Abstract
Facio-Scapulo Humeral dystrophy (FSHD) is the third most common myopathy, affecting 1 amongst 10,000 individuals (FSHD1, OMIM #158900). This autosomal dominant pathology is associated in 95% of cases with genetic and epigenetic alterations in the subtelomeric region at the extremity of the long arm of chromosome 4 (q arm). A large proportion of the remaining 5% of cases carry a mutation in the SMCHD1 gene (FSHD2, OMIM #158901). Here, we explored the 3D organization of the 4q35 locus by three-dimensions DNA in situ fluorescent hybridization (3D-FISH) in primary fibroblasts isolated from patients and healthy donors. We found that D4Z4 contractions and/or SMCHD1 mutations impact the spatial organization of the 4q35 region and trigger changes in the expression of different genes. Changes in gene expression were corroborated in muscle biopsies suggesting that the modified chromatin landscape impelled a modulation in the level of expression of a number of genes across the 4q35 locus in FSHD. Using induced pluripotent stem cells (hIPSC), we further examined whether chromatin organization is inherited after reprogramming or acquired during differentiation and showed that folding of the 4q35 region is modified upon differentiation. These results together with previous findings highlight the role of the D4Z4 macrosatellite repeat in the topological organization of chromatin and further indicate that the D4Z4-dependent 3D structure induces transcriptional changes of 4q35 genes expression.
Highlights
Over the recent years, sequence distribution within the nuclear space, nuclear topology and long-distance interactions have emerged as key elements in the regulation of gene expression and cell fate determination
In order to get a precise insight into the 3D DNA interactions within the 4q35 locus in normal and pathological conditions, i.e., influence of D4Z4 array size or SMCHD1 mutation, we investigated the three-dimensional chromatin organization of the locus using hybridization techniques in primary cells isolated from Facio-Scapulo-Humeral Dystrophy (FSHD) individuals and controls
Given the peculiar organization of the 4q35 region and the topological role played by D4Z4 in healthy and diseased cells[12,13,16], we aimed at deciphering the higher-order changes of this locus in FSHD1 and 2 patients compared to healthy donors
Summary
Sequence distribution within the nuclear space, nuclear topology and long-distance interactions have emerged as key elements in the regulation of gene expression and cell fate determination. Regarding this disease-associated topological disorganization, one intriguing locus is the 4q35 subtelomere[17,18] This gene-poor locus characterized by the presence of gene deserts and large blocks of repetitive DNA sequence, including blocks of (CA)n microsatellites, variable number of tandem 3.3 Kb D4Z4 macrosatellite repeats and β satellite elements is localized at the nuclear periphery, a nuclear compartment enriched in heterochromatin[12,17,18,19,20]. Affected individuals exhibit between 1–10 repeats whereas the general population have a number of repeats above 10 (up to 100)[27] Shortening of this repetitive the array is associated with DNA hypomethylation and relaxation of the macrosatellite chromatin suggesting the involvement of epigenetic changes in the disease[16,28,29,30]. Smchd[1] is involved in silencing of repetitive DNA sequences and formation of long distance loops at the Hox genes loci and inactive X chromosome[33]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
