Silver staining as an indicator of active ribosomal genes.

Silver nitrate has been used as a cytological stain since the late 1800s. A modification of the Bielschowsky technique preferentially stains nucleoli and chromosomal nucleolus organizer regions (NORs). The specificity of staining is related to the method of preparation of the cytological specimens. The silver binds proteins and may be associated with the phosphate groups of certain phosphoproteins. Biochemical analyses of nucleolar proteins indicate that a limited array of specific proteins bind silver. A number of investigations have demonstrated that silver staining is indicative of active ribosomal RNA transcription, although a minor component may be associated with the fibrillar centers of cells in which ribosomal genes are inactive. Silver staining is a simple, reliable cytological method for the demonstration of ribosomal gene activity.