A simple model for estimating the active reactions of embryonic tissues to a deforming mechanical force.

Active reactions of embryonic tissues to mechanical forces play an important role in morphogenesis. To study these reactions, experimental models that enable to evaluate the applied forces and the deformations of the tissues are required. A model based upon the active intrusion of a living early gastrula Xenopus embryo into a tube half the embryo in diameter is described. The intrusion is initially triggered by a suction force of several dozen Pa but then continues in the absence of external driving force, stopping immediately after the entire embryo has penetrated into the tube. The process can be stopped by cytoskeletal drugs or by the damage of the part of the embryo still non-aspirated and is associated with the transversal contraction and meridional elongation of the non-aspirated part of the embryo surface and quasi-periodic longitudinal contractions/extensions of the cells within the part already aspirated. We suggest that this reaction is an active response to the embryo deformation and discuss its morphogenetic role. The problem of estimating the elastic modules of embryonic tissues is also discussed.