bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the chlamydomonas flagellar collar
Authors: Snell William J. 
Published: February 2005

AbstractThe flagella of Chlamydomonas reinhardtii protrude through the cell wall via short, tunnel‐like openings that are lined with 11 nm × 500 nm fibers arranged in parallel array. These cylindrical collections of fibers presumably permit free movement of the flagella within the cell wall. In this report electron‐microscopic evidence is presented showing that during the initial stages of the mating reaction intact collars slip off of the ends of the flagella when cell wall loss occurs. Electrophoretic analysis of isolated collars reveals one major protein and several minor species.
Crawling caenorhabditis elegans spermatozoa contact the substrate only by their pseudopods and contain 2‐nm filaments
Authors: Roberts Thomas M. 
Published: February 2005

AbstractThe locomotion of C. elegans spermatozoa resembles, in many respects, the crawling movements of other eukaryotic cells. However, these sperm contain surprising little actin, which plays no apparent role in this cell's motility. Electron microscopy has revealed that crawling spermatozoa retain a strict morphological polarity so that the organelle‐filled cell body is separated from the pseudopod by an array of cytoplasmic laminar membranes. When sperm crawl only the pseudopod contacts the substrate; the cell body is either pulled behind or carried on top of the rear portion of the pseudopod. Fingerlike projections which extend forward from the leading edge of the pseudopod initiate contact with the substrate. The underside of the pseudopod exhibits areas of close (40 nm separation) membrane‐substrate association with intervening areas of wide (up to 300 nm) membrane‐substrate gaps. The pseudopod cytoplasm contains 2‐nm filaments but no filamentous actin has been observed. These 2‐nm filaments were detected in thin sections of crawling cells and in negative‐stained remnants of spermatozoa disrupted by either hypotonic buffer on Triton X‐100. The filaments are found both free in the cytoplasm and closely associated with the cytoplasmic face of the plasma membrane and are usually oriented along the long axis of the cell. Neither the identity nor the function of these filaments has been established although their location and orientation suggest that they may be involved in generating propulsion.
Microfilament rearrangements during fibroblast‐induced contraction of three‐dimensional hydrated collagen gels
Authors: Farsi Jamila M. A. , Aubin Jane E. 
Published: February 2005

AbstractIn vitro models have been developed recently to study the ability of fibroblasts to generate tensile force within collagen gels. The present study was initiated to assess the role of the cytoskeleton in the cell shape changes and force generation in one such model system. Porcine periodontal ligament fibroblasts (PPLF) were cultured within three‐dimensional collagen gels attached to glass coverslips. Fluorescence microscopy, using nitrobenzooxadizole (NBD)‐phallacidin labeling for microfilaments and tubulin antibody staining for microtubules, was combined with phase and Nomarski optics to determine the intra‐ and extracellular architecture of the cells and collagen fibers. Samples were observed from 30 minutes to 24 hours after initiation of cell attachment. During attachment and spreading, NBD‐phallacidin staining changed dramatically until large microfilament bundles became prominent. Collagen fiber alignment, compaction, and finally tearing from the coverslip occurred during this time. After release of tension, microfilament bundles were no longer evident. The change in microtubule distribution during these processes was less dramatic, appearing to follow the change in cell shape. These results indicate that microfilaments play an essential role in generating force to align and compact collagen, while microtubules may have a secondary role only.
An unusual mechanism of cell contraction: Leptodiscinae Dinoflagellates
Authors: Cachon Jean , Cachon Monique 
Published: February 2005

AbstractThe Leptodiscinae, a group of marine Dinoflagellates, are good material for the study of contraction though they cannot be collected in abundance. Their cell bodies are flattened anteroposteriorly (Leptodiscus, Leptophyllus, and Leptospathium) and are able to contract suddenly when the surrounding water is disturbed.Electron microscopical observations have shown that the structures responsible for the contraction consist of a layer of parallel filaments located beneath the cell membrane of some specialized parts of the body. These filaments seem to be nonactin (NAF) because of their diameter (2.5–3 nm) and because they are not decorated by heavy meromyosin (HMM). They appear helically coiled and doubly twisted, and form tubular structures when contracted.
Dynamics of keratin filaments and the intermediate filament distribution center during shape change in PtK1 cells
Authors: Eckert Barry S. , Caputi Susan E. , Warren Robert H. 
Published: February 2005

AbstractReorganization of intermediate filaments during cell spreading is examined by immunofluorescence, electron microscopy, and time‐lapse video microscopy. A juxtanuclear cap, believed to correspond to the intermediate filament distribution center, was observed to be spatially related to the organization of the intermediate filament network as cells spread. A keratin cap was observed, which appeared spontaneously in motile PtK1 cells. Cap formation may be a consequence of retraction of intermediate filaments from the cytoplasm as cells move. The position of this juxtanuclear cap is related to the direction of movement, located on the side of the nucleus near the advancing edge of the cell. As the cell spreads, the cap disappears as the keratin filament network returns to the cytoplasm. Evidence presented here is consistent with the hypothesis that the distribution center mediates keratin filament organization during cell shape change.
Evidence against surf‐riding as a general mechanism for surface motility
Authors: Bowser Samuel S. , Bloodgood Robert A. 
Published: February 2005

AbstractThe mechanism responsible for the energy‐dependent movement of membrane components (ie, surface motility) is unknown. Recently a potentially unifying model, termed “surf‐riding” [Hewitt, 1979] or “surf‐boarding” [Berlin and Oliver, 1982], has been proposed to explain surface motility. Using phase‐contrast light microscopy and membrane surface markers (polystyrene microspheres), we have tested the surf‐riding/surf‐boarding hypothesis on two protozoan systems: the axopodia of the heliozoan Echinosphaerium nucleofilum and the reticulopodial networks of the allogromiid foraminiferans Allogromia laticollaris and Allogromia sp, strain NF. Our evidence indicates that surface motility, as displayed by these organisms, does not occur by a surf‐riding/surf‐boarding mechanism. Previouś observations on surface motility associated with the Chlamydomonas flagellum indicate that this system is also incompatible with the surf‐boarding/surf‐riding hypothesis.
Cytoplasmic tubulin from the unfertilized sea urchin egg: II. Variation of the intrinsic calcium sensitivity of strongylocentrotus purpuratus egg tubulin as a function of temperature and brain microtubule‐associated proteins
Authors: Suprenant Kathy A. , Rebhun Lionel I. 
Published: February 2005

AbstractCytoplasmic tubulin purified from unfertilized sea urchin eggs self‐assembles in the absence of microtubule‐associated proteins (MAPs) [Suprenant and Rebhun, 1983; Detrich and Wilson, 1983] with a critical concentration for polymerization of 0.8 mg/ml at 15–18°C, a value well below the 3 mg/ml tubulin present in these eggs [Pfeffer et al, 1976]. Studies of the calcium sensitivity of unfertilized S. purpuratus (sea urchin) egg tubulin were initiated to help understand how this tubulin is maintained unassembled in the unfertilized egg. Egg microtubules, assembled at physiological temperatures (15–18°C) were depolymerized by a 100‐fold lower free calcium concentration than egg microtubules assembled at the higher temperatures (25–37°C) generally used to assemble mammalian brain microtubules. The initial rate of egg microtubule assembly was much more sensitive to calcium than was microtubule depolymerization at steady state at 37°C. However, both processes were sensitive to near physiological free calcium of free calcium for depolymerization than microtubules assembled at 18°C from egg tubulin alone. While calcium regulatory MAPs have not yet been found in sea urchin eggs, the fact that brain MAPs interact with egg tubulin and regulate both its critical concentration for polymerization [Suprenant and Rebhun, 1983] and its calcium sensitivty, suggests that such regulatory molecules exist. These results suggest that sea urchin egg tubulin assembly in vivo could be controlled by variations in interacellular calcium levels acting in concert with urchin egg proteins similar in function to brain MAPs.
Energy requirements for pigment aggregation in Fundulus melanophores
Authors: Clark Theodore G. , Rosenbaum Joel L. 
Published: February 2005

AbstractTeleost chromatophores are filled with individual pigment granules that rapidly aggregate to the cell center or become dispersed throughout the cytoplasm in response to environmental stimuli. Microtubules appear to be required for pigment aggregation (movement toward the cell center), and recent findings have suggested that a dynein‐like ATPase may participate in force production. Based on previous studies, however, it has been argued that pigment aggregation does not require energy directly, a view that supports the involvement of an elastic component in granule movement. To examine this point further, we have reinvestigated the energy requirements for pigment aggregation using both intact cells and detergent‐permeabilized cell models of Fundulus melanophores. Poisons of oxidative phosphorylation, namely, 2,4 dinitrophenol and NaCN, reversibly inhibit melanosome aggregation in response to adrenaline. Inhibition of movement results directly from depletion of intracellular ATP, since pigment translocation can be reactivated in permeabilized cells by the addition of exogenous ATP to the lysis buffer. Non‐hydrolyzable analogues, including β,γ‐imidoadenosine‐5′‐triphosphate (AMPPNP), β,γ‐methylene adenosine‐5′‐triphosphate (AMPPCP), and ATPγS, will not substitute for ATP in reactivation of movement. Similarly, other nucleotides such as ADP, AMP, GTP, CTP, and ITP, have limited ability to support melanosome aggregation in metabolically poisoned cells subjected to detergent lysis. ATP itself has no effect on intact cells. These results indicate that melanosome aggregation is ATP‐dependent and energy‐driven, and are consistent with a role for a force‐transducing ATPase in particle movement.
Non‐actin filaments and cell contraction in Kofoidinum and other Dinoflagellates
Authors: Cachon Jean , Cachon Monique 
Published: February 2005

AbstractThe motility and fine structure of the marine planktonic dinoflagellate Kofoidinium and members of other related genera have been investigated. Several types of shape change were found to occur: slow morphogenetic changes (which also occurred as restitution movements in response to injury), movements associated with the ingestion of food and the evacuation of wastes, and more rapid movements concerned with the capture of prey. All these movements seemed to be brought about by the contraction of refractile tracts within the cytoplasm, which were found to contain 2.3‐nm filaments, some with a complex striated appearance. This and other evidence suggests that these filaments, which have counterparts in many other protists, are not actin filaments.
Study of the properties of MgATP2−‐induced stationary bends in demembranated sea urchin sperm
Authors: Sale Winfield S. 
Published: February 2005

AbstractMethods of demembranation and reactivation of Lytechinus pictus sperm were developed that result in non‐motile sperm which take on a stable bend of about 3.5 radians at the proximal end of the cell. The middle and distal portion of the flagellum is relatively straight or slightly bent in the same direction forming a somewhat “C” shaped sperm cell. In these studies, we refer to this characteristic shape as the quiescent form, and as opposed to “rigor wave” sperm, the quiescent form is induced and maintained by a relatively high concentration of MgATP2− (> 0.2 mM). Other conditions important to the production and maintenance of the quiescent form in demembranated sperm include: starting with concentrated, undiluted sperm, maintaining low Ca++ in the demembranation buffer, using a minimum of 0.2 mM MgATP2− and pH of 7.9–8.1 in the reactivation buffer. Deviation from some of these conditions results in a dramatic increase in motile, asymmetrically beating sperm. Addition of 0.4 mM CaCl2 to the reactivation buffer increased the proximal bend angle to 5 radians. The induction and maintenance of the stationary bend is mediated by dynein activity: “rigor wave” sperm were transformed to the quiescent form upon 0.2 mM ATP addition; micromolar vanadate abolished the quiescent form by “relaxation” of the proximal bend; and the vanadate relaxed sperm were restored to quiescent form by catechol. Importantly, 20 μM cAMP activated motility of the otherwise quiescent‐form sperm. Quiescent‐form, demembranated sperm were also activated by mild trypsin digestion. These and other data suggest that the quiescent‐form sperm are trapped at the end of the principal bend, and these data are consistent with the proposal that the single stationary bend results from asymmetry of active microtubule sliding [Gibbons and Gibbons, (1980): J. Cell Biol. 84:13–27].
Tension in the culture dish: Microfilament organization and migratory behavior of quail neural crest cells
Authors: Tucker R. P. , Edwards B. F. , Erickson C. A. 
Published: February 2005

AbstractWe have investigated one aspect of the migratory behavior of quail neural crest (NC) cells by comparing the organization of microfilament bundles and the ability to distort migratory substrata by NC, somite, and notochord cells in vitro. In contrast to the numerous cytoplasmic stress fibers in somite‐derived fibroblasts and notochord cells revealed by rhodamine‐phalloidin staining and thin‐section electron microscopy, microfilaments in NC cells are restricted to the cell cortex. To test the relative degrees of tension generated by these cell types on the underlying substratum, cells were cultured in collagen gels and on distortable silicone rubber sheets. Explanted somites and notochords produced dramatic radial alignment of 750 μg/ml collagen gels, whereas neural crest cells only aligned gels of lower concentrations. Fibroblasts did not migrate individually from explanted somites and notochords into 250 μg/ml collagen gels as readily as into higher concentration collagen lattices. In contrast, neural crest cells migrated into matrices of low concentration as well as into higher concentration collagen gels. Neural crest cells and their pigmented derivatives did not distort silicone rubber sheets, whereas somite and notochord‐derived fibroblasts wrinkle this substratum after 4 days in culture. Thus, the differences in organization of the actin cytoskeleton reflect the tractional force exerted by these cells on their substratum. We hypothesize that the migratory behavior of NC cells in vivo may be related to their ability to translocate through embryonic extracellular matrices while generating relatively weak adhesions with the substratum, whereas the stronger forces generated by other embryonic cell types upon the delicate extracellular matrix may restrict their migration and may be associated with other morphogenetic events.
Isolation of newt lung ciliated cell models: Characterization of motility and coordination thresholds
Authors: Weaver Alice , Hard Robert 
Published: February 2005

AbstractDemembranated ciliated cell models are useful for studying mechanisms responsible for the regulation of ciliary coordination and waveform. This paper describes procedures for isolating ciliated cells from the newt, Taricha granulosa, by trypsin dissociation, their subsequent demembranation by Triton X‐100, and their reactivation with MgATP to produce highly motile, coordinated, ciliated cell models. Reactivation of cell models with a high degree of mechanochemical coupling depended on avoiding mechanical damage and maintaining optimal conditions during all stages of isolation and reactivation. Highly motile models were prepared from cells incubated in trypsin, treated briefly with EDTA, separated by gentle agitation, and concentrated by centrifugation at low gravitational forces. Optimal demembranation and reactivation conditions were similar to those described previously for isolated newt lung axonemes. Under these conditions, nearly 100% of the models were reactivated when provided with MgATP and 90–95% beat with coordinated waves. The ciliary tufts beat at frequencies within the range measured in living cells and their reactivated motility was stable for at least 30 min at constant MgATP. These highly coupled models were used to show (1) that development of coordination in the ciliary tuft occurs at a higher substrate concentration range (10–25 μM) than that required to initiate motility per se (2–10 μM); (2) that outer dynein arms may not contribute to beat frequency at substrate concentrations below 35 μM; and (3) that vanadate has effects both on beat frequency and coordination of the tufts.
Fungal nuclear behavior analysed by ultraviolet microbeam irradiation
Authors: McKerracher Lisa J. , Heath I. Brent 
Published: February 2005

AbstractDuring hyphal tip growth in the fungus Basidiobolus magnus, nuclei normally maintain a constant distance from the advancing cell apex by continuously migrating forward. It is not known whether the mechanism that produces nuclear movement also mediates nuclear positioning, or whether these two processes are under separate control. By irradiating small cytoplasmic regions with an ultraviolet microbeam, the coordination between movement and positioning could be disrupted. Regardless of the distance of the target from the nucleus, anterior irradiations (those ahead of the nucleus) caused the nucleus to stop or move backwards, whereas posterior (behind the nucleus) irradiations caused an acceleration in the nuclear velocity. The nucleus retained its ability to move following irradiation, so there was only loss of control over normal positioning. These results suggest that movement and positioning are mediated by different mechanisms. Quantitative microtubule analysis demonstrated that microtubules in the target region had been depolymerized, but in other regions of the cell they were apparently normal. We suggest that the depolymerization of microtubules affects nuclear movement by altering the tensile strength of the cytoplasm, and that cytoskeletal tension mediate nuclear positioning.We also found that accelerated nuclear movement could occur when most of the microtubules surrounding the nucleus were depolymerized. A comparison of the microtubule population surrounding the nucleus in unirradiated versus irradiated cells suggested that microtubules move with nuclei. Therefore, the nucleus does not appear to move via a direct interaction with microtubules.
The use of submicroscopic gold particles combined with video contrast enhancement as a simple molecular probe for the living cell
Authors: De Brabander M. , Nuydens R. , Geuens G. , Moeremans M. , De Mey J. 
Published: February 2005

AbstractWe describe a new approach to probe the molecular biology of the living cell that uses small colloidal gold particles coupled to specific ligands. They are visualized in cells by bright‐field, video enhanced contrast microscopy. We describe the basic aspects of the technique and provide examples of applications to intracellular motility, cell membrane dynamics, receptor translocation, internalization, and intracellular routing. We also provide examples of the use of this approach in immunospecific labelling of cells and tissue sections.
Duplication of the flagellar apparatus and cytoskeletal microtubule system in the alga Polytomella
Authors: Aitchison William A. , Brown David L. 
Published: February 2005

AbstractWe have used immunofluorescence staining with monoclonal antibodies to tubulin and to components of the flagellar basal apparatus to examine duplication of the basal apparatus and the microtubule system assembled from it during cell division in the quadriflagellate alga Polytomella. The monoclonal antitubulin, prepared against Polytomella flagellar axonemes, detects Polytomella and mammalian tubulin by immunoblotting. By immunofluorescence and immunogold electron microscopy, it detects all microtubular structures that have been described in Polytomella. One of the antibodies generated using the isolated basal apparatus as immunogen appears to stain four of the eight basal body rootlets and is used in this study to detect early stages in the duplication of the flagellar apparatus. A cytoplasmic microtubule system is present, the elongate morphology of the cell is maintained, and the cells are motile throughout mitosis. The closed mitotic spindle forms perpendicular to the long axis of the cell. During mitosis, the newly formed basal bodies mature and four additional elongating flagella appear. Following mitosis, the eight flagella segregate into two groups, which begin to separate towards opposite poles of the cell. Concomitant with this separation, the rootlets of the parental basal apparatus separate and new rootlets are detected. We suggest that the components of the parental flagellar apparatus are segregated equally to the daughter cells. An interphase cytoskeletal microtubule array is assembled from each basal apparatus, and the morphology of the two cells is progressively established during cytokinesis.
Prelimlnary report on the ultrastructural organization of the contractile appendix of Tontonia appendiculariformis (ciliophora oligotrichina)
Authors: Greuet Claude , Gayol Philippe , Salvano Paule , Laval‐Peuto MichèLe 
Published: February 2005

AbstractTontonia appendiculariformis is a marine planktonic ciliate with a long tail. The tail can contract rapidly, becoming transformed into an oval mass one‐twentieth of its original length. The highly complex ulrastructure of the tail is described here in detail. A large part of the volume of the tail contains numerous more or less parallel membranous tubes. The membrane of the tubes has numerous invaginations and is probably derived from the smooth endoplasmic reticulum. This tubular material forms a continuous layer around the tail, interrupted in only one region, which contains cilia. Associated with the cilia are basal fibres with a periodically banded appearance. The tubular layer forms several folds separated by hyaloplasm containing many mitochondria. The pellicle of the tail is thrown into numerous pleats. It comprises a perilemma, a plasmalemma, and complex alveoli, but epiplasm and microtubules are absent. The alveoli appear to form septa within the folds of the layer of membranous tubes. In the region where the tail is attached to the body of the ciliate there are conspicuous bundles of microtubules and microfilaments. The membranous tubes and septa appear to be connected to small bundles of microfilaments, which presumably represent the contractile material. However, we consider the membranous tubes as potentially active in producing the change in shape. Although the structure of the tail of Tontonia is unique, there are certain similarities to the stalk of the Tintinnina and also to the motile extension of the dinoflagellate Erythropsidinium.