Fig. 1.

The order of coregulated gene expression networks increases during differentiation. (A) Potential differences between the expression patterns of 2 genes over time. (B) Pick any 2 genes (x and y) and measure the pairwise distance (relative entropy) during differentiation. (C) Example of a portion of the N × N distance matrix consisting of all pairwise comparisons at one time point. (D) Order is the fraction of genes at any given time point (0, 4, 8, 16, 24, 48, and 72 h) that are coregulated, thereby residing in a GC that reflects their hierarchical clustering. As genes entrain with or diverge from the expression pattern of the GC during the course of differentiation, the change in order as the system evolves can be determined. In the progenitor state (time 0), the GC corresponds to 84% of coregulated genes, is reduced to as low as 70% at 4 h, and reaches a maximum of 91% in the fully differentiated state. Red and black lines represent erythroid and neutrophil lineages, respectively.