scholarly journals Neo-formation of chromosomes in bacteria

2018 ◽  
Author(s):  
Olivier B. Poirion ◽  
Bénédicte Lafay
Keyword(s):  
Cell Cycle ◽  
Bacterial Genome ◽  
True Nature ◽  
Species Diversification ◽  
Essential Nature ◽  
Ancestral Chromosome ◽  
Complex Regulation

ABSTRACTAlthough the bacterial secondary chromosomes/megaplasmids/chromids, first noticed about forty years ago, are commonly held to originate from stabilized plasmids, their true nature and definition are yet to be resolved. On the premise that the integration of a replicon within the cell cycle is key to deciphering its essential nature, we show that the content in genes involved in the replication, partition and segregation of the replicons and in the cell cycle discriminates the bacterial replicons into chromosomes, plasmids, and another class of essential genomic elements that function as chromosomes. These latter do not derive directly from plasmids. Rather, they arise from the fission of a multi-replicon molecule corresponding to the co-integrated and rearranged ancestral chromosome and plasmid. All essential replicons in a distributed genome are thus neochromosomes. Having a distributed genome appears to extend and accelerate the exploration of the bacterial genome evolutionary landscape, producing complex regulation and leading to novel eco-phenotypes and species diversification.

scholarly journals Complex regulation of cell-cycle inhibitors by Fbxw7 in mouse embryonic fibroblasts

Oncogene ◽  
2009 ◽  
Vol 29 (12) ◽  
pp. 1798-1809 ◽  
Author(s):  
K Masuda ◽  
Y Ishikawa ◽  
I Onoyama ◽  
M Unno ◽  
I M de Alborán ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mouse Embryonic Fibroblasts ◽  
Embryonic Fibroblasts ◽  
Complex Regulation ◽  
Regulation Of Cell Cycle ◽  
Cell Cycle Inhibitors

scholarly journals A study of SeqA subcellular localization in Escherichia coli using photo-activated localization microscopy

2015 ◽  
Vol 184 ◽  
pp. 425-450 ◽  
Author(s):  
Jacek T. Mika ◽  
Aster Vanhecke ◽  
Peter Dedecker ◽  
Toon Swings ◽  
Jeroen Vangindertael ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Cycle ◽  
Bacterial Genome ◽  
Genetically Engineered ◽  
Replication Initiation ◽  
Cell Protein ◽  
Experimental Conditions ◽  
Localization Microscopy ◽  
E Coli ◽  
Copy Numbers

Escherichia coli (E. coli) cells replicate their genome once per cell cycle to pass on genetic information to the daughter cells. The SeqA protein binds the origin of replication, oriC, after DNA replication initiation and sequesters it from new initiations in order to prevent overinitiation. Conventional fluorescence microscopy studies of SeqA localization in bacterial cells have shown that the protein is localized to discrete foci. In this study we have used photo-activated localization microscopy (PALM) to determine the localization of SeqA molecules, tagged with fluorescent proteins, with a localization precision of 20–30 nm with the aim to visualize the SeqA subcellular structures in more detail than previously possible. SeqA–PAmCherry was imaged in wild type E. coli, expressed from plasmid or genetically engineered into the bacterial genome, replacing the native seqA gene. Unsynchronized cells as well as cells with a synchronized cell cycle were imaged at various time points, in order to investigate the evolution of SeqA localization during the cell cycle. We found that SeqA indeed localized into discrete foci but these were not the only subcellular localizations of the protein. A significant amount of SeqA–PAmCherry molecules was localized outside the foci and in a fraction of cells we saw patterns indicating localization at the membrane. Using quantitative PALM, we counted protein copy numbers per cell, protein copy numbers per focus, the numbers of foci per cell and the sizes of the SeqA clusters. The data showed broad cell-to-cell variation and we did not observe a correlation between SeqA–PAmCherry protein numbers and the cell cycle under the experimental conditions of this study. The numbers of SeqA–PAmCherry molecules per focus as well as the foci sizes also showed broad distributions indicating that the foci are likely not characterized by a fixed number of molecules. We also imaged an E. coli strain devoid of the dam methylase (Δdam) and observed that SeqA–PAmCherry no longer formed foci, and was dispersed throughout the cell and localized to the plasma membrane more readily. We discuss our results in the context of the limitations of the technique.

Maytansine-Induced Mitotic Arrest in Human Lymphoblasts

1977 ◽  
Vol 35 ◽  
pp. 460-461
Author(s):  
Tai-Te Chao ◽  
John Sullivan ◽  
Awtar Krishan
Keyword(s):  
Electron Microscopy ◽  
Cell Cycle ◽  
Transmission Electron Microscopy ◽  
Tubulin Polymerization ◽  
Vinca Alkaloids ◽  
Antimitotic Activity ◽  
Transmission Electron ◽  
Flow Microfluorometry ◽  
Brain Tubulin

Maytansine, a novel ansa macrolide (1), has potent anti-tumor and antimitotic activity (2, 3). It blocks cell cycle traverse in mitosis with resultant accumulation of metaphase cells (4). Inhibition of brain tubulin polymerization in vitro by maytansine has also been reported (3). The C-mitotic effect of this drug is similar to that of the well known Vinca- alkaloids, vinblastine and vincristine. This study was carried out to examine the effects of maytansine on the cell cycle traverse and the fine struc- I ture of human lymphoblasts.Log-phase cultures of CCRF-CEM human lymphoblasts were exposed to maytansine concentrations from 10-6 M to 10-10 M for 18 hrs. Aliquots of cells were removed for cell cycle analysis by flow microfluorometry (FMF) (5) and also processed for transmission electron microscopy (TEM). FMF analysis of cells treated with 10-8 M maytansine showed a reduction in the number of G1 cells and a corresponding build-up of cells with G2/M DNA content.

Fibronexus-Like Adhesion Sites are Present at the Invasive Zones of Human Epidermoid Carcinomas

1982 ◽  
Vol 40 ◽  
pp. 106-109
Author(s):  
Irwin I. Singer
Keyword(s):  
Cell Cycle ◽  
Serum Concentration ◽  
Substrate Binding ◽  
High Serum ◽  
Adhesion Sites ◽  
Substrate Adhesion ◽  
Focal Contacts ◽  
Adhesion Complex ◽  
Low Serum

Our previous results indicate that two types of fibronectin-cytoskeletal associations may be formed at the fibroblast surface: dorsal matrixbinding fibronexuses generated in high serum (5% FBS) cultures, and ventral substrate-adhering units formed in low serum (0.3% FBS) cultures. The substrate-adhering fibronexus consists of at least vinculin (VN) and actin in its cytoplasmic leg, and fibronectin (FN) as one of its major extracellular components. This substrate-adhesion complex is localized in focal contacts, the sites of closest substratum approach visualized with interference reflection microscopy, which appear to be the major points of cell-tosubstrate adhesion. In fibroblasts, the latter substrate-binding complex is characteristic of cultures that are arrested at the G1 phase of the cell cycle due to the low serum concentration in their medium. These arrested fibroblasts are very well spread, flattened, and immobile.

Immunocytochemical studies on the behavior of RuBisCO and LHCP II during the cell cycle of synchronized Euglena gracilis

1990 ◽  
Vol 48 (3) ◽  
pp. 662-663
Author(s):  
Tetsuaki Osafune ◽  
Shuji Sumida ◽  
Tomoko Ehara ◽  
Eiji Hase ◽  
Jerome A. Schiff
Keyword(s):  
Cell Cycle ◽  
Immunoelectron Microscopy ◽  
Growth Phase ◽  
Euglena Gracilis ◽  
Dark Period ◽  
Light Period ◽  
Carboxylase Activity ◽  
Immunocytochemical Studies ◽  
Lhcp Ii

Changes in the morphology of pyrenoid and the distribution of RuBisCO in the chloroplast of Euglena gracilis were followed by immunoelectron microscopy during the cell cycle in a light (14 h)- dark (10 h) synchronized culture under photoautotrophic conditions. The imrnunoreactive proteins wereconcentrated in the pyrenoid, and less densely distributed in the stroma during the light period (growth phase, Fig. 1-2), but the pyrenoid disappeared during the dark period (division phase), and RuBisCO was dispersed throughout the stroma. Toward the end of the division phase, the pyrenoid began to form in the center of the stroma, and RuBisCO is again concentrated in that pyrenoid region. From a comparison of photosynthetic CO2-fixation with the total carboxylase activity of RuBisCO extracted from Euglena cells in the growth phase, it is suggested that the carboxylase in the pyrenoid functions in CO2-fixation in photosynthesis.

Effect of Chrysanthemum flavonoids on growth and cell cycle regulators of gastric cancer cell

2010 ◽  
Vol 34 (8) ◽  
pp. S50-S50
Author(s):  
Xiaoyan Pan ◽  
Xinmei Zhou ◽  
Guangtao Xu ◽  
Lingfen Miao ◽  
Shuoru Zhu
Keyword(s):  
Gastric Cancer ◽  
Cell Cycle ◽  
Cancer Cell ◽  
Gastric Cancer Cell ◽  
Cell Cycle Regulators

Repair pathway choice for double-strand breaks

2020 ◽  
Vol 64 (5) ◽  
pp. 765-777 ◽  
Author(s):  
Yixi Xu ◽  
Dongyi Xu
Keyword(s):  
Cell Cycle ◽  
Double Strand Breaks ◽  
Homologous Region ◽  
Gene Repair ◽  
Repair Pathway ◽  
Dna Double Strand Breaks ◽  
Environmental Radiation ◽  
Strand Breaks ◽  
Dna End Resection ◽  
End Resection

Abstract Deoxyribonucleic acid (DNA) is at a constant risk of damage from endogenous substances, environmental radiation, and chemical stressors. DNA double-strand breaks (DSBs) pose a significant threat to genomic integrity and cell survival. There are two major pathways for DSB repair: nonhomologous end-joining (NHEJ) and homologous recombination (HR). The extent of DNA end resection, which determines the length of the 3′ single-stranded DNA (ssDNA) overhang, is the primary factor that determines whether repair is carried out via NHEJ or HR. NHEJ, which does not require a 3′ ssDNA tail, occurs throughout the cell cycle. 53BP1 and the cofactors PTIP or RIF1-shieldin protect the broken DNA end, inhibit long-range end resection and thus promote NHEJ. In contrast, HR mainly occurs during the S/G2 phase and requires DNA end processing to create a 3′ tail that can invade a homologous region, ensuring faithful gene repair. BRCA1 and the cofactors CtIP, EXO1, BLM/DNA2, and the MRE11–RAD50–NBS1 (MRN) complex promote DNA end resection and thus HR. DNA resection is influenced by the cell cycle, the chromatin environment, and the complexity of the DNA end break. Herein, we summarize the key factors involved in repair pathway selection for DSBs and discuss recent related publications.

Gut-enriched kruppel-like factor (GKLF) inhibits cellular proliferation by blocking the G1/S boundary of the cell cycle

2001 ◽  
Vol 120 (5) ◽  
pp. A103-A103
Author(s):  
X CHEN ◽  
D JOHNS ◽  
D GEIMAN ◽  
E MARBAN ◽  
V YANG
Keyword(s):  
Cell Cycle ◽  
Cellular Proliferation

PPAR-γ ligands induce G1 cell cycle arrest and reduce ornithine decarboxylase activity of human Barrett's adenocarcinoma cells

2001 ◽  
Vol 120 (5) ◽  
pp. A415-A415
Author(s):  
T TAKASHIMA ◽  
Y FUJIWARA ◽  
K HIGUCHI ◽  
T ARAKAWA ◽  
Y YANO ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Arrest ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Ornithine Decarboxylase Activity ◽  
Ppar Γ ◽  
Cycle Arrest ◽  
Adenocarcinoma Cells ◽  
Barrett’S Adenocarcinoma ◽  
G1 Cell Cycle Arrest
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