| Summary: | 碩士 === 國立臺灣師範大學 === 生命科學研究所 === 97 === Abstract
Spinocerebellar ataxia type 8 (SCA8) involves the expression of an expanded CTG/CAG combined repeats from opposite strands producing CUG expansion transcripts (ATXN8OS) and a polyglutamine expansion protein (ATXN8). SCA8 disease does not show complete penetrance and repeat expansions have been found among unaffected individuals and patients with other neurological diseases. An apparent CpG island was observed within the 5’ region of the ATXN8OS gene. In this study, we screened the SCA8 CTG repeats distribution in normal controls and in patients with various neurodegenerative diseases. A tatal of three subjects with expanded alleles was found, including one normal and two related oculopharyngeal muscular dystrophy. In the epigenetic studies, aberrant methylation in the overlapped ATXN8OS/KLHL1 gene exon 1 region was evaluated using DNA samples from patients with SCA8 expansions and stable HEK-293 lines carrying 0~157 combined repeats. PCR-based restriction enzyme assay and bisulfite-sequencing assay were performed for the measurement of CpG hypermethylation. No methylation was observed. Additionally, chromatin immunoprecipitation and PCR using antibody associated with repressed or open chromatin were performed to examine the chromatin structure of the SCA8 gene. A repeat length-dependent repression of chromatin structure, which is independent of DNA methylation, was observed. Finally, age and gender-matched lymphoblastoid cells with or without expanded SCA8 alleles were tested for their sensitivity to staurosporine (apoptotic stimulus) and MG-132 (proteosome inhibitor). The results of significant increase of cell death by staurosporine (50 nM) and MG-132 (200 nM) treatment further demonstrate that the expanded SCA8 repeats are toxic to human cells.
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