Localization of Trinucleotide Repeat Sequences in Myotonic Dystrophy Cells Using a Single Fluorochrome-Labeled PNA Probe

A labeled peptide nucleic acid (PNA) antisense probe was used to study the spatial distribution of triplet repeats (CTG) in human myotonic dystrophy (DM) cells by high-resolution fluorescence in situ hybridization (FISH). It was found that transcripts containing triplet repeats were present as a number of discrete foci in the DM nuclei. Greater numbers of foci were visible with the PNA probe than a comparable DNA probe. The PNA probe was also used to visualize the triplet-repeat expansion within the DM gene located on chromosome 19. Using the intensity of the expanded triplet-repeat on the chromosomes as a reference, it was estimated there were between 15-230 RNA molecules in each focus observed in DM nuclei.