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Spindle checkpoint activation at meiosis I advances anaphase II onset via meiosis-specific APC/C regulation.

Yamamoto A, Kitamura K, Hihara D, Hirose Y, Katsuyama S, Hiraoka Y - J. Cell Biol. (2008)

Bottom Line: Furthermore, anaphase onset was advanced and the SAC effect was reduced at meiosis II.The advancement of anaphase onset depended on a meiosis-specific, Cdc20-related factor, Fzr1/Mfr1, which contributed to anaphase cyclin decline and anaphase onset and was inefficiently inhibited by the SAC.Our findings show that impacts of SAC activation are not confined to a single division at meiosis due to meiosis-specific APC/C regulation, which has probably been evolved for execution of two meiotic divisions.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Shizuoka University, Suruga-ku, Shizuoka 422-8529, Japan. sayamam@ipc.shizuoka.ac.jp

ABSTRACT
During mitosis, the spindle assembly checkpoint (SAC) inhibits the Cdc20-activated anaphase-promoting complex/cyclosome (APC/C(Cdc20)), which promotes protein degradation, and delays anaphase onset to ensure accurate chromosome segregation. However, the SAC function in meiotic anaphase regulation is poorly understood. Here, we examined the SAC function in fission yeast meiosis. As in mitosis, a SAC factor, Mad2, delayed anaphase onset via Slp1 (fission yeast Cdc20) when chromosomes attach to the spindle improperly. However, when the SAC delayed anaphase I, the interval between meiosis I and II shortened. Furthermore, anaphase onset was advanced and the SAC effect was reduced at meiosis II. The advancement of anaphase onset depended on a meiosis-specific, Cdc20-related factor, Fzr1/Mfr1, which contributed to anaphase cyclin decline and anaphase onset and was inefficiently inhibited by the SAC. Our findings show that impacts of SAC activation are not confined to a single division at meiosis due to meiosis-specific APC/C regulation, which has probably been evolved for execution of two meiotic divisions.

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Functional relationship of Mes1 with Fzr1 and Slp1. (A) The population of cells that underwent MI and MII. MI and MII were judged by the formation of the MI and MII spindles, respectively. 21, 18, and 17 cells were examined for the wild type, mes1, and other mutant strains, respectively. (B) Duration of the spindle phases in the mes1 mutants. Wt, wild type. *, results of 4 spindles; **, results of 10 spindles. Error bars indicate standard deviation.
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fig5: Functional relationship of Mes1 with Fzr1 and Slp1. (A) The population of cells that underwent MI and MII. MI and MII were judged by the formation of the MI and MII spindles, respectively. 21, 18, and 17 cells were examined for the wild type, mes1, and other mutant strains, respectively. (B) Duration of the spindle phases in the mes1 mutants. Wt, wild type. *, results of 4 spindles; **, results of 10 spindles. Error bars indicate standard deviation.

Mentions: The critical role of Fzr1 in the meiotic progression was further supported by its relationship with a meiosis-specific factor, Mes1, that inhibits APC/CSlp1 to initiate MII. MII is not initiated in mes1 cells, but reduction of the APC/CSlp1 activity by an slp1-362 mutation restores MII in these cells (Izawa et al., 2005). Interestingly, it was also reported that Mes1 inhibits Fzr1 as well as Slp1 from interacting with Cdc13 in vitro. If APC/CFzr1 functions and is inhibited by Mes1 at anaphase I in vivo, the Fzr1 depletion may restore MII in the mes1 cells, as does the slp1-362 mutation. We examined this possibility by monitoring the spindle behavior in individual cells. Consistent with previous findings, the majority of the Mes1-lacking cells underwent only MI, and the population of the cells that underwent MI and MII was only ∼20% (Fig. 5 A, mes1). Introduction of the slp1-362 mutation restored MII in the Mes1-lacking cells, resulting in an increase in the population to ∼60% (Fig. 5 A, mes1 slp1). These results support the notion that Mes1 inhibits APC/CSlp1 to initiate MII. Importantly, the Fzr1 depletion restored MII more efficiently (Fig. 5 A, mes1 fzr1; Izawa, D., and M. Yamamoto, personal communication). These results suggest that Mes1 also inhibits APC/CFzr1 to initiate MII and that APC/CFzr1 degrades Cdc13 at anaphase I. The lower restoration efficiency of slp1-362 is not caused by metaphase arrest induced by the slp1-362 mutation because metaphase arrest was eliminated in the mes1 slp1 cells (Fig. 5 B, meiosis I), and this may rather reflect the remaining weak activity of Slp1 in the slp1-362 mutant or the distinct role of Slp1 in MII initiation. In the mes1 background, in addition, the Fzr1 depletion additively delayed anaphase II onset together with the slp1 mutation (Fig. 5 B, meiosis II), which supports the notion that Fzr1 contributes to anaphase. However, such an effect was not observed at MI (Fig. 5 B, meiosis I). This may mean that contribution of Fzr1 to anaphase is different at MI and MII.


Spindle checkpoint activation at meiosis I advances anaphase II onset via meiosis-specific APC/C regulation.

Yamamoto A, Kitamura K, Hihara D, Hirose Y, Katsuyama S, Hiraoka Y - J. Cell Biol. (2008)

Functional relationship of Mes1 with Fzr1 and Slp1. (A) The population of cells that underwent MI and MII. MI and MII were judged by the formation of the MI and MII spindles, respectively. 21, 18, and 17 cells were examined for the wild type, mes1, and other mutant strains, respectively. (B) Duration of the spindle phases in the mes1 mutants. Wt, wild type. *, results of 4 spindles; **, results of 10 spindles. Error bars indicate standard deviation.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2483520&req=5

fig5: Functional relationship of Mes1 with Fzr1 and Slp1. (A) The population of cells that underwent MI and MII. MI and MII were judged by the formation of the MI and MII spindles, respectively. 21, 18, and 17 cells were examined for the wild type, mes1, and other mutant strains, respectively. (B) Duration of the spindle phases in the mes1 mutants. Wt, wild type. *, results of 4 spindles; **, results of 10 spindles. Error bars indicate standard deviation.
Mentions: The critical role of Fzr1 in the meiotic progression was further supported by its relationship with a meiosis-specific factor, Mes1, that inhibits APC/CSlp1 to initiate MII. MII is not initiated in mes1 cells, but reduction of the APC/CSlp1 activity by an slp1-362 mutation restores MII in these cells (Izawa et al., 2005). Interestingly, it was also reported that Mes1 inhibits Fzr1 as well as Slp1 from interacting with Cdc13 in vitro. If APC/CFzr1 functions and is inhibited by Mes1 at anaphase I in vivo, the Fzr1 depletion may restore MII in the mes1 cells, as does the slp1-362 mutation. We examined this possibility by monitoring the spindle behavior in individual cells. Consistent with previous findings, the majority of the Mes1-lacking cells underwent only MI, and the population of the cells that underwent MI and MII was only ∼20% (Fig. 5 A, mes1). Introduction of the slp1-362 mutation restored MII in the Mes1-lacking cells, resulting in an increase in the population to ∼60% (Fig. 5 A, mes1 slp1). These results support the notion that Mes1 inhibits APC/CSlp1 to initiate MII. Importantly, the Fzr1 depletion restored MII more efficiently (Fig. 5 A, mes1 fzr1; Izawa, D., and M. Yamamoto, personal communication). These results suggest that Mes1 also inhibits APC/CFzr1 to initiate MII and that APC/CFzr1 degrades Cdc13 at anaphase I. The lower restoration efficiency of slp1-362 is not caused by metaphase arrest induced by the slp1-362 mutation because metaphase arrest was eliminated in the mes1 slp1 cells (Fig. 5 B, meiosis I), and this may rather reflect the remaining weak activity of Slp1 in the slp1-362 mutant or the distinct role of Slp1 in MII initiation. In the mes1 background, in addition, the Fzr1 depletion additively delayed anaphase II onset together with the slp1 mutation (Fig. 5 B, meiosis II), which supports the notion that Fzr1 contributes to anaphase. However, such an effect was not observed at MI (Fig. 5 B, meiosis I). This may mean that contribution of Fzr1 to anaphase is different at MI and MII.

Bottom Line: Furthermore, anaphase onset was advanced and the SAC effect was reduced at meiosis II.The advancement of anaphase onset depended on a meiosis-specific, Cdc20-related factor, Fzr1/Mfr1, which contributed to anaphase cyclin decline and anaphase onset and was inefficiently inhibited by the SAC.Our findings show that impacts of SAC activation are not confined to a single division at meiosis due to meiosis-specific APC/C regulation, which has probably been evolved for execution of two meiotic divisions.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Shizuoka University, Suruga-ku, Shizuoka 422-8529, Japan. sayamam@ipc.shizuoka.ac.jp

ABSTRACT
During mitosis, the spindle assembly checkpoint (SAC) inhibits the Cdc20-activated anaphase-promoting complex/cyclosome (APC/C(Cdc20)), which promotes protein degradation, and delays anaphase onset to ensure accurate chromosome segregation. However, the SAC function in meiotic anaphase regulation is poorly understood. Here, we examined the SAC function in fission yeast meiosis. As in mitosis, a SAC factor, Mad2, delayed anaphase onset via Slp1 (fission yeast Cdc20) when chromosomes attach to the spindle improperly. However, when the SAC delayed anaphase I, the interval between meiosis I and II shortened. Furthermore, anaphase onset was advanced and the SAC effect was reduced at meiosis II. The advancement of anaphase onset depended on a meiosis-specific, Cdc20-related factor, Fzr1/Mfr1, which contributed to anaphase cyclin decline and anaphase onset and was inefficiently inhibited by the SAC. Our findings show that impacts of SAC activation are not confined to a single division at meiosis due to meiosis-specific APC/C regulation, which has probably been evolved for execution of two meiotic divisions.

Show MeSH