Non-Turing stripes and spots: a novel mechanism for biological cell clustering

A classical model for developmental patterning invokes a chemical ‘prepattern’ which cells read out as developmental instructions. The ‘prepattern’ arises from the Turing Instability of two reacting and diffusing chemicals, an ‘activator’ and an ‘inhibitor.’ We propose a novel developmental mechanism, based on cell–cell adhesion and cell–extracellular matrix (ECM) adhesion, which depends only on biological mechanisms and chemicals shown experimentally to be significant during patterning. In our model, condensation results from random cell diffusion biased by preferential attachment of cells to ECM and enhanced local cell–cell adhesion. We implement a two-dimensional Cellular Potts Model (CPM) simulation of condensation to explore this mechanism and discuss the parameter dependencies of the patterns. The simulation reproduces much of the density-dependent phenomenology of in vitro biological cell clustering during the developmental process of chick limb precartilage mesenchymal condensation. We study pattern formation in our model and compare it to the standard Turing mechanism. The mechanism should apply to other condensation processes besides limb chondrogenesis in vivo. The existance of an overlooked and simple mechanism which explains the observed phenomenology better than the classical picture is genuinely surprising.