Gastrulation in Amphibian Embryos, Regarded As a Succession of Biomechanical Feedback Events

Gastrulation in amphibian embryos is a composition of several differently located morphogenetic movements which are perfectly coordinated with each other both in space and time. We hypothesize that this coordination is mediated by biomechanical interactions between different parts of a gastrulating embryo based upon the tendency of each part to hyper-restore the value of its mechanical stress. The entire process of gastrulation in amphibian embryos is considered as a chain of these mutually coupled reactions, which are largely dependent upon the geometry of a given embryo part. We divide gastrulation into several partly overlapped steps, give a theoretical interpretation for each of them, formulate the experiments for testing our interpretation and describe the experimental results which confirm our point of view. Among the predicted experimental results are: inhibition of radial cell intercalation by relaxation of tensile stresses at the blastula stage; inversion of convergent intercalation movements by relaxation of circumferential stresses at the early gastrula stage; stress-promoted reorientation of axial rudiments, and others. We also show that gastrulation is going on under a more or less constant average value of tensile stresses which may play a role as rate-limiting factors. A macro-morphological biomechanical approach developed in this paper is regarded as complementary to exploring the molecular machinery of gastrulation.