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ABSTRACT: BACKGROUND INFORMATION: The Kin1 protein kinase of fission yeast, which regulates cell surface cohesiveness during interphase cell growth, is also present at the cell division site during mitosis; however, its function in cell division has remained elusive. RESULTS: In FK506-mediated calcineurin deficient cells, mitosis is extended and ring formation is transiently compromised but septation remains normal. Here we show that Kin1 inhibition in these cells leads to polyseptation and defects in membrane closure. Actomyosin ring disassembly is prevented and ultimately the daughter cells fail to separate. We show that the Pmk1 MAP kinase pathway and the type V myosin MyoΔ act downstream of the cytokinetic function of Kin1. Kin1 inhibition also promotes polyseptation in myo3 , a type II myosin heavy chain mutant defective in ring assembly. In contrast Kin1 inactivation rescues septation in a myosin light chain cdc4-8 thermosensitive mutant. A structure/function analysis of the Kin1 protein sequence identified a novel motif outside the kinase domain that is important for its polarized localization and its catalytic activity. This motif is remarkably conserved in all fungal Kin1 homologues but is absent in related kinases of metazoans. CONCLUSIONS: We conclude that calcineurin and Kin1 activities must be tightly coordinated to link actomyosin ring assembly with septum synthesis and membrane closure and to ensure separation of the daughter cells.
Biology of the Cell 01/2013; · 3.60 Impact Factor
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ABSTRACT: Cell morphogenesis is a complex process that depends on cytoskeleton and membrane organization, intracellular signalling and vesicular trafficking. The rod shape of the fission yeast Schizosaccharomyces pombe and the availability of powerful genetic tools make this species an excellent model to study cell morphology. Here we have investigated the function of the conserved Kin1 kinase. Kin1-GFP associates dynamically with the plasma membrane at sites of active cell surface remodelling and is present in the membrane fraction. Kin1Δ null cells show severe defects in cell wall structure and are unable to maintain a rod shape. To explore Kin1 primary function, we constructed an ATP analogue-sensitive allele kin1-as1. Kin1 inhibition primarily promotes delocalization of plasma membrane-associated markers of actively growing cell surface regions. Kin1 itself is depolarized and its mobility is strongly reduced. Subsequently, amorphous cell wall material accumulates at the cell surface, a phenotype that is dependent on vesicular trafficking, and the cell wall integrity mitogen-activated protein kinase pathway is activated. Deletion of cell wall integrity mitogen-activated protein kinase components reduces kin1Δ hypersensitivity to stresses such as those induced by Calcofluor white and SDS. We propose that Kin1 is required for a tight link between the plasma membrane and the cell wall.
Molecular Microbiology 09/2010; 77(5):1186-202. · 5.01 Impact Factor
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ABSTRACT: Cytokinesis is the last step of the cell cycle, producing two daughter cells inheriting equal genetic information. This process involves the assembly of an actomyosin ring during mitosis. In the fission yeast Schizosaccharomyces pombe, cytokinesis occurs at the geometric cell centre, a position which is defined by the interphase nucleus and the anilin-related Mid1 protein. The pom1Delta, tea1Delta and tea4Delta mutants are defective in restricting Mid1 as a band around the nucleus and misplace the division site. We previously reported that inhibition of the protein kinase Kin1 promoted failure of cytokinesis in pom1Delta and tea1Delta cells but the mechanism involving Kin1 remained elusive. Here we investigated the contribution of Kin1 in cytokinesis. We show that Kin1-GFP has a dynamic cell cycle regulated distribution. Like pom1Delta and tea1Delta, tea4Delta exhibits a strong genetic interaction with kin1Delta. Using a conditional repressible kin1 allele that only alters interphase nuclear centering, we observed that Kin1 downregulation severely compromised actomyosin ring formation and septum synthesis in tea4Delta cells. In addition, nuclear displacement induced either by overexpression of a putative catalytically inactive Kin1 mutant, by chemically mediated microtubule depolymerization or by mutation in the par1Delta gene impaired cytokinesis in tea4Delta but not tea4(+) cells. We propose that nuclear mispositioning exacerbates the tea4Delta, pom1Delta and tea1Delta cell division phenotype. Our work reveal that nuclear centering becomes essential when Pom1/Tea1/Tea4 function is compromised and that Kin1 expression level is a key regulatory element in this situation. Our results suggest the existence of distinct overlapping control mechanisms to ensure efficient cell division.
Cell cycle (Georgetown, Tex.) 09/2009; 8(15):2451-62. · 5.36 Impact Factor
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ABSTRACT: In animal cells and fungi, cytokinesis is achieved by constriction of an actomyosin-based ring assembled during mitosis. The fission yeast Schizosaccharomyces pombe is an excellent model organism for unraveling cell division controls by combining molecular genetics with cell biology approaches. Once spatially defined, the ring assembly site is the place of sequential incorporation of a set of proteins during mitotic progression, most of which are evolutionarily conserved. Then, fission yeast divides medially to produce equally sized daughter cells. In the past years, several studies have explored mechanisms of division site determination. It has been demonstrated that positive signals for division plane positioning originate from the central region. Position of the predivided nucleus and the anilin-related protein Mid1 give spatial cues to establish the place of ring formation. In addition, negative signals controlled by the DYRK Pom1 kinase and emanating from the cell ends restrict ring formation in the central region. This dual system prevents illegitimate cell division outside the centre of the cell and subsequent polyploid cell formation. Recently, it has been shown that the mitotic regulator Cdr2 kinase is intrinsically involved in division plane specification by binding to Mid1 at the cell equator during interphase. Moreover, nuclear-to-cytoplasm shuttling of Mid1 is another independent crucial mechanism that couples nuclear position with the actomyosin ring assembly site late in the G2 phase. Kin1, another kinase that regulates morpho-genesis and intracellular organization, shares an essential function with Pom1 in cytokinesis. Recent advances have also identified distinct pathways involved in completion of CAR formation. Therefore, multiple regulatory mechanisms act in parallel to accurately specify and build up the actomyosin ring at the centre of the cell. Concomitant inhibition of these pathways dramatically affects cytokinesis and cell viability. Here we present these redundant pathways that contribute to faithful distribution of the genetic material into daughter cells.
Cell division: theory, variants and degradation.
