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Mitotic Chromosomes (mitotic + chromosome)
Selected AbstractsBir1/Cut17 moving from chromosome to spindle upon the loss of cohesion is required for condensation, spindle elongation and repairGENES TO CELLS, Issue 9 2001Jun Morishita Background In mammals, proteins containing BIR domains (IAPs and survivin) are implicated in inhibiting apoptosis and sister chromatid separation. In the nematode, Bir1 is required for a proper localization of aurora kinase, which moves from the mitotic chromosome in metaphase to the spindle midzone in anaphase as a passenger. Fission yeast Bir1/Pbh1 is essential for normal mitosis. Results A temperature sensitive mutant cut17-275 exhibits the defect in condensation and spindle elongation at 36 °C, while securin is degraded. Gene cloning shows that the cut17+ gene is identical to bir1+/pbh1+. At 26 °C, cut17-275 is UV sensitive as the repair of DNA damage is severely compromised. Bir1/Cut17 is a nuclear protein in interphase, which is then required for recruiting condensin to the mitotic nucleus, and concentrates to form a discrete number of dots from prometaphase to metaphase. Once the chromatids are separated, Bir1/Cut17 no longer binds to kinetochores and instead moves to the middle of spindle. Chromatin immunoprecipitation suggested that Bir1/Cut17 associates with the outer repetitious centromere region in metaphase. Following the initiation of anaphase the protein switches from being a chromosomal protein to a spindle protein. This transit is stringently regulated by the state of sister chromatid cohesion proteins Mis4 and Rad21. Ark1, is an aurora kinase homologue whose mitotic distribution is identical to, and under the control of Bir1/Cut17. Conclusions Bir1/Cut17 and Ark1 act as ,passengers' but they may play a main role as a recruitment factor, essential for condensation, spindle elongation and DNA repair. Bir1/Cut17 should have roles both in mitotic and in interphase chromosome. The proper location of Ark1 requires Bir1/Cut17, and the mitotic localization of Bir1/Cut17 requires sister cohesion. [source] Cloning of Xenopus orthologs of Ctf7/Eco1 acetyltransferase and initial characterization of XEco2FEBS JOURNAL, Issue 24 2008Masatoshi Takagi Sister chromatid cohesion is important for the correct alignment and segregation of chromosomes during cell division. Although the cohesin complex has been shown to play a physical role in holding sister chromatids together, its loading onto chromatin is not sufficient for the establishment of sister chromatid cohesion. The activity of the cohesin complex must be turned on by Ctf7/Eco1 acetyltransferase at the replication forks as the result of a specific mechanism. To dissect this mechanism in the well established in vitro system based on the use of Xenopus egg extracts, we cloned two Xenopus orthologs of Ctf7/Eco1 acetyltransferase, XEco1 and XEco2. Both proteins share a domain structure with known members of Ctf7/Eco1 family proteins. Moreover, biochemical analysis showed that XEco2 exhibited acetyltransferase activity. We raised a specific antibody against XEco2 and used it to further characterize XEco2. In tissue culture cells, XEco2 gradually accumulated in nuclei through the S phase. In nuclei formed in egg extract, XEco2 was loaded into the chromatin at a constant level in a manner sensitive to geminin, an inhibitor of the pre-replication complex assembly, but insensitive to aphidicolin, an inhibitor of DNA polymerases. In both systems, no specific localization was observed during mitosis. In XEco2-depleted egg extracts, DNA replication occurred with normal kinetics and efficiency, and the condensation and sister chromatid cohesion of subsequently formed mitotic chromosomes was unaffected. These observations will serve as a platform for elucidating the molecular function of Ctf7/Eco1 acetyltransferase in the establishment of sister chromatid cohesion in future studies, in which XEco1 and XEco2 should be dissected in parallel. [source] Mammalian CLASPs are required for mitotic spindle organization and kinetochore alignmentGENES TO CELLS, Issue 8 2006Yuko Mimori-Kiyosue CLASP1 and CLASP2 are homologous mammalian proteins, which associate with the ends of growing microtubules, as well as the cell cortex and the kinetochores of mitotic chromosomes. Previous studies have shown that in interphase cells CLASPs can attach microtubule plus ends to the cortex and stabilize them by repeatedly rescuing them from depolymerization. Here we show that CLASP1 and 2 play similar and redundant roles in organizing the mitotic apparatus in HeLa cells. Simultaneous depletion of both CLASPs causes mitotic spindle defects and a significant metaphase delay, which often results in abnormal exit from mitosis. Metaphase delay is associated with decreased kinetochore tension, increased kinetochore oscillations and more rapid microtubule growth. We show that the association of CLASP2 with the kinetochores relies on its C-terminal domain, but is independent of microtubules or association with CLIP-170. We propose that CLASPs exhibit at the kinetochores an activity similar to that at the cortex, providing apparent stabilization of microtubules by locally reducing the amplitude of growth/shortening episodes at the microtubule ends. This local stabilization of microtubules is essential for the formation of normal metaphase spindle, completion of anaphase and cytokinesis. [source] Nonselective DNA damage induced by a replication inhibitor results in the selective elimination of extrachromosomal double minutes from human cancer cellsGENES, CHROMOSOMES AND CANCER, Issue 10 2007Noriaki Shimizu Gene amplification plays a pivotal role in human malignancy. Highly amplified genes frequently localize to extrachromosomal double minutes (dmin), which usually segregate to daughter cells in association with mitotic chromosomes. We and others had shown that treatment with low-dose hydroxyurea (HU) results in the elimination of dmin and reversion of the cancer cell phenotype. HU treatment in early S-phase, when dmin are replicated, results in their detachment from chromosomes at the next M-phase, leading to the appearance of micronuclei enriched in dmin, followed by their elimination. In this article, we examined the effect of low-dose HU on the behavior of dmin in relation to DNA damage induction by simultaneously monitoring LacO-tagged dmin and phosphorylated histone H2AX (,H2AX). As expected, treatment with low-dose HU induced numerous ,H2AX foci throughout the nucleus in early S-phase, and these rarely coincided with dmin. Most chromosomal ,H2AX foci disappeared by metaphase, whereas, unexpectedly, those that persisted frequently associated with dmin. We found that these dmin aggregated, detached from anaphase chromosomes, and apparently formed micronuclei. Because ,H2AX foci likely represent DNA double strand breaks (DSBs), the response to DSBs sustained by extrachromosomal dmin appears to be different from that sustained by chromosomal loci, which may explain why DSB-inducing agents cause the selective elimination of dmin. © 2007 Wiley-Liss, Inc. [source] Variations of 18S rDNA Loci Among Six Populations of Paeonia obovata Maxim. (Paeoniaceae) Revealed by Fluorescence In Situ HybridizationJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 5 2006Rui Luo Abstract The localization of 18S ribosomal RNA genes (rDNA) by fluorescence in situ hybridization (FISH) had been performed for some species of Paeonia. However, the pattern of 18S rDNA loci among populations is indistinct. In the present study, we localized 18S rDNA loci on meiotic or mitotic chromosomes of six populations of Paeonia obovata Maxim. (Paeoniaceae). Different numbers of rDNA loci were found with different diploid (2n=10) populations, namely eight (Lushi and Mt. Jiuhua populations), 10 (Mt. Taibai population), and seven (Mt. Guandi population), whereas tetraploid (2n=20) populations were all found with 16 loci. All rDNA loci were mapped near telomeres of mitotic chromosomes and there was no chromosome with two loci. The present results show that molecular cytological polymorphism exists among P. obovata diploid populations, indicating that structural variations occurred frequently during the evolutionary history of this species, accompanied with differentiation among populations. (Managing editor: Wei Wang) [source] Molecular cytogenetic characterization of Thinopyrum genomes conferring perennial growth habit in wheat- Thinopyrum amphiploidsPLANT BREEDING, Issue 1 2001X. Cai Abstract Seven wheat- Thinopyrum amphiploids, AT 3425, AgCs, PI 550710, PI 550711, PI 550712, PI 550713 and PI 550714, were evaluated for perennial growth habit in the field. Three of them, AgCs, AT 3425, and PI 550713, were identified as perennials. Fluorescent genomic in situ hybridization (FGISH) patterns of mitotic chromosomes indicated that AgCs had seven pairs of Thinopyrum chromosomes and 21 pairs of wheat chromosomes. PI 550713 and AT 3425 showed similar FGISH patterns of mitotic chromosomes with three pairs of wheat- Thinopyrum translocated chromosomes, seven pairs of Thinopyrum chromosomes, and 18 pairs of wheat chromosomes. Thinopyrum chromosome pairing in the Fi hybrid of AT 3425 with AgCs demonstrated differences between Thinopyrum genomes in these two amphiploids. Based on chromosome constitutions, pairing and reported pedigrees, AgCs and AT 3425 were identified as a wheat- Thinopyrum elongatum amphiploid and partial wheat- Thinopyrum ponticum amphiploid, respectively. Chromosome pairing in the F1 hybrid between AT 3425 and PI 550713 revealed that these two amphiploids contained the same Thinopyrum genome. Two different Thinopyrum genomes conferring perennial growth habit were identified from the perennial amphiploids and characterized cytogenetically. [source] | ||||||||||