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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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Dynamics of the spindle, the chromosome, and Cdc13 at meiosis in the wild type. (A and B) Spindle behavior at MI and MII. Graphs show changes in spindle length. In the graph in B, lengths of the two MII spindles are shown as blue and red lines. (C) An approximate map of GFP-visualized loci on three chromosomes used in this study. (D and E) Behavior of homologous centromeres (cen2; white, arrowheads) and the SPB (yellow) at MI. The graph shows changes in distance between two SPBs (D3) and between one of the SPBs and each centromere (D1 and D2). (F) Behavior of the arm locus (ade8; bottom, white, arrowheads, and graph) and the SPB (yellow) at MI. The graph shows the mean time of sister locus separation. Time 0 is PIII onset. (G) Behavior of sister centromeres (arrowheads) at MII. Arrowheads in enlarged images highlight transient sister centromere separation before anaphase. The graph shows changes in SPB-cen (D1 and D2) and SPB-SPB (D3) distances at MII. (H) Centromeres were visualized by Mis6-GFP and the spindle was visualized by mDsRed-α2-tubulin at MII (8 min before anaphase). (right) Images are enlarged views of Mis6 dots (arrows). (I) Dynamics of Cdc13-GFP at meiosis in the wild type. White lines in images indicate cell shapes. Dotted lines in graphs show boundaries of the spindle phases. Error bars indicate standard deviation. PI, phase I; PII, phase II; PIII, phase III. Bars: (A, B, and D–H) 5 μm; (G, inset) 2 μm.
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fig1: Dynamics of the spindle, the chromosome, and Cdc13 at meiosis in the wild type. (A and B) Spindle behavior at MI and MII. Graphs show changes in spindle length. In the graph in B, lengths of the two MII spindles are shown as blue and red lines. (C) An approximate map of GFP-visualized loci on three chromosomes used in this study. (D and E) Behavior of homologous centromeres (cen2; white, arrowheads) and the SPB (yellow) at MI. The graph shows changes in distance between two SPBs (D3) and between one of the SPBs and each centromere (D1 and D2). (F) Behavior of the arm locus (ade8; bottom, white, arrowheads, and graph) and the SPB (yellow) at MI. The graph shows the mean time of sister locus separation. Time 0 is PIII onset. (G) Behavior of sister centromeres (arrowheads) at MII. Arrowheads in enlarged images highlight transient sister centromere separation before anaphase. The graph shows changes in SPB-cen (D1 and D2) and SPB-SPB (D3) distances at MII. (H) Centromeres were visualized by Mis6-GFP and the spindle was visualized by mDsRed-α2-tubulin at MII (8 min before anaphase). (right) Images are enlarged views of Mis6 dots (arrows). (I) Dynamics of Cdc13-GFP at meiosis in the wild type. White lines in images indicate cell shapes. Dotted lines in graphs show boundaries of the spindle phases. Error bars indicate standard deviation. PI, phase I; PII, phase II; PIII, phase III. Bars: (A, B, and D–H) 5 μm; (G, inset) 2 μm.

Mentions: As a first step toward understanding the SAC function in meiotic anaphase regulation, we characterized meiotic events in wild-type fission yeast cells. Conventional analysis of fixed specimens of cultures synchronously induced to enter meiosis was not suitable for characterization because of poor synchronization of the cultures and the rapid progression of meiosis. To circumvent this problem, we examined the dynamics of the spindle and the chromosome three-dimensionally in individual living cells. Visualization of the spindle using GFP-tagged α2-tubulin showed three distinct phases in spindle elongation at both divisions, as seen in mitosis (Fig. 1, A and B; Nabeshima et al., 1998). A short spindle forms in the first phase (Fig. 1, A and B, PI) and remains relatively constant in length in the second phase (PII); the spindle further elongates and eventually disappears in the third phase (PIII). At MII, the two spindles elongated synchronously with almost identical kinetics (Fig. 1 B, right). The behavior of the MI spindle was consistent with that described by Yamaguchi et al. (2003).


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)

Dynamics of the spindle, the chromosome, and Cdc13 at meiosis in the wild type. (A and B) Spindle behavior at MI and MII. Graphs show changes in spindle length. In the graph in B, lengths of the two MII spindles are shown as blue and red lines. (C) An approximate map of GFP-visualized loci on three chromosomes used in this study. (D and E) Behavior of homologous centromeres (cen2; white, arrowheads) and the SPB (yellow) at MI. The graph shows changes in distance between two SPBs (D3) and between one of the SPBs and each centromere (D1 and D2). (F) Behavior of the arm locus (ade8; bottom, white, arrowheads, and graph) and the SPB (yellow) at MI. The graph shows the mean time of sister locus separation. Time 0 is PIII onset. (G) Behavior of sister centromeres (arrowheads) at MII. Arrowheads in enlarged images highlight transient sister centromere separation before anaphase. The graph shows changes in SPB-cen (D1 and D2) and SPB-SPB (D3) distances at MII. (H) Centromeres were visualized by Mis6-GFP and the spindle was visualized by mDsRed-α2-tubulin at MII (8 min before anaphase). (right) Images are enlarged views of Mis6 dots (arrows). (I) Dynamics of Cdc13-GFP at meiosis in the wild type. White lines in images indicate cell shapes. Dotted lines in graphs show boundaries of the spindle phases. Error bars indicate standard deviation. PI, phase I; PII, phase II; PIII, phase III. Bars: (A, B, and D–H) 5 μm; (G, inset) 2 μm.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
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fig1: Dynamics of the spindle, the chromosome, and Cdc13 at meiosis in the wild type. (A and B) Spindle behavior at MI and MII. Graphs show changes in spindle length. In the graph in B, lengths of the two MII spindles are shown as blue and red lines. (C) An approximate map of GFP-visualized loci on three chromosomes used in this study. (D and E) Behavior of homologous centromeres (cen2; white, arrowheads) and the SPB (yellow) at MI. The graph shows changes in distance between two SPBs (D3) and between one of the SPBs and each centromere (D1 and D2). (F) Behavior of the arm locus (ade8; bottom, white, arrowheads, and graph) and the SPB (yellow) at MI. The graph shows the mean time of sister locus separation. Time 0 is PIII onset. (G) Behavior of sister centromeres (arrowheads) at MII. Arrowheads in enlarged images highlight transient sister centromere separation before anaphase. The graph shows changes in SPB-cen (D1 and D2) and SPB-SPB (D3) distances at MII. (H) Centromeres were visualized by Mis6-GFP and the spindle was visualized by mDsRed-α2-tubulin at MII (8 min before anaphase). (right) Images are enlarged views of Mis6 dots (arrows). (I) Dynamics of Cdc13-GFP at meiosis in the wild type. White lines in images indicate cell shapes. Dotted lines in graphs show boundaries of the spindle phases. Error bars indicate standard deviation. PI, phase I; PII, phase II; PIII, phase III. Bars: (A, B, and D–H) 5 μm; (G, inset) 2 μm.
Mentions: As a first step toward understanding the SAC function in meiotic anaphase regulation, we characterized meiotic events in wild-type fission yeast cells. Conventional analysis of fixed specimens of cultures synchronously induced to enter meiosis was not suitable for characterization because of poor synchronization of the cultures and the rapid progression of meiosis. To circumvent this problem, we examined the dynamics of the spindle and the chromosome three-dimensionally in individual living cells. Visualization of the spindle using GFP-tagged α2-tubulin showed three distinct phases in spindle elongation at both divisions, as seen in mitosis (Fig. 1, A and B; Nabeshima et al., 1998). A short spindle forms in the first phase (Fig. 1, A and B, PI) and remains relatively constant in length in the second phase (PII); the spindle further elongates and eventually disappears in the third phase (PIII). At MII, the two spindles elongated synchronously with almost identical kinetics (Fig. 1 B, right). The behavior of the MI spindle was consistent with that described by Yamaguchi et al. (2003).

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
Related in: MedlinePlus