Résumé :
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Facioscapulohumeral muscular dystrophy (FSHD) is a dominant hereditary disease with a prevalence of 7/100,000 births. It is associated with a partial deletion in the 4q35 D4Z4 repeat array that alters chromatin structure and induces gene expression in the FSHD locus (7, 8). Our group has identified the DUX4 gene in each D4Z4 repeat and shown its expression in affected but not control myotubes (2, 4, 5). We showed that the distal DUX4 mRNA extended to a polyadenylation signal in the flanking pLAM region (2). In a large population study this signal was found to provide a toxic gain of function that stabilizes this DUX4 mRNA (6).We have previously shown that the DUX4 promoter was more active in muscle cells compared to other cell type (1, 4). An inhibitory complex containing YY1 was described in HeLa cells and shown to bind to a cis-element in each D4Z4 unit (3). This inhibitory element maps to the DUX4 promoter where it overlaps with the GC box that mediates basal activity (4) and covers a DUX4 transcription start site. In addition, an E box (MyoD binding site) maps 3' of the TACAA box and covers the second transcription initiation site that is more often used in myoblasts (2).We evaluated the role of those cis-elements and trans-factors upon transient expression in muscle or non-muscle cells of the DUX4 promoter fused to the luciferase reporter gene. We tested promoter point mutations and over-expression of YY1 and MyoD. We confirmed the trans-factors interaction with their cis-element by electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP). In summary, we confirmed YY1 binding to the DUX4 promoter but no major inhibition in muscle cells while MyoD could slightly inhibit the DUX4 promoter activity. In conclusion, we propose that DUX4 expression occurs in myotubes because YY1 and MyoD are degraded at this differentiation stage. 1.Ansseau et al., 2009. PLoS One.4:e7482.2.Dixit et al., 2007. Proc Natl Acad Sci U S A. 104: 18157-623.Gabellini et al. 2002. Cell. 110: 339-48.4.Gabriels et al., 1999. Gene 236:25-32.5.Kowaljow et al., 2007. Neuromuscul Disord 17: 611-623. 6.Lemmers et al., 2010. Science 329: 1650-3.7.Petrov et al., 2006. Proc Natl Acad Sci U S A. 103: 6982-7.8.Petrov et al., 2008. Genome Res. 18: 39-45.
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