The tight control of tissue morphogenesis is important for the basic organization of multicellular organisms. Despite the tremendous diversity of shapes, all multicellular organisms are derived from a set of basic body plans, which implies that new forms represent variations on a few themes. Signalling pathways that spatially and temporally control cell behaviour orchestrate the mechanisms that govern cell-pattern formation. But how is this information processed to control cell shape and dynamics?

The integration of physics principles with cell and developmental biology has provided new ways to address how patterns arise in living organisms, based on the fundamental properties of cell surfaces. Thomas Lecuit and Pierre-François Lenne (page 633) propose a cellular framework of morphogenesis that posits adhesion and cortical actin networks as regulators of cell-surface mechanics, and they discuss how cell-shape changes and cell contacts are remodelled by the opposite actions of cortical tension and adhesion. Their proposed model provides a mechanistic understanding of tissue bending, elongation and cell-pattern formation at the multicellular level.

Many animal species exhibit similar body patterns, but have markedly different body sizes. Stimulating cell proliferation and/or cell growth should result in bigger body frames, but organisms have devised mechanisms that restrict cell numbers. Leslie J. Saucedo and Bruce A. Edgar (page 613) fill the gaps in the Hippo pathway, which regulates growth control in Drosophila melanogaster by restraining cell proliferation and promoting apoptosis in differentiating epithelial cells. The importance of this pathway in the control of cell numbers is emphasized by its evolutionary conservation and by increasing evidence that its deregulation occurs in human tumours.