Changes in topology and geometry of the embryonic epithelium of Xenopus during relaxation of mechanical tension

Abstract

The paper presents the results of statistical evaluation of the changes of cellular apex connections, apical angles, and apical indices of ventral cells of the epiectodermal gastrula of Xenopus during the first four hours after the relaxation of mechanical tension. In the unrelaxed epithelium, an overwhelming majority of cells have three apical connections, apical angles close to 120°, and apical indices around one (isodiametric cells); after relaxation, the number of cells with more than three connections, the number of apical angles deviating substantially from 120°, and the percentage of columnar cells with high apical index increase. Apices with more than three connections tend to gather in enclosed groups, forming a straightened line of cell walls. The length and curvature of cell walls with four apical connections significantly exceeds those same indicators for cells with three apical connections. The observed changes in topology and geometry of cells correspond to reconstructions observed during normal morphogenesis. They are considered in terms of the hyper-restoration model of mechanical tension in relaxed epithelial layers.