Differential silver-positive nucleolus organizer region activity in normal and malignant murine tissues.

Transcriptionally active nucleolus organizer regions (NORs) were analyzed using a silver-staining technique. The levels of silver-positive NOR activity for normal murine bone marrow and thymus cells were established, and significant differences in ribosomal RNA gene activity were observed. When tumor cells originating from these two tissue types were also studied, significant differences were seen not only between the normal and malignant tissues, but between the two tumor types as well. These differences in ribosomal RNA gene activity with respect to cell type and malignancy may be useful diagnostically.