Updated on 2022/06/30


TOYA, Mika
Faculty of Science and Engineering, Global Center for Science and Engineering
Job title
Associate Professor(without tenure)

Concurrent Post

  • Affiliated organization   Global Education Center

Research Institute

  • 2020

    理工学術院総合研究所   兼任研究員


  • 東京大学   博士(理学)

Professional Memberships






Research Areas

  • Cell biology

Research Interests

  • 細胞骨格

  • 微小管

  • Epithelial cells

  • 分裂酵母

  • 細胞構造・細胞形態と機能


  • Tracheal motile cilia in mice require CAMSAP3 for the formation of central microtubule pair and coordinated beating

    Hiroko Saito, Fumiko Matsukawa-Usami, Toshihiko Fujimori, Toshiya Kimura, Takahiro Ide, Takaki Yamamoto, Tatsuo Shibata, Kenta Onoue, Satoko Okayama, Shigenobu Yonemura, Kazuyo Misaki, Yurina Soba, Yasutaka Kakui, Masamitsu Sato, Mika Toya, Masatoshi Takeichi

    Molecular Biology of the Cell   32 ( 20 ) ar12 - ar12  2021.10  [Refereed]

     View Summary

    CAMSAP3, a protein that controls microtubule dynamics by binding to its minus-end, is localized at proximal regions of the axoneme in tracheal motile cilia. Its dysfunction results in a collapse of the central microtube pair, basal plate disorganization, and uncoordinated beating of multicilia.


  • Simplification of nutritional conditions in transformation procedures for genome editing with the CRISPR/Cas9 system for fission yeast

    Seibun Li, Mika Toya, Masamitsu Sato

    Gene   784   145595 - 145595  2021.06  [Refereed]


  • Dual Impact of a Benzimidazole Resistant β-Tubulin on Microtubule Behavior in Fission Yeast

    Mamika Minagawa, Minamo Shirato, Mika Toya, Masamitsu Sato

    Cells   10 ( 5 ) 1042 - 1042  2021.04  [Refereed]

     View Summary

    The cytoskeleton microtubule consists of polymerized αβ-tubulin dimers and plays essential roles in many cellular events. Reagents that inhibit microtubule behaviors have been developed as antifungal, antiparasitic, and anticancer drugs. Benzimidazole compounds, including thiabendazole (TBZ), carbendazim (MBC), and nocodazole, are prevailing microtubule poisons that target β-tubulin and inhibit microtubule polymerization. The molecular basis, however, as to how the drug acts on β-tubulin remains controversial. Here, we characterize the S. pombe β-tubulin mutant nda3-TB101, which was previously isolated as a mutant resistance to benzimidazole. The mutation site tyrosine at position 50 is located in the interface of two lateral β-tubulin proteins and at the gate of a putative binging pocket for benzimidazole. Our observation revealed two properties of the mutant tubulin. First, the dynamics of cellular microtubules comprising the mutant β-tubulin were stabilized in the absence of benzimidazole. Second, the mutant protein reduced the affinity to benzimidazole in vitro. We therefore conclude that the mutant β-tubulin Nda3-TB101 exerts a dual effect on microtubule behaviors: the mutant β-tubulin stabilizes microtubules and is insensitive to benzimidazole drugs. This notion fine-tunes the current elusive molecular model regarding binding of benzimidazole to β-tubulin.


  • Tell the Difference Between Mitosis and Meiosis: Interplay Between Chromosomes, Cytoskeleton, and Cell Cycle Regulation

    Masamitsu Sato, Yasutaka Kakui, Mika Toya

    Frontiers in Cell and Developmental Biology   9  2021.04  [Refereed]

     View Summary

    Meiosis is a specialized style of cell division conserved in eukaryotes, particularly designed for the production of gametes. A huge number of studies to date have demonstrated how chromosomes behave and how meiotic events are controlled. Yeast substantially contributed to the understanding of the molecular mechanisms of meiosis in the past decades. Recently, evidence began to accumulate to draw a perspective landscape showing that chromosomes and microtubules are mutually influenced: microtubules regulate chromosomes, whereas chromosomes also regulate microtubule behaviors. Here we focus on lessons from recent advancement in genetical and cytological studies of the fission yeast<italic>Schizosaccharomyces pombe</italic>, revealing how chromosomes, cytoskeleton, and cell cycle progression are organized and particularly how these are differentiated in mitosis and meiosis. These studies illuminate that meiosis is strategically designed to fulfill two missions: faithful segregation of genetic materials and production of genetic diversity in descendants through elaboration by meiosis-specific factors in collaboration with general factors.


  • Cyst formation in proximal renal tubules caused by dysfunction of the microtubule minus-end regulator CAMSAP3

    Yuto Mitsuhata, Takaya Abe, Kazuyo Misaki, Yuna Nakajima, Keita Kiriya, Miwa Kawasaki, Hiroshi Kiyonari, Masatoshi Takeichi, Mika Toya, Masamitsu Sato

    Scientific Reports   11 ( 1 )  2021.03  [Refereed]

    Authorship:Corresponding author

     View Summary

    <title>Abstract</title>Epithelial cells organize an ordered array of non-centrosomal microtubules, the minus ends of which are regulated by CAMSAP3. The role of these microtubules in epithelial functions, however, is poorly understood. Here, we show that the kidneys of mice in which<italic>Camsap3</italic>is mutated develop cysts at the proximal convoluted tubules (PCTs). PCTs were severely dilated in the mutant kidneys, and they also exhibited enhanced cell proliferation. In these PCTs, epithelial cells became flattened along with perturbation of microtubule arrays as well as of certain subcellular structures such as interdigitating basal processes. Furthermore, YAP and PIEZO1, which are known as mechanosensitive regulators for cell shaping and proliferation, were activated in these mutant PCT cells. These observations suggest that CAMSAP3-mediated microtubule networks are important for maintaining the proper mechanical properties of PCT cells, and its loss triggers cell deformation and proliferation via activation of mechanosensors, resulting in the dilation of PCTs.


  • Patronin Takes a Shot at Polarity

    Masatoshi Takeichi, Mika Toya

    DEVELOPMENTAL CELL   38 ( 1 ) 12 - 13  2016.07  [Invited]

     View Summary

    To specify the anterior-posterior axis of Drosophila embryos, noncentrosomal microtubules grow out from cortical regions of the oocyte and help transport axis determinants. In this issue of Developmental Cell, Nashchekin et al. (2016) report a Shot- and Patronin-dependent mechanism by which the oocyte cortex produces polarized microtubule arrays.

    DOI PubMed

  • CAMSAP3 orients the apical-to-basal polarity of microtubule arrays in epithelial cells

    Mika Toya, Saeko Kobayashi, Miwa Kawasaki, Go Shioi, Mari Kaneko, Takashi Ishiuchi, Kazuyo Misaki, Wenxiang Meng, Masatoshi Takeichi


     View Summary

    Polarized epithelial cells exhibit a characteristic array of microtubules that are oriented along the apicobasal axis of the cells. The minus-ends of these microtubules face apically, and the plus-ends face toward the basal side. The mechanisms underlying this epithelial-specific microtubule assembly remain unresolved, however. Here, using mouse intestinal cells and human Caco-2 cells, we show that the microtubule minus-end binding protein CAMSAP3 (calmodulin-regulated-spectrin-associated protein 3) plays a pivotal role in orienting the apical-to-basal polarity of microtubules in epithelial cells. In these cells, CAMSAP3 accumulated at the apical cortices, and tethered the longitudinal microtubules to these sites. Camsap3 mutation or depletion resulted in a random orientation of these microtubules; concomitantly, the stereotypic positioning of the nucleus and Golgi apparatus was perturbed. In contrast, the integrity of the plasma membrane was hardly affected, although its structural stability was decreased. Further analysis revealed that the CC1 domain of CAMSAP3 is crucial for its apical localization, and that forced mislocalization of CAMSAP3 disturbs the epithelial architecture. These findings demonstrate that apically localized CAMSAP3 determines the proper orientation of microtubules, and in turn that of organelles, in mature mammalian epithelial cells.

    DOI PubMed

  • Organization of Non-centrosomal Microtubules in Epithelial Cells

    Mika Toya, Masatoshi Takeichi

    CELL STRUCTURE AND FUNCTION   41 ( 2 ) 127 - 135  2016  [Refereed]  [Invited]

     View Summary

    Polarized epithelial cells contain a characteristic array of microtubules in which non-centrosomal microtubules are aligned along the apical-to-basal axis of the cell with their minus ends oriented towards the apical pole. Although this unique orientation of microtubules was discovered in the late 1980s, how this orientation is established remains unresolved partly because of limited information about molecular factors that regulate the minus ends of non-centrosomal microtubules. Recent studies, however, identified novel minus end-associated proteins, revealing mechanisms by which the polarized arrays of microtubules are established in epithelial cells. These studies have also demonstrated the importance of apico-basally orientated microtubules in intra-structural organization of cells. This review focuses on recent progress of our understanding of the molecular basis for epithelium-specific microtubule assembly and function.

    DOI PubMed

  • The UBXN-2/p37/p47 adaptors of CDC-48/p97 regulate mitosis by limiting the centrosomal recruitment of Aurora A

    Elsa Kress, Francoise Schwager, Rene Holtackers, Jonas Seiler, Francois Prodon, Esther Zanin, Annika Eiteneuer, Mika Toya, Asako Sugimoto, Hemmo Meyer, Patrick Meraldi, Monica Gotta

    JOURNAL OF CELL BIOLOGY   201 ( 4 ) 559 - 575  2013.05  [Refereed]

     View Summary

    Coordination of cell cycle events in space and time is crucial to achieve a successful cell division. Here, we demonstrate that UBXN-2, a substrate adaptor of the AAA ATPase Cdc48/p97, is required to coordinate centrosome maturation timing with mitosis. In UBXN-2-depleted Caenorhabditis elegans embryos, centrosomes recruited more AIR-1 (Aurora A), matured precociously, and alignment of the mitotic spindle with the axis of polarity was impaired. UBXN-2 and CDC-48 coimmunoprecipitated with AIR-1 and the spindle alignment defect was partially rescued by co-depleting AIR-1, indicating that UBXN-2 controls these processes via AIR-1. Similarly, depletion in human cells of the UBXN-2 orthologues p37/p47 resulted in an accumulation of Aurora A at centrosomes and a delay in centrosome separation. The latter defect was also rescued by inhibiting Aurora A. We therefore postulate that the role of this adaptor in cell cycle regulation is conserved.

    DOI PubMed

  • The nucleoporin Nup205/NPP-3 is lost near centrosomes at mitotic onset and can modulate the timing of this process in Caenorhabditis elegans embryos

    Virginie Hachet, Coralie Busso, Mika Toya, Asako Sugimoto, Peter Askjaer, Pierre Goenczy

    MOLECULAR BIOLOGY OF THE CELL   23 ( 16 ) 3111 - 3121  2012.08  [Refereed]

     View Summary

    Regulation of mitosis in time and space is critical for proper cell division. We conducted an RNA interference-based modifier screen to identify novel regulators of mitosis in Caenorhabditis elegans embryos. Of particular interest, this screen revealed that the Nup205 nucleoporin NPP-3 can negatively modulate the timing of mitotic onset. Furthermore, we discovered that NPP-3 and nucleoporins that are associated with it are lost from the nuclear envelope (NE) in the vicinity of centrosomes at the onset of mitosis. We demonstrate that centrosomes are both necessary and sufficient for NPP-3 local loss, which also requires the activity of the Aurora-A kinase AIR-1. Our findings taken together support a model in which centrosomes and AIR-1 promote timely onset of mitosis by locally removing NPP-3 and associated nucleoporins from the NE.

    DOI PubMed

  • Pob1 Ensures Cylindrical Cell Shape by Coupling Two Distinct Rho Signaling Events During Secretory Vesicle Targeting

    Kentaro Nakano, Mika Toya, Aki Yoneda, Yukiko Asami, Akira Yamashita, Naomi Kamasawa, Masako Osumi, Masayuki Yamamoto

    TRAFFIC   12 ( 6 ) 726 - 739  2011.06  [Refereed]

     View Summary

    Proper cell morphogenesis requires the co-ordination of cell polarity, cytoskeletal organization and vesicle trafficking. The Schizosaccharomyces pombe mutant pob1-664 has a curious lemon-like shape, the basis of which is not understood. Here, we found abundant vesicle accumulation in these cells, suggesting that Pob1 plays a role in vesicle trafficking. We identified Rho3 as a multicopy suppressor of this phenotype. Because Rho3 function is related to For3, an actin-polymerizing protein, and Sec8, a component of the exocyst complex, we analyzed their functional relationship with Pob1. Pob1 was essential for the formation of actin cables (by interacting with For3) and for the polarized localization of Sec8. Although neither For3 nor Sec8 is essential for polarized growth, their simultaneous disruption prevented tip growth and yielded a lemon-like cell morphology similar to pob1-664. Thus, Pob1 may ensure cylindrical cell shape of S. pombe by coupling actin-mediated vesicle transport and exocyst-mediated vesicle tethering during secretory vesicle targeting.

    DOI PubMed

  • A kinase-independent role for Aurora A in the assembly of mitotic spindle microtubules in Caenorhabditis elegans embryos

    Mika Toya, Masahiro Terasawa, Kayo Nagata, Yumi Tida, Asako Sugimoto

    NATURE CELL BIOLOGY   13 ( 6 ) 708 - U187  2011.06  [Refereed]

     View Summary

    The assembly of a functional mitotic spindle is crucial for achieving successful mitosis. Aurora A kinase is one of the key regulators of mitotic events, including mitotic entry, centrosome maturation and spindle bipolarity(1,2). Caenorhabditis elegans Aurora A (AIR-1) is responsible for the assembly of gamma-tubulin-independent microtubules in early embryos(3); however, the mechanism by which AIR-1 contributes to microtubule assembly during mitosis has been unclear. Here we show by live-cell imaging and RNA-mediated interference (RNAi)-based modulation of gene activity that AIR-1 has a crucial role in the assembly of chromatin-stimulated microtubules that is independent of the gamma-tubulin complex. Surprisingly, the kinase activity of AIR-1 is dispensable for this process. Although the kinase-inactive form of AIR-1 was detected along the microtubules as well as on centrosomes, the kinase-active form of AIR-1 was restricted to centrosomes. Thus, we propose that AIR-1 has a kinase-dependent role at centrosomes and a kinase-independent role for stabilizing spindle microtubules and that coordination of these two roles is crucial for the assembly of mitotic spindles.

    DOI PubMed

  • Caenorhabditis elegans ortholog of the p24/p22 subunit, DNC-3, is essential for the formation of the dynactin complex by bridging DNC-1/p150Glued and DNC-2/dynamitin

    Masahiro Terasawa, Mika Toya, Fumio Motegi, Miyeko Mana, Kuniaki Nakamura, Asako Sugimoto

    GENES TO CELLS   15 ( 11 ) 1145 - 1157  2010.11  [Refereed]

     View Summary

    Dynactin is a multisubunit protein complex required for the activity of cytoplasmic dynein. In Caenorhabditis elegans, although 10 of the 11 dynactin subunits were identified based on the sequence similarities to their orthologs, the p24/p22 subunit has not been detected in the genome. Here, we demonstrate that DNC-3 (W10G11.20) is the functional counterpart of the p24/p22 subunit in C. elegans. RNAi phenotypes and subcellular localization of DNC-3 in early C. elegans embryos were nearly identical to those of the known dynactin components. All other dynactin subunits were co-immunoprecipitated with DNC-3, indicating that DNC-3 is a core component of dynactin. Furthermore, the overall secondary structure of DNC-3 resembles to those of the mammalian and yeast p24/p22. We found that DNC-3 is required for the localization of the DNC-1/p150Glued and DNC-2/dynamitin, the two components of the projection arm of dynactin, to the nuclear envelope of meiotic nuclei in the adult gonad. Moreover, DNC-3 physically interacted with DNC-1 and DNC-2 and significantly enhanced the binding ability between DNC-1 and DNC-2 in vitro. These results suggest that DNC-3 is essential for the formation of the projection arm subcomplex of dynactin.

    DOI PubMed

  • Imaging of Mitotic Spindle Dynamics in Caenorhabditis elegans Embryos

    Mika Toya, Yumi Iida, Asako Sugimoto

    MICROTUBULES: IN VIVO   97   359 - 372  2010  [Refereed]

     View Summary

    Development of the nematode Caenorhabditis elegans is highly reproducible, and the cell division patterns are virtually invariant. Transparency of the eggshell and cells enables the observation of intracellular events with a high temporal and spatial resolution. These unique features, along with the sophisticated genetic techniques, make this organism one of the most attractive model systems for dissecting regulatory mechanisms of dynamic cellular behaviors, such as mitosis, at an organismal level. In this chapter, we describe immunofluorescence and live imaging methods for analyzing mitotic spindle regulation. In particular, we present the use of double- or triple-labeled fluorescent strains for high-resolution two-dimensional and three-dimensional live imaging to analyze dynamic behaviors of mitotic spindles.

    DOI PubMed

  • Visualization of fluorescence-tagged proteins in fission yeast: The analysis of mitotic spindle dynamics using GFP-tubulin under the native promoter

    Masamitsu Sato, Mika Toya, Takashi Toda

    Methods in Molecular Biology   545   185 - 203  2009  [Refereed]

     View Summary

    Mitotic spindle microtubules pull chromosomes toward each pole to generate two daughter cells. Proper spindle formation and function are required to prevent tumorigenesis and cell death. The fission yeast Schizosaccharomyces pombe has been widely used as a model organism to understand the molecular mechanism of mitosis due to its convenience in genetics, molecular biology, and cell biology. The development of fluorescent protein systems and microscopy enables us to investigate the "true" behavior of proteins in living fission yeast cells using a strain with a fluorescence-tagged gene under its native promoter. In this way the level of expression of tagged protein is similar to the level of wild-type nontagged protein. In this chapter we illustrate standard methods to generate strains expressing fluorescently tagged proteins and to observe them under the microscope. Specifically, we introduce a GFP-tubulin strain to analyze the dynamic behavior of spindle microtubules. Observation of GFP-tubulin under its native promoter has illuminated the process of kinetochore-microtubule attachment process in fission yeast. © 2009 Humana Press, a part of Springer Science+Business Media, LLC.

    DOI PubMed

  • [Is spindle formation in fission yeast specific to the species?: from the viewpoint of nuclear transport and spindle pole body].

    Sato M, Toya M, Toda T

    Tanpakushitsu kakusan koso. Protein, nucleic acid, enzyme   53 ( 3 ) 197 - 206  2008.03  [Refereed]


  • gamma-Tubulin complex-mediated anchoring of spindle microtubules to spindle-pole bodies requires Msd1 in fission yeast

    Mika Toya, Masamitsu Sato, Uta Haselmann, Kazuhide Asakawa, Damian Brunner, Claude Antony, Takashi Toda

    NATURE CELL BIOLOGY   9 ( 6 ) 646 - U55  2007.06  [Refereed]

     View Summary

    The anchoring of microtubules to subcellular structures is critical for cell polarity and motility. Although the process of anchoring cytoplasmic microtubules to the centrosome has been studied in some detail(1-4), it is not known how spindle microtubules are anchored to the mitotic centrosome and, particularly, whether anchoring and nucleation of mitotic spindles are functionally separate. Here, we show that a fission yeast coiled-coil protein, Msd1, is required for anchoring the minus end of spindle microtubules to the centrosome equivalent, the spindle-pole body (SPB). msd1 deletion causes spindle microtubules to abnormally extend beyond SPBs, which results in chromosome missegregation. Importantly, this protruding spindle is phenocopied by the amino-terminal deletion mutant of Alp4, a component of the gamma-tubulin complex(5) (gamma-TuC), which lacks the potential Msd1-interacting domain. We propose that Msd1 interacts with gamma-TuC, thereby specifically anchoring the minus end of microtubules to SPBs without affecting microtubule nucleation.

    DOI PubMed

  • Mal3, the fission yeast EB1 homologue, cooperates with Bub1 spindle checkpoint to prevent monopolar attachment

    K Asakawa, M Toya, M Sato, M Kanai, K Kume, T Goshima, MA Garcia, D Hirata, T Toda

    EMBO REPORTS   6 ( 12 ) 1194 - 1200  2005.12  [Refereed]

     View Summary

    Bipolar microtubule attachment is central to genome stability. Here, we investigate the mitotic role of the fission yeast EB1 homologue Mal3. Mal3 shows dynamic inward movement along the spindle, initial emergence at the spindle pole body (SPB) and translocation towards the equatorial plane, followed by sudden disappearance. Deletion of Mal3 results in early mitotic delay, which is dependent on the Bub1, but not the Mad2, spindle checkpoint. Consistently, Bub1, but not Mad2, shows prolonged kinetochore localization. Double mutants between mal3 and a subset of checkpoint mutants, including bub1, bub3, mad3 and mph1, but not mad1 or mad2, show massive chromosome mis-segregation defects. In mal3bub1 mutants, both sister centromeres tend to remain in close proximity to one of the separating SPBs. Further analysis indicates that mis-segregated centromeres are exclusively associated with the mother SPB. Mal3, therefore, has a role in preventing monopolar attachment in cooperation with the Bub1/Bub3/Mad3/Mph1-dependent checkpoint.

    DOI PubMed

  • Identification and functional analysis of the gene for type I myosin in fission yeast

    M Toya, F Motegi, K Nakano, Mabuchi, I, M Yamamoto

    GENES TO CELLS   6 ( 3 ) 187 - 199  2001.03  [Refereed]

     View Summary

    Background: Type I myosin is highly conserved among eukaryotes, and apparently plays important roles in a number of cellular processes. In the budding yeast, two myosin I species have been identified and their role in F-actin assembly has been inferred.
    Results: We cloned the fission yeast myo1 gene, which apparently encoded a myosin I protein. Disruption of myo1 was not lethal, but it caused growth retardation at high and low temperatures, sensitivity to a high concentration of KCl, and aberrance in cell morphology associated with an abnormal distribution of F-actin patches. An abnormal deposition of cell wall materials was also seen. Homothallic myo1 Delta cells could mate, but heterothallic myo1 Delta cells were poor in conjugation. Myo1p was necessary for the encapsulation of spores. The tail domain of Myo1p was pivotal for its function. Calmodulin could bind to Myo1p through the IQ domain at the neck.
    Conclusions: Myo1p appears to control the redistribution of F-actin patches during the cell cycle. Loss of Myo1p function is likely to slow down the actin assembly/disassembly process, which results in a failure of the actin cycle to catch up with other events in both the mitotic and meiotic cell cycles, including extension of the conjugation tubes.


  • Fission yeast Pob1p, which is homologous to budding yeast Boi proteins and exhibits subcellular localization close to actin patches, is essential for cell elongation and separation

    M Toya, Y Iino, M Yamamoto

    MOLECULAR BIOLOGY OF THE CELL   10 ( 8 ) 2745 - 2757  1999.08  [Refereed]

     View Summary

    The fission yeast pob1 gene encodes a protein of 871 amino acids carrying an SH3 domain, a SAM domain, and a PH domain. Gene disruption and construction of a temperature-sensitive pob1 mutant indicated that pob1 is essential for cell growth. Loss of its function leads to quick cessation of cellular elongation. Pob1p is homologous to two functionally redundant Saccharomyces cerevisiae proteins, Boi1p and Boi2p, which are necessary for cell growth and relevant to bud formation. Overexpression of pob1 inhibits cell growth, causing the host cells to become round and swollen. In growing cells, Pob1p locates at cell tips during interphase and translocates near the division plane at cytokinesis. Thus, this protein exhibits intracellular dynamics similar to F-actin patches. However, Pob1p constitutes a layer, rather than patches, at growing cell tips. It generates two split discs flanking the septum at cytokinesis. The pob1-defective cells no longer elongate but swell gradually at the middle, eventually assuming a lemon-like morphology. Analysis using the pob1-ts allele revealed that Pob1p is also essential for cell separation. We speculate that Pob1p is located on growing plasma membrane, possibly through the function of actin patches, and may recruit proteins required for the synthesis of cell wall.


  • Fission yeast protein kinase C gene homologues are required for protoplast regeneration: A functional link between cell wall formation and cell shape control

    Hiromi Kobori, Takashi Toda, Hiroko Yaguchi, Mika Toya, Mitsuhiro Yanagida, Masako Osumi

    Journal of Cell Science   107 ( 5 ) 1131 - 1136  1994.05  [Refereed]

     View Summary

    Two novel protein kinase C (n PKC) gene homologues, pck1+ and pck2+ were isolated from the fission yeast Schizosaccharomyces pombe. We examined the functional differences of pck1+ and pck2+ in cell wall formation and actin organization of S. pombe. Regenerating protoplasts of a wild-type strain, single gene disruptants of pck1+ (Δpck1) and pck2+ (Δpck2) were used as a simple model to examine the functional links between PKC, cell wall formation and actin organization. Protoplasts of the wild type strain and those of Δpck1 reverted to intact cells in osmotically stabilized liquid medium. A close spatial association between new cell wall formation and actin was observed in these two strains. In Δpck2, protoplasts did not revert to intact cells: (1) scarcely any new cell wall material was formed
    (2) actin was not reorganized
    and (3) nuclear division and an increase in the amount of cytoplasm were observed in the regenerating protoplasts. These findings demonstrate that the pck2+ gene has a function essential for protoplast regeneration but the pck1+ gene does not. Involvement of n PKCs in cell wall formation and actin organization was also clarified. The effect of staurosporine (a potent inhibitor of protein kinases) on regenerating protoplasts of the three strains confirmed the assumption that the pck2 protein is an in vivo target of staurosporine in the fission yeast.


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