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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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Mid2p localization is dependent on septins and the Mid2p PH domain. (A) spn4Δ cells (FC492) expressing Mid2p-GFP were imaged for GFP fluorescence. Only background fluorescence is observed. (B) Cells expressing only Mid2p-PHΔ were imaged by DIC microscopy. (C) mid2-YFP and mid2-PHΔ–YFP cells were imaged for YFP fluorescence. Only background fluorescence is observed in the mid2-PHΔ–YFP cells. Bar, 10 μm.
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fig7: Mid2p localization is dependent on septins and the Mid2p PH domain. (A) spn4Δ cells (FC492) expressing Mid2p-GFP were imaged for GFP fluorescence. Only background fluorescence is observed. (B) Cells expressing only Mid2p-PHΔ were imaged by DIC microscopy. (C) mid2-YFP and mid2-PHΔ–YFP cells were imaged for YFP fluorescence. Only background fluorescence is observed in the mid2-PHΔ–YFP cells. Bar, 10 μm.

Mentions: We also tested the dependence of Mid2p localization on septins. In spn4Δ cells, Mid2p-GFP was not localized to any specific structure (Fig. 7 A). Western blot showed that Mid2p-GFP was still expressed in spn4Δ cells (unpublished data). As described above, septins initially localize normally in mid2Δ cells. Thus, both the order of localization and localization dependence results suggest that septins first form a single medial ring and that Mid2p associates with the septin ring slightly later in the cell cycle.


Mid2p stabilizes septin rings during cytokinesis in fission yeast.

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

Mid2p localization is dependent on septins and the Mid2p PH domain. (A) spn4Δ cells (FC492) expressing Mid2p-GFP were imaged for GFP fluorescence. Only background fluorescence is observed. (B) Cells expressing only Mid2p-PHΔ were imaged by DIC microscopy. (C) mid2-YFP and mid2-PHΔ–YFP cells were imaged for YFP fluorescence. Only background fluorescence is observed in the mid2-PHΔ–YFP cells. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig7: Mid2p localization is dependent on septins and the Mid2p PH domain. (A) spn4Δ cells (FC492) expressing Mid2p-GFP were imaged for GFP fluorescence. Only background fluorescence is observed. (B) Cells expressing only Mid2p-PHΔ were imaged by DIC microscopy. (C) mid2-YFP and mid2-PHΔ–YFP cells were imaged for YFP fluorescence. Only background fluorescence is observed in the mid2-PHΔ–YFP cells. Bar, 10 μm.
Mentions: We also tested the dependence of Mid2p localization on septins. In spn4Δ cells, Mid2p-GFP was not localized to any specific structure (Fig. 7 A). Western blot showed that Mid2p-GFP was still expressed in spn4Δ cells (unpublished data). As described above, septins initially localize normally in mid2Δ cells. Thus, both the order of localization and localization dependence results suggest that septins first form a single medial ring and that Mid2p associates with the septin ring slightly later in the cell cycle.

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