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1.
Mol Biol Cell ; 12(12): 4044-53, 2001 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11739799

RESUMEN

Myo2 truncations fused to green fluorescent protein (GFP) defined a C-terminal domain essential for the localization of Myo2 to the cytokinetic actin ring (CAR). The localization domain contained two predicted phosphorylation sites. Mutation of serine 1518 to alanine (S(1518)A) abolished Myo2 localization, whereas Myo2 with a glutamic acid at this position (S(1518)E) localized to the CAR. GFP-Myo2 formed rings in the septation initiation kinase (SIN) mutant cdc7-24 at 25 degrees C but not at 36 degrees C. GFP-Myo2S(1518)E rings persisted at 36 degrees C in cdc7-24 but not in another SIN kinase mutant, sid2-250. To further examine the relationship between Myo2 and the SIN pathway, the chromosomal copy of myo2(+) was fused to GFP (strain myo2-gc). Myo2 ring formation was abolished in the double mutants myo2-gc cdc7.24 and myo2-gc sid2-250 at the restrictive temperature. In contrast, activation of the SIN pathway in the double mutant myo2-gc cdc16-116 resulted in the formation of Myo2 rings which subsequently collapsed at 36 degrees C. We conclude that the SIN pathway that controls septation in fission yeast also regulates Myo2 ring formation and contraction. Cdc7 and Sid2 are involved in ring formation, in the case of Cdc7 by phosphorylation of a single serine residue in the Myo2 tail. Other kinases and/or phosphatases may control ring contraction.


Asunto(s)
Actinas/metabolismo , Cadenas Pesadas de Miosina/metabolismo , Miosina Tipo II/metabolismo , Proteínas de Schizosaccharomyces pombe/metabolismo , Schizosaccharomyces/citología , Schizosaccharomyces/metabolismo , División Celular , Proteínas Fluorescentes Verdes , Proteínas Luminiscentes/metabolismo , Mutagénesis Sitio-Dirigida , Cadenas Pesadas de Miosina/genética , Miosina Tipo II/genética , Fosforilación , Estructura Terciaria de Proteína , Proteínas de Schizosaccharomyces pombe/genética , Factores de Tiempo
2.
Curr Biol ; 11(14): 1124-7, 2001 Jul 24.
Artículo en Inglés | MEDLINE | ID: mdl-11509236

RESUMEN

The class V myosins are actin-based motors that move a variety of cellular cargoes [1]. In budding yeast, their activity includes the relocation of a portion of the vacuole from the mother cell to the bud [2, 3]. Fission yeast cells contain numerous (approximately 80) small vacuoles. When S. pombe cells are placed in water, vacuoles fuse in response to osmotic stress [4]. Fission yeast possess two type V myosin genes, myo51(+) and myo52(+) [5]. In a myo51Delta strain, vacuoles were distributed throughout the cell, and mean vacuole diameter was identical to that seen in wild-type cells. When myo51Delta and wild-type cells were placed in water, vacuoles enlarged by fusion. In myo52Delta cells, by contrast, vacuoles were smaller and mostly clustered around the nucleus, and fusion in water was largely inhibited. When cells containing GFP-Myo52 were placed in water, Myo52 was seen to redistribute from the cell poles to the surface of the fusing vacuoles. Vacuole fusion in fission yeast was inhibited by the microtubule drug thiabendazole (TBZ) but not by the actin inhibitor latrunculin B. This is the first demonstration of the involvement of a type V myosin, possibly via an interaction with microtubules, in homotypic membrane fusion.


Asunto(s)
Proteínas de Unión a Calmodulina/metabolismo , Proteínas Fúngicas/metabolismo , Cadenas Ligeras de Miosina/metabolismo , Miosina Tipo V/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Schizosaccharomyces/metabolismo , Proteínas de Unión a Calmodulina/genética , Proteínas Fúngicas/genética , Genes Fúngicos , Fusión de Membrana/fisiología , Proteínas Motoras Moleculares/genética , Proteínas Motoras Moleculares/metabolismo , Mutación , Cadenas Ligeras de Miosina/genética , Miosina Tipo V/genética , Proteínas del Tejido Nervioso/genética , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/ultraestructura , Vacuolas/metabolismo
3.
EMBO J ; 20(6): 1259-70, 2001 Mar 15.
Artículo en Inglés | MEDLINE | ID: mdl-11250892

RESUMEN

Plo1-associated casein kinase activity peaked during mitosis before septation. Phosphatase treatment abolished this activity. Mitotic Plo1 activation had a requirement for prior activation of M-phase promoting factor (MPF), suggesting that Plo1 does not act as a mitotic trigger kinase to initiate MPF activation during mitotic commitment. A link between Plo1 and the septum initiating network (SIN) has been suggested by the inability of plo1 Delta cells to septate and the prolific septation following plo1(+) overexpression. Interphase activation of Spg1, the G protein that modulates SIN activity, induced septation but did not stimulate Plo1-associated kinase activity. Conversely, SIN inactivation did not affect the mitotic stimulation of Plo1-associated kinase activity. plo1.ts4 cells formed a misshapen actin ring, but rarely septated at 36 degrees C. Forced activation of Spg1 enabled plo1.ts4 mutant cells, but not cells with defects in the SIN component Sid2, to convert the actin ring to a septum. The ability of plo1(+) overexpression to induce septation was severely compromised by SIN inactivation. We propose that Plo1 acts before the SIN to control septation.


Asunto(s)
Proteínas de Drosophila , Mitosis , Proteínas Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Schizosaccharomyces/citología , Proteína Quinasa CDC2/metabolismo , Caseína Quinasas , Proteínas de Ciclo Celular/metabolismo , Activación Enzimática , Proteínas Fúngicas/metabolismo , Factor Promotor de Maduración/metabolismo , Fenotipo , ras-GRF1/metabolismo
4.
Nat Cell Biol ; 3(1): E10-2, 2001 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-11146639

RESUMEN

Myosin II regulatory light chains have an important role in the organization and function of the contractile machinery at cytokinesis. Two recent reports provide new insights into these important proteins.


Asunto(s)
Secuencias de Aminoácidos/fisiología , División Celular/fisiología , Cadenas Ligeras de Miosina/metabolismo , Miosinas/metabolismo , Animales , Cadenas Ligeras de Miosina/ultraestructura , Miosinas/ultraestructura , Schizosaccharomyces/citología , Schizosaccharomyces/genética , Schizosaccharomyces/metabolismo
5.
J Cell Sci ; 114(Pt 1): 69-79, 2001 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-11112691

RESUMEN

The fission yeast genome project has identified five myosin genes: one type I myosin, myo1(+), two type II myosins, myo2(+) and myp2(+), and two type V myosins, myo51(+) and myo52(+). Cells deleted for myo51(+) show normal morphology and growth rates whereas deletion of myo52(+) results in a partial loss of cell polarity, slow growth and cytokinetic defects. Combining both deletions in a single strain is phenotypically non-additive, myo52(delta) being epistatic to myo51(delta). Overproduction of Myo51 gives rise to elongated cells which fail to form functional septa whereas overproduction of Myo52 results in branched cells with aberrant septa that fail to cleave. Myo52 localises to the poles of growing cells but during cell division it relocalises to the cell equator as a bar that is bisected by the cytokinetic septum. Myo51 shows no obvious localisation during interphase but at cytokinesis it is associated with the contractile cytokinetic actin ring (CAR). Both myosins are dependent upon an intact actin cytoskeleton for localisation. Myo52 partially colocalises with the (alpha)-glucan synthase Mok1 at the cell tips and to a lesser extent at the septum. Mok1 is delocalised and upregulated in myo52(delta) and myo52(delta) cell walls are resistant to digestion by the cell wall degrading enzyme zymolyase. Thus myo52(+) appears to be involved in the local delivery or positioning of vesicles containing cell wall precursors at the cell tips and has a role in the maturation or cleavage of the septum. Myo51 has a non-essential role in cytokinesis as a component of the cytokinetic actin ring.


Asunto(s)
Actinas/metabolismo , Proteínas Fúngicas/fisiología , Miosinas/fisiología , Schizosaccharomyces/fisiología , Animales , Ciclo Celular , Pared Celular/metabolismo , Citoesqueleto/metabolismo , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Miosinas/genética , Miosinas/metabolismo , Fenotipo
6.
Microsc Res Tech ; 49(2): 152-60, 2000 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-10816254

RESUMEN

Cytokinesis in the fission yeast, Schizosaccharomyces pombe consists of two distinct but overlapping events: the assembly and constriction of a cytokinetic actomyosin ring (CAR) and the formation of a cross wall or septum. These two processes must be spatially and temporally coordinated both with each other and with other cell cycle events, most notably spindle formation and anaphase chromosome segregation. In fission yeast, the CAR contains two unusual type II myosins, Myo2, encoded by the gene myo2(+), and Myp2, encoded by myp2(+). The relationship of these two proteins to each other and their relative contribution to CAR assembly and contraction is largely unknown. Here we review what is known about the role of each myosin in cytokinesis and present some new information concerning their regulation and possible physical interaction.


Asunto(s)
Proteínas Portadoras/metabolismo , División Celular , Proteínas Fúngicas/metabolismo , Cadenas Pesadas de Miosina , Miosina Tipo II , Miosina Tipo V , Miosinas/metabolismo , Proteínas de Saccharomyces cerevisiae , Proteínas de Schizosaccharomyces pombe , Schizosaccharomyces/citología , Actinas/metabolismo , Proteínas Portadoras/genética , Proteínas de Ciclo Celular/metabolismo , Proteínas Fúngicas/genética , Regulación Fúngica de la Expresión Génica , Modelos Biológicos , Miosinas/genética , Proteínas Serina-Treonina Quinasas/metabolismo , Schizosaccharomyces/genética , Schizosaccharomyces/fisiología
7.
Mol Biol Cell ; 10(8): 2771-85, 1999 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-10436027

RESUMEN

Polo kinases execute multiple roles during cell division. The fission yeast polo related kinase Plo1 is required to assemble the mitotic spindle, the prophase actin ring that predicts the site for cytokinesis and for septation after the completion of mitosis (Ohkura et al., 1995; Bahler et al., 1998). We show that Plo1 associates with the mitotic but not interphase spindle pole body (SPB). SPB association of Plo1 is the earliest fission yeast mitotic event recorded to date. SPB association is strong from mitotic commitment to early anaphase B, after which the Plo1 signal becomes very weak and finally disappears upon spindle breakdown. SPB association of Plo1 requires mitosis-promoting factor (MPF) activity, whereas its disassociation requires the activity of the anaphase-promoting complex. The stf1.1 mutation bypasses the usual requirement for the MPF activator Cdc25 (Hudson et al., 1990). Significantly, Plo1 associates inappropriately with the interphase SPB of stf1.1 cells. These data are consistent with the emerging theme from many systems that polo kinases participate in the regulation of MPF to determine the timing of commitment to mitosis and may indicate that pole association is a key aspect of Plo1 function. Plo1 does not associate with the SPB when septation is inappropriately driven by deregulation of the Spg1 pathway and remains SPB associated if septation occurs in the presence of a spindle. Thus, neither Plo1 recruitment to nor its departure from the SPB are required for septation; however, overexpression of plo1+ activates the Spg1 pathway and causes transient Cdc7 recruitment to the SPB and multiple rounds of septation.


Asunto(s)
Proteínas de Drosophila , Proteínas Serina-Treonina Quinasas/metabolismo , Schizosaccharomyces/metabolismo , Proteínas de Soja , Huso Acromático/metabolismo , Complejos de Ubiquitina-Proteína Ligasa , Ciclosoma-Complejo Promotor de la Anafase , Factores de Transcripción con Cremalleras de Leucina de Carácter Básico , Proteína Quinasa CDC2/metabolismo , Proteínas de Ciclo Celular/metabolismo , División Celular/fisiología , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , GTP Fosfohidrolasas/metabolismo , Interfase/fisiología , Ligasas/metabolismo , Factor Promotor de Maduración/metabolismo , Mitosis/fisiología , Fosfoproteínas Fosfatasas/metabolismo , Schizosaccharomyces/citología , Ubiquitina-Proteína Ligasas , Fosfatasas cdc25
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