depend on BM composition and structure, which in turn determine BM mechanical properties. BMs control epithelial morphogenesis by providing a physical scaffold to oppose the contractile forces generated by cell shape changes, by directing growth factor delivery and by regulating cell adhesion ( Hynes, 2014). For instance, epithelial sheets are found to be associated with basement membranes (BMs) and, importantly, epithelial morphogenetic processes that occur during development are known to be partly regulated by BMs. ECMs are specialised in the cells, organs or tissues with which they are associated. ECM proteins form a network that fills spaces between organs and mechanically supports them ( Hynes and Naba, 2012). Altogether, these results show that BM mechanical properties are modified during development and that, in turn, such mechanical modifications influence both cell and tissue shapes.Įxtracellular matrices (ECMs) are essential for the development of multicellular eukaryotic organisms ( Ozbek et al., 2010). We also demonstrate that interactions between BM constituents are necessary for cell flattening.
We prove that BM softens around the squamous cells and that this softening depends on the TGFβ pathway. Second, epithelial cells change their shape from cuboidal to either squamous or columnar. In addition, stiffness heterogeneity, due to oriented fibrils, is important for egg elongation. Our data show that BM stiffness increases during this migration and that fibril incorporation enhances BM stiffness. First, follicle elongation depends on epithelial cells that collectively migrate, secreting BM fibrils perpendicularly to the anteroposterior axis. To test this, we developed an atomic force microscopy-based method to measure BM mechanical stiffness during two key processes in Drosophila ovarian follicle development.
The regulation of morphogenesis by the basement membrane (BM) may rely on changes in its mechanical properties.
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