Molecular and Cellular Biology, March 1999, p. 1901-1909, Vol. 19, No. 3
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Locus
Required for Tissue-Specific Locus Control Region Activity
Department of Molecular and Cell Biology, Cancer Research Laboratory and Division of Immunology, University of California, Berkeley, California 94720-3200
Received 25 August 1998/Returned for modification 14 October 1998/Accepted 9 December 1998
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
chain
(TCR
) is exclusively expressed in T cells, and the chromatin at its
locus displays differentially open configurations in expressing and
nonexpressing tissues. Mouse TCR
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 TCR
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
TCR
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 TCR
LCR, which influences tissue-specific
chromatin structure and gene expression.
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