Meta-phosphoric acid-its use in the selective extraction of RNA from fixed tissue sections

This communication presents a new quick method for selective extraction of RNA from formalin-fixed tissues, such as kidney, intestine, ovary and testis of white rat and liver of rodents, Tatera indica and Millardia meltada and of the frog, Rana tigrina as well as of human wart. Sections of pancreas and kidney fixed in acetic acid-alcohol were also tried. The method is to treat deparaffinised sections in 20% and 15% meta-phosphoric acid at 5 degrees C for 10-20 and 20-30 min, respectively, and then to stain nuclear DNA with 0.5% aqueous solution of methyl green, methylene green, Giemsa, toluidine blue O or 0.125% pyronin G for 2 min, rinsed with water, treated with n-butanol for 2-3 min, cleared in xylene and mounted. It has been found that liver sections of rodents require 24 hours of treatment in 15% cold meta-phosphoric acid for complete removal of RNA, whereas those of the frog require only 20 min at 20% acid. It has been concluded that following treatment of sections in cold meta-phosphoric acid, RNA is extracted selectively leaving DNA in a native state. Therefore, staining of DNA in tissue sections from which RNA has been extracted is due to binding of its negatively charged phosphate groups with the positively charged dye molecules.