Chromosomal detection of simple sequence repeats (SSRs) using nondenaturing FISH (ND-FISH)

Simple Sequence Repeats (SSRs) are known to be scattered and present in high number in eukaryotic genomes. We demonstrate that dye-labeled oligodeoxyribonucleotides with repeated mono-, di-, tri, or tetranucleotide motifs (15-20 nucleotides in length) have an unexpected ability to recognize SSR target sequences in non-denatured chromosomes. The results show that all these probes are able to invade chromosomes, independent of the size of the repeat motif, their nucleotide sequence, or their ability to form alternative B-DNA structures such as triplex DNA. This novel and remarkable property of binding SSR oligonucleotides to duplex DNA targets permitted the development of a non-denaturing fluorescence in situ hybridization method that quickly and efficiently detects SSR-enriched chromosome regions in mitotic, meiotic, and polytene chromosome spreads of different model organisms. These results have implications for genome analysis and for investigating the roles of SSRs in chromosome structure and function.