Coculture of Astroglial and Vascular Endothelial Cells as Apposing Layers Enhances the Transcellular Transport of Hypoxanthine

Abstract: In brain, astrocytes and endothelial cells are a major site of adenosine degradation. These two cell types, found in close apposition, constitute the wall of the brain's capillaries and serve as a site of hypoxanthine production and degradation. Both cell types possess the hypoxanthine salvage pathway and can incorporate hypoxanthine into nucleotides. This suggests that the endothelial-astrocyte anatomical complex might play an important role in the brain's purine homeostasis. To test this hypothesis, cocultures of monolayers of vascular endothelial cells and astrocytes were grown over a porous membrane, in close apposition to one another, and studies on hypoxanthine transport and metabolism to uric acid were performed. The flux of hypoxanthine across the cell layers was simultaneously determined and compared with the flux of sucrose, as a probe of passive diffusion. Our results show that in endothelial, glial, and endothelial-glial cell layers the hypoxanthine flux was greater than that of sucrose, and that the flux of hypoxanthine, but not of sucrose, was inhibited by adenine or by lowering the temperature. These results suggest that hypoxanthine moves across endothelial, glial, and endothelial-glial cell layers by a transport process. Furthermore, we found that hypoxanthine transport is enhanced when glial and endothelial cells are cocultured compared with that in glial or endothelial monolayers. In addition the coculture also resulted in a depression of xanthine oxidase activity.     

Mechanisms of host discrimination and intraspecific competition in the aphid parasitoid Ephedrus cerasicola

The aphid parasitoid Ephedrus cerasicola Starý (Hymenoptera: Aphidiidae) discriminates between parasitized and unparasitized aphid hosts (Myzus persicae (Sulzer), Homoptera: Aphididae) in two different ways. By antennal contact with the parasitized host, it can detect an external marking pheromone which is effective only for a few hours. The behaviour of the parasitoid also indicated that it responded to an internal marker, probably by means of chemoreceptors on the ovipositor. The parasitoid behaviour was studied in encounters with parasitized hosts 0–10 min, 2–3 h, 6–7 h and 23–24 h after the first parasitization. Aphids were superparasitized within 1 h or after 24 h, and aphids in each experiment were later dissected at two different times. It is suggested that the supernumerary offspring were eliminated by chemical means, whether the time between the two ovipositions was 0–1 h or 24 h.

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Résumé Le parasitoïde de puceron, E. cerasicola Starý (Hym.: Aphidiidae) sélectionne les pucerons, Myzus persicae (Sulzer), parasités ou non, de deux façons différentes. Il peut percevoir une phéromone externe de marquage perceptible seulement pendant quelques heures par contact antennaire. Son comportement montre qu'il réagit aussi à un marquage interne, probablement par des chémorécepteurs de sa tarière. Le comportement du parasitoïde a été étudié en le mettant en contact avec des hôtes parasités depuis 0–10 min, 2–3 h, 6–7 h et 23–24 h. Les pucerons ont été surparasités pendant la première heure ou après 24 heures. Les pucerons de toutes les expériences ont été disséqués à deux moments différents. Ceci a conduit à estimer que les descendants en surnombre ont été éliminés chimiquement quand la période entre deux pontes successives était inférieure à 1 h ou supérieure à 24 h.

     

Culturing Selenastrum capricornutum (Chlorophyta) in a synthetic algal nutrient medium with defined mineral particulates

Algal nutrient studies in chemically-defined media typically employ a synthetic chelator to prevent iron hydroxide precipitation. Micronutrient-particulate interactions may, however, significantly affect chemical speciation and hence biovailability of these nutrients in natural waters. A technique is described by which Selenastrum capricornutum Printz (Chlorophyta) may be cultured in a medium where trace metal speciation (except iron) is controlled, not by organic chelation, but by sorption onto titanium dioxide. Application of this culturing protocol in conjunction with results from sorption studies of nutrient ions on mineral particles provides a means of studying biological impacts of sorptive processes in aquatic environments.     

A microbial sensor for discovering structural probes of protein misfolding and aggregation

In all cell types, protein homeostasis, or “proteostasis,” is maintained by sophisticated quality control networks that regulate protein synthesis, folding, trafficking, aggregation, disaggregation, and degradation. In one notable example, Escherichia coli employ a proteostasis system that determines whether substrates of the twin-arginine translocation (Tat) pathway are correctly folded and thus suitable for transport across the tightly sealed cytoplasmic membrane. Herein, we review growing evidence that the Tat translocase itself discriminates folded proteins from those that are misfolded and/or aggregated, preferentially exporting only the former. Genetic suppressors that inactivate this mechanism have recently been isolated and provide direct evidence for the participation of the Tat translocase in structural proofreading of its protein substrates. We also discuss how this discriminatory “folding sensor” has been exploited for the discovery of structural probes (e.g., sequence mutations, pharmacologic chaperones, intracellular antibodies) that modulate the folding and solubility of virtually any protein-of-interest, including those associated with aggregation diseases (e.g., α-synuclein, amyloid-β protein). Taken together, these studies highlight the utility of engineered bacteria for rapidly and inexpensively uncovering potent anti-aggregation factors.     

Geographic variation of flavonoids in Phlox carolina

Non-anthocyanin flavonoid expression was determined among 64 continuous range and nine disjunct range populations of Phlox carolina. The species contains four flavone nuclei and a total of 25 derivatives, most of which are $\text{C-}\text{glycosides}$. Nearly all populations express unique flavone patterns. Using a qualitative similarity index of minimum biosynthetic step distance (MBSD), the average population contains only ca. 50% of the overall substitutional diversity. The separate ranges are distinctive in the % occurrence of most compounds but only weakly divergent in comparative mean MBSD. Proximity and MBSD are significantly correlated overall but local variability is extensive and no discrete racism is apparent. Within the continuous range 18 compounds are distributed in independent but overlapping gradients and 13 of these extend consistently through the disjunct range. The patch-work continuum of flavone variation is the apparent consequence of dissection and contraction of a historically more widespread distribution. Other general aspects of the variation patterns are discussed.     

马尾松胚乳愈伤组织发生的初步研究

为获取马尾松(Pinus massoniana)单倍体材料，建立其胚乳组织培养体系，对马尾松胚乳不同的消毒方法进行筛选，并分析不同基本培养基、生长调节剂配比和热激处理对愈伤诱导的影响。结果表明，胚乳的最佳消毒方式为75%酒精处理30 s+2% NaClO消毒15 min，外植体污染率为0，死亡率仅为15.56%；生长素可促进愈伤诱导且是必需的；细胞分裂素浸泡种子可代替培养基中的细胞分裂素，并能取得比较好的胚乳愈伤诱导效果，1.0 mg·mL-1 6-BA浸泡30 min处理的效果最佳，在培养基WPM+NAA 2.0 mg·L-1+2,4-D 1.0 mg·L-1+蔗糖30 g·L-1+琼脂7 g·L-1中，愈伤诱导率高达87.78%；培养基DCR+NAA 2.0 mg·L-1+6-BA 1.0 mg·L-1+蔗糖30 g·L-1+琼脂7 g·L-1的胚乳愈伤诱导率最高(68.75%)；热激处理可提高胚乳愈伤的诱导率和质量，以相对湿度85%下45 ℃热激10 min最佳，总愈伤诱导率为66.25%，成团愈伤诱导率达8.75%；增殖培养以培养基WPM+NAA 0.1 mg·L-1+6-BA 2.0 mg·L-1+蔗糖30 g·L-1+琼脂7 g·L-1最佳，增殖率达83.33%。     

Relationship between Baccharis dracunculifolia DC. and B. microdonta DC. (Asteraceae) by Their Different Seasonal Volatile Expression

Baccharis dracunculifolia DC. and Baccharis microdonta DC. (Asteraceae) are woody species morphologically similar growing in Uruguay, where not taxonomists people often confuse them in field conditions. As the essential oil of B. dracunculifolia (‘vassoura’ oil) is highly prized by the flavor and fragrance industry, the correct differentiation of the two species is a key factor in exploiting them profitably and reasonably. To differentiate both Baccharis species, in this work their volatile expression profiles were studied as an alternative tool to determine authenticity and quality. Volatile organic compounds (VOCs) were monthly extracted during an entire year from aerial parts of wild populations by simultaneous distillation extraction (SDE), and studied by gas chromatography/mass spectrometry (GC/MS; identification) and conventional gas chromatography (GC-FID; component abundances determination). Enantioselective gas chromatography/mass spectrometry (Es-GC/MS) was applied in the search of parameters able to ensure genuineness of each species extract. Qualitative VOCs profiles were found to be similar for both species, being β-pinene, limonene, spathulenol, caryophyllene oxide, and viridiflorol the main components. However, the abundance of those VOCs were two to ten times higher in B. dracunculifolia than in B. microdonta during the year of study. These Baccharis spp. showed species-specific patterns of VOCs expression according to the seasonality, and interestingly, oxygenated compounds (trans-pinocarveol and myrtenal) increased their abundances at full-flowering stages. The enantiomeric distribution of selected monoterpenes (α- and β-pinenes, limonene, linalool, terpinen-4-ol, and α-terpineol) presented differential values for both Baccharis spp., meaning that Es-GC might be a useful tool for differentiating chemically both species in Uruguay for genuineness determination purposes.     

A morphological and histological comparison of the initiation and development of pecan (Carya illinoinensis) somatic embryogenic cultures induced with naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid

Summary Somatic embryos produced in vitro may exhibit structural abnormalities that affect their subsequent germination and conversion into plants. To assess the influence of auxin type on embryo initiation and development, a morphological and histological comparison was made of pecan (Carya illinoinensis) somatic embryogenic cultures induced on media with naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid (2,4-D), using light and scanning electron microscopy. Both auxins promoted enhanced cell division, particularly in subepidermal cell layers. However, notable differences were observed in mitotic activity, location of embryogenic cell proliferation, epidermal continuity, callus growth, and embryo morphology. Cultures induced on naphthaleneacetic acid had embryogenic regions composed of homogeneous, isodiametric, meristematic cells. Embryos derived from these cultures generally had a normal morphology, were single, and had a discrete apical meristem. In contrast, tissues induced on media with 2,4-D had more intense and heterogeneous regions of cell division. Proliferating cell regions were composed of meristematic cells interspersed with callus and involved more extensive regions of the mesophyll. Marked callus proliferation caused epidermal rupture in some areas. Embryos induced on medium with 2,4-D had a higher incidence of abnormalities that included fasciated, fan-shaped, and tubular embryos. Defined apical meristems were often lacking or partially obliterated due to callus proliferation. The heterogeneous, often intensive proliferation of cells in cultures induced with 2,4-D may interfere with normal patterns of embryo development.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BAP 6-benzylaminopurine - NAA naphthaleneacetic acid - SEM scanning electron microscopy     

Hard-sphere/pseudo-particle modelling (HS-PPM) for efficient and scalable molecular simulation of dilute gaseous flow and transport

Continuum methods are not accurate enough for flows at high Knudsen numbers, whereas rigorous molecular dynamics (MD) methods are too costly for simulations at practical dimensions. Hard-sphere (HS) model is a simplified MD method efficient for dilute gaseous flow but is of poor parallelism due to its event-driven nature, which sets a strong limitation to its large-scale applications. In this work, pseudo-particle modelling, a time-driven modelling approach is coupled with HS model to construct a scalable parallel method capable of simulating flows and transport processes at high Knudsen numbers without losing necessary molecular details in describing their macro-scale behaviours. The method is validated in several classical simulation cases and its performance is evaluated to be favourable. To demonstrate the potential applications of this method, we also simulate the diffusion of small molecules in multi-scale porous media which is related to catalysis, material preparation and micro chemical engineering in the long term.