Molecular insight into how HIV-1 Vpr protein impairs cell growth through two genetically distinct pathways

Vpr, a small HIV auxiliary protein, hijacks the CUL4 ubiquitin ligase through DCAF1 to inactivate an unknown cellular target, leading to cell cycle arrest at the G(2) phase and cell death. Here we first sought to delineate the Vpr determinants involved in the binding to DCAF1 and to the target. On the one hand, the three α-helices of Vpr are necessary and sufficient for binding to DCAF1; on the other hand, nonlinear determinants in Vpr are required for binding to the target, as shown by using protein chimeras. We also underscore that a SRIG motif conserved in the C-terminal tail of Vpr proteins from HIV-1/SIVcpz and HIV-2/SIVsmm lineages is critical for G(2) arrest. Our results suggest that this motif may be predictive of the ability of Vpr proteins from other SIV lineages to mediate G(2) arrest. We took advantage of the characterization of a subset of G(2) arrest-defective, but DCAF1 binding-proficient mutants, to investigate whether Vpr interferes with cell viability independently of its ability to induce G(2) arrest. These mutants inhibited cell colony formation in HeLa cells and are cytotoxic in lymphocytes, unmasking a G(2) arrest-independent cytopathic effect of Vpr. Furthermore these mutants do not block cell cycle progression at the G(1) or S phases but trigger apoptosis through caspase 3. Disruption of DCAF1 binding restored efficiency of colony formation. However, DCAF1 binding per se is not sufficient to confer cytopathicity. These data support a model in which Vpr recruits DCAF1 to induce the degradation of two host proteins independently required for proper cell growth.     

DNA/NYVAC vaccine regimen induces HIV-specific CD4 and CD8 T-cell responses in intestinal mucosa

In the present study, we have investigated the anatomic distribution in blood and gut mucosal tissues of memory poxvirus-specific CD4 and CD8 T cells in subjects vaccinated with smallpox and compared it with vector (NYVAC)-specific and HIV insert-specific T-cell responses induced by an experimental DNA-C/ NYVAC-C vaccine regimen. Smallpox-specific CD4 T-cell responses were present in the blood of 52% of the subjects studied, while smallpox-specific CD8 T cells were rarely detected (12%). With one exception, smallpox-specific T cells were not measurable in gut tissues. Interestingly, NYVAC vector-specific and HIV-specific CD4 and CD8 T-cell responses were detected in almost 100% of the subjects immunized with DNA-C/NYVAC-C in blood and gut tissues. The large majority (83%) of NYVAC-specific CD4 T cells expressed α4β7 integrins and the HIV coreceptor CCR5. These results demonstrate that the experimental DNA-C/NYVAC-C HIV vaccine regimen induces the homing of potentially protective HIV-specific CD4 and CD8 T cells in the gut, the port of entry of HIV and one of the major sites for HIV spreading and the depletion of CD4 T cells.     

Isolated cell walls exhibit cation binding properties distinct from those of plant roots

Aims

The principal contributor to the cation binding properties of roots is currently considered to be the cell wall or, alternatively, the plasma membrane. The aim of this study was to highlight their respective contributions in the binding properties.

Methods

Cell walls of a dicotyledon (Solanum lycopersicum L.) and monocotyledon (Triticum aestivum L.) were isolated from roots and their binding properties were compared to those of their respective roots. Cell wall and root binding capacities were evaluated by potentiometric titrations and cation exchange capacity measurements, while their biochemical composition was analyzed by ¹³C-NMR spectroscopy.

Results

The lower binding capacity of isolated cell walls compared to roots revealed that cell plasma membranes had a higher binding site density than cell walls. The significant decrease in some NMR signals, i.e. carbonyl C, N alkyl/methoxyl C and alkyl C regions, suggested that carboxyl, amine and phosphate binding sites, borne by proteins and phospholipid plasma membranes, contribute to the binding capacity.

Conclusions

Cell walls and plasma membranes were found to be jointly involved in root binding properties and their respective contributions seemed vary between plants.     

SLK-dependent activation of ERMs controls LGN–NuMA localization and spindle orientation

Mitotic spindle orientation relies on a complex dialog between the spindle microtubules and the cell cortex, in which F-actin has been recently implicated. Here, we report that the membrane–actin linkers ezrin/radixin/moesin (ERMs) are strongly and directly activated by the Ste20-like kinase at mitotic entry in mammalian cells. Using microfabricated adhesive substrates to control the axis of cell division, we found that the activation of ERMs plays a key role in guiding the orientation of the mitotic spindle. Accordingly, impairing ERM activation in apical progenitors of the mouse embryonic neocortex severely disturbed spindle orientation in vivo. At the molecular level, ERM activation promotes the polarized association at the mitotic cortex of leucine-glycine-asparagine repeat protein (LGN) and nuclear mitotic apparatus (NuMA) protein, two essential factors for spindle orientation. We propose that activated ERMs, together with Gαi, are critical for the correct localization of LGN–NuMA force generator complexes and hence for proper spindle orientation.     

TNF and IL-1 exhibit distinct ubiquitin requirements for inducing NEMO–IKK supramolecular structures

Nuclear factor κB (NF-κB) essential modulator (NEMO), a regulatory component of the IκB kinase (IKK) complex, controls NF-κB activation through its interaction with ubiquitin chains. We show here that stimulation with interleukin-1 (IL-1) and TNF induces a rapid and transient recruitment of NEMO into punctate structures that are anchored at the cell periphery. These structures are enriched in activated IKK kinases and ubiquitinated NEMO molecules, which suggests that they serve as organizing centers for the activation of NF-κB. These NEMO-containing structures colocalize with activated TNF receptors but not with activated IL-1 receptors. We investigated the involvement of nondegradative ubiquitination in the formation of these structures, using cells deficient in K63 ubiquitin chains or linear ubiquitin chain assembly complex (LUBAC)-mediated linear ubiquitination. Our results indicate that, unlike TNF, IL-1 requires K63-linked and linear ubiquitin chains to recruit NEMO into higher-order complexes. Thus, different mechanisms are involved in the recruitment of NEMO into supramolecular complexes, which appear to be essential for NF-κB activation.     

Effects of mute swans on wetlands: a synthesis

The increases in mute swan (Cygnus olor Gmelin) population size have caused concern among stakeholders, who sometimes consider it as a pest species. Here, we aim to review existing studies on the ecological effects that mute swans have on wetlands. Claim that mute swans threaten other waterbirds were partly supported: mute swans sometimes behave territorially towards conspecifics and other waterbird species, but this does not systematically occur. A second common claim, that mute swans damage aquatic plant beds, was upheld in that the species did indeed affect aquatic plant communities in several studies. However, grazing by mute swans does not systematically have negative effects on aquatic plants. Habitat patch size, distance between habitat patches, resource availability and water velocity affect habitat selection process by mute swans, with varying effects depending on season and mute swan breeding status. Scientific knowledge does not support the idea that mute swan population increase can be considered as a biological invasion in Europe. Conversely, there is a genuine risk of biological invasion in North America. In light of the literature review, we discuss the relevance of mute swan population management in Europe and in North America, and propose future research avenues.     

Linkage Disequilibrium with Linkage Analysis of Multiline Crosses Reveals Different Multiallelic QTL for Hybrid Performance in the Flint and Dent Heterotic Groups of Maize

Multiparental designs combined with dense genotyping of parents have been proposed as a way to increase the diversity and resolution of quantitative trait loci (QTL) mapping studies, using methods combining linkage disequilibrium information with linkage analysis (LDLA). Two new nested association mapping designs adapted to European conditions were derived from the complementary dent and flint heterotic groups of maize (Zea mays L.). Ten biparental dent families (N = 841) and 11 biparental flint families (N = 811) were genotyped with 56,110 single nucleotide polymorphism markers and evaluated as test crosses with the central line of the reciprocal design for biomass yield, plant height, and precocity. Alleles at candidate QTL were defined as (i) parental alleles, (ii) haplotypic identity by descent, and (iii) single-marker groupings. Between five and 16 QTL were detected depending on the model, trait, and genetic group considered. In the flint design, a major QTL (R² = 27%) with pleiotropic effects was detected on chromosome 10, whereas other QTL displayed milder effects (R² < 10%). On average, the LDLA models detected more QTL but generally explained lower percentages of variance, consistent with the fact that most QTL display complex allelic series. Only 15% of the QTL were common to the two designs. A joint analysis of the two designs detected between 15 and 21 QTL for the five traits. Of these, between 27 for silking date and 41% for tasseling date were significant in both groups. Favorable allelic effects detected in both groups open perspectives for improving biomass production.     

How much are stranding records affected by variation in reporting rates? A case study of small delphinids in the Bay of Biscay

Marine vertebrate strandings offer an opportunistic sampling scheme that can provide abundant data over long periods. Because the stranding process involves biological, physical and sociological parameters, confounding complicates the interpretation of results. The statistical analysis of these data relies on generalized linear or additive models in order to infer long-term trends, but does not easily account for drift or variation in reporting rates. Here, we capitalized on county-level (administrative) variation following the passing of a law for compulsory reporting of stranded marine mammals in France to investigate how variation in reporting rates may affect the observed trend in stranded small delphinids in the Bay of Biscay. Using a time-series spanning more than 30 years across eight administrative counties, we built variance partitioning models for the analysis of count data. We discussed the choice of an appropriate likelihood to conclude the Negative Binomial useful and interpretable in the context of small delphinid strandings. We expanded the model with a recent methodology to detect structural breaks in the time series, focusing on overdispersion. We performed statistical robustness checks with respect to variations in reporting rates and discuss their causal interpretation in the context of observational data. Stranding frequencies increased on average 7-fold over 30 years. We conclude that reporting rates to the French stranding network have been stable since the early 1990s, and the average 3-fold increase in stranded small delphinids observed in the Bay of Biscay since 1990 is due to other factors, including bycatch. Codes and data are available to replicate the analysis to other national stranding networks.