| Facioscapulohumeral muscular dystrophy (FSHD) is the third most common genetic disease of skeletal muscle, affecting approximately 1 in 20,000 births. Unlike other muscular dystrophies, the molecular mechanism responsible for FSHD remains unknown. More than 95% of cases of FSHD are associated with a partial deletion in repeated DNA units near the end of chromosome 4; however, a specific genetic abnormality that causes the disease has not been identified. Recently, Winokur et al. have discovered that the majority of genes found to be misregulated in FSHD are involved in muscle differentiation and many of them were direct targets of MyoD (Winokur et al., 2003). However, it was unclear whether this defect in MyoD-dependent network resulted directly from the deletion of D4Z4 repeats at 4q35 or as a secondary defect from dystrophic changes in FSHD muscle or other factors upstream of MyoD. Utilizing mRNA expression profiling, I show in this dissertation that the defect in MyoD-dependent network in FSHD is a secondary defect. I further show that there are inherent transcriptional regulation defects in FSHD fibroblasts and suggest that these defects may directly or indirectly influence the myogenic development program in FSHD. As it was hypothesized that transcripts from the D4Z4 repeat, or an adjacent region, is expressed on the deleted allele due to loss of repressive chromatin, in the latter half of my dissertation I show that multiple bidirectional small RNA transcripts arise from the D4Z4 repeat, whereas the full-length DUX4 encoding transcript is not detected. I also explore the possibility that the full-length DUX4 encoding transcripts might be processed to produce regulatory RNA fragments, such as microRNA. I show that 5 microRNA-like fragments were generated from the D4Z4 region using probes specific to those regions on microRNA northern blots. I also show that in both fibroblast and myoblast cell lines, there is a trend for higher abundance of the microRNA-like fragments in FSHD cells and in cells differentiated to muscle. Overall, my works highlighted the possibility that these RNAs or their encoded peptides contribute to the pathophysiology of FSHD independently of the full-length DUX4. |
