Fig. 7

Photo-Isolation Chemistry (PIC). RNAs in tissue sections undergo in situ reverse transcription using primers containing UV-cleavable caged nucleotides. Because these modified nucleotides prevent second-strand synthesis by DNA polymerase, double-stranded cDNA is synthesized only in UV-irradiated regions. Subsequent in vitro transcription by T7 polymerase is initiated from a double-stranded promoter sequence