Tip Of Filament Research Articles

Corallophila eatoniana comb. nov. (Ceramiaceae, Rhodophyta) from the Pacific coast of North America

A new combination is proposed for plants previously referred to as Ceramium eatonianum (Farlow) De Toni [= Centroceras eatonianum Farlow 1875] (Ceramiaceae, Rhodophyta). This red algal species is transferred to the genus Corallophila mostly on the basis of the following characteristics. It has rhizoids that arise from periaxial and inner cortical cells, outer cortical cells that are rectangular and arranged in longitudinal rows, spermatangia that develop on ordinary cortical cells, and tetrasporangia that are covered by cortical cells. Corallophila eatoniana is further characterized by having uniseriate rhizoids, pinnate branches. six to eight (usually seven) periaxial cells at the nodes, large gland cells on the tips of acropetal cortical filaments, and tetrasporangia on the upper parts of regular branches. The species occurs on the Pacific coast of North America from British Columbia, Canada, to Baja California, Mexico. Corallophila eatoniana is here neotypified by a specimen collected at Seal Rock, Oregon, on 10 July 1998. Generic comparisons between Corallophila and the fully corticated species of Ceramium and Centroceras are also given.

Terminal regions of mouse nebulin: sequence analysis and complementary localization with N-RAP.

The regions of mouse nebulin extending from the ends of the super repeats to the C-terminus and N-terminus were cloned and sequenced. Comparison of the mouse sequence with the previously published human sequence shows that the terminal regions of nebulin are highly conserved. The four phosphorylation motifs and SH3 domain found at the C-terminus of mouse nebulin are identical to those found in human nebulin, with the exception of four conservative substitutions. The modules linking this C-terminal region to the super repeats have deletions relative to both fetal and adult human nebulins that correspond to integral numbers of modules, making the mouse C-terminal simple repeat region among the shortest observed to date. The N-terminal region and the C-terminal modules were expressed in Escherichia coli and used for antibody production. Immunofluorescent labeling of these regions of nebulin in isolated myofibrils demonstrates that they are located near the center of the sarcomere and near the Z-line, respectively. Immunogold labeling with antibodies raised against the N-terminal nebulin sequence localizes this region in the A-band near the tips of the thin filaments. Nebulin localization is complementary to that of N-RAP, another muscle-specific protein containing nebulin-like super repeats; nebulin is exclusively found in the sarcomeres, while N-RAP is confined to the terminal bundles of actin filaments at the myotendinous junction. Cell Motil. Cytoskeleton 3:211-222, 2000 Published 2000 Wiley-Liss, Inc.

Terminal regions of mouse nebulin: Sequence analysis and complementary localization with N-RAP This article is a US Government work and, as such, is in the public domain in the United States of America.

The regions of mouse nebulin extending from the ends of the super repeats to the C-terminus and N-terminus were cloned and sequenced. Comparison of the mouse sequence with the previously published human sequence shows that the terminal regions of nebulin are highly conserved. The four phosphorylation motifs and SH3 domain found at the C-terminus of mouse nebulin are identical to those found in human nebulin, with the exception of four conservative substitutions. The modules linking this C-terminal region to the super repeats have deletions relative to both fetal and adult human nebulins that correspond to integral numbers of modules, making the mouse C-terminal simple repeat region among the shortest observed to date. The N-terminal region and the C-terminal modules were expressed in Escherichia coli and used for antibody production. Immunofluorescent labeling of these regions of nebulin in isolated myofibrils demonstrates that they are located near the center of the sarcomere and near the Z-line, respectively. Immunogold labeling with antibodies raised against the N-terminal nebulin sequence localizes this region in the A-band near the tips of the thin filaments. Nebulin localization is complementary to that of N-RAP, another muscle-specific protein containing nebulin-like super repeats; nebulin is exclusively found in the sarcomeres, while N-RAP is confined to the terminal bundles of actin filaments at the myotendinous junction. Cell Motil. Cytoskeleton 3:211–222, 2000 Published 2000 Wiley-Liss, Inc.

Models for spatial polymerization dynamics of rod-like polymers.

We investigate the polymerization kinetics of rod-like polymer filaments interacting with a distribution of monomer in one spatial dimension (e.g. along a narrow tube). We consider a variety of possible cases, including competition by the filament tips for the available monomer, and behaviour analogous to "treadmilling" in which the polymer adds subunits to one end and loses them at the other end so as to maintain a constant length. Applications to biological polymers such as actin filaments and microtubules are discussed.

Myxobolus infection of the gills of common bream (Abramis brama L.) in Lake Balaton and in the Kis-Balaton reservoir, Hungary.

During a five-year survey including studies on the parasite fauna of bream (Abramis brama), four gill-parasitic Myxobolus species (M. bramae, M. hungaricus, M. impressus and M. macrocapsularis) were recorded in a total of 313 breams from Lake Balaton. The commonest species, M. bramae showed a prevalence of 33%, while the other species occurred sporadically. Myxobolus bramae and M. macrocapsularis infected the tips of the gill filaments and caused both intralamellar and interlamellar infection. Intralamellar plasmodia of small size developed in the capillary network of the gill lamellae whereas the much larger interlamellar plasmodia were formed in the arteria afferens. The intralamellar plasmodia of M. hungaricus always infected the basal or central part of the gill filaments. In contrast to the above species developing in the blood vessels, M. impressus proved to be an epithelial parasite, as its plasmodia always developed in the adjacent gill filaments of two opposite haemibranchia, in the stratified epithelium between the respiratory plates, causing changes of the haemibranchium which were well visible even by the naked eye.

Buoyancy and electrically driven convection models in thin-layer electrodeposition

Recent work demonstrates the inevitable role of convection during the growth of patterns in thin-layer electrochemical deposition. Convection is driven mainly by Coulombic forces due to local charges and by buoyant forces due to concentration gradients that lead to density gradients. Here we study by theoretical and numerical modeling the limiting regimes under which electroconvection or gravitoconvection prevail. The model describes the diffusive, migratory, and convective motion of ions in a fluid subject to an electric field. The equations are written in terms of dimensionless quantities, in particular, the gravity Grashof and the electrical Grashof numbers. The simulations reveal that gravitoconvection becomes increasingly important as the gravity Grashof number increases, while electroconvection becomes increasingly important as the electrical Grashof number increases. For both regimes the model predicts concentration, electric potential, and velocity patterns that are in qualitative agreement with typical electrodeposition experiments. In gravitoconvection, the model predicts the evolution, before collision, of the convection rolls near each electrode growing first as ${t}^{4/5}$ and then slowing down to ${t}^{1/2};$ the same scaling behavior was observed in experiments. After collision, the cathodic and anodic rolls merge into a single roll. In electroconvection, the model predicts the existence of vortex pairs formed by the electrical force on space charge accumulating near the growing filament tip. Such vortex rolls and pairs have been observed in experiments.

Immunocytochemical Observations on Muscle Cell Proteins in the Antarctic Mussel Shrimp Acetabulastoma sp. (Crustacea, Ostracoda)

In the antarctic ostracode Acetabulastoma sp., a singular type of muscle cell has tentatively been classified as transversely striated with continuous Z-line, interrupted by tubules of sarcoplasmic reticulum. We investigated the presence and distribution of different regulatory, contractile, and structural proteins in this muscle by electron microscopical immunocytochem- istry. Troponin, caldesmon, and calponin are three proteins suitable to identify muscle cell types that do not show the classical ultrastructural patterns expected of striated or smooth muscles. Reaction to troponin T was positive (the protein was located along the thin filaments), but no immunoreaction was observed to caldesmon and calponin. Thus, the muscle clearly belongs to the striated class. The contractile proteins myosin, paramyosin, and miniparamyosin were lo- cated along the thick filaments. Paramyosin and miniparamyosin are known only from inver- tebrate thick filaments and have no known vertebrate homolog. A nebulin-like protein was found and, as in vertebrates, may be involved in regulating sarcomere length. Instead of the giant protein titin, known from vertebrate striated muscle, minititin, a protein of the same family but lower molecular weight, was developed. The presence and distribution of proteins such as myosin, troponin, and nebulin as well as the absence of caldesmon and calponin suggest that despite its small size and parasitic life style, Acetabulastoma sp. is an active invertebrate quite unlike those in which the contractile proteins were found to be discontinuously distributed or concentrated at the tips of the thick filaments.

Filament tip-associated antigens involved in adherence to and invasion of murine pulmonary epithelial cells in vivo and HeLa cells in vitro by Nocardia asteroides.

The interactions of Nocardia asteroides GUH-2 with pulmonary epithelial cells of C57BL/6 mice and with HeLa cells were studied. Electron microscopy demonstrated that only the tips of log-phase cells penetrated pulmonary epithelial cells following intranasal administration, and nocardiae were recovered from the brain. Coccobacillary cells neither invaded nor disseminated. Serum from immunized mice (IMS) decreased attachment to and penetration of pulmonary epithelial cell surfaces by log-phase GUH-2 and inhibited spread to the brain. IMS was adsorbed against stationary-phase cells. Western immunoblots suggested that this adsorbed IMS was reactive primarily with 43- and 62-kDa proteins. Immunofluorescence showed that adsorbed IMS preferentially labeled the tips of log-phase GUH-2 cells. Since this IMS was reactive to culture filtrate antigens, several of these proteins were cut from gels, and mice were immunized. Sera against 62-, 55-, 43-, 36-, 31-, and 25-kDa antigens were obtained. The antisera against the 43- and 36-kDa proteins labeled the filament tips of GUH-2 cells. Only the antiserum against the 43-kDa antigen increased pulmonary clearance, inhibited apical attachment to and penetration of pulmonary epithelial cells, and prevented spread to the brain. An in vitro model with HeLa cells demonstrated that the tips of log-phase cells of GUH-2 adhered to and penetrated the surface of HeLa cells. Invasion assays with amikacin treatment demonstrated that nocardiae were internalized. Adsorbed IMS blocked attachment to and invasion of these cells. These data suggested that a filament tip-associated 43-kDa protein was involved in attachment to and invasion of pulmonary epithelial cells and HeLa cells by N. asteroides GUH-2.

The genus Predaea (Nemastomataceae, Rhodophyta) in the Alborán Sea (western Mediterranean Sea), with the description of Predaea pusilla f. alboranensis f. nov.

Predaea pusilla (Berthold) J. Feldmann f. alboranensis Conde, López-Mielgo et Flores-Moya f. nov. (Nemastomataceae, Rhodophyta) is described from the waters near Alboran Island (western Mediterranean Sea). The new taxon differs from Predaea pusilla f. pusilla by the presence of bicelled propagules, 8–12 μm long and 4–5 μm wide, formed at the tips of cortical filaments. Bicelled structures have also been reported in Predaea bisporifera Kajimura as bisporangia. The nature of these bicelled structures in P. pusilla f. alboranensis and P. bisporijera is discussed, and it is suggested that they are propagules rather than bisporangia. The first record of the Mediterranean endemic Predaea ollivieri J. Feldmann is also reported for the Alborán Sea.

Corona emission thresholds for three types of hydrometeor interaction in thunderclouds

Laboratory studies have been conducted of the conditions under which glancing collisions, at relative velocities V characteristic of those occurring in thunderstorms, of three types of hydrometeor pairs of precipitation dimension (such as (1) warm drop pairs, (2) supercooled drop pairs, and (3) a supercooled drop and a graupel pellet) produce a corona discharge in an electric field E. In each case, the observed corona is emitted at the tip of an ephemeral liquid filament, of length greater than the dimensions of the interacting hydrometeors, drawn out during each interaction. For each type of hydrometeor pair, the probability f that corona was produced during an interaction increased steadily from zero for increasing values of E above about 150 kV/m, and was significantly in excess of 50% for values of E = 400 kV/m, which is probably about the maximum ambient value occurring in a thunderstorm. We conclude that if the associated hydrometeors are present in strongly electrified regions of thunderstorms (unlikely for interaction type 1 but manifestly possible for types 2 and 3, corona initiation leading to the production of lightning could result from each of the three types of interaction studied.

Assembly characteristics of flagellar cap protein HAP2 of Salmonella: decamer and pentamer in the ph-sensitive equilibrium

The cap of the bacterial flagellum is an oligomeric assembly of HAP2 protein (also called FliD), tightly attached to the tip of the flagellar filament. Flagellar growth does not occur in fliD-deficient mutants because flagellin monomers transported through the central channel of the flagellum leak out without polymerizing at the distal end. The structure of the cap complex is not known yet. An in vitro assembly of HAP2 proteins was found to have a pentagonal shape, while its molecular mass corresponded roughly to that of a dodecamer. To characterize the structure and assembly behavior of the complex formed in vitro in more detail, the stoichiometry of the complex and the association equilibrium have been studied. Crosslinking experiments now clearly show that the HAP2 complex is decameric. The assembly equilibrium is mainly between the monomer and decamer with a minor population of intermediate oligomers involved, and is highly dependent on the solution pH as well as the salt concentration: the fraction of the decamer sharply rises as the pH decreases from 8.5 to 8.0; the physiological concentration of salt partially suppresses the decamer formation. A preferential crosslinking within a pentameric unit together with a bipolar feature of the complex particle observed by electron microscopy suggests that the decamer is a bipolar pair of pentamers. Because of the polar nature of the filament cap structure, the pentamer is suggested to be the cap complex with its decamer forming surface involved in interactions with the filament.

Time Histories of Water Contents in a Burning Emulsified Fuel Droplet.

An experimental study has been carried out of the combustion behavior of an emulsified fuel droplet in a quiescent gaseous environment. Attention was mainly paid to time histories of water contents in the droplet and microexplosion. The fuel in water emulsions consisting base fuel and water doped with small amount of surfactant were tested after degasification. An emulsified fuel droplet suspended at the tip of a quartz filament was ignited and the droplet flame was quenched by a jet of gaseous nitrogen at an arbitrary instant of time after ignition. Several droplets were sampled in a micropipette, being heated to cause the separation of water and oil layers. Thus, the time histories of the volume of fuel and water in the emulsion droplet were determined for the base fuels of n-dodecane and n-hexadecane. The results showed that the water volume in the droplet was almost constant during the combustion while the fuel volume decreased remarkably with the lapse of time. The effects of the time histories of water content on the onset rate of microexplosion were also revealed.

Analysis of Filament Deformation for a Freely Rotating Cup Brush

In this paper, a mechanics formulation is outlined and used for evaluating the steady-state, large deflection of a slender member subjected to displacement-dependent centrifugal load. The problem is examined within the context of rotating filamentary cup brushes that are used in surface finishing operations. Several parameters which are closely related to the machining performance and service life of cup brushes are identified and reported, including filament tip spatial distribution and orientation, filament stress, and the steady-state configuration of the working surface of the cup brush during free rotation. Numerical results indicate that filament inertia forces can lead to significant fiber displacement and stress and thus, must be included as an integral part of the design of rotary cup brushes.

Multiple strategies for a high light existence in a tropical marine macroalga

Acclimation to high light conditions on the top of coral reefs was examined in the coenocytic, filamentous green macroalga Chlorodesmis fastigiata (C. Ag.) Ducker. Despite having a pool of violaxanthin, high light does not induce formation of zeaxanthin in this macroalga. Exposure to 11 and 33% of surface irradiance resulted in parallel, reversible declines in Fv/Fmand in the number of functional PSII centers. The quantum requirement for PSII inactivation was calculated to be approx. 2×107photons. Recovery of PSII activity after low photon exposures did not depend on protein synthesis, unlike at higher photon exposures, where recovery was inhibited by 50% in the presence of lincomycin. Accumulation of inactive, quenching PSII centers is proposed as a mechanism of energy dissipation; only some of these centers require protein synthesis for reactivation. In natural-sized populations, midday photoinhibition was greater in filament tips than in bases, but the number of inactive PSII centers within entire filaments did not significantly change over the course of the day. It is proposed that the higher chlorophyll concentration in the tips provides protective shading to chloroplasts in lower regions, and that cytoplasmic streaming of chloroplasts within this siphonous alga limits the cumulative exposure to high light, thereby providing another level of protection from high light stress.

Immunocytochemical electron microscopic study and western blot analysis of myosin, paramyosin and miniparamyosin in the striated muscle of the fruit fly Drosophila melanogaster and in obliquely striated and smooth muscles of the earthworm Eisenia foetida.

Miniparamyosin is a paramyosin isoform (55-60 kDa) that has been isolated in insects (Drosophila) and immunolocalized in several species of arthropods, molluscs, annelids and nematodes. In this study, the presence and distribution of this protein, in comparison with that of paramyosin and myosin, has been examined in the striated muscle (tergal depressor of trochanter) of Drosophila melanogaster, and the obliquely striated muscle (body wall) and the smooth muscle (outer layer of the pseudoheart) of the earthworm Eisenia foetida by means of immunocytochemical electron microscopic study and Western blot analysis miniparamyosin paramyosin and myosin antibodies from Drosophila. In the striated muscle of D. melanogaster, the three proteins were immunolocalized along the length of the thick filaments (A-bands). The distribution of immunogold particles along these filaments was uniform. The relative proportions miniparamyosin/paramyosin/myosin (calculated by counting the number of immunogold particles) were: 1/10/68. In the obliquely striated muscle of E. foetida, immunoreactions to the three proteins were also found in the thick filaments, and the relative proportions miniparamyosin/paramyosin/myosin were 1/2.4/6.9. However, whereas the distribution of both myosin and miniparamyosin along the thick filament length was uniform, paramyosin immunolabelling was more abundant in the extremes of thick filaments (the outer zones of A-bands in the obliquely striated muscle), where the thick filaments become thinner than in the centre (the central zone of A-bands), where these filaments are thicker. The relative proportions of paramyosin in the outer and of paramyosin in the central zones of A-bands were 4/1. This irregular distribution of paramyosin along the thick filament length might be actual but it may also be explained by the fusiform shape of thick filaments in the earthworm: assuming that paramyosin is covered by myosin, paramyosin antigens would be more exposed in the tips than in the centre of thick filaments. If miniparamyosin is, in turn, covered by paramyosin, the exposure of miniparamyosin antigens would be low even in the tips of thick filaments, and this might explain the scanty immunoreaction observed for this protein and the absence of a higher number of immunogold particles in the extremes of thick filaments. The distribution of the three proteins in the earthworm smooth muscle was as in the obliquely striated muscle, although the proportions miniparamyosin/paramyosin/myosin were 1/1.5/5.2; this is, immunoreactions to paramyosin and miniparamyosin were lower than in the obliquely striated muscle.

Interaction between titin and thin filaments in intact cardiac muscle.

A 'freeze break' technique and immunoelectron microscopy were used to study the elastic properties of cardiac titin filaments. Small bundles consisting of a few fibres from freshly prepared dog papillary muscle were quickly frozen and broken under liquid nitrogen to fracture sarcomeres in planes perpendicular to the filament axes. Breaks occurred at each of several regions along the sarcomeres. The still-frozen specimens were thawed during fixation to allow elastic filaments to retract. The broken muscle segments were then treated with monoclonal titin antibody 9D10 which labelled a unique epitope in the I-band. In sarcomeres broken at the A-I junction, the titin filaments reacted toward the Z-line, independently of the thin filaments. The retracted epitopes did not reach the Z-line; retraction stopped at the N1-line level. In sarcomeres broken near the Z-line, the titin filaments retracted in the opposite direction, to the tip of the thick filaments. When the break occurred in the A-band, by contrast, the titin-epitope position was unaffected. On the basis of these results, and despite the reported interaction of titin and actin in vitro, it appears that cardiac titin molecules form elastic filaments that are functionally independent of the thin filaments. Near the Z-line, however, the titin filaments seem to associate firmly with the thin filaments.

Self-assembly of the Filament Capping Protein, FliD, of Bacterial Flagella into an Annular Structure

A bacterial flagellum has a cap structure at the tip of the external filament. The cap is composed of the FliD protein ( M r, 49 × 10 3), and plays an essential role in the polymerization of the filament protein, flagellin, which is believed to be transported through a central channel in the flagellum. A fliD-deficient mutant becomes non-motile because it lacks flagellar filaments and leaks flagellin monomer out into the medium. We have constructed a FliD-overproducing plasmid and purified the protein. The purified FliD at high concentration formed a large complex ( M r, ca. 600 × 10 3) under physiological conditions. The complex was found by electron microscopy to be ring shaped. Image analysis revealed that the complex consisted of five substructures arranged in a pentagonal shape. Its outer diameter, approximately 10 nm, was about the same as that of the cap at the tip of the wild-type flagella. When the annular structure was added to the culture medium of a Salmonella fliDmutant, almost all of the cells became able to swim. Overall, about ten molecules of FliD self-assemble into an annular structure in vitro, forming the functional capping structure by incorporating flagellin at the tip of the flagellar filament in vivo.

Immunocytochemical electron microscopic study and western blot analysis of paramyosin in different invertebrate muscle cell types of the fruit fly Drosophila melanogaster, the earthworm Eisenia foetida, and the snail Helix aspersa.

The presence and distribution pattern of paramyosin have been examined in different invertebrate muscle cell types by means of Western blot analysis and electron microscopy immunogold labelling. The muscles studied were: transversely striated muscle with continuous Z lines (flight muscle from Drosophila melanogaster), transversely striated muscle with discontinuous Z lines (heart muscle from the snail Helix aspersa), obliquely striated body wall muscle from the earthworm Eisenia foetida, and smooth muscles (retractor muscle from the snail and pseudoheart outer muscular layer from the earthworm). Paramyosin-like immunoreactivity was localized in thick filaments of all muscles studied. Immunogold particle density was similar along the whole thick filament length in insect flight muscle but it predominated in filament tips of fusiform thick filaments in both snail heart and earthworm body wall musculature when these filaments were observed in longitudinal sections. In obliquely sectioned thick filaments, immunolabelling was more abundant at the sites where filaments disappeared from the section. These results agree with the notion that paramyosin extended along the whole filament length, but that it can only be immunolabelled when it is not covered by myosin. In all muscles examined, immunolabelling density was lower in cross-sectioned myofilaments than in longitudinally sectioned myofilaments. This suggests that paramyosin does not form a continuous filament. The results of a semiquantitative analysis of paramyosin-like immunoreactivity indicated that it was more abundant in striated than in smooth muscles, and that, within striated muscles, transversely striated muscles contain more paramyosin than obliquely striated muscles.

Suspended droplet evaporation modeling in a laminar convective environment

A detailed numerical model is used to analyze the evaporation characteristics of a fuel droplet which is suspended concentrically from a spherical bead born at the tip of a thin cylindrical filament. The suspended droplet is exposed to a high-temperature, laminar, gaseous stream with a relevant Reynolds number Re ∼ 50. The model solves the time-dependent axisymmetric Navier-Stokes and energy equations in both fluid phases, in conjunction with the heat conduction equation within the suspender material. The various mechanisms through which the suspender affects the heat and mass transport processes in the droplet interior are evaluated. The effects of suspender size and material are investigated at a pressure typical of gas-turbine combustor environments. The model predictions indicate that when quartz suspenders are implemented to determine liquid-fuel evaporation characteristics, the droplet surface regression rates do not vary appreciably with suspender sizes. The results also show that mean surface temperatures of free-traveling droplets are fairly well represented by those of suspended stationary droplets exposed to identical ambient conditions. However, the suspended-droplet configuration overestimates liquid evaporation rates of free-convecting droplets, thus underpredicting droplet lifetimes.

Mortality, growth, swimming activity and gill morphology of brook trout ( Salvelinus fontinalis) and Atlantic salmon ( Salmo salar) exposed to low pH with and without aluminum

Measurements were made of mortality, growth, swimming activity, and gill morphology of young-of-the-year brook trout ( Salvelinus fontinalis) and Atlantic salmon ( Salmo salar), exposed for 30 days to pH 5·6 ± 0·5 (mean ± 1 standard deviation) with and without addition of 107 ± 57 μg liter −1 exchangeable (labile monomeric) aluminum. The experiment was conducted in artificial stream channels adjacent to a natural stream and subject to daily and seasonal changes in temperature, light, and chemical conditions. There were no differences in survival or growth for brook trout in any treatment; Atlantic salmon survival and growth were significantly decreased in the acid + Al treatment. Scanning electron microscopy showed no damage to gills of either species in the acid treatments, but the acid + Al treatment caused slight swelling of brook trout gills near the filament tips and significant swelling and fusion of secondary lamellae of Atlantic salmon gills. The acid treatment increased swimming activity in brook trout, but both the acid and acid + Al treatments reduced activity in Atlantic salmon.