Sites of Nucleolus Production in Cultured Chinese Hamster Cells

Abstract

Chinese hamster cell strains in the early passages in culture display wide variation in number of nucleolus-like bodies per cell, though such strains are characteristically euploid. A variety of criteria indicate that the nucleolus-like bodies are true nucleoli. Their Azure B-and fast green-staining properties indicate the presence of RNA and protein; they have typical nucleolar fine structure, including both fibrous and granular components; radioautography reveals that their patterns of uptake of uridine-3H into RNA are similar to those reported for nucleoli of other cell types; actinomycin D, at a level which selectively inhibits ribosomal RNA synthesis, greatly reduces their RNA synthesis and also causes segregation of fibrous and granular nucleolar components. Colchicine was used to experimentally fragment the nuclei of these cells into a number of separate karyomeres, each presumably containing some, or only one, of the chromosomes of the complement. Almost all the karyomeres contain nucleolus-like bodies which, by the same criteria applied to the multiple nucleolus-like bodies of uninuclear cells, appear to be true nucleoli. The nucleoli of individual karyomeres of the same cell often differ from each other in fine structure while the multiple nucleoli of a uninuclear cell generally resemble each other. The evidence presented in this study indicates that Chinese hamster cells contain many nucleolus-producing sites scattered through the genome.Diploid, nontransformed Chinese hamster cells in tissue culture were found to possess widely varying numbers of nuclear bodies which appeared cytologically to be nucleoli. This finding seemed inconsistent with numerous studies demonstrating that somatic cells are normally characterized by a set number of nucleoli which consistently arise in association with specific chromosomal loci. The number of nucleoli produced is found to be one per haploid chromosome complement, i.e., two per diploid cell, in a great many organisms, for instance, Hyacinthus (de Mol, 1926(de Mol, , 1928,

Repopulation of the Postmitotic Nucleolus by Preformed Rna

“…Variable numbers of nucleoli (Philhps and Phillips, 1969) were clearly visible in nuclei of sister cells which had entered G1 in the 3 hr since harvesting In preparations stained for nucleic acids with azure B, these nucleoli appeared as irregu-FIGVnES 1 and ~ Chinese hamster cells g hr after mitosis. Azure B.…”

Nucleoli and ploidy in Potorous cells (PTK2) in vitro

“…In most cells in vitro, the number of nucleoli per cell is quite variable (Phillips and Phillips, 1969;Alvarez-Lomeli, 1963 ;Gonzalez and Nardone, 1968). However, despite all the variations in nucleolar number between and within cells, there is considerable evidence to link the formation of each nucleolus with a nucleolar organizer region of the chromosome.…”

Structural differentiation of the nucleolus-organizing regions between mitotic and epidermal cells inVicia faba

“…McCuNTOCK (1934) has first proposed that the NORs have ability to assemble the nucleolar precursors dispersed in the cytoplasm. Afterwards, this proposition has been reinforced by several cytological evidence; exposure to colchicine or 5-azacytidine produces nuclei lacking the NOR, in which the prenucleolar material does not assemble at a settled site but coagulates to form many round bodies throughout the nucleoplasm (PHILLIPS and PHILLIPS 1969;HERNANDEZ-VERDUN et al 1979;SATO 1988b). Hence, the particular structure of the secondary constrictions seems to be indispensable for the assembly of the prenucleolar material incorporated into the daughter nuclei by chromosomes.…”