The morphology of erythroid cells separated by density gradient centrifugation through Ficoll

Mutant mouse L-cells: a model for megaloblastic anaemia

When temperature-sensitive (ts) mutant lines of mouse L-cells, ts AIS9 and ts CI, are shifted from 34C to 38.5C, a rapid inhibition of DNA synthesis and mitosis occurs. During this phase, cell and nuclear growth continues and results in a substantial increase in cell and nuclear volume. Such cellular modifications are also associated with a marked dispersal of the condensed chromatin masses of interphase nuclei, so that after 48-72 h of incubation at 38.5C, nuclear profiles of both ts cell lines bear a striking resemblance to the nuclear features characteristic of megaloblastic anaemia. Despite these marked alterations in nuclear chromatin organization, morphometric analysis indicates that the volume of condensed chromatin does not decrease. Current biochemical, cytological and morphometric data on the two ts lines of mutant mouse L-cells during expression of the mutation, suggest that they might provide a useful model to further elucidate cytological features of megaloblastic anaemia.

The organization, composition and matrix of hepatocyte nuclei exposed to alpha-amanitin

Alterations in the structure and molecular composition of avian hepatocyte nuclei were compared following administration in vivo of lethal and sub-lethal doses of alpha-amanitin. This toxin interferes with extranucleolar transcription by direct inhibition of RNA polymerase II activity. the resultant effects include: extensive condensation of chromatin, displacement of nucleoplasmic contents and fragmentation of nucleoli. Changes in nuclear morphology were quantitated by stereometry and related to variations in RNA and residual, non-histone proteins (NHP). Gross alterations in nuclear structure and depletion of RNA and NHP levels were of similar magnitude with both doses of amanitin. The effects were fully reversible, however, with a minimal dose but terminal with a lethal dose. DNA and histone protein levels remained unchanged at all stages. These results imply that the process of transciption may itself keep and/or maintain chromatin in a dispersed state, and that in the absence of transcription chromatin naturally condenses. Modification of nuclear proteins may be necessary only to maintain chromatin compacted permanently or for extended periods of time. A model of nuclear organization is proposed to incorporate these considerations and to identify the probable location of the nuclear matrix in situ.