bluuebunny/crossref_metadata_2025_split huggingface dataset:
Movement of Myzostomum spermatozoa: Calcium ion regulation of swimming direction
Authors: Ishijima Sumio , Ishijima Sanae A. , Afzelius Björn A. 
Published: February 2005

AbstractSpermatozoa of the small myzostomid worm Myzostomum cirriferum usually swim with the flagellum foremost but occasionally stop and then swim with the head foremost. The spermatozoa have axoneme of the 9+0 type; thus each lacks the central pair microtubules. The flagellum emerges in the anterior end of the cell body and attaches to it with junctions. To understand the mechanism regulating the swimming direction of the spermatozoa, we recorded the sperm and their flagellar movements using a video camera with a high‐speed shutter. The effects of calcium and viscosity on these movements were also examined.The cell body with the flagellum attached to it formed a curved plate during beating, while the free portion of the flagellum beats with small helical bends. Motive force to propel a spermatozoon was mainly due to the bends in the cell body. The spermatozoa reversed the direction of their swimming as a result of a change in the direction of bend propagation. The direction of bend propagation was regulated by calcium; the bends in the cell body propagated from the end of the head toward the free portion of the flagellum at low concentrations of Ca2+, whereas the direction of bend propagation was reversed at high concentrations of this ion. High viscosity of the medium stimulated a change in the direction of bend propagation. © 1994 Wiley‐Liss, Inc.
Assembly and bundling of marginal band microtubule protein: Role of tau
Authors: Sanchez Ivelisse , Cohen William D. 
Published: February 2005

AbstractMicrotubule protein extracted from dogfish erythrocyte cytoskeletons by disassembly of marginal bands at low temperature formed linear microtubule (MT) bundles upon reassembly at 22°C. The bundles, which were readily visible by video‐enhanced phase contrast or DIC microscopy, increased in length and thickness with time. At steady state after 1 hour, most bundles were 6–11 μm in length and 2–5 MTs in thickness. No inter‐MT cross‐bridges were visible by negative staining. The bundles exhibited mechanical stability in flow as well as flexibility, in this respect resembling native marginal bands. As analyzed by SDS‐PAGE and immunoblotting, our standard extraction conditions yielded MT protein preparations and bundles containing tau protein but not high molecular weight MAPs such as MAP‐2 or syncolin. In addition, late fractions of MT protein obtained by gel filtration were devoid of high molecular weight proteins but still produced MT bundles. The marginal band tau was salt‐extractable and heat‐stable, bound antibodies to mammalian brain tau, and formed aggregates upon desalting. Antibodies to tau blocked MT assembly, but both assembly and bundling occurred in the presence of antibodies to actin or syncolin. The MTs were “unbundled” by subtilisin or by high salt (0.5–1 M KCl or NaCl), consistent with tau involvement in bundling. High salt extracts retained bundling activity, and salt‐induced unbundling was reversible with desalting. However, reversibility was observed only after salt‐induced MT disassembly had occurred. Reconstitution experiments showed that addition of marginal band tau to preassembled MTs did not produce bundles, whereas tau presence during MT reassembly did yield bundles. Thus, in this system, tau appears to play a role in both MT assembly and bundling, serving in the latter function as a coassembly factor. © 1994 Wiley‐Liss, Inc.
Effects of 6‐dimethylaminopurine on the length of the cell cycle and on the state of phosphorylation of putative intermediate filament proteins in sea urchin embryos
Authors: St‐Pierre Johanne , Vincent Michel , Dufresne Louise 
Published: February 2005

AbstractThe effects of 6‐dimethylaminopurine (6‐DMAP) on the length of the cell cycle and on the state of phosphorylation of a putative intermediate filament protein, p117, have been studied in sea urchin embryos. Embryos were transferred into sea water containing 600 μM 6‐DMAP at 0.5, 2 or 5 min after insemination, and incubated for 30 or 90 min. The effects of 6‐DMAP on cell cycle length were studied by determining the time required for completion of mitosis upon return of the embryos in normal sea water. In all instances, except for the embryos transferred 0.5 min after insemination (AI) and incubated for 30 min, the duration of the M phase was shortened compared to controls, being faster in the embryos incubated for 90 minutes compared to the 30 min incubation period. However, embryos transferred 0.5 min AI have a longer M‐phase than those transferred 2 minutes or later after fertilization, suggesting that between 0.5 and 2 min after fertilization, critical phosphorylating events occur which affect the commitment of the cells to enter M‐phase.To study the pattern of p117 phosphorylation during the cell cycle, the eggs were transferred 2 minutes after fertilization in presence of 600 μM 6‐DMAP and with 200 μCi/ml of 32P‐orthophosphate. Analyses of 32P‐labelled proteins after exposure of SDS‐PAGE gels and their corresponding blots suggested that phosphorylation of p117 greatly increases at the time of pronuclear fusion, and then declines slightly at prophase‐metaphase. This decrease is markedly enhanced when the cells are treated with 6‐DMAP during metaphase in order to induce a premature breakdown of the mitotic apparatus. A causal link is suggested between the level of phosphorylation of p117 and its state of assembly. © 1994 Wiley‐Liss, Inc.
Intermittent swimming in the spermatozoa of the lugworm Arenicola marina (L.) (Annelida: Polychaeta)
Authors: Pacey A. A. , Cosson J. C. , Bentley M. G. 
Published: February 2005

AbstractMotile spermatozoa of the polychaete Arenicola marina were observed to swim intermittently. On the basis of the behaviour of the flagellum, the quiescent periods can be classified into two main types. The first are those in which, although the generation of the flagellar wave appears to be initiated, its passage down the axoneme appears blocked. This results in the formation of an acute bend (of approximately 2.65 rad) in the proximal region of the flagellum with the remainder of the axoneme remaining straight. These have been termed Type I quiescent periods and are very similar to the “cane‐shaped” configuration which has been described in the spermatozoa of some sea urchins. Sperm may also enter a Type II quiescent period, in which both the propagation and the generation of flagellar waves appears blocked. The flagellum of such sperm appears straight or slightly curved and they can remain in this configuration for several minutes. With increased intensity and duration of irradiation, the length of time spent in Type II quiescent period was increased significantly. Both types of quiescent period were (1) reduced in duration and frequency by deletion of calcium from artificial sea water (ASW); (2) either abolished or reduced in duration by the addition of 1 mM cadmium chloride to ASW. In addition, flagellar waveforms very similar to those displayed by spermatozoa in Type I quiescent periods could be induced (if only for a short time) by the addition of the divalent cation ionophore A23187 to ASW. It is suggested that this type of behaviour may be induced following an influx of calcium into the intraflagellar compartment of spermatozoa and that this may be mediated by certain intensities and wavelengths of light. © 1994 Wiley‐Liss, Inc.
Subtraction scanning acoustic microscopy reveals motility domains in cells in vitro
Authors: Veselý P. , Lüers H. , Riehle M. , Bereiter‐Hahn J. 
Published: February 2005

AbstractScanning acoustic microscopy (SAM) observes all mechanical properties of living cells. Subtraction of the SAM images (SubSAM) of live cells was developed as a method for investigating minimal changes in cellular topography and elasticity. The image formation in the SubSAM takes into account the motion of cell mass as well as the changes of tension. High spatial and temporal resolution of the SubSAM revealed the structure of motile processes that develops at increasing time intervals, thus allowing the arising complexity of motion to be registered and investigated. Independent spots of activity emerge on a quiescent background as motility domains; they may change position, divide, merge, or disappear after a long time interval. In addition, zones of quiescence were identified over central parts of cytoplasmic lamellae. Nonmalignant (Ep: tadpole epidermal cells, XTH2: endothelial cells from tadpole hearts, 3T3 cells) and neoplastic cells (K2 cells of rat fibrosarcoma, A870N cells selected from K2) were investigated with the SubSAM. Three types of domains of subcellular cytoplasmic motility were identified in time series of two‐dimensional SubSAM images in normal and neoplastic cells. Of them only the wave‐like domain is self‐evident, being derived from ruffling and protruding activity at the cell margin. Two other domains wait for detailed analysis. The oscillating domain is a visualization of tension within the cell(s), and the nucleating domain indicates intracellular processes possibly preceding locomotion. Differences in motile domains were found between low K2 and high A870N metastatic cells. The dynamics of motility domains of the A870N cells resembled that of the highly motile Ep cells. Cell morphotype and motile activity of the A870N cells are significantly influenced by the pH of the medium. It became evident that identification of the otherwise invisible motile domains in living cells by SubSAM opens a new approach to a characterization of cell motility in vitro and to an understanding of early cellular reactions to various stimuli. © 1994 Wiley‐Liss, Inc.
Characteristics of pronuclear migration in Beroe ovata
Authors: Rouvière Christian , Houliston Evelyn , Carré Danièle , Chang Patrick , Sardet Christian 
Published: February 2005

AbstractIn the large eggs (∼1 mm) of the ctenophore Beroe ovata, female pronuclei migrate long distances to join stationary male pronuclei in the peripheral cytoplasm that surrounds the yolky interior. We have investigated the mechanism of nuclear migration using time lapse video recording, automated image analysis, visualization of microtubules by immunofluorescence and rhodamine‐tubulin injection, and electron microscopy. Female pronuclei migrated at average speeds of 0.2 μm/sec, and were found to show periodic oscillations in velocity. Alternating phases of acceleration and deceleration occurred with an average periodicity of 235 seconds covering distances of 47 μm (about 3 times the nuclear diameter). Migration velocities and velocity oscillations were similar in fertilized and unfertilized eggs; however, changes in migration direction were much more frequent in unfertilized eggs. Characteristic deformations of the pronuclear membrane and occasional rotation of the nuclear contents were observed during migration. Inhibitor studies indicated that microtubules are required for nuclear migration. In fertilized eggs the top of the nucleus was found to move through the dense layer of aligned sperm aster microtubules. The frequent changes in direction of pronuclear migration in unfertilized eggs reflect the random organization of the microtubule layer in the absence of sperm derived centrosomes. Densely packed endoplasmic reticulum was found intermeshed with sperm aster microtubules and connected extensively with the nuclear membrane during migration. Most nuclear pores were grouped in an infolding of the nuclear membrane. We suggest that in fertilized eggs the female pronucleus is transported to the minus ends of sperm aster microtubules using motor molecules attached either to the outer nuclear membrane and/or to the network of connecting ER. © 1994 Wiley‐Liss, Inc.
Concentration of cofilin, a small actin‐binding protein, at the cleavage furrow during cytokinesis
Authors: Nagaoka Rie , Abe Hiroshi , Kusano Ken‐Ichi , Obinata Takashi 
Published: February 2005

AbstractCofilin is a small actin‐binding protein which reguiates actin polymerization in a pH‐dependent manner. Immunofluorescence microscopy with a monoclonal antibody for cofilin revealed that this protein is temporarily concentrated at the contractile ring during cytokinesis. Cofilin appeared to accumulate rapidly at the contractile ring during late stages of furrowing, and was finally enriched at the midbody. The concentration of cofilin at the contractile ring was observed in several kinds of cultured cells. Furthermore, cofilin introduced into living cells by a microinjection method was also concentrated at the contractile ring. These results suggest that cofilin is involved in actin reorganization during cytokinesis. © 1995 Wiley‐Liss, Inc.
Dynamics of triton‐insoluble and triton‐soluble F‐actin pools in calcium‐activated human polymorphonuclear leukocytes: Evidence for regulation by gelsolin
Authors: Watts Raymond G. , Deaton Jane D. , Howard Thomas H. 
Published: February 2005

AbstractGelsolin, a Ca++ activated, 90 kd actin binding protein, can regulate actin polymerization in polymorphonuclear leukocytes (PMNs) via severing of filaments to dissolve gels or by capping of filament ends to limit polymerization. In Triton‐lysed PMNs, 30% of gelsolin is bound to the Triton‐soluble F‐actin (TSF) pool and none is bound to the Triton‐insoluble F‐actin (TIF) pool. Calcium‐activated PMNs exhibit concurrent temporal and quantitative TIF growth and TSF and total F‐actin loss. To determine if gelsolin plays a role in regulating TSF pool size, we monitored gelsolin‐actin interactions and TIF, TSF and G‐actin content at 5 second intervals in PMNs activated with the calcium ionophore, ionomycin. Actin pools were measured by NBDphallacidin binding and by gel scans and expressed relative to basal; gelsolin‐actin interactions were measured as change in the amount of EGTA‐resistant gelsolin:actin (G:A) complexes and by immunoblot quantification of gelsolin in actin pools. In basal PMNs, 33% of PMN gelsolin is bound in 1:1 EGTA‐resistant G:A complexes and TSF and TIF retain 30% and 0% of PMN gelsolin, respectively. By 20 seconds after ionomycin addition, TSF decreases, TIF increases and a fraction of gelsolin repartitions from the TSF to the TIF pool. At maximum change (60 seconds), total F‐actin (TIF + TSF) and TSF decrease and TIF increases by 25%; gelsolin is bound to both TSF and TIF (35% of total gelsolin in each pool), and 1:1 EGTA‐resistant G:A complexes increase from 33% to 70%. No changes occur in cells activated by ionomycin in the absence of Ca++. The data show Ca++ activated TIF growth and TSF loss are temporally and quantitatively associated with an increase in the percent of gelsolin bound to actin and the translocation of gelsolin from TSF to TIF. This is unique, since no other PMN activator is known to repartition gelsolin into TIF actin. Further, the Ca++ activated initial increase in TIF concurrent with a fall in TSF without a change in total F‐actin or G‐actin content suggest that TIF grows initially only by TSF annealing/cross‐linking to TIF. Gelsolin may regulate these events. © 1995 Wiley‐Liss, Inc.
Comparative study of the colchicine binding site and the assembly of fish and mammalian microtubule proteins
Authors: de Pereda J. M. , Wallin M. , Billger M. , Andreu J. M. 
Published: February 2005

AbstractIsolated microtubules from cod (Gadus morhua) are apparently more stable to colchicine than bovine microtubules. In order to further characterize this difference, the effect of the colchicine analogue 2‐methoxy‐5‐(2,3,4‐trimethoxyphenyl)‐2,4,6‐cyclo heptatrien‐1‐one (MTC) was studied on assembly, as measured by turbidity and sedimentation analysis, and on polymer morphology. MTC has the advantage to bind fast and reversible to the colchicine binding site of tubulin even at low temperatures. It was found to bind to one site in cod brain tubulin, with affinity (6.5 ± 1.5) × 105M 1at both low or high temperature, similarly to bovine brain tubulin. However, the effect of the binding differed. At substoichiometric concentrations of MTC bovine brain microtubule assembly was almost completely inhibited, while less effect was seen on the mass of polymerized cod microtubule proteins. A preformed bovine tubulin‐colchicine complex inhibited the assembly of both cod and bovine microtubules at substoichiometric concentrations, but the effect on the assembly of cod microtubules was less. At higher concentrations (5 × 10−5 to 1 × 10−3M), MTC induced a large amount of cold‐stable spirals of cod proteins, whereas abnormal polymers without any defined structure were formed from bovine proteins. Spirals of cod microtubule proteins were only formed in the presence of microtubule associated proteins (MAPs), indicating that the morphological effect of MTC can be modulated by MAPs. The effects of colchicine and MTC differed. At 10−5M colchicine no spirals were formed, while at 10−4M and 10−3M, a mixture of spirals and aggregates was found. The morphology of the spirals differed both from vinblastine spirals and from the spirals previously found when cod microtubule proteins polymerize in the presence of high Ca2concentrations. The present data show that even if the colchicine binding site is conserved between many different species, the bindings have different effects which seem to depend on intrinsic properties of the different tubulins. © 1995 Wiley‐Liss, Inc.
Growth cone enrichment and cytoskeletal association of non‐receptor tyrosine kinases
Authors: Helmke Steve , Pfenninger Karl H. 
Published: February 2005

AbstractFetal rat brain (E18) expresses at least three c‐src‐like, membrane‐associated non‐receptor tyrosine kinases: c‐src, fyn, and lyn. c‐src and fyn are the most abundant and are highly enriched in a subcellular fraction of nerve growth cones (GCPs). To study the cytoskeletal association of these tyrosine kinases, Triton X‐100‐resistant fractions were prepared from GCPs. All three non‐receptor tyrosine kinases are associated with the cytoskeleton to a significant degree with the relative affinities: fyn > c‐src > lyn. The binding is sensitive to ionic strength and to phosphotyrosine, but not to phosphoserine or phosphothereonine. To investigate the regulation of this association we used phosphatese inhibitors to increase phosphotyrosine levels in GCPs. This resulted in the release of c‐src from the cytoskeleton. Under these conditions tyrosine phosphorylation was increased selectively in released c‐src and primarily on tyrosine 527. Cytoskeletally bound c‐src had a higher specific kinase activity than Triton X‐100‐soluble c‐src. These findings indicate that src family members interact in a regulated manner with the cytoskeleton in non‐transformed cells. This regulation is explained by a model in which c‐src binds to the cytoskeleton via its SH2 domain and is released when phosphorylated tyrosine‐527 binds to this domain intramolecularly, inhibiting kinase activity. © 1995 Wiley‐Liss, Inc.
A 62‐kDA mitotic apparatus protein required for mitotic progression is sequestered to the interphase nucleus by associating with the chromosomes during anaphase
Authors: Ye Xiaojian , Sloboda Roger D. 
Published: February 2005

AbstractA protein component of 62‐kDa (p62) in the mitotic apparatus of the sea urchin embryo has been shown to be important for the proper progression of mitosis [Dinsmore and Sloboda, 1989: Cell 57:127–134]. To study the subcellular distribution of p62 during the cell cycle of sea urchin embryos, indirect immunofluorescence microscopy was used coupled to a modified detergent extraction procedure. The improved fluorescent images obtained by this procedure provide new information concerning the subcellular localization of p62 during the cell cycle that could not be obtained with previous conventional staining procedures [Johnston and Sloboda, 1992: J. Cell Biol. 119:843–854]. Using affinity purified antibodies to p62, we observed a cell cycle‐dependent localization of p62 to the chromosomes/chromatin. Prior to nuclear envelope breakdown of the first or second cell cycle, p62 localizes to chromatin in the nucleus. During mitosis, p62 associates with the region of the spindle occupied by the microtubules of the mitotic apparatus. As anaphase proceeds, but before the nuclear envelope reforms, p62 becomes progressively associated with the chromosomes. Thus, p62 is incorporated into the forming interphase nucleus due to its association with chromosomes during late anaphase, rather than by active translocation into the newly formed daughter nuclei through the nuclear pores. The protein is not unique to marine embryos, as demonstrated by immunofluorescence of Y‐1 cells, a mouse adrenal tumor cell line In these cells, the localization of p62 is similar to the localization of the protein in echinoderm embryos, suggesting its possible function in mitotic progression in mammalian somatic cells as well. © 1995 Wiley‐Liss, Inc.
Topographic compensation: Guidance and directed locomotion of fibroblasts on grooved micromachined substrata in the absence of microtubules
Authors: Oakley C. , Brunette D. M. 
Published: February 2005

AbstractFibroblats cultured on grooved substrata align themselves and migrate in the direction of the grooves, a phenomenon called contact guidance. Microtubules have been deemed important for cell polarization, directed locomotion, and contact guidance. Because microtubules were the first cytoskeletal element to align with the grooves when fibroblasts spread on grooved substrata, we investigated the consequences of eliminating the influence of microtubules by seeding fibro‐blasts onto smooth and grooved micromachined substrata in the presence of colcemid. Fibroblasts were examined by time‐lapse cinematography and epifluorescence or confocal microscopy to determine cell shape and orientation and the distribution of cytoskeletal or associated elements including actin filaments, vinculin, intermediate filaments, microtubules, and kinesin.As expected, cells spreading on smooth surfaces in the presence of colcemid did not polarize or locomote. Surprisingly however, by 24 hours, cells spread on grooves in the presence of colcemid were morphologically indistinguishable from controls spread on grooves. Both groups were aligned and polarized with the direction of the grooves and demonstrated directional locomotion along the grooves. In the absence of microtubules, kinesin localized to some of the aligned stress fibers and to leading edges of cells spreading on grooves. The grooved substratum compensated for the microtubule deficiency by organizing and maintaining an aligned actin filament framework. Thus, microtubules are not required to establish or maintain stable, polarized cell shapes or directed locomotion, provided an alternate oriented cytoskeletal component is available.