Epigenetic Hierarchies May Be Topped by Tissue-Specific Pioneer Factors

In any given tissue, the elements that regulate gene expression may settle into a hierarchy, one determined by an element called a pioneer factor. Evidence for such a hierarchy has been found in epithelial cells, where a pioneer factor called Grainy head plays the role of master regulator by determining the accessibility of enhancer sequences.Grainy head doesn’t activate the enhancer sequences itself. It merely exposes them to other regulatory elements that assume the activation duties. In