Hoxa1 and TALE proteins display cross-regulatory interactions and form a combinatorial binding code on Hoxa1 targets

Hoxa1 has diverse functional roles in differentiation and development. We have identified and characterized properties of regions bound by Hoxa1 on a genome-wide basis in differentiating mouse ES cells. Hoxa1 bound regions are enriched for clusters of consensus binding motifs for Hox, Pbx and Meis and many display co-occupancy of Pbx and Meis. Pbx and Meis are members of the TALE family and genome-wide analysis of multiple TALE members (Pbx, Meis, TGIF, Prep1 and Prep2) show that nearly all Hoxa1 targets display occupancy of one or more TALE members. The combinatorial binding patterns of TALE proteins defines distinct classes of Hoxa1 targets and indicates a role as cofactors in modulating the specificity of Hox proteins. We also discovered extensive auto- and cross-regulatory interactions among the Hoxa1 and TALE genes. This study provides new insight into a regulatory network involving combinatorial interactions between Hoxa1 and TALE proteins.