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An anillin homologue, Mid2p, acts during fission yeast cytokinesis to organize the septin ring and promote cell separation.

Tasto JJ, Morrell JL, Gould KL - J. Cell Biol. (2003)

Bottom Line: Simanis. 1996.Mid2p colocalizes with septins, and mid2 Delta cells display disorganized, diffuse septin rings and a cell separation defect similar to septin deletion strains. mid2 gene expression and protein levels fluctuate during the cell cycle in a sep1- and Skp1/Cdc53/F-box (SCF)-dependent manner, respectively, implying that Mid2p activity must be carefully regulated.Overproduction of Mid2p depolarizes cell growth and affects the organization of both the septin and actin cytoskeletons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.

ABSTRACT
Anillin is a conserved protein required for cell division (Field, C.M., and B.M. Alberts. 1995. J. Cell Biol. 131:165-178; Oegema, K., M.S. Savoian, T.J. Mitchison, and C.M. Field. 2000. J. Cell Biol. 150:539-552). One fission yeast homologue of anillin, Mid1p, is necessary for the proper placement of the division site within the cell (Chang, F., A. Woollard, and P. Nurse. 1996. J. Cell Sci. 109(Pt 1):131-142; Sohrmann, M., C. Fankhauser, C. Brodbeck, and V. Simanis. 1996. Genes Dev. 10:2707-2719). Here, we identify and characterize a second fission yeast anillin homologue, Mid2p, which is not orthologous with Mid1p. Mid2p localizes as a single ring in the middle of the cell after anaphase in a septin- and actin-dependent manner and splits into two rings during septation. Mid2p colocalizes with septins, and mid2 Delta cells display disorganized, diffuse septin rings and a cell separation defect similar to septin deletion strains. mid2 gene expression and protein levels fluctuate during the cell cycle in a sep1- and Skp1/Cdc53/F-box (SCF)-dependent manner, respectively, implying that Mid2p activity must be carefully regulated. Overproduction of Mid2p depolarizes cell growth and affects the organization of both the septin and actin cytoskeletons. In the presence of a nondegradable Mid2p fragment, the septin ring is stabilized and cell cycle progression is delayed. These results suggest that Mid2p influences septin ring organization at the site of cell division and its turnover might normally be required to permit septin ring disassembly.

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Septin ring disassembly is delayed by the presence of nondegradable Mid2p. (A) Spn3p–GFP cells (KGY3244) expressing high levels of Mid2p (1–704) or Mid2p (336–704) driven by the nmt1 promoter were fixed with formaldehyde and stained with AlexaFluor®594-phalloidin. Images of actin and Spn3p–GFP were taken separately and also merged. (B) Spn3p–GFP cells expressing high levels of Mid2p (336–704) were fixed in ethanol and the following septin localization patterns were quantified in ∼2,000 cells and compared with cells containing empty vector: None1; Middle2; End(s)3; Both4; or Depolarized5. Bars, 5 μm.
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fig8: Septin ring disassembly is delayed by the presence of nondegradable Mid2p. (A) Spn3p–GFP cells (KGY3244) expressing high levels of Mid2p (1–704) or Mid2p (336–704) driven by the nmt1 promoter were fixed with formaldehyde and stained with AlexaFluor®594-phalloidin. Images of actin and Spn3p–GFP were taken separately and also merged. (B) Spn3p–GFP cells expressing high levels of Mid2p (336–704) were fixed in ethanol and the following septin localization patterns were quantified in ∼2,000 cells and compared with cells containing empty vector: None1; Middle2; End(s)3; Both4; or Depolarized5. Bars, 5 μm.

Mentions: Given that mid2Δ cells had disorganized septin rings, we tested if excess amounts of wild type or the stable form of Mid2p would affect the septin cytoskeleton. Cells overproducing full-length Mid2p from the strong nmt1 promoter grew very slowly, became rounded, and had depolarized actin patches (Fig. 8 A), but did form colonies (unpublished data). In these cells, Spn3p–GFP was detected in aberrant filamentous structures that lacked F-actin, and very few cells were observed undergoing cytokinesis (Fig. 8 A). Overproduction of stable Mid2p (amino acids 336–704; Fig. 7 F) produced slightly elongated, rather than depolarized, cells that also grew very slowly (Fig. 8 A; unpublished data). In this case, septin rings did not disassemble on schedule. Instead, septin rings persisted at the new ends of cells well into the next cell cycle, and prominent remnants of septin structures could even be detected into a third cell division because they were observed at both tips in addition to the middle of the cell (Fig. 8 A).


An anillin homologue, Mid2p, acts during fission yeast cytokinesis to organize the septin ring and promote cell separation.

Tasto JJ, Morrell JL, Gould KL - J. Cell Biol. (2003)

Septin ring disassembly is delayed by the presence of nondegradable Mid2p. (A) Spn3p–GFP cells (KGY3244) expressing high levels of Mid2p (1–704) or Mid2p (336–704) driven by the nmt1 promoter were fixed with formaldehyde and stained with AlexaFluor®594-phalloidin. Images of actin and Spn3p–GFP were taken separately and also merged. (B) Spn3p–GFP cells expressing high levels of Mid2p (336–704) were fixed in ethanol and the following septin localization patterns were quantified in ∼2,000 cells and compared with cells containing empty vector: None1; Middle2; End(s)3; Both4; or Depolarized5. Bars, 5 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172762&req=5

fig8: Septin ring disassembly is delayed by the presence of nondegradable Mid2p. (A) Spn3p–GFP cells (KGY3244) expressing high levels of Mid2p (1–704) or Mid2p (336–704) driven by the nmt1 promoter were fixed with formaldehyde and stained with AlexaFluor®594-phalloidin. Images of actin and Spn3p–GFP were taken separately and also merged. (B) Spn3p–GFP cells expressing high levels of Mid2p (336–704) were fixed in ethanol and the following septin localization patterns were quantified in ∼2,000 cells and compared with cells containing empty vector: None1; Middle2; End(s)3; Both4; or Depolarized5. Bars, 5 μm.
Mentions: Given that mid2Δ cells had disorganized septin rings, we tested if excess amounts of wild type or the stable form of Mid2p would affect the septin cytoskeleton. Cells overproducing full-length Mid2p from the strong nmt1 promoter grew very slowly, became rounded, and had depolarized actin patches (Fig. 8 A), but did form colonies (unpublished data). In these cells, Spn3p–GFP was detected in aberrant filamentous structures that lacked F-actin, and very few cells were observed undergoing cytokinesis (Fig. 8 A). Overproduction of stable Mid2p (amino acids 336–704; Fig. 7 F) produced slightly elongated, rather than depolarized, cells that also grew very slowly (Fig. 8 A; unpublished data). In this case, septin rings did not disassemble on schedule. Instead, septin rings persisted at the new ends of cells well into the next cell cycle, and prominent remnants of septin structures could even be detected into a third cell division because they were observed at both tips in addition to the middle of the cell (Fig. 8 A).

Bottom Line: Simanis. 1996.Mid2p colocalizes with septins, and mid2 Delta cells display disorganized, diffuse septin rings and a cell separation defect similar to septin deletion strains. mid2 gene expression and protein levels fluctuate during the cell cycle in a sep1- and Skp1/Cdc53/F-box (SCF)-dependent manner, respectively, implying that Mid2p activity must be carefully regulated.Overproduction of Mid2p depolarizes cell growth and affects the organization of both the septin and actin cytoskeletons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.

ABSTRACT
Anillin is a conserved protein required for cell division (Field, C.M., and B.M. Alberts. 1995. J. Cell Biol. 131:165-178; Oegema, K., M.S. Savoian, T.J. Mitchison, and C.M. Field. 2000. J. Cell Biol. 150:539-552). One fission yeast homologue of anillin, Mid1p, is necessary for the proper placement of the division site within the cell (Chang, F., A. Woollard, and P. Nurse. 1996. J. Cell Sci. 109(Pt 1):131-142; Sohrmann, M., C. Fankhauser, C. Brodbeck, and V. Simanis. 1996. Genes Dev. 10:2707-2719). Here, we identify and characterize a second fission yeast anillin homologue, Mid2p, which is not orthologous with Mid1p. Mid2p localizes as a single ring in the middle of the cell after anaphase in a septin- and actin-dependent manner and splits into two rings during septation. Mid2p colocalizes with septins, and mid2 Delta cells display disorganized, diffuse septin rings and a cell separation defect similar to septin deletion strains. mid2 gene expression and protein levels fluctuate during the cell cycle in a sep1- and Skp1/Cdc53/F-box (SCF)-dependent manner, respectively, implying that Mid2p activity must be carefully regulated. Overproduction of Mid2p depolarizes cell growth and affects the organization of both the septin and actin cytoskeletons. In the presence of a nondegradable Mid2p fragment, the septin ring is stabilized and cell cycle progression is delayed. These results suggest that Mid2p influences septin ring organization at the site of cell division and its turnover might normally be required to permit septin ring disassembly.

Show MeSH
Related in: MedlinePlus