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Assembly of normal actomyosin rings in the absence of Mid1p and cortical nodes in fission yeast.

Huang Y, Yan H, Balasubramanian MK - J. Cell Biol. (2008)

Bottom Line: In this study, we test this model in cells that are unable to assemble cortical nodes.Although the cortical nodes play a role in the timing of ring assembly, we find that they are dispensable for the assembly of orthogonal actomyosin rings.Thus, a mechanism that is independent of cortical nodes is sufficient for the assembly of normal actomyosin rings.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604.

ABSTRACT
Cytokinesis in many eukaryotes depends on the function of an actomyosin contractile ring. The mechanisms regulating assembly and positioning of this ring are not fully understood. The fission yeast Schizosaccharomyces pombe divides using an actomyosin ring and is an attractive organism for the study of cytokinesis. Recent studies in S. pombe (Wu, J.Q., V. Sirotkin, D.R. Kovar, M. Lord, C.C. Beltzner, J.R. Kuhn, and T.D. Pollard. 2006. J. Cell Biol. 174:391-402; Vavylonis, D., J.Q. Wu, S. Hao, B. O'Shaughnessy, and T.D. Pollard. 2008. Science. 319:97-100) have suggested that the assembly of the actomyosin ring is initiated from a series of cortical nodes containing several components of this ring. These studies have proposed that actomyosin interactions bring together the cortical nodes to form a compacted ring structure. In this study, we test this model in cells that are unable to assemble cortical nodes. Although the cortical nodes play a role in the timing of ring assembly, we find that they are dispensable for the assembly of orthogonal actomyosin rings. Thus, a mechanism that is independent of cortical nodes is sufficient for the assembly of normal actomyosin rings.

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Mid1p and associated medial nodes are required for the organization of actomyosin rings in early mitosis. (A and B) cps1-191 and cps1-191 mid1Δ cells expressing Rlc1p-GFP (myosin II ring) and Pcp1p-GFP (SPBs) were imaged by time-lapse microscopy. The SPBs are marked with pink asterisks. The elapsed time is shown in minutes. (C) cps1-191 and cps1-191 mid1Δ cells were fixed and stained with antibodies against tubulin and Cdc4p. Representative images of cells with intermediate length and elongated spindles as well as those with postanaphase arrays (PAA) are shown. (D) Quantitation of orthogonal rings and randomly oriented cables in cps1-191 and cps1-191 mid1Δ cells at various stages of mitosis. At least 50 cells were scored in each category. Bars, 5 μm.
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fig3: Mid1p and associated medial nodes are required for the organization of actomyosin rings in early mitosis. (A and B) cps1-191 and cps1-191 mid1Δ cells expressing Rlc1p-GFP (myosin II ring) and Pcp1p-GFP (SPBs) were imaged by time-lapse microscopy. The SPBs are marked with pink asterisks. The elapsed time is shown in minutes. (C) cps1-191 and cps1-191 mid1Δ cells were fixed and stained with antibodies against tubulin and Cdc4p. Representative images of cells with intermediate length and elongated spindles as well as those with postanaphase arrays (PAA) are shown. (D) Quantitation of orthogonal rings and randomly oriented cables in cps1-191 and cps1-191 mid1Δ cells at various stages of mitosis. At least 50 cells were scored in each category. Bars, 5 μm.

Mentions: Although normal actomyosin rings were assembled in cps1-191 mid1Δ cells, the assembly process appeared to be slower. To characterize ring assembly in cps1-191 mid1Δ cells, we imaged dynamics of myosin II ring assembly and mitosis simultaneously in cells expressing Rlc1p-GFP and Pcp1p-GFP (a spindle pole body [SPB] marker; Flory et al., 2002). In cps1-191 mutants (Fig. 3 A), myosin II ring assembly was initiated soon after separation of SPBs at prometaphase. Organization of a myosin II ring was completed in <10 min (9.7 ± 1.4 min; n = 7 cells) from the time of SPB separation. In contrast, although myosin II cable assembly was initiated soon after SPB separation in cps1-191 mid1Δ cells (Fig. 3 B), organization of normal myosin II rings was accomplished only after full separation of the SPBs to the opposite ends of the cell. Starting at the point of SPB separation, organization of normal myosin II rings took at least twice as long (32.3 ± 19.5 min; n = 8 cells) in cps1-191 mid1Δ cells.


Assembly of normal actomyosin rings in the absence of Mid1p and cortical nodes in fission yeast.

Huang Y, Yan H, Balasubramanian MK - J. Cell Biol. (2008)

Mid1p and associated medial nodes are required for the organization of actomyosin rings in early mitosis. (A and B) cps1-191 and cps1-191 mid1Δ cells expressing Rlc1p-GFP (myosin II ring) and Pcp1p-GFP (SPBs) were imaged by time-lapse microscopy. The SPBs are marked with pink asterisks. The elapsed time is shown in minutes. (C) cps1-191 and cps1-191 mid1Δ cells were fixed and stained with antibodies against tubulin and Cdc4p. Representative images of cells with intermediate length and elongated spindles as well as those with postanaphase arrays (PAA) are shown. (D) Quantitation of orthogonal rings and randomly oriented cables in cps1-191 and cps1-191 mid1Δ cells at various stages of mitosis. At least 50 cells were scored in each category. Bars, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC2600752&req=5

fig3: Mid1p and associated medial nodes are required for the organization of actomyosin rings in early mitosis. (A and B) cps1-191 and cps1-191 mid1Δ cells expressing Rlc1p-GFP (myosin II ring) and Pcp1p-GFP (SPBs) were imaged by time-lapse microscopy. The SPBs are marked with pink asterisks. The elapsed time is shown in minutes. (C) cps1-191 and cps1-191 mid1Δ cells were fixed and stained with antibodies against tubulin and Cdc4p. Representative images of cells with intermediate length and elongated spindles as well as those with postanaphase arrays (PAA) are shown. (D) Quantitation of orthogonal rings and randomly oriented cables in cps1-191 and cps1-191 mid1Δ cells at various stages of mitosis. At least 50 cells were scored in each category. Bars, 5 μm.
Mentions: Although normal actomyosin rings were assembled in cps1-191 mid1Δ cells, the assembly process appeared to be slower. To characterize ring assembly in cps1-191 mid1Δ cells, we imaged dynamics of myosin II ring assembly and mitosis simultaneously in cells expressing Rlc1p-GFP and Pcp1p-GFP (a spindle pole body [SPB] marker; Flory et al., 2002). In cps1-191 mutants (Fig. 3 A), myosin II ring assembly was initiated soon after separation of SPBs at prometaphase. Organization of a myosin II ring was completed in <10 min (9.7 ± 1.4 min; n = 7 cells) from the time of SPB separation. In contrast, although myosin II cable assembly was initiated soon after SPB separation in cps1-191 mid1Δ cells (Fig. 3 B), organization of normal myosin II rings was accomplished only after full separation of the SPBs to the opposite ends of the cell. Starting at the point of SPB separation, organization of normal myosin II rings took at least twice as long (32.3 ± 19.5 min; n = 8 cells) in cps1-191 mid1Δ cells.

Bottom Line: In this study, we test this model in cells that are unable to assemble cortical nodes.Although the cortical nodes play a role in the timing of ring assembly, we find that they are dispensable for the assembly of orthogonal actomyosin rings.Thus, a mechanism that is independent of cortical nodes is sufficient for the assembly of normal actomyosin rings.

View Article: PubMed Central - PubMed

Affiliation: Temasek Life Sciences Laboratory, National University of Singapore, Singapore 117604.

ABSTRACT
Cytokinesis in many eukaryotes depends on the function of an actomyosin contractile ring. The mechanisms regulating assembly and positioning of this ring are not fully understood. The fission yeast Schizosaccharomyces pombe divides using an actomyosin ring and is an attractive organism for the study of cytokinesis. Recent studies in S. pombe (Wu, J.Q., V. Sirotkin, D.R. Kovar, M. Lord, C.C. Beltzner, J.R. Kuhn, and T.D. Pollard. 2006. J. Cell Biol. 174:391-402; Vavylonis, D., J.Q. Wu, S. Hao, B. O'Shaughnessy, and T.D. Pollard. 2008. Science. 319:97-100) have suggested that the assembly of the actomyosin ring is initiated from a series of cortical nodes containing several components of this ring. These studies have proposed that actomyosin interactions bring together the cortical nodes to form a compacted ring structure. In this study, we test this model in cells that are unable to assemble cortical nodes. Although the cortical nodes play a role in the timing of ring assembly, we find that they are dispensable for the assembly of orthogonal actomyosin rings. Thus, a mechanism that is independent of cortical nodes is sufficient for the assembly of normal actomyosin rings.

Show MeSH
Related in: MedlinePlus