Cell–cell adhesion is crucial for establishing multicellular structures and maintaining tissue integrity. Changes in cadherin-mediated adhesion are thought to be responsible for cell sorting and tissue boundary formation. Whereas in vitro studies support the notion that quantitative differences in adhesion lead to cell sorting, in vivo evidence for such a link has been missing so far. On page , Rudolf Winklbauer and colleagues now provide evidence that the cell sorting events that occur in response to alterations in cell adhesion in vitro do not necessarily reflect the complex range of factors that influence this process in vivo. By using a C-cadherin morpholino antisense oligonucleotide and a C-cadherin mutant construct that lacks the cytoplasmic domain, and thus cannot recruit β-catenin, they modulate C-cadherin expression and signalling during Xenopus laevis gastrulation. Morphogenesis is surprisingly tolerant of changes in cell–cell adhesion: a moderate reduction in adhesion does not affect larvae formation, and only the dissociation of tissues under conditions of very low adhesion affects development. In addition, differences in cadherin expression and adhesion that induce cell sorting in vitro are not sufficient to drive sorting in the intact embryo. Thus, tissue boundary formation and maintenance in vivo seems to require a broader range of factors.
