Identification of an enhancer that regulates DNA demethylation-dependent Cd4 expression following thymocyte positive selection

The inheritance of gene expression patterns is dependent on epigenetic regulation, but the establishment and maintenance of epigenetic landscapes during T cell differentiation are incompletely understood. Here we show that two stage-specific Cd4 cis-elements, the previously characterized enhancer E4p and a novel enhancer E4m, coordinately promote Cd4 transcription in mature thymic MHC-II-specific T cells, in part through the canonical Wnt pathway. Specifically, E4p licenses E4m to orchestrate DNA demethylation by TET1 and TET3, which in turn poises the Cd4 locus for transcription in peripheral T cells. Cd4 locus demethylation was important for subsequent Cd4 transcription in activated peripheral T cells wherein these cis-elements became dispensable. By contrast, in developing thymocytes the loss of TET1/3 did not affect Cd4 transcription, highlighting an uncoupled event between transcription and epigenetic modifications. Together our findings reveal an important role for thymic cis-elements in governing gene expression in the periphery via a heritable epigenetic mechanism.