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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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mid1 and mid2 do not show genetic interactions. (A) Wild-type, mid1Δ, mid2Δ, and mid1Δmid2Δ strains were assayed for growth rates and cellular integrity at 30 and 36°C by growth on agar plates containing phloxin, a dye that stains dead cells. Three independent mid1Δmid2Δ strains are represented in the bottom three streaks of each plate. (B) Cells grown in liquid cultures were stained with Calcofluor to visualize septa. (C) Localization of Mid1p-GFP in mid2Δ cells and localization of Mid2p-GFP in mid1Δ cells.
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fig8: mid1 and mid2 do not show genetic interactions. (A) Wild-type, mid1Δ, mid2Δ, and mid1Δmid2Δ strains were assayed for growth rates and cellular integrity at 30 and 36°C by growth on agar plates containing phloxin, a dye that stains dead cells. Three independent mid1Δmid2Δ strains are represented in the bottom three streaks of each plate. (B) Cells grown in liquid cultures were stained with Calcofluor to visualize septa. (C) Localization of Mid1p-GFP in mid2Δ cells and localization of Mid2p-GFP in mid1Δ cells.

Mentions: Since Mid2p and Mid1p share significant amino acid similarity, we tested whether they may share overlapping functions. Wild-type, single mid1Δ, and mid2Δ mutants, and mid1Δmid2Δ double mutants were assayed for growth and cell integrity at multiple temperatures on agar plates containing phloxin, a red dye that stains dead cells. We also assayed for septum placement defects in cells grown in liquid cultures. In these assays, the phenotype of the mid1Δmid2Δ double mutant was not more severe than that of either single mutant (Fig. 8, A and B). Mid1p-GFP was properly localized as a medial broad band of dots at the cell surface and in a tight ring in mid2Δ mutant cells (Fig. 8 C) (Paoletti and Chang, 2000). Mid2p-GFP was properly localized in single or double rings in the mid1Δ mutant (Fig. 8 D). Thus, together our data suggest that Mid1p and Mid2p do not have overlapping functions and act in different aspects of cytokinesis.


Mid2p stabilizes septin rings during cytokinesis in fission yeast.

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

mid1 and mid2 do not show genetic interactions. (A) Wild-type, mid1Δ, mid2Δ, and mid1Δmid2Δ strains were assayed for growth rates and cellular integrity at 30 and 36°C by growth on agar plates containing phloxin, a dye that stains dead cells. Three independent mid1Δmid2Δ strains are represented in the bottom three streaks of each plate. (B) Cells grown in liquid cultures were stained with Calcofluor to visualize septa. (C) Localization of Mid1p-GFP in mid2Δ cells and localization of Mid2p-GFP in mid1Δ cells.
© Copyright Policy
Related In: Results  -  Collection

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

fig8: mid1 and mid2 do not show genetic interactions. (A) Wild-type, mid1Δ, mid2Δ, and mid1Δmid2Δ strains were assayed for growth rates and cellular integrity at 30 and 36°C by growth on agar plates containing phloxin, a dye that stains dead cells. Three independent mid1Δmid2Δ strains are represented in the bottom three streaks of each plate. (B) Cells grown in liquid cultures were stained with Calcofluor to visualize septa. (C) Localization of Mid1p-GFP in mid2Δ cells and localization of Mid2p-GFP in mid1Δ cells.
Mentions: Since Mid2p and Mid1p share significant amino acid similarity, we tested whether they may share overlapping functions. Wild-type, single mid1Δ, and mid2Δ mutants, and mid1Δmid2Δ double mutants were assayed for growth and cell integrity at multiple temperatures on agar plates containing phloxin, a red dye that stains dead cells. We also assayed for septum placement defects in cells grown in liquid cultures. In these assays, the phenotype of the mid1Δmid2Δ double mutant was not more severe than that of either single mutant (Fig. 8, A and B). Mid1p-GFP was properly localized as a medial broad band of dots at the cell surface and in a tight ring in mid2Δ mutant cells (Fig. 8 C) (Paoletti and Chang, 2000). Mid2p-GFP was properly localized in single or double rings in the mid1Δ mutant (Fig. 8 D). Thus, together our data suggest that Mid1p and Mid2p do not have overlapping functions and act in different aspects of cytokinesis.

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