Identifying and characterizing genes near the Huntington's disease gene

The human genome is large and its gene organization is complex. Since current molecular technology has not proven that all of the genes in the human genome can be isolated and characterized, new and modified techniques are constantly being developed. Huntington's disease (HD) is an autosomal dominant disorder that was mapped to a small segment of the human genome in 1983. Since the gene that causes the HD defect lies in an unusual segment of the human genome, it is highly likely that new technology will be required to clone and characterize this gene. This thesis describes a simple method for identifying gene-specific DNA probes and the application of this technology to the HD gene region. This technique couples the subcloning of small genomic fragments with an extensive screening system that eliminates repetitive DNA sequences. These low copy probes are then used to identify transcripts using Northern blot analysis of RNA isolated from a number of transformed human cell lines. Several potential transcripts were identified which were physically linked to the HD gene. Of this set, two genes were isolated and characterized in more detail. The first transcript proved to be related to a human ribosomal protein gene; however, further studies have suggested that this probe was isolated from a nontranscribed pseudogene which maps to the HD gene region. A second gene was isolated and was found to be homologous to a rat neuron-specific gene. Since the pathologic hallmark of Huntington's disease is a neuron-specific cell death, additional work examined this gene for potential HD-specific mutations. Although no mutations have been identified to date, the isolation of this gene proves that the methods developed in this thesis are effective for identifying tissue-specific genes. The continued application of this system to the HD gene region will aid in the identification of additional candidate disease genes and could contribute to the identification and cloning of the gene which causes this common neurodegenerative disease.