Adaptive Mutations in the V3 Loop of gp120 Enhance Fusogenicity of Human Immunodeficiency Virus Type 1 and Enable Use of a CCR5 Coreceptor That Lacks the Amino-Terminal Sulfated Region

To identify sites in gp120 that interact with the CCR5 coreceptor and to analyze the mechanisms of infection, we selected variants of the CCR5-dependent JRCSF molecular clone of human immunodeficiency virus type 1 (HIV-1) that adapted to replicate in HeLa-CD4 cells that express the mutant coreceptor CCR5(Y14N) or CCR5(G163R), which were previously shown to bind purified gp120-CD4 complexes only weakly. Correspondingly, these mutant CCR5s mediate infections of wild-type virus only at relatively high cell surface concentrations, demonstrating a concentration-dependent assembly requirement for infection. The plots of viral infectivity versus concentration of coreceptors had sigmoidal shapes, implying involvement of multiple coreceptors, with an estimated stoichiometry of four to six CCR5s in the active complexes. All of the adapted viruses had mutations in the V3 loops of their gp120s. The titers of recombinant HIV-1 virions with these V3 mutations were determined in previously described panels of HeLa-CD4 cell clones that express discrete amounts of CCR5(Y14N) or CCR5(G163R). The V3 loop mutations did not alter viral utilization of wild-type CCR5, but they specifically enhanced utilization of the mutant CCR5s by two distinct mechanisms. Several mutant envelope glycoproteins were highly fusogenic in syncytium assays, and these all increased the efficiency of infection of the CCR5(Y14N) or CCR5(G163R) clonal panels without enhancing virus adsorption onto the cells or viral affinity for the coreceptor. In contrast, V3 loop mutation N300Y was selected during virus replication in cells that contained only a trace of CCR5(Y14N) and this mutation increased the apparent affinity of the virus for this coreceptor, as indicated by a shift in the sigmoid-shaped infectivity curve toward lower concentrations. Surprisingly, N300Y increased viral affinity for the second extracellular loop of CCR5(Y14N) rather than for the mutated amino terminus. Indeed, the resulting virus was able to use a mutant CCR5 that lacks 16 amino acids at its amino terminus, a region previously considered essential for CCR5 coreceptor function. Our results demonstrate that the role of CCR5 in infection involves at least two steps that can be strongly and differentially altered by mutations in either CCR5 or the V3 loop of gp120: a concentration-dependent binding step that assembles a critical multivalent virus-coreceptor complex and a postassembly step that likely involves a structural rearrangement of the complex. The postassembly step can severely limit HIV-1 infections and is not an automatic consequence of virus-coreceptor binding, as was previously assumed. These results have important implications for our understanding of the mechanism of HIV-1 infection and the factors that may select for fusogenic gp120 variants during AIDS progression.     

Rapid evolution in response to increased temperature maintains population viability despite genetic erosion in a tropical ectotherm

Climate change is predicted to increase the average global air temperature by up to 4.0 °C by the end of the century. This increased temperature could have negative effects on many life history traits that are closely linked to fitness. Many species will therefore have to adapt to the warmer environment, but life history traits often have limited additive genetic variance. Here, we investigated population demographics and the evolutionary response of life history traits, as well as genetic diversity in guppies (Poecilia reticulata), in response to an experimentally increased temperature. There were fewer successful pregnancies, smaller brood sizes, and males matured earlier at a higher temperature as compared to control populations. However, there was no sign of an evolutionary response in these traits after 24 months of exposure to the increased temperature. We also found that population size, brood survivorship, sex ratio, and male length at maturity were unaffected by the increased temperature. Genetic diversity decreased rapidly in the increased temperature populations at a rate equivalent to an effective population size of only one quarter of the controls, revealing a clear signature of selection in response to increased temperature. This genetic erosion, however, could hamper the adaptive potential of the populations to other environmental changes associated with climate change.     

Genetic Perturbation of the Maize Methylome

DNA methylation can play important roles in the regulation of transposable elements and genes. A collection of mutant alleles for 11 maize (Zea mays) genes predicted to play roles in controlling DNA methylation were isolated through forward- or reverse-genetic approaches. Low-coverage whole-genome bisulfite sequencing and high-coverage sequence-capture bisulfite sequencing were applied to mutant lines to determine context- and locus-specific effects of these mutations on DNA methylation profiles. Plants containing mutant alleles for components of the RNA-directed DNA methylation pathway exhibit loss of CHH methylation at many loci as well as CG and CHG methylation at a small number of loci. Plants containing loss-of-function alleles for chromomethylase (CMT) genes exhibit strong genome-wide reductions in CHG methylation and some locus-specific loss of CHH methylation. In an attempt to identify stocks with stronger reductions in DNA methylation levels than provided by single gene mutations, we performed crosses to create double mutants for the maize CMT3 orthologs, Zmet2 and Zmet5, and for the maize DDM1 orthologs, Chr101 and Chr106. While loss-of-function alleles are viable as single gene mutants, the double mutants were not recovered, suggesting that severe perturbations of the maize methylome may have stronger deleterious phenotypic effects than in Arabidopsis thaliana.     

Contrasting primary successional trajectories of fungi and bacteria in retreating glacier soils

Early community assembly of soil microbial communities is essential for pedogenesis and development of organic legacies. We examined fungal and bacterial successions along a well‐established temperate glacier forefront chronosequence representing ~70 years of deglaciation to determine community assembly. As microbial communities may be heavily structured by establishing vegetation, we included nonvegetated soils as well as soils from underneath four plant species with differing mycorrhizal ecologies (Abies lasiocarpa, ectomycorrhizal; Luetkea pectinata, arbuscular mycorrhizal; Phyllodoce empetriformis, ericoid mycorrhizal; Saxifraga ferruginea, nonmycorrhizal). Our main objectives were to contrast fungal and bacterial successional dynamics and community assembly as well as to decouple the effects of plant establishment and time since deglaciation on microbial trajectories using high‐throughput sequencing. Our data indicate that distance from glacier terminus has large effects on biomass accumulation, community membership, and distribution for both fungi and bacteria. Surprisingly, presence of plants rather than their identity was more important in structuring bacterial communities along the chronosequence and played only a very minor role in structuring the fungal communities. Further, our analyses suggest that bacterial communities may converge during assembly supporting determinism, whereas fungal communities show no such patterns. Although fungal communities provided little evidence of convergence in community structure, many taxa were nonrandomly distributed across the glacier foreland; similar taxon‐level responses were observed in bacterial communities. Overall, our data highlight differing drivers for fungal and bacterial trajectories during early primary succession in recently deglaciated soils.     

Larvae from deep-sea methane seeps disperse in surface waters

Many species endemic to deep-sea methane seeps have broad geographical distributions, suggesting that they produce larvae with at least episodic long-distance dispersal. Cold-seep communities on both sides of the Atlantic share species or species complexes, yet larval dispersal across the Atlantic is expected to take prohibitively long at adult depths. Here, we provide direct evidence that the long-lived larvae of two cold-seep molluscs migrate hundreds of metres above the ocean floor, allowing them to take advantage of faster surface currents that may facilitate long-distance dispersal. We collected larvae of the ubiquitous seep mussel “Bathymodiolus” childressi and an associated gastropod, Bathynerita naticoidea, using remote-control plankton nets towed in the euphotic zone of the Gulf of Mexico. The timing of collections suggested that the larvae might disperse in the water column for more than a year, where they feed and grow to more than triple their original sizes. Ontogenetic vertical migration during a long larval life suggests teleplanic dispersal, a plausible explanation for the amphi-Atlantic distribution of “B.” mauritanicus and the broad western Atlantic distribution of B. naticoidea. These are the first empirical data to demonstrate a biological mechanism that might explain the genetic similarities between eastern and western Atlantic seep fauna.     

Ceftriaxone increases glutamate uptake and reduces striatal tyrosine hydroxylase loss in 6-OHDA Parkinson's model

Excess glutamatergic neurotransmission may contribute to excitotoxic loss of nigrostriatal neurons in Parkinson's disease (PD). Here, we determined if increasing glutamate uptake could reduce the extent of tyrosine hydroxylase (TH) loss in PD progression. The beta-lactam antibiotic, ceftriaxone, increases the expression of glutamate transporter 1 (GLT-1), a glutamate transporter that plays a major role in glutamate clearance in central nervous system and may attenuate adverse behavioral or neurobiological function in other neurodegenerative disease models. In association with >80 % TH loss, we observed a significant decrease in glutamate uptake in the established 6-hydroxydopamine (6-OHDA) PD model. Ceftriaxone (200 mg/kg, i.p.) increased striatal glutamate uptake with >5 consecutive days of injection in nonlesioned rats and lasted out to 14 days postinjection, a time beyond that required for 6-OHDA to produce >70 % TH loss (～9 days). When ceftriaxone was given at the time of 6-OHDA, TH loss was ～57 % compared to ～85 % in temporally matched vehicle-injected controls and amphetamine-induced rotation was reduced about 2-fold. This attenuation of TH loss was associated with increased glutamate uptake, increased GLT-1 expression, and reduced Serine 19 TH phosphorylation, a calcium-dependent target specific for nigrostriatal neurons. These results reveal that glutamate uptake can be targeted in a PD model, decrease the rate of TH loss in a calcium-dependent manner, and attenuate locomotor behavior associated with 6-OHDA lesion. Given that detection of reliable PD markers will eventually be employed in susceptible populations, our results give credence to the possibility that increasing glutamate uptake may prolong the time period before locomotor impairment occurs.     

Morbidity and Mortality of Invertebrates,Amphibians, Reptiles,and Mammals at a Major Exotic Companion Animal Wholesaler

The authors formally investigated a major international wildlife wholesaler and subsequently confiscated more than 26,400 nonhuman animals of 171 species and types. Approximately 80% of the nonhuman animals were identified as grossly sick, injured, or dead, with the remaining in suspected suboptimal condition. Almost 3,500 deceased or moribund animals (12% of stock), mostly reptiles, were being discarded on a weekly basis. Mortality during the 6-week “stock turnover” period was determined to be 72%. During a 10-day period after confiscation, mortality rates (including euthanasia for humane reasons) for the various taxa were 18% for invertebrates, 44.5% for amphibians, 41.6% for reptiles, and 5.5% for mammals. Causes of morbidity and mortality included cannibalism, crushing, dehydration, emaciation, hypothermic stress, infection, parasite infestation, starvation, overcrowding, stress/injuries, euthanasia on compassionate grounds, and undetermined causes. Contributing factors for disease and injury included poor hygiene; inadequate, unreliable, or inappropriate provision of food, water, heat, and humidity; presumed high levels of stress due to inappropriate housing leading to intraspecific aggression; absent or minimal environmental enrichment; and crowding. Risks for introduction of invasive species through escapes and/or spread of pathogens to naive populations also were identified.     

Gβ1 controls collective cell migration by regulating the protrusive activity of leader cells in the posterior lateral line primordium

Collective cell migration is critical for normal development, tissue repair and cancer metastasis. Migration of the posterior lateral line primordium (pLLP) generates the zebrafish sensory organs (neuromasts, NMs). This migration is promoted by the leader cells at the leading edge of the pLLP, which express the G protein-coupled chemokine receptor Cxcr4b and respond to the chemokine Cxcl12a. However, the mechanism by which Cxc112a/Cxcr4b signaling regulates pLLP migration remains unclear. Here we report that signal transduction by the heterotrimeric G protein subunit Gβ1 is essential for proper pLLP migration. Although both Gβ1 and Gβ4 are expressed in the pLLP and NMs, depletion of Gβ1 but not Gβ4 resulted in an arrest of pLLP migration. In embryos deficient for Gβ1, the pLLP cells migrated in an uncoordinated fashion and were unable to extend protrusions at the leading front, phenocopying those in embryos deficient for Cxcl12a or Cxcr4b. A transplantation assay showed that, like Cxcr4b, Gβ1 is required only in the leader cells of the pLLP. Analysis of F-actin dynamics in the pLLP revealed that whereas wild-type leader cells display extensive actin polymerization in the direction of pLLP migration, counterparts defective for Gβ1, Cxcr4b or Cxcl12a do not. Finally, synergy experiments revealed that Gβ1 and Cxcr4b interact genetically in regulating pLLP migration. Collectively, our data indicate that Gβ1 controls migration of the pLLP, likely by acting downstream of the Cxcl12a/Cxcr4b signaling. This study also provides compelling evidence for functional specificity among Gβ isoforms in vivo.     

Psoriatic arthritis and sacroiliitis are associated with increased vascular inflammation by 18-fluorodeoxyglucose positron emission tomography computed tomography: baseline report from the Psoriasis Atherosclerosis and Cardiometabolic Disease Initiative

Introduction

Psoriasis and psoriatic arthritis (PsA) increase cardiovascular disease (CVD) risk, but surrogate markers for CVD in these disorders are inadequate. Because the presence of sacroiliitis may portend more severe PsA, we hypothesized that sacroiliitis defined by computed tomography (CT) would be associated with increased vascular inflammation defined by 18-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT), which is an established measure of CVD.

Methods

Participants (n = 65) underwent whole-body FDG-PET/CT. Metabolic activity of the aorta was measured using the maximal standardized uptake value (SUV_max), a measure of atherosclerotic plaque activity. The primary outcome was aortic vascular inflammation. Linear regression (with β-coefficients (β) and P-values reported for PsA and sacroiliitis) was used to adjust for CVD risk factors to determine associations of PsA or sacroiliitis with vascular inflammation. Likelihood ratio testing was performed to evaluate the contribution of sacroiliitis to vascular disease estimation compared to the effects of PsA and traditional CVD risk factors.

Results

Vascular inflammation (measured as SUV_max) was greater (P < 0.001) in patients with sacroiliitis (mean ± SD = 7.33 ± 2.09) defined by CT compared to those without sacroiliitis (6.39 ± 1.49, P = 0.038). There were associations between PsA and aortic inflammation (β = 0.124, P < 0.001) and between sacroiliitis and aortic inflammation (β = 0.270, P < 0.001) after adjusting for CVD risk factors. Sacroiliitis predicted vascular inflammation beyond PsA and CVD risk factors (χ² = 124.6, P < 0.001).

Conclusions

Sacroiliitis is associated with increased vascular inflammation detected by FDG-PET/CT, suggesting that sacroiliac joint disease may identify patients at greater risk for CVD. Large, ongoing prospective studies are required to confirm these findings.

Electronic supplementary material

The online version of this article (doi:10.1186/ar4676) contains supplementary material, which is available to authorized users.