Gene regulation and lateral signaling network. In cell i, the common names of the transcription factors are used. In cell j, these are replaced by the respective model variables. Cells i and j are coupled by lateral inhibition of factors X, and by lateral stabilization between factors Y. For each cell, the upstream factor A induces expression of X and Y, while X also induces Z expression, which activates itself. Both endocrine factors X and Z antagonize exocrine factor Y. Once differentiated, the markers Y and Z down-regulate A. Parameters in small lower case represent strengths of the interactions.