Thymocyte maturation is regulated by the activity of the helix-loop-helix protein, E47.

The E2A proteins, E12 and E47, are required for progression through multiple developmental pathways, including early B and T lymphopoiesis. Here, we provide in vitro and in vivo evidence demonstrating that E47 activity regulates double-positive thymocyte maturation. In the absence of E47 activity, positive selection of both major histocompatibility complex (MHC) class I- and class II-restricted T cell receptors (TCRs) is perturbed. Additionally, development of CD8 lineage T cells in an MHC class I-restricted TCR transgenic background is sensitive to the dosage of E47. Mice deficient for E47 display an increase in production of mature CD4 and CD8 lineage T cells. Furthermore, ectopic expression of an E2A inhibitor helix-loop-helix protein, Id3, promotes the in vitro differentiation of an immature T cell line. These results demonstrate that E2A functions as a regulator of thymocyte positive selection.