Cellular deformability during maturation of the myeloblast. Possible role in marrow egress.
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Blood Preservation↗
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Results for “Cytoplasmic Streaming”
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Organelles in neuroplasmic ("axonal") flow: neurofilaments.
The electronmicroscopically conspicuous "neurofilaments" in axons manifest a marked constancy of mutual distance at all levels of a nerve fiber regardless of the wide variation of cross-sectional area along the course of a single axon or between different axons. The filaments conform to the rheological flow patterns of the axonal flow and must be viewed as discontinuous, metastable, and transitory linear assemblies of subunits present in the axonal matrix. The grid-like distribution of the filaments in the matrix suggests properties akin to those of liquid crystals of heterogeneous composition.
Animals↗
Structure and movement of Entamoeba.
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Cell Movement↗
Stimulation of action potentials with radiation in single cells of Nitella gracilis.
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Action Potentials↗
Myosin II heavy chain null mutant of Dictyostelium exhibits defective intracellular particle movement.
Both cellular motility and intracellular particle movement are compared between normal Dictyostelium amebae of strain AX4 and amebae of a myosin II heavy chain null mutant, HS2215, using the computer assisted "Dynamic Morphology System." In AX4 cells rapidly translocating in buffer, cytoplasmic expansion is apical and the majority of intracellular particles move anteriorly, towards the site of expansion. When these cells are pulsed with 10(-6) M cAMP, the peak concentration of the natural cAMP wave, cells stop translocating and average particle velocity decreases threefold within 2-4 s after cAMP addition. After 8 s, there is a partial rebound both in cytoplasmic expansion and particle velocity, but in both cases, original apical polarity is lost. In HS2215 cells in buffer, both cellular translocation and average particle velocity are already at the depressed levels observed in normal cells immediately after cAMP addition, and no anterior bias is observed in either the direction of cytoplasmic expansion or the direction of particle movement. The addition of cAMP to myosin-minus cells results in no additional effect. The results demonstrate that myosin II is necessary for (a) the rapid rate of intracellular particle movement, (b) the biased anterior directionality of particle movement, and (c) the rapid inhibition of particle movement by cAMP.
Biological Transport↗
Cortical and cytoplasmic flow polarity in early embryonic cells of Caenorhabditis elegans.
We have examined the cortex of Caenorhabditis elegans eggs during pseudocleavage (PC), a period of the first cell cycle which is important for the generation of asymmetry at first cleavage (Strome, S. 1989. Int. Rev. Cytol. 114: 81-123). We have found that directed, actin dependent, cytoplasmic, and cortical flow occurs during this period coincident with a rearrangement of the cortical actin cytoskeleton (Strome, S. 1986. J. Cell Biol. 103: 2241-2252). The flow velocity (4-7 microns/min) is similar to previously determined particle movements driven by cortical actin flows in motile cells. We show that directed flows occur in one of the daughters of the first division that itself divides asymmetrically, but not in its sister that divides symmetrically. The cortical and cytoplasmic events of PC can be mimicked in other cells during cytokinesis by displacing the mitotic apparatus with the microtubule polymerization inhibitor nocodazole. In all cases, the polarity of the resulting cortical and cytoplasmic flows correlates with the position of the attenuated mitotic spindle formed. These cortical flows are also accompanied by a change in the distribution of the cortical actin network. The polarity of this redistribution is similarly correlated with the location of the attenuated spindle. These observations suggest a mechanism for generating polarized flows of cytoplasmic and cortical material during embryonic cleavages. We present a model for the events of PC and suggest how the poles of the mitotic spindle mediate the formation of the contractile ring during cytokinesis in C. elegans.
Actin Cytoskeleton↗
Myo4p and She3p are required for cortical ER inheritance in Saccharomyces cerevisiae.
Myo4p is a nonessential type V myosin required for the bud tip localization of ASH1 and IST2 mRNA. These mRNAs associate with Myo4p via the She2p and She3p proteins. She3p is an adaptor protein that links Myo4p to its cargo. She2p binds to ASH1 and IST2 mRNA, while She3p binds to both She2p and Myo4p. Here we show that Myo4p and She3p, but not She2p, are required for the inheritance of cortical ER in the budding yeast Saccharomyces cerevisiae. Consistent with this observation, we find that cortical ER inheritance is independent of mRNA transport. Cortical ER is a dynamic network that forms cytoplasmic tubular connections to the nuclear envelope. ER tubules failed to grow when actin polymerization was blocked with the drug latrunculin A (Lat-A). Additionally, a reduction in the number of cytoplasmic ER tubules was observed in Lat-A-treated and myo4Delta cells. Our results suggest that Myo4p and She3p facilitate the growth and orientation of ER tubules.
Actin Cytoskeleton↗
Myosin V and the endoplasmic reticulum: the connection grows.
In this issue, Estrada et al. (2003) provide new and important insights into how the endoplasmic reticulum (ER) of budding yeast cells is inherited. Together with other studies in plant and animal cells, the results of Estrada et al. (2003) support the idea that myosin V acts as a universal motor for the transport of ER membranes.
Carrier Proteins↗
Control of mitochondrial motility and distribution by the calcium signal: a homeostatic circuit.
Mitochondria are dynamic organelles in cells. The control of mitochondrial motility by signaling mechanisms and the significance of rapid changes in motility remains elusive. In cardiac myoblasts, mitochondria were observed close to the microtubular array and displayed both short- and long-range movements along microtubules. By clamping cytoplasmic [Ca2+] ([Ca2+]c) at various levels, mitochondrial motility was found to be regulated by Ca2+ in the physiological range. Maximal movement was obtained at resting [Ca2+]c with complete arrest at 1-2 microM. Movement was fully recovered by returning to resting [Ca2+]c, and inhibition could be repeated with no apparent desensitization. The inositol 1,4,5-trisphosphate- or ryanodine receptor-mediated [Ca2+]c signal also induced a decrease in mitochondrial motility. This decrease followed the spatial and temporal pattern of the [Ca2+]c signal. Diminished mitochondrial motility in the region of the [Ca2+]c rise promotes recruitment of mitochondria to enhance local Ca2+ buffering and energy supply. This mechanism may provide a novel homeostatic circuit in calcium signaling.
Actin Cytoskeleton↗
Holographic, motion-induced-contrast images.
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Cytoplasmic Streaming↗
Motility in Echinosphaerium nucleofilum. I. An analysis of particle motions in the axopodia and a direct test of the involvement of the axoneme.
The motion of particles in the axopodia of Echinosphaerium nucleofilum is saltatory. In the present study, photokymograph records of 123 motions from six axopodia have been analyzed. Particles followed rectilinear paths of from 1 to 15 mum while in continuous motion at an average velocity of 0.66 plus or minus 0.32 mum/s. The velocity of the particles was variable in 36% of the cases measured. Some motions were punctuated by pauses either before continuing in the same direction or reversing. Frequently, several particles were moving at the same velocity, but neighboring particles showed no motion or moved in the opposite direction. Two particles occasionally contacted one another and travelled as a unit for varying lengths of time but subsequently moved independently. These motions reflect the underlying mechanism of motive force production. Furthermore, a glass microneedle can be substituted for the microtubular axoneme in the axopodia. In these artificial axopodia, bidirectional particle motions occurred which were similar to those in normal axopodia. Colchicine, at the threshold dose for axonemal dissolution, had no affect on these particel motions. It is concluded that the microtubular axoneme is not responsible for particle motions and also that individual microtubules are unlikely candidates for motive force production in this system.
Animals↗
Motility in Echinosphaerium nucleofilum. II. Cytoplasmic contractility and its molecular basis.
Echinosphaerium nucleofilum exhibits at least three kinds of movement: locomotion by the bending and shortening of its many axopodia, feeding by means of food-cup pseudopodia formed from its cortical cytoplasm, and saltatory motion of cytoplasmic particles, especially in the cortex and axopodia. Since previously presented evidence indicated that the microtubular axoneme is not essential for particle motion, the cytoplasm was investigated for the possible existence of contractile behavior and for the possible presence of linear elements other than microtubules. Cytoplasm can be isolated in physiological media in which rigor, relaxation, and contraction can be induced, as in muscle, by manipulating the concentrations of calcium ions and magnesium-adenosine triphosphate. Contraction is initiated by calcium ions at concentrations above 2.4 times 10-minus 7 M. The rigor-to-relaxation transition occurs at subthreshold calcium concentrations on the addition of 10-minus 3 M ATP. Negatively stained preparations of isolated cytoplasm show two types of filaments: thin filaments identified as cytoplasmic actin by virtue of their binding heavy meromyosin from striated muscle in characteristic arrowhead arrays, and thicker filaments which do not strictly resemble myosin aggregates from muscle or amoeba but could conceivably by myosin aggregated in an unfamiliar form.
Actins↗
Oscillations of calcium ion concentrations in Physarum polycephalum.
Aequorin is a photoprotein which emits light in response to changes in free calcium concentration. When aequorin was microinjected into plasmodia of Physarum polycephalum, light emission varied in synchrony with the motile oscillations of the organisms. Therefore, movement is correlated which changes in the concentration of free calcium.
Aequorin↗
The contractile basis of ameboid movement. II. Structure and contractility of motile extracts and plasmalemma-ectoplasm ghosts.
The role of calcium and magnesium-ATP on the structure and contractility in motile extracts of Amoeba proteus and plasmalemma-ectoplasm "ghosts" of Chaos carolinensis has been investigated by correlating light and electron microscope observations with turbidity and birefringence measurements. The extract is nonmotile and contains very few F-actin filaments and myosin aggregates when prepared in the presence of both low calcium ion and ATP concentrations at an ionic strength of I = 0.05, pH 6.8. The addition of 1.0 mM magnesium chloride, 1.0 mM ATP, in the presence of a low calcium ion concentration (relaxation solution) induced the formation of some fibrous bundles of actin without contracting, whereas the addition of a micromolar concentration of calcium in addition to 1.0 mM magnesium-ATP (contraction solution) (Taylor, D. L., J. S. Condeelis, P. L. Moore, and R. D. Allen. 1973. J. Cell Biol. 59:378-394) initiated the formation of large arrays of F-actin filaments followed by contractions. Furthermore, plasmalemma-ectoplasm ghosts prepared in the relaxation solution exhibited very few straight F-actin filaments and myosin aggregates. In contrast, plasmalemmaectoplasm ghosts treated with the contraction solution contained many straight F-actin filaments and myosin aggregates. The increase in the structure of ameba cytoplasm at the endoplasm-ectoplasm interface can be explained by a combination of the transformation of actin from a less filamentous to a more structured filamentous state possibly involving the cross-linking of actin to form fibrillar arrays (see above-mentioned reference) followed by contractions of the actin and myosin along an undetermined distance of the endoplasm and/or ectoplasm.
Actins↗
Regulation of motility in nonmuscle cells.
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Actins↗
The contractile basis of amoeboid movement. V. The control of gelation, solation, and contraction in extracts from Dictyostelium discoideum.
Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (beta-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.
Actins↗
The contractile basis of ameboid movement. VI. The solation-contraction coupling hypothesis.
The contracted pellets derived from a high-speed supernate of Dictyostelium discoideum (S3) were investigated to determine the functional activity associated with this specific subset of the cellular motile apparatus. A partially purified model system of gelation and contraction (S6) was prepared from the contracted pellets, and the presence of calcium- and pH-sensitive gelation and contraction in this model demonstrated that a functional cytoskeletal-contratile complex remained at least partially associated with the actin and myosin during contraction. Semi-quantitative assays of gelation and solation in the myosin-free preparation S6 included measurements of turbidity, relative viscosity, and strain birefringence. The extent of gelation was optimal at pH 6.8 and a free calcium ion concentration of approximately 3.0 x 10(-8) M. Solation was favored when the free calcium ion concentration was greater than 7.6 x 10(-7) M or when the pH was increased or decreased from pH 6.8. Gelation was reversibly inhibited by increasing the free calcium ion concentration to approxomately 4.6 x 10(-6) M at pH 6.8. The solation-gelation process of this model has been interpreted to involve the reversible cross-linking of actin filaments. The addition of purified D. discoideum myosin to S6 served to reconstitute calcium- and pH-regulated contraction. The results from this study indicate that contraction is coupled functionally to the local breakdown (solation) of the gel. Therefore, solation has been identified as a structural requirement for extensive shortening during contraction. We have called this concept the solation-contraction coupling hypothesis. Fractionation of a preparation derived from the contracted pellets yielded a fraction consisting of actin and a 95,000-dalton polypeptide that exhibited calcium-sensitive gelation at 28 degrees C and a fraction composed of actin and 30,000- and 18,000-dalton polypeptides that demonstrated calcium-sensitive genlation at 0 degrees C.
Calcium↗