What factors shape female phenotypes of a poleward‐moving damselfly at the edge of its range?

Individuals at the expansion front during a climate‐driven range expansion are expected to differ phenotypically from those individuals in core populations. Little information is known about the joint, potentially opposing, effects of stressful conditions at the range edge versus evolutionary changes that take place during range expansion in shaping the phenotypes at the range front. We investigated the effect of range expansion on immune function, body condition and flight‐related morphology (flight muscle ratio, wing loading, and wing aspect ratio) of field‐collected females of the poleward‐moving damselfly Coenagrion scitulum. Individuals at the expansion front had a lower body condition, which indicated more stressful conditions at the range edge. Despite the counteracting effect of the shorter growth season, the higher flight muscle ratios at the expansion front indicated a strong selection for dispersal ability during range expansion. The current study suggests that models need to incorporate the interplay of stressful conditions and evolutionary processes at the expansion front to arrive at robust predictions of future species distributions under global warming. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 556–568.     

Temperature-sensitive paramagnetic liposomes for image-guided drug delivery: Mn versus [Gd(HPDO3A)(H2O)]

Temperature-sensitive liposomes (TSLs) loaded with doxorubicin (Dox), and Magnetic Resonance Imaging contrast agents (CAs), either manganese (Mn^2 +) or [Gd(HPDO3A)(H₂O)], provide the advantage of drug delivery under MR image guidance. Encapsulated MRI CAs have low longitudinal relaxivity (r₁) due to limited transmembrane water exchange. Upon triggered release at hyperthermic temperature, the r₁ will increase and hence, provides a means to monitor drug distribution in situ. Here, the effects of encapsulated CAs on the phospholipid bilayer and the resulting change in r₁ were investigated using MR titration studies and ¹H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles. Our results show that Mn^2 + interacted with the phospholipid bilayer of TSLs and consequently, reduced doxorubicin retention capability at 37 °C within the interior of the liposomes over time. Despite that, Mn^2 +-phospholipid interaction resulted in higher r₁ increase, from 5.1 ± 1.3 mM^− 1 s^− 1 before heating to 32.2 ± 3 mM^− 1 s^− 1 after heating at 60 MHz and 37 °C as compared to TSL(Gd,Dox) where the longitudinal relaxivities before and after heating were 1.2 ± 0.3 mM^− 1 s^− 1 and 4.4 ± 0.3 mM^− 1 s^− 1, respectively. Upon heating, Dox was released from TSL(Mn,Dox) and complexation of Mn^2 + to Dox resulted in a similar Mn^2 + release profile. From 25 to 38 °C, r₁ of [Gd(HPDO3A)(H₂O)] gradually increased due to increase transmembrane water exchange, while no Dox release was observed. From 38 °C, the release of [Gd(HPDO3A)(H₂O)] and Dox was irreversible and the release profiles coincided. By understanding the non-covalent interactions between the MRI CAs and phospholipid bilayer, the properties of the paramagnetic TSLs can be tailored for MR guided drug delivery.     

Optimizing I/O forwarding techniques for extreme-scale event tracing

Programming development tools are a vital component for understanding the behavior of parallel applications. Event tracing is a principal ingredient to these tools, but new and serious challenges place event tracing at risk on extreme-scale machines. As the quantity of captured events increases with concurrency, the additional data can overload the parallel file system and perturb the application being observed. In this work we present a solution for event tracing on extreme-scale machines. We enhance an I/O forwarding software layer to aggregate and reorganize log data prior to writing to the storage system, significantly reducing the burden on the underlying file system. Furthermore, we introduce a sophisticated write buffering capability to limit the impact. To validate the approach, we employ the Vampir tracing toolset using these new capabilities. Our results demonstrate that the approach increases the maximum traced application size by a factor of 5× to more than 200,000 processes.     

Glu-333 of Nicastrin Directly Participates in ��-Secretase Activity

γ-Secretase is a proteolytic membrane complex that processes a variety of substrates including the amyloid precursor protein and the Notch receptor. Earlier we showed that one of the components of this complex, nicastrin (NCT), functions as a receptor for γ-secretase substrates. A recent report challenged this, arguing instead that the Glu-333 residue of NCT predicted to participate in substrate recognition only participates in γ-secretase complex maturation and not in activity per se. Here, we present evidence that Glu-333 directly participates in γ-secretase activity. By normalizing to the active pool of γ-secretase with two separate methods, we establish that γ-secretase complexes containing NCT-E333A are indeed deficient in intrinsic activity. We also demonstrate that the NCT-E333A mutant is deficient in its binding to substrates. Moreover, we find that the cleavage of substrates by γ-secretase activity requires a free N-terminal amine but no minimal length of the extracellular N-terminal stub. Taken together, these studies provide further evidence supporting the role of NCT in substrate recognition. Finally, because γ-secretase cleaves itself during its maturation and because NCT-E333A also shows defects in γ-secretase complex maturation, we present a model whereby Glu-333 can serve a dual role via similar mechanisms in the recruitment of both Type 1 membrane proteins for activity and the presenilin intracellular loop during complex maturation.The brains of Alzheimer disease patients are characterized by dense neuritic plaques that consist of the insoluble β-amyloid peptide (Aβ)² and neurons containing neurofibrillary tangles of the Tau protein (1, 2). The Aβ peptide is produced via the sequential proteolysis of APP by β- and γ-secretase (3). γ-secretase is a multisubunit complex consisting of at least four proteins: presenilin (PS), NCT, APH-1, and PEN-2, all of which are necessary and sufficient for activity (4–9). The formation of the γ-secretase complex is tightly controlled, with an ordered assembly of subunits coupled to spatial restriction (10). It is believed that the last step of the complicated γ-secretase maturation and activation process involves in cis endoproteolysis of the PS holoprotein (11–13). It is this form of γ-secretase with PS in its N- and C-terminal fragments (NTF and CTF, respectively) that represents the fully mature, proteolytically active enzyme.γ-Secretase is a unique protease that cleaves within the lipid bilayer a large number of Type 1 single transmembrane-spanning proteins that vary widely in their sequence and size (14–16). In a previous report, we demonstrated that NCT functions as a substrate receptor for γ-secretase (4). In that report, we showed that NCT recruits substrates that have had their large extracellular domains first removed by an upstream protease in a process termed “ectodomain shedding.” This process generates a new, short extracellular stub with a free N terminus, which is required for proteolysis by γ-secretase. We also established that Glu-333 of NCT participates in activity within the larger context of the DYIGS and peptidase-like (DAP) domain, which shares distant homology to amino- and carboxypeptidases. A recent study by Chávez-Gutiérrez et al. (17) confirmed that mutations at the equivalent rodent residue impair γ-secretase. However, the authors attributed the reduction in activity to a role for Glu-333 in γ-secretase maturation but not directly in activity per se. Although a role for NCT and Glu-333 in γ-secretase assembly and maturation is consistent with our early work (4, 18, 19), the authors'' conclusion that mature γ-secretase complexes containing the Glu-333 mutant NCT are fully active presents a challenge to the model that NCT is a receptor for γ-secretase substrates in mature, active enzyme. Although PS-NTF or -CTF alone is an adequate measure of active γ-secretase complexes, Chávez-Gutiérrez et al. (17) measured specific activity by normalizing γ-secretase products to the sum of PS1-CTF and PEN-2 presumably due to the levels of PS-NTF/CTF by themselves being at the detection limit of Western blotting with electrochemiluminescence (ECL). Such an approach has caveats, as normalizing to the sum of PS1 and PEN-2 does not represent a measurement of the intrinsic activity per single, active enzyme; rather, this mode of normalization instead skews the data to minimize the effects of the mutations, especially when compounded with the unreliability of ECL measurement at the detection limit of Western blotting. Indeed, normalizing to the amount of mature, active γ-secretase in a rigorous, quantitative manner would be necessary to accurately compare the intrinsic activities of wild-type and mutant enzymes.In this study we used two γ-secretase reconstitution methods, including one that bypasses endoproteolysis and two separate normalization approaches to demonstrate that γ-secretase complexes containing NCT-E333A are indeed intrinsically less active than wild-type NCT. We show that this mutant is deficient in its ability to directly bind to γ-secretase substrates. Moreover, we confirm our observations with a second γ-secretase substrate, C83, which is itself the physiological product of α-secretase cleavage of APP. We also examine a series of substrate truncation mutants and find that γ-secretase can cleave substrates that lack the entire extracellular domain, provided that such substrates also contain a free N-terminal amine. Taken together, we conclude that Glu-333 participates directly in activity after γ-secretase complex maturation. Finally, we put forth a model wherein the dual role of Glu-333 in γ-secretase maturation and substrate recognition could be explained in the context of NCT being a substrate receptor. In this model Glu-333 partakes in the recruitment of not only the ectodomain-shed Type 1 membrane proteins but also of the intracellular loop of PS for its endoproteolysis, a hallmark event of γ-secretase maturation and activation.     

Relative importance of biotic and abiotic soil components to plant growth and insect herbivore population dynamics

Background

Plants are affected by several aspects of the soil, which have the potential to exert cascading effects on the performance of herbivorous insects. The effects of biotic and abiotic soil characteristics have however mostly been investigated in isolation, leaving their relative importance largely unexplored. Such is the case for the dune grass Ammophila, whose decline under decreasing sand accretion is argued to be caused by either biotic or abiotic soil properties.

Methodology/Principal Findings

By manipulating dune soils from three different regions, we decoupled the contributions of region, the abiotic and biotic soil component to the variation in characteristics of Ammophila arenaria seedlings and Schizaphis rufula aphid populations. Root mass fraction and total dry biomass of plants were affected by soil biota, although the latter effect was not consistent across regions. None of the measured plant properties were significantly affected by the abiotic soil component. Aphid population characteristics all differed between regions, irrespective of whether soil biota were present or absent. Hence these effects were due to differences in abiotic soil properties between regions. Although several chemical properties of the soil mixtures were measured, none of these were consistent with results for plant or aphid traits.

Conclusions/Significance

Plants were affected more strongly by soil biota than by abiotic soil properties, whereas the opposite was true for aphids. Our results thus demonstrate that the relative importance of the abiotic and biotic component of soils can differ for plants and their herbivores. The fact that not all effects of soil properties could be detected across regions moreover emphasizes the need for spatial replication in order to make sound conclusions about the generality of aboveground-belowground interactions.     

Plant-soil feedback as a mechanism of invasion by Carpobrotus edulis

Invasive plant species have been suggested to change the composition of the soil community in a way that results in a positive feedback for them and a negative feedback for the native plant community. Carpobrotus edulis, a species native to South Africa, is one of the most aggressive exotic species in Mediterranean Europe. Although several aspects of its invasion biology have been studied, the occurrence of plant-soil feedback has been scarcely investigated. We first checked for the existence of biotic resistance in soils from two invaded sites of Mediterranean Europe and one site in the native area. Secondly, we evaluated the effects of soil conditioning on the germination and plant growth of C. edulis and two key species of native dunes. Finally, we tested the effects of short- and long-term soil conditioning on the performance and reproductive effort of C. edulis. Our results show that at first there is a natural resistance to invasion by the soil biota. Later, biotic resistance in invaded soil is suppressed by the establishment of a soil community that enhances the growth of C. edulis and that negatively influences the growth and survival of the native plants. Long-term soil conditioning in the field resulted in shifts in the balance between vegetative growth and sexual reproduction. Long-term invasion was also reflected in high levels of endophyte colonization by chytrids in roots, although the physiological consequences of this colonization remain unknown. The results obtained illustrate a mechanism that explains how C. edulis breaks the initial biotic resistance of newly-invaded landscapes. Finally, this study highlights the importance of studying plant-soil interactions on different members of the plant community and temporal stages in order to fully understand invasion.     

Culturing in vitro produced blastocysts in sequential media promotes ES cell derivation

Embryonic stem (ES) cell lines are routinely derived from in vivo produced blastocysts. We investigated the efficiency of ES cells derivation from in vitro produced blastocysts either in monoculture or sequential culture. Zygotes from hybrid F1 B6D2 mice were cultured in vitro to the blastocyst stage in Potassium (K(+)) simplex optimised medium (KSOM) throughout or in KSOM and switched to COOK blastocyst medium on day 3 (KSOM-CBM). Blastocysts were explanted on a feeder layer of mitomycin C-inactivated murine embryonic fibroblasts (MEF) in TX-WES medium for ES cell derivation. Sequential KSOM-CBM resulted in improved blastocyst formation compared to KSOM monoculture. ES cells were obtained from 32.1% of explanted blastocsyts cultured in KSOM-CBM versus 18.4% in KSOM alone. ES cell lines were characterized by morphology, expression of SSEA-1, Oct-4 and alkaline phosphatase activity, and normal karyotype. These results indicate that in vitro culture systems to produce blastocysts can influence the efficiency of ES cell line derivation.     

Ultrasmall particle of iron oxide—RGD peptidomimetic conjugate: synthesis and characterisation

Ultrasmall particles of iron oxide (USPIOs) coated with 3,3′-bis(phosphonate)propionic acid were covalently coupled to a home-made Arg-Gly-Asp (RGD) peptidomimetic molecule via a short oligoethyleneglycol (OEG) spacer. The conjugation rate was measured by X-ray photoelectron spectroscopy (XPS). The particle size and magnetic characteristics were kept. Our novel conjugate targeted efficiently Jurkat cells (increase of 229% vs the control).