scholarly journals Localization of Microtubules during Macronuclear Division in Tetrahymena and Possible Involvement of Macronuclear Microtubules in 'Amitotic' Chromatin Distribution.

1999 ◽  
Vol 24 (5) ◽  
pp. 401-404 ◽  
Author(s):  
Kenta Fujiu ◽  
Osamu Numata
Keyword(s):  
Macronuclear Division

Spatiotemporal control of functional specification and distribution of spindle microtubules with 13, 14 and 15 protofilaments during mitosis in the ciliate Nyctotherus

1985 ◽  
Vol 76 (1) ◽  
pp. 337-355
Author(s):  
U. Eichenlaub-Ritter
Keyword(s):  
Differential Sensitivity ◽  
Microtubule Depolymerization ◽  
Functional Specification ◽  
Microtubule Stability ◽  
Early Anaphase ◽  
Late Telophase ◽  
Spindle Microtubules ◽  
Elongation Phase ◽  
Spatiotemporal Control ◽  
Macronuclear Division

The formation of microtubules with more than 13 protofilaments in the ciliate Nyctotherus ovalis Leidy seems to be a highly ordered process. Such microtubules are restricted to the nucleoplasm and, moreover, to certain stages of nuclear division. They assemble during anaphase of micronuclear mitosis and during the elongation phase of macronuclear division. The number of microtubules with more than 13 protofilaments in the micronuclear nucleoplasm increases as anaphase progresses. Furthermore, assembly of microtubules with 14 and 15 protofilaments seems to proceed concomitantly with net disassembly of 13-protofilament microtubules, because the total amount of polymerized tubulin in the interpolar spindle region remains approximately constant between mid anaphase and late telophase. In addition, evidence for spatial control of the distribution of microtubules with different protofilament numbers in the micronuclear stembody has been found. The percentage of microtubules with 13 protofilaments per stembody cross-section is highest at the ends of the stembody, while the percentage of microtubules with either 14 or 15 protofilaments increases as the middle of the stembody is approached. Temporal control of polymerization of microtubules with high protofilament numbers seems to be exerted independently in the two types of nuclei. For example, when the macronucleus starts to elongate it contains microtubules with more than 13 protofilaments but the metaphase micronucleus still possesses only microtubules with 13 protofilaments at this stage. Control of fidelity of protofilament numbers is not lost in the early stages of micronuclear or macronuclear division when cells are exposed to 2H2O or media containing taxol. Even microtubules that reassemble during recovery of metaphase micronuclei from nocodazole-induced microtubule depolymerization, in either the absence or presence of 2H2O and taxol, possess 13 protofilaments. Similarly, if the introduction of microtubules with 14 and 15 protofilaments is inhibited during early micronuclear anaphase and delayed for 60 min by exposure to nocodazole, such microtubules still assemble during telophase when recovery is permitted. Microtubules that have been assembled under normal conditions show differential sensitivity to nocodazole. During metaphase, nocodazole induces disassembly of most microtubules. There is an increase in microtubule stability that coincides with the appearance of microtubules with high protofilament numbers during early anaphase. However, considerable numbers of 13-protofilament microtubules, as well as microtubules with 14 and 15 protofilaments, exhibit such stability during anaphase.(ABSTRACT TRUNCATED AT 400 WORDS)

Antimitotic agents and macronuclear division of ciliates

1969 ◽  
Vol 56 (5) ◽  
pp. 285-286 ◽  
Author(s):  
F. Wunderlich ◽  
D. Peyk
Keyword(s):  
Macronuclear Division

Macronuclear division with and without microtubules in Tetrahymena

1976 ◽  
Vol 20 (1) ◽  
pp. 61-77
Author(s):  
N.E. Williams ◽  
R.J. Williams
Keyword(s):  
Molecular Mechanisms ◽  
Force Production ◽  
Focus Attention ◽  
Macronuclear Division

The effects of cold shocks (0 degrees C) and colchicine (4 mg/ml) on macronuclear microtubules and macronuclear division have been investigated in Tetrahymena. Macronuclear division was affected by both treatments, but loss of microtubules occurred only in the presence of colchicine. When colchicine was applied immediately prior to macronuclear elongation, the nuclei underwent a partial elongation without microtubules, but were unable to constrict and separate into daughter nuclei. Such nuclei were cut in two by the advancing cytoplasmic fission furrow. When colchicine was applied to macronuclei in the fully elongated state, that maintained their elongation in the absence of microtubules, and were subsequently separated into daughter nuclei by the cytoplasmic furrow. It is suggested that macronuclear microtubules, most probably the membrane-associated microtubules, are required for the terminal stages of nuclear elongation and separation. However, the considerable macronuclear elongation which takes place in the absence of microtubules serves to focus attention on molecular mechanisms of force production which must reside elsewhere in the macronucleus.

scholarly journals THE SYNTHESES OF TOTAL MACRONUCLEAR PROTEIN, HISTONE, AND DNA DURING THE CELL CYCLE IN EUPLOTES EURYSTOMUS

1966 ◽  
Vol 31 (1) ◽  
pp. 1-9 ◽  
Author(s):  
David M. Prescott
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Total Protein ◽  
Tritiated Thymidine ◽  
S Phase ◽  
Protein Labeling ◽  
Constant Rate ◽  
Tritiated Amino Acids ◽  
Histone Synthesis ◽  
Macronuclear Division

The syntheses of histone, total protein, and DNA during the cell cycle were measured in the macronucleus of Euplotes eurystomus by assaying the incorporation of tritiated amino acids and tritiated thymidine in groups of 800 to 1000 synchronized cells. The synthesis of DNA begins at 30% completion of the cell cycle, proceeds at a constant rate, and ends very shortly before the beginning of macronuclear division. Histone labeling is absent during G1, begins in phase with DNA synthesis, continues at an unchanging rate during the S phase, and ends with the completion of DNA synthesis. The results support the view that the syntheses of histone and DNA are closely coupled events. Label in total protein accumulates at a constant rate during G1 and appears to shift to a slightly higher rate when histone synthesis begins. At division, radioactive DNA, histone, and total protein are distributed equally between the daughter macronuclei without loss of radioactivity. Radioautographic analysis showed that protein labeling occurs throughout the macronucleus during the entire life cycle. There was no clear difference in the degree of protein labeling between replicated and unreplicated regions of the macronucleus. The distribution of label suggests that most of macronuclear protein labeling during the cell cycle is concerned with the events of transcription rather than replication.

Antimitotic agents and macronuclear division of ciliates

PROTOPLASMA ◽  
1970 ◽  
Vol 70 (2) ◽  
pp. 139-152 ◽  
Author(s):  
F. Wunderlich ◽  
V. Speth
Keyword(s):  
Macronuclear Division

scholarly journals Microtubules and control of macronuclear ‘amitosis’ in Paramecium

1980 ◽  
Vol 44 (1) ◽  
pp. 135-151
Author(s):  
J.B. Tucker ◽  
J. Beisson ◽  
D.L. Roche ◽  
J. Cohen
Keyword(s):  
Spatial Relationship ◽  
Longitudinal Axis ◽  
Nuclear Shape ◽  
Dorsal Cortex ◽  
Spatially Correlated ◽  
Sliding Mechanism ◽  
Intranuclear Microtubules ◽  
Oriented Parallel ◽  
And Control ◽  
Macronuclear Division

The ‘amitotic’ division of the macronucleus during binary fission in P. tetraurelia includes a detailed sequence of shape changes that are temporally coordinated with the adoption of a series of well-defined positions and orientations inside the cell. The deployment of nucleoplasmic microtubules that is spatially correlated with the shaping ritual is more complex and precise than has been reported previously. Macronuclear division is not amitotic. It is not a simple constriction into two halves. As a dividing macronucleus starts to elongate it becomes dorsoventrally flattened against the dorsal cortex of the organism and assumes an elliptical shape. Concurrently, an elliptical marginal band of intranuclear microtubules assembles that has the same spatial relationship to nuclear shape as the marginal microtubules assembles that has the same spatial relationship to nuclear shape as the marginal microtubule bands of certain elliptical vertebrate blood cells have to cell shape. The band breaks down as further elongation occurs and the nucleus adopts the shape of a straight and slender sausage. Most of the intranuclear microtubules assemble as elongation starts and break down shortly after elongation is completed; the majority are oriented parallel to the longitudinal axis of the nucleus throughout elongation. Some of them are attached to nucleoli and are coated with granules which are almost certainly derived from the cortices of nucleoli. The peripheral concentration, interconnexion, orientation, and overlapping arrangement of microtubules, and the reduction in microtubule number per nuclear cross-section as elongation proceeds at a rate of about 40 micrometers min-1, are all compatible with the provision of a microtubule sliding mechanism as the main skeletal basis for elongation. There are indications that this mechanism is augmented by anchorage and/or active propulsion of nucleoli that may perhaps facilitate fairly equitable segregation of chromosomal material to daughter nuclei.

scholarly journals Evolutionary constraints on quantitative variation and regulation of macronuclear dna content in the genus Tetrahymena

1981 ◽  
Vol 49 (1) ◽  
pp. 177-193
Author(s):  
F.P. Doerder ◽  
J. Ditaranto ◽  
L.E. DeBault
Keyword(s):  
Dna Content ◽  
Gene Dosage ◽  
Interspecific Variation ◽  
S Phase ◽  
Quantitative Variation ◽  
Evolutionary Constraints ◽  
Regular Feature ◽  
Species Complexes ◽  
Macronuclear Division ◽  
Dna Amounts

Fluorescence cytophotometry was used to examine quantitative variation and regulation of macronuclear DNA content in 44 clones representing 13 species in 3 species-complexes of the genus Tetrahymena. Mean DNA amounts for G2 macronuclei generally ranged from 20–50 pg, with extreme means of 10 and 196 pg. Both intra- and interspecific variation was usually significant at the 5% level, and in some instances DNA amounts for the same clone in repeated experiments were significant different. Nevertheless, intraclonal ranges both within and among species frequently showed considerable overlap and, in the context of all the ciliates, the range of means is small. Calculations suggest that a biologically more meaningful measure, gene dosage, is also evolutionarily conserved. Additional evolutionary constraints are found in the regulation of macronuclear DNA content. Analysis of G1 and G2 intraclonal variances shows that in all species the variance added by regular unequal macronuclear division is removed by modification of cell-cycle events according to Model II regulation. In Model II, macronuclei with a small amount of DNA undergo an additional S phase before nuclear and cell division, whereas macronuclei with a large amount of DNA omit an S phase. Chromatin extrusion is also a regular feature of macronuclear division in most species, but its role in regulation is unclear. Extrusion regulates downward the mean amount of DNA but may actually contribute to unequal division and therefore add rather than remove variance.

scholarly journals A β-Tubulin Mutation Selectively Uncouples Nuclear Division and Cytokinesis in Tetrahymena thermophila

2004 ◽  
Vol 3 (5) ◽  
pp. 1217-1226 ◽  
Author(s):  
Joshua J. Smith ◽  
J. Sebastian Yakisich ◽  
Geoffrey M. Kapler ◽  
Eric S. Cole ◽  
Daniel P. Romero
Keyword(s):  
Elevated Temperatures ◽  
Kinase Inhibitor ◽  
Nuclear Division ◽  
Tetrahymena Thermophila ◽  
Cell Formation ◽  
Dependent Manner ◽  
Cytoplasmic Microtubule ◽  
High Concentrations ◽  
Macronuclear Division ◽  
Β Tubulin

ABSTRACT The ciliated protozoan Tetrahymena thermophila contains two distinct nuclei within a single cell—the mitotic micronucleus and the amitotic macronucleus. Although microtubules are required for proper division of both nuclei, macronuclear chromosomes lack centromeres and the role of microtubules in macronuclear division has not been established. Here we describe nuclear division defects in cells expressing a mutant β-tubulin allele that confers hypersensitivity to the microtubule-stabilizing drug paclitaxel. Macronuclear division is profoundly affected by the btu1-1 (K350M) mutation, producing cells with widely variable DNA contents, including cells that lack macronuclei entirely. Protein expressed by the btu1-1 allele is dominant over wild-type protein expressed by the BTU2 locus. Normal macronuclear division is restored when the btu1-1 allele is inactivated by targeted disruption or expressed as a truncated protein. Immunofluorescence studies reveal elongated microtubular structures that surround macronuclei that fail to migrate to the cleavage furrows. In contrast, other cytoplasmic microtubule-dependent processes, such as cytokinesis, cortical patterning, and oral apparatus assembly, appear to be unaffected in the mutant. Micronuclear division is also perturbed in the K350M mutant, producing nuclei with elongated early-anaphase spindle configurations that persist well after the initiation of cytokinesis. The K350M mutation affects tubulin dynamics, as the macronuclear division defect is exacerbated by three treatments that promote microtubule polymerization: (i) elevated temperatures, (ii) sublethal concentrations of paclitaxel, and (iii) high concentrations of dimethyl sulfoxide. Inhibition of phosphatidylinositol 3-kinase (PI 3-kinase) with 3-methyladenine or wortmannin also induces amacronucleate cell formation in a btu1-1-dependent manner. Conversely, the myosin light chain kinase inhibitor ML-7 has no effect on nuclear division in the btu1-1 mutant strain. These findings provide new insights into microtubule dynamics and link the evolutionarily conserved PI 3-kinase signaling pathway to nuclear migration and/or division in Tetrahymena.

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