PU.1 represses and activates gene expression in early T cells by redirection of transcription factor ensembles [RNA-Seq]

Transcription factors normally regulate gene expression through their action at sites where they bind to DNA. However, the balance of activating and repressive functions that a transcription factor can mediate is not completely understood. Here, we show that PU.1 regulates gene expression in early stages of T-cell development both by recruiting partner transcription factors to its own binding sites and by depleting them from the binding sites that they may prefer when PU.1 is absent. Importantly, the loss of partner factors Satb1 and Runx1 occurs primarily from sites where PU.1 itself does not establish any detectable local binding. Genes linked to sites of partner factor 'theft' are enriched for considerable subsets of the genes PU.1 represses both in a model cell-line system and in normal T-cell development. Thus, system-level competitive recruitment dynamics permit PU.1 to affect gene expression both through own target sites and through action at a distance. Overall design: RNA-seq; Total RNA was isolated from 300,000 cells using an RNAeasy MicroKit (Qiagen). Libraries were constructed using NEBNext Ultra RNA Library Prep Kit for Illumina (E7530, NEB) from ~1 µg of total RNA following manufacturer's instructions. Libraries were sequenced on Illumina HiSeq2500 in single read mode with the read length of 50 nt.