Cytokinesis in Animal Cells

224

162

Microtubules have been proposed to function as rigid struts which oppose cellular contraction. Consistent with this hypothesis, microtubule disruption strengthens the contractile force exerted by many cell types. We have investigated an alternative explanation for the mechanical effects of microtubule disruption: that microtubules modulate the mechanochemical activity of myosin by influencing phosphorylation of the myosin regulatory light chain (LC2o). We measured the force produced by a population of fibroblasts within a collagen lattice attached to an isometric force transducer. Treatment of cells with nocodazole, an inhibitor of microtubule polymerization, stimulated an isometric contraction that reached its peak level within 30 min and was typically 30-45% of the force increase following maximal stimulation with 30%o fetal bovine serum. The contraction following nocodazole treatment was associated with a 2-to 4-fold increase in LC2. phosphorylation. The increases in both force and LC20 phosphorylation, after addition of nocodazole, could be blocked or reversed by stabilizing the microtubules with paclitaxel (former generic name, taxol). Increasing force and LC20 phosphorylation by pretreatment with fetal bovine serum decreased the subsequent additional contraction upon microtubule disruption, a finding that appears inconsistent with a load-shifting mechanism. Our results suggest that phosphorylation of LC20 is a common mechanism for the contractions stimulated both by microtubule poisons and receptor-mediated agonists. The modulation of myosin activity by alterations in microtubule assembly may coordinate the physiological functions of these cytoskeletal components.

Section: Discussionmentioning

confidence: 99%

Contraction due to microtubule disruption is associated with increased phosphorylation of myosin regulatory light chain.

Kolodney

Elson

1995

224

162

“…Two other theories have also been proposed to explain furrowing: polar expansion and polar relaxation (reviewed in ref. 18). In polar expansion, the force responsible for cleavage is developed in the poles; the equatorial region remains passive.…”

Section: Discussionmentioning

confidence: 99%

“…This we did not observe. Polar relaxation mechanisms postulate a uniform cortical tension throughout the cell followed by a decrease in polar tension leading to cleavage (18). This theory could accommodate either a uniform distribution of actin over the cell during cleavage or an initially uniform distribution of actin followed, at cleavage, by a withdrawal of actin from the poles.…”

Section: Discussionmentioning

confidence: 99%

Changing patterns of actin localization during cell division.

Sanger¹

1975

123

Changing patterns of actin localization have been studied on a light microscopic level by means of fluorescently labeled heavy meromyosin. The cellular distribution of actin is characterized by four major patterns, each of which corresponds to a particular phase of cell division. Long actin fibers are a prominent feature of the interphase cell. They disappear as the cell rounds up for mitosis and are replaced by a diffuse distribution of actin throughout the cytoplasm. During cytokinesis, the actin is localized predominantly in the cleavage furrow. The final shift of actin occurs after the completion of cytokinesis. At this time the actin becomes concentrated in the distal poles of the cell where pseudopods form to pull the daughter cells apart. When the daughter cells have separated, they flatten on the culture dish and the fibrous pattern of actin characteristic of interphase cells returns. All of these changes take place during the 1-hr period required for cell division.

“…Much attention has been directed towards a topographical analysis of the progressive changes in membrane and submembrane structures. Microdissection studies of dividing cells have indicated that the cleavage furrow region is stronger and more rigid than the rest of the cell (18). Scanning electron microscopic studies of the fine structure of the cell surface in the cleavage furrow region show a very active region, with many microvilli and folds.…”

Section: Discussionmentioning

confidence: 99%

“…The folds become larger with the development of the furrow, a change assumed to be associated with increased tension within the cleavage furrow cortex (19). A dense layer containing microfilaments closely associated with the membrane encircles the dividing cell in the region of the cleavage furrow; the layer is thought to act as a contractile ring, drawing the membrane inwards and continuously deepening the furrow (13,(18)(19)(20)(21) (6), and promotion of cell fusion (7). The inhibition of cytoplasmic cleavage found in the present study may thus be due to the "disordering" effect of membrane mobility agent on critical membrane regions, including the anchoring of microfilaments to the membrane, but agent action inside the cell is not excluded.…”

Section: Discussionmentioning

confidence: 99%

Inhibition of cytokinesis in Friend leukemia cells by membrane mobility agents.

Lustig¹,

Kosower²,

Pluznik³

et al. 1977

Treatment of a line of Friend leukemia cells with a dispersion of the membrane mobility agent, A2C, yields cells that undergo successive nuclear divisions without cytokinesis, resulting eventually in cells with as many as 30 nuclei. Neither the DNA replication rate of the cells nor the generation time is different after treatment; in addition, the multiple nuclei divide synchronouly, and the chromosome number corresponds to the number of nuclei in the cell. Inhibition of cytokinesis is not observed if the cells are washed with reagent-free medium within 1 hr of treatment, but is observed if washing is delayed for 24 hr. Membrane mobility agent loaded with the fluorescent probe, Flomol F20C, leads to fluorescent membrane; fluorescence disappears from the membrane after a change of medium within 1 hr, but not after a change of medium within 24 hr.Some stages in the overall development resemble those seen for cytochalasin B inhibition of cytokinesis, although the mechanisms may well be different for the inhibition promoted by membrane mobility agent. The inhibition of cytokinesis by A2C provides a potentially interesting means for studying cytokinesis and the regulation of differentiation.As the result of an attempt to cause the differentiation of a line of Friend leukemia cells towards hemoglobin production (1-4) with membrane mobility agents (5)