Nucleus interphase

The DNA in a eukaryotic cell nucleus during the interphase between cell divisions exists as a nucleoprotein complex called chromatin. The proteins of chromatin fall into two classes histones and nonhistone chromosomal proteins. 

When cells enter mitosis, the interphase array of MTs is dismantled. The centrosome duplicates, and the daughters move to opposite poles of the nucleus. After disassembly of the nuclear envelope, MTs emanat-... 

Ciba-Geigy Ltd. 1984a. Nucleus anomaly test in somatic interphase nuclei of Chinese hamster TK 10 507 (REOFOS 50) Test No. 830071. Ciba-Geigy Ltd, Basle, Switzerland. NTIS OTS0507280. 

The very beginning of the first mitotic cell cycle of the mouse embryo seems to be controlled by the mechanisms characteristic for both meiotic and mitotic cell cycles. Active MAP kinase, its substrate p90rsk and the CSF activity itself could influence the cellular processes within the one-cell embryo. Indeed, we have observed that despite the entry into the interphase (as judged by the low activity of MPF) some proteins are actively phosphorylated as during the meiotic M phase (e.g. 35 kDa complex Howlett et al 1986, Szollosi et al 1993), the nuclei and the microtubule interphase network start to form only 1.5 hours after activation (Szollosi et al 1993). This delay in the phenomena characteristic for the interphase could be linked to the mixed meiotic/mitotic character of this early period. This delay probably allows the correct transformation of the sperm nucleus into the male pronucleus. In species like Xenopus or Drosophila the transitional period between the meiotic and the mitotic cell cycle control is probably much shorter since it is proportional to duration of the short first cell cycle of these rapidly cleaving embryos. Mammalian embryos are perhaps the most suitable to study this transition because of the exceptionally long first embryonic cell cycle. 

Figure 1. Hierarchical model of chromosome structure, (a) In interphase cells, DNA is packed in a nucleus as forming nucleosome and chromatin, (b) DNA forms nucleosome structure together with core histone octamer, which is then folded up into 30nm fiber with a help of linker histone HI. This 30 nm fiber is further folded into 80 nm fiber and 300 nm loop structures in a nucleus. In mitosis, chromosome is highly condensed. Proteins which are involved in each folding step are indicated above and non-protein factors are indicated below, (c) The amino acid sequences of histone tails (H2A, H2B, H3 and H4) are shown to indicate acetylation, methylation and phosphorylation sites. (See Colour Plate 1.)...

Vazquez J, Belmont AS, Sedat JW (2001) Multiple regimes of constrained chromosome motion are regulated in the interphase Drosophila nucleus. Curr Biol 11 1227-1239... 

Transcription regulators are also known to be sumoylated. One of tbe early studies of tbis phenomenon showed that promyelocytic leukemia protein (PML) is a substrate for SUMO conjugation. Once SUMO is attached to the PML protein it is directed to a subdomain of tbe nucleus called tbe PML oncogenic domain (POD). It is thought that POD localization of the PML protein allows it to recruit other proteins such as transcription factors. Transcription factors in the POD can activate or inhibit transcription. Another transcription factor known to be sumoylated is Sp3. ° SUMO also has roles in chromatin condensation and interphase chromosome organization. ... 

Euchromatin generally corresponds to looped 30-nm fibers. Heterochromatin is more highly condensed. Figure 1-1-14 shows an electron micrograph of an interphase nucleus containing euchromatin, heterochromatin, and a nucleolus. The nudeolus is a nuclear region spedalized for ribosome assembly (discussed in Chapter 3). 

Fig. 2. Exchange of histones Hl.l and H2B from chromatin in interphase cells by analysis with fluorescence recovery after photobleaching (FRAP). Half of a nucleus of an SK-N cell expressing GFP-Hl.l was bleached (upper panel), and the recovery monitored over the times shown. Similarly, a region of a nucleus of an SK-N cell stably expressing H2B-CFP was bleached (lower panel), and the recovery monitored over the times shown. Whereas unbleached HI molecules move into the bleached region after a few minutes, the H2B histones are much less mobile, since the bleached region shows no recovery (from Ref [23]). Scale bar 5 pm.

Yokota, H., van den Engh, G., Hearst, J., Sachs, R.K., and Trask, B.J. (1995) Evidence for the organization of chromatin in megabase pair-sized loops arranged along a random walk path in the human GO/Gl interphase nucleus. J. Cell Biol. 130, 1239-1249. 

Fig. 16 General aspect of T. foetus in interphase (a) and under division (b-d). Notice that in interphase the hydrogenosomes are aligned on the costa and axostyle (a), whereas during the division they are close to the nucleus (b-d). Bars = 300 nm. (Fig. 16a from Benchimol, unpublished Fig. 16b,c from Benchimol and Engelke 2003 Fig. 16d from...

Figure 6.3d The phases of the cell cycle. G, S, and G2 are all parts of interphase. In M phase, the nucleus and then cytoplasm divide.

The eukaryotic cell cycle (see Fig. 12-41) produces remarkable changes in the structure of chromosomes (Fig. 24-25). In nondividing eukaryotic cells (in GO) and those in interphase (Gl, S, and G2), the chromosomal material, chromatin, is amorphous and appears to be randomly dispersed in certain parts of the nucleus. In the S phase of interphase the DNA in this amorphous state replicates, each chromosome producing two sister chromosomes (called sister chromatids) that remain associated with each other after replication is complete. The chromosomes become much more condensed during prophase of mitosis, taking the form of a species-specific number of well-defined pairs of sister chromatids (Fig. 24-5). 

Nucleolus. A spherical structure visible in the nucleus during interphase. The nucleolus is associated with a site on the chromosome that is involved in ri-bosomal RNA synthesis. 

During the period of mitosis, the nucleus and cytoplasm divide to form two new cells. The rest of the cell cycle is known as interphase. 

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