Fig 2. The network schematic for the single-cell model of Drosophila segment polarity genes [35] (left) and expanded network (right).

The color key (right inset) summarizes observed characteristics of cells in the Drosophila embryonic segments (parasegments) ([34–36]; see S1 Appendix section 7 for parameter values and the full names of abbreviated variables). Each column represents an individual cell, arranged by anterior-posterior position in the parasegment. Columns are colored and named according to cell type, which is determined by prevalence of the proteins labeling each row. Black-filled ovals represent high levels of the protein, while white-filled ovals represent low levels. In the expanded network (right), dotted lines represent the node maintenance relation and asymptotic implication. Solid lines indicate the maintenance relation and implication in finite time. Nodes are colored according to membership in each of four biologically relevant stable modules, which correspond to the four cell types identified in the right inset. Node shape indicates participation in feedback loops that sustain these stable modules.