Assessing a role for enhancer‐blocking activity in gene regulation within the murine T‐cell receptor α/δ locus

Summary Although situated close together within the T‐cell receptor (TCR) α/δ locus, TCR δ and TCR α gene segments are controlled by two developmental stage‐specific enhancers and are activated according to distinct developmental programmes. We previously used a stable transfection colony assay to identify an enhancer‐blocking element, blocking element alpha/delta‐1 (BEAD‐1), between the TCR δ and α gene segments of the human TCR α/δ locus. We hypothesized that enhancer‐blocking by BEAD‐1 might be required to prevent the TCR δ enhancer from activating TCR α gene segment transcription and rearrangement at the double negative stage of thymocyte development. Here, we used a transfection approach to define partial enhancer‐blocking activity in an analogous position of the murine TCR α/δ locus. To test the functional significance of this activity in vivo , we used gene targeting to delete the region from the endogenous locus. We found no perturbation of TCR δ and TCR α gene expression and rearrangement on targeted alleles, indicating that enhancer‐blocking activity in this region is not required to maintain the developmentally distinct activation profiles of the two genes. We suggest that appropriate regulation may be achieved as a result of intrinsic biases in enhancer–promoter interactions or a developmental stage specificity to promoter function that is distinct from any additional specificity imposed by the enhancers themselves.