The Krüppel-like factor 15 as a molecular link between myogenic factors and a chromosome 4q transcriptional enhancer implicated in facioscapulohumeral dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD), a dominant hereditary disease with a prevalence of 7 per 100,000 individuals, is associated with a partial deletion in the subtelomeric D4Z4 repeat array on chromosome 4q. The D4Z4 repeat contains a strong transcriptional enhancer that activates promoters of several FSHD-related genes. We report here that the enhancer within the D4Z4 repeat binds the Krüppel-like factor KLF15. KLF15 was found to be up-regulated during myogenic differentiation induced by serum starvation or by overexpression of the myogenic differentiation factor MYOD. When overexpressed, KLF15 activated the D4Z4 enhancer and led to overexpression of DUX4c (Double homeobox 4, centromeric) and FRG2 (FSHD region gene 2) genes, whereas its silencing caused inactivation of the D4Z4 enhancer. In immortalized human myoblasts, the D4Z4 enhancer was activated by the myogenic factor MYOD, an effect that was abolished upon KLF15 silencing or when the KLF15-binding sites within the D4Z4 enhancer were mutated, indicating that the myogenesis-related activation of the D4Z4 enhancer was mediated by KLF15. KLF15 and several myogenesis-related factors were found to be expressed at higher levels in myoblasts, myotubes, and muscle biopsies from FSHD patients than in healthy controls. We propose that KLF15 serves as a molecular link between myogenic factors and the activity of the D4Z4 enhancer, and it thus contributes to the overexpression of the DUX4c and FRG2 genes during normal myogenic differentiation and in FSHD.

A nuclear matrix attachment site in the 4q35 locus has an enhancer-blocking activity in vivo: implications for the facio-scapulo-humeral dystrophy.

Facio-scapulo-humeral dystrophy (FSHD), a muscular hereditary disease with a prevalence of 1 in 20,000, is caused by a partial deletion of a subtelomeric repeat array on chromosome 4q. Earlier, we demonstrated the existence in the vicinity of the D4Z4 repeat of a nuclear matrix attachment site, FR-MAR, efficient in normal human myoblasts and nonmuscular human cells but much weaker in muscle cells from FSHD patients. We now report that the D4Z4 repeat contains an exceptionally strong transcriptional enhancer at its 5'-end. This enhancer up-regulates transcription from the promoter of the neighboring FRG1 gene. However, an enhancer blocking activity was found present in FR-MAR that in vitro could protect transcription from the enhancer activity of the D4Z4 array. In vivo, transcription from the FRG1 and FRG2 genes could be down- or up-regulated depending on whether or not FR-MAR is associated with the nuclear matrix. We propose a model for an etiological role of the delocalization of FR-MAR in the genesis of FSHD.

A functional role for 4qA/B in the structural rearrangement of the 4q35 region and in the regulation of FRG1 and ANT1 in facioscapulohumeral dystrophy.

The number of D4Z4 repeats in the subtelomeric region of chromosome 4q is strongly reduced in patients with Facio-Scapulo-Humeral Dystrophy (FSHD). We performed chromosome conformation capture (3C) analysis to document the interactions taking place among different 4q35 markers. We found that the reduced number of D4Z4 repeats in FSHD myoblasts was associated with a global alteration of the three-dimensional structure of the 4q35 region. Indeed, differently from normal myoblasts, the 4qA/B marker interacted directly with the promoters of the FRG1 and ANT1 genes in FSHD cells. Along with the presence of a newly identified transcriptional enhancer within the 4qA allele, our demonstration of an interaction occurring between chromosomal segments located megabases away on the same chromosome 4q allows to revisit the possible mechanisms leading to FSHD.

Chromatin loop domain organization within the 4q35 locus in facioscapulohumeral dystrophy patients versus normal human myoblasts.

Fascioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disorder linked to partial deletion of integral numbers of a 3.3 kb polymorphic repeat, D4Z4, within the subtelomeric region of chromosome 4q. Although the relationship between deletions of D4Z4 and FSHD is well established, how this triggers the disease remains unclear. We have mapped the DNA loop domain containing the D4Z4 repeat cluster in human primary myoblasts and in murine-human hybrids. A nuclear matrix attachment site was found located in the vicinity of the repeat. Prominent in normal human myoblasts and nonmuscular human cells, this site is much weaker in muscle cells derived from FSHD patients, suggesting that the D4Z4 repeat array and upstream genes reside in two loops in nonmuscular cells and normal human myoblasts but in only one loop in FSHD myoblasts. We propose a model whereby the nuclear scaffold/matrix attached region regulates chromatin accessibility and expression of genes implicated in the genesis of FSHD.

Surface potential mapping of dispersed proteins.

We describe a method for detecting proteins after transfer to PVDF membranes, based on the surface potential attributed to each protein. Proteins separated by classical two-dimensional polyacrylamide gel electrophoresis could be detected by scanning the membrane surface with a vibrating capacitor (also called a Kelvin probe) on the basis of differences between their surface potential and that of the membrane. Coupled to colloidal gold staining, the technique enables detection of proteins previously undetectable by classical staining methods. Plotting variations of the surface potential in two dimensions visualizes proteins which migrate close together. Finally, we demonstrate that the Kelvin probe detects proteins over a concentration range from micro to sub-nanogram with increased sensitivity at lower concentrations, and unlike other methods, appears to be similar for all proteins tested so far. The method described is fast, reliable, and it can be automated for high throughput.

Identification of new proteins in follicular fluid of mature human follicles.

Proteins present in human follicular fluid (HFF) have been poorly characterized to date. The purpose of our study was to analyse the protein content and identify new proteins originating from fluid of mature human follicles. A total of six females from infertile couples referred for in vitro fertilization (IVF) were stimulated and 44 follicular fluid samples from mature follicles yielding an oocyte were collected 34-36 h after human chorionic gonadotropin administration. HFF samples were processed for high-resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). Comparative analysis of the 2-D gels revealed up to 600 spots, of which four were selected because of variations in their expression level. Using direct sequencing procedures (Edman degradation) or matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS), these four spots were identified as three new proteins: thioredoxin peroxydase 1 (TDPX1), transthyretin (TTR) and retinol-binding protein (RBP). The proteins identified here may emerge as potential candidates for specific functions during folliculogenesis and may prove useful as biomedical markers for follicle and/or oocyte maturation.