The bending of cell sheets - from folding to rolling
- PDF / 432,183 Bytes
- 4 Pages / 612.28 x 793.7 pts Page_size
- 67 Downloads / 183 Views
CO M M E N TA R Y
Open Access
The bending of cell sheets - from folding to rolling Ray Keller* and David Shook* See research article: http://www.biomedcentral.com/1741-7007/9/89
Abstract The bending of cell sheets plays a major role in multicellular embryonic morphogenesis. Recent advances are leading to a deeper understanding of how the biophysical properties and the forceproducing behaviors of cells are regulated, and how these forces are integrated across cell sheets during bending. We review work that shows that the dynamic balance of apical versus basolateral cortical tension controls specific aspects of invagination of epithelial sheets, and recent evidence that tissue expansion by growth contributes to neural retinal invagination in a stem cell-derived, self-organizing system. Of special interest is the detailed analysis of the type B inversion in Volvox reported in BMC Biology by Höhn and Hallmann, as this is a system that promises to be particularly instructive in understanding morphogenesis of any monolayered spheroid system.
Commentary Cell sheet bending is an active process, required for normal morphogenesis in many instances of multicellular embryogenesis, including the formation of the germ layers during gastrulation, the gut and neural tube, the eye, the otic system and the diverticula of the gut. A number of mechanisms have been proposed for cell sheet bending, including growth pressure, cell shape changes driven by cell-cell or cell-matrix adhesion, or by the cytoskeleton, for example, each with varying levels of experimental support. Recent combinations of live imaging, molecular interdictions, biophysical analysis, and computational modeling are providing a much better understanding of the key biomechanical processes underlying how cells generate forces, how local forces are integrated over large cell sheets, and how morphogenic function depends on geometric and biomechanical context. *Correspondence: [email protected], [email protected] Department of Biology, 241 Gilmer Hall, University of Virginia, Charlottesville, VA 22904, USA
Cell wedging - balancing cellular tensions One of the most studied mechanisms of bending a cell sheet is the ‘wedging’ of individual epithelial cells by contraction of their apical ends driven by myosin motor proteins acting on actin filaments (actomyosin-mediated contraction). The apical ends of these cells are mechanically linked to one another by adherens junctions, which integrate these locally generated apical constriction forces over the entire sheet, causing it to bend (Figure 1, steps a to e). Apical constriction does not act alone, however, as recent work shows that the dynamic balance of cortical tension in apical versus basolateral cell domains plays a large role in regulating the specific aspects of cell shape, such as apical-basal elongation, that determine how the sheet is bent. In some systems, such as in the formation of the ‘bottle-shaped’ cells at the site of blastopore invagination in amphibians, bending of the cell sheet is monophasic. With apic
Data Loading...
