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

Organization of septin rings is not maintained in mid2Δ cells. (A) Wild-type (FC937) and mid2Δ (FC881) cells expressing Spn4p-GFP were imaged for GFP fluorescence using confocal three-dimensional time-lapse microscopy. Spn4p-GFP structures were rendered in three dimensions at each time point. Side (0°) and cross-sectional (90°) views of the Spn4p-GFP medial structures are shown in wild-type (left) and mid2Δ (right) at representative time points. Note that in mid2Δ cells, Spn4p-GFP forms a single ring (0 min), an abnormal washer (3–13 min), and then a disc structure (24 min). Bar, 2 μm. (B) mid2Δ cells expressing Spn4p-YFP (green) and the contractile ring marker Cdc12-CFP (red) were imaged on a wide field microscope and rendered in three dimensions. Spn4p-YFP is present on the membrane behind the contractile ring in a washer structure. (C) Summary of the distribution of septins in wild-type and mid2Δ cells during contractile ring closure.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172768&req=5

fig4: Organization of septin rings is not maintained in mid2Δ cells. (A) Wild-type (FC937) and mid2Δ (FC881) cells expressing Spn4p-GFP were imaged for GFP fluorescence using confocal three-dimensional time-lapse microscopy. Spn4p-GFP structures were rendered in three dimensions at each time point. Side (0°) and cross-sectional (90°) views of the Spn4p-GFP medial structures are shown in wild-type (left) and mid2Δ (right) at representative time points. Note that in mid2Δ cells, Spn4p-GFP forms a single ring (0 min), an abnormal washer (3–13 min), and then a disc structure (24 min). Bar, 2 μm. (B) mid2Δ cells expressing Spn4p-YFP (green) and the contractile ring marker Cdc12-CFP (red) were imaged on a wide field microscope and rendered in three dimensions. Spn4p-YFP is present on the membrane behind the contractile ring in a washer structure. (C) Summary of the distribution of septins in wild-type and mid2Δ cells during contractile ring closure.

Mentions: Because of this similarity in phenotypes, we tested whether mid2Δ cells may have defects in septin organization. We examined septin distribution in living wild-type and mid2Δ cells expressing a Spn4p-GFP fusion construct using time-lapse confocal microscopy. In wild-type cells, septins first appeared in anaphase as a collection of medial dots that were then incorporated into a single medial ring around the circumference of the cell (Fig. 4 A). This single ring then changed into a double ring structure that persisted throughout septation. At the end of septation, septins were present in discrete dots at the new cell ends. During interphase, cells sometimes exhibited small septin dots at the cell ends and also occasionally contained a single bright cytoplasmic motile dot or small ring shaped particle (unpublished data).


Mid2p stabilizes septin rings during cytokinesis in fission yeast.

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

Organization of septin rings is not maintained in mid2Δ cells. (A) Wild-type (FC937) and mid2Δ (FC881) cells expressing Spn4p-GFP were imaged for GFP fluorescence using confocal three-dimensional time-lapse microscopy. Spn4p-GFP structures were rendered in three dimensions at each time point. Side (0°) and cross-sectional (90°) views of the Spn4p-GFP medial structures are shown in wild-type (left) and mid2Δ (right) at representative time points. Note that in mid2Δ cells, Spn4p-GFP forms a single ring (0 min), an abnormal washer (3–13 min), and then a disc structure (24 min). Bar, 2 μm. (B) mid2Δ cells expressing Spn4p-YFP (green) and the contractile ring marker Cdc12-CFP (red) were imaged on a wide field microscope and rendered in three dimensions. Spn4p-YFP is present on the membrane behind the contractile ring in a washer structure. (C) Summary of the distribution of septins in wild-type and mid2Δ cells during contractile ring closure.
© Copyright Policy
Related In: Results  -  Collection

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

fig4: Organization of septin rings is not maintained in mid2Δ cells. (A) Wild-type (FC937) and mid2Δ (FC881) cells expressing Spn4p-GFP were imaged for GFP fluorescence using confocal three-dimensional time-lapse microscopy. Spn4p-GFP structures were rendered in three dimensions at each time point. Side (0°) and cross-sectional (90°) views of the Spn4p-GFP medial structures are shown in wild-type (left) and mid2Δ (right) at representative time points. Note that in mid2Δ cells, Spn4p-GFP forms a single ring (0 min), an abnormal washer (3–13 min), and then a disc structure (24 min). Bar, 2 μm. (B) mid2Δ cells expressing Spn4p-YFP (green) and the contractile ring marker Cdc12-CFP (red) were imaged on a wide field microscope and rendered in three dimensions. Spn4p-YFP is present on the membrane behind the contractile ring in a washer structure. (C) Summary of the distribution of septins in wild-type and mid2Δ cells during contractile ring closure.
Mentions: Because of this similarity in phenotypes, we tested whether mid2Δ cells may have defects in septin organization. We examined septin distribution in living wild-type and mid2Δ cells expressing a Spn4p-GFP fusion construct using time-lapse confocal microscopy. In wild-type cells, septins first appeared in anaphase as a collection of medial dots that were then incorporated into a single medial ring around the circumference of the cell (Fig. 4 A). This single ring then changed into a double ring structure that persisted throughout septation. At the end of septation, septins were present in discrete dots at the new cell ends. During interphase, cells sometimes exhibited small septin dots at the cell ends and also occasionally contained a single bright cytoplasmic motile dot or small ring shaped particle (unpublished data).

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