AgNOR quantification with special reference to staining patterns

Abstract

Silver staining of nucleolar organizer regions (AgNORs) is now widely used as a marker of malignancy in tumor pathology. Standardization of the AgNOR technique has thereby been shown to be of central importance. Basically, three types of AgNOR evaluation have been used: the counting method, image analysis and pattern recognition. Today, image analytical determination of AgNOR area per nucleus is considered to be the state of art method of AgNOR evaluation. In contrast, counting of every single AgNOR dot is laborious and less reproducible. For routine purposes, however, a rapid evaluation of AgNORs would be desirable. In order to elucidate the value of AgNOR distribution patterns systematic in vitro studies using four different urothelial cell lines (HU609, RT4, J82, MGHU1) were performed. AgNOR number (NORN) and AgNOR area (NORA) were closely related to the population doubling time (PDT) and increased during transition from G0/G1 to S/G2 cell cycle phase. In addition, both parameters were significantly elevated in the polyploid RT4 cell line. In contrast, number and area of AgNOR cluster (aggregates of at least two AgNOR dots) were less significantly correlated to PDT. Formation of large AgNOR clusters (maximum diameter over 6 microns) was, however, restricted to the well differentiated cell lines (HU609, RT4) although PDT was almost identical in all 4 cell lines at exponential growth phase. Thus, NORN and NORA are not only related to cell proliferation but also to cell cycle phases and ploidy.(ABSTRACT TRUNCATED AT 250 WORDS)