Vesicle Shape Research Articles

Pyroclast textural variation as an indicator of eruption column steadiness in andesitic Plinian eruptions at Mt. Ruapehu

Between 27 and 11 cal. ka BP, a transition is observed in Plinian eruptions at Mt. Ruapehu, indicating evolution from non-collapsing (steady and oscillatory) eruption columns to partially collapsing columns (both wet and dry). To determine the causes of these variations over this eruptive interval, we examined lapilli fall deposits from four eruptions representing the climactic phases of each column type. All eruptions involve andesite to basaltic andesite magmas containing plagioclase, clinopyroxene, orthopyroxene and magnetite phenocrysts. Differences occur in the dominant pumice texture, the degree of bulk chemistry and textural variability, the average microcrystallinity and the composition of groundmass glass. In order to investigate the role of ascent and degassing processes on column stability, vesicle textures were quantified by gas volume pycnometry (porosity), X-ray synchrotron and computed microtomography (μ-CT) imagery from representative clasts from each eruption. These data were linked to groundmass crystallinity and glass geochemistry. Pumice textures were classified into six types (foamy, sheared, fibrous, microvesicular, microsheared and dense) according to the vesicle content, size and shape and microlite content. Bulk porosities vary from 19 to 95 % among all textural types. Melt-referenced vesicle number density ranges between 1.8 × 102 and 8.9 × 102 mm−3, except in fibrous textures, where it spans from 0.3 × 102 to 53 × 102 mm−3. Vesicle-free magnetite number density varies within an order of magnitude from 0.4 × 102 to 4.5 × 102 mm−3 in samples with dacitic groundmass glass and between 0.0 and 2.3 × 102 mm−3 in samples with rhyolitic groundmass. The data indicate that columns that collapsed to produce pyroclastic flows contained pumice with the greatest variation in bulk composition (which overlaps with but extends to slightly more silicic compositions than other eruptive products); textures indicating heterogeneous bubble nucleation, progressively more complex growth history and shear-localization; and the highest degrees of microlite crystallization, most evolved melt compositions and lowest relative temperatures. These findings suggest that collapsing columns in Ruapehu have been produced when strain localization is prominent, early bubble nucleation occurs and variation in decompression rate across the conduit is greatest. This study shows that examination of pumice from steady phases that precede column collapse may be used to predict subsequent column behaviour.

Morphological variation of a lipid vesicle confined in a spherical vesicle.

Morphologies of a double-bilayer vesicle were explored experimentally by fast confocal laser microscopy and numerically by a dynamically triangulated membrane model with area-difference elasticity. The confinement was found to induce several shapes of the inner vesicles that had not been observed in unilamellar vesicles: double and quadruple stomatocytes, slit vesicle, and vesicles of two or three compartments with various shapes. The simulations reproduced the experimental results very well and some of the shape transitions can be understood by a simple theoretical model for axisymmetric shapes.

Human cytomegalovirus pUL37x1-induced calcium flux activates PKCα, inducing altered cell shape and accumulation of cytoplasmic vesicles

The human cytomegalovirus immediate-early protein pUL37x1 induces the release of Ca(2+) stores from the endoplasmic reticulum into the cytosol. This release causes reorganization of the cellular actin cytoskeleton with concomitant cell rounding. Here we demonstrate that pUL37x1 activates Ca(2+)-dependent protein kinase Cα (PKCα). Both PKCα and Rho-associated protein kinases are required for actin reorganization and cell rounding; however, only PKCα is required for the efficient production of virus progeny, arguing that HCMV depends on the kinase for a second function. PKCα activation is also needed for the production of large (1-5 μm) cytoplasmic vesicles late after infection. The production of these vesicles is blocked by inhibition of fatty acid or phosphatidylinositol-3-phosphate biosynthesis, and the failure to produce vesicles is correlated with substantially reduced production of enveloped virus capsids. These results connect earlier work identifying a requirement for lipid synthesis with specific morphological changes, and support the argument that the PKCα-induced large vesicles are either required for the efficient production of mature virus particles or serve as a marker for the process.

Affinities of Palaeozoic encrusting ascodictyid ‘pseudobryozoans’

Small encrusting marine organisms belonging to the genera Ascodictyon, Eliasopora and Vinella were originally described as ctenostome bryozoans. Well-preserved ascodictyid specimens from the Early and Middle Devonian of Poland allow us to exclude such an affinity due to the absence of any aperture in the ascodictyid vesicles for the protrusion or withdrawal of the lophophore during feeding. The ctenostome bryozoans are soft-bodied, but the ascodictyid vesicles and filaments have calcified walls. Reinterpretation of Eliasopora stellata (Nicholson & Etheridge, 1877), Eliasopora sparsiforme (Kiepura, 1965) and ‘Ascodictyon’ venustum Kiepura, 1965, provides a basis for the recognition of a new group of extinct Palaeozoic organisms, defined by a combination of morphological features including the presence of a thread-like network of perforate branching filaments, perforate vesicles formed by swollen tips of the filaments, and the ability of filaments to fuse. This distinguishes Ascodictyidae from all other known extant microorganisms. The shape, size and perforated walls of vesicles make ascodictyids similar to the Palaeozoic tuberitinid ‘foraminifers’. It remains to be determined which morphology is plesiomorphic and which is derived.

New digeneans (Opecoelidae) from hydrothermal vent fishes in the south eastern Pacific Ocean, including one new genus and five new species.

A new genus and five new species of digeneans are reported from fishes at hydrothermal vent sites in the South East Pacific Rise region. Biospeedotrema n. gen. (Opecoelidae: Stenakrinae) is distinguished from other stenakrines by the more or less symmetrical testicular configuration, with the uterus passing between the testes, sometimes distinctly into the post-testicular region. Biospeedotrema jolliveti n. gen., n. sp. from Ventichthys biospeedoi (Ophidiidae) is distinguished by the vitelline fields which extend only slightly into the post-testicular region, the intestinal bifurcation is dorsal to the ventral sucker, the genital pore is slightly dextrally submedian or median, the cirrus sac is short and the caeca are broad and overlap the testes, usually reaching into the post-testicular region. Biospeedotrema parajolliveti n. sp. from Thermichthys hollisi differs from Biospeedotrema jolliveti in being squat, always just wider than long, the tegument is wrinkled, the testes are lobate, and the caeca only just reach to the testes. Biospeedotrema biospeedoi n. sp. from T. hollisi differs from its congeners in its body-shape, uterine extent posterior to the testes and the small vitellarium. Caudotestis ventichthysi n. sp. (Opecoelidae: Stenakrinae) from V. biospeedoi is distinguished from its five congeners in various combinations of caecal length, cirrus sac length, internal seminal vesicle shape, vitelline extent and distribution, forebody length and egg-size. Buticulotrema thermichthysi n. sp. (Opecoelidae: Opecoelininae) from T. hollisi (Bythitidae) is distinguished from its only congener by its very long, very strongly muscular oesophagus, bifurcating dorsally to the posterior part of the ventral sucker, the long, narrow pars prostatica and distal male duct and the sinistral genital pore at the level of the pharynx. The phylogenetic position for three of these species, Buticulotrema thermichthysi, Biospeedotrema jolliveti and Biospeedotrema biospeedoi, is assessed based on ssrDNA and lsrDNA sequences, which verify the position of these species in the Opecoelidae.

Statistical analysis of vesicle morphology dynamics based on a free energy landscape.

We here present a method to reconstruct effective free energy landscapes (FELs) of lipid vesicles from the statistical analysis of a large number of microscope images. This method, not only allows us to define possible energy landscapes, but also highlights minority vesicle shapes that were otherwise hidden in the majority. When compared with temporal evolution of deforming lipid vesicles, it was found that the trajectory of deforming vesicles was in accordance with the reconstructed landscape, in which the minority shapes play a key role. When compared with theoretical models, it revealed that the vesicle shapes characterised in the reconstructed FELs were consistent with the theoretically predicted shapes. These results suggest that the FEL analysis can be a useful tool to investigate the morphological dynamics of lipid vesicles, in conjunction with other analytical methods.

Wetting transitions within membrane compartments.

A biomimetic membrane in contact with several aqueous phases is theoretically studied using a combination of Helfrich curvature elasticity theory for fluid membranes and self-consistent field theory for polymers in solutions. Two phases that are thermodynamically formed by phase separation of aqueous solutions, as well as stable and metastable shapes of fluid vesicles, have been observed. The wetting transitions from complete to partial wetting and to complete dewetting are identified within a membrane compartment. The dependences of wetting transitions on material parameters, such as the intrinsic contact angles θin, the interaction strengths between the polymers χαβ and between the membrane and the polymer ηp, and impermeability of the membrane to the enclosed polymers ζp, are investigated. For a given χαβ, impermeability ζp and affinity to the membrane ηp, θin is found to be a constant and independent of the reduced volume of vesicles and the volume fraction of two phases.

Macro and micromorphological characterization of differentAspergillusisolates

Aflatoxin contamination of groundnut (Arachis hypogaea L.) is a serious problem through out the world which leads to significant economic losses every year. Invasion of groundnut seed by the aflatoxin-producing fungi Aspergillus flavus and Aspergillus parasiticus, and subsequent contamination with aflatoxins, may occur at any stage during the postharvest handling of its seeds, which necessitates development of suitable procedures for identification of the pathogen. An identification key for different fungal isolates was developed on the basis of macromorphological features viz. diameter, elevation, margins, texture of the colony as well as colour of the colony from the top and reverse of the plate, extent of sporulation (low, medium and heavy) and presence and absence of radial sulcation after seven days of culture. Microscopic features such as shape and size of conidia, vesicles and hyphae have also been included in the key. On the basis of this key different Aspergillus isolates viz. A. Niger, A. fumigatus, A flavus, A.terreus, A.parasiticus, A.oryzae could be differentiated thereby showing a potential for detection of aflatoxigenic fungi in the infected lot.

Vesicle deformation in DC electric pulses

The transient deformation of giant vesicles in square DC electric pulses is investigated. We experimentally observe the theoretically predicted transition from an oblate to prolate ellipsoidal shape in the case of a quasi-spherical vesicle encapsulating solution less conducting than the suspending medium. The transition is detected by utilizing a two-step pulse in order to avoid electroporation and vesicle collapse. We develop a theoretical model to describe both the deformation under an electric field and relaxation after the field is turned off. Agreement between experiment and theory demonstrates that the time-dependent vesicle shape can be used to measure membrane properties such as viscosity and capacitance.

Nanovesicles for transdermal delivery of felodipine: Development, characterization, and pharmacokinetics.

Aim:The research traces development of nanovesicles to attain enhanced transdermal delivery of felodipine and also investigates parameters for optimization of variable membrane compositions containing soya- and egg lecithin and edge activator.Materials and Methods:Rotary evaporation sonication method was employed to obtain tranfersomal formulation that was characterized for vesicle shape and size, polydispersity index (PDI), zeta potential, entrapment and loading efficiency, deformability index and in vitro skin permeation.Results:Spherical nanovesicles of 75.71 ± 5.4 nm with PDI 0.228 and zeta potential of −49.8 were adjudged as the best formulation (MF8). MF8 displayed maximum entrapment and loading efficiency with a high deformability index of 119.68. In vitro permeation across rat skin by MF8 reported 256% enhancement in permeation (flux = 23.72 ± 0.64) when compared with transdermal control formulation and followed zero order kinetics (Case-II). Pharmacokinetic studies revealed that transdermal administration, in contrast to oral delivery provided relatively constant, sustained blood concentration with minimal plasma fluctuation, rapid and prolonged peak time. The relative bioavailability of felodipine was found 358.42% versus oral administration that was well supported by the outcomes of confocal laser scanning microscopic studies that suggested rapid permeation of drugs to across dermal layers.Conclusion:The results conclude that composition variation and method of preparation elicited significant effect on the vesicle characteristic and proved the transcendency of felodipine loaded transfersomes.

Shapes of vesicles encapsulating two aqueous phases

Motivated by recent experiments, vesicles encapsulating two aqueous phases are theoretically explored using a combination of Helfrich curvature elasticity theory for fluid membranes and self-consistent field theory for polymers. The spatial distributions of two polymers, α and β, have been obtained, and two thermodynamic phases occur, as expected. Stable or metastable shapes of fluid and closed vesicles have also been achieved. Due to the impenetrability of the membrane to polymer, the available spaces of polymers α and β are limited and the conformational entropies for the polymers are reduced. Different chain segments that possess different permeability to the membrane would induce different inhomogeneous entropic pressures on the membrane, thereby leading to shape transformations of the vesicles. In the present study, the typical shapes of vesicles encapsulating two phases are studied as functions of the concentrations of polymers α and β, and the interactions between the chain segments and the membrane. The two phases formed by polymers α and β are also found to be altered and have been discussed in detail. In addition, morphological phase diagrams are presented as a function of the reduced volume, v. The phase boundaries between oblates and prolates, and oblates and stomatocytes of vesicles encapsulating two phases are found to move toward the higher reduced volume, and oblates occupy a much wider range of the reduced volume compared with 'neat' vesicles.

Equilibrium electrodeformation of a spheroidal vesicle in an ac electric field

In this work, we develop a theoretical model to explain the equilibrium spheroidal deformation of a giant unilamellar vesicle (GUV) under an alternating (ac) electric field. Suspended in a leaky dielectric fluid, the vesicle membrane is modeled as a thin capacitive spheroidal shell. The equilibrium vesicle shape results from the balance between mechanical forces from the viscous fluid, the restoring elastic membrane forces, and the externally imposed electric forces. Our spheroidal model predicts a deformation-dependent transmembrane potential, and is able to capture large deformation of a vesicle under an electric field. A detailed comparison against both experiments and small-deformation (quasispherical) theory showed that the spheroidal model gives better agreement with experiments in terms of the dependence on fluid conductivity ratio, permittivity ratio, vesicle size, electric field strength, and frequency. The spheroidal model also allows for an asymptotic analysis on the crossover frequency where the equilibrium vesicle shape crosses over between prolate and oblate shapes. Comparisons show that the spheroidal model gives better agreement with experimental observations.

Physicochemical properties of liposomes as potential anticancer drugs carriers. Interaction of etoposide and cytarabine with the membrane: Spectroscopic studies

The interactions between etoposide, cytarabine and 1,2-dihexadecanoyl-sn-glycerol-3-phosphocholine bilayers were studied using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR). These techniques have proven to be a very powerful tool in studying the structure and dynamics of phospholipid bilayers. In particular, DSC can provide information on the phase transition temperature and cooperativity of the lipid molecules in the absence and presence of the drug. Vibrational spectroscopy is well suited to the study of drug–lipid interactions, since it allows for an investigation of the conformation of phospholipid molecules at different levels in lipid bilayers and follows structural changes that occur during the gel to liquid–crystalline phase transition. NMR supported the determination of the main phase transition temperatures (TC) of 1,2-dihexadecanoyl-sn-glycerol-3-phosphocholine (DPPC). The main phase transition temperature (TC) determined by 1H NMR is comparable with values obtained by DSC for all studied liposomes. The location of cytarabine and etoposide in liposomes was also determined by NMR. Atomic force microscopy (AFM) images, acquired immediately after sample deposition on a mica surface, revealed the spherical shape of lipid vesicles.

Reduced Expression of the Vesicular Acetylcholine Transporter and Neurotransmitter Content Affects Synaptic Vesicle Distribution and Shape in Mouse Neuromuscular Junction

In vertebrates, nerve muscle communication is mediated by the release of the neurotransmitter acetylcholine packed inside synaptic vesicles by a specific vesicular acetylcholine transporter (VAChT). Here we used a mouse model (VAChT KDHOM) with 70% reduction in the expression of VAChT to investigate the morphological and functional consequences of a decreased acetylcholine uptake and release in neuromuscular synapses. Upon hypertonic stimulation, VAChT KDHOM mice presented a reduction in the amplitude and frequency of miniature endplate potentials, FM 1–43 staining intensity, total number of synaptic vesicles and altered distribution of vesicles within the synaptic terminal. In contrast, under electrical stimulation or no stimulation, VAChT KDHOM neuromuscular junctions did not differ from WT on total number of vesicles but showed altered distribution. Additionally, motor nerve terminals in VAChT KDHOM exhibited small and flattened synaptic vesicles similar to that observed in WT mice treated with vesamicol that blocks acetylcholine uptake. Based on these results, we propose that decreased VAChT levels affect synaptic vesicle biogenesis and distribution whereas a lower ACh content affects vesicles shape.

An immersed boundary method for simulating the dynamics of three-dimensional axisymmetric vesicles in Navier–Stokes flows

In this paper, we develop a simple immersed boundary method to simulate the dynamics of three-dimensional axisymmetric inextensible vesicles in Navier–Stokes flows. Instead of introducing a Lagrangeʼs multiplier to enforce the vesicle inextensibility constraint, we modify the model by adopting a spring-like tension to make the vesicle boundary nearly inextensible so that solving for the unknown tension can be avoided. We also derive a new elastic force from the modified vesicle energy and obtain exactly the same form as the originally unmodified one. In order to represent the vesicle boundary, we use Fourier spectral approximation so we can compute the geometrical quantities on the interface more accurately. A series of numerical tests on the present scheme have been conducted to illustrate the applicability and reliability of the method. We first perform the accuracy check of the geometrical quantities of the interface, and the convergence check for different stiffness numbers as well as fluid variables. Then we study the vesicle dynamics in quiescent flow and in gravity. Finally, the shapes of vesicles in Poiseuille flow are investigated in detail to study the effects of the reduced volume, the confinement, and the mean flow velocity. The numerical results are shown to be in good agreement with those obtained in literature.

Anharmonic magnetic deformation of spherical vesicle: Field-induced tension and swelling effects

We have derived an equation, based on Helfrich’s curvature elasticity, describing the equilibrium shape of membrane vesicles in the presence of magnetic fields. We have solved this equation with and without the constraint of constant vesicle area. For vesicles with constant area, an exact calculation using our model confirms Helfrich’s estimate (Helfrich, 1973) [20] and predicts a magnetic field induced surface tension. Without the constant area constraint, our model predicts that vesicles with positive diamagnetic susceptibility anisotropy will swell in magnetic fields. It also predicts the anharmonic magnetic deformation of self-assembled nanocapsules of bola-amphiphilic molecules and the linear birefringence observed by Manyuhina et al. (2007) [22] .

Counting molecules in single organelles with superresolution microscopy allows tracking of the endosome maturation trajectory

Cells tightly regulate trafficking of intracellular organelles, but a deeper understanding of this process is technically limited by our inability to track the molecular composition of individual organelles below the diffraction limit in size. Here we develop a technique for intracellularly calibrated superresolution microscopy that can measure the size of individual organelles as well as accurately count absolute numbers of molecules, by correcting for undercounting owing to immature fluorescent proteins and overcounting owing to fluorophore blinking. Using this technique, we characterized the size of individual vesicles in the yeast endocytic pathway and the number of accessible phosphatidylinositol 3-phosphate binding sites they contain. This analysis reveals a characteristic vesicle maturation trajectory of composition and size with both stochastic and regulated components. The trajectory displays some cell-to-cell variability, with smaller variation between organelles within the same cell. This approach also reveals mechanistic information on the order of events in this trajectory: Colocalization analysis with known markers of different vesicle maturation stages shows that phosphatidylinositol 3-phosphate production precedes fusion into larger endosomes. This single-organelle analysis can potentially be applied to a range of small organelles to shed light on their precise composition/structure relationships, the dynamics of their regulation, and the noise in these processes.

Placental Glucose Transporter GLUT1 Expression in Pre-eclampsia

Placental Glucose Transporter (GLUT1) Expression in Pre- Eclampsia. INTRODUCTION: Glucose is the most important substrate for fetal growth. Indeed, there is no significant de novo glucose synthesis in the fetus and the fetal up-take of glucose rely on maternal supply and transplacental transport. Therefore, a defective placental transporter system may affect the intrauterine environment compromising fetal as well as mother well-being. On this line, we speculated that the placental glucose transport system could be impaired in pre-eclampsia (PE). METHODS: Placentae were obtained after elective caesarean sections following normal pregnancies and pre-eclamptic pregnancies. Syncytial basal membrane (BM) and apical microvillus membrane (MVM) fractions were prepared using differential ultra-centrifugation and magnesium precipitation. Protein expression was assessed by western blot. mRNA levels were quantified by quantitative real-time PCR. A radiolabeled substrate up-take assay was established to assess glucose transport activity. FACS analysis was performed to check the shape of MVM. Statistical analysis was performed using one way ANOVA test. RESULTS: GLUT1 protein levels were down-regulated (70%; P<0.01) in pre-eclamptic placentae when compared to control placentae. This data is in line with the reduced glucose up-take in MVM prepared from preeclamptic placentae. Of note, the mRNA levels of GLUT1 did not change between placentae affected by PE and normal placentae, suggesting that the levels of GLUT1 are post-transcriptionally regulated. FACS analysis on MVM vesicles from both normal placentae and pre-eclamptic placentae showed equal heterogeneity in the complexes formed. This excluded the possibility that the altered glucose up-take observed in pre-eclamptic MVM was caused by a different shape of these vesicles. CONCLUSIONS: Protein and functional studies of GLUT1 in MVM suggest that in pre-eclampsia the glucose transport between mother and fetus might be defective. To further investigate this important biological aspect we will increase the number of samples obtained from patients and use primary cells to study trans epithelial transport system in vitro.

The equilibria of vesicles adhered to substrates by short-ranged potentials

In equilibrium, a vesicle that is adhered to a horizontal substrate by a long-range attractive, short-range repulsive force traps a thin layer of fluid beneath it. In the asymptotic limit that this layer is very thin, there are quasi-two-dimensional boundary-layer structures near the edges of the vesicle, where the membrane's shape is governed by a balance between bending and adhesive stresses. These boundary layers are analysed to obtain corrections to simpler models that instead represent the adhesive interaction by a contact potential, thereby resolving apparent discontinuities that arise when such models are used. Composite expansions of the shapes of two-dimensional vesicles are derived. When, in addition, the adhesive interaction is very strong, there is a nested boundary-layer structure for which the adhesive boundary layers match towards sharp corners where bending stresses remain important but adhesive stresses are negligible. Outside these corners, bending stresses are negligible and the vesicle's shape is given approximately by the arc of a circle. Simple composite expansions of the vesicle's shape are derived that account for the shape of the membrane inside these corners.

Growth kinetics of circular liquid domains on vesicles by diffusion-controlled coalescence

Motivated by recent experiments on multicomponent membranes, the growth kinetics of domains on vesicles are theoretically studied. It is known that the steady-state rate of coalescence cannot be obtained by taking the long-time limit of the coalescence rate when the membrane is regarded as an infinite two-dimensional (2D) system. The steady-state rate of coalescence is obtained by explicitly taking into account the spherical vesicle shape. Using the expression for the 2D diffusion coefficient obtained in the limit of small domain size, an analytical expression for domain growth kinetics is obtained when a circular shape is always maintained. For large domains, the growth kinetics are discussed by investigating the size dependence of the coalescence rate, using the expression for the diffusion coefficient of arbitrary domain size.