Limits...
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.

Show MeSH

Related in: MedlinePlus

Mid2p colocalizes with Spn4p. Cells (FC882) expressing Mid2p-YFP (green) and Spn4p-CFP (red) were imaged for YFP and CFP fluorescence. (Top) Cells in late mitosis just after initial assembly of the single septin ring. Some of these cells exhibit septin but not Mid2p staining (left cell). (Middle) Cells during septation with double septin rings. (Bottom) Cells during cell–cell separation and during interphase. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172768&req=5

fig6: Mid2p colocalizes with Spn4p. Cells (FC882) expressing Mid2p-YFP (green) and Spn4p-CFP (red) were imaged for YFP and CFP fluorescence. (Top) Cells in late mitosis just after initial assembly of the single septin ring. Some of these cells exhibit septin but not Mid2p staining (left cell). (Middle) Cells during septation with double septin rings. (Bottom) Cells during cell–cell separation and during interphase. Bar, 10 μm.

Mentions: Next, we tested whether Mid2p colocalizes with septins. We examined the localization of functional Mid2p-GFP or Mid2p-YFP fusions expressed from the chromosomal endogenous mid2+ promoter. Using dual labeling with Mid2p-YFP and Spn4p-CFP constructs, we found that Mid2p and Spn4p colocalized precisely in single and double rings during mitosis (Fig. 6). The two proteins colocalized even during interphase when they were sometimes localized in dots at the cell tip or in a single large cytoplasmic dot. 20% of mitotic or septating cells (n = 176) had Spn4p-CFP present in a single ring but had no detectable Mid2p-YFP (Fig. 6, top). No cells were found with Mid2p-YFP present but Spn4p-CFP absent. Since the cells exhibiting rings of Spn4p without Mid2p were in the initial stages of septin ring localization, these results show that Spn4p may precede Mid2p localization at the septin ring.


Mid2p stabilizes septin rings during cytokinesis in fission yeast.

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

Mid2p colocalizes with Spn4p. Cells (FC882) expressing Mid2p-YFP (green) and Spn4p-CFP (red) were imaged for YFP and CFP fluorescence. (Top) Cells in late mitosis just after initial assembly of the single septin ring. Some of these cells exhibit septin but not Mid2p staining (left cell). (Middle) Cells during septation with double septin rings. (Bottom) Cells during cell–cell separation and during interphase. Bar, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

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

fig6: Mid2p colocalizes with Spn4p. Cells (FC882) expressing Mid2p-YFP (green) and Spn4p-CFP (red) were imaged for YFP and CFP fluorescence. (Top) Cells in late mitosis just after initial assembly of the single septin ring. Some of these cells exhibit septin but not Mid2p staining (left cell). (Middle) Cells during septation with double septin rings. (Bottom) Cells during cell–cell separation and during interphase. Bar, 10 μm.
Mentions: Next, we tested whether Mid2p colocalizes with septins. We examined the localization of functional Mid2p-GFP or Mid2p-YFP fusions expressed from the chromosomal endogenous mid2+ promoter. Using dual labeling with Mid2p-YFP and Spn4p-CFP constructs, we found that Mid2p and Spn4p colocalized precisely in single and double rings during mitosis (Fig. 6). The two proteins colocalized even during interphase when they were sometimes localized in dots at the cell tip or in a single large cytoplasmic dot. 20% of mitotic or septating cells (n = 176) had Spn4p-CFP present in a single ring but had no detectable Mid2p-YFP (Fig. 6, top). No cells were found with Mid2p-YFP present but Spn4p-CFP absent. Since the cells exhibiting rings of Spn4p without Mid2p were in the initial stages of septin ring localization, these results show that Spn4p may precede Mid2p localization at the septin ring.

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