Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells

Abstract

SUMMARY The review examines the structured organization of interphase nuclei using a range of examples from the plants, animals, and fungi. Nuclear organization is shown to be an important phenomenon in cell differentiation and development. The review commences by examining nuclei in dividing cells and shows that the organization patterns can be dynamic within the time frame of the cell cycle. When cells stop dividing, derived differentiated cells often show quite different nuclear organizations. The developmental fate of nuclei is divided into three categories. (i) The first includes nuclei that undergo one of several forms of polyploidy and can themselves change in structure during the course of development. Possible function roles of polyploidy is given. (ii) The second is nuclear reorganization without polyploidy, where nuclei reorganize their structure to form novel arrangements of proteins and chromosomes. (iii) The third is nuclear disintegration linked to programmed cell death. The role of the nucleus in this process is described. The review demonstrates that recent methods to probe nuclei for nucleic acids and proteins, as well as to examine their intranuclear distribution in vivo, has revealed much about nuclear structure. It is clear that nuclear organization can influence or be influenced by cell activity and development. However, the full functional role of many of the observed phenomena has still to be fully realized.

Insulation of the Chicken β-Globin Chromosomal Domain from a Chromatin-Condensing Protein, MENT

“…Methylation of histone H3 at lysine 9 (H3meK9) has been suggested to be a primary signal in establishing the heterochromatin/euchromatin segregation in concert with histone methyltransferase and the ubiquitous H3meK9-binding protein HP1 (35,42). Since the amount of cytologically detectable heterochromatin is dramatically increased during terminal blood cell differentiation (14,40), we compared the levels of H3meK9 and HP1 in proliferating and terminally differentiated avian hemopoietic cells. In parallel, we also monitored the level of MENT, a heterochromatin protein expressed during terminal avian blood cell differentiation (25).…”

Form follows function: the genomic organization of cellular differentiation

“…For example, as genes are silenced, the extent of chromatin condensation often increases, and extended regions of DNA are packaged into heterochromatin (John 1988). The amount and distribution of condensed chromatin is similar in differentiated cells of the same lineage, but the pattern varies in the nuclei of different cell types (Leitch 2000). These types of observations have led to the idea that nuclear organization may be cell-type-specific; the topological organization of the interphase nucleus may reflect the differentiated state of the cell and may be involved in the establishment and propagation of tissue-specific patterns of gene expression .…”

Evolution and structure of 5S rDNA loci in allotetraploid Nicotiana tabacum and its putative parental species

“…(3) The interphase nucleus of plants is a highly structured entity showing domains of condensed and decondensed chromatin (Leitch, 2000). We argued in Lim et al (2000a) that gene conversion between homoeologous 18-26S rDNA loci is most likely to occur during interphase of the cell cycle.…”