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157 records · Page 9Linked to original sources
PubMed2001

A novel role of the budding yeast separin Esp1 in anaphase spindle elongation: evidence that proper spindle association of Esp1 is regulated by Pds1.

In Saccharomyces cerevisiae, the metaphase-anaphase transition is initiated by the anaphase-promoting complex-dependent degradation of Pds1, whereby Esp1 is activated to promote sister chromatid separation. Although this is a fundamental step in the cell cycle, little is known about the regulation of Esp1 and how loss of cohesion is coordinated with movement of the anaphase spindle. Here, we show that Esp1 has a novel role in promoting anaphase spindle elongation. The localization of Esp1 to the spindle apparatus, analyzed by live cell imaging, is regulated in a manner consistent with a function during anaphase B. The protein accumulates in the nucleus in G2 and is mobilized onto the spindle pole bodies and spindle midzone at anaphase onset, where it persists into midanaphase. Association with Pds1 occurs during S phase and is required for efficient nuclear targeting of Esp1. Spindle association is not fully restored in pds1 mutants expressing an Esp1-nuclear localization sequence fusion protein, suggesting that Pds1 is also required to promote Esp1 spindle binding. In agreement, Pds1 interacts with the spindle at the metaphase-anaphase transition and a fraction remains at the spindle pole bodies and the spindle midzone in anaphase cells. Finally, mutational analysis reveals that the conserved COOH-terminal region of Esp1 is important for spindle interaction.

Anaphase↗
PubMed2003

The small molecule Hesperadin reveals a role for Aurora B in correcting kinetochore-microtubule attachment and in maintaining the spindle assembly checkpoint.

The proper segregation of sister chromatids in mitosis depends on bipolar attachment of all chromosomes to the mitotic spindle. We have identified the small molecule Hesperadin as an inhibitor of chromosome alignment and segregation. Our data imply that Hesperadin causes this phenotype by inhibiting the function of the mitotic kinase Aurora B. Mammalian cells treated with Hesperadin enter anaphase in the presence of numerous monooriented chromosomes, many of which may have both sister kinetochores attached to one spindle pole (syntelic attachment). Hesperadin also causes cells arrested by taxol or monastrol to enter anaphase within <1 h, whereas cells in nocodazole stay arrested for 3-5 h. Together, our data suggest that Aurora B is required to generate unattached kinetochores on monooriented chromosomes, which in turn could promote bipolar attachment as well as maintain checkpoint signaling.

Anaphase↗
PubMed2004

At the interface between signaling and executing anaphase--Cdc14 and the FEAR network.

Anaphase is the stage of the cell cycle when the duplicated genome is separated to opposite poles of the cell. The irreversible nature of this event confers a unique burden on the cell and it is therefore not surprising that the regulation of this cell cycle stage is complex. In budding yeast, a signaling network known as the Cdc fourteen early anaphase release (FEAR) network and its effector, the protein phosphatase Cdc14, play a key role in the coordination of the multiple events that occur during anaphase, such as partitioning of the DNA, regulation of spindle stability, activation of microtubule forces, and initiation of mitotic exit. These functions of the FEAR network contribute to genomic stability by coordinating the completion of anaphase and the execution of mitotic exit.

Anaphase↗
PubMed2006

A mitotic topoisomerase II checkpoint in budding yeast is required for genome stability but acts independently of Pds1/securin.

Topoisomerase II (Topo II) performs topological modifications on double-stranded DNA molecules that are essential for chromosome condensation, resolution, and segregation. In mammals, G2 and metaphase cell cycle delays induced by Topo II poisons have been proposed to be the result of checkpoint activation in response to the catenation state of DNA. However, the apparent lack of such controls in model organisms has excluded genetic proof that Topo II checkpoints exist and are separable from the conventional DNA damage checkpoint controls. But here, we define a Topo II-dependent G2/M checkpoint in a genetically amenable eukaryote, budding yeast, and demonstrate that this checkpoint enhances cell survival. Conversely, a lack of the checkpoint results in aneuploidy. Neither DNA damage-responsive pathways nor Pds1/securin are needed for this checkpoint. Unusually, spindle assembly checkpoint components are required for the Topo II checkpoint, but checkpoint activation is not the result of failed chromosome biorientation or a lack of spindle tension. Thus, compromised Topo II function activates a yeast checkpoint system that operates by a novel mechanism.

Anaphase-Promoting Complex-Cyclosome↗
PubMed2002

Segregating sister genomes: the molecular biology of chromosome separation.

During cell division, each daughter cell inherits one copy of every chromosome. Accurate transmission of chromosomes requires that the sister DNA molecules created during DNA replication are disentangled and then pulled to opposite poles of the cell before division. Defects in chromosome segregation produce cells that are aneuploid (containing an abnormal number of chromosomes)-a situation that can have dire consequences. Aneuploidy is a leading cause of spontaneous miscarriages in humans and is also a hallmark of many human cancer cells. Recent work with yeast, Xenopus, and other model systems has provided new information about the proteins that control chromosome segregation during cell division and how the activities of these proteins are coordinated with the cell cycle.

Adenosine Triphosphatases↗
PubMed1999

Identification of a vertebrate sister-chromatid separation inhibitor involved in transformation and tumorigenesis.

A vertebrate securin (vSecurin) was identified on the basis of its biochemical analogy to the Pds1p protein of budding yeast and the Cut2p protein of fission yeast. The vSecurin protein bound to a vertebrate homolog of yeast separins Esp1p and Cut1p and was degraded by proteolysis mediated by an anaphase-promoting complex in a manner dependent on a destruction motif. Furthermore, expression of a stable Xenopus securin mutant protein blocked sister-chromatid separation but did not block the embryonic cell cycle. The vSecurin proteins share extensive sequence similarity with each other but show no sequence similarity to either of their yeast counterparts. Human securin is identical to the product of the gene called pituitary tumor-transforming gene (PTTG), which is overexpressed in some tumors and exhibits transforming activity in NIH 3T3 cells. The oncogenic nature of increased expression of vSecurin may result from chromosome gain or loss, produced by errors in chromatid separation.

3T3 Cells↗
PubMed2000

Splitting the chromosome: cutting the ties that bind sister chromatids.

In eukaryotic cells, sister DNA molecules remain physically connected from their production at S phase until their separation during anaphase. This cohesion is essential for the separation of sister chromatids to opposite poles of the cell at mitosis. It also permits chromosome segregation to take place long after duplication has been completed. Recent work has identified a multisubunit complex called cohesin that is essential for connecting sisters. Proteolytic cleavage of one of cohesin's subunits may trigger sister separation at the onset of anaphase.

Anaphase↗
PubMedDate not supplied

Complexity of mitotic exit.

Completion of mitosis in budding yeast is triggered by activation of the protein phosphatase Cdc14, which is the ultimate effector of a signalling cascade, known as the mitotic exit network. Cdc14 activation leads to eradication of mitotic kinase activity, which is pivotal for mitotic exit and cytokinesis in all eukaryotes. The complexity in mitotic exit regulation is underscored by the recent discovery of a novel network, the so-called FEAR pathway that regulates early Cdc14 activation. Surprisingly, this has revealed an unexpected role for Spo12, a protein involved in meiosis, in Cdc14 activation. In this review, we will discuss these findings together with recent advances in deciphering the function of the FEAR circuit, which has unravelled an exciting new side of Cdc14.

Anaphase↗
PubMedDate not supplied

The FEAR Before MEN: networks of mitotic exit.

Variations in the normal regulation of the mitotic cell cycle can lead to such global cellular changes as differential development or malignant transformation. Studies on the control of mitosis are particularly important to discover the details of the basic mechanisms responsible for normal cell division, as well as to learn about strategies employed by cancerous cells to indefinitely proliferate. The past years have brought noteworthy progress in elucidating the molecular pathways that regulate crucial events during mitosis such as: chromosome condensation, formation of the mitotic spindle, chromosome segregation, cytokinesis, and disassembly of the mitotic spindle.

Cell Cycle Proteins↗
PubMed2004

Cdc14p/FEAR pathway controls segregation of nucleolus in S. cerevisiae by facilitating condensin targeting to rDNA chromatin in anaphase.

The condensin complex is the chief molecular machine of mitotic chromosome condensation. Nucleolar concentration of condensin in mitosis was previously shown to correlate with proficiency of rDNA condensation and segregation. To uncover the mechanisms facilitating this targeting we conducted a screen for mutants that impair mitotic condensin congression to the nucleolus. Mutants in the cdc14, esp1 and cdc5 genes, which encode FEAR-network components, showed the most prominent defects in mitotic condensin localization. We established that Cdc14p activity released by the FEAR pathway was required for proper condensin-to-rDNA targeting in anaphase. The MEN pathway was dispensable for condensin-to-rDNA targeting, however MEN-mediated release of Cdc14p later in anaphase allowed for proper, albeit delayed, condensin targeting to rDNA and successful segregation of nucleolus in the slk19 FEAR mutant. Although condensin was physically dislodged from rDNA in the cdc14 mutant, it was properly assembled, phosphorylated and chromatin-bound, suggesting that condensin was mis-targeted but active. This study identifies a novel pathway promoting condensin targeting to a specific chromosomal address, the rDNA locus.

Adenosine Triphosphatases↗
PubMed2002

Embryonic stem cell differentiation and the analysis of mammalian development.

Molecular and cellular analysis of early mammalian development is compromised by the experimental inaccessibility of the embryo. Pluripotent embryonic stem (ES) cells are derived from and retain many properties of the pluripotent founder population of the embryo, the inner cell mass. Experimental manipulation of these cells and their environment in vitro provides an opportunity for the development of differentiation systems which can be used for analysis of the molecular and cellular basis of embryogenesis. In this review we discuss strengths and weaknesses of the available ES cell differentiation methodologies and their relationship to events in vivo. Exploitation of these systems is providing novel insight into embryonic processes as diverse as cell lineage establishment, cell progression during differentiation, patterning, morphogenesis and the molecular basis for cell properties in the early mammalian embryo.

Animals↗