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Coordinated collective cellular movements underlie embryonic development. Mechanosensitivity of collective movements of cells in model systems allows us to suggest that cellular migration can be regulated in normal development by the stage-specific patterns of mechanical forces within the tissue, which was first described for the embryos of Anura. Experimental validation of this hypothesis is incomplete and requires further research. One of the key findings supporting this hypothesis will be registration of trajectories of cell movement in an explant subjected to mechanical deformation comparable to that in normal development. This task requires protocol for controlled deformation to embryonic tissues that will allow subsequent time-lapse imaging of stretched samples with a resolution sufficient to recognize individual cells. In this article, we performed stretching of embryonic tissue explants on an elastic substrate using the device for controlled uniaxial deformation developed in our laboratory. This allowed us to capture the movements of individual cells in stretched explants of the blastocoel roof of the middle gastrula of X. laevis and reveal the threshold values of the rate and time of stretching required to initiate cell movements within the explant. [ABSTRACT FROM AUTHOR]

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. Stronger stretching caused a partial ordering of the whole axial complex and its reorientation toward stretching. We concluded that induction factors determine short-range order in their arrangement in SBA, whereas anisotropic cell movements in any direction are needed for long-range order. Moderate transverse stretching destroys normally oriented anisotropy, but it is not enough for establishment of the anisotropy oriented perpendicular to the normal. This explains the disorder at light stretching. The main conclusion of this study is that anisotropic tensions of embryonic tissues play role of long-range order parameters of cell differentiation. [ABSTRACT FROM AUTHOR]