SEARCH · PubMed Health

Results for “Cytoplasmic Streaming”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources

PubMed2005

Arabidopsis VILLIN1 generates actin filament cables that are resistant to depolymerization.

Dynamic cytoplasmic streaming, organelle positioning, and nuclear migration use molecular tracks generated from actin filaments arrayed into higher-order structures like actin cables and bundles. How these arrays are formed and stabilized against cellular depolymerizing forces remains an open question. Villin and fimbrin are the best characterized actin-filament bundling or cross-linking proteins in plants and each is encoded by a multigene family of five members in Arabidopsis thaliana. The related villins and gelsolins are conserved proteins that are constructed from a core of six homologous gelsolin domains. Gelsolin is a calcium-regulated actin filament severing, nucleating and barbed end capping factor. Villin has a seventh domain at its C terminus, the villin headpiece, which can bind to an actin filament, conferring the ability to crosslink or bundle actin filaments. Many, but not all, villins retain the ability to sever, nucleate, and cap filaments. Here we have identified a putative calcium-insensitive villin isoform through comparison of sequence alignments between human gelsolin and plant villins with x-ray crystallography data for vertebrate gelsolin. VILLIN1 (VLN1) has the least well-conserved type 1 and type 2 calcium binding sites among the Arabidopsis VILLIN isoforms. Recombinant VLN1 binds to actin filaments with high affinity (K(d) approximately 1 microM) and generates bundled filament networks; both properties are independent of the free Ca(2+) concentration. Unlike human plasma gelsolin, VLN1 does not nucleate the assembly of filaments from monomer, does not block the polymerization of profilin-actin onto barbed ends, and does not stimulate depolymerization or sever preexisting filaments. In kinetic assays with ADF/cofilin, villin appears to bind first to growing filaments and protects filaments against ADF-mediated depolymerization. We propose that VLN1 is a major regulator of the formation and stability of actin filament bundles in plant cells and that it functions to maintain the cable network even in the presence of stimuli that result in depolymerization of other actin arrays.

Actin Cytoskeleton↗

PubMed2005

Kinase partner protein interacts with the LePRK1 and LePRK2 receptor kinases and plays a role in polarized pollen tube growth.

The pollen-specific receptor kinases LePRK1 and LePRK2 have localization and expression profiles that strongly suggest they play roles in pollen germination and tube growth. To identify downstream components of LePRK signaling, we used their cytoplasmic domains (CDs) as baits in yeast two-hybrid screens of a tomato pollen cDNA library. A pollen-specific protein we named kinase partner protein (KPP) interacted with the CDs of both LePRK1 and LePRK2 in yeast and in an in vitro pull-down assay, and with LePRK2 in a co-immunoprecipitation assay. KPP is a peripheral membrane protein and is phosphorylated in pollen. Pollen tubes over-expressing KPP developed balloon-like tips with abnormal cytoplasmic streaming and F-actin arrangements and plants over-expressing KPP exhibited impaired transmission of the transgene through the male. KPP-like genes are found only in plants; the 14 family members in Arabidopsis thaliana exhibit diverse expression patterns and potentially play roles in signaling pathways in other tissues.

Flowers↗

PubMed1975

Induced transfer of higher plant chloroplasts into fungal protoplasts.

Chloroplasts isolated from spinach leaves have been transferred in large numbers into protoplasts of Neurospora crassa with the help of polyethylene glycol. The chloroplasts show high photosynthetic activity--at least until the time of uptake--and the protoplasts continue to show active cytoplasmic streaming after chloroplast uptake.

Chloroplasts↗

PubMed1991

Rhizobium lipopolysaccharide modulates infection thread development in white clover root hairs.

The interaction between Rhizobium lipopolysaccharide (LPS) and white clover roots was examined. The Limulus lysate assay indicated that Rhizobium leguminosarum bv. trifolii (hereafter called R. trifolii) released LPS into the external root environment of slide cultures. Immunofluorescence and immunoelectron microscopy showed that purified LPS from R. trifolii 0403 bound rapidly to root hair tips and infiltrated across the root hair wall. Infection thread formation in root hairs was promoted by preinoculation treatment of roots with R. trifolii LPS at a low dose (up to 5 micrograms per plant) but inhibited at a higher dose. This biological activity of LPS was restricted to the region of the root present at the time of exposure to LPS, higher with LPS from cells in the early stationary phase than in the mid-exponential phase, incubation time dependent, incapable of reversing inhibition of infection by NO3- or NH4+, and conserved among serologically distinct LPSs from several wild-type R. trifolii strains (0403, 2S-2, and ANU843). In contrast, infections were not increased by preinoculation treatment of roots with LPSs from R. leguminosarum bv. viciae strain 300, R. meliloti 102F28, or members of the family Enterobacteriaceae. Most infection threads developed successfully in root hairs pretreated with R. trifolii LPS, whereas many infections aborted near their origins and accumulated brown deposits if pretreated with LPS from R. meliloti 102F28. LPS from R. leguminosarum 300 also caused most infection threads to abort. Other specific responses of root hairs to infection-stimulating LPS from R. trifolii included acceleration of cytoplasmic streaming and production of novel proteins. Combined gas chromatography-mass spectroscopy and proton nuclear magnetic resonance analyses indicated that biologically active LPS from R. trifolii 0403 in the early stationary phase had less fucose but more 2-O-methylfucose, quinovosamine, 3,6-dideoxy-3-(methylamino)galactose, and noncarbohydrate substituents (O-methyl, N-methyl, and acetyl groups) on glycosyl components than did inactive LPS in the mid-exponential phase. We conclude that LPS-root hair interactions trigger metabolic events that have a significant impact on successful development of infection threads in this Rhizobium-legume symbiosis.

Blotting, Western↗

PubMed2001

Analysis of the myosins encoded in the recently completed Arabidopsis thaliana genome sequence.

BACKGROUND: Three types of molecular motors play an important role in the organization, dynamics and transport processes associated with the cytoskeleton. The myosin family of molecular motors move cargo on actin filaments, whereas kinesin and dynein motors move cargo along microtubules. These motors have been highly characterized in non-plant systems and information is becoming available about plant motors. The actin cytoskeleton in plants has been shown to be involved in processes such as transportation, signaling, cell division, cytoplasmic streaming and morphogenesis. The role of myosin in these processes has been established in a few cases but many questions remain to be answered about the number, types and roles of myosins in plants. RESULTS: Using the motor domain of an Arabidopsis myosin we identified 17 myosin sequences in the Arabidopsis genome. Phylogenetic analysis of the Arabidopsis myosins with non-plant and plant myosins revealed that all the Arabidopsis myosins and other plant myosins fall into two groups - class VIII and class XI. These groups contain exclusively plant or algal myosins with no animal or fungal myosins. Exon/intron data suggest that the myosins are highly conserved and that some may be a result of gene duplication. CONCLUSIONS: Plant myosins are unlike myosins from any other organisms except algae. As a percentage of the total gene number, the number of myosins is small overall in Arabidopsis compared with the other sequenced eukaryotic genomes. There are, however, a large number of class XI myosins. The function of each myosin has yet to be determined.

Arabidopsis↗

PubMed1999

Spire contains actin binding domains and is related to ascidian posterior end mark-5.

Spire is a maternal effect locus that affects both the dorsal-ventral and anterior-posterior axes of the Drosophila egg and embryo. It is required for localization of determinants within the developing oocyte to the posterior pole and to the dorsal anterior corner. During mid-oogenesis, spire mutants display premature microtubule-dependent cytoplasmic streaming, a phenotype that can be mimicked by pharmacological disruption of the actin cytoskeleton with cytochalasin D. Spire has been cloned by transposon tagging and is related to posterior end mark-5, a gene from sea squirts that encodes a posteriorly localized mRNA. Spire mRNA is not, however, localized to the posterior pole. SPIRE also contains two domains with similarity to the actin monomer-binding WH2 domain, and we demonstrate that SPIRE binds to actin in the interaction trap system and in vitro. In addition, SPIRE interacts with the rho family GTPases RHOA, RAC1 and CDC42 in the interaction trap system. Thus, our evidence supports the model that SPIRE links rho family signaling to the actin cytoskeleton.

Actins↗

PubMed1985

Synchronous exocytosis in Paramecium cells. VI. Ultrastructural analysis of membrane resealing and retrieval.

After the synchronous induction of exocytosis of secretory organelles (trichocysts) in Paramecium tetraurelia cells the process of membrane resealing and retrieval could be followed under synchronous conditions. The characteristic aggregates of membrane intercalated particles (MIPs) contained within the freeze-fractured cell membrane (rings and rosettes) and trichocyst membranes (annulus MIPs), in addition to collar striations on the top of trichocyst membranes, served as endogenous ultrastructural markers. This allowed us to follow the re-arrangement of membrane constituents during and after exocytosis with high temporal and spatial precision. Membrane specificity is maintained to a considerable extent (approximately 99.5%), as judged from the rare occurrence of aberrant resealing (according to freeze-fracture data) and from the rather minute shift of glycocalyx components (according to electron staining experiments) during normal membrane resealing. Coated pits are not involved in membrane retrieval (155 ghosts analysed); since the membrane regions involved in exocytotic fusion are backed by apposed materials, probably proteins, this may restrain membrane constituents from intermixing. Another factor for maintaining membrane specificity is the fact that resealing of the exocytotic opening occurs much more rapidly than in most other systems. The retrieval operates with a half-life of 3 (strain 7S) to 9 min (K401); the involvement of cortical microtubules in the retrieval can be largely excluded, since only two microtubules (of unidentified origin) were seen to approach ghost structures in 4074 cases analysed during this period of intense ghost retrieval. Phalloidin microinjected at a dose that blocked all cytoplasmic streaming (before synchronous exocytosis was induced) did not abolish membrane resealing and retrieval, which, therefore, may be passive processes.

Animals↗

PubMed1988

Diacylglycerol-induced shape changes, movements and altered F-actin distribution in human neutrophils.

The study shows that diacylglycerols (DAGs) as physiological activators of protein kinase C induce characteristic shape changes in human neutrophil granulocytes. In contrast to chemotactic peptides, which can induce front-tail polarity characterized by a contracted tail and an expanding front, DAGs elicit the formation of non-polar cells with surface projections. These cells exhibit a distinct type of motility characterized by vigorous and continuous shape changes without front-tail polarity and without the unidirectional movement and cytoplasmic streaming seen in polarized cells. In neutrophils exposed to DAGs, F-actin is shifted to the cell periphery and mainly into the surface projections of activated cells. DAGs induce the formation of large intracellular vacuoles in neutrophils producing surface projections, and these vacuoles persist after the cells have reacquired a spherical shape. Combined stimulation of human neutrophils with DAG and fNLPNTL results in a suppression of peptide-induced polarity and the formation of non-polar motile cells resembling those stimulated with DAG alone. These results suggest that the diacylglycerol-protein kinase C pathway may be instrumental in transducing or modulating signals to both the locomotor apparatus and the exocytotic and/or pinocytic system of the cell. Neutrophil stimulation with DAGs thus represents a useful model with which to study further the hypothesis that distinct types of neutrophil shapes and movements are preferentially associated with distinct functions and to characterize signalling pathways.

Actins↗

PubMed2000

[Response of siphoneal alga (Vaucheria sessilis) to the gravity factor].

Growth and development of siphonal alga Vaucheria sessilis under changed gravity and the role of cytoskeletal structures in gravitational response were studied. Hypergravity (3 g) and "hypogravity" were generated by slow clinostating at 7-8 rev/min and rapid clinostating at 35, 70, 135 rev/min, respectively. The experiments in microgravity were flown aboard biosatellite Bion-11. As was shown, V. sessilis responded to changed gravity by inhibition of rate of growth and increasing the number of nuclei in the strand as a result of activation of mitotic processes. Modulation of the course of the gravitational response with anticytoskeletal agents points to involvement of the cytoskeleton. The cortical circuit of actin microfilaments and the cytoplasm stream directed by this structure appear to be the most sensitive to changes in gravity. Gravity-sensitive V. sessilis is another promising object of research in the field of gravitational biology.

Eukaryota↗

PubMed1992

Time-lapse analysis of gravitropism in Ceratodon protonemata.

The tip cell of the protonema of the moss Ceratodon purpureus (Hedw.) Brid. is negatively gravitropic when grown in the dark on supplemented agar. Gravitropism, plastid distribution, and plastid movement were studied in living cells using time-lapse video microscopy and infrared light. A wrong-way (downward) curvature preceded upward curvature and was detected as early as 2 minutes after reorientation. Upward curvature began 30-45 minutes after reorientation to the horizontal. Cell division temporarily reversed upward curvature, but did not inhibit wrong-way curvature. Since significant amyloplast sedimentation always occurred before the start of upward curvature, it is possible that these amyloplasts function as statoliths for upward curvature. However, no significant amyloplast sedimentation occurred before wrong-way curvature. Thus, this early phase of gravitropism cannot require plastid sedimentation for gravity sensing. Most plastids moved within and between zones, and plastid zonation was highly dynamic. Plastids moved toward the apex and toward the base of the cell at rates much slower than cytoplasmic streaming. Despite the dynamic nature of plastid movement and zonation, during upward curvature the distance between sedimented plastids and the apex stayed constant. Time-lapse analysis has revealed intriguing events not readily seen previously using destructive sampling.

Cell Cycle↗

PubMed1988

Cultivation of single cells in space.

The purpose of this review is to present an updated and comprehensive analysis of the experiments with single cells performed in space. Especially the results of the investigations performed in Biorack on the D-1 mission clearly show that important cellular functions are changing in microgravity. Cell proliferation, differentiation, metabolism, membrane properties, and cytoplasmic streaming underwent significant alteration during exposure to space flight conditions in a variety of single cells cultures spanning from bacteria to mammalian cells. These findings open new and interesting perspectives to basic and applied research in microgravity. The focus of this paper is on the cultivation of mammalian cells in space laboratories and on the related instrumentation. While Biorack is a useful and efficient instrument for simple studies in Spacelab, the development of new facilities like incubators with automated fixation devices as well as of more complex bioreactors is strongly recommended.

Animals↗

PubMed1991

Calcium channel blocker and calmodulin antagonists affect the gradient of free calcium ions in lily pollen tubes.

The distribution of intracellular free calcium ions ([Ca2+]i) was measured in pollen tubes of Lilium longiflorum using video imaging microscopy and the calcium sensitive indicators fura-2 and quin-2. The mean [Ca2+]i in growing pollen tubes measured with fura-2 shows a maximum of 1.7 to 2.6 microM in the tube tip and decreases almost exponentially to 60 to 100 nM at 100 microns behind the tip. Using quin-2, the maximum [Ca2+]i was also found in the tube tip but with a lower Ca2+ concentration, namely 1 microM. Addition of the calcium channel blocker La3+ caused a decrease of the [Ca2+]i maximum in the tube tip, indicating a heterogeneous distribution of Ca2+ channels along the plasma membrane of pollen tubes. The [Ca2+]i increased after addition of vanadate or compound 48/80. This suggests an involvement of a calmodulin-dependent Ca2+ pump in generation of the Ca2+ gradient in lily pollen tubes. The high [Ca2+]i found in the tube tip with fura-2 seems to indicate the real Ca2+ concentration and is probably responsible for vesicle fusion, fragmentation of actin filaments, and inhibition of cytoplasmic streaming.

Aminoquinolines↗

PubMed1989

Capillary growth in the mesentery of normal young rats. Intravital video and electron microscope analyses.

Capillary sprouting was studied by a combination of intravital video recording and subsequent electron microscopy in the mesentery of young female rats without previous experimental manipulation. Selected segments of the mesenteric microvascular bed with capillary sprouts were carefully surveyed and mapped at a monitor magnification of 255 times and submitted to detailed in vivo analysis concerning flow pattern and cells at 2000 times magnification. The mesentery was preserved for light and electron microscopy by a superfusion of glutaraldehyde while observed and recorded on video, confirming earlier investigations that this type of fixation does preserve exceptionally well vascular topography and diameters of the mesenteric microvascular bed. Capillary sprouts originated as endothelial spurs from arteriolar-venular arcades and continued to grow in size through a bipolar rearrangement of endothelial cells, forming a solid sprout tip which progressively lengthened by alternately rapid and slow growth phases. The extended leading tip of the migrating endothelial cells displayed microspikes and pseudopodia denuded of basal lamina. The cytoplasm of the leading tip contained an array of microtubules, 75 A filaments and many small vesicles. In similarity with the situation in nerve growth cones, all these organelles probably participate in cytoplasmic streaming and cell migration. The sprout lumen arose between endothelial cells of the solid sprout. Mesenteric connective tissue fibroblasts approached and settled down on the sprouts, being converted to pericytes as the fibroblasts became enveloped by a basal lamina. The pericytes reinforced the wall of the delicate and fragile capillary sprouts, and trapped plasma, platelets and red blood cells which had leaked out temporarily, in the process assuming an umbrella shape. The arteriolar feeder of the arcades was surrounded by cells which were classified as intermediate between pericytes and true smooth muscle cells. Sprouts that presumably were on the verge of merging with other capillaries were analyzed for indications of how anastomoses are formed.

Animals↗

PubMed1988

Heavy water (D2O)-induced shape changes, movements and F-actin redistribution in human neutrophil granulocytes.

Heavy water (D2O) induces characteristic shape changes and a distinct type of movement in human neutrophil granulocytes. In contrast to front-tail polarity as evoked by chemotactic peptides and microtubule-disassembling agents, D2O-based media produce non-polar neutrophils with many small or long surface projections. This phenotype is similar to that elicited by both phorbol myristate acetate and diacylglycerols, but the surface projections are smaller and more densely placed and are often associated with a single large projection. D2O-induced non-polar cells with surface projections perform continuous shape changes without front-tail polarity and without the unidirectional movement and cytoplasmic streaming seen in cells with front-tail polarity. Some of the cells show circus movements of a large projection indicating circular polarity. In neutrophils suspended in D2O, F-actin is shifted to the cell periphery, mainly into the surface projections of activated cells. The D2O-induced effects are reversed in H2O-based medium. D2O is dominant over the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), colchicine and taxol in that the combined action of D2O with any of these agents results in the D2O-induced phenotype. In contrast, cytochalasin B alone and in combination with fMLP induces a considerable decrease of non-polar cells and an increase of spherical cells similar to non-stimulated cells in H2O-based medium. Earlier studies indicated that D2O acts on microtubules. Our results suggest that D2O may act on the microfilament system. Neutrophils suspended in D2O-based medium may represent a useful model to study the relationship between shapes, movements, and particular functions of these cells.

Actins↗

PubMed1979

Effects of oxybarbiturates on the germination behaviour of Impatiens bolstii pollen.

Swelling of and cytoplasmic streaming within the grain, germination pore expansion, and pollen tube emergence, in that order, constitute the normal germination pattern of Impatiens holstii pollen grains. This normal sequence of events becomes manifest when the pollen grains are placed on water-agar, barbituric acid-agar, and on barbital-agar media whereas this sequence of events is interfered with when the pollen grains are incubated on amytal-agar or on seconal-agar media. Evidence is presented which demonstrates that the normal sequence of events which make up the normal germination pattern of Impatiens holstii pollen grains can be separated from each other by varying the concentrations of the oxybarbiturates amytal and seconal used. Evidence is also presented which indicates that the actions of barbituric acid and the oxybarbiturates barbital, amytal, and seconal on Impatiens holstii pollen germination behaviour correlate well with certain aspects of the pharmacological literature concerning the actions of these organic compounds on the central nervous system (CNS).

Amobarbital↗

PubMed1984

Regeneration of actin bundles in Chara: polarized growth and orientation by endoplasmic flow.

Strong irradiation of localized areas of the alga Chara produces chloroplast damage and extensive loss of the actin bundles responsible for cytoplasmic streaming. Immunofluorescence using a monoclonal antibody binding to the actin bundles has been used to follow their regrowth. Bundle regeneration is polarized so that new bundles develop from the ends of the actin bundles delivering endoplasm to the damaged area and not from bundles removing endoplasm. According to the previously established polarity of the actin filaments this growth is occurring from the "barbed" but not the "pointed" ends of the component filaments. The frequently irregular orientation of the regenerated bundles contrasts with the straight, parallel arrangement of the bundles before destruction. The arrangement of the regenerated bundles is suggested to depend on orientation by passive endoplasmic flow rather than a cortical template. As a result, bundles follow sweeping curves and can form a U-turn connecting oppositely polarized bundles normally separated by the neutral line. In addition to development in continuity with the free ends of pre-existing bundles, visualization of small, discrete fluorescent structures suggests that bundles can begin to form in isolation within the damaged areas. The results are discussed in terms of the polarized actin polymerisation seen in vitro, additional controls which may operate on bundle growth in vivo, and the ability of flow to orient F-actin. The relevance of the findings to normal cell ontogeny is assessed.

Actins↗

PubMed1983

Ca2+-dependent actin-binding phosphoprotein in Physarum polycephalum. II. Ca2+-dependent f-actin-capping activity of subunit a and its regulation by phosphorylation of subunit b.

Cap 42 (a + b), a Ca2+-dependent, actin-binding and phosphorylatable protein consisting of two distinct subunits a and b of 42,000 Da in Physarum polycephalum, has been identified as a new F-actin-capping protein. It capped or bound to the fast growing ends of actin filaments and blocked actin polymerization at this end. The capping activity residing in subunit a and its Ca2+-dependency were regulated by phosphorylation of subunit b; subunit a required Ca2+ for its capping activity when subunit b was phosphorylated, whereas this activity became Ca2+ independent when subunit b was dephosphorylated. Subunit b contained at least two phosphorylatable threonine residues and probably three additional phosphorylation sites. Like cytochalasins and other F-actin-capping proteins, Cap 42 (a + b) was able to induce a rapid depolymerization of actin filaments at the slow growing end, and also to nucleate actin polymerization. However, unlike Physarum fragmin, Cap 42 (a + b) had no severing activity leading to the fragmentation of actin filaments. Our results indicate that Cap 42 (a + b) is the first Ca2+-dependent F-actin-capping phosphoprotein whose phosphorylation regulates its actin-binding and vice versa. A possible mechanism of the capping action of Cap 42 (a + b) in vitro and also its conceivable role in the regulation of the Ca2+/actin-dependent cytoplasmic streaming in plasmodia are discussed.

Actins↗

PubMed1982

Extravascular migration of tumor cells in the brain: an electron microscopic study.

The mechanisms of extravasation of rat ascites hepatoma AH7974 cells arrested in the cerebral capillaries of Donryu strain rats were studied by transmission electron microscopy. Until 2 days after the injection of tumor cells into the carotid artery, the surfaces of tumor cells were generally smooth without microvilli. At 3 and 4 days after injection, some of the tumor cells formed filopodia in regions facing the endothelial cells. These protrusions were in front as the cells left the vessel. First, the tumor cells inserted these cytoplasmic projections into the endothelial cell lining until they completely breached endothelial cells, or caused fragmentation of the endothelium resulting in the exposure of underlying basal lamina. Next, the tumor cells appeared to push the endothelial cells aside and attach directly to the basal lamina. They penetrated the basal lamina by producing small (0.07-1.8 micron) pores through which they thrusted cytoplasmic projections. Finally, the tumor cells migrated by cytoplasmic streaming through the pores in the basal lamina to complete the extravascular process.

Animals↗