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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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Mid2p is required for septin ring organization. (A) Cells producing both Mid2p–GFP and Spn1p–CFP (KGY3295) were imaged separately using a YFP/CFP filter set, and these images were also merged. (B) Time-lapse images of Spn3p–GFP in a wild-type background (KGY3244; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). (C) Time-lapse images of Spn3p–GFP in a mid2Δ strain background (KGY3304; see Video 3). (D) Spn3p–GFP (KGY4220) and (E) Mid2p–GFP (KGY4216) were visualized in live ppb1Δ cells. Bars, 5 μm.
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fig6: Mid2p is required for septin ring organization. (A) Cells producing both Mid2p–GFP and Spn1p–CFP (KGY3295) were imaged separately using a YFP/CFP filter set, and these images were also merged. (B) Time-lapse images of Spn3p–GFP in a wild-type background (KGY3244; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). (C) Time-lapse images of Spn3p–GFP in a mid2Δ strain background (KGY3304; see Video 3). (D) Spn3p–GFP (KGY4220) and (E) Mid2p–GFP (KGY4216) were visualized in live ppb1Δ cells. Bars, 5 μm.

Mentions: Because the loss of mid2 produced a strikingly similar phenotype to that of the spn4Δ mutant (Fig. 5 C) (J. Pringle, personal communication; Longtine et al., 1996), and the phenotype of a mid2Δ spn4Δ double mutant strain was similar to either single mutant (Fig. 5 C), it seemed likely that Mid2p and septins were involved in the same step of cell division. We therefore examined if Mid2p depended upon septins for its medial ring association. In spn4Δ cells, Mid2p–GFP was expressed (unpublished data) but failed to localize to the medial ring and was instead distributed throughout the cytoplasm (Fig. 5 D). We next determined whether or not septins and Mid2p colocalized. Images taken from a strain expressing endogenously tagged Mid2p–GFP and Spn1p–CFP show that their localization patterns are indistinguishable (Fig. 6 A). We also tested whether septin localization was affected by the lack of Mid2p function. To perform this experiment, the spn3 locus was modified to encode an Spn3p–GFP fusion protein. This strain was morphologically wild type, implying that the epitope does not disrupt septin function. By time-lapse microscopy, Spn3–GFP was observed to form a single ring, then form two rings, and finally disperse upon the completion of cell separation (Fig. 6 B; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). In a mid2Δ strain, Spn3p–GFP was recruited to the site of cell division in a loosely organized ring and then appeared to spread bilaterally across the septum as a disc over time (Fig. 6 C; see Video 3, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1).


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)

Mid2p is required for septin ring organization. (A) Cells producing both Mid2p–GFP and Spn1p–CFP (KGY3295) were imaged separately using a YFP/CFP filter set, and these images were also merged. (B) Time-lapse images of Spn3p–GFP in a wild-type background (KGY3244; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). (C) Time-lapse images of Spn3p–GFP in a mid2Δ strain background (KGY3304; see Video 3). (D) Spn3p–GFP (KGY4220) and (E) Mid2p–GFP (KGY4216) were visualized in live ppb1Δ cells. Bars, 5 μm.
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fig6: Mid2p is required for septin ring organization. (A) Cells producing both Mid2p–GFP and Spn1p–CFP (KGY3295) were imaged separately using a YFP/CFP filter set, and these images were also merged. (B) Time-lapse images of Spn3p–GFP in a wild-type background (KGY3244; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). (C) Time-lapse images of Spn3p–GFP in a mid2Δ strain background (KGY3304; see Video 3). (D) Spn3p–GFP (KGY4220) and (E) Mid2p–GFP (KGY4216) were visualized in live ppb1Δ cells. Bars, 5 μm.
Mentions: Because the loss of mid2 produced a strikingly similar phenotype to that of the spn4Δ mutant (Fig. 5 C) (J. Pringle, personal communication; Longtine et al., 1996), and the phenotype of a mid2Δ spn4Δ double mutant strain was similar to either single mutant (Fig. 5 C), it seemed likely that Mid2p and septins were involved in the same step of cell division. We therefore examined if Mid2p depended upon septins for its medial ring association. In spn4Δ cells, Mid2p–GFP was expressed (unpublished data) but failed to localize to the medial ring and was instead distributed throughout the cytoplasm (Fig. 5 D). We next determined whether or not septins and Mid2p colocalized. Images taken from a strain expressing endogenously tagged Mid2p–GFP and Spn1p–CFP show that their localization patterns are indistinguishable (Fig. 6 A). We also tested whether septin localization was affected by the lack of Mid2p function. To perform this experiment, the spn3 locus was modified to encode an Spn3p–GFP fusion protein. This strain was morphologically wild type, implying that the epitope does not disrupt septin function. By time-lapse microscopy, Spn3–GFP was observed to form a single ring, then form two rings, and finally disperse upon the completion of cell separation (Fig. 6 B; see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1). In a mid2Δ strain, Spn3p–GFP was recruited to the site of cell division in a loosely organized ring and then appeared to spread bilaterally across the septum as a disc over time (Fig. 6 C; see Video 3, available at http://www.jcb.org/cgi/content/full/jcb.200211126/DC1).

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