Model of pattern formation in animal coatings

One of the most universal phenomena in embryological morphogenesis is the formation of domains of morphologically polarized (apico-basally elongated) epithelial cells. It has been observed that cell polarization precedes many “obvious” events in embryogenesis, such as invagination and evagination, folding and curling of cell sheets, differentiation of cells in eye development, emergence of skin derivates, and even the budding in Marine Hydrozoa. Domains of polarized and unpolarized cells form “reliefs” in epithelial sheets that are the pre-patterns to the above-mentioned patterns. This paper gives a model for the pigment pattern formation in animal coatings. del simulates cell polarization as a co-operative self-organized process of cells in an epithelial sheet. It is based upon the following experimentally proven properties of cells and their interactions: (i) each individual cell in an epithelial tissue is able to change shape from unpolarized to polarized and back, the transition being the “all or none” type (both forms are the only stable ones); (ii) polarization is transmitted from cell to cell via their contacts; (iii) local polarization forces generate tangential elastic tensions throughout the surrounding unpolarized cells which, in turn, inhibit further polarization, thus establishing a negative feedback mechanism. These two types of force form the basis of the model, which is referred to as the PE model (polarization-elasticity) for brevity.