Application of the AgNOR technique to neurooncology.

The silver staining of interphase nucleolar organizer regions (NORs) is a recently developed method to measure cell proliferation in tissue specimens. The major silver staining protein is nucleolin, a 92 kd nucleolar protein, which probably controls rDNA transcription. Nucleolin itself is under control of p34cdc2 kinase, which is a subunit of M phase kinase. The specific silver staining of NORs measures ribosomal gene activity and is therefore useful in measuring cell proliferation via nucleolar biosynthetic activity. Although human tumors of different malignancy grades usually can be distinguished by their AgNOR number, there is considerable overlap between different grades which significantly hampers their use in individual cases. For routine application of the AgNOR technique in histopathology we propose a standardised staining protocol with use of internal control cells and the use of image analysis for AgNOR enumeration.