| Description |
Approximately 10% of all American women develop breast cancer during their lifetimes. A genetic trait which is passed through families in an autosomal dominant fashion is responsible for 5% to 10% of the cases. Women who care a breast cancer susceptibility gene have an 85% lifetime risk of breast cancer and also often have an increased risk of ovarian cancer. In 1990, a report was published that demonstrated that breast and ovarian cancer susceptibility in some families was genetically linked to chromosome 17q. This thesis describes work performed in the research group led by Mark H. Skolnick which ultimately cloned the gene, BRCA1. To clone BRCA1, it was first necessary to confirm and refine the genetic linkage in Utah breast cancer families. For this purpose, polymorphic microsatellites were used as genetic markers. Initially the physical positions of genetic markers which flanked BRCA1 were confirmed through a panel of hybrid cell lines. Markers with the region containing the gene were then used as starting points for the assembly of YAC contigs, which were subsequently used as frameworks for fine-scale physical mapping. This finer mapping utilized small clones in vectors, such as P1s and BACs, from which additional genetic and physical markers could be readily obtained to increasingly refine the region. During this work, one new PCR-based technique was developed that significantly aided in obtaining markers from YACs as well as other clones. Ultimately, BRCA1 was localized to a 600 kilobase region that was entirely covered by a P1 and PAC contig. It was necessary to identify and characterize the potential candidate genes which were present. Each candidate gene was amplified in segments by PCR from the DNA or cDNA of mutation-carriers, then completely sequenced to identify germline mutations which would indicate the gene was BRCA1. Ultimately, loss of function mutations in affected BRCA1 family members pinpointed one gene with a 7.8 kilobase transcript as BRCA1. BRCA1 proved to have little similarity to other know genes. Current research suggest that BRCA1 and the more recently-discovered BRCA2 are both involved in DNA double strand break repair. |
