The length of vesicular stomatitis virus particles dictates a need for actin assembly during clathrin-dependent endocytosis

Microbial pathogens exploit the clathrin endocytic machinery to enter host cells. Vesicular stomatitis virus (VSV), an enveloped virus with bullet-shaped virions that measure 70 x 200 nm, enters cells by clathrin-dependent endocytosis. We showed previously that VSV particles exceed the capacity of typical clathrin-coated vesicles and instead enter through endocytic carriers that acquire a partial clathrin coat and require local actin filament assembly to complete vesicle budding and internalization. To understand why the actin system is required for VSV uptake, we compared the internalization mechanisms of VSV and its shorter (75 nm long) defective interfering particle, DI-T. By imaging the uptake of individual particles into live cells, we found that, as with parental virions, DI-T enters via the clathrin endocytic pathway. Unlike VSV, DI-T internalization occurs through complete clathrin-coated vesicles and does not require actin polymerization. Since VSV and DI-T particles display similar surface densities of the same attachment glycoprotein, we conclude that the physical properties of the particle dictate whether a virus-containing clathrin pit engages the actin system. We suggest that the elongated shape of a VSV particle prevents full enclosure by the clathrin coat and that stalling of coat assembly triggers recruitment of the actin machinery to finish the internalization process. Since some enveloped viruses have pleomorphic particle shapes and sizes, our work suggests that they may use altered modes of endocytic uptake. More generally, our findings show the importance of cargo geometry for specifying cellular entry modes, even when the receptor recognition properties of a ligand are maintained.     

Lipid and fatty acid composition of canine lipoproteins

Lipid classes and their fatty acids were studied in the major lipoprotein fractions from canine, in comparison with human, plasma. In dogs, high-density-lipoprotein (HDL), the main carrier of plasma phospholipid (PL), cholesterol ester (CE) and free cholesterol, was the most abundant lipoprotein, followed by low and very-low density lipoproteins (LDL and VLDL). Notably, LDL and VLDL contributed similarly to the total dog plasma triacylglycerol (TG). The PL composition was similar in all three lipoproteins, dominated by phosphatidylcholine (PC). Even though the content and composition of lipids within and among lipoproteins differed markedly between dog and man, the total amount of circulating lipid was similar. All canine lipoproteins were relatively richer than those from humans in long-chain (C20-C22) n-6 and n-3 polyunsaturated fatty acids (PUFA) but had comparable proportions of total saturated and monoenoic fatty acids, with 18:2n-6 being the main PUFA in both mammals. The fatty acid profile of canine and human lipoproteins differed because they had distinct proportions of their major lipids. There were more n-3 and n-6 long-chain PUFA in canine than in human plasma, because dogs had more HDL, their HDL had more PC and CE, and both these lipids were richer in such PUFA.     

Diabetes Alters KIF1A and KIF5B Motor Proteins in the Hippocampus

Diabetes mellitus is the most common metabolic disorder in humans. Diabetic encephalopathy is characterized by cognitive and memory impairments, which have been associated with changes in the hippocampus, but the mechanisms underlying those impairments triggered by diabetes, are far from being elucidated. The disruption of axonal transport is associated with several neurodegenerative diseases and might also play a role in diabetes-associated disorders affecting nervous system. We investigated the effect of diabetes (2 and 8 weeks duration) on KIF1A, KIF5B and dynein motor proteins, which are important for axonal transport, in the hippocampus. The mRNA expression of motor proteins was assessed by qRT-PCR, and also their protein levels by immunohistochemistry in hippocampal slices and immunoblotting in total extracts of hippocampus from streptozotocin-induced diabetic and age-matched control animals. Diabetes increased the expression and immunoreactivity of KIF1A and KIF5B in the hippocampus, but no alterations in dynein were detected. Since hyperglycemia is considered a major player in diabetic complications, the effect of a prolonged exposure to high glucose on motor proteins, mitochondria and synaptic proteins in hippocampal neurons was also studied, giving particular attention to changes in axons. Hippocampal cell cultures were exposed to high glucose (50 mM) or mannitol (osmotic control; 25 mM plus 25 mM glucose) for 7 days. In hippocampal cultures incubated with high glucose no changes were detected in the fluorescence intensity or number of accumulations related with mitochondria in the axons of hippocampal neurons. Nevertheless, high glucose increased the number of fluorescent accumulations of KIF1A and synaptotagmin-1 and decreased KIF5B, SNAP-25 and synaptophysin immunoreactivity specifically in axons of hippocampal neurons. These changes suggest that anterograde axonal transport mediated by these kinesins may be impaired in hippocampal neurons, which may lead to changes in synaptic proteins, thus contributing to changes in hippocampal neurotransmission and to cognitive and memory impairments.     

Reproductive biology of Oreocereus fossulatus (Cactaceae), a long‐lived columnar cactus endemic to the tropical Andes

The geographic dichotomy hypothesis suggests that columnar cacti inhabiting the tropics depend on flower visitors (birds and bats) for their pollination, showing highly specialized animal‐pollinated systems. This pattern has been demonstrated for the northern hemisphere; however, our knowledge of the species of columnar cacti growing in the southern tropics is still scarce. In this study, we studied the reproductive biology of Oreocereus fossulatus (Cactaceae, Tribe Trichocereae), an endemic, columnar cactus of the tropical Andes, to determine if its pollination system tends to be more generalized (mixed systems of autogamy and xenogamy) than specialized (xenogamy) as a consequence of the geographic position of where it lives. Observations of the frequency of visits showed that Patagona gigas (Trochillidae) is its main pollinator. It visits the flowers when they are open, coinciding with the periods of greater floral reward (dusk and dawn of the first day of anthesis). The treatments of autogamy, xenogamy and geitonogamy produced fruits, showing that O. fossulatus exhibits a generalized pollination system, in the same way as its congeneric species O. celsianus, which is distributed farther south in the Prepuna biogeographical region. Our results suggest that species partially specializing in pollination by hummingbirds and, besides, capable of autopollination, could be common in the tropical and subtropical Andes, probably as a response to the unpredictable environments present in their ecosystems.     

Contrasting effects of fire frequency on plant traits of three dominant perennial herbs from Chaco Serrano

Fire frequencies are currently increasing in many regions across the world as a result of anthropic activities, affecting ecological processes and plant population dynamics. Fire can generate important changes in soil properties, altering nutrient dynamics and thereby plant growth. Here we analyse fire frequency effects on soil quality and plant traits of three native perennial herbaceous plants (Cologania broussonetii, Desmodium uncinatum and Rhynchosia edulis; Fabaceae) with the capacity for biological N₂ fixation that resprouts and are abundant after fire in Chaco Serrano forests. Based on 22‐year fire history, we assessed plant traits in sites with low and high fire frequencies along with unburned scenarios. We found significantly lower water content, nitrates and electrical conductivity in frequently burned soils. As a result, the three species showed consistently lower leaf area and specific leaf area in both fire frequencies, implying lower growth rates in comparison to unburned sites. However, total leaf biomass was not affected by fire, leaf phosphorus concentration was higher in R. edulis in high fire frequency and leaf N concentration was twice as large in plants growing in sites of high fire frequency in C. broussonetii and R. edulis. Such an increase in N and phosphorus concentrations is likely a result of both their conservative use of resources and their biological N₂ fixation capacity. To our knowledge, this is the first record of such contrasting fire effects observed consistently in three co‐occurring species: while plant growth decreased with fire frequency, leaf nutritional traits remain unchanged or increased in frequently burned sites. Quality‐depleted and drier soils that result from increased fire frequencies may not only affect trait variation at the intraspecific level but can also drive to a homogenization of the plant community, selecting species with particular combinations of morphological and functional traits.     

Environmental and genetic interactions reveal FLOWERING LOCUS C as a modulator of the natural variation for the plasticity of flowering in Arabidopsis

The timing of flowering initiation depends strongly on the environment, a property termed as the plasticity of flowering. Such plasticity determines the adaptive potential of plants because it provides phenotypic buffer against environmental changes, and its natural variation contributes to evolutionary adaptation. We addressed the genetic mechanisms of the natural variation for this plasticity in Arabidopsis thaliana by analysing a population of recombinant inbred lines derived from Don‐0 and Ler accessions collected from distinct climates. Quantitative trait locus (QTL) mapping in four environmental conditions differing in photoperiod, vernalization treatment and ambient temperature detected the folllowing: (i) FLOWERING LOCUS C (FLC) as a large effect QTL affecting flowering time differentially in all environments; (ii) numerous QTL displaying smaller effects specifically in some conditions; and (iii) significant genetic interactions between FLC and other loci. Hence, the variation for the plasticity of flowering is determined by a combination of environmentally sensitive and specific QTL, and epistasis. Analysis of FLC from Don identified a new and more active allele likely caused by a cis‐regulatory deletion covering the non‐coding RNA COLDAIR. Further characterization of four FLC natural alleles showed different environmental and genetic interactions. Thus, FLC appears as a major modulator of the natural variation for the plasticity of flowering to multiple environmental factors.     

Improvement of photovoltaic performance by substituent effect of donor and acceptor structure of TPA-based dye-sensitized solar cells

We report a computational study of a series of organic dyes built with triphenylamine (TPA) as an electron donor group. We designed a set of six dyes called (TPA-n, where n?=?0–5). In order to enhance the electron-injection process, the electron-donor effect of some specific substituent was studied. Thus, we gave insights into the rational design of organic TPA-based chromophores for use in dye-sensitized solar cells (DSSCs). In addition, we report the HOMO, LUMO, the calculated excited state oxidized potential E^dye*(eV) and the free energy change for electron-injection ΔG_inject(eV), and the UV-visible absorption bands for TPA-n dyes by a time-dependent density functional theory (TDDFT) procedure at the B3LYP and CAM-B3LYP levels with solvent effect. The results demonstrate that the introduction of the electron-acceptor groups produces an intramolecular charge transfer showing a shift of the absorption wavelengths of TPA-n under studies.

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Graphical Abstract Several organic dyes TPA-n with different donors and acceptors are modeled. A strong conjugation acrros the donor and anchoring groips (TPA-n) bas been studied. Candidate TPA-3 shows a promising results.

     

An Evidenced-Based Scale of Disease Severity following Human Challenge with Enteroxigenic Escherichia coli

Background

Experimental human challenge models have played a major role in enhancing our understanding of infectious diseases. Primary outcomes have typically utilized overly simplistic outcomes that fail to entirely account for complex illness syndromes. We sought to characterize clinical outcomes associated with experimental infection with enterotoxigenic Escherichia coli (ETEC) and to develop a disease score.

Methods

Data were obtained from prior controlled human ETEC infection studies. Correlation and univariate regression across sign and symptom severity was performed. A multiple correspondence analysis was conducted. A 3-parameter disease score with construct validity was developed in an iterative fashion, compared to standard outcome definitions and applied to prior vaccine challenge trials.

Results

Data on 264 subjects receiving seven ETEC strains at doses from 1x10⁵ to 1x10¹⁰ cfu were used to construct a standardized dataset. The strongest observed correlation was between vomiting and nausea (r = 0.65); however, stool output was poorly correlated with subjective activity-impacting outcomes. Multiple correspondence analyses showed covariability in multiple signs and symptoms, with severity being the strongest factor corresponding across outcomes. The developed disease score performed well compared to standard outcome definitions and differentiated disease in vaccinated and unvaccinated subjects.

Conclusion

Frequency and volumetric definitions of diarrhea severity poorly characterize ETEC disease. These data support a disease severity score accounting for stool output and other clinical signs and symptoms. Such a score could serve as the basis for better field trial outcomes and gives an additional outcome measure to help select future vaccines that warrant expanded testing in pivotal pre-licensure trials.