Three-dimensional super-resolution microscopy of the inactive X chromosome territory reveals a collapse of its active nuclear compartment harboring distinct Xist RNA foci

Epigenetics & Chromatin

Marion Cremer¹  Lothar Schermelleh³  Thomas Cremer¹  Neil Brockdorff³  Heinrich Leonhardt¹  Jens Popken¹  Justin Demmerle³  Susanne Fiedler¹  Michael Sterr¹  Andrea Cerase³  Anna Tattermusch³  Felix Kraus³  Volker J Schmid²  Yolanda Markaki¹  Daniel Smeets³ 

[1] Biocenter, Department of Biology II, Ludwig Maximilians University (LMU), Martinsried, Germany;Institute of Statistics, Ludwig Maximilians University (LMU), Munich, Germany;Department of Biochemistry, University of Oxford, Oxford, UK

关键词: SAF-A;    Interchromatin compartment;    Chromatin domain;    Barr body;    Xist RNA;    CT;    Chromosome territory;    Inactive X chromosome;    X chromosome inactivation;    Super-resolution microscopy;   

Others  :  813325
DOI  :  10.1186/1756-8935-7-8

 received in 2014-04-02, accepted in 2014-04-11,  发布年份 2014

【 摘 要 】

Background

A Xist RNA decorated Barr body is the structural hallmark of the compacted inactive X territory in female mammals. Using super-resolution three-dimensional structured illumination microscopy (3D-SIM) and quantitative image analysis, we compared its ultrastructure with active chromosome territories (CTs) in human and mouse somatic cells, and explored the spatio-temporal process of Barr body formation at onset of inactivation in early differentiating mouse embryonic stem cells (ESCs).

Results

We demonstrate that all CTs are composed of structurally linked chromatin domain clusters (CDCs). In active CTs the periphery of CDCs harbors low-density chromatin enriched with transcriptionally competent markers, called the perichromatin region (PR). The PR borders on a contiguous channel system, the interchromatin compartment (IC), which starts at nuclear pores and pervades CTs. We propose that the PR and macromolecular complexes in IC channels together form the transcriptionally permissive active nuclear compartment (ANC). The Barr body differs from active CTs by a partially collapsed ANC with CDCs coming significantly closer together, although a rudimentary IC channel system connected to nuclear pores is maintained. Distinct Xist RNA foci, closely adjacent to the nuclear matrix scaffold attachment factor-A (SAF-A) localize throughout Xi along the rudimentary ANC. In early differentiating ESCs initial Xist RNA spreading precedes Barr body formation, which occurs concurrent with the subsequent exclusion of RNA polymerase II (RNAP II). Induction of a transgenic autosomal Xist RNA in a male ESC triggers the formation of an ‘autosomal Barr body’ with less compacted chromatin and incomplete RNAP II exclusion.

Conclusions

3D-SIM provides experimental evidence for profound differences between the functional architecture of transcriptionally active CTs and the Barr body. Basic structural features of CT organization such as CDCs and IC channels are however still recognized, arguing against a uniform compaction of the Barr body at the nucleosome level. The localization of distinct Xist RNA foci at boundaries of the rudimentary ANC may be considered as snap-shots of a dynamic interaction with silenced genes. Enrichment of SAF-A within Xi territories and its close spatial association with Xist RNA suggests their cooperative function for structural organization of Xi.

【 授权许可】

   
2014 Smeets et al.; licensee BioMed Central Ltd.

【 图 表 】

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