Vif Proteins from Diverse Primate Lentiviral Lineages Use the Same Binding Site in APOBEC3G

APOBEC3G (A3G) is a cytidine deaminase that restricts human immunodeficiency virus type 1 (HIV-1) and other lentiviruses. Most of these viruses encode a Vif protein that directly binds A3G and leads to its proteasomal degradation. Both Vif proteins of HIV-1 and African green monkey simian immunodeficiency virus (SIVagm) bind residue 128 of A3G. However, this position does not control the A3G degradation by Vif variants derived from HIV-2 and SIVmac, which both originated from SIV of sooty mangabey monkeys (SIVsmm), suggesting that the A3G binding site for Vif proteins of the SIVsmm/HIV-2 lineage differs from that of HIV-1. To map the SIVsmm Vif binding site of A3G, we performed immunoprecipitations of individual A3G domains, Vif/A3G degradation assays and a detailed mutational analysis of human A3G. We show that A3G residue 129, but not the adjacent position 128, confers susceptibility to degradation by SIVsmm Vif. An artificial A3G mutant, the P129D mutant, was resistant to degradation by diverse Vifs from HIV-1, HIV-2, SIVagm, and chimpanzee SIV (SIVcpz), suggesting a conserved lentiviral Vif binding site. Gorilla A3G naturally contains a glutamine (Q) at position 129, which makes its A3G resistant to Vifs from diverse lineages. We speculate that gorilla A3G serves as a barrier against SIVcpz strains. In summary, we show that Vif proteins from distinct lineages bind to the same A3G loop, which includes positions 128 and 129. The multiple adaptations within this loop among diverse primates underscore the importance of counteracting A3G in lentiviral evolution.     

CD4+ T Cells Support Production of Simian Immunodeficiency Virus Env Antibodies That Enforce CD4-Dependent Entry and Shape Tropism In Vivo

CD4⁺ T cells rather than macrophages are the principal cells infected by human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) in vivo. Macrophage tropism has been linked to the ability to enter cells through CCR5 in conjunction with limiting CD4 levels, which are much lower on macrophages than on T cells. We recently reported that rhesus macaques (RM) experimentally depleted of CD4⁺ T cells before SIV infection exhibit extensive macrophage infection as well as high chronic viral loads and rapid progression to AIDS. Here we show that early-time-point and control Envs were strictly CD4 dependent but that, by day 42 postinfection, plasma virus of CD4⁺ T cell-depleted RM was dominated by Envs that mediate efficient infection using RM CCR5 independently of CD4. Early-time-point and control RM Envs were resistant to neutralization by SIV-positive (SIV⁺) plasma but became sensitive if preincubated with sCD4. In contrast, CD4-independent Envs were highly sensitive to SIV⁺ plasma neutralization. However, plasma from SIV-infected CD4⁺ T cell-depleted animals lacked this CD4-inducible neutralizing activity and failed to neutralize any Envs regardless of sCD4 pre-exposure status. Enhanced sensitivity of CD4-independent Envs from day 42 CD4⁺ T cell-depleted RM was also seen with monoclonal antibodies that target both known CD4-inducible and other Env epitopes. CD4 independence and neutralization sensitivity were both conferred by Env amino acid changes E84K and D470N that arose independently in multiple animals, with the latter introducing a potential N-linked glycosylation site within a predicted CD4-binding pocket of gp120. Thus, the absence of CD4 T cells results in failure to produce antibodies that neutralize CD4-independent Envs and CD4-pretriggered control Envs. In the absence of this constraint and with a relative paucity of CD4⁺ target cells, widespread macrophage infection occurs in vivo accompanied by emergence of variants carrying structural changes that enable entry independently of CD4.     

Mucosal Immunization of Lactating Female Rhesus Monkeys with a Transmitted/Founder HIV-1 Envelope Induces Strong Env-Specific IgA Antibody Responses in Breast Milk

We previously demonstrated that vaccination of lactating rhesus monkeys with a DNA prime/vector boost strategy induces strong T-cell responses but limited envelope (Env)-specific humoral responses in breast milk. To improve vaccine-elicited antibody responses in milk, hormone-induced lactating rhesus monkeys were vaccinated with a transmitted/founder (T/F) HIV Env immunogen in a prime-boost strategy modeled after the moderately protective RV144 HIV vaccine. Lactating rhesus monkeys were intramuscularly primed with either recombinant DNA (n = 4) or modified vaccinia virus Ankara (MVA) poxvirus vector (n = 4) expressing the T/F HIV Env C.1086 and then boosted twice intramuscularly with C.1086 gp120 and the adjuvant MF59. The vaccines induced Env-binding IgG and IgA as well as neutralizing and antibody-dependent cellular cytotoxicity (ADCC) responses in plasma and milk of most vaccinated animals. Importantly, plasma neutralization titers against clade C HIV variants MW965 (P = 0.03) and CAP45 (P = 0.04) were significantly higher in MVA-primed than in DNA-primed animals. The superior systemic prime-boost regimen was then compared to a mucosal-boost regimen, in which animals were boosted twice intranasally with C.1086 gp120 and the TLR 7/8 agonist R848 following the same systemic prime. While the systemic and mucosal vaccine regimens elicited comparable levels of Env-binding IgG antibodies, mucosal immunization induced significantly stronger Env-binding IgA responses in milk (P = 0.03). However, the mucosal regimen was not as potent at inducing functional IgG responses. This study shows that systemic MVA prime followed by either intranasal or systemic protein boosts can elicit strong humoral responses in breast milk and may be a useful strategy to interrupt postnatal HIV-1 transmission.     

A comparison of the strength of biodiversity effects across multiple functions

In order to predict which ecosystem functions are most at risk from biodiversity loss, meta-analyses have generalised results from biodiversity experiments over different sites and ecosystem types. In contrast, comparing the strength of biodiversity effects across a large number of ecosystem processes measured in a single experiment permits more direct comparisons. Here, we present an analysis of 418 separate measures of 38 ecosystem processes. Overall, 45 % of processes were significantly affected by plant species richness, suggesting that, while diversity affects a large number of processes not all respond to biodiversity. We therefore compared the strength of plant diversity effects between different categories of ecosystem processes, grouping processes according to the year of measurement, their biogeochemical cycle, trophic level and compartment (above- or belowground) and according to whether they were measures of biodiversity or other ecosystem processes, biotic or abiotic and static or dynamic. Overall, and for several individual processes, we found that biodiversity effects became stronger over time. Measures of the carbon cycle were also affected more strongly by plant species richness than were the measures associated with the nitrogen cycle. Further, we found greater plant species richness effects on measures of biodiversity than on other processes. The differential effects of plant diversity on the various types of ecosystem processes indicate that future research and political effort should shift from a general debate about whether biodiversity loss impairs ecosystem functions to focussing on the specific functions of interest and ways to preserve them individually or in combination.     

About Bullockia gen. nov., Trichomycterus mendozensis n. sp. and revision of the family Trichomycteridae (Pisces,Siluriformes)

A new genus of the family Trichomycteridae, Bullockia, and a new species of Trichomycterus are described. Bullockia gen. nov. is a monospecific and relict genus in the freshwaters of Chile. Trichomycterus mendozensis n. sp. is a freshwater relict from Argentina. Preliminary diagnoses of the subfamilies Pygidiinae and Nematogenyinae and the genera Trichomycterus, Hatcheria and Nematogenys are given.     

Caspase-1 deficiency in mice reduces intestinal triglyceride absorption and hepatic triglyceride secretion

Caspase-1 is known to activate the proinflammatory cytokines IL-1β and IL-18. Additionally, it can cleave other substrates, including proteins involved in metabolism. Recently, we showed that caspase-1 deficiency in mice strongly reduces high-fat diet-induced weight gain, at least partly caused by an increased energy production. Increased feces secretion by caspase-1-deficient mice suggests that lipid malabsorption possibly further reduces adipose tissue mass. In this study we investigated whether caspase-1 plays a role in triglyceride-(TG)-rich lipoprotein metabolism using caspase-1-deficient and wild-type mice. Caspase-1 deficiency reduced the postprandial TG response to an oral lipid load, whereas TG-derived fatty acid (FA) uptake by peripheral tissues was not affected, demonstrated by unaltered kinetics of [³H]TG-labeled very low-density lipoprotein (VLDL)-like emulsion particles. An oral gavage of [³H]TG-containing olive oil revealed that caspase-1 deficiency reduced TG absorption and subsequent uptake of TG-derived FA in liver, muscle, and adipose tissue. Similarly, despite an elevated hepatic TG content, caspase-1 deficiency reduced hepatic VLDL-TG production. Intestinal and hepatic gene expression analysis revealed that caspase-1 deficiency did not affect FA oxidation or FA uptake but rather reduced intracellular FA transport, thereby limiting lipid availability for the assembly and secretion of TG-rich lipoproteins. The current study reveals a novel function for caspase-1, or caspase-1-cleaved substrates, in controlling intestinal TG absorption and hepatic TG secretion.     

Responses of epidermal cell turgor pressure and photosynthetic activity of leaves of the atmospheric epiphyte Tillandsia usneoides (Bromeliaceae) after exposure to high humidity

It has been well-established that many epiphytic bromeliads of the atmospheric-type morphology, i.e., with leaf surfaces completely covered by large, overlapping, multicellular trichomes, are capable of absorbing water vapor from the atmosphere when air humidity increases. It is much less clear, however, whether this absorption of water vapor can hydrate the living cells of the leaves and, as a consequence, enhance physiological processes in such cells. The goal of this research was to determine if the absorption of atmospheric water vapor by the atmospheric epiphyte Tillandsia usneoides results in an increase in turgor pressure in leaf epidermal cells that subtend the large trichomes, and, by using chlorophyll fluorescence techniques, to determine if the absorption of atmospheric water vapor by leaves of this epiphyte results in increased photosynthetic activity. Results of measurements on living cells of attached leaves of this epiphytic bromeliad, using a pressure probe and of whole-shoot fluorescence imaging analyses clearly illustrated that the turgor pressure of leaf epidermal cells did not increase, and the photosynthetic activity of leaves did not increase, following exposure of the leaves to high humidity air. These results experimentally demonstrate, for the first time, that the absorption of water vapor following increases in atmospheric humidity in atmospheric epiphytic bromeliads is mostly likely a physical phenomenon resulting from hydration of non-living leaf structures, e.g., trichomes, and has no physiological significance for the plant's living tissues.     

Integrating multiple lines of evidence to better understand the evolutionary divergence of humpback dolphins along their entire distribution range: a new dolphin species in Australian waters?

The conservation of humpback dolphins, distributed in coastal waters of the Indo‐West Pacific and eastern Atlantic Oceans, has been hindered by a lack of understanding about the number of species in the genus (Sousa) and their population structure. To address this issue, we present a combined analysis of genetic and morphologic data collected from beach‐cast, remote‐biopsied and museum specimens from throughout the known Sousa range. We extracted genetic sequence data from 235 samples from extant populations and explored the mitochondrial control region and four nuclear introns through phylogenetic, population‐level and population aggregation frameworks. In addition, 180 cranial specimens from the same geographical regions allowed comparisons of 24 morphological characters through multivariate analyses. The genetic and morphological data showed significant and concordant patterns of geographical segregation, which are typical for the kind of demographic isolation displayed by species units, across the Sousa genus distribution range. Based on our combined genetic and morphological analyses, there is convincing evidence for at least four species within the genus (S. teuszii in the Atlantic off West Africa, S. plumbea in the central and western Indian Ocean, S. chinensis in the eastern Indian and West Pacific Oceans, and a new as‐yet‐unnamed species off northern Australia).     

Common and divergent functions of Beclin 1 and Beclin 2

In a recent paper published in Cell, He and colleagues reported the identification and functional characterization of Beclin 2, a mammal-specific homolog of the evolutionarily conserved autophagy-regulatory and oncosuppressive factor Beclin 1. In spite of a non-negligible degree of sequence identity, Beclin 1 and Beclin 2 differ from each other in multiple aspects, including their functional profile as well as the genomic organization of the respective loci.Originally identified as a BCL-2-interacting partner capable of protecting mice from viral encephalitis¹, Beclin 1 — the mammalian ortholog of yeast Atg6 — is nowadays well known as a core component of the class III phosphoinosite-3-kinase (PI3K) enzymatic complex that initiates the formation of autophagosomes in the course of macroautophagy (hereafter referred to as autophagy)². Presumably owing to the critical function of autophagy in embryonic development, mice lacking both copies of the Beclin 1-coding gene (Becn1) die early during embryogenesis. Moreover, Becn1^+/− mice suffer from a high incidence of spontaneous tumors, indicating that Beclin 1 acts as a haploinsufficient tumor suppressor³. At least in part, this reflects the central role that autophagy plays in the maintenance of intracellular homeostasis. Indeed, baseline levels of autophagy mediate the removal of various cytoplasmic entities that might favor oncogenesis, including damaged mitochondria and protein aggregates⁴. Conversely, established neoplasms often harness the cytoprotective functions of autophagy to their own benefit². The pathophysiological relevance of autophagy is not limited to cancer, but extends to a large panel of human diseases, including neurodegenerative, cardiovascular and infectious conditions⁵. Thus, during the last decade autophagy-regulatory signaling pathways have been intensively investigated.Until now, Beclin 1 was considered as the only Beclin encoded by the mammalian genome, sharing some degree of structural homology with so-called “BH3-only” proteins, pro-apoptotic members of the BCL-2 family that are involved in the activation of cell death in response to stress⁶. In a recent paper published in Cell, the research group led by Beth Levine⁷ identified a human and a mouse protein sharing 57% and 44% sequence identity with human and mouse Beclin 1, respectively, de facto unveiling the existence of an additional, mammal-specific ortholog of Atg6, Beclin 2. The mouse Beclin 2 mRNA was detected in multiple organs including the brain, skeletal muscle, placenta, thymus and uterus, as was the human protein in both fetal and adult brain tissues. These data demonstrate that the current classification of mouse and human Beclin 2-encoding genes (i.e., {"type":"entrez-nucleotide","attrs":{"text":"NG_022940","term_id":"298676453","term_text":"NG_022940"}}NG_022940 and {"type":"entrez-nucleotide","attrs":{"text":"NG_028451","term_id":"331028236","term_text":"NG_028451"}}NG_028451) as pseudogenes is incorrect.The knockdown of Beclin 2 reduced several manifestations of basal or starvation-induced autophagy in cultured mammalian cells, including the degradation of the autophagic substrate p62, the aggregation of a fluorescent form of LC3 into cytoplasmic dots and the lipidation of endogenous LC3. All such effects, which were not due to an increased autophagosomal turnover (as verified in the presence of the lysosomal inhibitor bafilomycin A1), could be rescued upon the transgene-driven expression of a non-interferable Beclin 2 variant. Thus, similar to Beclin 1, Beclin 2 regulates autophagy⁷. In fact, Beclin 2 turned out to physically interact with several (but not all) components of the class III PI3K complex organized around Beclin 1, including the catalytic subunit VPS34 as well as the regulatory factors ATG14, AMBRA1 and UVRAG, but not RUBICON (Figure 1A). Beclin 2 also appeared to share with Beclin 1 the ability to bind BCL-2, although only the latter gets dissociated from such an interaction in the course of stress-induced autophagy^7,8. As the greatest divergence between mammalian Beclins involves their N terminus, He and colleagues employed the N-terminal domain of Beclin 2 as a bait in a yeast two-hybrid screen, and identified G protein-coupled receptor (GPCR)-associated sorting protein 1 (GASP1) as a Beclin 2-specific interactor. Thus, similar to GASP1 (but not to Beclin 1), Beclin 2 was required for the agonist-induced lysosomal degradation of a subset of GPCRs including opioid receptor δ1 (DOR) and cannabinoid receptor 1 (CB1R). Importantly, such an activity, but not the capacity of Beclin 2 to regulate autophagic responses, appears to rely on the physical interaction between Beclin 2 and GASP1.Open in a separate windowFigure 1Common and divergent functions of mammalian Beclins. Specificity of the main interactors (A) and functions (B) ascribed to mammalian Beclin 1 and Beclin 2 to date. GPCR, G protein-coupled receptor; RTK, receptor tyrosine kinase.To obtain insights into the physiological functions of Beclin 2, He and colleagues attempted to generate Becn2^−/− mice, finding that these animals survived embryonic and early post-natal development at sub-Mendelian rates (approximately 4%). Not only Becn2^+/− and Becn2^−/− mouse embryonic fibroblasts, but also the brain of Becn2^+/− animals exhibited significant autophagic defects, corroborating the role of Beclin 2 in the regulation of autophagy in vivo. Moreover, these genotypes were associated with increased basal levels of multiple GPCRs, including CB1R and dopamine receptor D2 (DRD2)⁷. In line with the notion that increased CB1R signaling accrues food intake and hence favors obesity and insulin resistance, while pharmacological or genetic CB1R inhibition has opposite effects⁹, Becn2^+/− mice accumulated more weight than their wild-type littermates in response to a standard (as well as to a high-fat) diet. At odds with their Becn1^+/− counterparts, Becn2^+/− mice also exhibited impaired glucose tolerance and decreased insulin sensitivity, two effects that could be reverted by a chemical CB1R antagonist⁷. Taken together, these data demonstrate that besides regulating autophagy, Beclin 2 plays a unique role in glucose metabolism.Beclin 1 is known to regulate various processes other than autophagy, including vacuolar protein sorting and the degradation of specific growth factor receptors¹⁰. Thus, in spite of 44% - 57% sequence identity, the two mammalian Beclins described to date are relatively different from each other, exhibiting functional profiles that overlap to a limited degree (Figure 1B). Interestingly, He and colleagues have previously shown that defects in stimulus-induced autophagy (including those introduced by the Becn1^+/− genotype) are coupled to decreased endurance and altered glucose metabolism during acute exercise, as well as with an impaired capacity of training to protect mice against diet-induced glucose intolerance⁸. Part of these phenomena were shown to reflect defects in the AMP-activated protein kinase (AMPK)-dependent exposure of glucose transporters on the plasma membrane of skeletal muscle cells. It is therefore tempting to speculate that the metabolic phenotype of Becn2^+/− may in part originate from peripheral defects in glucose handling linked to autophagy. Thus, although the force driving the divergence of mammalian Beclins remains to be elucidated, it may reflect the need for an integrated regulation of central and peripheral mechanisms of metabolic homeostasis. Further studies are required to address this hypothesis.