Methyl green-pyronin stain distinguishes proliferating from differentiated nonproliferating cell nuclei after acid denaturation of DNA.

We applied methyl green-pyronin (MG-P) stain, which is usually used for the selective staining of DNA and RNA, to frozen sections of rat jejunal and esophageal mucosa, following digestion with RNase and treatment with various concentrations of HCl. The pyroninophilia of the nuclei increased with increasing strength of the acid, but the susceptibility of the nuclei to acid differed among cell populations. In the jejunal epithelium, at an appropriate acid strength the nuclei in the crypts of Lieberkuhn were less acid-sensitive and remained blue-green, whereas those in the villi were more pyroninophilic and stained lavender. Under the same conditions, the nuclei in the basal layer of the esophageal epithelium were blue-green and those in the spinous and granular layers were increasingly lavender. These results suggest that in cell-renewal systems the differentiated, nonproliferating cells are more sensitive to acid denaturation of DNA than the undifferentiated, actively proliferating cells. MG-P stain, which is able to distinguish double-stranded from single-stranded DNA, may be used as a tool to stain proliferating and nonproliferating cell nuclei differentially in tissue sections.