E-proteins set the threshold for optimal TCF1 expression during αβ T cell development.

Expression of T Cell Factor-1 (TCF1), encoded by Tcf7, regulates lineage fate decisions during T cell development. Here we demonstrate that E-proteins control the threshold of TCF1 expression required for development of T cells. E-proteins bind to five elements (EPEs) in the Tcf7 locus. The third element, EPE3, interacts directly with Tcf7 promoter in Hi-ChIP analyses, suggesting it is an active enhancer. CRISPR-ablation of EPE3 reduces TCF1 protein expression in precursor thymocytes by 2-fold and dramatically impairs development of {beta} and {gamma}{delta} T cells. Single cell gene expression analysis identified differentiation blocks at multiple CD4-CD8- stages and subsequent transition to CD4+CD8+ stage. These data identify E-proteins and EPE3 as critical for the optimal TCF1 expression required for T cell development.