Relationship between chromatin structure and replication in mouse L-cells

Abstract

Mouse L-cells treated with cytosine arabinoside, hydroxyurea, fluorodeoxyuridine, methotrexate, or mitomycin C rapidly cease DNA synthesis and stop dividing. Such inhibition of DNA replication is followed by interruption of formation of lysine- and arginine-containing proteins, including chromatin-bound histones, and by a major reorganization of the heterochromatin of the central nucleoplasm, manifest as disaggregation of large clumps of this condensed chromatin. Morphometric analysis revealed both cell and nuclear enlargement in cells treated with such antimetabolites of DNA replication. These observations are in contrast to those made with WT-4 cells starved of isoleucine or treated with cycloheximide. Isoleucine depletion was associated with inhibition of DNA synthesis and continued increase of cell and nuclear volume, but not with massive disaggregation of heterochromatin. Cycloheximide produced inhibition of DNA synthesis and protoplasmic growth, and also prevented structural reorganization of chromatin. A model is presented which suggests that initiation of chromatin replication is associated with a process, dependent upon de novo protein synthesis, which results in chromatin disaggregation. This can be revealed by inhibition of the correct replication of chromatin DNA and chromatin protein.

Ultrastructural morphometric image analysis applied to estimation of condensed chromatin in normal and neoplastic lymphocytes

“…Increases in condensed chromatin volume in morphotype 3 nuclei may reflect the fact that some lymphocytes at this stage are in various stages of DNA synthesis (Dardick et al, 1981(Dardick et al, , 1983Setterfield et al, 1983). The illusionary appearance of a dispersal of condensed chromatin in enlarging nuclei, rather than the disaggregation of preexisting condensed chromatin mass that actually occurs, has been noted previously Dardick, 1984a;Setterfield et al, 1978;Sheinin et al, 1980). It is important to be aware of the disparity that can exist between data derived from tissue sections (twodimensional) and three-dimensional values, and this obviously applies to quantitation of nuclear features in malignant lymphomas as well as normal lymphocytes.…”

DNA synthesis in Balb/C-3T3 ts 2 cells is restricted by a temperature-sensitive function of late G1 phase

“…The cells are therefore dna's/Gf. Expression of the ts 2 defect results in inactivation 0006-2960/86/0425-1208S01.50/0 © 1986 American Chemical Society of cellular DNA formation, under conditions in which de novo synthesis of RNA and protein is apparently unaffected [see also Sheinin et al (1986)]. Sheinin and Lewis (1980) found that the ts 2 cells could be distinguished from dna,s/S,s cells by an important property.…”