scholarly journals Mechanism of Ca2+ inhibition of cytoplasmic streaming in lily pollen tubes

1988 ◽  
Vol 91 (4) ◽  
pp. 501-509 ◽  
Author(s):  
TADASHI KOHNO ◽  
TERUO SHIMMEN
Keyword(s):  
Actin Filaments ◽  
Cytoplasmic Streaming ◽  
Lilium Longiflorum ◽  
Pollen Tubes ◽  
Ionophore A23187 ◽  
Filamentous Actin ◽  
Actin Bundles ◽  
Lily Pollen ◽  
Subsequent Decrease

Using a Ca2+ ionophore, A23187, the free Ca2+ concentration ([Ca2+]) in the cytoplasm of pollen tubes of Lilium longiflorum was controlled from the cell exterior. At [Ca2+] higher than 1.0x10−5M (pCa5.0), cytoplasmic streaming was inhibited, and the inhibition was irreversible. The ATP content did not change, but actin filaments were fragmented and formed aggregates. A subsequent decrease in [Ca2+] almost stopped the progress of the actin filament fragmentation, but filamentous actin did not re-form from the fragmented actin. In a previous paper, we reported that pollen tube organelle movement along characean actin bundles was inhibited by Ca2+ at 10−5M levels and the inhibition was reversible. In the present study, the reversibility was also demonstrated using an in situ Ca2+ treatment. Organelles were isolated from pollen tubes that had been treated with high [Ca2+] and A23187. They moved along characean actin bundles in Ca2+-free medium. It is concluded that Ca2+ inhibition of cytoplasmic streaming can be attributed to both inactivation of myosin and fragmentation of actin. The irreversibility of Ca2+ inhibition in situ is attributed to the irreversible fragmentation of actin filaments.

scholarly journals The elusive actin cytoskeleton of a green alga expressing both conventional and divergent actins

2019 ◽  
Vol 30 (22) ◽  
pp. 2827-2837 ◽  
Author(s):  
Evan W. Craig ◽  
David M. Mueller ◽  
Brae M. Bigge ◽  
Miroslava Schaffer ◽  
Benjamin D. Engel ◽  
...  
Keyword(s):  
Green Alga ◽  
Actin Filaments ◽  
Electron Tomography ◽  
Filamentous Actin ◽  
Cellular Processes ◽  
Cellular Environment ◽  
Actin Structure ◽  
Actin Isoform ◽  
Labeling Method

The green alga Chlamydomonas reinhardtii is a leading model system to study photosynthesis, cilia, and the generation of biological products. The cytoskeleton plays important roles in all of these cellular processes, but to date, the filamentous actin network within Chlamydomonas has remained elusive. By optimizing labeling conditions, we can now visualize distinct linear actin filaments at the posterior of the nucleus in both live and fixed vegetative cells. Using in situ cryo-electron tomography, we confirmed this localization by directly imaging actin filaments within the native cellular environment. The fluorescently labeled structures are sensitive to the depolymerizing agent latrunculin B (Lat B), demonstrating the specificity of our optimized labeling method. Interestingly, Lat B treatment resulted in the formation of a transient ring-like filamentous actin structure around the nucleus. The assembly of this perinuclear ring is dependent upon a second actin isoform, NAP1, which is strongly up-regulated upon Lat B treatment and is insensitive to Lat B–induced depolymerization. Our study combines orthogonal strategies to provide the first detailed visual characterization of filamentous actins in Chlamydomonas, allowing insights into the coordinated functions of two actin isoforms expressed within the same cell.

Cytoplasmic streaming in Chara: a cell model activated by ATP and inhibited by cytochalasin B

1975 ◽  
Vol 17 (3) ◽  
pp. 655-668
Author(s):  
R.E. Williamson
Keyword(s):  
Actin Filaments ◽  
Cytoplasmic Streaming ◽  
Cytochalasin B ◽  
Cell Model ◽  
Motive Force ◽  
Inorganic Pyrophosphate ◽  
A Cell ◽  
Shear Type

After vacuolar perfusion of Chara internode cells, the cytoplasm remaining in situ can be reactivated by ATP to give full rates of streaming. Observations during both perfusion and reactivation indicated that the generation of the motive force was associated with fibres consisting of bundles of microfilaments. In the absence of ATP, the remaining endoplasmic organelles were immobilized along such fibres. When ATP was introduced, organelles moved along the fibres at speeds up to 50 mum S minus 1, but but were progressively released from contact to leave the fibres in a conspicuously clean state. Inorganic pyrophosphate freed the organelles from the fibres without supporting movements. Motility required millimolar Mg2nlevels, free Ca2nat 10 minus 7 M or less and was inhibited by high levels of Clminus and by pH's on either side of 7.0. The reactivated movements were rapidly and completely inhibited by 25mug ml minus 1 cytochalasin B. The results are interpreted in terms of actin filaments in the stationary cortex interacting with a myosin-like protein which is able to link to endoplasmic organelles. Movement results from an active shear type of mechanism.

scholarly journals Accelerated sliding of pollen tube organelles along Characeae actin bundles regulated by Ca2+.

1988 ◽  
Vol 106 (5) ◽  
pp. 1539-1543 ◽  
Author(s):  
T Kohno ◽  
T Shimmen
Keyword(s):  
Heat Treatment ◽  
Pollen Tube ◽  
Cytoplasmic Streaming ◽  
Pollen Tubes ◽  
The Other ◽  
Cell Models ◽  
Organelle Movement ◽  
Actin Bundles ◽  
Other Hand ◽  
Order Of Magnitude

Pollen tubes show active cytoplasmic streaming. We isolated organelles from pollen tubes and tested their ability to slide along actin bundles in characean cell models. Here, we show that sliding of organelles was ATP-dependent and that motility was lost after N-ethylmaleimide or heat treatment of organelles. On the other hand, cytoplasmic streaming in pollen tube was inhibited by either N-ethylmaleimide or heat treatment. These results strongly indicate that cytoplasmic streaming in pollen tubes is supported by the "actomyosin"-ATP system. The velocity of organelle movement along characean actin bundles was much higher than that of the native streaming in pollen tubes. We suggested that pollen tube "myosin" has a capacity to move at a velocity of the same order of magnitude as that of characean myosin. Moreover, the motility was high at Ca2+ concentrations lower than 0.18 microM (pCa 6.8) but was inhibited at concentration higher than 4.5 microM (pCa 5.4). In conclusion, cytoplasmic streaming in pollen tubes is suggested to be regulated by Ca2+ through "myosin" inactivation.

scholarly journals The elusive actin cytoskeleton of a green alga expressing both conventional and divergent actins

2019 ◽  
Author(s):  
Evan W. Craig ◽  
David M. Mueller ◽  
Miroslava Schaffer ◽  
Benjamin D. Engel ◽  
Prachee Avasthi
Keyword(s):  
Green Alga ◽  
Actin Filaments ◽  
Electron Tomography ◽  
Filamentous Actin ◽  
Cellular Processes ◽  
Cellular Environment ◽  
Actin Structure ◽  
Actin Isoform ◽  
Labeling Method

AbstractThe green alga Chlamydomonas reinhardtii is a leading model system to study photosynthesis, cilia, and the generation of biological products. The cytoskeleton plays important roles in all of these cellular processes, but to date, the filamentous actin network within Chlamydomonas has remained elusive. By optimizing labeling conditions, we can now visualize distinct linear actin filaments at the posterior of the nucleus in both live and fixed vegetative cells. Using in situ cryo-electron tomography, we confirmed this localization by directly imaging actin filaments within the native cellular environment. The fluorescently-labeled structures are sensitive to the depolymerizing agent Latrunculin B (Lat B), demonstrating the specificity of our optimized labeling method. Interestingly, Lat B treatment resulted in the formation of a transient ring-like filamentous actin structure around the nucleus. The assembly of this perinuclear ring is dependent upon a second actin isoform, NAP1, which is strongly upregulated upon Lat B treatment and is insensitive to Lat B-induced depolymerization. Our study combines orthogonal strategies to provide the first detailed visual characterization of filamentous actins in Chlamydomonas, allowing insights into the coordinated functions of two actin isoforms expressed within the same cell.

scholarly journals Actin and secretion of surfactant.

1983 ◽  
Vol 31 (11) ◽  
pp. 1298-1304 ◽  
Author(s):  
E C Tsilibary ◽  
M C Williams
Keyword(s):  
Actin Filaments ◽  
Beta Agonist ◽  
Type Ii ◽  
Lamellar Bodies ◽  
Adrenergic Stimulation ◽  
Filamentous Actin ◽  
Agonist Stimulation ◽  
Intracellular Movement ◽  
Cell Profile

Type II cells were examined in situ in order to study the role played by actin filaments in secretion of surfactant. Following beta-adrenergic stimulation, the number of lamellar bodies per cell profile decreased substantially, an indication that exocytosis had occurred. In isoproterenol-stimulated cells decoration of actin by S1 revealed greater numbers of filaments associated with lamellar bodies, free in the cytoplasm, and associated with the cellular apex than in control cells. If cells were treated prior to beta-agonist stimulation with cytochalasin D, a drug which disrupts filamentous actin, the secretory response to the agonist was abolished. Together these two observations suggest that actin filaments participate in the intracellular movement and/or extrusion of lamellar bodies from the cells.

scholarly journals Nifedipine-sensitive calcium channels are involved in polar growth of lily pollen tubes

1985 ◽  
Vol 76 (1) ◽  
pp. 247-254
Author(s):  
H.D. Reiss ◽  
W. Herth
Keyword(s):  
Calcium Channels ◽  
Tip Growth ◽  
Lilium Longiflorum ◽  
Pollen Tubes ◽  
Polar Growth ◽  
Treatment Results ◽  
High Tendency ◽  
Lily Pollen ◽  
Internal Calcium

Pollen germination and tube growth of Lilium longiflorum in vitro are affected by 10(−5) M-nifedipine. Germinating ‘tubes’ form broad protuberances along the whole colpus. Short tubes show a high tendency to grow ‘amoeboid-like’ and to branch; or a second tube emerges in another region of the colpus. Longer tubes (greater than or equal to 100 micron) broaden irregularly or swell at their tips. The diameter of the tube can vary drastically within the same tube. With increasing time of treatment many tubes burst. Normal tip growth stops within 10 min, but protoplasmic streaming continues even after 15 h. More or less regularly, wall thickenings are formed along the whole tube or on the flanks of the germinating region after some hours. The internal calcium gradient, visualized by chlorotetracycline (CTC) fluorescence, is also disturbed. Nifedipine treatment results in uniform or irregular CTC fluorescence. Branching tubes temporarily show a new subapical CTC gradient. After 6–8 h of nifedipine treatment many cells are no longer stainable with CTC. The results indicate the presence of nifedipine-sensitive calcium channels in pollen tubes.

scholarly journals SCP1 encodes an actin-bundling protein in yeast

2003 ◽  
Vol 375 (2) ◽  
pp. 287-295 ◽  
Author(s):  
Steven J. WINDER ◽  
Thomas JESS ◽  
Kathryn R. AYSCOUGH
Keyword(s):  
Actin Filaments ◽  
Binding Proteins ◽  
Actin Binding ◽  
Filamentous Actin ◽  
Actin Bundles ◽  
Latrunculin A ◽  
The Stability ◽  
Order Structures

The association of F-actin (filamentous actin) with a large number of binding proteins is essential for cellular function. Actin-binding proteins control the dynamics of actin filaments, nucleate new filaments and facilitate formation of higher-order structures such as actin bundles. The yeast gene SCP1 encodes a small protein with significant homology to mammalian SM22/transgelin. We have investigated the role of Scp1p in budding yeast to probe the fundamental role of this family of proteins. Here, we demonstrate that Scp1p binds to F-actin and induces the formation of tight F-actin bundles in vitro. Deletion of SCP1 in yeast lacking the actin-bundling protein, fimbrin (Sac6p), exacerbates the disrupted actin phenotype and enhances latrunculin-A sensitivity. Furthermore, Scp1p co-localizes with actin in cortical patches and its localization is lost in the presence of latrunculin-A. Our data support a role for Scp1p in bundling actin filaments and, in concert with Sac6p, acting as a second actin-bundling activity crucial to the stability of the yeast actin cytoskeleton.

Myofibrillar degeneration with diphtheria toxin

2020 ◽  
Vol 45 (4) ◽  
pp. 351-357
Author(s):  
Bilge Özerman Edis ◽  
Muhammet Bektaş ◽  
Rüstem Nurten
Keyword(s):  
Protein Synthesis ◽  
Actin Filaments ◽  
Diphtheria Toxin ◽  
Cardiac Tissue ◽  
Culture Conditions ◽  
Bacterial Toxin ◽  
Filamentous Actin ◽  
Cardiac Damage ◽  
Tissue Samples

AbstractObjectivesCardiac damage in patient with diphtheritic myocarditis is reported as the leading cause of mortality. Diphtheria toxin (DTx) is a well-known bacterial toxin inducing various cytotoxic effects. Mainly, catalytic fragment inhibits protein synthesis, induces cytotoxicity, and depolymerizes actin filaments. In this study, we aimed to demonstrate the extent of myofibrillar damage under DTx treatment to porcine cardiac tissue samples.MethodsTissue samples were incubated with DTx for 1–3 h in culture conditions. To analyze whole toxin (both fragments) distribution, conjugation of DTx with FITC was performed. Measurements were carried out with fluorescence spectrophotometer before and after dialysis. Immunofluorescence microscopy was used to show localization of DTx-FITC (15 nM) on cardiac tissue incubated for 2 h. Ultrastructural characterization of cardiac tissue samples treated with DTx (15 or 150 nM) was performed with transmission electron microscopy.ResultsDTx exerts myofibrillar disorganization. Myofilament degeneration, mitochondrial damage, vacuolization, and abundant lipid droplets were determined with 150 nM of DTx treatment.ConclusionsThis finding is an addition to depolymerization of actin filaments as a result of the DTx-actin interactions in in vitro conditions, indicating that myofilament damage can occur with DTx directly besides protein synthesis inhibition. Ultrastructural results support the importance of filamentous actin degeneration at diphtheritic myocarditis.

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