Biomechanical feedback in morphogenesis, as exemplified by stretch responses of amphibian embryonic tissues

We explore the idea that morphogenetical processes may be self-regulated by the biomechanical feedback established between the active stress-generating devices and the passive stresses of stretching and (or) compression, these feedback directed towards hyperrestoration (restoration with overlapping) of the initial stress values. As an example, a stretch-induced behaviour of the pieces of ventral ectoderm of Xenopus laevis early gastrulae is considered. By stretching the explants in 1.3-1.7 times, we induced several active poststretching cell responses, including further autonomous elongation of an explant in the stretch direction and contraction in the perpendicular direction, as well as more complicated shape changes. At the cellular level, these responses were associated with the return of the stretched cells to isodiametrical shapes and with the production of extensive cell protrusions along the stretch direction. As shown by dissections, the stretch-induced tissue tensions were considerably diminished in the poststretching period. The results obtained are discussed within the framework of the hyperrestoration hypothesis.