Exploiting dinucleotide microsatellites conserved among mammalian species.

Dinucleotide microsatellites are useful for gene mapping projects. Depending upon definition of conservation, published estimates of dinucleotide microsatellite conservation levels vary dramatically (30% to 100%). This study focused on well-characterized genes that contain microsatellites in the human genome. The objective was to examine the feasibility of developing microsatellite markers within genes on the basis of the assumption of microsatellite conservation across distantly related species. Eight genes (Gamma-actin, carcinoembryonic antigen, apolipoprotein A-II, cardiac beta myosin heavy chain, laminin B2 chain, MHC class I CD8 alpha chain, c-reactive protein, and retinoblastoma susceptibility protein) containing large dinucleotide repeat units (N > or = 15), complete genomic structure information, and homologous gene sequences in a second species were selected. Heterologous primers were designed from conserved exon sequences flanking a microsatellite motif. PCR products from bovine and porcine genomic DNA were tested for the presence of microsatellite sequences by Southern blot hybridization with biotin-labeled (CA)12 oligonucleotides. Fragments containing microsatellites were cloned and sequenced. Homology was verified by sequence comparisons between human and corresponding bovine or porcine fragments. Four of sixteen (25%) cross-amplified PCR products contained dinucleotide repetitive sequences with repeat unit lengths of 5 to 23. Two dinucleotide repetitive sequences showed microsatellite length polymorphism, and an additional sequence displayed single-strand conformational polymorphism. Results from this study suggest that exploitation of conserved microsatellite sequences is a useful approach for developing specific genetic markers for comparative mapping purposes.