Comparison of N banding and silver staining of human NORs

A comparison of the sensitivity of silver and Giemsa N band staining for detection of the human nucleolar organizer regions (NORs) was carried out in cultured lymphocytes from three unrelated individuals. In sequentially stained cells examined from each subject, the mean number of Ag-NORs was greater than the mean number of N bands. The difference in stainability between the two techniques was shown to be highly significant (chi 2 = 430.2; P less than 0.01) when 100 cells pooled from all individuals were analyzed. These results suggest a greatly reduced sensitivity of the NOR for Giemsa, as opposed to silver. This conclusion is also supported by the finding that slides aged for over 1 week did not N band, while silver staining was accomplished on slides of any age. Several possible factors that might be responsible for the difference in staining response are discussed.