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Myosin–cell wall interactions during cytokinesis in fission yeast: a framework for understanding plant cytokinesis?
Cell Biology International
Cell Biology International 27 (2003) 239–240
www.elsevier.com/locate/jnlabr/ycbir
Short communication
Myosin–cell wall interactions during cytokinesis in fission yeast: a framework for understanding plant cytokinesis? Daniel P. Mulvihill, Jeremy S. Hyams * Department of Biology, University College London, Gower Street, London WC1E 6BT, UK Accepted 14 October 2002
Myosins are associated with the division machinery in plants, animals and fungi. In the fission yeast, Schizosaccharomyces pombe, cytokinesis involves a contractile actomyosin ring (CAR). Constriction of the CAR on the inside of the cell membrane is coordinated with the deposition of the septum, the new cell wall that partitions the two newly created daughter cells, on the outside of the cell membrane. S. pombe possesses five myosins, two type II myosins, Myo2 and Myp2, two type V myosins, Myo51 and Myo52, and a single type I myosin, Myo1 (Win et al., 2002). Myo2, Myp2 and Myo51 are components of the cytokinetic actin ring (CAR) while Myo1 and Myo52 are involved in the deposition of the septum. The accumulation of all five myosins at the division plane in M-phase is a function of the septation initiation network (SIN), a signal transduction pathway that couples cytokinesis to mitotic exit. The targets of SIN pathway remain to be defined but probably include Myo2 (Mulvihill et al., 2001) and the 1-3--glucan synthase Cps1 which is involved in the deposition of the septum (Liu et al., 2002). We have developed a new procedure to directly examine the spatial and temporal relationships between CAR formation and contraction and septum formation in living fission yeast cells expressing GFP-tagged Myo2 in combination with the cell wall stain Calcofluor. In wild type cells, CAR contraction is a continuous, smooth process and the centripetal deposition of the septum precisely follows the constricting ring. The dynamics of CAR contraction is identical in cells lacking either Myp2 or Myo51. In the absence of the type V myosin, Myo52, however, CAR contraction is slower and discontinuous. These findings demonstrate the interdependence of CAR contraction and septum deposition and show that * Corresponding author. Tel.: +44-20-7679-7343; fax: +44-20-7679-7343.
Myo52 links the two processes. The class VIII myosins in plants may play a comparable role in the organisation and deposition of new cell wall material at the cell plate (Reichelt et al., 1999). Myo2 and Myp2 have no role other than cytokinesis. The myo2+ is an essential gene. Germinating myo2 spores go through a few cell divisions forming short filaments with septa that fail to cleave (May et al., 1997). Cells lacking Myp2 show only a mild cytokinetic defect (Mulvihill et al., 2000). Myo2 and Myp2 contain 1527 and 2104 amino acids, respectively, the difference being entirely due to the length of the -helical tail. The two type II myosins share common essential and regulatory light chains, Cdc4 and Rlc1, respectively. Myo2 is believed to be a conventional two-headed dimer while Myp2 is thought to be monomeric (Bezanilla and Pollard, 2000). The Myo2 tail contains nine proline residues dispersed throughout the structure whereas the Myp2 tail contains 25 prolines, 19 of which are concentrated at the centre, dividing the tail into two subdomains which are thought to fold back on one another to form an anti-parallel coiled coil (Bezanilla and Pollard, 2000). Since we were unable to find an obvious function for Myp2 we wondered whether other fungi that divide by formation of a cytokinetic septum also possessed a second type II myosin. We therefore screened the genome projects of Aspergillus fumigatus, Neurospora crassa for myosin sequences. In each case three myosin genes were found, one each of myosin types I, II and V. This might represent the minimum number of myosins required to sustain cell function eukaryotic cells other than plants which have their own unique myosin inventory (Reddy and Day, 2001). Inspection of the tails of the type II myosins revealed that both were Myp2-like in both length and in the number and disposition of proline residues. A. fumigatus Myo2 contains 2409 amino acids and has 15 prolines within its
1065-6995/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1065-6995(02)00311-6
240
D.P. Mulvihill, J.S. Hyams / Cell Biology International 27 (2003) 239–240
tail while the numbers for N. crassa Myo2 are 2397 and 11, respectively. In both cases a number of prolines are conspicuously clustered near the centre of the tail. Aspergillus contains homologues of both Spg1 (Harris, 2001) and Cdc7 (Bruno et al., 2001), components of the fission yeast SIN. A Cdc7 homologue is also present in plants, raising the possibility that the control of cyto kinesis has been conserved among walled cells. A major difference between cytokinesis in S. pombe and both Aspergillus and Neurospora is that in the former the septum cleaves while in the latter it does not. Our current model is that in filamentous fungi a CAR containing only Myp2 is sufficient to guide the septum such that it creates an effective partition between newly created cytoplasmic compartments which remain attached. In unicellular fungi, on the other hand, a CAR containing only both Myo2 and Myp2 is required to physically separate daughter cells. The phenotype of myo2 cells is consistent with such a view.
References Bezanilla M, Pollard TD. Myosin-II tails confer unique functions in Schizosaccharomyces pombe: characterization of a novel myosin-II tail. Mol Biol Cell 2000;11:79–91.
Bruno KS, Morrell JL, Hamer JE, Staiger CJ. SEPH, a Cdc7p orthologue from Aspergillus nidulans, functions upstream of actin ring formation during cytokinesis. Mol Microbiol 2001; 42:3–12. Harris SD. Septum formation in Aspergillus nidulans. Curr Opin Microbiol 2001;4:736–9. Liu J, Tang X, Wang H, Oliferenko S, Balasubramanian MK. The localization of the integral membrane protein Cps1p to the cell division site is dependent on the actomyosin ring and the septationinducing network in Schizosaccharomyces pombe. Mol Biol Cell 2002;13:989–1000. May KM, Watts FZ, Jones N, Hyams JS. A type II myosin involved in cytokinesis in the fission yeast, Schizosaccharomyces pombe. Cell Motil Cytoskel 1997;38:385–96. Mulvihill DP, Barretto C, Hyams JS. Localisation of the fission yeast type II myosin, Myo2, to the cytokinetic actin ring is regulated by phosphorylation of a C-terminal coiled coil domain and requires a functional septation initiation network. Mol Biol Cell 2001; 12:4044–53. Mulvihill DP, Win TZ, Pack TP, Hyams JS. Cytokinesis in fission yeast: a myosin pas de deux. In: Fukui Y, editor. The biology of cytokinesis. Microsc Res Tech 2000;49:155–60. Reddy ASN, Day IS. Analysis of the myosins encoded in the recently completed Arabidopsis thaliana genome sequence. Genome Biol 2001;2:0024.1–24.17. Reichelt S, Knight AE, Hodge TP, Baluska F, Samaj J, Volkmann D et al. Characterization of the unconventional myosin VIII in plant cells and its localization at the post-cytokinetic cell wall. Plant J 1999;19:555–67. Win TZ, Mulvihill DP, Hyams JS. Take five: a myosin class act in fission yeast. Cell Motil Cytoskel 2002;51:53–6.
Cell Biology International 27 (2003) 239–240
www.elsevier.com/locate/jnlabr/ycbir
Short communication
Myosin–cell wall interactions during cytokinesis in fission yeast: a framework for understanding plant cytokinesis? Daniel P. Mulvihill, Jeremy S. Hyams * Department of Biology, University College London, Gower Street, London WC1E 6BT, UK Accepted 14 October 2002
Myosins are associated with the division machinery in plants, animals and fungi. In the fission yeast, Schizosaccharomyces pombe, cytokinesis involves a contractile actomyosin ring (CAR). Constriction of the CAR on the inside of the cell membrane is coordinated with the deposition of the septum, the new cell wall that partitions the two newly created daughter cells, on the outside of the cell membrane. S. pombe possesses five myosins, two type II myosins, Myo2 and Myp2, two type V myosins, Myo51 and Myo52, and a single type I myosin, Myo1 (Win et al., 2002). Myo2, Myp2 and Myo51 are components of the cytokinetic actin ring (CAR) while Myo1 and Myo52 are involved in the deposition of the septum. The accumulation of all five myosins at the division plane in M-phase is a function of the septation initiation network (SIN), a signal transduction pathway that couples cytokinesis to mitotic exit. The targets of SIN pathway remain to be defined but probably include Myo2 (Mulvihill et al., 2001) and the 1-3--glucan synthase Cps1 which is involved in the deposition of the septum (Liu et al., 2002). We have developed a new procedure to directly examine the spatial and temporal relationships between CAR formation and contraction and septum formation in living fission yeast cells expressing GFP-tagged Myo2 in combination with the cell wall stain Calcofluor. In wild type cells, CAR contraction is a continuous, smooth process and the centripetal deposition of the septum precisely follows the constricting ring. The dynamics of CAR contraction is identical in cells lacking either Myp2 or Myo51. In the absence of the type V myosin, Myo52, however, CAR contraction is slower and discontinuous. These findings demonstrate the interdependence of CAR contraction and septum deposition and show that * Corresponding author. Tel.: +44-20-7679-7343; fax: +44-20-7679-7343.
Myo52 links the two processes. The class VIII myosins in plants may play a comparable role in the organisation and deposition of new cell wall material at the cell plate (Reichelt et al., 1999). Myo2 and Myp2 have no role other than cytokinesis. The myo2+ is an essential gene. Germinating myo2 spores go through a few cell divisions forming short filaments with septa that fail to cleave (May et al., 1997). Cells lacking Myp2 show only a mild cytokinetic defect (Mulvihill et al., 2000). Myo2 and Myp2 contain 1527 and 2104 amino acids, respectively, the difference being entirely due to the length of the -helical tail. The two type II myosins share common essential and regulatory light chains, Cdc4 and Rlc1, respectively. Myo2 is believed to be a conventional two-headed dimer while Myp2 is thought to be monomeric (Bezanilla and Pollard, 2000). The Myo2 tail contains nine proline residues dispersed throughout the structure whereas the Myp2 tail contains 25 prolines, 19 of which are concentrated at the centre, dividing the tail into two subdomains which are thought to fold back on one another to form an anti-parallel coiled coil (Bezanilla and Pollard, 2000). Since we were unable to find an obvious function for Myp2 we wondered whether other fungi that divide by formation of a cytokinetic septum also possessed a second type II myosin. We therefore screened the genome projects of Aspergillus fumigatus, Neurospora crassa for myosin sequences. In each case three myosin genes were found, one each of myosin types I, II and V. This might represent the minimum number of myosins required to sustain cell function eukaryotic cells other than plants which have their own unique myosin inventory (Reddy and Day, 2001). Inspection of the tails of the type II myosins revealed that both were Myp2-like in both length and in the number and disposition of proline residues. A. fumigatus Myo2 contains 2409 amino acids and has 15 prolines within its
1065-6995/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1065-6995(02)00311-6
240
D.P. Mulvihill, J.S. Hyams / Cell Biology International 27 (2003) 239–240
tail while the numbers for N. crassa Myo2 are 2397 and 11, respectively. In both cases a number of prolines are conspicuously clustered near the centre of the tail. Aspergillus contains homologues of both Spg1 (Harris, 2001) and Cdc7 (Bruno et al., 2001), components of the fission yeast SIN. A Cdc7 homologue is also present in plants, raising the possibility that the control of cyto kinesis has been conserved among walled cells. A major difference between cytokinesis in S. pombe and both Aspergillus and Neurospora is that in the former the septum cleaves while in the latter it does not. Our current model is that in filamentous fungi a CAR containing only Myp2 is sufficient to guide the septum such that it creates an effective partition between newly created cytoplasmic compartments which remain attached. In unicellular fungi, on the other hand, a CAR containing only both Myo2 and Myp2 is required to physically separate daughter cells. The phenotype of myo2 cells is consistent with such a view.
References Bezanilla M, Pollard TD. Myosin-II tails confer unique functions in Schizosaccharomyces pombe: characterization of a novel myosin-II tail. Mol Biol Cell 2000;11:79–91.
Bruno KS, Morrell JL, Hamer JE, Staiger CJ. SEPH, a Cdc7p orthologue from Aspergillus nidulans, functions upstream of actin ring formation during cytokinesis. Mol Microbiol 2001; 42:3–12. Harris SD. Septum formation in Aspergillus nidulans. Curr Opin Microbiol 2001;4:736–9. Liu J, Tang X, Wang H, Oliferenko S, Balasubramanian MK. The localization of the integral membrane protein Cps1p to the cell division site is dependent on the actomyosin ring and the septationinducing network in Schizosaccharomyces pombe. Mol Biol Cell 2002;13:989–1000. May KM, Watts FZ, Jones N, Hyams JS. A type II myosin involved in cytokinesis in the fission yeast, Schizosaccharomyces pombe. Cell Motil Cytoskel 1997;38:385–96. Mulvihill DP, Barretto C, Hyams JS. Localisation of the fission yeast type II myosin, Myo2, to the cytokinetic actin ring is regulated by phosphorylation of a C-terminal coiled coil domain and requires a functional septation initiation network. Mol Biol Cell 2001; 12:4044–53. Mulvihill DP, Win TZ, Pack TP, Hyams JS. Cytokinesis in fission yeast: a myosin pas de deux. In: Fukui Y, editor. The biology of cytokinesis. Microsc Res Tech 2000;49:155–60. Reddy ASN, Day IS. Analysis of the myosins encoded in the recently completed Arabidopsis thaliana genome sequence. Genome Biol 2001;2:0024.1–24.17. Reichelt S, Knight AE, Hodge TP, Baluska F, Samaj J, Volkmann D et al. Characterization of the unconventional myosin VIII in plant cells and its localization at the post-cytokinetic cell wall. Plant J 1999;19:555–67. Win TZ, Mulvihill DP, Hyams JS. Take five: a myosin class act in fission yeast. Cell Motil Cytoskel 2002;51:53–6.