TCR-mediated ThPOK induction promotes development of mature (CD24-) γδ thymocytes

T lymphocytes develop into two major lineages characterized by expression of the alpha beta and gamma delta T cell receptor (TCR) heterodimers. Within each major lineage, further specialization occurs, resulting in distinct subsets that differ in TCR specificity, phenotype and functional attributes. Thus, in the murine thymus, two distinct subsets of mature (CD24-) gamma delta cells have been identified, that is NK1.1+ cells, which are enriched for V gamma 1.1 usage and selectively produce IFN gamma on stimulation, and CCR6+ cells, which are enriched for V gamma 2 usage produce IL17. The upstream signals and transcriptional pathways that promote development of these distinct gamma delta subsets remain relatively poorly understood. Here, we show that the Zn-finger transcription factor ThPOK has a critical function in the development of gamma delta thymocytes. Thus, lack of functional ThPOK causes a marked reduction in the percentage and absolute number of mature gamma delta thymocytes, and a particularly severe reduction of NK1.1+ cells. Conversely, constitutive ThPOK expression leads to a striking increase in mature NK1.1+ gamma delta thymocytes. Further, we show that ThPOK induction in gamma delta thymocytes is induced by strong TCR signals mediated by engagement with antibody or high-affinity endogenous ligands, and that an important ThPOK cis-acting element, the distal regulatory element (DRE), is sufficient for this TCR-dependent induction. These results show that ThPOK expression in gamma delta thymocytes is regulated in part by the strength of TCR signalling, identify ThPOK as an important mediator of gamma delta T cell development/maturation, and lend strong support to the view that development of a significant fraction of gamma delta T cells depends on TCR engagement/signalling. The EMBO Journal (2010) 29, 2329-2341. doi:10.1038/emboj.2010.113; Published online 15 June 2010