Photoelectrochemical Behavior of Planar and Microwire‐Array Si|GaP Electrodes

Gallium phosphide exhibits a short diffusion length relative to its optical absorption length, and is thus a candidate for use in wire array geometries that allow light absorption to be decoupled from minority carrier collection. Herein is reported the photoanodic performance of heteroepitaxially grown gallium phosphide on planar and microwire‐array Si substrates. The n‐GaP|n‐Si heterojunction results in a favorable conduction band alignment for electron collection in the silicon. A conformal electrochemical contact to the outer GaP layer is produced using the ferrocenium/ferrocene (Fc⁺/Fc) redox couple in acetonitrile. Photovoltages of ～750 mV under 1 sun illumination are observed and are attributed to the barrier formed at the (Fc⁺/Fc)|n‐GaP junction. The short‐circuit current densities of the composite microwire‐arrays are similar to those observed using single‐crystal n‐GaP photoelectrodes. Spectral response measurements along with a finite‐difference‐time‐domain optical model indicate that the minority carrier diffusion length in the GaP is ～80 nm. Solid‐state current–voltage measurements show that shunting occurs through thin GaP layers that are present near the base of the microwire‐arrays. The results provide guidance for further studies of 3D multi‐junction photoelectrochemical cells.     

Automated tracking of whiskers in videos of head fixed rodents

We have developed software for fully automated tracking of vibrissae (whiskers) in high-speed videos (>500 Hz) of head-fixed, behaving rodents trimmed to a single row of whiskers. Performance was assessed against a manually curated dataset consisting of 1.32 million video frames comprising 4.5 million whisker traces. The current implementation detects whiskers with a recall of 99.998% and identifies individual whiskers with 99.997% accuracy. The average processing rate for these images was 8 Mpx/s/cpu (2.6 GHz Intel Core2, 2 GB RAM). This translates to 35 processed frames per second for a 640 px×352 px video of 4 whiskers. The speed and accuracy achieved enables quantitative behavioral studies where the analysis of millions of video frames is required. We used the software to analyze the evolving whisking strategies as mice learned a whisker-based detection task over the course of 6 days (8148 trials, 25 million frames) and measure the forces at the sensory follicle that most underlie haptic perception.     

Mgat1-dependent N-glycosylation of Membrane Components Primes Drosophila melanogaster Blood Cells for the Cellular Encapsulation Response

In nature, larvae of the fruitfly Drosophila melanogaster are commonly infected by parasitoid wasps, and so have evolved a robust immune response to counter wasp infection. In this response, fly immune cells form a multilayered capsule surrounding the wasp egg, leading to death of the parasite. Many of the molecular mechanisms underlying this encapsulation response are conserved with human immune responses. Our findings suggest that protein N-glycosylation, a common protein post-translational modification of human immune proteins, may be one such conserved mechanism. We found that membrane proteins on Drosophila immune cells are N-glycosylated in a temporally specific manner following wasp infection. Furthermore we have identified mutations in eight genes encoding enzymes of the N-glycosylation pathway that decrease fly resistance to wasp infection. More specifically, loss of protein N-glycosylation in immune cells following wasp infection led to the formation of defective capsules, which disintegrated over time and were thereby unsuccessful at preventing wasp development. Interestingly, we also found that one species of Drosophila parasitoid wasp, Leptopilina victoriae, targets protein N-glycosylation as part of its virulence mechanism, and that overexpression of an N-glycosylation enzyme could confer resistance against this wasp species to otherwise susceptible flies. Taken together, these findings demonstrate that protein N-glycosylation is a key player in Drosophila cellular encapsulation and suggest that this response may provide a novel model to study conserved roles of protein glycosylation in immunity.     

A mutation affecting the synthesis of 4-chloroindole-3-acetic acid

Traditionally, schemes depicting auxin biosynthesis in plants have been notoriously complex. They have involved up to four possible pathways by which the amino acid tryptophan might be converted to the main active auxin, indole-3-acetic acid (IAA), while another pathway was suggested to bypass tryptophan altogether. It was also postulated that different plants use different pathways, further adding to the complexity. In 2011, however, it was suggested that one of the four tryptophan-dependent pathways, via indole-3-pyruvic acid (IPyA), is the main pathway in Arabidopsis thaliana,¹ although concurrent operation of one or more other pathways has not been excluded. We recently showed that, for seeds of Pisum sativum (pea), it is possible to go one step further.² Our new evidence indicates that the IPyA pathway is the only tryptophan-dependent IAA synthesis pathway operating in pea seeds. We also demonstrated that the main auxin in developing pea seeds, 4-chloroindole-3-acetic acid (4-Cl-IAA), which accumulates to levels far exceeding those of IAA, is synthesized via a chlorinated version of the IPyA pathway.     

EM-fold: de novo atomic-detail protein structure determination from medium-resolution density maps

Electron density maps of membrane proteins or large macromolecular complexes are frequently only determined at medium resolution between 4?? and 10??, either by cryo-electron microscopy or X-ray crystallography. In these density maps, the general arrangement of secondary structure elements (SSEs) is revealed, whereas their directionality and connectivity remain elusive. We demonstrate that the topology of proteins with up to 250 amino acids can be determined from such density maps when combined with a computational protein folding protocol. Furthermore, we accurately reconstruct atomic detail in loop regions and amino acid side chains not visible in the experimental data. The EM-Fold algorithm assembles the SSEs de novo before atomic detail is added using Rosetta. In a benchmark of 27 proteins, the protocol consistently and reproducibly achieves models with root mean square deviation values <3??.     

Characterization of a hypertriglyceridemic transgenic miniature pig model expressing human apolipoprotein CIII

Hypertriglyceridemia has recently been considered to be an independent risk factor for coronary heart disease, in which apolipoprotein (Apo)CIII is one of the major contributory factors, as it is strongly correlated with plasma triglyceride levels. Although ApoCIII transgenic mice have been generated as an animal model for the study of hypertriglyceridemia, the features of lipoprotein metabolism in mice differ greatly from those in humans. Because of the great similarity between pigs and humans with respect to lipid metabolism and cardiovascular physiology, we generated transgenic miniature pigs expressing human ApoCIII by the transfection of somatic cells combined with nuclear transfer. The expression of human ApoCIII was detected in the liver and intestine of the transgenic pigs. As compared with nontransgenic controls, transgenic pigs showed significantly increased plasma triglyceride levels (83 ± 36 versus 38 ± 4 mg·dL(-1), P < 0.01) when fed a chow diet. Plasma lipoprotein profiling by FPLC in transgenic animals showed a higher peak in large-particle fractions corresponding to very low-density lipoprotein/chylomicrons when triglyceride content in the fractions was assayed. There was not much difference in cholesterol content in FPLC fractions, although a large low-density lipoprotein peak was identified in both nontransgenic and transgenic animals, resembling that found in humans. Further analysis revealed markedly delayed clearance of plasma triglyceride, accompanied by significantly reduced lipoprotein lipase activity in post-heparin plasma, in transgenic pigs as compared with nontransgenic controls. In summary, we have successfully generated a novel hypertriglyceridemic ApoCIII transgenic miniature pig model that could be of great value for studies on hyperlipidemia in relation to atherosclerotic disorders.     

Winter severity predicts the timing of host shifts in the mosquito Culex erraticus

In temperate regions, seasonal epidemics of many mosquito-borne viruses are triggered when mosquito populations shift from feeding on avian to mammalian hosts. We investigated effects of temperature on the timing of bird-to-mammal shifts using an 8 year dataset of blood-meals from a mosquito (Culex erraticus) in Alabama, USA. As expected, Cx. erraticus shifted from avian to mammalian hosts each year. The timing of the shift, however, varied considerably among years. Harshness of the preceding winter (chill accumulation) explained 93 per cent of the variation in the timing of bird-to-mammal shifts, with shifts occurring later in years following harsher winters. We hypothesize that winter temperatures drive the timing of bird-to-mammal shifts through effects on host reproductive phenology. Because mosquitoes target birds during the nesting season, and bird nesting occurs later in years following colder winters, later nesting dates result in a concomitant delay in the timing of bird-to-mammal host shifts. Global increases in winter temperatures could cause significant changes in the timing of seasonal host shifts by mosquitoes, with prolonged periods of epidemic transmission of mosquito-borne diseases.     

e-Cow: an animal model that predicts herbage intake, milk yield and live weight change in dairy cows grazing temperate pastures, with and without supplementary feeding

This animal simulation model, named e-Cow, represents a single dairy cow at grazing. The model integrates algorithms from three previously published models: a model that predicts herbage dry matter (DM) intake by grazing dairy cows, a mammary gland model that predicts potential milk yield and a body lipid model that predicts genetically driven live weight (LW) and body condition score (BCS). Both nutritional and genetic drives are accounted for in the prediction of energy intake and its partitioning. The main inputs are herbage allowance (HA; kg DM offered/cow per day), metabolisable energy and NDF concentrations in herbage and supplements, supplements offered (kg DM/cow per day), type of pasture (ryegrass or lucerne), days in milk, days pregnant, lactation number, BCS and LW at calving, breed or strain of cow and genetic merit, that is, potential yields of milk, fat and protein. Separate equations are used to predict herbage intake, depending on the cutting heights at which HA is expressed. The e-Cow model is written in Visual Basic programming language within Microsoft Excel^R. The model predicts whole-lactation performance of dairy cows on a daily basis, and the main outputs are the daily and annual DM intake, milk yield and changes in BCS and LW. In the e-Cow model, neither herbage DM intake nor milk yield or LW change are needed as inputs; instead, they are predicted by the e-Cow model. The e-Cow model was validated against experimental data for Holstein–Friesian cows with both North American (NA) and New Zealand (NZ) genetics grazing ryegrass-based pastures, with or without supplementary feeding and for three complete lactations, divided into weekly periods. The model was able to predict animal performance with satisfactory accuracy, with concordance correlation coefficients of 0.81, 0.76 and 0.62 for herbage DM intake, milk yield and LW change, respectively. Simulations performed with the model showed that it is sensitive to genotype by feeding environment interactions. The e-Cow model tended to overestimate the milk yield of NA genotype cows at low milk yields, while it underestimated the milk yield of NZ genotype cows at high milk yields. The approach used to define the potential milk yield of the cow and equations used to predict herbage DM intake make the model applicable for predictions in countries with temperate pastures.