Analysis of minisatellites in humans and mice
thesisposted on 15.12.2014, 10:38 by John David Hadley. Stead
Mutation processes have previously been studied in human minisatellites with mutation rates of 1-15% per sperm. In this thesis, this work was expanded in two directions. The first was to characterise mouse minisatellites to generate a mouse model for the detailed analysis of minisatellite instability. The second was to analyse mutation in human minisatellites with lower mutation rates, to determine whether common mutation mechanisms operate at all human minisatellites.;A screen for endogenous mouse minisatellites identified 77 loci, the majority of which were structurally similar to human minisatellites. There was no evidence for the existence of mouse minisatellites with mutation rates above 10-4 per gamete, suggesting a fundamental difference between germline tandem repeat instability in humans and mice.;To extend mutation analysis in humans to minisatellites with lower mutation rates, the insulin minisatellite was investigated. Allele diversity was characterised by mapping variant repeat distribution in 876 alleles, and de novo mutations were isolated from both germline and soma. Two forms of mutation were identified, the major resulting in simple deletions and duplications which were at least partially of premeiotic origin, and a minor form involving complex intra- and inter-allelic rearrangements of repeats, similar to mutation processes observed at hypermutable minisatellites, and almost certainly of meiotic origin. Homozygosity had not effect on either the rate or complexity of germline mutation.;The insulin minisatellite is the best known candidate for the type 1 diabetes susceptibility locus IDDM2. Variant repeat distribution and flanking haplotypes were combined to identify five newly defined ancestral lineages which were used to further characterise association of the insulin-linked region with disease. This study found that type 1 diabetes risk was influenced by extended haplotype, raising doubts over the role of the minisatellite in disease susceptibility. A model to account for IDDM2-associated pathology is presented.