scholarly journals Bir1 Is Required for the Tension Checkpoint

2009 ◽  
Vol 20 (3) ◽  
pp. 915-923 ◽  
Author(s):  
Michelle M. Shimogawa ◽  
Per O. Widlund ◽  
Michael Riffle ◽  
Michael Ess ◽  
Trisha N. Davis
Keyword(s):  
Aurora B ◽  
Temperature Sensitive ◽  
Sensitive Mutant ◽  
Checkpoint Response ◽  
Temperature Sensitive Mutant ◽  
The Third ◽  
Chromosomal Passenger ◽  
Chromosomal Passenger Proteins ◽  
Passenger Proteins

The Saccharomyces cerevisiae chromosomal passenger proteins Ipl1 (Aurora B) and Sli15 (INCENP) are required for the tension checkpoint, but the role of the third passenger, Bir1, is controversial. We have isolated a temperature-sensitive mutant (bir1-107) in the essential C-terminal region of Bir1 known to be required for binding to Sli15. This allele reveals a checkpoint function for Bir1. The mutant displays a biorientation defect, a defective checkpoint response to lack of tension, and an inability to detach mutant kinetochores. Ipl1 localizes to aberrant foci when Bir1 localization is disrupted in the bir1-107 mutant. Thus, one checkpoint role of Bir1 is to properly localize Ipl1 and allow detachment of kinetochores. Quantitative analysis indicates that the chromosomal passengers colocalize with kinetochores in G1 but localize between kinetochores that are under tension. Bir1 localization to kinetochores is maintained in an mcd1-1 mutant in the absence of tension. Our results suggest that the establishment of tension removes Ipl1, Bir1, and Sli15, and their kinetochore detachment activity, from the vicinity of kinetochores and allows cells to proceed through the tension checkpoint.

scholarly journals Shugoshin 2 Regulates Localization of the Chromosomal Passenger Proteins in Fission Yeast Mitosis

2007 ◽  
Vol 18 (5) ◽  
pp. 1657-1669 ◽  
Author(s):  
Vincent Vanoosthuyse ◽  
Sergey Prykhozhij ◽  
Kevin G. Hardwick
Keyword(s):  
Fission Yeast ◽  
Spindle Checkpoint ◽  
Aurora B ◽  
Checkpoint Activation ◽  
C Terminus ◽  
Chromosomal Passenger ◽  
Chromosomal Passenger Proteins ◽  
Passenger Proteins ◽  
Meiosis I ◽  
Mitotic Cells

Fission yeast has two members of the Shugoshin family, Sgo1 and Sgo2. Although Sgo1 has clearly been established as a protector of centromere cohesion in meiosis I, the roles of Sgo2 remain elusive. Here we show that Sgo2 is required to ensure proper chromosome biorientation upon recovery from a prolonged spindle checkpoint arrest. Consistent with this, Sgo2 is essential for maintaining the Passenger proteins on centromeres upon checkpoint activation. Interestingly, lack of Sgo2 has a more penetrant effect on the localization of Survivin than on the two other Passenger proteins INCENP and Aurora B, and the Survivin-INCENP complex but not the INCENP-Aurora B complex is destabilized in the absence of Sgo2. Finally we show that the conserved C-terminus of Sgo2 is crucial to maintain Sgo2 and Passenger proteins localization on centromeres upon prolonged checkpoint activation. Taken together, our results demonstrate that Sgo2 is important for chromosome biorientation and that it controls docking of the Passenger proteins on chromosomes in early mitotic cells.

Megakaryocytes express functional Aurora-B kinase in endomitosis

Blood ◽  
2004 ◽  
Vol 104 (4) ◽  
pp. 1017-1024 ◽  
Author(s):  
Amy E. Geddis ◽  
Kenneth Kaushansky
Keyword(s):  
Aurora Kinase ◽  
Aurora B ◽  
Aurora A Kinase ◽  
Aurora B Kinase ◽  
Late Anaphase ◽  
Chromosomal Passenger ◽  
Early Anaphase ◽  
Chromosomal Passenger Proteins ◽  
Diploid Cells ◽  
Passenger Proteins

AbstractEndomitosis (EnM) in megakaryocytes (MKs) is characterized by abortion of mitosis in late anaphase and failure of cytokinesis; subsequent reinitiation of DNA synthesis results in polyploidy. Ablation of chromosomal passenger proteins including Aurora-B kinase causes defects in late anaphase and cytokinesis in diploid cells; thus one hypothesis is that the expression or function of these proteins in polyploid MKs is abnormal. It has been reported that Aurora-B kinase mRNA is decreased in polyploid megakaryocytic cells, suggesting that deficiency of Aurora-B kinase is responsible for EnM. We examined the localization of Aurora-B kinase and additional members of the chromosomal passenger protein and aurora kinase families in MKs. We found that in EnM MKs (1) Aurora-B kinase is present and appropriately localized to centromeres in early EnM; (2) in low-ploidy human MKs, centromeric localization of survivin and inner centromere protein (INCENP) can also be demonstrated; (3) the function of Aurora-B kinase, as measured by Ser10 phosphorylation of histone H3, is intact; and (4) aurora-A kinase localizes appropriately to centrosomes in EnM. These results suggest that EnM MKs appropriately express functional Aurora-B kinase and related proteins in early anaphase, making a simple deficiency of this protein an unlikely explanation for polyploidy in this cell type.

The role of centromere-binding factor 3 (CBF3) in spindle stability, cytokinesis, and kinetochore attachment

2005 ◽  
Vol 83 (6) ◽  
pp. 696-702 ◽  
Author(s):  
David Bouck ◽  
Kerry Bloom
Keyword(s):  
Essential Role ◽  
Anaphase Onset ◽  
Binding Factor ◽  
Chromosomal Passenger ◽  
Chromosomal Passenger Proteins ◽  
Spindle Midzone ◽  
Spindle Stability ◽  
Passenger Proteins ◽  
Passenger Protein

The spindle midzone is critical for spindle stability and cytokinesis. Chromosomal passenger proteins relocalize from chromosomes to the spindle midzone after anaphase onset. The recent localization of the inner-kinetochore, centromere-binding factor 3 (CBF3) complex to the spindle midzone in budding yeast has led to the discovery of novel functions for this complex in addition to its essential role at kinetochores. In G1/S cells, CBF3 components are detected along dynamic microtubules, where they can "search-and-capture" newly replicated centromeres. During anaphase, CBF3 is transported to the microtubule plus-ends of the spindle midzone. Consistent with this localization, cells containing a mutation in the CBF3 subunit Ndc10p show defects in spindle stability during anaphase. In addition, ndc10-1 cells show defects during cytokinesis, resulting in a defect in cell abscission. These results highlight the importance of midzone-targeted proteins in coordinating mitosis with cell division. Here we discuss these findings and explore the significance of CBF3 transport to microtubule plus-ends at the spindle midzone.Key words: spindle midzone, passenger protein, inner centromere protein (INCENP), microtubule plus-end.

scholarly journals The conserved role of Smu1 in splicing is characterized in its mammalian temperature-sensitive mutant

2006 ◽  
Vol 119 (23) ◽  
pp. 4944-4951 ◽  
Author(s):  
K. Sugaya ◽  
E. Hongo ◽  
Y. Ishihara ◽  
H. Tsuji
Keyword(s):  
Temperature Sensitive ◽  
Sensitive Mutant ◽  
Temperature Sensitive Mutant

Ecdysteroids during the third larval instar in I(3)ecd-1ts, a temperature-sensitive mutant of Drosophila melanogaster

1984 ◽  
Vol 54 (1) ◽  
pp. 76-84 ◽  
Author(s):  
P. Berreur ◽  
P. Porcheron ◽  
M. Moriniere ◽  
J. Berreur-Bonnenfant ◽  
S. Belinski-Deutsch ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Larval Instar ◽  
Temperature Sensitive ◽  
Sensitive Mutant ◽  
Temperature Sensitive Mutant ◽  
The Third

scholarly journals Apg5p Functions in the Sequestration Step in the Cytoplasm-to-Vacuole Targeting and Macroautophagy Pathways

2000 ◽  
Vol 11 (3) ◽  
pp. 969-982 ◽  
Author(s):  
Michael D. George ◽  
Misuzu Baba ◽  
Sidney V. Scott ◽  
Noboru Mizushima ◽  
Brian S. Garrison ◽  
...  
Keyword(s):  
Biochemical Analysis ◽  
Temperature Sensitive ◽  
Vesicle Formation ◽  
Concerted Action ◽  
Sensitive Mutant ◽  
Temperature Sensitive Mutant ◽  
Dynamic Events

The cytoplasm-to-vacuole targeting (Cvt) pathway and macroautophagy are dynamic events involving the rearrangement of membrane to form a sequestering vesicle in the cytosol, which subsequently delivers its cargo to the vacuole. This process requires the concerted action of various proteins, including Apg5p. Recently, it was shown that another protein required for the import of aminopeptidase I (API) and autophagy, Apg12p, is covalently attached to Apg5p through the action of an E1-like enzyme, Apg7p. We have undertaken an analysis of Apg5p function to gain a better understanding of the role of this novel nonubiquitin conjugation reaction in these import pathways. We have generated the first temperature-sensitive mutant in the Cvt pathway, designated apg5 ts. Biochemical analysis of API import in theapg5 ts strain confirmed that Apg5p is directly required for the import of API via the Cvt pathway. By analyzing the stage of API import that is blocked in theapg5 ts mutant, we have determined that Apg5p is involved in the sequestration step and is required for vesicle formation and/or completion.

Aurora-B Kinase Translocates to the Midzone in Endomitotic Megakaryocytes.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 1263-1263
Author(s):  
Amy E. Geddis ◽  
Kenneth Kaushansky
Keyword(s):  
Actin Dynamics ◽  
Aurora B ◽  
Cleavage Furrow ◽  
Aurora B Kinase ◽  
Metaphase Chromosomes ◽  
Late Anaphase ◽  
Chromosomal Passenger ◽  
Chromosomal Passenger Proteins ◽  
Spindle Midzone ◽  
Passenger Proteins

Abstract Megakaryocyte (MK) differentiation is marked by the development of progressive polyploidy, facilitating platelet production by the creation of a large cytoplasmic volume. MKs become polyploid through repeated cycles of endomitosis (EnM), in which mitosis is initiated but subsequently aborted in late anaphase with failure to complete karyokinesis and cytokinesis. However, the mechanisms underlying EnM remain poorly understood. Recent hypotheses explored in the literature have focused on the possible absence or mislocalization of the chromosomal passenger protein Aurora-B kinase, as it has a pivotal role in many aspects of cytokinesis. Along with the other passenger proteins, Aurora-B kinase transits from the centromeres of metaphase chromosomes to the bundled microtubules of the spindle midzone and overlying cortex between separating chromosomes in anaphase. The midzone and its associated proteins, are thought to be critical for determining the position of the cleavage furrow. One of these proteins, the kinesin MKLP-2, is required for the translocation of Aurora-B kinase to the midzone, where it co-localizes with the GTPase MgcRacGAP and stimulates its activity towards RhoA, potentially regulating actin dynamics at the cleavage furrow. We have previously demonstrated that several chromosomal passenger proteins including Aurora-B kinase are normally expressed and localized to centromeres in EnM MKs. In this work, we use deconvolution microscopy in primary murine and human MKs to extend those findings and demonstrate that EnM MKs form midzone structures that are characteristic of late anaphase; in addition, Aurora-B kinase is clearly present on the spindle midzone, as are MKLP-2 and MgcRacGAP. Although we found images suggestive of initial cleavage furrow formation with cortical localization of Aurora-B kinase in late phase cells, we were unable to demonstrate enhanced localization of actin or anillin to the furrow in EnM cells, despite their normal localization in diploid control cells. Therefore, many of the components of the central spindle are intact during MK EnM, but the formation of the cleavage furrow appears to be incomplete. These data add to our understanding of the possible mechanisms underlying EnM and offer an alternative hypothesis to that of failed expression or localization of the chromosomal passenger proteins. Ongoing studies will focus on the assembly and function of the cleavage furrow in this enigmatic process.

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