Simultaneous in situ detection of RNA, DNA, and protein using tyramide-coupled immunofluorescence

The use of tyramide-coupled immunofluorescence at the single cell level provides expedient, clean, and sensitive signals for detection of DNA, RNA, or proteins. The principle is based on the ability of horseradish peroxidase (HRP) to cleave tyramides into a free radical species with a very short diffusion radius. The free radicals are then covalently bound to electron-rich moieties such as tyrosine in proteins proximal to the targets. Here we present protocols for tyramide fluorescent in situ hybridization (T-FISH), which detects unique DNA species using DNA probes as short as approx 300-500 bp, or unique RNA species with probes as small as an oligonucleotide. We also present a protocol for tyramide immunofluorescence (T-IF) to detect protein antigens. By combining these protocols with several tyramide-coupled fluorophores, multiple targets can be detected simultaneously in situ, which is ideal for in-depth analyses at the molecular and cellular levels. Finally, we describe the detection of nascent viral RNA transcripts simultaneously with integrated viral genomes or chromosomal domains in single cells or tissue sections.