Background:

Pyronin Y is an intercalating cationic dye that shows specificity towards RNA.

Pyronin Y forms fluorescent complexes with double-stranded nucleic acids, especially RNA, enabling semi-quantitative analysis of cellular RNA in flow cytometry, to estimate the RNA content per cell in formalin fixed EL4 leukosis tumor cells, enzyme dispersed R3327-G rat prostatic adenocarcinoma cells, mouse spleen cells stimulated with concanavalin A, and human peripheral blood lymphocytes stimulated with phytohemagglutinin[1]. A fluorescent staining procedure based on pyronin Y is described. The technique has been used to stain RNA in human reticulocytes for subsequent flow analysis and sorting[2]. In viable cells this dye also accumulates in mitochondria. At a concentration of 1.7 to 3.3 μM, pyronin Y is localized almost exclusively in mitochondria of cultured cells, similar to another mitochondria! probe, rhodamine 123. At that concentration PY is not toxic but suppressed cell growth, arresting cells[3]. Pyronin Y has long been used, in combination with other dyes such as Methyl Green, as a differential stain for nucleic acids in paraffin tissue sections. In sections stained with Methyl Green-pyronin Y, red blood cells, elastic fibre of blood vessels, zymogen granules of pancreatic acinar cells, surface membrane of heptocytes and kidney tubular cells showed strikingly strong green and/or red fluorescence, while the nuclei of cells appeared non-fluorescent[4].

[1]. Pollack A, et al. Flow cytometric analysis of RNA content in different cell populations using pyronin Yand methyl green. Cytometry. 1982 Jul;3(1):28-35. [2]. Tanke HJ, et al. Flow cytometry of human reticulocytes based on RNA fluorescence. Cytometry. 1981 Mar;1(5):313-20. [3]. Darzynkiewicz Z, et al. Cytostatic and cytotoxic properties of pyronin Y: relation to mitochondrial localization of the dye and its interaction with RNA. Cancer Res. 1986 Nov;46(11):5760-6. [4]. Li B, et al. Pyronin Y as a fluorescent stain for paraffin sections. Histochem J. 2002 Jun-Jul;34(6-7):299-303.