Length of uninterrupted repeats determines instability at the unstable mouse expanded simple tandem repeat family MMS10 derived from independent SINEB1 elements

Mouse expanded simple tandem repeats (ESTRs) provide highly informative loc i for analyzing spontaneous and induced germline mutation. We have conducte d an extensive sequence database search and identified 17 new members of th e highly unstable rodent-specific ESTR family called MMS10. This family has arisen by independent expansions of a common GGCAGA repeat unit from withi n a subset of both ancestral and modern SINE Fl elements during the course of mouse evolution. Analysis of the interspersion patterns of variant repea ts along alleles of 20 of these MMS10 loci revealed two distinct classes of tandem arrays: one composed of uninterrupted GGCAGA repeats and the second with generally larger arrays interrupted by variant units. Surveys of alle lic diversity at 11 representative members of these two classes of loci in various laboratory strains and BXD recombinant inbred lines revealed that t he level of repeat instability was positively correlated with the length of uninterrupted repeats. Turnover processes at MMS 10 loci, therefore, appea r similar to the type of mechanism observed at human microsatellites. The M MS10 family thus provides a potentially useful murine model for studying dy namic mutation at simple tandem repeats.