A New Element within the T-Cell Receptor α Locus Required for Tissue-Specific Locus Control Region Activity

Abstract

Locus control regions (LCRs) are cis-acting regulatory elements thought to provide a tissue-specific open chromatin domain for genes to which they are linked. The gene for T-cell receptor α chain (TCRα) is exclusively expressed in T cells, and the chromatin at its locus displays differentially open configurations in expressing and nonexpressing tissues. Mouse TCRα exists in a complex locus containing three differentially regulated genes. We previously described an LCR in this locus that confers T-lineage-specific expression upon linked transgenes. The 3′ portion of this LCR contains an unrestricted chromatin opening activity while the 5′ portion contains elements restricting this activity to T cells. This tissue-specificity region contains four known DNase I hypersensitive sites, two located near transcriptional silencers, one at the TCRα enhancer, and another located 3′ of the enhancer in a 1-kb region of unknown function. Analysis of this region using transgenic mice reveals that the silencer regions contribute negligibly to LCR activity. While the enhancer is required for complete LCR function, its removal has surprisingly little effect on chromatin structure or expression outside the thymus. Rather, the region 3′ of the enhancer appears responsible for the tissue-differential chromatin configurations observed at the TCRα locus. This region, herein termed the “HS1′ element,” also increases lymphoid transgene expression while suppressing ectopic transgene activity. Thus, this previously undescribed element is an integral part of the TCRαLCR, which influences tissue-specific chromatin structure and gene expression.

ACKNOWLEDGMENTS

We thank D. Kioussis for the human β-globin reporter gene fragment, Peter Schow for expert flow cytometry services, and Buyung Santoso for technical assistance. We thank Bill Sha, Jeanne Baker, Herb Kasler, and Jeff Wallin for critical reading of the manuscript.

B.D.O. was supported by a postdoctoral fellowship from the National Science Foundation. A.W. is an NSF Presidential Faculty Fellow. This work was supported by NIH grant AI-31558 to A.W.