Formation of multinuclear cells induced by dimethyl sulfoxide: inhibition of cytokinesis and occurrence of novel nuclear division in Dictyostelium cells

Structure and function of the cytoskeleton of a Dictyostelium myosin-defective mutant

To study the role of conventional myosin in nonmuscle cells, we determined the cytoskeletal organization and physiological responses of a Dictyostelium myosin-defective mutant. Dictyostelium hmm cells were created by insertional mutagenesis of the myosin heavy chain gene (De Lozanne, A., and J. A. Spudich. 1987. Science (Wash. DC). 236: 1086-1091). Western blot analysis using different mAbs confirms that hmm cells express a truncated myosin fragment of 140 kD (HMM-140 protein) instead of the normal 243-kD myosin heavy chain (MHC). Spontaneous revertants appear at a frequency less than 4 x 10(-5), which synthesize normal myosin and are capable of forming thick filaments. In hmm cells, the HMM-140 protein is diffusely distributed in the cytoplasm, indicating that it cannot assemble into thick filaments. The actin distribution in these mutant cells appears similar to that of wild-type cells. However, there is a significant abnormality in the organization of cytoplasmic microtubules, which penetrate into lamellipodial regions. The microtubule networks consist of approximately 13 microtubules on average and their pattern is abnormal. Although hmm cells can form mitotic spindles, mitosis is not coordinated with normal furrow formation. The hmm cells are clearly defective in the contractile events that lead to normal cytokinesis. The retraction of different regions of the cell can result in the occasional pinching off of part of the cell. This process is not coupled with formation of mitotic spindles. There is no specific accumulation of HMM-140 in such constrictions, whereas 73% of such cells show actin concentrated in these regions. The mutant hmm cells are also deficient in capping of Con-A-bound surface receptors, but instead internalize this complex into the cytoplasm. The hmm cells display active phagocytosis of bacteria. Whereas actin is concentrated in the phagocytic cups, HMM-140 protein is not localized in these regions. cAMP, a chemoattractant that induces drastic rounding up and formation of surface blebs in wild type cells, does not induce rounding up in the hmm cells. A Triton-permeabilized cell model of the wild-type amebae contracts on reactivation with Mg-ATP, whereas a model of the hmm cell shows no detectable contraction. Our data demonstrate that the conventional myosin participates in the significant cortical motile activities of Dictyostelium cells, which include rounding up, constriction of cleavage furrows, capping surface receptors, and establishing cell polarity.

Effect of dimethyl sulfoxide on the in vitro and in vivo bactericidal activity of human and mouse neutrophils and mononuclear phagocytes

Dimethyl sulfoxide (DMSO) is reported to have antiinflammatory activity in various systems. Since resistance to bacterial infection can be thought of as a specialized type of inflammation, we were interested in determining the effect of DMSO on phagocyte bactericidal activity. The results indicated that in vitro DMSO treatment of human and mouse neutrophils and mononuclear phagocytes caused a dose-dependent inhibition of the killing of Escherichia coli and Listeria monocytogenes. However, pretreatment of mice with DMSO in vivo caused only a slight decrease in the subsequent in vitro bactericidal activity of neutrophils and macrophages from those mice. In addition, repeated injection of mice with a physiologically relevant dosage of DMSO did not enhance the lethality of either E. coli or L. monocytogenes, nor did it affect the clearance of a sublethal Listeria challenge from the spleen and liver. These results suggest that clinical usage of DMSO should not predispose human subjects to bacterial infection.

Filopodelike projections induced with dimethyl sulfoxide and their relevance to cellular polarity in Dictyostelium

When 5% dimethyl sulfoxide (DMSO) was applied to Dictyostelium cells, the cells rounded up in shape and cytoplasmic streaming ceased. The cells resumed both cytoplasmic streaming and locomotion in 20 min. SDS PAGE of isolated plasma membrane fractions showed that actin and myosin apparently became dissociated from the plasma membrane by the action of DMSO. Scanning electron microscopy revealed that many filopodelike projections formed on the surface of cells treated with 5% DMSO for 5 min. Interestingly, the projections were formed on a restricted portion of the cell surface. The phagokinetic track technique of Albrecht-Buehler (1977, Cell, 11: 395-404) showed that the projection region corresponded to the anterior part of a migrating cell. The possible relationship between the DMSO-induced projection region on the cell surface and intracellular organization of cell organelles was investigated using serial thin sections. The DMSO-induced projections contained arrays of microfilaments; and the microtubule organizing center (MTOC), nucleus, and vesicular structure were usually located in this order from the anterior end of the cell. The indirect immunofluorescent study using monoclonal anti-alpha-tubulin antibody was performed with a new fixation technique, which greatly improved the phase as well as immunofluorescent microscopy. It was verified that the intracellular positioning of the MTOC and nucleus had significant correlation with the cell polarity. The results show that DMSO is a powerful tool with which to manipulate the cellular microfilaments and to make visible the differentiation in the cortex layer, which apparently is relevant to the intracellular positioning of cell organelles and cell polarity.

Competitive inhibition by dimethylsulfoxide of molluscan and vertebrate acetylcholinesterase

Anticholinesterase-like effects of dimethylsulfoxide (DMSO) were demonstrated on a variety of invertebrate muscles. The excitatory effects of acetylcholine (ACh) on the isolated preparations of the Geukensia demissa heart and anterior byssus retractor muscle (ABRM), and of the Busycon contrarium radula protractor muscle, were potentiated by DMSO (1-5 microliters/ml; 1 microliter/ml = 14 mM). The negative chronotropic effects of ACh, but not of 4-ketoamyltrimethylammonium, were potentiated by DMSO (1-5 microliters/ml) on the isolated heart of the oyster Crassostrea virginica. These four muscles have acetylcholinesterase enzymes of high activity. In contrast, Mercenaria mercenaria hearts have weak cholinesterase activity, and the effects of ACh on this isolated myocardium were not potentiated by DMSO (2-20 microliters/ml). DMSO (0.1-15 microliters/ml) was a competitive inhibitor of both a crude preparation of oyster heart acetylcholinesterase (AChE) (the Km increased 24-fold with DMSO at 15 microliters/ml; the I50 was 1.3 microliters/ml DMSO when [ACh] = Km) and a purified Electrophorus AChE (the Km increased 4.5-fold when DMSO was 10 microliters/ml; the I50 was 10 microliters/ml DMSO near [ACh] = Km). The same doses of DMSO were needed to potentiate the pharmacological effects of ACh on the oyster heart, as to inhibit the AChE of this tissue.

Local and spatially coordinated movements in Dictyostelium discoideum amoebae during chemotaxis

We have studied chemotaxis by individual Dictyostelium discoideum amoebae using strong, local gradients of the chemoattractant cyclic AMP. Gradients were provided by diffusion of cyclic AMP from a microneedle, which could be positioned at various points around the cell. Responses to changes in the gradient indicate how the cell is structurally organized for chemotactic movement. There is a polarity in the responsiveness of the surface to stimulation by cyclic AMP along the length of the amoeba. Furthermore, two aspects of chemotactic movement can be distinguished. The first response to cyclic AMP is a locally generated extension of a hyaline pseudopod from the region of the surface nearest the stimulus. The second response, is coordinated and separate from the first response. The coordination appears to depend on the nucleus or on the microtubule-organizing center.