The Huntington's disease gene promoter

Recent studies have demonstrated that affected regions of the striatum show increased HD immunoreactivity, suggesting that subtle differences in expression of the HD protein may be relevant to pathogenesis. Current information regarding control of HD gene expression is limited, and to date has been based entirely upon sequence analysis of the promoter region. The overall aim of this thesis, therefore, was to carry out a more detailed analysis of the HD gene promoter, in order to identify its key regulatory elements, and to attempt to determine the relationship between promoter activity and various aspects of HD pathogenesis. Single-stranded conformation polymorphism analysts, heteroduplex and sequencing analyses were used to demonstrate that the HD gene promoter is highly polymorphic. Seven allelic forms were identified. This region of the promoter was found to be highly conserved in non-human primates, which may reflect a common mechanism of gene regulation. Reporter gene assays were used to localise the key regulatory regions, whilst the ability of specific transcription factors to bind the putative sites was studied using the Electrophoretic Mobility Shift Assay. The critical positive-acting region of the HD gene promoter was shown to arise from the synergistic action of two sites in a tandem repeat, which each bind the transcription factor, Sp1. Differences in expression control have been found to exist between a neuronal and a non-neuronal cell line, and the regions of the promoter responsible for these effects have been localised. Both 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and forskolin were found to elicit a cell-type specific response in transcription from the HD gene promoter. The responses to TPA have been mapped in detail in the neuronal SK-N-SH cell line and in HeLa cells. Additional experiments, including a comparison of promoter activity in undifferentiated and differentiated neurons, and a study of the effects of excitotoxins upon activity, have addressed questions regarding temporal patterns and modulations of expression from the HD gene promoter.