Molecular Segregation Research Articles

Primed T Cell Responses to Chemokines Are Regulated by the Immunoglobulin-Like Molecule CD31

CD31, an immunoglobulin-like molecule expressed by leukocytes and endothelial cells, is thought to contribute to the physiological regulation T cell homeostasis due to the presence of two immunotyrosine-based inhibitory motifs in its cytoplasmic tail. Indeed, loss of CD31 expression leads to uncontrolled T cell-mediated inflammation in a variety of experimental models of disease and certain CD31 polymorphisms correlate with increased disease severity in human graft-versus-host disease and atherosclerosis. The molecular mechanisms underlying CD31-mediated regulation of T cell responses have not yet been clarified. We here show that CD31-mediated signals attenuate T cell chemokinesis both in vitro and in vivo. This effect selectively affects activated/memory T lymphocytes, in which CD31 is clustered on the cell membrane where it segregates to the leading edge. We provide evidence that this molecular segregation, which does not occur in naïve T lymphocytes, might lead to cis-CD31 engagement on the same membrane and subsequent interference with the chemokine-induced PI3K/Akt signalling pathway. We propose that CD31-mediated modulation of memory T cell chemokinesis is a key mechanism by which this molecule contributes to the homeostatic regulation of effector T cell immunity.

Surface Organization of a Perfluorocarbon-Functionalized Polystyrene Homopolymer

We use the perfluorocarbon-functionalized polymer, poly(4-((1H,1H,2H,2H-perfluorodecyl)oxycarbonyl)styrene) [PPFOCS], as a model system with both surface molecular segregation and molecular orientation to test the capabilities of a near-edge X-ray absorption fine structure (NEXAFS) spectroscopy analysis scheme for polymer surfaces. Both NEXAFS spectroscopy and angle-resolved X-ray photoelectron spectroscopy (XPS) show segregation of the −(CF2)7CF3 chain to the air/polymer interface with the styrenic portion underneath. Postedge analysis of the NEXAFS spectra indicates a low carbon atom density surface layer, of thickness 1.0–1.4 nm, due to the overlayer of perfluorocarbon chains. An analysis of the NEXAFS C 1s → π*C═C and C 1s → σ*C–F transitions accounting for the different depth distributions of the phenyl rings and fluorocarbon helices reveals strong orientational ordering with the orientational order parameter SC═C for the phenyl ring equal to −0.27 and for the C–F bonds in the fluorocarbon helix SC–F...

Geographic variation and molecular evidence of the Blackish Deer Mouse complex (Peromyscus furvus, Rodentia: Muridae)

Several authors have discussed whether Peromyscus furvus is a monotypic species rather than a polytypic entity, that it includes more than one species. Here, we analyze these questions by means of traditional morphometrics and by genetic analyses using ND3-ND4 mtDNA genes as markers. In spite of a generalized overlap of the measurable characters among populations, our analyses show that the northernmost populations, which was assignable to P. latirostris, consistently show larger dimensions overall. The amount of genetic differentiation revealed by our molecular data, support conclusive evidence to suggest this taxon is a valid species. Our results also disclose that morphometric and molecular segregation between P. furvus and P. angustirostris is still incomplete. Finally, the two populations from the state of Oaxaca showed more morphometric affinity with those attributable to P. furvus and revealed a discrete degree of genetic differentiation. Nevertheless, their systematic position is not clear yet.

Segregation behavior of polyethylene with broad molecular weight distribution by annealing procedure in temperature gradient

An annealing treatment in a molten state, in which temperature of the top plate is different from that of the bottom one in a compression-molding, leads to molecular weight segregation of high-density polyethylene (HDPE) prepared by mixture of two types of HDPE with different molecular weights (Mw = 1.8 × 105 and 2.9 × 104). Low molecular weight fraction tends to localize at the surface attached to the higher temperature and vice versa. The segregation behavior is obvious at a large temperature gradient. Although the accuracy and mechanism of the phenomenon have not been clarified yet, this could be applied as a new fractionation method, which does not use a solvent.

Elastic energy of polyhedral bilayer vesicles

In recent experiments [M. Dubois, B. Demé, T. Gulik-Krzywicki, J.-C. Dedieu, C. Vautrin, S. Désert, E. Perez, and T. Zemb, Nature (London) 411, 672 (2001)] the spontaneous formation of hollow bilayer vesicles with polyhedral symmetry has been observed. On the basis of the experimental phenomenology it was suggested [M. Dubois, V. Lizunov, A. Meister, T. Gulik-Krzywicki, J. M. Verbavatz, E. Perez, J. Zimmerberg, and T. Zemb, Proc. Natl. Acad. Sci. USA 101, 15082 (2004)] that the mechanism for the formation of bilayer polyhedra is minimization of elastic bending energy. Motivated by these experiments, we study the elastic bending energy of polyhedral bilayer vesicles. In agreement with experiments, and provided that excess amphiphiles exhibiting spontaneous curvature are present in sufficient quantity, we find that polyhedral bilayer vesicles can indeed be energetically favorable compared to spherical bilayer vesicles. Consistent with experimental observations we also find that the bending energy associated with the vertices of bilayer polyhedra can be locally reduced through the formation of pores. However, the stabilization of polyhedral bilayer vesicles over spherical bilayer vesicles relies crucially on molecular segregation of excess amphiphiles along the ridges rather than the vertices of bilayer polyhedra. Furthermore, our analysis implies that, contrary to what has been suggested on the basis of experiments, the icosahedron does not minimize elastic bending energy among arbitrary polyhedral shapes and sizes. Instead, we find that, for large polyhedron sizes, the snub dodecahedron and the snub cube both have lower total bending energies than the icosahedron.

Glomerular Filtration Barrier and Molecular Segregation

The normal phenotype of the glomerular filtration barrier (GFB) and the mechanisms that underlie it have intrigued physiologists, microvascular biologists, and renal physicians for decades, especially because, in health, the multilayered barrier differentially restricts the passage of molecules of

Biochemical and molecular analysis of pink tomatoes: deregulated expression of the gene encoding transcription factor SlMYB12 leads to pink tomato fruit color.

The color of tomato fruit is mainly determined by carotenoids and flavonoids. Phenotypic analysis of an introgression line (IL) population derived from a cross between Solanum lycopersicum 'Moneyberg' and the wild species Solanum chmielewskii revealed three ILs with a pink fruit color. These lines had a homozygous S. chmielewskii introgression on the short arm of chromosome 1, consistent with the position of the y (yellow) mutation known to result in colorless epidermis, and hence pink-colored fruit, when combined with a red flesh. Metabolic analysis showed that pink fruit lack the ripening-dependent accumulation of the yellow-colored flavonoid naringenin chalcone in the fruit peel, while carotenoid levels are not affected. The expression of all genes encoding biosynthetic enzymes involved in the production of the flavonol rutin from naringenin chalcone was down-regulated in pink fruit, suggesting that the candidate gene underlying the pink phenotype encodes a regulatory protein such as a transcription factor rather than a biosynthetic enzyme. Of 26 MYB and basic helix-loop-helix transcription factors putatively involved in regulating transcription of genes in the phenylpropanoid and/or flavonoid pathway, only the expression level of the MYB12 gene correlated well with the decrease in the expression of structural flavonoid genes in peel samples of pink- and red-fruited genotypes during ripening. Genetic mapping and segregation analysis showed that MYB12 is located on chromosome 1 and segregates perfectly with the characteristic pink fruit color. Virus-induced gene silencing of SlMYB12 resulted in a decrease in the accumulation of naringenin chalcone, a phenotype consistent with the pink-colored tomato fruit of IL1b. In conclusion, biochemical and molecular data, gene mapping, segregation analysis, and virus-induced gene silencing experiments demonstrate that the MYB12 transcription factor plays an important role in regulating the flavonoid pathway in tomato fruit and suggest strongly that SlMYB12 is a likely candidate for the y mutation.

Macromolecular effect on crystal pattern formation in ultra-thin films: Molecular segregation in a binary blend of PEO fractions

In this work we report our investigation on the crystal patterns of a 50/50 blend of two polyethylene oxide (PEO) fractions with different molecular weights ( M ¯ w = 5040 and 35000 g / m o l ) in ultra-thin films. Using AFM with a hot stage the samples on the surface of silicon wafer were isothermally crystallized at 20.0 ≤ T c ≤ 60.0 °C. The crystal patterns are different from those of the two pure fractions. Co-crystallization, partial segregation and full segregation have been observed. Especially, within 47.0 ≤ T c ≤ 54.0 °C dual thickness crystals formed. The thickness of the middle part of the crystal corresponds to the lamella thickness of 35k-PEO fraction with multiple folds, while the thickness of the edge part is nearly equal to an extended-chain lamella thickness of 5k-PEO fraction. We suppose that the appearance of the dual thickness crystals is due to molecular partial segregation. Utilizing in-situ AFM, the growth of the crystal with dual thicknesses as a function of time was monitored at T c = 54.0 °C. Two growth processes were observed and a pattern formation mechanism was suggested on the basis of specified molecular motion and chain-fold crystallization of polymers.

Concentration and temperature dependence of the refractive index of ethanol-water mixtures: Influence of intermolecular interactions

The temperature and concentration dependence of the refractive index, nD(x, T), in ethanol-water mixtures agrees with previous data in the ethanol-rich concentration range. The refractive index versus concentration x determined at 20 degrees C shows the expected maximum at about 41 mol% water (22 mass% water). The temperature derivative of the refractive index, dnD/dT, shows anomalies at lower water concentrations at about 10 mol% water but no anomaly at 41 mol% water. Both anomalies are related to intermolecular interactions, the one in nD seems to be due to molecular segregation and cluster formation while the origin of the second one in dnD/dT is still not clear.

SOX6 controls dorsal progenitor identity and interneuron diversity during neocortical development

SummaryThe extraordinary neuronal diversity of the central nervous system emerges largely from controlled spatial and temporal segregation of cell type-specific molecular regulators. Here, we report that the transcription factor SOX6 controls the molecular segregation of dorsal (pallial) from ventral (subpallial) telencephalic progenitors, and the differentiation of cortical interneurons, regulating forebrain progenitor and interneuron heterogeneity. During corticogenesis in mice, SOX6 and highly related SOX5 expression is largely mutually exclusive in pallial and subpallial progenitors, respectively, and remains mutually exclusive in a reverse pattern in postmitotic neuronal progeny. Loss of SOX6 from pallial progenitors causes their inappropriate expression of normally subpallium-restricted developmental controls, conferring mixed dorsal-ventral identity. In postmitotic cortical interneurons, loss of SOX6 dramatically disrupts the differentiation and diversity of cortical interneuron subtypes, analogous to SOX5 control over cortical projection neuron development. These data reveal SOX6 as a novel transcription factor regulator of both progenitor and cortical interneuron diversity during neocortical development.

The relationship between morphology and performance of donor–acceptor rod–coil block copolymer solar cells

Self-assembled functional rod–coil block copolymers (poly(3-hexylthiophene)-b-poly(n-butyl acrylate-stat-acrylate perylene)) containing electron donor (poly(3-hexylthiophene)) and acceptor (perylene) moieties were synthesized, characterized, and studied in photovoltaic devices. The block copolymers were synthesized by a combination of the McCullough route yielding monodisperse polythiophene, living radical polymerization and finally “click chemistry”. The self-assembled nanostructure was tuned via time to control the degree of order. As a result, devices with active layers which were completely disordered (molecularly mixed), contain short range order in which the nanodomains were molecularly pure, but were poorly organized, or consisted of cylindrical fibrils with their long axes running parallel to the electrodes were compared. Active layers with well formed but poorly organized nanodomains had the highest photovoltaic efficiencies indicating that molecular scale segregation has a significant effect on device performance. The poor performance of the well defined cylindrical nanostructures is probably a reflection of the poor charge transport properties associated with the misorientation of the long axes parallel to the electrodes.

Quantitative trait locus responsible for resistance to Aphanomyces root rot (black root) caused by Aphanomyces cochlioides Drechs. in sugar beet

Aphanomyces root rot, caused by Aphanomyces cochlioides Drechs., is one of the most serious diseases of sugar beet (Beta vulgaris L.). Identification and characterization of resistance genes is a major task in sugar beet breeding. To ensure the effectiveness of marker-assisted screening for Aphanomyces root rot resistance, genetic analysis of mature plants' phenotypic and molecular markers' segregation was carried out. At a highly infested field site, some 187 F(2) and 66 F(3) individuals, derived from a cross between lines 'NK-310mm-O' (highly resistant) and 'NK-184mm-O' (susceptible), were tested, over two seasons, for their level of resistance to Aphanomyces root rot. This resistance was classified into six categories according to the extent and intensity of whole plant symptoms. Simultaneously, two selected RAPD and 159 'NK-310mm-O'-coupled AFLP were used in the construction of a linkage map of 695.7 cM. Each of nine resultant linkage groups was successfully anchored to one of nine sugar beet chromosomes by incorporating 16 STS markers. Combining data for phenotype and molecular marker segregation, a single QTL was identified on chromosome III. This QTL explained 20% of the variance in F(2) population (in the year 2002) and 65% in F(3) lines (2003), indicating that this QTL plays a major role in the Aphanomyces root rot resistance. This is the first report of the genetic mapping of resistance to Aphanomyces-caused diseases in sugar beet.

Terrestrial methane seeps and mud volcanoes: A global perspective of gas origin

A global database of gas composition and methane stable isotopes of 143 terrestrial mud volcanoes from 12 countries and 60 seeps independent from mud volcanism from eight countries, was compiled and examined in order to provide the first worldwide statistics on the origin of methane seeping at the earth's surface. Sixteen seep data were coupled with their associated subsurface reservoirs. The surface seepage data indicate that at least 76% of the mud volcanoes release thermogenic gas, with only 4% biogenic and 20% with mixed character. The average (201 data) of methane concentration and methane carbon isotope ratios ( δ 13 C 1 ) of mud volcanoes are 90% v/v and - 46.4 ‰ , respectively. The other types of seeps, which are independent from mud volcanism, have an average δ 13 C 1 value that is slightly higher ( - 42.9 ‰ ) . Gases from mud volcanoes are generally lighter (more methane, less ethane and propane) than their associated reservoir gases, suggesting a molecular fractionation during advective fluid migration. Other types of seeps, especially “dry” seeps, maintain the reservoir C 1 / ( C 2 + C 3 ) “Bernard” ratio. Mud volcanoes behave like a “natural refinery” and the origin of gas more isotopically enriched than - 50 ‰ and with C 1 / ( C 2 + C 3 ) > 500 should be attributed to a thermogenic source, rather than partial oxidation of biogenic gas. Some data that appear biogenic in the “Bernard diagram” can be explained by molecular fractionation of mixed gas. Consequently, the “Bernard” parameter may be misleading when applied to mud volcanoes since it does not always reflect the original gas composition. The mechanisms of the molecular advective segregation should be studied quantitatively by specific models and experiments.

Characterization of LDPE grafted with Diethylmaleate by Gamma Radiation: Application of FTIR, GPC and SSA Techniques

AbstractSummary: The grafting of diethyl maleate onto low‐density polyethylene using gamma irradiation as initiator has been evaluated. The grafting degree was estimated by FTIR and with the use of a calibration curve. The functionalized polymers were characterized by DSC, MFI, SSA and GPC. An increase in the grafting degree with the radiation dose and the concentration of the functional monomer was found. Branching seemed to be the preferential reaction induced by radiation, causing an increase in average molecular weights with the consequently reduction of melt flow index values. The molecular segregation induced by the calorimetric treatment showed that grafting occurs preferentially through secondary carbon sequences.

Molecular Weight Segregation on Surfaces of Polyethylene Blended Films as Estimated from Nanoscratch Tests Using Scanning Probe Microscopy

Nanoscratch tests using scanning probe microscopy (SPM) were performed on films prepared from two polyethylene (PE) materials polymerized by using a metallocene catalyst system with different molecular weights (MWs). Blended samples were prepared by dissolving both PE materials at various ratios in hot p-xylene. The pure and blended samples were compression molded into films at 180 degrees C for different holding times in the molten state. The results of SPM nanoscratch tests with an applied load of 30 nN indicated that the lower-MW surface could be easily plowed with wear debris but the higher-MW surface was less deformed. However, the deformation pattern of the blended film surface was similar to that of the lower-MW surface. These results suggest that MW segregation occurs during holding in the molten state as lower-MW components rise to the film surface.

Real dispersion of isolated fumed silica nanoparticles in highly filled PMMA prepared by high energy ball milling

Fumed silica nanoparticles with 14 nm of diameter were blended with poly(methylmethacrylate), PMMA, by means of a high energy ball milling process. AFM analysis revealed how this process of blending allows obtaining a very homogeneous dispersion of the nanoparticles within the PMMA. Furthermore, it was observed that the properties of the composite are highly dependent on the active milling time: (i) SEM inspection showed that the particle size of the silica–PMMA nanocomposite decreases and (ii) DSC analysis demonstrated that the T g also decreases due to a reduction in the molecular weight of the PMMA caused by chain scission during the high energy blending process. Two T g 's were obtained in the case of the nanocomposite when milling times were higher than 6 h, one of them being even higher than that of the PMMA without being subjected to the HEBM process. This result was assigned to surface-induced molecular weight segregation near the nanoparticles surface. It has been demonstrated the possibility of preparing transparent nanocomposites with excellent moldability.

Study of the Packing Density and Molecular Orientation of Bimolecular Self-Assembled Monolayers of Aromatic and Aliphatic Organosilanes on Silica

Bimolecular self-assembled monolayers (SAMs) of aromatic and aliphatic chlorosilanes were self-assembled onto silica, and their characteristics were established by contact angle measurement, near-edge X-ray absorption fine structure spectroscopy, and Fourier transform infrared spectroscopy. Three aromatic constituents (phenyltrichlorosilane, benzyltrichlorosilane, and phenethyltrichlorosilane) were studied in combination with four aliphatic coadsorbates (butyltrichlorosilane, butyldimethylchlorosilane, octadecyltrichlorosilane, and octadecyldimethylchlorosilane). Our results demonstrate that whereas SAMs made of trichlorinated organosilanes are densely packed, SAMs prepared from monochlorinated species are less dense and poorly ordered. In mixed systems, trichlorinated aromatics and trichlorinated aliphatics formed SAMs with highly tunable compositions; their surfaces were compositionally homogeneous with no large-scale domain separation. The homogeneous nature of the resulting SAM was a consequence of the formation of in-plane siloxane linkages among neighboring molecules. In contrast, when mixing monochlorinated aliphatics with trichlorinated aromatics, molecular segregation occurred. Although the two shortest aromatic species did not display significant changes in orientation upon mixing with aliphatics, the aromatic species with the longest polymethylene spacer, phenethyltrichlorosilane, displayed markedly different orientation behavior in mixtures of short- and long-chain aliphatics.

Detection of Ks-excess stars in the 14 Myr open cluster NGC 4755

Aims. We derive the structure, distribution of MS and PMS stars and dynamical state of the young open cluster NGC4755. We explore the possibility that, at the cluster age, some MS and PMS stars still present infrared excesses related to dust envelopes and proto-planetary discs. Methods. J, H and K, 2MASS photometry is used to build CMD and colour-colour diagrams, radial density profiles, luminosity and mass functions. Field-star decontamination is applied to uncover the cluster's intrinsic CMD morphology and detect candidate PMS stars. Proper motions from UCAC2 are used to determine cluster membership. Results. The radial density profile follows King's law with a core radius R core = 0.7 ± 0.1 pc and a limiting radius R lim = 6.9 ± 0.1 pc. The cluster age derived from Padova isochrones is 14 ± 2 Myr. Field-star decontamination reveals a low-MS limit at ≈1.4 M ⊙ . The core MF (Χ = 0.94 ± 0.16) is flatter than the halo's (Χ = 1.58 ± 0.11). NGC4755 contains ∼285 candidate PMS stars of age ∼1-15 Myr, and a few evolved stars. The mass locked up in PMS, MS and evolved stars amounts to ∼1150 M ⊙ . Proper motions show that /;,-excess MS and PMS stars are cluster members. K s -excess fractions in PMS and MS stars are 5.4 ± 2.1% and 3.9 ± 1.5% respectively, consistent with the cluster age. The core is deficient in PMS stars, as compared with MS ones. NGC 4755 hosts binaries in the halo but they are scarce in the core. Conclusions. Compared to open clusters in different dynamical states studied with similar methods, NGC 4755 fits relations involving structural and dynamical parameters in the expected locus for its age and mass. On the other hand, the flatter core MF probably originates from primordial processes related to parent molecular cloud fragmentation and mass segregation over ∼14 Myr. Star formation in NGC4755 began ≈ 14 Myr ago and proceeded for about the same length of time. Detection of K s -excess emission in member MS stars suggests that some circumstellar dust discs survived for ∼10 7 yr, occurring both in some MS and PMS stars for the age and spread observed in NGC 4755.

Effect of Molecular Weight on Network Formation in Linear ABC Triblock Copolymers

A series of linear poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock copolymers were synthesized to investigate the effects of molecular weight and segregation strength on block copolymer network phases. Analysis of small-angle X-ray scattering (SAXS), dynamic mechanical spectroscopy (DMS), and transmission electron microscopy (TEM) data shows that several factors influence network formation. Increasing the polymer molecular weight 50−100% above the value necessary to place the order−disorder transition temperature within an experimentally accessible range leads to disruption of long-range order at compositions associated with the orthorhombic O70 phase in freeze-dried and annealed specimens. Comparable molecular weight three-domain lamellae (LAM3) behave differently, exhibiting well-ordered morphologies that closely resemble the correlated layers found in diblock copolymers. These findings are interpreted on the basis of the reduction in molecular diffusion that accompanies increasing molecular weight and segregation strength, bridging across the poly(styrene) middle block, and differences in domain topology. These kinetic restrictions can inhibit establishment of equilibrium phase behavior in ABC triblock copolymers but do not necessarily eliminate formation of multifunctional triply periodic materials.

Voltage-gated ion channels in the axon initial segment of human cortical pyramidal cells and their relationship with chandelier cells

The axon initial segment (AIS) of pyramidal cells is a critical region for the generation of action potentials and for the control of pyramidal cell activity. Here we show that Na+ and K+ voltage-gated channels, together with other molecules involved in the localization of ion channels, are distributed asymmetrically in the AIS of pyramidal cells situated in the human temporal neocortex. There is a high density of Na+ channels distributed along the length of the AIS together with the associated proteins spectrin betaIV and ankyrin G. In contrast, Kv1.2 channels are associated with the adhesion molecule Caspr2, and they are mostly localized to the distal region of the AIS. In general, the distal region of the AIS is targeted by the GABAergic axon terminals of chandelier cells, whereas the proximal region is innervated, mostly by other types of GABAergic interneurons. We suggest that this molecular segregation and the consequent regional specialization of the GABAergic input to the AIS of pyramidal cells may have important functional implications for the control of pyramidal cell activity.