where X is the concentration of an activating signaling factor that affects cell type m, K 1 is the activation coefficient, n is the Hill coefficient, Y is the concentration of a repressive signaling factor that affects cell type m, and K 2 is the repression coefficient. Unlike enzyme kinetics, K 1 and K 2 are related to a cell response, not strictly biochemical dissociation constants. The concentrations of X and Y can be defined by ODEs or algebraic equations. It is important to note that a signaling factor Cook and Lighty et al.