Date of Award
Doctor of Philosophy (PhD)
Lymphocytes are the work horses of adaptive immunity. Compared to the B lymphocyte lineage, early stage progenitors of T lymphocytes maintain considerable potential for differentiation into other hematopoietic lineages. T lineage commitment requires the continuous coordination of transcription factors (TFs) by Notch1 signaling after multi-potent progenitors (MPPs) migrate to thymus. One of the first hall marks of T lineage commitment is expression of the T cell receptor β (TCRβ), which is encoded by the Tcrb locus following its assembly by V(D)J recombination, a somatic shuffling of the genome that joins one V, one D, and one J gene segment. Tcrb assembly is initiated at its recombination center (RC), composed of two DβJβ clusters. Tcrb-RC exhibits features of regulatory regions called super-enhancers (SEs), which are characterized by high level of active histone mark, H3K27ac, and by clusters of binding for TFs involved in cell fate decisions. A key Tcrb-RC enhancer, called Eβ, harbors two composite ETS1-RUNX1 binding motifs, which widely exist in regulatory elements for genes involved in T lymphopoiesis. ETS1 is sharply upregulated during T cell lineage commitment and recruits constitutively expressed RUNX1 to Eβ. However, the independent roles of these two TFs remain unclear, especially since both are potent transactivators. In this study, I have shown that both ETS1 and RUNX1 are sufficient to independently activate Eβ in extrachromosomal reporter substrates. However, ETS1 by itself fails to activate Eβ in its native chromosomal context. By contrast, RUNX1 is sufficient to activate the endogenous Eβ element and its neighboring 25 kb region independently from ETS1. In addition, RUNX1 is sufficient to mediate long-range promoter-Eβ interactions, nucleosome clearance, and robust transcription throughout the Tcrb recombination center (RC). We also find that a RUNX1 domain, termed the negative regulatory domain for DNA binding (NRDB), can compensate for loss of ETS1 binding at adjacent sites. Thus, we have defined independent roles for RUNX1 in the activation of a T cell developmental enhancer, as well as its ability to mediate specific changes in chromatin landscapes that accompany long-range induction of RC promoters.
Chair and Committee
Eugene M. Oltz
Shiming Chen, Takeshi Egawa, Jason Mills, Barry Sleckman,
Zhao, Jiangyang, "Epigenetic Activation of the Mouse T Cell Receptor Beta Recombination Center" (2017). Arts & Sciences Electronic Theses and Dissertations. 1157.