Morphogenetic and differentiation sequelae to relaxation of mechanical tensions in Xenopus laevis blastula]

Using microsurgical technique, we have conducted relaxation of circular tensions on the surface of X. laevis embryo at the stage of late blastula. Results of these operations were examined by optical and scanning electron microscopy, heteroplastic marking, and morphometry. The most important outcomes of tension relaxation included disappearance of blastocoel, intermixing of cells of the animal part of the embryo and their local migration from the embryo surface. This was followed by the appearance of slit-like depressions and protuberances, some of the protuberances showed branching. Morphological abnormalities of several types were observed 1.5-2 days later. Some of the abnormal embryos resembled the embryos of lower chordates. We have noted sharp increase in the variation of absolute volumes and mutual volume ratios of axial rudiments. Incubation of the operated animals in a hypotonic solution restored the blastocoel and led to significant normalization of development. The results obtained demonstrate that at the stage of late blastula mechanical tensions play an important role in the maintenance of normal morphological and differentiational structure of amphibian embryos.