Genetic and morphological evidence for two parallel pathways of cell-cycle-coupled cytokinesis inDictyostelium

Myosin-II-null cells of Dictyostelium discoideum cannot divide in suspension, consistent with the dogma that myosin II drives constriction of the cleavage furrow and, consequently, cytokinesis (cytokinesis A). Nonetheless, when grown on substrates, these cells exhibit efficient,cell-cycle-coupled division, suggesting that they possess a novel,myosin-II-independent, adhesion-dependent method of cytokinesis (cytokinesis B). Here we show that double mutants lacking myosin II and either AmiA or coronin, both of which are implicated in cytokinesis B, are incapable of cell-cycle-coupled cytokinesis. These double mutants multiplied mainly by cytokinesis C, a third, inefficient, method of cell division, which requires substrate adhesion and is independent of cell cycle progression. In contrast,double mutants lacking AmiA and coronin were no sicker than each of the single mutants, indicating that the severe defects of myosin II-/AmiA- or myosin II-/coronin-mutants are not simple additive effects of two mutations. We take this as genetic evidence for two parallel pathways both of which lead to cell-cycle-coupled cytokinesis. This conclusion is supported by differences in morphological changes during cytokinesis in the mutant cell lines.

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Differential Modulation and Subsequent Blockade of Mitogenic Signaling and Cell Cycle Progression by Pasteurella multocida Toxin

Infection and Immunity ◽

10.1128/iai.68.8.4531-4538.2000 ◽

2000 ◽

Vol 68 (8) ◽

pp. 4531-4538 ◽

Cited By ~ 28

Author(s):

Brenda A. Wilson ◽

Lyaylya R. Aminova ◽

Virgilio G. Ponferrada ◽

Mengfei Ho

Keyword(s):

Cell Cycle ◽

Cell Cycle Progression ◽

Pasteurella Multocida ◽

Morphological Changes ◽

Cell Types ◽

Vero Cells ◽

3T3 Cells ◽

Mitogenic Response ◽

Cycle Progression ◽

Swiss 3T3

ABSTRACT The intracellularly acting protein toxin of Pasteurella multocida (PMT) causes numerous effects in cells, including activation of inositol 1,4,5-trisphosphate (IP3) signaling, Ca2+ mobilization, protein phosphorylation, morphological changes, and DNA synthesis. The direct intracellular target of PMT responsible for activation of the IP3 pathway is the Gq/11α-protein, which stimulates phospholipase C (PLC) β1. The relationship between PMT-mediated activation of the Gq/11-PLC-IP3pathway and its ability to promote mitogenesis and cellular proliferation is not clear. PMT stimulation of p42/p44 mitogen-activated protein kinase occurs upstream via Gq/11-dependent transactivation of the epidermal growth factor receptor. We have further characterized the effects of PMT on the downstream mitogenic response and cell cycle progression in Swiss 3T3 and Vero cells. PMT treatment caused dramatic morphological changes in both cell lines. In Vero cells, limited multinucleation, nuclear fragmentation, and disruption of cytokinesis were also observed; however, a strong mitogenic response occurred only with Swiss 3T3 cells. Significantly, this mitogenic response was not sustained. Cell cycle analysis revealed that after the initial mitogenic response to PMT, both cell types subsequently arrested primarily in G1and became unresponsive to further PMT treatment. In Swiss 3T3 cells, PMT induced up-regulation of c-Myc; cyclins D1, D2, D3, and E; p21; PCNA; and the Rb proteins, p107 and p130. In Vero cells, PMT failed to up-regulate PCNA and cyclins D3 and E. We also found that the initial PMT-mediated up-regulation of several of these signaling proteins was not sustained, supporting the subsequent cell cycle arrest. The consequences of PMT entry thus depend on the differential regulation of signaling pathways within different cell types.

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Cell morphology and nucleoid dynamics in dividing D. radiodurans

10.1101/582304 ◽

2019 ◽

Cited By ~ 1

Author(s):

Kevin Floc’h ◽

Françoise Lacroix ◽

Pascale Servant ◽

Yung-Sing Wong ◽

Jean-Philippe Kleman ◽

...

Keyword(s):

Cell Cycle ◽

Single Molecule ◽

Cell Morphology ◽

Cell Cycle Progression ◽

Deinococcus Radiodurans ◽

Morphological Changes ◽

Cycle Progression ◽

Chromosomal Arrangement ◽

Tightly Coupled ◽

Large Spherical

AbstractOur knowledge of bacterial nucleoids originates mostly from studies of rod- or crescent-shaped bacteria. Here, we reveal that Deinococcus radiodurans, a relatively large, spherical bacterium, possessing a multipartite genome, and well-known for its radioresistance, constitutes a valuable system for the study of nucleoids in cocci. Using advanced microscopy, we show that as D. radiodurans progresses through its cell cycle, it undergoes coordinated morphological changes at both the cellular and nucleoid level. D. radiodurans nucleoids were found to be highly condensed, but also surprisingly dynamic, adopting multiple distinct configurations and presenting a novel chromosomal arrangement in which oriC loci are radially distributed around clustered ter sites maintained at the centre of cells. Single-molecule and ensemble studies of the abundant histone-like HU protein suggest that its loose binding to DNA may contribute to this remarkable plasticity. These findings clearly demonstrate that nucleoid organization is complex and tightly coupled to cell cycle progression.

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