Secondary constrictions and nucleolus organizer regions in man

Abstract

This chapter describes the nucleolar organizer region activity in human chromosomes and interphase nuclei of normal, leukemic, and tumor cells as evaluated by silver staining. In 1976, the nucleolar organizer regions (NORs) with silver salts had created the opportunities to evaluate the activity of the ribosomal genes. Hybridization experiments in situ and silver staining have revealed that rRNA gene synthesis in human genome occurs on the short arm secondary constrictions or stalks of chromosomes 13–15 and 21–22. Silver ions are widely used in the studies of ribosomal cistron activity. The NOR Ag-staining patterns in somatic and sexual cells differ and greatly depend upon the degree of cellular maturity and proliferative activity. Leukemic and tumor cell populations differ from normal ones in greater heterogeneity of ribosomal RNA synthesis both because of a loss of some active NORs by the pathological cells and because of their acquisition. Some of these defects appear to be inhibited by the cells, but others are assimilated. The silver staining of human metaphase chromosome NORs and of interphase nuclei is a systematically used method.