Nucleic Acids Research Advance Access originally published online on August 20, 2009
Nucleic Acids Research 2009 37(18):6019-6027; doi:10.1093/nar/gkp677
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Nucleic Acids Research, 2009, Vol. 37, No. 18 6019-6027
© The Author 2009. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses?by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Gene Regulation, Chromatin and Epigenetics |
BRG1 directly regulates nucleosome structure and chromatin looping of the 
globin locus to activate transcription
1Department of Pharmacology, University of Wisconsin School of Medicine and Public Health, Medical Sciences Center, Madison, WI and 2Department of Genetics, University of North Carolina, Chapel Hill, NC 27599-7264, USA
*To whom correspondence should be addressed. Email: scott_bultman{at}med.unc.edu
Received May 18, 2009. Revised July 13, 2009. Accepted July 31, 2009.
globin expression must be regulated properly to prevent the occurrence of -thalassemias, yet many questions remain unanswered regarding the mechanism of transcriptional activation. Identifying factors that regulate chromatin structure of the endogenous globin locus in developing erythroblasts will provide important mechanistic insight. Here, we demonstrate that the BRG1 catalytic subunit of SWI/SNF-related complexes co-immunoprecipitates with GATA-1 and EKLF in murine fetal liver cells in vivo and is recruited to the far-upstream major-regulatory element (MRE) and 2 promoter. Furthermore, based on our analysis of Brg1null/ENU1 mutant mice, BRG1 regulates DNase I sensitivity, H3ac, and H3K4me2 but not CpG methylation at both sites. Most importantly, BRG1 is required for chromatin loop formation between the MRE and 2 promoter and for maximal RNA Polymerase II occupancy at the 2 promoter. Consequently, Brg1 mutants express globin mRNA at only 5–10% of wild-type levels and die at mid-gestation. These data identify BRG1 as a chromatin-modifying factor required for nucleosome remodeling and transcriptional activation of the globin locus. These data also demonstrate that chromatin looping between the MRE and 2 promoter is required as part of the transcriptional activation mechanism.