Supplementary Figure 6: Hes1-mediated constraint of myeloid gene expression programs is essential for T cell development; the thymus is settled by a myelo-lymphoid progenitor from the bone marrow.

Early thymic progenitors (ETP) develop under the influence of Notch signaling in the thymus. Shortly after thymic entry, Notch induces the expression of the transcriptional repressor Hes1, which directly inhibits C/EBP-α, a critical myeloid regulator and perhaps other myeloid lineage genes. Hes1 is expressed in CD4/CD8 double-negative (DN) thymocytes, including ETP, DN2, and DN3 progenitors, but is no longer expressed at the CD4/CD8 double-positive (DP) stage. DN3 and DP thymocytes are committed to the T-cell lineage.