title: Ribosomal RNA gene amplification: a selective advantage in tissue culture.
abstract: A CCRF-CEM (human T-cell leukemia) line, initially made resistant to methotrexate by a four-step increase in drug concentration, revealed a large marker of one chromosome #14 in all cells after a 6-month period of culture in the absence of drug. The marker is the result of a triple duplication of both the satellite and stalk. In situ hybridization with 3H-cRNA and NOR banding proved that ribosomal DNA had been amplified and was actively transcribed. Flow cytometric analysis showed a significant increase of RNA versus DNA in G1 cells compared with those of the original drug-resistant parent. The abnormal chromosome appeared after the removal of methotrexate from culture and may be related to the faster doubling time of this line compared with the parent line.
mesh_terms: D002871:Chromosome Banding; D046508:Culture Techniques; D004273:DNA, Neoplasm / Q000235:genetics; D004351:Drug Resistance; D005434:Flow Cytometry; D005784:Gene Amplification; D005819:Genetic Markers; D006801:Humans; D007621:Karyotyping; D007938:Leukemia / Q000235:genetics / Q000473:pathology; D008727:Methotrexate / Q000494:pharmacology; D009697:Nucleolus Organizer Region; D012334:RNA, Neoplasm / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics*
chemical_list: D004273:DNA, Neoplasm; D005819:Genetic Markers; D012334:RNA, Neoplasm; D012335:RNA, Ribosomal; D008727:Methotrexate