Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
* Author for correspondence (e-mail: joshi{at}cellbio.emory.edu)
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Summary |
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Key words: Spindle assembly checkpoint, Mitosis, Chromosome, Kinetochore, Microtubule, Attachment, Tension
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Introduction |
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The kinetochore-microtubule attachment |
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|
![]() |
The checkpoint components |
---|
The function of each of these checkpoint proteins is needed to prevent
anaphase entry when the spindle has a defect or when chromosomes are not
properly attached (for a review, see Amon,
1999). Cells harboring mutations in many of these checkpoint genes
proceed to anaphase prematurely and split sister chromatids regardless of
whether the prerequisites for chromosome segregation have been satisfied. As a
consequence, the delivery of exactly one copy of each chromosome to each
daughter cell cannot be guaranteed, which can result in the production of
daughter cells that have gained or lost one or more chromosomes, a phenomenon
termed aneuploidy (Fig. 1).
Missing or extra chromosomes in germ-line cells can result in premature
abortion of the fetus or generation of offspring with birth defects such as
Patau syndrome, Edwards syndrome, Down syndrome and Klinefelter syndrome,
which are characterized by the presence of an extra copy of chromosome 13,
chromosome 18, chromosome 21 and the X chromosome, respectively
(Sluder and McCollum, 2000
).
Unequal chromosome segregation can also have severe consequences in adults by
fostering tumor malignancy (Manchester,
1995
). In fact, mutations in or reduced expression of spindle
assembly checkpoint components has recently been found in some types of human
cancer (Li and Benezra, 1996
;
Cahill et al., 1998
;
Lee et al., 1999
;
Takahashi et al., 1999
;
Michel et al., 2001
;
Wang et al., 2002
). For
example, mutational inactivation of Bub1 has been implicated in human
colorectal cancer (Cahill et al.,
1998
), and reduced expression of Mad2 has been implicated in human
breast and ovarian cancers (Li and
Benezra, 1996
; Wang et al.,
2002
).
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The checkpoint signaling pathway |
---|
|
It is now clear that the ubiquitin ligase activity of the APC towards
securin requires association of APC with Cdc20 (Slp 1p in fission yeast, Fizzy
in flies and p55cdc in mammals), which activates the APC by direct binding
(Visintin et al., 1997;
Hwang et al., 1998
;
Shirayama et al., 1998
;
Fang et al., 1998a
). The
checkpoint component Mad2 inhibits activation of the APC by interacting with
Cdc20 (Li et al., 1997
;
Fang et al., 1998b
;
Hwang et al., 1998
;
Kim et al., 1998
).
Immunofluorescence microscopy studies with antibodies to Mad2 show that it
localizes to unattached but not to fully attached kinetochores in vertebrates
(Chen et al., 1996
;
Li and Benezra, 1996
), and
real-time visualization of Mad2 in living mammalian cells demonstrates that it
is dynamically associated with unattached kinetochores
(Howell et al., 2000
). A
catalytic model for the role of Mad2 in the generation of the
anaphase-delaying signal has therefore been proposed
(Howell et al., 2000
)
(Fig. 2). According to this
model, unattached kinetochores on chromosomes provide sites for the activation
of Mad2. Activated Mad2 (Mad2*) is then released into the cytoplasm
and prevents the onset of anaphase by inhibiting the Cdc20-bound APC. After
microtubules have attached to all the kinetochores, sites for Mad2 activation
are no longer available, which eventually leads to APC activation by Cdc20 and
triggering of anaphase onset.
More recently, BubR1, the mammalian homolog of the checkpoint protein Mad3,
has been shown to be even more potent in vitro than Mad2 at inhibiting APC
activity in purified preparations (Sudakin
et al., 2001; Tang et al.,
2001
; Fang, 2002
).
BubR1 is a protein kinase that associates with Cdc20 and the APC
(Chan et al., 1999
;
Wu et al., 2000
;
Skoufias et al., 2001
). Tang
et al. found that recombinant BubR1 directly inhibits the ubiquitin ligase
activity of the APC and that the kinase activity of BubR1 is not required for
this inhibition (Tang et al.,
2001
). In addition, they purified a checkpoint complex from HeLa
cells that contains BubR1, Bub3 and substoichiometric amounts of Cdc20.
Independently, Sudakin et al. purified a mitotic checkpoint complex (MCC) that
contains nearly stoichiometric amounts of BubR1, Bub3, Mad2 and Cdc20
(Sudakin et al., 2001
). They
found that the isolated MCC is about 3000-fold more potent than purified Mad2
alone at inhibiting the ubiquitin ligase activity of the APC. In experiments
consistent with these studies, Fang found that BubR1 binds to Cdc20 with a
high affinity and is more efficient than Mad2 as an inhibitor of Cdc20-APC in
vitro (Fang, 2002
). Moreover,
this study demonstrated that BubR1 functions synergistically with Mad2 at
physiological concentrations to inhibit APC activity. Interestingly, studies
in fission yeast by Millband and Hardwick demonstrated that Mad3 also
associates with Bub3, Cdc20 and Mad2 and that Mad3 is required for metaphase
arrest caused by Mad2 overexpression
(Millband and Hardwick, 2002
).
Collectively, these studies suggest that BubR1 and Mad2 cooperate in
transducing the anaphase-delaying signal by inhibiting APC activity
(Fig. 2).
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Turning off the checkpoint signaling: attachment or tension? |
---|
Attachment of kinetochores to spindle microtubules probably involves
kinesin- or dynein-like microtubule motors, although neither CENP-E
(centromere protein E, a kinesin-like motor protein) nor
dynein, the two known motor proteins present at kinetochores
(Pfarr et al., 1990;
Steuer et al., 1990
;
Yen et al., 1992
;
Lombillo et al., 1995
;
Cooke et al., 1997
;
Yao et al., 1997
), is
required for kinetochore microtubule formation
(McEwen et al., 2001
;
Howell et al., 2001
). When a
pair of kinetochores becomes attached to microtubules from two opposite
spindle poles, tension develops across the sister kinetochores
(Fig. 3), even for those that
are oscillating, by switching directions between poleward motion and
away-from-the-pole motion (a phenomenon called kinetochore directional
instability) (Mitchison and Salmon,
1992
; Skibbens et al.,
1993
; Waters et al.,
1996b
). Tension is generated by the mitotic force that tends to
pull the chromatids toward two opposite spindle poles against the glue
(cohesin) that holds sister chromatids together
(McIntosh, 1984
;
Nicklas, 1988a
;
Mitchison and Salmon, 1992
;
Rieder and Salmon, 1994
). The
tension across sister kinetochores is apparent as a visible increase in the
distance between them in organisms from yeast to humans (a phenomenon termed
kinetochore stretching) (Waters et al.,
1996b
; Shelby et al.,
1996
; Nicklas,
1997
; Waters et al.,
1998
; Goshima and Yanagida,
2000
; He et al.,
2000
; Tanaka et al.,
2000
; Skoufias et al.,
2001
; Zhou et al.,
2002
).
|
McIntosh first proposed that the mechanical tension exerted on kinetochores
acts as a checkpoint for regulating anaphase entry
(McIntosh, 1991). Li and
Nicklas tested this proposal by ingenious experiments using praying mantid
spermatocytes, which have three sex chromosomes: a Y chromosome and two
genetically different X chromosomes (Li
and Nicklas, 1995
). Balance in the genetic information requires
sperm that contain either both X chromosomes or the Y chromosome; this takes
place only if the two X chromosomes attach to microtubules from the same
spindle pole and the Y chromosome attaches to microtubules from the opposite
pole (Nicklas, 1997
). In some
cells the three sex chromosomes fail to be connected trivalently, and they
appear as an X-Y bivalent and a free X chromosome, whose kinetochore lacks
tension (Li and Nicklas,
1995
). Under these circumstances, the onset of anaphase is delayed
by up to 9 hours. However, the cell proceeds to anaphase shortly after
mechanical tension is applied to the lagging X chromosome by a
force-calibrated microneedle (Li and
Nicklas, 1995
). These findings thus provided an experimental basis
for the tension model.
The role of tension in spindle assembly checkpoint signaling is not easy to
distinguish from that of attachment, however, as application of tension on
kinetochores can enhance both the stability of individual microtubule
attachments and the overall occupancy of kinetochores (by slowing the turnover
rate of kinetochore microtubules) (Nicklas
and Koch, 1969; Nicklas,
1988b
; Nicklas and Ward,
1994
; Nicklas,
1997
; King and Nicklas,
2000
; Nicklas et al.,
2001
) (see below for more discussion). It is possible that, in the
experiment performed by Li and Nicklas, the spindle assembly checkpoint was
switched off by tension-induced accumulation of microtubules at the
kinetochore (Li and Nicklas,
1995
) and not by the applied tension itself, as suggested by
others (Rieder and Khodjakov,
1997
). In fact, Rieder and colleagues found that, during mitosis
in the rat kangaroo kidney epithelial cell line PtK1, selectively destroying
(by laser-irradiation) the unattached kinetochore on the last, mono-oriented
chromosome immediately triggered anaphase onset
(Rieder et al., 1995
). In this
experiment, anaphase onset was not inhibited, despite the lack of tension
between sister kinetochores on the last chromosome. Furthermore, using PtK1
cells, Waters et al. demonstrated that loss of Mad2 staining at kinetochores,
a sign that the spindle assembly checkpoint has turned off, depends on
microtubule attachment not tension (Waters, 1998).
Interestingly, in a study performed in maize, Yu et al. found that during
mitosis, loss of Mad2 staining at kinetochores correlates with attachment of
kinetochores to spindle microtubules (Yu
et al., 1999). However, during meiosis in the same organism, loss
of Mad2 staining at kinetochores instead correlates with the tension exerted
on kinetochores by bipolar microtubule attachment. It has therefore been
proposed that the controversy between the attachment model and the tension
model could reflect differences between mitosis and meiosis, attachment being
used in mitosis and tension being used in meiosis.
Lessons from budding yeast
Studies on the roles of attachment and tension in spindle assembly
checkpoint signaling have mainly focused on multicellular organisms. In these
organisms, because each kinetochore can attach to multiple spindle
microtubules (e.g. up to 30 in mammals)
(Rieder, 1982), it has been
difficult to distinguish whether a given kinetochore is fully or partially
occupied. However, studying attachment and tension in budding yeast avoids the
issue of full or partial kinetochore occupancy, because the budding yeast
kinetochore captures only a single microtubule during mitosis
(Winey et al., 1995
).
Taking advantage of this system, Murray and colleagues recently performed a
series of elegant experiments in budding yeast to test the role of tension in
spindle assembly checkpoint signaling
(Shonn et al., 2000;
Stern and Murray, 2001
;
Biggins and Murray, 2001
). They
first directly visualized chromosome segregation in budding yeast by targeting
homologs of a chromosome with green fluorescence protein (GFP), a method
initially developed by (Straight et al.,
1996
). Mad2-deficient cells had increased frequencies of
chromosome missegregation in meiosis I
(Shonn et al., 2000
). In
addition, blocking recombination between homologous chromosomes, which causes
a loss of tension between them without affecting microtubule attachment (a
probable consequence is attachment of homologs to the same pole), led to a
remarkable delay in anaphase entry. Furthermore, forcing bipolar attachment of
the unrecombined homologs restored tension between them and allowed the cell
to overcome the delay in anaphase entry
(Shonn et al., 2000
).
In another experiment, Stern and Murray demonstrated that loss of tension
at the budding yeast kinetochore, when cells enter mitosis without a prior
round of DNA replication, is sufficient to cause the spindle assembly
checkpoint to block anaphase entry (Stern
and Murray, 2001). Similarly, Biggins and Murray found that, in
budding yeast mitosis, the spindle assembly checkpoint was activated when they
reduced tension by preventing DNA replication or sister chromatid cohesin
(Biggins and Murray, 2001
);
neither of these two manipulations affects attachment of kinetochores to
microtubules. These studies thus indicate that proper tension exerted upon
kinetochores, resulting from bipolar microtubule attachment, is crucial for
turning off the spindle assembly checkpoint in both meiosis and mitosis in
budding yeast. However, since spindle disruption and microtubule detachment
induced by nocodazole produces a long-term block in budding yeast, but loss of
tension produces only a delay, the role of tension in the checkpoint signaling
needs to be investigated further.
Taken together, the above studies in insect, yeast, maize and mammalian cells have significantly extended our knowledge of how the spindle assembly checkpoint is monitored during mitosis and meiosis. The contradictory results among these studies could reflect differences among cell types or organisms; some cell types or organisms might use both attachment and tension, whereas others might use only one of these mechanisms. However, considering the known interdependence of attachment and tension in higher eukaryotes, checkpoint signaling is most probably monitored by both attachment and tension, although the relative contributions of each mechanism may be different, depending on the cell type or organism.
It remains a riddle as to how tension enhances the stability and the number
of kinetochore microtubules, which are dynamically attached at both minus ends
(to spindle poles) and plus ends (to kinetochores)
(Mitchison, 1989;
Mitchison and Salmon, 1992
;
Zhai et al., 1995
;
Waters et al., 1996a
). Nicklas
and Ward speculated that tension might promote stability of kinetochore
microtubules at the spindle pole, and not at the kinetochores
(Nicklas and Ward, 1994
). For
the effect of tension on microtubule number at kinetochores, since kinetochore
microtubules can turn over slowly (Zhai
et al., 1995
), it is possible that tension affects the kinetic
balance between the capture of new microtubules, the release of the existing
kinetochore microtubules and their assembly dynamics.
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How do attachment and tension monitor the checkpoint? |
---|
Compared with what is known about attachment, much less is known about how
tension, a mechanical property, monitors the spindle assembly checkpoint. A
possible mechanism is tension-sensitive kinetochore protein phosphorylation,
which might link kinetochore mechanics to the chemical regulation of the
spindle assembly checkpoint, as suggested early on by Gorbsky and Nicklas
(Gorbsky, 1995;
Nicklas, 1997
). In particular,
a phosphorylated kinetochore protein recognized by the 3F3/2 antibody seems to
participate in this tension-mediated signaling pathway
(Gorbsky and Ricketts, 1993
;
Nicklas et al., 1995
;
Campbell and Gorbsky, 1995
;
Li and Nicklas, 1997
). Gorbsky
and Ricketts first reported that, in mitotic PtK1 cells, this phosphorylated
epitope stains brightly with the 3F3/2 antibody at unattached kinetochores but
very weakly at attached kinetochores
(Gorbsky and Ricketts, 1993
).
However, during meiosis I in grasshopper and mantid spermatocytes,
phosphorylation of this 3F3/2-recognized kinetochore epitope is regulated by
tension exerted upon kinetochores instead of just microtubule attachment
(Nicklas et al., 1995
;
Li and Nicklas, 1997
).
Tension, whether from normal mitotic forces or from a micromanipulation
needle, could cause dephosphorylation of the 3F3/2 phosphoepitope at
kinetochores (Nicklas et al.,
1995
; Li and Nicklas,
1997
) and could also trigger anaphase onset
(Li and Nicklas, 1995
).
Furthermore, when the 3F3/2 antibody was injected into mitotic cells, the
normal dephosphorylation of the 3F3/2 phosphoepitope and onset of anaphase
were inhibited (Campbell and Gorbsky,
1995
). It is thus very likely that tension-sensitive
phosphorylation and dephosphorylation of this kinetochore epitope regulates
the spindle assembly checkpoint signaling.
Recently, Biggins and Murray reported that in budding yeast, aurora/Ipl1p,
a protein kinase, plays an important role in tension-dependent spindle
assembly checkpoint signaling (Biggins and
Murray, 2001). In their experiments, aurora/Ipl1p function was
required for the spindle assembly checkpoint activity induced by kinetochores
not under tension yet attached to microtubules (manipulated by preventing DNA
replication or sister chromatid cohesin). However, aurora/Ipl1p was not
required for the checkpoint activity induced by microtubule depolymerization.
The role of aurora/Ipl1p in tension-dependent checkpoint signaling is further
supported by a more recent study by Tanaka et al. in which aurora/Ipl1p was
demonstrated to be critical for reorienting monopolar-attached sister
chromatids whose sister kinetochores are not under tension so that they attach
to microtubules from two opposite spindle poles
(Tanaka et al., 2002
). It will
be of great interest to investigate whether aurora/Ipl1p is the kinase that
phosphorylates the 3F3/2-recognized epitope at kinetochores that lack tension
(Gorbsky and Ricketts, 1993
;
Nicklas et al., 1995
;
Campbell and Gorbsky, 1995
;
Li and Nicklas, 1997
).
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Why does the checkpoint need both attachment and tension? |
---|
To have both attachment and tension mechanisms might be an advantage even
after bipolar attachment of kinetochores: stabilization of kinetochore
attachment by proper tension might be essential for the correct alignment of
kinetochores at the metaphase plate, the final event before anaphase entry.
This idea is supported by three recent studies in mammalian cells
(Hoffman et al., 2001;
Skoufias et al., 2001
;
Zhou et al., 2002
). Hoffman
et al. reported that, in PtK1 cells, when chromosomes are bipolar-attached and
aligned at the metaphase plate, Mad2 was completely gone from the kinetochores
whereas BubR1 was still visible (Hoffman
et al., 2001
). Skoufias et al. found that, in the presence of
low-dose vinblastine, which arrests HeLa cells at mitosis with normal
chromosome alignment yet without tension, Bub1 and BubR1 are recruited to
kinetochores but Mad2 is not (Skoufias et
al., 2001
). Mad2 is recruited to kinetochores at higher
vinblastine doses, which disrupt attachment of kinetochores to microtubules.
Zhou et al. studied noscapine-arrested mitotic HeLa cells, which have bipolar
spindles but do not complete chromosome alignment; some chromosomes are
aligned at the metaphase plate and others remain near spindle poles
both groups of chromosomes lack tension to a similar extent
(Zhou et al., 2002
). Upon
chromosome alignment, Mad2 became undetectable at kinetochores (138-fold
reduction); by contrast, Bub1 and BubR1 were only diminished to 3.7- and
3.9-fold, respectively (Zhou et al.,
2002
).
Collectively, these studies suggest that the checkpoint proteins Mad2 and
Bub1/BubR1 primarily sense attachment and tension, respectively. It is worth
calling attention to a previous study conducted in PtK1 cells by Waters et
al., in which loss of tension was insufficient to recruit Mad2 to kinetochores
although some kinetochores did exhibit Mad2 and antibodies to Mad2 disrupted
this checkpoint (Waters et al.,
1998). The recent finding that BubR1 is a more potent APC
inhibitor in vitro (Sudakin et al.,
2001
; Tang et al.,
2001
; Fang, 2002
)
also indicates that Mad2 and Bub1/BubR1 have distinct roles in spindle
assembly checkpoint signaling. However, current evidence for this model is not
firm. By contrast, in a recent study performed in PtK1 cells by Hoffman et
al., the average amount of BubR1 at metaphase kinetochores did not change with
the loss of kinetochore tension induced by taxol stabilization of microtubules
(Hoffman et al., 2001
). In
addition, Taylor et al. show that Bub1 and BubR1 respond differently to
microtubule inhibitor-induced changes in kinetochore-microtubule attachment
and tension (Taylor et al.,
2001
). Thus, whether Mad2 and Bub1/BubR1 have respective roles in
sensing attachment and tension remains a challenge to be solved in the
future.
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Acknowledgments |
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References |
---|
Amon, A. (1999). The spindle checkpoint. Curr. Opin. Cell Biol. 9, 69-75.
Basto, R., Gomes, R. and Karess, R. E. (2000). Rough deal and Zw10 are required for the metaphase checkpoint in Drosophila. Nat. Cell Biol. 2, 939-943.[CrossRef][Medline]
Basu, J., Logarinho, E., Herrmann, S., Bousbaa, H., Li, Z., Chan, G. K., Yen, T. J., Sunkel, C. E. and Goldberg, M. L. (1998). Localization of the Drosophila checkpoint control protein Bub3 to the kinetochore requires Bub1 but not Zw10 or Rod. Chromosoma 107,376 -385.[CrossRef][Medline]
Basu, J., Bousbaa, H., Logarinho, E., Li, Z., Williams, B. C.,
Lopes, C., Sunkel, C. E. and Goldberg, M. L. (1999).
Mutations in the essential spindle checkpoint gene bub1 cause chromosome
missegregation and fail to block apoptosis in Drosophila. J. Cell
Biol. 146,13
-28.
Bernard, P., Hardwick, K. and Javerzat, J. P.
(1998). Fission yeast bub1 is a mitotic centromere protein
essential for the spindle checkpoint and the preservation of correct ploidy
through mitosis. J. Cell Biol.
143,1775
-1787.
Biggins, S. and Murray, A. W. (2001). The
budding yeast protein kinase Ipl1/Aurora allows the absence of tension to
activate the spindle checkpoint. Genes Dev.
15,3118
-3129.
Cahill, D. P., Lengauer, C., Yu, J., Riggins, G. J., Willson, J. K., Markowitz, S. D., Kinzler, K. W. and Vogelstein, B. (1998). Mutations of mitotic checkpoint genes in human cancers. Nature 392,300 -303.[CrossRef][Medline]
Campbell, M. S. and Gorbsky, G. J. (1995). Microinjection of mitotic cells with the 3F3/2 anti-phosphoepitope antibody delays the onset of anaphase. J. Cell Biol. 129,1195 -1204.[Abstract]
Chan, G. K., Jablonski, S. A., Starr, D. A., Goldberg, M. L. and Yen, T. J. (2000). Human Zw10 and ROD are mitotic checkpoint proteins that bind to kinetochores. Nat. Cell Biol. 2, 944-947.[CrossRef][Medline]
Chan, G. K., Jablonski, S. A., Sudakin, V., Hittle, J. C. and
Yen, T. J. (1999). Human BUBR1 is a mitotic checkpoint kinase
that monitors CENP-E functions at kinetochores and binds the cyclosome/APC.
J. Cell Biol. 146,941
-954.
Chan, G. K., Schaar, B. T. and Yen, T. J.
(1998). Characterization of the kinetochore binding domain of
CENP-E reveals interactions with the kinetochore proteins CENP-F and hBUBR1.
J. Cell Biol. 143,49
-63.
Chen, R. H., Brady, D. M., Smith, D., Murray, A. W. and
Hardwick, K. G. (1999). The spindle checkpoint of budding
yeast depends on a tight complex between the Mad1 and Mad2 proteins.
Mol. Biol. Cell 10,2607
-2618.
Chen, R. H., Waters, J. C., Salmon, E. D. and Murray, A. W.
(1996). Association of spindle assembly checkpoint component
XMAD2 with unattached kinetochores. Science
274,242
-246.
Chen, R. H., Shevchenko, A., Mann, M. and Murray, A. W.
(1998). Spindle checkpoint protein Xmad1 recruits Xmad2 to
unattached kinetochores. J. Cell Biol.
143,283
-295.
Ciosk, R., Zachariae, W., Michaelis, C., Shevchenko, A., Mann, M. and Nasmyth, K. (1998). An ESP1/PDS1 complex regulates loss of sister chromatid cohesion at the metaphase to anaphase transition in yeast. Cell 93,1067 -1076.[Medline]
Cohen-Fix, O., Peters, J. M., Kirschner, M. W. and Koshland, D. (1996). Anaphase initiation in Saccharomyces cerevisiae is controlled by the APC-dependent degradation of the anaphase inhibitor Pds1p. Genes Dev. 10,3081 -3093.[Abstract]
Cooke, C. A., Schaar, B., Yen, T. J. and Earnshaw, W. C. (1997). Localization of CENP-E in the fibrous corona and outer plate of mammalian kinetochores from prometaphase through anaphase. Chromosoma 106,446 -455.[CrossRef][Medline]
Fang, G. (2002). Checkpoint protein BubR1 acts
synergistically with Mad2 to inhibit anaphase-promoting complex.
Mol. Biol. Cell 13,755
-766.
Fang, G., Yu, H. and Kirschner, M. W. (1998a). Direct binding of CDC20 protein family members activates the anaphase-promoting complex in mitosis and G1. Mol. Cell 2,163 -171.[Medline]
Fang, G., Yu, H. and Kirschner, M. W. (1998b).
The checkpoint protein MAD2 and the mitotic regulator CDC20 form a ternary
complex with the anaphase-promoting complex to control anaphase initiation.
Genes Dev. 12,1871
-1883.
Fang, G., Yu, H. and Kirschner, M. W. (1999). Control of mitotic transitions by the anaphase-promoting complex. Philos. Trans. R. Soc. Lond. B Biol. Sci. 354,1583 -1590.[CrossRef][Medline]
Funabiki, H., Yamano, H., Kumada, K., Nagao, K., Hunt, T. and Yangida, M. (1996). Cut2 proteolysis required for sister-chromatid separation in fission yeast. Nature 381,438 -441.[CrossRef][Medline]
Gorbsky, G. J. (1995). Kinetochores, microtubules and the metaphase checkpoint. Trends Cell Biol. 5,143 -148.[CrossRef]
Gorbsky, G. J. and Ricketts, W. A. (1993). Differential expression of a phosphoepitope at the kinetochores of moving chromosomes. J. Cell Biol. 122,1311 -1321.[Abstract]
Goshima, G. and Yanagida, M. (2000). Establishing biorientation occurs with precocious separation of the sister kinetochores, but not the arms, in the early spindle of budding yeast. Cell 100,619 -633.[Medline]
Guacci, V., Koshland, D. and Strunnikov, A. (1997). A direct link between sister chromatid cohesion and chromosome condensation revealed through the analysis of MCD1 in S. cerevisiae. Cell 91,47 -57.[CrossRef][Medline]
Hartwell, L. H. and Weinert, T. A. (1989). Checkpoints: controls that ensure the order of cell cycle events. Science 246,629 -634.[Medline]
Hauf, S., Waizenegger, I. C. and Peters, J. M.
(2001). Cohesion cleavage by separase required for anaphase and
cytokinesis in human cells. Science
293,1320
-1323.
He, X., Asthana, S. and Sorger, P. K. (2000). Transient sister chromatid separation and elastic deformation of chromosomes during mitosis in budding yeast. Cell 101,763 -775.[Medline]
He, X., Patterson, T. and Sazer, S. (1997). The
Schizosaccharomyces pombe spindle checkpoint protein mad2p blocks
anaphase and genetically interacts with the anaphase-promoting complex.
Proc. Natl. Acad. Sci. USA
94,7965
-7970.
He, X., Jones, M. H., Winey, M. and Sazer, S.
(1998). mph 1, a member of the Mps1-like family of dual
specificity protein kinases, is required for the spindle checkpoint in S.
pombe. J. Cell Sci. 111,1635
-1647.
Hoffman, D. B., Pearson, C. G., Yen, T. J., Howell, B. J. and
Salmon, E. D. (2001). Microtubule-dependent changes in
assembly of microtubule motor proteins and mitotic spindle checkpoint proteins
at PtK1 kinetochores. Mol. Biol. Cell
12,1995
-2009.
Hoyt, M. A., Totis, L. and Roberts, B. T. (1991). S. cerevisiae genes required for cell cycle arrest in response to loss of microtubule function. Cell 66,507 -517.[Medline]
Howell, B. J., Hoffman, D. B., Fang, G., Murray, A. W. and
Salmon, E. D. (2000). Visualization of Mad2 dynamics at
kinetochores, along spindle fibers, and at spindle poles in living cells.
J. Cell Biol. 150,1233
-1250.
Howell, B. J., McEwen, B. F., Canman, J. C., Hoffman, D. B.,
Farrar, E. M., Rieder, C. L. and Salmon, E. D. (2001).
Cytoplasmic dynein/dynactin drives kinetochore protein transport to the
spindle poles and has a role in mitotic spindle checkpoint inactivation.
J. Cell Biol. 155,1159
-1172.
Hwang, L. H., Lau, L. F., Smith, D. L., Mistrot, C. A.,
Hardwick, K. G., Hwang, E. S., Amon, A. and Murray, A. W.
(1998). Budding yeast Cdc20: a target of the spindle checkpoint.
Science 279,1041
-1044.
Jin, D. Y., Spencer, F. and Jeang, K. T. (1998). Human T cell leukemia virus type 1 oncoprotein Tax targets the human mitotic checkpoint protein MAD1. Cell 93,81 -91.[Medline]
Kim, S. H., Lin, D. P., Matsumoto, S., Kitazono, A. and
Matsumoto, T. (1998). Fission yeast Slp1: an effector of the
Mad2-dependent spindle checkpoint. Science
279,1045
-1047.
King, J. M. and Nicklas, R. B. (2000). Tension
on chromosomes increases the number of kinetochore microtubules but only
within limits. J. Cell Sci.
113,3815
-3823.
King, R. W., Peters, J. M., Tugendreich, S., Rolfe, M., Hieter, P. and Kirschner, M. W. (1995). A 20S complex containing CDC27 and CDC16 catalyzes the mitosis-specific conjugation of ubiquitin to cyclin B. Cell 81,279 -288.[Medline]
Kitagawa, R. and Rose, A. M. (1999). Components of the spindle-assembly checkpoint are essential in Caenorhabditis elegans. Nat. Cell Biol. 1,514 -521.[CrossRef][Medline]
Lee, H., Trainer, A. H., Friedman, L. S., Thistlethwaite, F. C., Evans, M. J., Ponder, B. A. J. and Venkitaraman, A. R. (1999). Mitotic checkpoint inactivation fosters transformation in cells lacking the breast cancer susceptibility gene, Brca2. Mol. Cell 4,1 -10.[Medline]
Li, R. and Murray, A. W. (1991). Feedback control of mitosis in budding yeast. Cell 66,519 -531.[Medline]
Li, X. and Nicklas, R. B. (1995). Mitotic forces control a cell-cycle checkpoint. Nature 373,630 -632.[CrossRef][Medline]
Li, X. and Nicklas, R. B. (1997).
Tension-sensitive kinetochore phosphorylation and the chromosome distribution
checkpoint in praying mantid spermatocytes. J. Cell
Sci. 110,537
-545.
Li, Y. and Benezra, R. (1996). Identification
of a human mitotic checkpoint gene:hsMAD2. Science
274,246
-248.
Li, Y., Gorbea, C., Mahaffey, D., Rechsteiner, M. and Benezra,
R. (1997). MAD2 associates with the
cyclosome/anaphase-promoting complex and inhibits its activity.
Proc. Natl. Acad. Sci. USA
94,12431
-12436.
Lombillo, V. A., Nislow, C., Yen, T. J., Gelfand, V. I. and McIntosh, J. R. (1995). Antibodies to the kinesin motor domain and CENP-E inhibit microtubule depolymerization-dependent motion of chromosomes in vitro. J. Cell Biol. 128,107 -115.[Abstract]
Manchester, K. L. (1995). Boveri, Theodor and the origin of malignant-tumors. Trends Cell Biol. 5, 384-387.[Medline]
Martinez-Exposito, M. J., Kaplan, K. B., Copeland, J. and
Sorger, P. K. (1999). Retention of the BUB3 checkpoint
protein on lagging chromosomes. Proc. Natl. Acad. Sci.
USA 96,8493
-8498.
Mazia, D. (1961). Mitosis. In The Cell Vol. 3 (ed. J. Brachet and A. E. Mirsky), pp. 77-142. New York: Academic Press.
McEwen, B. F., Chan, G. K. T., Zubrowski, B., Savoian, M. S.,
Sauer, M. T. and Yen, T. J. (2001). CENP-E is essential for
reliable bioriented spindle attachment, but chromosome alignment can be
achieved via redundant mechanisms in mammalian cells. Mol. Biol.
Cell 12,2776
-2789.
McIntosh, J. R. (1984). Mechanisms of mitosis. Trends Biochem. Sci. 9,195 -198.[CrossRef]
McIntosh, J. R. (1991). Structural and mechanical control of mitotic progression. Cold Spring Harbor Symp. Quant. Biol. 56,613 -619.[Medline]
Michaelis, C., Ciosk, R. and Nasmyth, K. (1997). Cohesins: chromosomal proteins that prevent premature separation of sister chromatids. Cell 91, 35-45.[CrossRef][Medline]
Michel, L. S., Liberal, V., Chatterjee, A., Kirchwegger, R., Pasche, B., Gerald, W., Dobles, M., Sorger, P. K., Murty, V. V. and Benezra, R. (2001). MAD2 haplo-insufficiency causes premature anaphase and chromosome instability in mammalian cells. Nature 409,355 -359.[CrossRef][Medline]
Millband, D. N. and Hardwick, K. G. (2002).
Fission yeast mad3p is required for mad2p to inhibit the anaphase-promoting
complex and localizes to kinetochores in a bub1p-, bub3p-, and mph1p-dependent
manner. Mol. Cell. Biol.
22,2728
-2742.
Mitchison, T. J. (1989). Polewards microtubule flux in the mitotic spindle: evidence from photoactivation of fluorescence. J. Cell Biol. 109,637 -652.[Abstract]
Mitchison, T. J. and Salmon, E. D. (1992). Poleward kinetochore fiber movement occurs during both metaphase and anaphase-A in newt lung cell mitosis. J. Cell Biol. 119,569 -582.[Abstract]
Nicklas, R. B. (1988a). The forces that move chromosomes in mitosis. Annu. Rev. Biophys. Biophys. Chem. 17,431 -449.[CrossRef][Medline]
Nicklas, R. B. (1988b). Chance encounters and precision in mitosis. J. Cell Sci. 89,283 -285.[Medline]
Nicklas, R. B. (1997). How cells get the right
chromosomes. Science
275,632
-637.
Nicklas, R. B. and Koch, C. A. (1969).
Chromosome manipulation III. Induced reorientation and the experimental
control of segregation in meiosis. J. Cell Biol.
43, 40-50.
Nicklas, R. B. and Ward, S. C. (1994). Elements of error correction in mitosis: microtubule capture, release, and tension. J. Cell Biol. 126,1241 -1253.[Abstract]
Nicklas, R. B., Ward, S. C. and Gorbsky, G. J. (1995). Kinetochore chemistry is sensitive to tension and may link mitotic forces to a cell cycle checkpoint. J. Cell Biol. 130,929 -939.[Abstract]
Nicklas, R. B., Waters, J. C., Salmon, E. D. and Ward, S. C.
(2001). Checkpoint signals in grasshopper meiosis are sensitive
to microtubule attachment, but tension is still essential. J. Cell
Sci. 114,4173
-4183.
Pfarr, C. M., Coue, M., Grissom, P. M., Hays, T. S., Porter, M. E. and McIntosh, J. R. (1990). Cytoplasmic dynein is localized to kinetochores during mitosis. Nature 345,263 -265.[CrossRef][Medline]
Rieder, C. L. (1982). The formation, structure, and composition of the mammalian kinetochore and kinetochore fiber. Int. Rev. Cytol. 79,1 -58.[Medline]
Rieder, C. L. and Khodjakov, A. (1997). Mitosis and checkpoints that control progression through mitosis in vertebrate somatic cells. Prog. Cell Cycle Res. 3, 301-312.[Medline]
Rieder, C. L. and Salmon, E. D. (1994). Motile kinetochores and polar ejection forces dictate chromosome position on the vertebrate mitotic spindle. J. Cell Biol. 124,223 -233.[Abstract]
Rieder, C. L. and Salmon, E. D. (1998). The vertebrate cell kinetochore and its roles during mitosis. Trends Cell Biol. 8,310 -318.[CrossRef][Medline]
Rieder, C. L., Schultz, A., Cole, R. and Sluder, G. (1994). Anaphase onset in vertebrate somatic cells is controlled by a checkpoint that monitors sister kinetochore attachment to the spindle. J. Cell Biol. 127,1301 -1310.[Abstract]
Rieder, C. L., Cole, R. W., Khodjakov, A. and Sluder, G. (1995). The checkpoint delaying anaphase in response to chromosome monoorientation is mediated by an inhibitory signal produced by unattached kinetochores. J. Cell Biol. 130,941 -948.[Abstract]
Rudner, A. D. and Murray, A. W. (1996). The spindle assembly checkpoint. Curr. Opin. Cell Biol. 8, 773-780.[CrossRef][Medline]
Shan, J. V. and Cleveland, D. W. (2000). Waiting for anaphase: Mad2 and the spindle assembly checkpoint. Cell 103,997 -1000.[Medline]
Shelby, R. D., Hahn, K. M. and Sullivan, K. F. (1996). Dynamic elastic behavior of alpha-satellite DNA domains visualized in situ in living human cells. J. Cell Biol. 135,545 -557.[Abstract]
Shirayama, M., Zachariae, W., Ciosk, R. and Nasmyth, K.
(1998). The Polo-like kinase Cdc5p and the WD-repeat protein
Cdc20/fizzy are regulators and substrates of the anaphase promoting complex in
Saccharomyces cerevisiae. EMBO J.
17,1336
-1349.
Shonn, M. A., McCarroll, R. and Murray, A. W.
(2000). Requirement of the spindle checkpoint for proper
chromosome segregation in budding yeast meiosis.
Science 289,300
-303.
Sironi, L., Melixetian, M., Faretta, M., Prosperini, E., Helin,
K. and Musacchio, A. (2001). Mad2 binding to Mad1 and Cdc20,
rather than oligomerization, is required for the spindle checkpoint.
EMBO J. 20,6371
-6382.
Skibbens, R. V., Skeen, V. P. and Salmon, E. D. (1993). Directional instability of kinetochore motility during chromosome congression and segregation in mitotic newt lung cells: a push-pull mechanism. J. Cell Biol. 122,859 -875.[Abstract]
Skoufias, D. A., Andreassen, P. R., Lacroix, F. B., Wilson, L.
and Margolis, R. L. (2001). Mammalian mad2 and bub1/bubR1
recognize distinct spindle-attachment and kinetochore-tension checkpoints.
Proc. Natl. Acad. Sci. USA
98,4492
-4497.
Sluder, G. and McCollum, D. (2000). The mad
ways of meiosis. Science
289,254
-255.
Stern, B. M. and Murray, A. W. (2001). Lack of tension at kinetochores activates the spindle checkpoint in budding yeast. Curr. Biol. 11,1462 -1467.[CrossRef][Medline]
Steuer, E. R., Wordeman, L., Schroer, T. A. and Sheetz, M. P. (1990). Localization of cytoplasmic dynein to mitotic spindles and kinetochores. Nature 345,266 -268.[CrossRef][Medline]
Straight, A. F., Belmont, A. S., Robinett, C. C. and Murray, A. W. (1996). GFP tagging of budding yeast chromosomes reveals that protein-protein interactions can mediate sister chromatid cohesion. Curr. Biol. 6,1599 -1608.[Medline]
Sudakin, V., Chan, G. K. T. and Yen, T. J.
(2001). Checkpoint inhibition of the APC/C in HeLa cells is
mediated by a complex of BUBR1, BUB3, CDC20, MAD2. J. Cell
Biol. 154,925
-936.
Takahashi, T., Haruki, N., Nomoto, S., Masuda, A., Saji, S. and Osada, H. (1999). Identification of frequent impairment of the mitotic checkpoint and molecular analysis of the mitotic checkpoint genes, hsMAD2 and p55CDC, in human lung cancers. Oncogene, 18,4295 -4300.[CrossRef][Medline]
Tanaka, T., Fuchs, J., Loidl, J. and Nasmyth, K. (2000). Cohesin ensures bipolar attachment of microtubules to sister centromeres and resists their precocious separation. Nat. Cell Biol. 2,492 -499.[CrossRef][Medline]
Tanaka, T. U., Rachidi, N., Janke, C., Pereira, G., Galova, M., Schiebel, E., Stark, M. J. and Nasmyth, K. (2002). Evidence that the Ipl1-Sli15 (Aurora kinase-INCENP) complex promotes chromosome bi-orientation by altering kinetochore-spindle pole connections. Cell 108,317 -329.[Medline]
Tang, Z., Bharadwaj, R., Li, B. and Yu, H. (2001). Mad2-independent inhibition of APCCdc20 by the mitotic checkpoint protein BubR1. Dev. Cell 1, 227-237.[Medline]
Taylor, S. S. and McKeon, F. (1997). Kinetochore localization of murine Bub1 is required for normal mitotic timing and checkpoint response to spindle damage. Cell 89,727 -735.[Medline]
Taylor, S. S., Ha, E. and McKeon, F. (1998).
The human homologue of Bub3 is required for kinetochore localization and a
Mad3/Bub1-related protein kinase. J. Cell Biol.
142, 1-11.
Taylor, S. S., Hussein, D., Wang, Y., Elderkin, S. and Morrow,
C. J. (2001). Kinetochore localisation and phosphorylation of
the mitotic checkpoint components Bub1 and BubR1 are differentially regulated
by spindle events in human cells. J. Cell Sci.
114,4385
-4395.
Uhlmann, F., Lottspeich, F. and Nasmyth, K. (1999). Sister-chromatid separation at anaphase onset is promoted by cleavage of the cohesin subunit Scc1. Nature 400, 37-42.[CrossRef][Medline]
Uhlmann, F., Wernek, W., Poupart, M. A., Koonin, E. and Nasmyth, K. (2000). Cleavage of cohesin by the CD clan protease separin triggers anaphase in yeast. Cell 103,375 -386.[Medline]
Visintin, R., Prinz, S. and Amon, A. (1997).
CDC20 and CDH1: A family of substrate-specific activators of APC-dependent
proteolysis. Science
278,460
-463.
Wang, X., Jin, D. Y., Ng, R. W., Feng, H., Wong, Y. C., Cheung,
A. L. and Tsao, S. W. (2002). Significance of MAD2 expression
to mitotic checkpoint control in ovarian cancer cells. Cancer
Res. 62,1662
-1668.
Waters, J. C., Chen, R. H., Murray, A. W. and Salmon, E. D.
(1998). Localization of Mad2 to kinetochores depends on
microtubule attachment, not tension. J. Cell Biol.
141,1181
-1191.
Waters, J. C., Mitchison, T. J., Rieder, C. L. and Salmon, E. D. (1996a). The kinetochore microtubule minus-end disassembly associated with poleward flux produces a force that can do work. Mol. Biol. Cell 7,1547 -1558.[Abstract]
Waters, J. C., Skibbens, R. V. and Salmon, E. D.
(1996b). Oscillating mitotic newt lung cell kinetochores are, on
average, under tension and rarely push. J. Cell Sci.
109,2823
-2831.
Weiss, E. and Winey, M. (1996). The S. cerevisiae SPB duplication gene MPS1 is part of a mitotic checkpoint. J. Cell Biol. 132,111 -123.[Abstract]
Wells, W. A. E. (1996). The spindle-assembly checkpoint: Aiming for a perfect mitosis, every time. Trends Cell Biol. 6,228 -234.[CrossRef]
Winey, M., Mamay, C. L., O'Toole, E. T., Mastronarde, D. N., Giddings, T. H., Jr, McDonald, K. L. and McIntosh, J. R. (1995). Three-dimensional ultrastructural analysis of the Saccharomyces cerevisiae mitotic spindle. J. Cell Biol. 129,1601 -1615.[Abstract]
Wu, H., Lan, Z., Li, W., Wu, S., Weinstein, J., Sakamoto, K. M. and Dai, W. (2000). p55CDC/hCDC20 is associated with BUBR1 and may be a downstream target of the spindle checkpoint kinase. Oncogene 19,4557 -4562.[CrossRef][Medline]
Yamamoto, A., Guacci, V. and Koshland, D. (1996). Pds1p, an inhibitor of anaphase in budding yeast, plays a critical role in the APC and checkpoint pathway(s). J. Cell Biol. 133,99 -110.[Abstract]
Yao, X., Anderson, K. L. and Cleveland, D. W.
(1997). The microtubule-dependent motor centromere-associated
protein E (CENP-E) is an integral component of kinetochore corona fibers that
link centromeres to spindle microtubules. J. Cell
Biol. 139,435
-447.
Yen, T. J., Li, G., Schaar, B. T., Szilak, I. and Cleveland, D. W. (1992). CENP-E is a putative kinetochore motor that accumulates just before mitosis. Nature 359,536 -539.[CrossRef][Medline]
Yu, H. G., Muszynski, M. G. and Kelly Dawe, R.
(1999). The maize homologue of the cell cycle checkpoint protein
MAD2 reveals kinetochore substructure and contrasting mitotic and meiotic
localization patterns. J. Cell Biol.
145,425
-435.
Zachariae, W. and Nasmyth, K. (1999). Whose end
is destruction: cell division and the anaphase-promoting complex.
Genes Dev. 13,2039
-2058.
Zhai, Y., Kronebusch, P. J. and Borisy, G. G. (1995). Kinetochore microtubule dynamics and the metaphase-anaphase transition. J. Cell Biol. 131,721 -734.[Abstract]
Zhou, J., Panda, D., Landen, J. W., Wilson, L. and Joshi, H.
C. (2002). Minor alteration of microtubule dynamics causes
loss of tension across kinetochore pairs and activates the spindle checkpoint.
J. Biol. Chem. 277,17200
-17208.
Zou, H., McGarry, T. J., Bernal, T. and Kirschner, M. W.
(1999). Identification of a vertebrate sister-chromatid
separation inhibitor involved in transformation and tumorigenesis.
Science 285,418
-422.
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