The histone lysine methyltransferase MLL1 regulates the activation and functional specialization of regulatory T cells [RNA-seq]

The activation and specialization of regulatory T cells (Tregs) are crucial for maintaining immune self-tolerance, but the epigenetic regulation of these processes remains largely unexplored. Here, we show that T-cell-specific deletion of the lysine methyltransferase MLL1 results in a spontaneous lymphocyte proliferation phenotype in aged mice without disturbing the development of conventional T cells and Tregs. Treg-specific MLL1 ablation leads to a systemic autoimmune disease associated with Treg dysfunction. RNA sequencing demonstrated that the induction of multiple genes involved in Treg activation, functional specialization and tissue immigration is defective in MLL1-deficient Tregs. This dysregulation is associated with defects in H3K4 trimethylation at the transcription start sites (TSSs) of these genes. Finally, using a T-bet fate-mapping mouse system, we determined that MLL1 is required to establish stable Th1-type Tregs. Thus, MLL1 plays an essential role in optimal Treg function by providing a coordinated epigenetic context for activation and specialization. Overall design: Lymphocytes were isolated from the spleen and lymph nodes of 6- to 8-week-old Foxp3RFP-Cre.RosaYFPMll1fl/fl male mice and enriched for CD4+ T cells using magnetic beads. RFP+YFP+ and RFP+YFP- Tregs (3 x 105) were sorted to a typical purity of > 95 for RNA sequencing. RNA was extracted using the RNeasy MicroRNA Kit (QIAGEN 74004). RNA sequencing (RNA-seq) and bioinformatics analysis were conducted by Novogene as described previously.Differential expression analysis of two conditions was performed using the DEGSeq R package (1.16.1). The p values were adjusted using the Benjamini-Hochberg method. Corrected q value = 0.05 and log2 (fold change) = 1 were set as the threshold for significantly differential expression.