Dirk Schübeler*, Mark Groudine*, 1, @, and M. A. Bender*, 2
* Fred Hutchinson Cancer Research Center, Seattle, WA 98109; and Departments of 1 Radiation Oncology and 2 Pediatrics, University of Washington School of Medicine, Seattle, WA 98195
@ To whom reprint requests should be addressed at: Fred
Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle,
WA 98109.
E-mail: markg@fhcrc.org.
Locus control regions (LCRs) are defined by their ability to confer
high-level tissue-specific expression to linked genes in transgenic assays.
Previously, we reported that, at its native site, the murine b-globin
LCR is required for high-level b-globin gene
expression, but is not required to initiate an open chromatin conformation
of the locus. To further investigate the mechanism of LCR-mediated transcriptional
enhancement, we have analyzed allele-specific b-globin
expression and the pattern of histone acetylation in the presence and absence
of the LCR. In single cells from mice heterozygous for a deletion of the
LCR, b-globin expression from the LCR-deleted
allele is consistently low (1-4% of wild type). Thus, the endogenous LCR
enhances globin gene expression by increasing the rate of transcription
from each linked allele rather than by increasing the probability of establishing
transcription per se. Furthermore, in erythroid cells from mice homozygous
for the highly expressing wild-type b-globin
locus, hyperacetylation of histones H3 and H4 is localized to the LCR and
active genes. In mice homozygous for the LCR
deletion reduced histone hyperacetylation is observed in LCR proximal
sequences; however, deletion of the LCR has no effect on the localized
hyperacetylation of the genes. Together, our results suggest that, in its
native genomic context, the LCR follows the rate model of enhancer function,
and that the developmentally specific hyperacetylation of the globin genes
is independent of both the rate of transcription and the presence of the
LCR.
1. Dirk Schübeler, Matthew C. Lorincz, Daniel M. Cimbora, Agnes Telling, Yong-Quing Feng, Eric E. Bouhassira, and Mark Groudine, "Genomic Targeting of Methylated DNA: Influence of Methylation on Transcription, Replication, Chromatin Structure, and Histone Acetylation", Molecular and Cellular Biology, vol. 20, no. 24: pp. 9103-9112 ( December, 2000).
2. "Activation of DNA Transcription within Repressed Chromatin".
3. "Nuclear Polyanions as De-Repressors of Synthesis of Ribonucleic Acid".
4. "Mated Models of Gene Regulation in Eukaryotes".
5. "Selective Gene De-Repression by De-Repressor RNA".
6. "Oncogenes as Molecular Targets within Active Chromatin".