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Large-scale chromatin structure of inducible genes: transcription on a condensed, linear template

Department of Cell and Developmental Biology, University of Illinois, Urbana, IL 61801

Correspondence to Andrew S. Belmont: asbel{at}illinois.edu

The structure of interphase chromosomes, and in particular the changes in large-scale chromatin structure accompanying transcriptional activation, remain poorly characterized. Here we use light microscopy and in vivo immunogold labeling to directly visualize the interphase chromosome conformation of 1–2 Mbp chromatin domains formed by multi-copy BAC transgenes containing 130–220 kb of genomic DNA surrounding the DHFR, Hsp70, or MT gene loci. We demonstrate near-endogenous transcription levels in the context of large-scale chromatin fibers compacted nonuniformly well above the 30-nm chromatin fiber. An approximately 1.5–3-fold extension of these large-scale chromatin fibers accompanies transcriptional induction and active genes remain mobile. Heat shock–induced Hsp70 transgenes associate with the exterior of nuclear speckles, with Hsp70 transcripts accumulating within the speckle. Live-cell imaging reveals distinct dynamic events, with Hsp70 transgenes associating with adjacent speckles, nucleating new speckles, or moving to preexisting speckles. Our results call for reexamination of classical models of interphase chromosome organization.

© 2009 Hu et al.
This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jcb.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

N. Ashourian's present address is Laboratory of Biochemistry and Molecular Biology, National Cancer Institute, Bethesda, MD 20814.

Abbreviations used in this paper: AAD, acidic activation domain; BAC, bacterial artificial chromosome; DHFR, dihydrofolate reductase; DRB, 5,6-dichloro-1-β-D-ribobenzimidazole; Hsp 70, heat shock protein 70; IGC, interchromatin granule clusters; Mbp, megabase pair; mRFP, monomeric red fluorescent protein; MT, metallothionein; qPCR, quantitative PCR; qRT-PCR, quantitative RT-PCR.

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This article has been cited by other articles:

• Vitali, P., Royo, H., Marty, V., Bortolin-Cavaille, M.-L., Cavaille, J. (2010). Long nuclear-retained non-coding RNAs and allele-specific higher-order chromatin organization at imprinted snoRNA gene arrays. J. Cell Sci. 123: 70-83 [Abstract] [Full Text]  
• McNally, J. G. (2009). Transcription, chromatin condensation, and gene migration. JCB 185: 7-9 [Abstract] [Full Text]  

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