Signal Amplification in the Detection of Single-copy DNA and RNA by Enzyme-catalyzed Deposition (CARD) of the Novel Fluorescent Reporter Substrate Cy3.29-Tyramide

We demonstrate that the CAtalyzed Reporter Deposition method (CARD), utilizing the novel fluorescent reporter Cy3.29-tyramide, is successful in the Fluorescent in Situ Hybridization (FISH) detection of RNA and single-copy DNA. Histone 4 expression is detected in RNA extracts of 5-phase, synchronized HeLa cells by dot-blot analysis. Gene expression of histone 4 in HeLa cells is demonstrated by FISH via CARD, utilizing oligonucleotide probes. Fluorescence intensity measurements on CARD-amplified histone 4 RNA detection showed (a) a 25-fold amplification of the signal brightness by biotinylated oligonucleotide probes and (b) a sixfold amplification of the signal brightness by horseradish peroxidase (HRP)-labeled histone 4 probes vs the directly stained control. The sensitivity of the CARD method is demonstrated by the FISH detection of single-copy DNA on human corneal fibroblast and HeLa S5 interphase nuclei. Chromosomal localization of the single copy DNA is demonstrated on HeLa S3 metaphase chromosome spreads.