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Rae1 is an essential mitotic checkpoint regulator that cooperates with Bub3 to prevent chromosome missegregation.

Babu JR, Jeganathan KB, Baker DJ, Wu X, Kang-Decker N, van Deursen JM - J. Cell Biol. (2003)

Bottom Line: Here we show that haplo-insufficiency of either Rae1 or Bub3 results in a similar phenotype involving mitotic checkpoint defects and chromosome missegregation.We also show that overexpression of Rae1 can correct for Rae1 haplo-insufficiency and, surprisingly, Bub3 haplo-insufficiency.Thus, our data demonstrate a novel function for Rae1 and characterize Rae1 and Bub3 as related proteins with essential, overlapping, and cooperating roles in the mitotic checkpoint.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN 55905, USA.

ABSTRACT
The WD-repeat proteins Rae1 and Bub3 show extensive sequence homology, indicative of functional similarity. However, previous studies have suggested that Rae1 is involved in the mRNA export pathway and Bub3 in the mitotic checkpoint. To determine the in vivo roles of Rae1 and Bub3 in mammals, we generated knockout mice that have these genes deleted individually or in combination. Here we show that haplo-insufficiency of either Rae1 or Bub3 results in a similar phenotype involving mitotic checkpoint defects and chromosome missegregation. We also show that overexpression of Rae1 can correct for Rae1 haplo-insufficiency and, surprisingly, Bub3 haplo-insufficiency. Rae1- and Bub3- mice are embryonic lethal, although cells from these mice did not have a detectable defect in nuclear export of mRNA. Unlike mice, compound haplo-insufficient Rae1/Bub3 mice are viable. However, cells from these mice exhibit much greater rates of premature sister chromatid separation and chromosome missegregation than single haplo-insufficient cells. Finally, we show that mice with mitotic checkpoint defects are more susceptible to dimethylbenzanthrene-induced tumorigenesis than wild-type mice. Thus, our data demonstrate a novel function for Rae1 and characterize Rae1 and Bub3 as related proteins with essential, overlapping, and cooperating roles in the mitotic checkpoint.

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Model for Rae1 function in mitosis. We propose that Rae1 targets to unattached kinetochores at the onset of mitosis together with Bub1, just like Bub3. There, Rae1–Bub1 and Bub3–Bub1 proteins act to activate the mitotic checkpoint, potentially by producing anaphase wait signals. Unlike Rae1, Bub3 also interacts with BubR1 and localizes to the cytosolic component of the mitotic checkpoint complex that acts to inhibit the APC activator Cdc20 when anaphase wait signals are present. For simplicity, only part of the components of the checkpoint is shown in the model.
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fig10: Model for Rae1 function in mitosis. We propose that Rae1 targets to unattached kinetochores at the onset of mitosis together with Bub1, just like Bub3. There, Rae1–Bub1 and Bub3–Bub1 proteins act to activate the mitotic checkpoint, potentially by producing anaphase wait signals. Unlike Rae1, Bub3 also interacts with BubR1 and localizes to the cytosolic component of the mitotic checkpoint complex that acts to inhibit the APC activator Cdc20 when anaphase wait signals are present. For simplicity, only part of the components of the checkpoint is shown in the model.

Mentions: What then could be the mechanism by which Rae1 regulates the activity of the mitotic checkpoint and how may Rae1 be able to compensate for Bub3 haplo-insufficiency? Because Rae1 has been shown to localize to unattached kinetochores at the onset of mitosis (Wang et al., 2001), it is possible that Rae1 might play a role in the production of anaphase wait signals at that position. Given that the checkpoint protein Bub1 also targets to unattached kinetochores in mitosis and can bind to Rae1 (Wang et al., 2001), it is further possible that Rae1 and Bub1 might participate in such signaling events as a protein complex. Interestingly, like Rae1, Bub3 also targets to unattached kinetochores and interacts with Bub1. We have shown that the GLEBS sequence of Bub1 serves as a shared binding motif for Rae1 and Bub3 (Wang et al., 2001). Given that both Rae1–Bub1 and Bub3–Bub1 complexes coexist in prometaphase-arrested HeLa cells (Wang et al., 2001), one possible explanation for the phenotypic similarity between Rae1 and Bub3 haplo-insufficient cells could be that Rae1–Bub1 and Bub3–Bub1 complexes fulfill redundant functions at unattached kinetochores. Correction of the mitotic checkpoint in Bub3 haplo-insufficient cells by overexpression of HA-tagged Rae1 could then simply result from the assembly of “unbound” Bub1 molecules into Rae1–Bub1 complexes that would be capable of performing the functions of the missing Bub3–Bub1 complexes (Fig. 10). Bub3 also interacts with BubR1 (Taylor et al., 1998), and Bub3–BubR1 complexes positioned in the mitotic cytosol seem to play a critical role in inhibiting the APC (Fig. 10) (Sudakin et al., 2001; Tang et al., 2001; Fang, 2002). Because Rae1 does not interact with BubR1 (Wang et al., 2001), the mechanism by which Rae1 overexpression acts to correct Bub3 haplo-insufficient cells is unlikely to involve the formation of compensatory Rae1–BubR1.


Rae1 is an essential mitotic checkpoint regulator that cooperates with Bub3 to prevent chromosome missegregation.

Babu JR, Jeganathan KB, Baker DJ, Wu X, Kang-Decker N, van Deursen JM - J. Cell Biol. (2003)

Model for Rae1 function in mitosis. We propose that Rae1 targets to unattached kinetochores at the onset of mitosis together with Bub1, just like Bub3. There, Rae1–Bub1 and Bub3–Bub1 proteins act to activate the mitotic checkpoint, potentially by producing anaphase wait signals. Unlike Rae1, Bub3 also interacts with BubR1 and localizes to the cytosolic component of the mitotic checkpoint complex that acts to inhibit the APC activator Cdc20 when anaphase wait signals are present. For simplicity, only part of the components of the checkpoint is shown in the model.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172680&req=5

fig10: Model for Rae1 function in mitosis. We propose that Rae1 targets to unattached kinetochores at the onset of mitosis together with Bub1, just like Bub3. There, Rae1–Bub1 and Bub3–Bub1 proteins act to activate the mitotic checkpoint, potentially by producing anaphase wait signals. Unlike Rae1, Bub3 also interacts with BubR1 and localizes to the cytosolic component of the mitotic checkpoint complex that acts to inhibit the APC activator Cdc20 when anaphase wait signals are present. For simplicity, only part of the components of the checkpoint is shown in the model.
Mentions: What then could be the mechanism by which Rae1 regulates the activity of the mitotic checkpoint and how may Rae1 be able to compensate for Bub3 haplo-insufficiency? Because Rae1 has been shown to localize to unattached kinetochores at the onset of mitosis (Wang et al., 2001), it is possible that Rae1 might play a role in the production of anaphase wait signals at that position. Given that the checkpoint protein Bub1 also targets to unattached kinetochores in mitosis and can bind to Rae1 (Wang et al., 2001), it is further possible that Rae1 and Bub1 might participate in such signaling events as a protein complex. Interestingly, like Rae1, Bub3 also targets to unattached kinetochores and interacts with Bub1. We have shown that the GLEBS sequence of Bub1 serves as a shared binding motif for Rae1 and Bub3 (Wang et al., 2001). Given that both Rae1–Bub1 and Bub3–Bub1 complexes coexist in prometaphase-arrested HeLa cells (Wang et al., 2001), one possible explanation for the phenotypic similarity between Rae1 and Bub3 haplo-insufficient cells could be that Rae1–Bub1 and Bub3–Bub1 complexes fulfill redundant functions at unattached kinetochores. Correction of the mitotic checkpoint in Bub3 haplo-insufficient cells by overexpression of HA-tagged Rae1 could then simply result from the assembly of “unbound” Bub1 molecules into Rae1–Bub1 complexes that would be capable of performing the functions of the missing Bub3–Bub1 complexes (Fig. 10). Bub3 also interacts with BubR1 (Taylor et al., 1998), and Bub3–BubR1 complexes positioned in the mitotic cytosol seem to play a critical role in inhibiting the APC (Fig. 10) (Sudakin et al., 2001; Tang et al., 2001; Fang, 2002). Because Rae1 does not interact with BubR1 (Wang et al., 2001), the mechanism by which Rae1 overexpression acts to correct Bub3 haplo-insufficient cells is unlikely to involve the formation of compensatory Rae1–BubR1.

Bottom Line: Here we show that haplo-insufficiency of either Rae1 or Bub3 results in a similar phenotype involving mitotic checkpoint defects and chromosome missegregation.We also show that overexpression of Rae1 can correct for Rae1 haplo-insufficiency and, surprisingly, Bub3 haplo-insufficiency.Thus, our data demonstrate a novel function for Rae1 and characterize Rae1 and Bub3 as related proteins with essential, overlapping, and cooperating roles in the mitotic checkpoint.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN 55905, USA.

ABSTRACT
The WD-repeat proteins Rae1 and Bub3 show extensive sequence homology, indicative of functional similarity. However, previous studies have suggested that Rae1 is involved in the mRNA export pathway and Bub3 in the mitotic checkpoint. To determine the in vivo roles of Rae1 and Bub3 in mammals, we generated knockout mice that have these genes deleted individually or in combination. Here we show that haplo-insufficiency of either Rae1 or Bub3 results in a similar phenotype involving mitotic checkpoint defects and chromosome missegregation. We also show that overexpression of Rae1 can correct for Rae1 haplo-insufficiency and, surprisingly, Bub3 haplo-insufficiency. Rae1- and Bub3- mice are embryonic lethal, although cells from these mice did not have a detectable defect in nuclear export of mRNA. Unlike mice, compound haplo-insufficient Rae1/Bub3 mice are viable. However, cells from these mice exhibit much greater rates of premature sister chromatid separation and chromosome missegregation than single haplo-insufficient cells. Finally, we show that mice with mitotic checkpoint defects are more susceptible to dimethylbenzanthrene-induced tumorigenesis than wild-type mice. Thus, our data demonstrate a novel function for Rae1 and characterize Rae1 and Bub3 as related proteins with essential, overlapping, and cooperating roles in the mitotic checkpoint.

Show MeSH
Related in: MedlinePlus