A cell-contact model for cellular position determination in development.

The fate of a cell in a developing organism is a function of its position within the organism. The molecular mechanism that cells use to determine their position and to convert positional information into a form that can be used to regulate the expression of genes is not understood. This paper presents a model in which contacts between complementary molecules on plasma membranes of adjacent cells regulate the concentration of a morphogenetic substance and transmit positional information. This model is described by four equations that, when solved with realistic parameters, demonstrated that this mechanism will produce discrete populations of cells within a few hours from an initially undifferentiated array of cells. The model suggests an explanation for several phenomena that have been observed and suggests experiments to test it and to clearly differentiate it from other models for position determination.