Satb1 Orchestrates the Expression of Lineage-Specifying Genes in Post-Selection Thymocytes

T-cell receptor (TCR) signaling by MHC class-I and -II induces thymocytes to acquire cytotoxic and helper fates via induction of Runx3 or ThPOK transcription factors, respectively. The mechanisms by which TCR signaling is translated into transcriptional programs for each cell fate remain elusive. We show that a genome organizer, Satb1, activates genes for lineage-specifying factors, including ThPOK and Runx3, in post-selection thymocytes. Indeed, Satb1-deficient thymocytes are partially redirected to inappropriate T lineages after MHC selection. Although Satb1 is dispensable for maintaining ThPOK in CD4+ T cells, it is necessary for restraining expression of the Treg factor FoxP3. Collectively, our findings demonstrate that Satb1 shapes the primary T-cell pool by initially directing lineage-specific transcriptional programs and subsequently balancing effector versus regulatory subsets via FoxP3 repression. Overall design: sequencing of Satb1-ChIP and input control from 6 wk old thymus