Intriniscally disordered domain of transcription factor TCF-1 is requried for T cell developmental fidelity [CUT&RUN]

The transcription factor TCF-1 has long been demonstrated to be essential for normal T cell development, with a critical role at the earliest stages of lineage specification downstream of Notch signaling in the thymus. Recent work has shown that TCF-1 targets and is essential for the opening of chromatin in T cells to orchestrate the gene regulatory cascade that occurs during development. However, besides the high mobility group DNA binding domain, no portion of the TCF-1 protein has been characterized to determine its role in hematopoiesis. In this study, we fully characterize all regions of TCF-1 and assess their importance in TCF-1-driven epigenetic and transcriptional regulation as well as in endowing developmental competency to the T cell lineage. Surprisingly, we identified an intrinsically disordered N-terminal region of TCF-1 termed “L1” that is necessary for efficient transition from early thymic progenitors to double-negative (DN)2 T cells. The few T cells that develop from progenitor cells expressing mutant TCF-1 lacking the L1 region exhibit lineage infidelity that was distinct and unique from the lineage diversion of TCF-1-deficient cells. Transcriptional and epigenetic profiling indicated that the L1 region was required for efficient target gene transactivation which correlated with the de-repression of a set of Gata2-driven genes normally restricted to the mast cell and dendritic cell lineages. DL1 mutant DN2 cells showed aberrant opening of previously silent chromatin at mast cell genes and Gata2-bound enhancers. These data support an essential role for TCF-1’s intrinsically disordered N-terminus in maintaining fidelity to the T cell lineage through carefully balanced activation of partner transcription factors that are required to repress alternative lineages. CUT&RUN in DN3 TCF-1KO cell line and in primary developing T cells from Tcf7eGFP fl/fl Cre+ progenitors cultures on OP9-DLL1 cells.