[Statistical study of rapid mechanodependent cell movements in deformed explants of African clawed frog Xenopus laevis embryonic tissues].

Computer analysis of artificially deformed (stretched or compressed) double explants (sandwiches) of the blastocoel roof (BRs) and suprablastoporal region (SBRs) of African clawed frog Xenopus laevis early gastrula has been performed using frames of time-lapse microfilming. During the first 14 min after cutting off, the velocities and displacement angles of several hundreds of cells relative to one another, as well as to fixed points and the extension axis, were measured in the control and deformed samples. It has been found that the deformation of samples leads to a rapid reorientation of large cell masses and increase in the velocities of movements along the extension axes or perpendicularly to the compression axes. In addition, an increase in the velocities of mutual cell displacements in the stretched BRs and cell convergence to the extension axes have been observed. Comparison of different angular sectors demonstrates a statistically significant positive correlation between the mean velocities of cell movements and the number of cells moving within an individual sector. This suggests cooperativity of mechanodependent cell movements. In general, these results demonstrate an important role of mechanical factors in regulation of collective cell movements.

[A quantitative study of regional and stage specific reaction of African clawed frog embryonic tissues on mechanical stress]. / Kolichestvennoe issledovanie regional'nykh i stadiespetsifichnykh reaktsii émbrional'nykh tkanei shportsevoi liagushki na mekhanicheskuiu razgruzku.

Residual deformation of fragments of the embryonic tissues preserved after relaxation of the stretching force serve as a criterion of active redistribution of their cells caused by this stretching. We measured residual deformations of the Xenopus laevis ventral and dorsal ectoderm at the early gastrula and lateral ectoderm at the late gastrula-early neurula after stretching of varying time and force. While the samples responded to moderate (up to 40%) short-term stretching as elastic bodies (residual deformations were absent), residual deformation appeared in the early gastrula tissues after 30-60-min stretching, which were more pronounced in the ventral tissues than in the dorsal ones. On the contrary, a contractile reaction developed in the late gastrula-early neurula tissues in response to 60-min stretching, which almost relaxed residual deformation within 20 min after unloading. A conclusion was drawn that gastrulation and neurulation proceed under the conditions of relaxing and nonrelaxing mechanical tensions, respectively. Mechanical bases and morphogenetic role of the described reactions is discussed.