bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pre‐prophase band of microtubules, absent from tip‐growing moss filaments, arises in leafy shoots during transition to intercalary growth
Authors: Doonan John H. , Cove David J. , Corke Fiona M. K. , Lloyd Clive W. 
Published: February 2005

AbstractIn the presence of cytokinin, undetermined side branch initials of the moss, Physcomitrella patens, arc induced to form buds and then leafy shoots rather than to develop as tip‐growing filaments. This represents a transition between the two modes of plant cell expansion–tip growth and uniform intercalary growth. The organization of microtubules in filaments is different from that in leafy shoots and can be traced back to the influence of phytohormones on side branch initials. Microtubules either focus at a particular region (as in tip‐growing cells) or in the presence of high levels of cytokinin form swollen bud initials in which microtubules are more diffusely organized. Higher levels of cytokinin are capable of destabilizing tip microtubules in caulonemal filaments. Although caulonemata are not normally target cells, this implies that cytokinin may exert its morphogenetic effects by altering microtubule organization.In tip‐growing filaments, interphase microtubules trace a meandering course through the cytoplasm towards the tip and are not for the main part associated with the plasma membrane as are cortical arrays. There is no pre‐prophase band of microtubules to indicate the future division plane, even though the oblique division plane is known to be precisely controlled relative to environmental factors. This microtubule cycle contrasts with cells of the leafy shoots that develop from buds: in these, the interphase array is cortical, consisting of flat‐pitched microtubular helices that do not focus upon a growing tip. It is now shown that pre‐prophase hands occur at this stage.The absence of bands does not readily correlate with imprecise control of the division plane. Instead, it is proposed that the ability to form pre‐prophase bands depends upon the arrangement of microtubules in the preceding interphase array. Ways in which bands might be formed are discussed and the generality of these ideas is tested by observations on higher plant cells.
New evidence for a “biased baseline” mechanism for calcium‐regulated asymmetry of flagellar bending
Authors: Eshel Dan , Brokaw Charles J. 
Published: February 2005

AbstractTime‐averaged data covering six to ten beat cycles for ATP‐reactivated spermatozoa of a sea urchin and Ciona, and from a uniflagellate mutant of Chlamydomonas, were analyzed to obtain parameters of oscillation and mean shear angle at each point along the flagellum. The mean shear angles usually show a sharp change near the base of Ihc flagellum. This sharp basal change in angle is correlated with perceived asymmetry in the development times of principal and reverse bends when these bends are measured directly from the asymmetric bending patterns, without subtracting out the mean shear angle. The asymmetry in development times was previously considered to be evidence against a “biased baseline” mechanism for asymmetric bending waves, in which completely symmetric bending waves develop and propagate on a curved flagellum. Our analysis now shows that the asymmetry in development times can be fully explained by the presence of a sharp static bend near the base of the flagellum, which can confuse the determination of the times of initiation of new bends at the base of the flagellum. Our reinterpretation of these data removes previous objections to the “biased baseline” mechanism for the regulation of bending wave asymmetry by calcium, and supports other evidence favoring a biased baseline mechanism, rather than a “biased switching” mechanism.
Myosin filaments in cytoskeletons of Dictyostelium amoebae
Authors: Clarke Margaret , Baron Andre 
Published: February 2005

AbstractCytoskeletons were prepared from vegetative amoebae of Dictyostelium discoideum by extraction with Triton X‐100. The cytoskeletons were suspended in buffers known to induce the assembly or disassembly of myosin filaments. The samples were fixed, and thin sections were examined by transmission electron microscopy. In both types of buffers, myosin‐containing cytoskeletons exhibited a ring of densely staining proteinaceous material within the cortical filament matrix; this ring was not observed in myosin‐free cytoskeletons. When myosin‐containing cytoskeletons were placed in buffers that induced myosin polymerization, the ring appeared as an array of rodlike filaments approximately 13 nm wide and up to 0.5 μm in length—dimensions appropriate for myosin thick filaments. If ATP was added to cytoskeletons containing such filaments, the cytoskeletons contracted and the ring of filaments disappeared. ATP‐induced contraction of cytoskeletons was also visualized by indirect immunofluorescence by using monoclonal antibodies to Dictyosielium myosin. All data were consistent with the identification of the protein ring seen by electron microscopy as cortical myosin. Its location and organization were appropriate for the production of cortical contraction through a sliding filament mechanism.
Protein phosphorylation and dynamics of cytoskeletal structures associated with basal bodies in Paramecium
Authors: Keryer Guy , Davis Frances M. , Rao Potu N. , Beisson Janine 
Published: February 2005

AbstractThe presence of phosphorylated proteins associated with microtubule organizing centers in tissue culture cells during mitosis has been demonstrated by the use of monoclonal antibodies raised against mitotic HeLa cells [Vandre et al., Proc. Natl. Acad. Sci. U.S.A. 81:4439–4443, 1984]. We report here that in Paramecium two of the mitosis specific antibodies, MPM‐1 and MPM‐2, decorate throughtout the cell cycle all the microtubule organizing centers (MTOCs) located in the cortex and in the oral apparatus (gullet). Immuno‐electron microscopy showed that these antibodies labeled the electron‐dense material surrounding basal bodies from which several microtubule networks as well as kinetodesmal fibers originate. During mitosis, these antibodies also stained other cortical cytoskeletal structures, the kinetodesmal fibers (MPM‐1 and MPM‐2) and the epiplasm (MPM‐1). Among the different polypeptides recognized by the antibodies on immunoblots, three major ones of 60, 63, and 116 kDa were found to be common to the cortex (where several thousand ciliary basal bodies are anchored) and the oral apparatus (which comprises several hundred basal bodies around which various arrays of cytoplasmic microtubules are organized). Alkaline phosphatase treatment abolished the immunoreactivity of the polypeptides and the labeling observed by immunofluorescence. These results demonstrate that phosphorylated proteins are associated with all the known active microtubule organizing centers present in the cortex throughout the cell cycle of Paramecium. Furthermore they indicate that in Paramecium phosphorylation of proteins could also be involved in the cell cycle dependent dynamics of cortical cytoskeletal structures other than microtubules.
Bending patterns of Chlamydomonas flagella: IV. Mutants with defects in inner and outer dynein arms indicate differences in dynein arm function
Authors: Brokaw C. J. , Kamiya R. 
Published: February 2005

AbstractMutants with outer dynein arm defects or deficiencies all show a major reduction in beat frequency to about half the normal value; some of these mutants show an additional decrease in sliding velocity associated with reduced shear amplitude and an additional reduction in beat frequency, as well as other more minor modifications of the normal forward mode bending pattern. New mutants (ida98, pf30), which appear to be deficient in a subset of inner dynein arms show a reduction in sliding velocity that is primarily associated with a reduction in shear amplitude, with only a small reduction in beat frequency. These differences in motility phenotype between inner and outer dynein arm mutants suggest that inner and outer dynein arms may have distinct functions. The relatively large decrease in sliding velocity associated with partial loss of inner arms is consistent with earlier observations on pf23, a nonmotile mutant lacking inner arms, suggesting that inner arms may have an essential function in motility. The ability to generate reverse mode bending patterns is retained in some inner or outer dynein arm mutants, but appears to be decreased in those mutants which show reduced shear amplitude for the forward mode bending pattern.
Axonal tubulin and microtubules: Morphologic evidence for stable regions on axonal microtubules
Authors: Sahenk Zarife , Brady Scott T. 
Published: February 2005

AbstractBiochemical studies indicate that axonal tubulin is composed of at least two distinct pools that differ in cold solubility and biochmical composition [Brady et al: J. Cell Biol. 99:1716–1724]. To determine the morphologic correlate of cold‐insoluble tubulin, segemnts of rat optic nerves were exposed to a series of in vitro experimental conditions that affect microtubules (MTs), including cold, podophyllotoxin (PT), triflupromazine (TFP), and taxol, and then examined by electron microscopy. Longitudinal sections of control axons showed MTs oriented parallel to the long axis of the axons. Axond exposed to Cold, PT, and TFP showed short segments of MTs in association with cytoskeletal disarray. Morphometric studies were used to distinguish between a simple malorientation of MTs (undulation or zigzags in their course) and the loss of labile segments of MTs, leaving the stable portions behind. The lengths of MT segments were measured in longitudinal sections, and the numbers of MTs were determined in the cross sections. All MT segment‐length histograms showed a unimodal distribution. Cold and PT produced a simple shift of the control histogram to the shorter length MTs. In cross sections the numbers of MTs in cold‐ and PT‐exposed axons were significantly decreased, indicating that the presence of short segments of MTs. Taxol, an agent that promotes MT assembly, reversed the cold effect partially and resulted in increases in both MT segment lenght and number. These studies indicate that stable MT segments are portions of longer MTs containing both stable and labile regions. Furthermore, these findings are consistent with the hypothesis that cold‐insoluble tubulin functions as a transportable MT‐organizing complex in the axon.
Binding of mammalian brain microtubule‐associated proteins (MAPs) to insect ovarian microtubules
Authors: Stebbings Howard , Anastasi Angela , Indi Shantinath , Hunt Cherryl 
Published: February 2005

AbstractIn this study we have applied microtubule‐associated proteins (MAPs) from mammalian brain to both native and reassembled insect ovarian microtubules. Such microtubules, which are normally smooth walled, become decorated with projections similar to those observed when mammalian brain MAPs are added back to assembling or assembled mammalian brain microtubules. The mammalian MAPs were also detected as components of insect microtubules when analyzed by polyacrylamide gel electrophoresis. Our observations suggest that mammalian brain MAPs have common binding sites on microtubules from two widely different sources and indicate the degree of evolutionary conservation of such sites.
Stimulation of in vitro motility of Chlamydomonas axonemes by inhibition of cAMP‐dependent phosphorylation
Authors: Hasegawa Etsuko , Hayashi Hiroshi , Asakura Sho , Kamiya Ritsu 
Published: February 2005

AbstractWhen demembranted axonemes of Chlamydomonas were reactivated with Mg ATP, the proportion of motile axonemes was significantly increased by the preence of either phosphodiesterase (PDE) or protein inhibitor of cAMP‐dependent kinase (PKI). The effect of PDE was cancelled by the addition of cAMP. These findings strongly suggest that the axoneme samples have endogenous cAMP, which can reduce the proportion of motile axonemes via phosphorylation. This inhibitory effect of cAMP on Chlamydomonas axonemes is opposite to its stimulatory effect on the axonemal motility in other organisms so far reported. PKI or PDE activated the motility motility either in the absence of Ca2+, when the axonemes beat with an asymmetric waveform, or in 10−5M Ca2+, when the axonemes beat with a symmetric waveform. This cAMP‐dependent regulation of motility was observed with the axonemes from which detergent‐soluble material had been removed, indicating that the proteins responsible for the regulation still remained in the axonemes. Preliminary in vitro phosphorylation stdies have implicated two polypetides as candidates for the target protein of cAMP‐dependent protein kinase: one with a molecular weight of 270 kD and the other with a much larger molecular weight.
Characterization of villin from the intestinal brush border of the rat, and comparative analysis with avian villin
Authors: Alicea H. A. , Mooseker M. S. 
Published: February 2005

AbstractThe biochemical properties of villin purified from the brush borders of chicken and rat small intestines were compared, with emphasis on their physical properties and their Ca++‐dependent interaction with actin. Like chicken villin, rat villin exists as two isoforms present in equimolar concentrations; the rat isoforms are slightly more acidic than those of chicken villin (6.08 and 6.11 versus 6.26 and 6.34). Rabbit antisera raised against either villin crossreacted with the other one. Like the avian protein, rat villin bundled F‐actin at calcium concentrations below 0.1 μM. Above ∼︁1 μM calcium, it accelerated the rate of actin assembly and restricted filament lengths of F‐actin formed either during coassembly with villin or by addition of villin to preformed filaments. The threshold calcium concentration required for effective severing of preformed filaments was approximately tenfold higher than that required for restricting lengths during coassembly. The extent of filament shortening was proportional to the amount of villin present. At a fixed villin concentration, filament length decreased with increasing [Ca++] over a broad range from 10−7−10−4 M. In general, the mean filament lengths and the dispersion about the mean value were lower in samples where filaments were coassembled with villin than when villin was added to preformed filaments.
Motility of the spirochete leptospira
Authors: Goldstein Stuart F. , Charon Nyles W. 
Published: February 2005

AbstractSpirochetes are a group of bacteria with a unique ultrastructure and a fascinating swimming behavior. This article reviews the hydrodynamics of spirochete motility, and examines the motility of the spirochete Leptospira in detail. Models of Leptospira motility are discussed, and future experiments are proposed.The outermost structure of Leptospira is a membrane sheath, and within this sheath are a helically shaped cell cylinder and two periplasmic flagella. One periplasmic flagellum is attached subterminally at either end of the cell cylinder and extends partway down the length of the cell. In swimming cells, each end of the cell may assume either a spiral or a hook shape. Translational cells have the anterior end spiral shaped, and the posterior end hook shaped. In the model of Berg et al., the periplasmic flagella are believed to rotate between the sheath and the cell cylinder. Rotation of the anterior periplasmic flagellum causes the generation of a gyrating spiral‐shaped wave. This wave is believed sufficient to propel the cells forward in a low‐viscosity medium. The cell cylinder concomitantly rolls around the periplasmic flagella in the opposite direction—which allows the cell to literally screw through a gel‐like viscous medium without slippage. This model is presented, and it is contrasted to previous models of Leptospira motility.
51‐kd protein, a component of microtubule‐organizing granules in the mitotic apparatus involved in aster formation in vitro
Authors: Toriyama Masaru , Ohta Kunihiro , Endo Sachiko , Sakai Hikoichi 
Published: February 2005

AbstractMitotic apparatuses (MAs) isolated from sea urchin metaphase eggs were chilled on ice to depolymerize microtubules, homogenized, and incubated with tubulin. This caused formation of many small asters with microtubules focusing on granules which were probably fragments of the centrosome. The aster‐forming protein components of the granules in the homogenized MAs were solubilized in 0.5 M KCl containing 50% glycerol. After dialysis against low‐ionic‐strength buffer solution, proteins congregated to form granular assembly capable of initiating aster formation. Phosphocellulose column chromatography enabled the separation of the aster‐forming protein fraction which contained a 51,000 molecular weight protein (51‐kd protein) as a major component. The protein fraction possessing the aster‐forming activity was also prepared from methaphase whole egg homogenate, and the elution profile of the 51‐kd protein on phosphocellulose column also coincided with that of the aster‐forming activity. The granular assembly reconstituted from the phosphocellulose fraction formed asters whose microtubules show the same growth rate and length distribution as those of asters reconstructed from the granules in the homogenized MAs. Anti‐51‐kd protein antibody that was raised in rabbit and affinity‐purified stained the center of asters which were reconstructed either from the granules in the homogenized MAs or from the granular assembly reconstituted from the phosphocellulose fraction. These results suggest that the 51‐kd protein is a component in the aster‐forming activity of the centrosomal component in vitro.
Interaction of chlamydomonas dynein with tubulin
Authors: Haimo Leah T. , Fenton Raymond D. 
Published: February 2005

AbstractStudies were conducted to determine if dynein could bind to unpolymerized tubulin. Tubulin alone normally fractionated in the included volume of a molecular sieve Bio‐Gel A‐1.5m column. Incubated together, tubulin and dynein coeluted in the void volumn, suggesting that a complex had formed between the two. In addition, immunoelectron microscopy revealed preassembled microtubules were labeled with biotin antibody only when incubated in both dynein and biotinylated tubulin, evidence that dynein with bound biotinylated tubulin had decorated the microtubules. A fraction of the tubulin could be dissociated from dynein by addition of ATP and vanadate, as assayed by molecular sieve chromatography followed by densitometry of gels, suggesting that some tubulin bound to the B end of the dynein arm. Additional tubulin dissociated from the dynein under conditions of high salt. These studies, together with those indicating that tubulin blocked the A end of the dynein arm from binding to microtubules and promoted the interaction of two arms at their A ends, provide evidence that the A end of the arm also can bind tubulin. Thus, the tubulin subunits, themselves, on a microtubule rather than a particular surface lattice structure formed by adjacent protofilaments may provide the binding sites for both ends of the dynein arm.
Subcellular sequestration of an antigenically unique β‐tubulin
Authors: Gallo Jean‐Marc , Précigout Eric , Schrével Joseph 
Published: February 2005

AbstractTubulin from Trypanosoma brucei was characterized by Western blotting using well defined monoclonal antibodies reacting with α‐ or β‐tubulin and a new monoclonal antibody, 1B41, raised against a microtubule‐enriched fraction of T. brucei, which specifically reacts with the β‐subunit of tubulin from either T. brucei or rat brain. This antibody has been used to examine the subcellular distribution of the corresponding antigen in T. brucei by indirect immunofluorescence. The epitope recognized by 1B41 is restricted to a thin line extending from the basal body region to the anterior end of the cell body. To determine the relationship between the immunoreactive zone and the flagellum, double‐label immunofluorescence was performed in both interphase and mitotic cells with 1B41 and a flagellar marker, the monoclonal antibody 5E9, specific for the paraflagellar rod polypeptides of trypanosomes. These experiments revealed that the immunoreactive tubulin was contained in a part of the subpellicular cytoskeleton that remained in a constant spatial correspondence with the flagellum throughout the cell division cycle. The β‐tubulin recognized by 1B41 may be segregated into the microtubular structures associated with a cisterna of the endoplasmic reticulum forming the subflagellar microtubule quartet (SFMQ). These results suggest that the presence of an antigenically unique β‐tubulin defines a subpopulation of microtubules possessing specfic dynamic properties that may be involved in the morphogenesis of daughter cells during the division of T. brucei.
Colocalization of F‐actin and 34‐kilodalton actin bundling protein in dictyostelium amoebae and cultured fibroblasts
Authors: Johns Julie A. , Brock Alice M. , Pardee Joel D. 
Published: February 2005

AbstractThe Ca+2‐sensitive actin‐binding protein isolated from Dictyostelium discoideum, 30,000‐D protein (Fechheimer and Taylor: J. Biol. Chem. 259:4514–4520, 1984;) has recently been localized in filipodia of substrate‐adhered amoebae (Fechheimer: J. Cell Biol. 104:1539–1551, 1987). We have determined that this protein has a Mr of 34,000 daltons and is strictly colocalized with actin filaments in both substrate‐attached Dictyostelium amoebae and cultured fibroblasts. 3T3 fibroblasts, as well as normal and virally transformed rat kidney fibroblasts (NRK) contain a 34‐kilodalton (kD) protein that cross‐reacts specifically with antibody to the Dictyostelium bundling protein. Mammalian 34‐kD protein is colocalized with F‐actin in stress fibers and the cortical cytoskeleton in substratadhered fibroblasts. In substrate‐adhered vegetative Dictyostelium, F‐actin and 34‐kD protein are concentrated in regions of the cell cortex exhibiting filipodia and membrane ridges. Multiple filipodia formed after exposure to the chemoattractant folic acid stain intensely for 34‐kD protein, implying participation in the assembly of actin bundles during filipod formation. The cortex of pseudopodia also contained high concentrations of bundling protein, but pseudopod interiors did not. In contrast to vegetative Dictyostelium, F‐actin and 34‐kD protein were not colocalized in cells that had progressed through the development cycle. In fruiting bodies, 34‐kD protein was detected by immunofluorescence microscopy only in prespore cells, while F‐actin appeared in stalk cells and spores.