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In hovering flight, hummingbirds reverse the angle of attack of their wings through pitch reversal in order to generate aerodynamic lift during both downstroke and upstroke. In addition, the wings may pitch during translation to further enhance lift production. It is not yet clear whether these pitching motions are caused by the wing inertia or actuated through the musculoskeletal system. Here we perform a computational analysis of the pitching dynamics by incorporating the realistic wing kinematics to determine the inertial effects. The aerodynamic effect is also included using the pressure data from a previous three-dimensional computational fluid dynamics simulation of a hovering hummingbird. The results show that like many insects, pitch reversal of the hummingbird is, to a large degree, caused by the wing inertia. However, actuation power input at the root is needed in the beginning of pronation to initiate a fast pitch reversal and also in mid-downstroke to enable a nose-up pitching motion for lift enhancement. The muscles on the wing may not necessarily be activated for pitching of the distal section. Finally, power analysis of the flapping motion shows that there is no requirement for substantial elastic energy storage or energy absorption at the shoulder joint.
A three-dimensional computational fluid dynamics simulation is performed for a ruby-throated hummingbird (Archilochus colubris) in hovering flight. Realistic wing kinematics are adopted in the numerical model by reconstructing the wing motion from high-speed imaging data of the bird. Lift history and the three-dimensional flow pattern around the wing in full stroke cycles are captured in the simulation. Significant asymmetry is observed for lift production within a stroke cycle. In particular, the downstroke generates about 2.5 times as much vertical force as the upstroke, a result that confirms the estimate based on the measurement of the circulation in a previous experimental study. Associated with lift production is the similar power imbalance between the two half strokes. Further analysis shows that in addition to the angle of attack, wing velocity and surface area, drag-based force and wing-wake interaction also contribute significantly to the lift asymmetry. Though the wing-wake interaction could be beneficial for lift enhancement, the isolated stroke simulation shows that this benefit is buried by other opposing effects, e.g. presence of downwash. The leading-edge vortex is stable during the downstroke but may shed during the upstroke. Finally, the full-body simulation result shows that the effects of wing-wing interaction and wing-body interaction are small.
© 2014 The Author(s) Published by the Royal Society. All rights reserved.
Rotaviruses (RVs) are segmented double-stranded RNA viruses that cause gastroenteritis in mammals and birds. Within the RV genus, eight species (RVA-RVH) have been proposed. Here, we report the first RVF and RVG sequences for the viral RNA polymerase (VP1)-encoding segments and compare them to those of other RV species. Phylogenetic analyses indicate that the VP1 RNA segments and proteins resolve into two major clades, with RVA, RVC, RVD and RVF in clade A, and RVB, RVG and RVH in clade B. Plus-strand RNA of clade A viruses, and not clade B viruses, contain a 3'-proximal UGUG cassette that serves as the VP1 recognition signal. VP1 structures for a representative of each RV species were predicted using homology modeling. Structural elements involved in interactions with the UGUG cassette were conserved among VP1 of clade A, suggesting a conserved mechanism of viral RNA recognition for these viruses.
Published by Elsevier Inc.
Currently, the spatial distribution of human respiratory syncytial virus (hRSV) proteins and RNAs in infected cells is still under investigation, with many unanswered questions regarding the interaction of virus-induced structures and the innate immune system. Very few studies of hRSV have used subcellular imaging as a means to explore the changes in localization of retinoic-acid-inducible gene-I (RIG-I)-like receptors or the mitochondrial antiviral signaling (MAVS) protein, in response to the infection and formation of viral structures. In this investigation, we found that both RIG-I and melanoma differentiation-associated gene 5 (MDA5) colocalized with viral genomic RNA and the nucleoprotein (N) as early as 6 h postinfection (hpi). By 12 hpi, MDA5 and MAVS were observed within large viral inclusion bodies (IB). We used a proximity ligation assay (PLA) and determined that the N protein was in close proximity to MDA5 and MAVS in IBs throughout the course of the infection. Similar results were found with the transient coexpression of N and the phosphoprotein (P). Additionally, we demonstrated that the localization of MDA5 and MAVS in IBs inhibited the expression of interferon β mRNA 27-fold following Newcastle disease virus infection. From these data, we concluded that the N likely interacts with MDA5, is in close proximity to MAVS, and localizes these molecules within IBs in order to attenuate the interferon response. To our knowledge, this is the first report of a specific function for hRSV IBs and of the hRSV N protein as a modulator of the innate immune response.
With the recent emergence of a novel pandemic strain, there is presently intense interest in understanding the molecular signatures of virulence of influenza viruses. PB1-F2 proteins from epidemiologically important influenza A virus strains were studied to determine their function and contribution to virulence. Using 27-mer peptides derived from the C-terminal sequence of PB1-F2 and chimeric viruses engineered on a common background, we demonstrated that induction of cell death through PB1-F2 is dependent upon BAK/BAX mediated cytochrome c release from mitochondria. This function was specific for the PB1-F2 protein of A/Puerto Rico/8/34 and was not seen using PB1-F2 peptides derived from past pandemic strains. However, PB1-F2 proteins from the three pandemic strains of the 20(th) century and a highly pathogenic strain of the H5N1 subtype were shown to enhance the lung inflammatory response resulting in increased pathology. Recently circulating seasonal influenza A strains were not capable of this pro-inflammatory function, having lost the PB1-F2 protein's immunostimulatory activity through truncation or mutation during adaptation in humans. These data suggest that the PB1-F2 protein contributes to the virulence of pandemic strains when the PB1 gene segment is recently derived from the avian reservoir.
The highly pathogenic (HP) influenza viruses H5 and H7 are usually nonpathogenic in mallard ducks. However, the currently circulating HP H5N1 viruses acquired a different phenotype and are able to cause mortality in mallards. To establish the molecular basis of this phenotype, we cloned the human A/Vietnam/1203/04 (H5N1) influenza virus isolate that is highly pathogenic in ferrets, mice, and mallards and found it to be a heterogeneous mixture. Large-plaque isolates were highly pathogenic to ducks, mice, and ferrets, whereas small-plaque isolates were nonpathogenic in these species. Sequence analysis of the entire genome revealed that the small-plaque and the large-plaque isolates differed in the coding of five amino acids. There were two differences in the hemagglutinin (HA) gene (K52T and A544V), one in the PA gene (T515A), and two in the PB1 gene (K207R and Y436H). We inserted the amino acid changes into the wild-type reverse genetic virus construct to assess their effects on pathogenicity in vivo. The HA gene mutations and the PB1 gene K207R mutation did not alter the HP phenotype of the large-plaque virus, whereas constructs with the PA (T515A) and PB1 (Y436H) gene mutations were nonpathogenic in orally inoculated ducks. The PB1 (Y436H) construct was not efficiently transmitted in ducks, whereas the PA (T515A) construct replicated as well as the wild-type virus did and was transmitted efficiently. These results show that the PA and PB1 genes of HP H5N1 influenza viruses are associated with lethality in ducks. The mechanisms of lethality and the perpetuation of this lethal phenotype in ducks in nature remain to be determined.
We previously demonstrated the susceptibility of pheasants to infection with influenza A viruses of 15 hemagglutinin (HA) subtypes: 13/23 viruses tested were isolated for >or=14 days, all in the presence of serum-neutralizing antibodies; one virus (H10) was shed for 45 days postinfection. Here we confirmed that 20% of pheasants shed low-pathogenic influenza viruses for prolonged periods. We aimed to determine why the antibody response did not clear the virus in the usual 3 to 10 days, because pheasants serve as a long-term source of influenza viruses in poultry markets. We found evidence of virus replication and histological changes in the large intestine, bursa of Fabricius, and cecal tonsil. The virus isolated 41 days postinfection was antigenically distinct from the parental H10 virus, with corresponding changes in the HA and neuraminidase. Ten amino acid differences were found between the parental H10 and the pheasant H10 virus; four were in potential antigenic sites of the HA molecule. Prolonged shedding of virus by pheasants results from a complex interplay between the diversity of virus variants and the host response. It is often argued that vaccination pressure is a mechanism that contributes to the generation of antigenic-drift variants in poultry. This study provided evidence that drift variants can occur naturally in pheasants after prolonged shedding of virus, thus strengthening our argument for the removal of pheasants from live-bird retail markets.
Expertise with unfamiliar objects ('greebles') recruits face-selective areas in the fusiform gyrus (FFA) and occipital lobe (OFA). Here we extend this finding to other homogeneous categories. Bird and car experts were tested with functional magnetic resonance imaging during tasks with faces, familiar objects, cars and birds. Homogeneous categories activated the FFA more than familiar objects. Moreover, the right FFA and OFA showed significant expertise effects. An independent behavioral test of expertise predicted relative activation in the right FFA for birds versus cars within each group. The results suggest that level of categorization and expertise, rather than superficial properties of objects, determine the specialization of the FFA.
NF-kappaB is a ubiquitous transcription factor involved in the signal transduction mechanisms of the immune response, acute phase reactions, and viral infections. NF-kappaB proteins are retained in the cytoplasm by association with an inhibitor, termed IkappaB. Studies on the regulation of mammalian IkappaB-alpha have revealed that two amino-terminal conserved phosphoserines are the target sites of incoming signals. We report that the corresponding amino-terminal phosphoserines of avian IkappaB-alpha are phosphorylation targets leading to inactivation of IkappaB-alpha upon stimulation. In addition, we show differential roles for these two serines. Mutation of serine 40 to alanine blocks all stimuli tested (TNF-alpha, phorbol ester, and anti-CD3 and anti-CD28), leading to NF-kappaB activation, while mutation of serine 36 to alanine attenuates only certain transduced signals (PMA, TNF-alpha). These novel findings support the hypothesis that the amino-terminal phosphoserine residues of avian IkappaB-alpha differentially mediate NF-kappaB signal transduction pathways and activation by distinct signals, thereby resulting in the activation NF-kappaB.
Copyright 1999 Academic Press.