Amplification and abnormal chromosomal distribution of ribosomal genes (rDNA) in rat erythroleukemia cells

The ribosomal cistrons (rDNA)/genome ratio was measured in five cell lines derived from three chemically induced erythroblastic leukemias (D-1, D-2, and NE26) in the Long-Evans (LE) rat and compared with values in the normal liver, bone marrow, and fetus. The ratio was 20-42% higher in the leukemias than in normal tissues. The number of autoradiographic silver grains of 125I-labeled rRNA hybridized in situ over three nucleolus organizer regions (NORs) of leukemia cells was determined and compared with that of the normal cells. Although the distribution of silver grains of normal cells averaged 44.6%, 25.9%, and 29.5% in NORs of chromosomes #3, #11, and #12, respectively, their distribution was abnormal in two of the leukemias examined; rDNA was amplified in chromosomes #12 of two sublines (K1DA and K1DB) of one leukemias (D-1), and in one chromosome #3 of two sublines (K2D and K3D) of another leukemia (D-2). We consider the possibility that these abnormal patterns of rDNA distribution are related to the increase in rDNA in leukemia cells.