Sequence analysis of trinucleotide repeat microsatellites from an enrichment library of the equine genome

Microsatellites are useful tools for the construction of a linkage map and parentage testing of equines, but only a limited number of equine microsatellites have been elucidated. Thus, we constructed the equine genomic library enriched for DNA fragments containing (CAG)n repeats. The enriched method includes hybridization-capture of repeat regions using biotin-conjugated oligonucleotides, nucleotide substrate-biased polymerase reaction with the oligonucleotides and subsequent PCR amplification, because these procedures are useful for the cloning of less abundant trinucleotide microsatellites. Microsatellites containing (CAG)n repeats were obtained at the ratio of one per 3-4 clones, indicating an enrichment value about 10(4)-fold, resulting in less time consumption and less cost for cloning. In this study, 66 different microsatellites, (CAG)n repeats, were identified. The number of complete simple CAG repeats in our clones ranged 4-33, with an average repeat length of 8.8 units. The microsatellites were useful as sequence-tagged site (STS) markers. In addition, some clones containing (CAG)n repeats showed homology to human (CAG)n-containing genes, which have been previously mapped. These results indicate that the clones might be a useful tool for chromosome comparison between equines and humans.