Besides the differentiation grade, the body symmetry suited for scaling may be a prerequisite for the advantageous regeneration capability.Hydra displays total regeneration of a new organism based on reaggregation of single cells. This gives rise to the fundamental question of how the global tissue organization can arise from local information.The cells of this organism are permanently replaced due to homeostatic ow.It remains unclear how hydra conserves its size, which seems to require precise coordination of cellular differentiation and apoptosis.Shortrange activators were introduced triggering the activation of head formation, while longrange inhibitors suppress it.A fundamental question aims at the inuence of differentiation versus migration during morphogenesis, distinguishing between constant and variable lineages.Constant lineage cells, as found in nematodes, are determined by their origin resulting in malformations upon cell removal. Even mammalian cells stay entirely variable during early phases of embryonic development.These cells are determined by their position and not by their origin.They further show extensive cell migration enabling a signicantly higher plasticity and compensation capacity in case of cellular loss or damage during early development. In zebrash, the primordial germ cells, initially dividing in a perfectly ordered manner, undergo a Fenoprofen calcium hydrate transition to motile cells.This transition correlates with cadherin expression and presumably calcium gradients, but the underlying mechanisms remain unexplained. To a small percentage cells even migrate opposite to the homeostatic ow direction and bulk movement has been observed after grafting. Head cells are supposed to Desonide segregate head inhibitors.Inserting a head fragment close to a head inhibits new head formation. Although at rst, this approach appears simple, it encounters the problem that cells do not possess calibrated sensors that are precise enough.Even worse, sensing is exposed to thermal and concentration uctuations being considerable at a molecular scale as well as uctuations due to active cellular movements.The dynamic nature of cells is, in fact, rather an advantage when registering differential signals in time or space instead of absolute levels.Their model is a nonlinear spatiotemporal eld theory ignoring the cellular nature of tissues including mechanical cues.Two coupled time and spacedependent elds with corresponding diffusion constants were introduced representing the concentrations of a shortrange activator and a longrange inhibitor as well as a spatial source density distribution for each eld.Numerical simulations revealed that slightly asymmetric source density distributions produce stable patterns when starting from uniform distributions of activator and inhibitor elds. The hope was to reveal the diffusive properties of the actual molecular signaling components based on the proposed reactiondiffusion model. Nuclear divisions in this phase are accompanied by the formation of several different morphogen gradients triggering local gene expression. The mechanism for establishing the respective gradients differ substantially between morphogens. It has been shown that both the gradient and the local readout are very precies, close to the limits set by basic physical principles. This is an instructive example for gradientinduced patterning conrming the relevance of reactiondiffusion systems for development.Nevertheless, it remains unknown to what extent morphogen gradients are involved in tissue organization in multicellular nonsyncytial embryos and tissues.It might be asked if sensing of global gradients is already sufcient to organize more complex tissues and ne structures as the zebrash lateral line.