Cadherin function during Xenopus gastrulation.

Xenopus gastrulation consists of the orderly deformation of a single, multilayered cell sheet that resembles a multilayered epithelium, and flexible cell-cell adhesion has to provide tissue cohesion while allowing for cell rearrangements that drive gastrulation. A few classic cadherins are expressed in the Xenopus early embryo. The prominent C-cadherin is essential for the cohesion of the animal part of the gastrula including ectoderm and chordamesoderm, and it contributes to the adhesion of endoderm and anterior mesoderm in the vegetal moiety. The cadherin/catenin complex is expressed in a graded pattern which is stable during early development. Regional differences in cell adhesion conform to the graded cadherin/catenin expression pattern. However, although the cadherin/catenin pattern seems to be actively maintained, and cadherin function is modulated to reinforce differential adhesiveness, it is not clear how regional differences in tissue cohesion affect gastrulation. Manipulating cadherin expression or function does not induce cell sorting or boundary formation in the embryo. Moreover, known boundary formation mechanisms in the gastrula are based on active cell repulsion. Cell rearrangement is also compatible with variable tissue cohesion. Thus, identifying roles for differential adhesion in the Xenopus gastrula remains a challenge.