Notch Signaling Controls Transcription via the Recruitment of RUNX1 and MYB to Enhancers during T Cell Development

Abstract

<i>Tcrd</i> and <i>Tcrg</i> display identical developmental programs that depend on the activity of the enhancers Eδ and Eγ being "on" in pre-β-selection thymocytes to activate transcription and V(D)J recombination of the unrearranged genes and "off" in post-β-selection CD4⁺CD8⁺ double-positive thymocytes to inhibit transcription of the rearranged genes and avoid the expression of TCR δ- and TCR γ-chains in αβ T lymphocytes. Eδ and Eγ activity depends on transcription factor binding to essential Runx and Myb sites and parallels that of Notch signaling. We performed Notch gain- and loss-of-function experiments and found that Notch signaling activates <i>Tcrd</i> and <i>Tcrg</i> transcription by favoring the recruitment of RUNX1 and MYB to the enhancers. Our results suggest that the dissociation of RUNX1 and MYB from Eδ and Eγ chromatin in double-positive thymocytes, which results in enhancer inactivation, is caused by decreased Notch signaling triggered by pre-TCR signaling, thereby deciphering the molecular mechanism of <i>Tcrd</i> and <i>Tcrg</i> silencing during β-selection. These findings reveal a novel molecular mechanism for gene regulation via Notch signaling through the recruitment of RUNX1 and MYB to enhancer chromatin during thymocyte development.