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Mid2p stabilizes septin rings during cytokinesis in fission yeast.

Berlin A, Paoletti A, Chang F - J. Cell Biol. (2003)

Bottom Line: In wild-type cells, septins assembled first during mitosis in a single ring and during septation developed into double rings that did not contract.No genetic interactions were found between mid2 and the related gene mid1.Thus, these studies identify a new factor responsible for the proper stability and function of septins during cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.

ABSTRACT
Septins are filament-forming proteins with a conserved role in cytokinesis. In the fission yeast Schizosaccharomyces pombe, septin rings appear to be involved primarily in cell-cell separation, a late stage in cytokinesis. Here, we identified a protein Mid2p on the basis of its sequence similarity to S. pombe Mid1p, Saccharomyces cerevisiae Bud4p, and Candida albicans Int1p. Like septin mutants, mid2delta mutants had delays in cell-cell separation. mid2delta mutants were defective in septin organization but not contractile ring closure or septum formation. In wild-type cells, septins assembled first during mitosis in a single ring and during septation developed into double rings that did not contract. In mid2delta cells, septins initially assembled in a single ring but during septation appeared in the cleavage furrow, forming a washer or disc structure. FRAP studies showed that septins are stable in wild-type cells but exchange 30-fold more rapidly in mid2delta cells. Mid2p colocalized with septins and required septins for its localization. A COOH-terminal pleckstrin homology domain of Mid2p was required for its localization and function. No genetic interactions were found between mid2 and the related gene mid1. Thus, these studies identify a new factor responsible for the proper stability and function of septins during cytokinesis.

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mid2Δ and spn4Δ cells have similar cell–cell separation defects. (A) DIC images of representative wild-type (FC937), mid2Δ (FC881), and spn4Δ (FC867) mutant cells grown in rich medium at 30°C to the exponential phase of growth. (B) Numbers of septa in wild-type, mid2Δ, and spn4Δ cells (n > 400). Bar, 10 μm.
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fig2: mid2Δ and spn4Δ cells have similar cell–cell separation defects. (A) DIC images of representative wild-type (FC937), mid2Δ (FC881), and spn4Δ (FC867) mutant cells grown in rich medium at 30°C to the exponential phase of growth. (B) Numbers of septa in wild-type, mid2Δ, and spn4Δ cells (n > 400). Bar, 10 μm.

Mentions: Microscopic examination of mid2Δ cells revealed a significant defect in cell–cell separation in cytokinesis (Fig. 2 A). When grown in rich liquid medium, 16% of asynchronous wild-type cells exhibited a septum, whereas 66% of mid2Δ cells possessed one septum (Fig. 2 B). A small percentage (<5% of cells) had two or three septa (grown in rich medium in exponential phase) and grew in short chains of cells. No cells were seen with more than three septa. Careful microscopic examination of the septa in multiple focal planes using differential interference contrast (DIC) or calcofluor staining suggested that most of the septa were complete. Chains of cells occasionally contained a cell that had lysed, suggesting that these mutants had rare defects in cellular integrity and that cells in each chain were completely separated by membrane and septum. Robust growth rates suggest that these mutants do not have a significant delay in progression of the nuclear cell cycle but have a specific delay of approximately one generation time in digestion of the septum for cell–cell separation.


Mid2p stabilizes septin rings during cytokinesis in fission yeast.

Berlin A, Paoletti A, Chang F - J. Cell Biol. (2003)

mid2Δ and spn4Δ cells have similar cell–cell separation defects. (A) DIC images of representative wild-type (FC937), mid2Δ (FC881), and spn4Δ (FC867) mutant cells grown in rich medium at 30°C to the exponential phase of growth. (B) Numbers of septa in wild-type, mid2Δ, and spn4Δ cells (n > 400). Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172768&req=5

fig2: mid2Δ and spn4Δ cells have similar cell–cell separation defects. (A) DIC images of representative wild-type (FC937), mid2Δ (FC881), and spn4Δ (FC867) mutant cells grown in rich medium at 30°C to the exponential phase of growth. (B) Numbers of septa in wild-type, mid2Δ, and spn4Δ cells (n > 400). Bar, 10 μm.
Mentions: Microscopic examination of mid2Δ cells revealed a significant defect in cell–cell separation in cytokinesis (Fig. 2 A). When grown in rich liquid medium, 16% of asynchronous wild-type cells exhibited a septum, whereas 66% of mid2Δ cells possessed one septum (Fig. 2 B). A small percentage (<5% of cells) had two or three septa (grown in rich medium in exponential phase) and grew in short chains of cells. No cells were seen with more than three septa. Careful microscopic examination of the septa in multiple focal planes using differential interference contrast (DIC) or calcofluor staining suggested that most of the septa were complete. Chains of cells occasionally contained a cell that had lysed, suggesting that these mutants had rare defects in cellular integrity and that cells in each chain were completely separated by membrane and septum. Robust growth rates suggest that these mutants do not have a significant delay in progression of the nuclear cell cycle but have a specific delay of approximately one generation time in digestion of the septum for cell–cell separation.

Bottom Line: In wild-type cells, septins assembled first during mitosis in a single ring and during septation developed into double rings that did not contract.No genetic interactions were found between mid2 and the related gene mid1.Thus, these studies identify a new factor responsible for the proper stability and function of septins during cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.

ABSTRACT
Septins are filament-forming proteins with a conserved role in cytokinesis. In the fission yeast Schizosaccharomyces pombe, septin rings appear to be involved primarily in cell-cell separation, a late stage in cytokinesis. Here, we identified a protein Mid2p on the basis of its sequence similarity to S. pombe Mid1p, Saccharomyces cerevisiae Bud4p, and Candida albicans Int1p. Like septin mutants, mid2delta mutants had delays in cell-cell separation. mid2delta mutants were defective in septin organization but not contractile ring closure or septum formation. In wild-type cells, septins assembled first during mitosis in a single ring and during septation developed into double rings that did not contract. In mid2delta cells, septins initially assembled in a single ring but during septation appeared in the cleavage furrow, forming a washer or disc structure. FRAP studies showed that septins are stable in wild-type cells but exchange 30-fold more rapidly in mid2delta cells. Mid2p colocalized with septins and required septins for its localization. A COOH-terminal pleckstrin homology domain of Mid2p was required for its localization and function. No genetic interactions were found between mid2 and the related gene mid1. Thus, these studies identify a new factor responsible for the proper stability and function of septins during cytokinesis.

Show MeSH
Related in: MedlinePlus