Research article

Remodeling of the chromatin structure of the facioscapulohumeral muscular dystrophy (FSHD) locus and upregulation of FSHD-related gene 1 (FRG1) expression during human myogenic differentiation

Beatrice Bodega¹ , Gabriella Di Capua Ramirez¹ , Florian Grasser² , Stefania Cheli¹ , Silvia Brunelli³ , Marina Mora⁴ , Raffaella Meneveri³ , Anna Marozzi¹ , Stefan Mueller² , Elena Battaglioli^{* 1} and Enrico Ginelli^{* 1}

¹Department of Biology and Genetics for Medical Sciences, University of Milan, Milan, Italy

²Department of Biology II, Anthropology and Human Genetics, Ludwig Maximilians University, Munich, Germany

³Department of Experimental Medicine, University of Milan-Bicocca, Monza, Italy

⁴Neuromuscular Diseases and Neuroimmunology Unit, Muscle Cell Biology Laboratory, C. Besta Neurological Institute, Milan, Italy

author email corresponding author email* Contributed equally

BMC Biology 2009, 7:41doi:10.1186/1741-7007-7-41

Published:	16 July 2009

Abstract

Background

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder associated with the partial deletion of integral numbers of 3.3 kb D4Z4 DNA repeats within the subtelomere of chromosome 4q. A number of candidate FSHD genes, adenine nucleotide translocator 1 gene (ANT1), FSHD-related gene 1 (FRG1), FRG2 and DUX4c, upstream of the D4Z4 array (FSHD locus), and double homeobox chromosome 4 (DUX4) within the repeat itself, are upregulated in some patients, thus suggesting an underlying perturbation of the chromatin structure. Furthermore, a mouse model overexpressing FRG1 has been generated, displaying skeletal muscle defects.

Results

In the context of myogenic differentiation, we compared the chromatin structure and tridimensional interaction of the D4Z4 array and FRG1 gene promoter, and FRG1 expression, in control and FSHD cells. The FRG1 gene was prematurely expressed during FSHD myoblast differentiation, thus suggesting that the number of D4Z4 repeats in the array may affect the correct timing of FRG1 expression. Using chromosome conformation capture (3C) technology, we revealed that the FRG1 promoter and D4Z4 array physically interacted. Furthermore, this chromatin structure underwent dynamic changes during myogenic differentiation that led to the loosening of the FRG1/4q-D4Z4 array loop in myotubes. The FRG1 promoter in both normal and FSHD myoblasts was characterized by H3K27 trimethylation and Polycomb repressor complex binding, but these repression signs were replaced by H3K4 trimethylation during differentiation. The D4Z4 sequences behaved similarly, with H3K27 trimethylation and Polycomb binding being lost upon myogenic differentiation.

Conclusion

We propose a model in which the D4Z4 array may play a critical chromatin function as an orchestrator of in cis chromatin loops, thus suggesting that this repeat may play a role in coordinating gene expression.