Stress-generating tissue deformations in Xenopus embryos: Long-range gradients and local cell displacements.

Background: Although the role of endogenous mechanical stresses in regulating morphogenetic movements and cell differentiation is now well established, many aspects of mechanical stress generation and transmission in developing embryos remain unclear and require quantitative studies.

Results: By measuring stress-bearing linear deformations (caused by differences in cell movement rates) in the outer cell layer of blastula - early tail-bud Xenopus embryos, we revealed a set of long-term tension-generating gradients of cell movement rates, modulated by short-term cell-cell displacements much increasing the rates of local deformations. Experimental relaxation of tensions distorted the gradients but preserved and even enhanced local cell-cell displacements.

[Role of Mechano-Dependent Cell Movements in the Establishment of Spatial Organization of Axial Rudiments in Xenopus laevis Embryos].

Trajectories of individual cell movements and patterns of differentiation in the axial rudiments in suprablastoporal areas (SBA) in whole embryos of Xenopus laevis artificially stretched in the transverse direction up to 120–200% from the initial length at the early gastrula stage were mapped. We observed the impairment of anisotropic cell movements of longitudinal stretching and latero-medial convergence inherent for SBA. Axial rudiments occurred in all cases, but their location was completely impaired and dramatically different from the normal topology for moderate (120–140%) stretching.

[Surface Microdeformations and Regulation of Cell Movements in Xenopus Development].

The velocities and directions of movements of individual outer ectodermal cells of Xenopus embryos in the course of normal development from the blastula to the early tail-bud stage, as well as after mechanical relaxation in the early gastrula, were measured. An alternation of the periods of directed movements of large cell masses and local cell wanderings was detected. In both cases, the trajectories of individual cells consisted primarily of orthogonal segments.

[Topology and planar polarity of the Xenopus embryonic ciliated epithelium].

The effect of mechanical stress on the topology and planar polarity (PP) of the Xenopus embryonic ciliated epithelium was studied. It was found that the explantation of different sections of the blastocoel roof of the early gastrula disrupted the normal orientation of rows of ciliated cells (CCs) and led to the partition of zones with a single PP into several sections with different polarity or to the occurrence of chaotic patterns. Mechanical stretching of explants increased the order of their PP and oriented it predominantly perpendicular to the stretching axis.

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

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 HC-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 degrees, 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 degrees, 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 smooth line of cell walls.