Effects of mechanical stretching of embryonic tissues on axial structure formation in <Emphasis Type="Italic">Xenopus laevis</Emphasis>

Effect of mechanical stretch on the differentiation of axial anlages and Chordin gene expression was studied in sandwich explants prepared from embryonic tissues of Xenopus laevis at the early gastrula stage in two variants: with dissected or intact dorso-medial region. In the first case, convergent cell movements were suppressed and properly organized axial organs (notochord and somites) were almost completely absent. However, they developed if the explants of such type were artificially stretched in the ventro-dorsal direction. In this case, axial organs elongated in the line of stretching, that is in the direction vertical to their normal orientation. Segmented mesoderm was always in contact with the chord anlage. In situ hybridization revealed that the area of Chordin gene expression was also extended in the direction of stretching. PCR showed that Chordin gene expression in stretched explants with disrupted dorso-medial region was statistically at the same level as in the explants with intact dorso-medial region. At the same time, the corresponding gene expression in unstretched explants with disrupted dorso-medial region was statistically higher. The obtained data indicate that mechanical stretch and associated cell movements are a necessary and sufficient condition for the formation of proper histological structure of axial organs and regulation of Chordin gene expression.