scholarly journals Degradation of cyclin B is critical for nuclear division in Trypanosoma brucei

2017 ◽  
Author(s):  
Hanako Hayashi ◽  
Bungo Akiyoshi
Keyword(s):  
Cell Cycle ◽  
Trypanosoma Brucei ◽  
Nuclear Division ◽  
Spindle Checkpoint ◽  
Nuclear Genome ◽  
Single Copy ◽  
Cyclin B ◽  
Daughter Cells ◽  
Mitotic Cyclin ◽  
Assembly Defect

AbstractKinetoplastids have a nucleus that contains the nuclear genome and a kinetoplast that contains the mitochondrial genome. These single-copy organelles must be duplicated and segregated faithfully to daughter cells at each cell division. In Trypanosoma brucei, although duplication of both organelles starts around the same time, segregation of the kinetoplast precedes that of the nucleus. Cytokinesis subsequently takes place so that daughter cells inherit a single copy of each organelle. Very little is known about the molecular mechanism that governs the timing of these events. Furthermore, it is thought that T. brucei lacks a spindle checkpoint that delays the onset of nuclear division in response to spindle damage. Here we show that a mitotic cyclin CYC6 has a dynamic localization pattern during the cell cycle, including kinetochore localization from G2 to metaphase. Using CYC6 as a molecular cell cycle marker, we confirmed that T. brucei cannot delay the onset of anaphase in response to a bipolar spindle assembly defect. Interestingly, expression of a stabilized form of CYC6 caused the nucleus to arrest in a metaphase-like state without preventing cytokinesis. We propose that trypanosomes have an ability to regulate the timing of nuclear division by modulating the CYC6 protein level, without a spindle checkpoint.

Overexpression of a truncated cyclin B gene arrests Dictyostelium cell division during mitosis

1994 ◽  
Vol 107 (11) ◽  
pp. 3105-3114 ◽  
Author(s):  
Q. Luo ◽  
C. Michaelis ◽  
G. Weeks
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Cell Growth ◽  
Dictyostelium Discoideum ◽  
Single Copy ◽  
Cyclin B ◽  
Dictyostelium Cell ◽  
Maximum Accumulation ◽  
Sequence Identity ◽  
Cyclin Gene

A cyclin gene has been isolated from Dictyostelium discoideum and the available evidence indicates that the gene encodes a B type cyclin. The cyclin box region of the protein encoded by the gene, clb1, has the highest degree of sequence identity with the B-type cyclins of other species. Levels of cyclin B mRNA and protein oscillate during the cell cycle with maximum accumulation of mRNA occurring prior to cell division and maximum levels of protein occurring during cell division. Overexpression of a N-terminally truncated cyclin B protein lacking the destruction box inhibits cell growth by arresting cell division during mitosis. The gene is present as a single copy in the Dictyostelium genome and there is no evidence for any other highly related cyclin B genes.

The cell division cycle of Trypanosoma brucei brucei : timing of event markers and cytoskeletal modulations

1989 ◽  
Vol 323 (1218) ◽  
pp. 573-588 ◽  
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Trypanosoma Brucei ◽  
Basal Body ◽  
Single Copy ◽  
Cell Division Cycle ◽  
Basal Bodies ◽  
Division Plane ◽  
Transmission Electron ◽  
Single Nucleus

We have analysed the timing and order of events occurring within the cell division cycle of Trypanosoma brucei . Cells in the earliest stages of the cell cycle possess a single copy of three major organelles: the nucleus, the kinetoplast and the flagellum. The first indication of progress through the cell cycle is the elongation of the pro-basal body lying adjacent to the mature basal body subtending the flagellum. This newly elongated basal body occupies a posterior position within the cell when it initiates growth of the new daughter flagellum. Genesis of two new pro-basal bodies occurs only after growth of the new daughter flagellum has been initiated. Extension of the new flagellum, together with the paraflagellar rod, then continues throughout a major portion of the cell cycle. During this period of flagellum elongation, kinetoplast division occurs and the two kinetoplasts, together with the two flagellar basal bodies, then move apart within the cell. Mitosis is then initiated and a complex pattern of organelle positions is achieved whereby a division plane runs longitudinally through the cell such that each daughter ultimately receives a single nucleus, kinetoplast and flagellum. These events have been described from observations of whole cytoskeletons by transmission electron microscopy together with detection of particular organelles by fluorescence microscopy. The order and timing of events within the cell cycle has been derived from analyses of the proportion of a given cell type occurring within an exponentially growing culture.

scholarly journals A role for Sar1 and ARF1 GTPases during Golgi biogenesis in the protozoan parasite Trypanosoma brucei

2017 ◽  
Vol 28 (13) ◽  
pp. 1782-1791 ◽  
Author(s):  
Sevil Yavuz ◽  
Graham Warren
Keyword(s):  
Cell Cycle ◽  
Trypanosoma Brucei ◽  
Protozoan Parasite ◽  
Small Gtpases ◽  
Intact Cells ◽  
Golgi Stack ◽  
Daughter Cells ◽  
Photoactivatable Gfp

A single Golgi stack is duplicated and partitioned into two daughter cells during the cell cycle of the protozoan parasite Trypanosoma brucei. The source of components required to generate the new Golgi and the mechanism by which it forms are poorly understood. Using photoactivatable GFP, we show that the existing Golgi supplies components directly to the newly forming Golgi in both intact and semipermeabilized cells. The movement of a putative glycosyltransferase, GntB, requires the Sar1 and ARF1 GTPases in intact cells. In addition, we show that transfer of GntB from the existing Golgi to the new Golgi can be recapitulated in semipermeabilized cells and is sensitive to the GTP analogue GTPγS. We suggest that the existing Golgi is a key source of components required to form the new Golgi and that this process is regulated by small GTPases.

Tubulin post-translational modifications and the construction of microtubular organelles in Trypanosoma brucei

1988 ◽  
Vol 90 (4) ◽  
pp. 577-589 ◽  
Author(s):  
R. Sasse ◽  
K. Gull
Keyword(s):  
Cell Cycle ◽  
Trypanosoma Brucei ◽  
Mitotic Spindle ◽  
Post Translational Modification ◽  
Post Translational Modifications ◽  
Alpha Tubulin ◽  
Daughter Cells ◽  
A Cell ◽  
Microtubular Organelles ◽  
Tubulin Content

We have used specific monoclonal antibodies to facilitate a study of acetylated and tyrosinated alpha-tubulin in the microtubule (MT) arrays in the Trypanosoma brucei cell. Acetylated alpha-tubulin is not solely located in the stable microtubular arrays but is present even in the ephemeral microtubules of the mitotic spindle. Moreover, there is a uniform distribution of this isoform in all arrays. Studies of flagella complexes show that acetylation is concomitant with assembly of MTs. There is no subsequent major modulation in the content of acetylated alpha-tubulin in MTs. Conversely, polymerizing flagellar MTs have a high tyrosinated alpha-tubulin content, which is subsequently reduced to a basal level at a discrete point in the cell cycle. The MTs of the intranuclear mitotic spindle appear never to contain tyrosinated alpha-tubulin, suggesting that they are actually constructed of detyrosinated alpha-tubulin or that detyrosination is extremely rapid at this time in the cell cycle. T. brucei therefore, represents a cell type with extremely active mechanisms for the post-translational modification of alpha-tubulin. Our analyses of the timing of acquisition and modulation in relation to MT construction in T. brucei, suggest that acetylation and detyrosination of alpha-tubulin are two independently regulated post-translational modifications, that are not uniquely associated with particular subsets of MTs of defined lability, position or function. Post-assembly detyrosination of alpha-tubulin may provide a mechanism whereby the cell could discriminate between new and old MTs, during construction of the cytoskeleton through the cell cycle. However, we also suggest that continuation of detyrosination, allows the cell, at cell division, to partition into daughter cells two equivalent sets of cytoskeletal MTs.

scholarly journals The Anaphase-Promoting Complex/Cyclosome Is Required for Anaphase Progression in Multinucleated Ashbya gossypii Cells

2006 ◽  
Vol 6 (2) ◽  
pp. 182-197 ◽  
Author(s):  
Amy S. Gladfelter ◽  
Nicoleta Sustreanu ◽  
A. Katrin Hungerbuehler ◽  
Sylvia Voegeli ◽  
Virginie Galati ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Nuclear Division ◽  
Eukaryotic Cell ◽  
Ashbya Gossypii ◽  
Anaphase Promoting Complex ◽  
Cycle Progression ◽  
Filamentous Ascomycete ◽  
Multinucleated Cells ◽  
Mitotic Cyclin

ABSTRACT Regulated protein degradation is essential for eukaryotic cell cycle progression. The anaphase-promoting complex/cyclosome (APC/C) is responsible for the protein destruction required for the initiation of anaphase and the exit from mitosis, including the degradation of securin and B-type cyclins. We initiated a study of the APC/C in the multinucleated, filamentous ascomycete Ashbya gossypii to understand the mechanisms underlying the asynchronous mitosis observed in these cells. These experiments were motivated by previous work which demonstrated that the mitotic cyclin AgClb1/2p persists through anaphase, suggesting that the APC/C may not be required for the division cycle in A. gossypii. We have now found that the predicted APC/C components AgCdc23p and AgDoc1p and the targeting factors AgCdc20p and AgCdh1p are essential for growth and nuclear division. Mutants lacking any of these factors arrest as germlings with nuclei blocked in mitosis. A likely substrate of the APC/C is the securin homologue AgPds1p, which is present in all nuclei in hyphae except those in anaphase. The destruction box sequence of AgPds1p is required for this timed disappearance. To investigate how the APC/C may function to degrade AgPds1p in only the subset of anaphase nuclei, we localized components and targeting subunits of the APC/C. Remarkably, AgCdc23p, AgDoc1p, and AgCdc16p were found in all nuclei in all cell cycle stages, as were the APC/C targeting factors AgCdc20p and AgCdh1p. These data suggest that the AgAPC/C may be constitutively active across the cell cycle and that proteolysis in these multinucleated cells may be regulated at the level of substrates rather than by the APC/C itself.

scholarly journals Asynchronous nuclear division cycles in multinucleated cells

2006 ◽  
Vol 172 (3) ◽  
pp. 347-362 ◽  
Author(s):  
Amy S. Gladfelter ◽  
A. Katrin Hungerbuehler ◽  
Peter Philippsen
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Nuclear Division ◽  
Protein Localization ◽  
Spindle Pole ◽  
Pedigree Analysis ◽  
Multinucleated Cells ◽  
Block Cell Cycle Progression ◽  
Mitotic Cyclin ◽  
Synchronous Mitosis

Synchronous mitosis is common in multinucleated cells. We analyzed a unique asynchronous nuclear division cycle in a multinucleated filamentous fungus, Ashbya gossypii. Nuclear pedigree analysis and observation of GFP-labeled spindle pole bodies demonstrated that neighboring nuclei in A. gossypii cells are in different cell cycle stages despite close physical proximity. Neighboring nuclei did not differ significantly in their patterns of cyclin protein localization such that both G1 and mitotic cyclins were present regardless of cell cycle stage, suggesting that the complete destruction of cyclins is not occurring in this system. Indeed, the expression of mitotic cyclin lacking NH2-terminal destruction box sequences did not block cell cycle progression. Cells lacking AgSic1p, a predicted cyclin-dependent kinase (CDK) inhibitor, however, showed aberrant multipolar spindles and fragmented nuclei that are indicative of flawed mitoses. We hypothesize that the continuous cytoplasm in these cells promoted the evolution of a nuclear division cycle in which CDK inhibitors primarily control CDK activity rather than oscillating mitotic cyclin proteins.

scholarly journals Study of Cyclin Proteolysis in Anaphase-Promoting Complex (APC) Mutant Cells Reveals the Requirement for APC Function in the Final Steps of the Fission Yeast Septation Initiation Network

2001 ◽  
Vol 21 (19) ◽  
pp. 6681-6694 ◽  
Author(s):  
Louise Chang ◽  
Jennifer L. Morrell ◽  
Anna Feoktistova ◽  
Kathleen L. Gould
Keyword(s):  
Kinase Activity ◽  
Nuclear Division ◽  
Cyclin B ◽  
Cyclin Dependent Kinase ◽  
Anaphase Promoting Complex ◽  
Wild Type ◽  
Mitotic Cyclin ◽  
Septation Initiation Network ◽  
Mutant Cells ◽  
Null Mutants

ABSTRACT Cytokinesis in eukaryotic cells requires the inactivation of mitotic cyclin-dependent kinase complexes. An apparent exception to this relationship is found in Schizosaccharomyces pombemutants with mutations of the anaphase-promoting complex (APC). These conditional lethal mutants arrest with unsegregated chromosomes because they cannot degrade the securin, Cut2p. Although failing at nuclear division, these mutants septate and divide. Since septation requires Cdc2p inactivation in wild-type S. pombe, it has been suggested that Cdc2p inactivation occurs in these mutants by a mechanism independent of cyclin degradation. In contrast to this prediction, we show that Cdc2p kinase activity fluctuates in APCcut mutants due to Cdc13/cyclin B destruction. In APC-null mutants, however, septation and cutting do not occur and Cdc13p is stable. We conclude that APC cut mutants are hypomorphic with respect to Cdc13p degradation. Indeed, overproduction of nondestructible Cdc13p prevents septation in APC cutmutants and the normal reorganization of septation initiation network components during anaphase.

scholarly journals Analysis of a Mad2 homolog in Trypanosoma brucei provides possible hints on the origin of the spindle checkpoint

2020 ◽  
Author(s):  
Bungo Akiyoshi
Keyword(s):  
Trypanosoma Brucei ◽  
Basal Body ◽  
Nuclear Dna ◽  
Spindle Checkpoint ◽  
Nuclear Genome ◽  
26S Proteasome ◽  
Basal Bodies ◽  
Body Area ◽  
Uncharacterized Protein ◽  
Starting Point

AbstractThe spindle checkpoint is a surveillance mechanism that ensures accurate nuclear DNA segregation in eukaryotes. It does so by delaying the onset of anaphase until all kinetochores have established proper attachments to spindle microtubules. The evolutionary origin of the spindle checkpoint remains unclear. The flagellated kinetoplastid parasite Trypanosoma brucei has a nucleus that contains the nuclear genome and a kinetoplast that contains the mitochondrial genome. The kinetoplast is physically linked to the basal body of the flagellum and its segregation is driven by the movement of basal bodies. While there is no strong evidence that T. brucei possesses a functional spindle checkpoint, it has been suggested that initiation of cytokinesis may be linked to the completion of kinetoplast segregation or basal body separation in this organism. Interestingly, the only identifiable spindle checkpoint component TbMad2 localizes at the basal body area. Here, I report identification of proteins that co-purified with TbMad2. One protein, which I propose to call TbMBP65, localizes at the basal body area and has a putative Mad2-interacting motif. Interestingly, 26S proteasome subunits also co-purified with TbMad2, raising a possibility that TbMad2 might regulate proteasome activity to regulate or monitor the segregation of basal bodies. I speculate that such a function might represent a prototype of the spindle checkpoint. I also show that TbAUK3, one of the three Aurora kinase homologs in T. brucei, localizes at the basal body area from late G1 until the time of kinetoplast separation. Immunoprecipitation of TbAUK3 identified an uncharacterized protein (termed TbABP79) that has a similar localization pattern as TbAUK3. These findings provide a starting point to reveal the function of TbMad2 and TbAUK3 as well as the origin of the spindle checkpoint.

scholarly journals Budding yeast relies on G1 cyclin specificity to couple cell cycle progression with morphogenetic development

2021 ◽  
Vol 7 (23) ◽  
pp. eabg0007
Author(s):  
Deniz Pirincci Ercan ◽  
Florine Chrétien ◽  
Probir Chakravarty ◽  
Helen R. Flynn ◽  
Ambrosius P. Snijders ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Cycle Progression ◽  
Budding Yeast ◽  
Quantitative Model ◽  
Cyclin Dependent Kinase ◽  
Cycle Progression ◽  
Model Cell ◽  
Mitotic Cyclin ◽  
Substrate Phosphorylation ◽  
The Cost

Two models have been put forward for cyclin-dependent kinase (Cdk) control of the cell cycle. In the qualitative model, cell cycle events are ordered by distinct substrate specificities of successive cyclin waves. Alternatively, in the quantitative model, the gradual rise of Cdk activity from G1 phase to mitosis leads to ordered substrate phosphorylation at sequential thresholds. Here, we study the relative contributions of qualitative and quantitative Cdk control in Saccharomyces cerevisiae. All S phase and mitotic cyclins can be replaced by a single mitotic cyclin, albeit at the cost of reduced fitness. A single cyclin can also replace all G1 cyclins to support ordered cell cycle progression, fulfilling key predictions of the quantitative model. However, single-cyclin cells fail to polarize or grow buds and thus cannot survive. Our results suggest that budding yeast has become dependent on G1 cyclin specificity to couple cell cycle progression to essential morphogenetic events.

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