Pestivirus virion morphogenesis in the absence of uncleaved nonstructural protein 2-3

The family Flaviviridae contains three genera of positive-strand RNA viruses, namely, Flavivirus, Hepacivirus (e.g., hepatitis C virus [HCV]), and Pestivirus. Pestiviruses, like bovine viral diarrhea virus (BVDV), bear a striking degree of similarity to HCV concerning polyprotein organization, processing, and function. Along this line, in both systems, release of nonstructural protein 3 (NS3) is essential for viral RNA replication. However, both viruses differ significantly with respect to processing efficiency at the NS2/3 cleavage site and abundance as well as functional relevance of uncleaved NS2-3. In BVDV-infected cells, significant amounts of NS2-3 accumulate at late time points postinfection and play an essential but ill-defined role in the production of infectious virions. In contrast, complete cleavage of the HCV NS2-3 counterpart has been reported, and unprocessed NS2-3 is not required throughout the life cycle of HCV, at least in cell culture. Here we describe the selection and characterization of the first pestiviral genome with the capability to complete productive infection in the absence of uncleaved NS2-3. Despite the insertion of a ubiquitin gene or an internal ribosomal entry site between the NS2 and NS3 coding sequences, the selected chimeric BVDV-1 genomes gave rise to infectious virus progeny. In this context, a mutation in the N-terminal third of NS2 was identified as a critical determinant for efficient production of infectious virions in the absence of uncleaved NS2-3. These findings challenge a previously accepted dogma for pestivirus replication and provide new implications for virion morphogenesis of pestiviruses and HCV.     

Extensive regulation of NAGNAG alternative splicing: new tricks for the spliceosome?

A recent study using massive parallel sequencing demonstrates unequivocally that alternative tandem acceptor splicing is tissue-specifically regulated.     

The axonal guidance receptor neogenin promotes acute inflammation

Neuronal guidance proteins (NGP) were originally described in the context of axonal growth and migration. Yet recent work has demonstrated that NGPs also serve as guidance cues for immune competent cells. A crucial target receptor for NGPs during embryonic development is the neogenin receptor, however its role during acute inflammation is unknown. We report here that neogenin is abundantly expressed outside the nervous system and that animals with endogenous repression of neogenin (Neo1(-/-)) demonstrate attenuated changes of acute inflammation. Studies using functional inhibition of neogenin resulted in a significant attenuation of inflammatory peritonitis. In studies employing bone marrow chimeric animals we found the hematopoietic presence of Neo1(-/-) to be responsible for the attenuated inflammatory response. Taken together our studies suggest that the guidance receptor neogenin holds crucial importance for the propagation of an acute inflammatory response and further define mechanisms shared between the nervous and the immune system.     

Ecosystem engineering by seagrasses interacts with grazing to shape an intertidal landscape

Self-facilitation through ecosystem engineering (i.e., organism modification of the abiotic environment) and consumer-resource interactions are both major determinants of spatial patchiness in ecosystems. However, interactive effects of these two mechanisms on spatial complexity have not been extensively studied. We investigated the mechanisms underlying a spatial mosaic of low-tide exposed hummocks and waterlogged hollows on an intertidal mudflat in the Wadden Sea dominated by the seagrass Zostera noltii. A combination of field measurements, an experiment and a spatially explicit model indicated that the mosaic resulted from localized sediment accretion by seagrass followed by selective waterfowl grazing. Hollows were bare in winter, but were rapidly colonized by seagrass during the growth season. Colonized hollows were heavily grazed by brent geese and widgeon in autumn, converting these patches to a bare state again and disrupting sediment accretion by seagrass. In contrast, hummocks were covered by seagrass throughout the year and were rarely grazed, most likely because the waterfowl were not able to employ their preferred but water requiring feeding strategy ('dabbling') here. Our study exemplifies that interactions between ecosystem engineering by a foundation species (seagrass) and consumption (waterfowl grazing) can increase spatial complexity at the landscape level.     

A screen for enhancers of clearance identifies huntingtin as a heat shock protein 90 (Hsp90) client protein

Mechanisms to reduce the cellular levels of mutant huntingtin (mHtt) provide promising strategies for treating Huntington disease (HD). To identify compounds enhancing the degradation of mHtt, we performed a high throughput screen using a hippocampal HN10 cell line expressing a 573-amino acid mHtt fragment. Several hit structures were identified as heat shock protein 90 (Hsp90) inhibitors. Cell treatment with these compounds reduced levels of mHtt without overt toxic effects as measured by time-resolved Förster resonance energy transfer assays and Western blots. To characterize the mechanism of mHtt degradation, we used the potent and selective Hsp90 inhibitor NVP-AUY922. In HdhQ150 embryonic stem (ES) cells and in ES cell-derived neurons, NVP-AUY922 treatment substantially reduced soluble full-length mHtt levels. In HN10 cells, Hsp90 inhibition by NVP-AUY922 enhanced mHtt clearance in the absence of any detectable Hsp70 induction. Furthermore, inhibition of protein synthesis with cycloheximide or overexpression of dominant negative heat shock factor 1 (Hsf1) in HdhQ150 ES cells attenuated Hsp70 induction but did not affect NVP-AUY922-mediated mHtt clearance. Together, these data provided evidence that direct inhibition of Hsp90 chaperone function was crucial for mHtt degradation rather than heat shock response induction and Hsp70 up-regulation. Co-immunoprecipitation experiments revealed a physical interaction of mutant and wild-type Htt with the Hsp90 chaperone. Hsp90 inhibition disrupted the interaction and induced clearance of Htt through the ubiquitin-proteasome system. Our data suggest that Htt is an Hsp90 client protein and that Hsp90 inhibition may provide a means to reduce mHtt in HD.     

Association of Varroa destructor females in multiply infested cells of the honeybee Apis mellifera

The genetic diversity of Varroa destructor (Anderson &Trueman)is limited outside its natural range due to population bottlenecks and its propensity to inbreed.In light of the arms race between V.destructor and its honeybee (Apis mellifera L.)host, any mechanism enhancing population admixture of the mite may be favored.One way that admixture can occur is when two genetically dissimilar mites coinvade a brood cell, with the progeny of the foundresses admixing.We determined the relatedness of 393 pairs of V.destructor foundresses,each pair collected from a single bee brood cell (n =five colonies).We used six microsatellites to identify the genotypes of mites coinvading a cell and calculated the frequency of pairs with different or the same genotypes.We found no deviation from random coinvasion,but the frequency of cells infested by mites with different genotypes was high.This rate of recombination,coupled with a high transmission rate of mites,homogenized the allelic pool of mites within the apiary.     

Dendritic cell actin dynamics control contact duration and priming efficiency at the immunological synapse

Dendritic cells (DCs) are crucial for the priming of naive T cells and the initiation of adaptive immunity. Priming is initiated at a heterologous cell–cell contact, the immunological synapse (IS). While it is established that F-actin dynamics regulates signaling at the T cell side of the contact, little is known about the cytoskeletal contribution on the DC side. Here, we show that the DC actin cytoskeleton is decisive for the formation of a multifocal synaptic structure, which correlates with T cell priming efficiency. DC actin at the IS appears in transient foci that are dynamized by the WAVE regulatory complex (WRC). The absence of the WRC in DCs leads to stabilized contacts with T cells, caused by an increase in ICAM1-integrin–mediated cell–cell adhesion. This results in lower numbers of activated and proliferating T cells, demonstrating an important role for DC actin in the regulation of immune synapse functionality.     

Reduced Oxygen Uptake Efficiency Slope in Patients with Cardiac Sarcoidosis

Background

The non-invasive diagnosis of cardiac sarcoidosis (CS) is difficult. Cardiovascular magnetic resonance (CMR) has become a very valuable diagnostic tool in patients with suspected CS, but usually a combination of different tests is used. Oxygen uptake efficiency slope (OUES) is a parameter of cardiopulmonary exercise testing (CPET), which is used as an indicator for cardiovascular impairment. We investigated the predictive value of OUES for the diagnosis of myocardial involvement in sarcoid patients.

Methods

Retrospectively 37 consecutive patients (44.9±13.8 years) with histologically confirmed sarcoidosis and clinical suspicion of heart involvement underwent noninvasive diagnostic testing including CMR. CS was diagnosed according to the guidelines from the Japanese Society of Sarcoidosis and other Granulomatous Disorders with additional consideration of CMR findings. Furthermore, CPET with calculation of predicted OUES according to equations by Hollenberg et al. was carried out.

Results

Patients with CS (11/37; 30%) had a worse cardiovascular response to exercise. OUES was significantly lower in CS-group compared to non-CS-group (59.3±19.1 vs 88.0±15.4%pred., p<0.0001). ROC curve method identified 70%pred. as the OUES cut-off point, which maximized sensitivity and specificity for detection of CS (96% sensitivity, 82% specificity, 89% overall accuracy). OUES <70%pred. was the single best predictor of CS (Odds ratio: 100.43, 95% CI: 1.99 to 5064, p<0.001) even in multivariate analyses.

Conclusion

OUES assessed in CPET may be helpful in identifying patient with cardiac involvement of sarcoidosis. Patient selection for CMR may be assisted by CPET findings in patients with sarcoidosis.     

Nanoscale segregation of actin nucleation and elongation factors determines dendritic spine protrusion

Actin dynamics drive morphological remodeling of neuronal dendritic spines and changes in synaptic transmission. Yet, the spatiotemporal coordination of actin regulators in spines is unknown. Using single protein tracking and super‐resolution imaging, we revealed the nanoscale organization and dynamics of branched F‐actin regulators in spines. Branched F‐actin nucleation occurs at the PSD vicinity, while elongation occurs at the tip of finger‐like protrusions. This spatial segregation differs from lamellipodia where both branched F‐actin nucleation and elongation occur at protrusion tips. The PSD is a persistent confinement zone for IRSp53 and the WAVE complex, an activator of the Arp2/3 complex. In contrast, filament elongators like VASP and formin‐like protein‐2 move outwards from the PSD with protrusion tips. Accordingly, Arp2/3 complexes associated with F‐actin are immobile and surround the PSD. Arp2/3 and Rac1 GTPase converge to the PSD, respectively, by cytosolic and free‐diffusion on the membrane. Enhanced Rac1 activation and Shank3 over‐expression, both associated with spine enlargement, induce delocalization of the WAVE complex from the PSD. Thus, the specific localization of branched F‐actin regulators in spines might be reorganized during spine morphological remodeling often associated with synaptic plasticity.