scholarly journals SIMULTANEOUS SYNTHESIS OF HISTONE AND DNA IN SYNCHRONOUSLY DIVIDING TETRAHYMENA PYRIFORMIS

1967 ◽  
Vol 32 (3) ◽  
pp. 709-717 ◽  
Author(s):  
John A. Hardin ◽  
Gerald E. Einem ◽  
David T. Lindsay
Keyword(s):  
Heat Treatment ◽  
Cell Division ◽  
Dna Content ◽  
Regulatory Mechanism ◽  
Tetrahymena Pyriformis ◽  
S Phase ◽  
Second Step ◽  
Partial Duplication ◽  
Dividing Cells ◽  
Simultaneous Synthesis

Histone and DNA syntheses have been studied in synchronously dividing Tetrahymena pyriformis GL. During the heat treatment necessary to synchronize cultures of this amicronucleate protozoan, the DNA content of the already polyploid macronucleus increases. When the cells begin synchronous division, their DNA content is reduced in a stepwise process which is closely paralleled by reduction of macronuclear histone content. During cell division, the contents of DNA and histone decrease by slightly more than twofold, and in the subsequent S phase, DNA and histone increase simultaneously to 85% of the values expected if all chromosomes were to double. The first step in the process of reduction of DNA and histone contents is their decrease in excess of twofold, and this is accomplished by removal of extrusion bodies from the nuclei of dividing cells. The second step is a mechanism which allows, in effect, only 70% of the chromatin in the average nucleus to duplicate. Such partial duplication suggests that both histone and DNA syntheses in synchronous Tetrahymena depend upon a regulatory mechanism, the mediating elements of which are localized in only certain chromosomes.

Effects of DMSO on Vacuole Formation, Contractile Vacuole Function, and Nuclear Division in Tetrahymena Pyriformis GL

1974 ◽  
Vol 16 (1) ◽  
pp. 39-47
Author(s):  
J. R. NILSSON
Keyword(s):  
Cell Division ◽  
Nuclear Division ◽  
Physiological State ◽  
Tetrahymena Pyriformis ◽  
Cell Number ◽  
Contractile Vacuole ◽  
Vacuole Formation ◽  
Control Value ◽  
Dividing Cells

Increasing concentrations of dimethyl sulphoxide (DMSO) affect vacuole formation in Tetrahymena, as measured quantitatively by the uptake of carmine particles. The rate of vacuole formation decreased to about 50% of the control value in 5.0% DMSO (v/v) and to zero in 7.5%. At the latter concentration, the inhibition was expressed immediately; however, the effect of 1-h exposure was reversible after removal of DMSO by washing. In vivo observations revealed abnormal function of the contractile vacuole in 7.5% DMSO, while cell motility and cell division appeared to be unaffected. Although cell division occurred there was little or no increase in cell number, as studied over a cell generation time. Feulgen preparations showed that nuclear division was inhibited and that cell division resulted in one anucleate and one nucleate daughter cell. This effect was also observed in some dividing cells at lower concentrations of DMSO. The effect of DMSO on Tetrahymena was dependent not only on the concentration of the compound but also on the physiological state of the cells.

scholarly journals Caspase-2 regulates S-phase cell cycle events to protect from DNA damage accumulation independent of apoptosis

2021 ◽  
Author(s):  
Ashley Boice ◽  
Raj Kumari Pandita ◽  
Karla Lopez ◽  
Melissa J Pourpak ◽  
Chloe I Charendoff ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Damage ◽  
Cell Division ◽  
S Phase ◽  
Phase Cell ◽  
Replication Forks ◽  
Cycle Arrest ◽  
Dividing Cells ◽  
Caspase 2 ◽  
Stalled Replication Forks

In addition to its classical role in apoptosis, accumulating evidence suggests that caspase-2 has non-apoptotic functions, including regulation of cell division. Loss of caspase-2 is known to increase proliferation rates but how caspase-2 is regulating this process is currently unclear. We show that caspase-2 is activated in dividing cells in G1- and early S-phase. In the absence of caspase-2, cells exhibit numerous S-phase defects including delayed exit from S-phase, S-phase-associated chromosomal aberrations, and increased DNA damage following S-phase arrest. In addition, caspase-2-deficient cells have a higher frequency of stalled replication forks, decreased DNA fiber length, and impeded progression of DNA replication tracts. This indicates that caspase-2 reduces replication stress and promotes replication fork protection to maintain genomic stability. These functions are independent of the pro-apoptotic function of caspase-2 because blocking caspase-2-induced cell death had no effect on cell division or DNA damage-induced cell cycle arrest. Thus, our data supports a model where caspase-2 regulates cell cycle events to protect from the accumulation of DNA damage independently of its pro-apoptotic function.

scholarly journals The DNA content of trophozoites and cysts of Giardia lamblia by microdensitometric quantitation of Feulgen staining and examination by laser scanning confocal microscopy.

1994 ◽  
Vol 42 (11) ◽  
pp. 1413-1416 ◽  
Author(s):  
S L Erlandsen ◽  
E M Rasch
Keyword(s):  
Confocal Microscopy ◽  
Genome Size ◽  
Dna Content ◽  
Giardia Lamblia ◽  
Laser Scanning ◽  
Laser Scanning Confocal Microscopy ◽  
Evolutionary Development ◽  
Scanning Confocal Microscopy ◽  
Dividing Cells ◽  
C Value

We investigated direct measurement of the DNA content of the parasitic intestinal flagellate Giardia lamblia through quantitation by Feulgen microspectrophotometry and also by visualization of Feulgen-stained DNA chromosomes within dividing cells by laser scanning confocal microscopy. Individual trophozoites of Giardia (binucleate) contained 0.144 +/- 0.018 pg of DNA/cell or 0.072 pg DNA/nucleus. Giardia lamblia cysts (quadranucleate) contained 0.313 +/- 0.003 pg DNA or 0.078 pg DNA/nucleus. The genome size (C) value per nucleus ranged between 6.5-7.1 x 10(7) BP for trophozoites and cysts, respectively. Confocal microscopic examination of Giardia trophozoites undergoing binary fission revealed five chromosome-like bodies within each nucleus. Further information about genome size and DNA content within different Giardia species may help to clarify the pivotal role of these primitive eukaryotic cells in evolutionary development.

scholarly journals Cytokinesis and Midzone Microtubule Organization inCaenorhabditis elegans Require the Kinesin-like Protein ZEN-4

1998 ◽  
Vol 9 (8) ◽  
pp. 2037-2049 ◽  
Author(s):  
William B. Raich ◽  
Adrienne N. Moran ◽  
Joel H. Rothman ◽  
Jeff Hardin
Keyword(s):  
Cell Division ◽  
Null Allele ◽  
Time Lapse ◽  
Equatorial Region ◽  
Microtubule Organization ◽  
Dividing Cells ◽  
Spindle Midzone ◽  
Cross Links ◽  
Complete Cell

Members of the MKLP1 subfamily of kinesin motor proteins localize to the equatorial region of the spindle midzone and are capable of bundling antiparallel microtubules in vitro. Despite these intriguing characteristics, it is unclear what role these kinesins play in dividing cells, particularly within the context of a developing embryo. Here, we report the identification of a null allele ofzen-4, an MKLP1 homologue in the nematodeCaenorhabditis elegans, and demonstrate that ZEN-4 is essential for cytokinesis. Embryos deprived of ZEN-4 form multinucleate single-celled embryos as they continue to cycle through mitosis but fail to complete cell division. Initiation of the cytokinetic furrow occurs at the normal time and place, but furrow propagation halts prematurely. Time-lapse recordings and microtubule staining reveal that the cytokinesis defect is preceded by the dissociation of the midzone microtubules. We show that ZEN-4 protein localizes to the spindle midzone during anaphase and persists at the midbody region throughout cytokinesis. We propose that ZEN-4 directly cross-links the midzone microtubules and suggest that these microtubules are required for the completion of cytokinesis.

fumble Encodes a Pantothenate Kinase Homolog Required for Proper Mitosis and Meiosis in Drosophila melanogaster

Genetics ◽  
2001 ◽  
Vol 157 (3) ◽  
pp. 1267-1276
Author(s):  
Katayoun Afshar ◽  
Pierre Gönczy ◽  
Stephen DiNardo ◽  
Steven A Wasserman
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Cell Division Cycle ◽  
Protein Isoforms ◽  
Pantothenate Kinase ◽  
Male Germline ◽  
Dividing Cells ◽  
Mutant Cells ◽  
Mitosis And Meiosis

Abstract A number of fundamental processes comprise the cell division cycle, including spindle formation, chromosome segregation, and cytokinesis. Our current understanding of these processes has benefited from the isolation and analysis of mutants, with the meiotic divisions in the male germline of Drosophila being particularly well suited to the identification of the required genes. We show here that the fumble (fbl) gene is required for cell division in Drosophila. We find that dividing cells in fbl-deficient testes exhibit abnormalities in bipolar spindle organization, chromosome segregation, and contractile ring formation. Cytological analysis of larval neuroblasts from null mutants reveals a reduced mitotic index and the presence of polyploid cells. Molecular analysis demonstrates that fbl encodes three protein isoforms, all of which contain a domain with high similarity to the pantothenate kinases of A. nidulans and mouse. The largest Fumble isoform is dispersed in the cytoplasm during interphase, concentrates around the spindle at metaphase, and localizes to the spindle midbody at telophase. During early embryonic development, the protein localizes to areas of membrane deposition and/or rearrangement, such as the metaphase and cellularization furrows. Given the role of pantothenate kinase in production of Coenzyme A and in phospholipid biosynthesis, this pattern of localization is suggestive of a role for fbl in membrane synthesis. We propose that abnormalities in synthesis and redistribution of membranous structures during the cell division cycle underlie the cell division defects in fbl mutant cells.

Freeze-fracture analysis of membrane events during early neogenesis of cilia in Tetrahymena: changes in fairy-ring morphology and membrane topography

1983 ◽  
Vol 60 (1) ◽  
pp. 137-156
Author(s):  
L.A. Hufnagel
Keyword(s):  
Cell Division ◽  
Membrane Structure ◽  
Freeze Fracture ◽  
Fracture Analysis ◽  
Basal Bodies ◽  
Membrane Topography ◽  
Fairy Rings ◽  
Dividing Cells ◽  
Cortical System ◽  
Membrane Particle

A freeze-fracture analysis of early neogenesis of somatic and oral cilia of Tetrahymena was conducted using exponentially grown cultures and also cells induced to undergo oral reorganization. In this report, presumptive ciliary domains (PCDs), sites of future outgrowth of somatic cilia, are identified and their membrane structure is described in detail. The fairy ring, an array of membrane particles that occurs within the PCD and appears to be a precursor of the ciliary necklace, is described. A sequence of early stages in the formation of the ciliary necklace of somatic cilia is deduced from topographical information and membrane particle arrangements and numbers. Evidence is presented that basal bodies are seated at the cell surface prior to initiation of necklace assembly and a possible role for the basal body in necklace assembly is suggested. In dividing cells, new oral cilia grow out prior to orientation of cilia-parasomal sac complexes relative to cell axes. In dividing cells and during oral reorganization, new cilia also develop prior to their alignment into membranelles. Thus, growth of cilia is independent of their spatial orientation. Fairy rings were not observed during oral reorganization. During cell division, proliferation of new cilia is accompanied by the formation of a network of junctions between a cortical system of membranous cisternae, the cortical ‘alveoli’. These interalveolar junctions may serve as tracks for early positioning and orientation of new oral basal bodies.

discordia mutations specifically misorient asymmetric cell divisions during development of the maize leaf epidermis

Development ◽  
1999 ◽  
Vol 126 (20) ◽  
pp. 4623-4633 ◽  
Author(s):  
K. Gallagher ◽  
L.G. Smith
Keyword(s):  
Cell Division ◽  
Preprophase Band ◽  
Cytochalasin D ◽  
Leaf Epidermis ◽  
Asymmetric Cell Divisions ◽  
Maize Leaf ◽  
Cell Divisions ◽  
Cytoskeletal Structure ◽  
Dividing Cells ◽  
Preprophase Bands

In plant cells, cytokinesis depends on a cytoskeletal structure called a phragmoplast, which directs the formation of a new cell wall between daughter nuclei after mitosis. The orientation of cell division depends on guidance of the phragmoplast during cytokinesis to a cortical site marked throughout prophase by another cytoskeletal structure called a preprophase band. Asymmetrically dividing cells become polarized and form asymmetric preprophase bands prior to mitosis; phragmoplasts are subsequently guided to these asymmetric cortical sites to form daughter cells of different shapes and/or sizes. Here we describe two new recessive mutations, discordia1 (dcd1) and discordia2 (dcd2), which disrupt the spatial regulation of cytokinesis during asymmetric cell divisions. Both mutations disrupt four classes of asymmetric cell divisions during the development of the maize leaf epidermis, without affecting the symmetric divisions through which most epidermal cells arise. The effects of dcd mutations on asymmetric cell division can be mimicked by cytochalasin D treatment, and divisions affected by dcd1 are hypersensitive to the effects of cytochalasin D. Analysis of actin and microtubule organization in these mutants showed no effect of either mutation on cell polarity, or on formation and localization of preprophase bands and spindles. In mutant cells, phragmoplasts in asymmetrically dividing cells are structurally normal and are initiated in the correct location, but often fail to move to the position formerly occupied by the preprophase band. We propose that dcd mutations disrupt an actin-dependent process necessary for the guidance of phragmoplasts during cytokinesis in asymmetrically dividing cells.

Changes of the DNA content of differentiating and adult macronuclei of the ciliate Loxodes magnus (Karyorelictida)

1980 ◽  
Vol 44 (1) ◽  
pp. 375-394
Author(s):  
N.N. Bobyleva ◽  
B.N. Kudrjavtsev ◽  
I.B. Raikov
Keyword(s):  
Cell Division ◽  
Dna Replication ◽  
Hydrochloric Acid ◽  
Dna Synthesis ◽  
Acid Hydrolysis ◽  
Gene Amplification ◽  
Dna Content

The DNA content of isolated micronuclei, differentiating macronuclei (macronuclear Anlagen), and adult macronuclei of Loxodes magnus was measured cytofluorimetrically in preparations stained with a Schiff-type reagent, auramine-SO2, following hydrochloric acid hydrolysis. The DNA content of the youngest macronuclear Anlagen proved to be the same as that of telophasic micronuclei (2 c). The Anlagen thus differentiate from micronuclei which are still in G1. The quantity of DNA in the macronuclear Anlagen thereafter rises to the 4-c level, simultaneously with DNA replication in the micronuclei which immediately follows mitosis. In non-dividing animals most micronuclei are already in G2. Adult macronuclei here contain on average 1.5 times more DNA than the micronuclei; their DNA content is about 5–6 c (in some individual nuclei, up to 10 c). These data are consistent with autoradiographic evidence indicating a weak DNA synthesis in the macronuclei of Loxodes and make likely the existence of partial DNA replication (e.g. gene amplification) in the macronuclei. The DNA content of adult macronuclei isolated from dividing animals proved to be significantly smaller than that of macronuclei isolated from non-dividing specimens of the same clone. In 3 clones studied, the former value amounted on average to 71–79, 78 and 95% of the latter, respectively. This drop of DNA content cannot be explained by ‘dilution’ of the old macronuclei with newly formed ones. The quantity of DNA in adult macronuclei thus seems to undergo cyclical changes correlated with cytokinesis, despite the fact that, in Loxodes magnus, the macronuclei themselves never divide and are simply segregated at every cell division. The macronuclei of Loxodes can be termed paradiploid or hyperdiploid.

Transcription of the histone H5 gene is not S-phase regulated

1986 ◽  
Vol 6 (2) ◽  
pp. 601-606
Author(s):  
S Dalton ◽  
J R Coleman ◽  
J R Wells
Keyword(s):  
Cell Cycle ◽  
Steady State ◽  
Northern Blotting ◽  
S Phase ◽  
Erythroid Cells ◽  
Dividing Cells ◽  
Steady State Levels ◽  
Avian Erythroblastosis Virus ◽  
Histone H5

Levels of the tissue-specific linker histone H5 are elevated in mature erythroid cells as compared with levels in dividing cells of the same lineage. We examined levels of H5 mRNA in relation to the cell cycle in early erythroid cells transformed by avian erythroblastosis virus to determine whether the gene for this unusual histone is S-phase regulated. Northern blotting analyses revealed that during the cell cycle steady-state levels of H5 mRNA remained relatively constant in contrast to levels of the major core and H1 mRNAs which increased approximately 15-fold during S phase. In vitro pulse-labeling experiments involving nuclei isolated from synchronized cells at various stages of the cell cycle revealed that transcription of the H5 gene was not initiated at any particular stage of the cell cycle but was constitutive. In contrast, transcription of the H2A gene(s) initiated in early S phase, was present throughout the DNA replicative phase, and was essentially absent in G1 and G2 phases.

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