The uncommon roles of common gene regulatory factors in the genomes of differentiating cells.

Viewed through the lens of comparative regulatory mechanisms in developmental processes, the article of Calero-Nieto et al (2014, this issue) is of particular interest. This work uncovers the causal combinatorial subtleties of the distinct enhancer occupancy profiles displayed by ten different transcription factors, which are expressed in common in two hematopoietic cell types, a stem cell-like precursor and primary mast cells.