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Search indexed bioRxiv preprints in genomics, neuroscience, cell biology and bioinformatics. Read source abstracts and check manuscript versions; preprints are not peer reviewed.

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At least 811 records · Page 45Linked to original sources

bioRxiv2017

Nuclear Abl Drives Extracellular-Vesicle Transfer of miR-34c to Induce Bystander Effects of Radiation

SUMMARYIonizing radiation stimulates nuclear accumulation of Abl tyrosine kinase that is required for directly irradiated cells to produce microRNA-34c-containing extracellular vesicles, which transfer the microRNA into non-irradiated cells to induce reactive oxygen species and bystander DNA damage.\n\nABSTRACTIonizing radiation (IR) activates an array of DNA damage response (DDR) that includes the induction of bystander effects (BE) in cells not targeted by radiation. How DDR pathways in irradiated cells stimulate BE in non-targeted cells is mostly unknown. We show here that extracellular vesicles from irradiated cells (EV-IR) induce reactive oxygen species (ROS) and DNA damage when internalized by un-irradiated cells. We found that EV-IR from Abl-NLS-mutated cells could not induce ROS or DNA damage, and restoration of nuclear Abl rescued those defects. Expanding a previous finding that Abl stimulates miR-34c expression, we show here that nuclear Abl also drives the vesicular secretion of miR-34c. Ectopic miR-34c expression, without irradiation, generated EV-miR-34c capable of inducing ROS and DNA damage. Furthermore, EV-IR from miR34-knockout cells could not induce ROS and raised {gamma}H2AX to lesser extent than EV-IR from miR34-wild type cells. These results establish a novel role for the Abl-miR-34c DDR pathway in stimulating radiation-induced bystander effects.

cell biology↗

bioRxiv2017

Morphological changes of plasma membrane and protein assembly during clathrin-mediated endocytosis

Clathrin-mediated endocytosis (CME) proceeds through a series of morphological changes of the plasma membrane induced by a number of protein components. Although the spatiotemporal assembly of these proteins has been elucidated by fluorescence-based techniques, the protein-induced morphological changes of the plasma membrane have not been fully clarified in living cells. Here we visualize membrane morphology together with protein localizations during CME by utilizing high-speed atomic force microscopy combined with a confocal laser scanning unit. The plasma membrane starts to invaginate ~30 seconds after clathrin starts to assemble, and the aperture diameter increases as clathrin accumulates. Actin rapidly accumulates around the pit and induces a small membrane swelling, which within 30 seconds rapidly covers the pit irreversibly. Inhibition of actin turnover abolishes the swelling and induces a reversible open-close motion of the pit, indicating that actin dynamics are necessary for efficient and irreversible pit closure at the end of the CME.

cell biology↗

bioRxiv2017

The self-organization of plant microtubules in three dimensions enables stable cortical localization and sensitivity to external cues

Many cell functions rely on the ability of microtubules to self-organize as complex networks. In plants, cortical microtubules are essential to determine cell shape as they guide the deposition of cellulose microfibrils, and thus control mechanical anisotropy in the cell wall. Here we analyze how, in turn, cell shape may influence microtubule behavior. Using a computational model of microtubules enclosed in a three-dimensional space, We show that the microtubule network has spontaneous configurations that could explain many experimental observations without resorting to specific regulation. In particular, we find that the preferred localization of microtubules at the cortex emerges from directional persistence of the microtubules, combined with their growth mode. We identified microtubule parameters that seem relatively insensitive to cell shape, such as length or number. In contrast, microtubule array anisotropy depends strongly on local curvature of the cell surface and global orientation follows robustly the longest axis of the cell. Lastly, we found that the network is capable of reorienting toward weak external directional cues. Altogether our simulations show that the microtubule network is a good transducer of weak external polarity, while at the same time, it easily reaches stable global configurations.\n\nAuthor summaryPlants exhibit an astonishing diversity in architecture and shape. A key to such diversity is the ability of their cells to coordinate and grow to reach a broad spectrum of sizes and shapes. Cell growth in plants is guided by the microtubule cytoskeleton. Here, we seek to understand how microtubules self-organize close to the cell surface. We build upon previous two-dimensional models and we consider microtubules as lines growing in three dimensions, accounting for interactions between microtubules or between microtubules and the cell surface. We show that microtubule arrays are able to adapt to various cell shapes and to reorient in response to factors such as signals or environment. Altogether, our results help to understand how the microtubule cytoskeleton contributes to the diversity of plant shapes and to how these shapes adapt to environment.

cell biology↗

bioRxiv2017

An evolutionary switch in the specificity of an endosomal CORVET tether underlies formation of regulated secretory vesicles in the ciliate Tetrahymena thermophila

In the endocytic pathway of animals, two related complexes, called CORVET (Class C Core Vacuole/Endosome Transport) and HOPS (Homotypic fusion and protein sorting), act as both tethers and fusion factors for early and late endosomes, respectively. Mutations in CORVET or HOPS lead to trafficking defects and contribute to human disease including immune dysfunction. HOPS and CORVET are conserved throughout eukaryotes but remarkably, in the ciliate Tetrahymena thermophila, the HOPS-specific subunits are absent while CORVET-specific subunits have proliferated. VPS8 (Vacuolar Protein Sorting), a CORVET subunit, expanded to 6 paralogs in Tetrahymena. This expansion correlated with loss of HOPS within a ciliate subgroup including the Oligohymenophorea, which contains Tetrahymena. As uncovered via forward genetics, a single VPS8 paralog in Tetrahymena (VPS8A) is required to synthesize prominent secretory granules called mucocysts. More specifically,{triangleup} vps8a cells fail to deliver a subset of cargo proteins to developing mucocysts, instead accumulating that cargo in vesicles also bearing the mucocyst sorting receptor, Sor4p. Surprisingly, although this transport step relies on CORVET, it does not appear to involve early endosomes. Instead, Vps8a associates with the late endosomal/lysosomal marker Rab7, indicating target specificity switching occurred in CORVET subunits during the evolution of ciliates. Mucocysts belong to a markedly diverse and understudied class of protist secretory organelles called extrusomes. Our results underscore that biogenesis of mucocysts depends on endolysosomal trafficking, revealing parallels with invasive organelles in apicomplexan parasites and suggesting that a wide array of secretory adaptations in protists, like in animals, depend on mechanisms related to lysosome biogenesis.\n\nAbbreviations

cell biology↗

bioRxiv2017

Comparative Analysis of Gene Expression Identifies Distinct Molecular Signatures of Bone Marrow- and Periosteal-Skeletal Stem/Progenitor Cells

Periosteum and bone marrow (BM) both contain skeletal stem/progenitor cells (SSCs) that participate in fracture repair. However, the functional difference and selective regulatory mechanisms of SSCs in different location are unknown due to the lack of specific markers. Here, we report a comprehensive gene expression analysis of bone marrow SSCs (BM-SSCs), periosteal SSCs (P-SSCs), and more differentiated osteoprogenitors by using reporter mice expressing Interferon-inducible Mx1 and NestinGFP, previously known SSC markers. We first defined that the BM-SSCs can be enriched by the combination of Mx1 and NestinGFP expression, while endogenous P-SSCs can be isolated by positive selection of Mx1, CD105 and CD140a (known SSC markers) combined with the negative selection of CD45, CD31, and osteocalcinGFP (a mature osteolineage marker). Comparative gene experession analysis with FACS-sorted BM-SSCs, P-SSCs, Osterix+ (OSX) preosteoblasts, CD51+ stroma cells and CD45+ hematopoietic cells as controls revealed that BM-SSCs and P-SSCs have high similarity with few potential differences without statistical significance. We also found that CD51+ cells are highly heterogeneous and little overlap with SSCs. This was further supported by the microarray cluster analysis, and the two populations clustered together. However, when comparing SSC population to controls, we found several genes that were uniquely upregulated in endogenous SSCs. Amongst these genes, we found KDR (aka Flk1 or VEGFR2) to be most interesting and discovered that it is highly and selectively expressed in P-SSCs. This finding suggests that endogenous P-SSCs are functionally very similar to BM-SSCs with undetectable significant differences in gene expression but there are distinct molecular signatures in P-SSCs, which can be useful to specify P-SSC subset in vivo.

cell biology↗

bioRxiv2017

Phosphorylation-induced K63-polyubiquitination of Connexin 43 regulates gap junction internalization

Gap junctions (GJs) assembled from connexin (Cx) proteins play a pivotal role in cell-to-cell communication by forming channels that connect the cytosols of adjacent cells. Connexin 43, the best-studied Cx, is ubiquitously expressed in vertebrates. While phosphorylation is known to regulate multiple aspects of GJ function, much less is known about the role ubiquitination plays in these processes. Here we show by using ubiquitination-type specific antibodies and Cx43 lysine (K) to arginine (R) mutants that a portion of Cx43 in GJs can become K63-polyubiquitinated on K264 and K303. Relevant Cx43 K/R mutants assembled significantly larger GJ plaques, exhibited much longer protein half-lives and were internalization impaired. Interestingly, ubiquitin-deficient Cx43 mutants accumulated as hyper-phosphorylated polypeptides in the plasma membrane, suggesting that K63-polyubiquitination may be triggered by phosphorylation. Phospho-specific Cx43 antibodies revealed that upregulated phosphorylation affected serines 368, 279/282, and 255, well-known regulatory PKC and MAPK phosphorylation sites. Together, these novel findings suggest that upon internalization, some Cx43 in GJs becomes K63-polyubiquitinated, ubiquitination is critical for GJ internalization, and that K63-polyubiquitination may be induced by Cx phosphorylation.\n\nSummary StatementHere we show that connexin 43 in gap junctions becomes K63-poly ubiquitinated on lysines 264 and 303 and its requirement for gap junction endocytosis. These novel findings significantly contribute to our understanding of GJ turnover and patho-/physiology.\n\nAbbreviations used

cell biology↗

bioRxiv2017

Phosphorylation of the synaptonemal complex protein SYP-1 promotes meiotic chromosome segregation

Chromosomes that have undergone crossing-over in meiotic prophase must maintain sister chromatid cohesion somewhere along their length between the first and second meiotic divisions. While many eukaryotes use the centromere as a site to maintain cohesion, the holocentric organism C. elegans instead creates two chromosome domains of unequal length termed the short arm and long arm, which become the first and second site of cohesion loss at meiosis I and II. The mechanisms that confer distinct functions to the short and long arm domains remain poorly understood. Here, we show that phosphorylation of the synaptonemal complex protein SYP-1 is required to create these domains. Once crossovers are made, phosphorylated SYP-1 and PLK-2 become cooperatively confined to short arms and guide phosphorylated histone H3 and the chromosomal passenger complex to the site of meiosis I cohesion loss. Our results show that PLK-2 and phosphorylated SYP-1 ensure creation of the short arm subdomain, promoting disjunction of chromosomes in meiosis I.

cell biology↗

bioRxiv2017

A size-invariant bud-length timer enables robustness in yeast cell size control

Cell populations across nearly all forms of life generally maintain a characteristic cell type-dependent size, but how size control is achieved has been a long-standing question. Prior work has uncovered diverse size control strategies operating at distinct cell cycle stages, but it is unclear how these numerous pathways are integrated to provide robust, systems-level cell size control for any organism. Here, we probe cell growth and size control in budding yeast that can be reversibly blocked from bud initiation. While blocked, cells continue to grow isotropically, increasing their volume by more than an order of magnitude over unperturbed cells. Upon release, these giant yeast resume budding and the population returns to its initial volume distribution within a few cell division cycles. Size control under these conditions does not require an explicit molecular size sensor. Instead, our observations are consistent with a size-invariant bud growth timer specifying the duration of S/G2/M to limit daughter cell size.

cell biology↗

bioRxiv2017

Local and global Cdc42 GEFs for fission yeast cell polarity are coordinated by microtubules and the Tea1/Tea4/Pom1 axis

The conserved Rho-family GTPase Cdc42 plays a central role in eukaryotic cell polarity. The rod-shaped fission yeast Schizosaccharomyces pombe has two Cdc42 guanine-nucleotide exchange factors (GEFs), Scd1 and Gef1, but little is known about how they are coordinated in polarized growth. Although the microtubule cytoskeleton is normally not required for polarity maintenance in fission yeast, here we show that when scdl function is compromised, disruption of microtubules or the polarity landmark proteins Tea1, Tea4, or Pom1 leads to isotropic rather than polarized growth. Surprisingly, this isotropic growth is due to spatially inappropriate activity of Gef1, which is a cytosolic protein rather than a membrane-associated protein at cell tips like Scd1. Microtubules and the Tea1/Tea4/Pom1 axis counteract inappropriate Gef1 activity by regulating the localization of the Cdc42 GTPase-activating protein Rga4. Our results thus demonstrate coordination of \"local\" (Scd1) and \"global\" (Gef1) Cdc42 GEFs via microtubules and microtubule-dependent polarity landmarks.

cell biology↗

bioRxiv2017

C24 sphingolipids play a surprising and central role in governing cholesterol and lateral organization of the live cell plasma membrane

Mammalian cell sphingolipids, primarily with C24 and C16 acyl chains, reside in the outer leaflet of the plasma membrane. Curiously, little is known how C24 sphingolipids impact cholesterol and membrane microdomains. Here, we generated giant unilamellar vesicles and live mammalian cells with C24 or C16 sphingomyelin exclusively in the outer leaflet and compared microdomain formation. In giant unilamellar vesicles, we observed that asymmetrically placed C24 sphingomyelin suppresses microdomains. Conversely, C16 sphingomyelin facilitates microdomains. Replacing endogenous sphingolipids with C24 or C16 sphingomyelin in live HeLa cells has a similar impact on microdomains, characterized by FRET between GPI-anchored proteins: C24, but not C16, sphingomyelin suppresses submicron domains in the plasma membrane. Molecular dynamics simulations indicated that, when in the outer leaflet, the acyl chain of C24 sphingomyelin interdigitates into the opposing leaflet, thereby favouring cholesterol in the inner leaflet. We indeed found that cholesterol prefers the inner over the outer leaflet of asymmetric unilamellar vesicles (80/20) when C24 sphingomyelin is in the outer leaflet. However, when C16 sphingomyelin is in the outer leaflet, cholesterol is evenly partitioned between leaflets (50/50). Interestingly, when a mixture of C24/C16 sphingomyelin is in the outer leaflet of unilamellar vesicles, cholesterol still prefers the inner leaflet (80/20). Indeed, in human erythrocyte plasma membrane, where a mixture of C24 and C16 sphingolipids are naturally in the outer leaflet, cholesterol prefers the cytoplasmic leaflet (80/20). Therefore, C24 sphingomyelin uniquely interacts with cholesterol and governs the lateral organization in asymmetric membranes, including the plasma membrane, potentially by generating cholesterol asymmetry.\n\nStatement of SignificanceThe plasma membrane bilayer of mammalian cells has distinct phospholipids between the outer and inner leaflet, with sphingolipids exclusively in the outer leaflet. A large portion of mammalian sphingolipids have very long acyl chains (C24). Little is known how C24 sphingolipids function in the outer leaflet. Mutations in the ceramide synthase 2 gene is found to decrease C24. This severely perturbs homeostasis in mice and humans. Here, we investigated unilamellar vesicles and mammalian cells with C24 sphingomyelin exclusively in the outer leaflet. We provide evidence that outer leaflet C24 sphingomyelin suppresses microdomains in model membranes and live cells by partitioning cholesterol into the inner leaflet. We propose that C24 sphingolipids are critical to the function of the plasma membrane.

cell biology↗

bioRxiv2017

Effects of mutating α-tubulin lysine 40 on sensory dendrite development

Microtubules are essential to neuronal structure and function. Axonal and dendritic microtubules are enriched in post-translational modifications that impact microtubule dynamics, transport, and microtubule-associated proteins. Acetylation of -tubulin lysine 40 (K40) is a prominent, conserved modification of neuronal microtubules. However, the cellular role of microtubule acetylation remains controversial. To resolve how microtubule acetylation might affect neuronal morphogenesis we mutated endogenous -tubulin in vivo using a new fly strain that facilitates the rapid knock-in of designer -tubulin alleles. Leveraging our new strain, we found that microtubule acetylation, as well as polyglutamylation and (de)tyrosination, is not essential for survival. However, we found that dendrite branch refinement in sensory neurons relies on -tubulin K40. Mutagenesis of K40 reveals moderate yet significant changes in dendritic lysosome transport, microtubule polymerization, and Futsch distribution in dendrites but not axons. Our studies point to an unappreciated role for -tubulin K40 and acetylation in dendrite morphogenesis. While our results are consistent with the idea that microtubule acetylation patterns microtubule function within neurons, they also suggest there may be a structural requirement for -tubulin K40.\n\nSummary StatementNeurons are enriched in post-translationally modified microtubules. Targeted mutagenesis of endogenous -tubulin in flies reveals that dendrite branch refinement is altered by acetylation-blocking mutations.

cell biology↗

bioRxiv2017

Variation in traction forces during cell cycle progression

Tissue morphogenesis results from the interplay between cell growth and mechanical forces. While the impact of forces on cell proliferation has been fairly well characterized, the inverse relationship is much less understood. Here we investigated how traction forces vary during cell cycle progression. Cell shape was constrained on micropatterned substrates in order to distinguish variations in cell contractility from cell size increase. We performed traction force measurements of asynchronously dividing cells expressing a cell-cycle reporter, to obtain measurements of contractile forces generated during cell division. We found that forces tend to increase as cells progress through G1, before reaching a plateau in S phase, and then decline during G2. This biphasic behaviour revealed a previously undocumented specific and opposite regulation of cell contractility during each cell cycle stage.

cell biology↗

bioRxiv2017

Perturbed Mitochondrial Metabolism in Islets from Donors with Type-2 Diabetes

There is a preponderance for genes involved in {beta}-cell function among gene variants associated with future risk of type-2 diabetes (T2D). {beta}-cell function is controlled by metabolism of glucose, yielding signals triggering and amplifying insulin secretion. Perturbed {beta}-cell metabolism is a likely, albeit not proven, cause of T2D. We profiled metabolites in islets from T2D and non-diabetic donors, and found altered levels of mitochondrial metabolites in T2D. Analysis of genes encoding proteins localized to mitochondria (MitoCarta) by RNA-seq in an extended sample of islets revealed genes whose expression was associated with glycaemia- and/or BMI. Expression of two of these, -methylacyl-CoA racemase (AMACR) and methylmalonyl-CoA mutase (MUT), was influenced by genetic variation (cis-eQTL). Silencing of AMACR and MUT in insulin-secreting cells reduced hormone secretion by 40-50%. In conclusion, by linking the metabolome to the transcriptome, we showed that perturbed mitochondrial metabolism is a feature of {beta}-cell dysfunction in T2D.\n\n[Supplementary material is available for this article.]

cell biology↗

bioRxiv2017

Coordination between discrete Mitotic Arrest Deficient 1 (MAD1) domains is required for efficient mitotic checkpoint signaling

As a sensitive signaling system, the mitotic checkpoint ensures faithful chromosome segregation by delaying anaphase onset when even a single kinetochore is unattached. The key signal amplification reaction for the checkpoint is the conformational conversion of open MAD2 (O-MAD2) into closed MAD2 (C-MAD2). The reaction was suggested to be catalyzed by an unusual catalyst, a MAD1:C-MAD2 tetramer, but how the catalysis is executed and regulated remains elusive. Here we report that in addition to the well-characterized middle region (MIM), both amino- and carboxyl-terminal domains (NTD and CTD) of MAD1 also contribute to the mitotic checkpoint. In contrast to MIM that stably associates with C-MAD2, MAD1-NTD and CTD surprisingly bind to both O-MAD2 and C-MAD2, suggesting their interactions with substrates and products of the O-C conversion. MAD1-NTD also interacts with CTD. MPS1 kinase interacts with and phosphorylates both NTD and CTD. The phosphorylation reduces the NTD:CTD interaction and CTD interaction with MPS1. Mutating CTD phosphorylation sites including Thr716 compromises MAD2 binding and the checkpoint responses. Ser610 and Tyr634 also contribute to the checkpoint. Our results have uncovered previously unknown interactions of MAD1-NTD and CTD with MAD2 conformers and their regulation by MPS1 kinase, providing novel insights into the mitotic checkpoint signaling.

cell biology↗

bioRxiv2017

NOTCH-mediated non-cell autonomous regulation of chromatinstructure during senescence

Senescent cells interact with the surrounding microenvironment achieving diverse functional outcomes. In addition to autocrine and paracrine signalling mediated by factors of the senescence-associated secretory phenotype, we have recently identified that NOTCH1 can drive lateral induction of a unique form of senescence in adjacent cells through specific induction of the NOTCH ligand JAG1. Here we show that NOTCH signalling can modulate chromatin structure both autonomously and non-autonomously. In addition to senescence-associated heterochromatic foci (SAHF), oncogenic RAS-induced senescent (RIS) cells in culture exhibit a massive increase in nucleosome-free regions (NRFs). NOTCH signalling suppresses both SAHF and NFR formation in this context. Strikingly, NOTCH-induced senescent cells, or cancer cells with high JAG1 expression, also drive similar chromatin architectural changes in adjacent cells through cell-cell contact. Mechanistically, we show that NOTCH signalling represses the chromatin architectural protein HMGA1, an association found in a range of human cancers. Thus, HMGA1 is involved not only in SAHFs, but also RIS-specific NFR formation. In conclusion, this study identifies that the JAG1-NOTCH-HMGA1 axis mediates the juxtacrine regulation of chromatin architecture.

cell biology↗

bioRxiv2017

The Fission Yeast S-Phase Cyclin Cig2 Can Drive Mitosis

Commitment to mitosis is regulated by cyclin-dependent kinase (CDK) activity. In the fission yeast Schizosaccharomyces pombe, the major B-type cyclin, Cdc13, is necessary and sufficient to drive mitotic entry. Furthermore, Cdc13 is also sufficient to drive S phase, demonstrating that a single cyclin can regulate alternating rounds of replication and mitosis and providing the foundation of the quantitative model of CDK function. It has been assumed that Cig2, a B-type cyclin expressed only during S-phase and incapable of driving mitosis in wild-type cells, was specialized for S-phase regulation. Here, we show that Cig2 is capable of driving mitosis. Cig2/CDK activity drives mitotic catastrophe--lethal mitosis in inviably small cells--in cells that lack CDK inhibition by tyrosine-phosphorylation. Moreover, Cig2/CDK can drive mitosis in the absence of Cdc13/CDK activity and constitutive expression of Cig2 can rescue loss of Cdc13 activity. These results demonstrate that in fission yeast, not only can the presumptive M-phase cyclin drive S phase, but the presumptive S-phase cyclin can drive M phase, further supporting the quantitative model of CDK function. Furthermore, these results provide an explanation, previously proposed on the basis of computational analyses, for the surprising observation that cells expressing a single-chain Cdc13-Cdc2 CDK do not require Y15 phosphorylation for viability. Their viability is due to the fact that in such cells, which lack Cig2/CDK complexes, Cdc13/CDK activity is unable to drive mitotic catastrophe.

cell biology↗

bioRxiv2017

Reconciling the clk-1 and aging paradox and categorizing lifespan curves by taking individual specificity into account

The clk-1 gene encodes the demethoxyubiquinone (DMQ) hydroxylase that is required for biosynthesis of ubiquinone (coenzyme Q). Deletion of clk-1 was lethal in mice, and its mutation in C. elegans mildly extended lifespan, slowed physiological rate and led to sickness. We found that if growth retardation was taken into account the average lifespan of clk-1 mutants would not be prolonged or would be shortened. In addition, recent study showed that knocking down of clk-1 shortened lifespan. Although the extension of lifespan in clk-1 mutants was mild and was not observed sometimes, some progenies indeed had prolonged maximum lifespan even if retardation of growth was taking into account. These paradoxes implicate the existence of individual specificity in the aging process even in the same cohort, just like a drug is beneficial for some people while for others it is detrimental. We further categorized lifespan curves into five kinds of patterns according to the lifespan alternations observed in organisms: N (normal); L (long-lived); S (short-lived); F (flattened); ST (steepened), and found that the curve of clk-1 mutants fit into the F pattern. The reasons behind the individual specificity and its implications in aging process deserves further investigations.

cell biology↗

bioRxiv2017

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

Kinetoplastids 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.

cell biology↗