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. Cell movements were measured on two scales. At a smallscale consideration (time intervals of the order of several hours and distances of the order of tens of microns), fairly slight linear stretching and compressive deformations were detected, which looked like gentle smooth gradients along which the upward morphogenetic movements of cells were directed. At a large-scale consideration (time intervals of the order of tens of minutes and distances of the order of microns), quasi-periodic fluctuations of velocities of individual cells partly correlated in time were found. The differences between these velocities generated microdeformations, which reached several tens of percent and developed within time intervals not more than 10 min. Measurements of relative magnitudes of mechanical forces influencing the cell walls suggests that microdeformations generate local stretching and compressive deformations modulating smoother tension gradients.