Dilute passage promotes expression of genetic and phenotypic variants of human immunodeficiency virus type 1 in cell culture.

We have studied the extent of genetic and phenotypic diversification of human immunodeficiency virus type 1 (HIV-1) upon 15 serial passages of clonal viral populations in MT-4 cell cultures. Several genetic and phenotypic modifications previously noted during evolution of HIV-1 in infected humans were also observed upon passages of the virus in cell culture. Notably, the transition from non-syncytium-inducing to syncytium-inducing phenotype (previously observed during disease progression) and fixation of amino acid substitutions at the main antigenic loop V3 of gp120 were observed in the course of replication of the virus in MT-4 cell cultures in the absence of immune selection. Interestingly, most genetic and phenotypic alterations occurred upon passage of the virus at a low multiplicity of infection (0.001 infectious particles per cell) rather than at a higher multiplicity of infection (0.1 infectious particles per cell). The degree of genetic diversification attained by HIV-1, estimated by the RNase A mismatch cleavage method and by nucleotide sequencing, is of about 0.03% of genomic sites mutated after 15 serial passages. This value is not significantly different from previous estimates for foot-and-mouth disease virus when subjected to a similar process and analysis. We conclude that several genetic and phenotypic modifications of HIV-1 previously observed in vivo occur also in the constant environment provided by a cell culture system. Dilute passage promotes in a highly significant way the expression of deviant HIV-1 genomes.     

Influence of liposome charge and composition on their interaction with human blood serum proteins

The roles of sulfhydryl and disulfide groups in the specific binding of synthetic cannabinoid CP-55,940 to the cannabinoid receptor in membrane preparations from the rat cerebral cortex have been examined. Various sulfhydryl blocking reagents including p-chloromercuribenzoic acid (p-CMB), N-ethylmaleimide (NEM), o-iodosobenzoic acid (o-ISB), and methyl methanethiosulfonate (MMTS) inhibited the specific binding of [³H]CP-55,940 to the cannabinoid receptor in a dose-dependent manner. About 80–95% inhibition was obtained at a 0.1 mM concentration of these reagents. Scatchard analysis of saturation experiments indicates that most of these sulfhydryl modifying reagents reduce both the binding affinity (K_d) and capacity (B_max). On the other hand, DL-dithiothreitol (DTT), a disulfide reducing agent, also irreversibly inhibited the specific binding of [³H]CP-55,940 to the receptor and about 50% inhibition was obtained at a 5 mM concentration. Furthermore, 5mM DTT was abelt to dissociate 50% of the bound ligand from the ligand-receptor complex. The marked inhibition of [³H]CP-55,940 binding by sulfhydryl reagents suggests that at least one free sulfhydryl group is essential to the binding of the ligand to the receptor. In addition, the inhibition of the binding by DTT implies that besides free sulfhydryl group(s), the integrity of a disulfide bridge is also important for [³H]CP-55,940 binding to the cannabinoid receptor.     

Neuronal types in the spinal dorsal gray of the turtle Chrysemys d'orbigny: a Golgi study

At thoracic and lumbar levels the spinal dorsal gray of young specimens of the turtle Chrysemys d'orbigny consists of a cell-free neuropil and an aggregation of perikarya termed here the lateral column of the dorsal horn (LCDH). Nerve cell clusters also occur in the dorsal commissure. The main neuropil area can be divided into a thin superficial layer containing some myelinated fibers (neuropil area Ib) and a compact core composed of unmyelinated axon terminals, dendritic branches, and thin glial processes (neuropil area II). A looser neuropil area is located at the horn base (neuropil area III). The so-called marginal zone of de Lange represents a fourth synaptic field termed here neuropil area Ia. The LCDH consists of neurons of different size and shape. Two peculiar nerve cell types have been recognized in the dorsal horn: giant and bitufted neurons. The former exhibits a large dendritic arbor, which after passing through neuropil areas II and Ib projects into neuropil area Ia and the adjacent white matter. Most frequently Golgi-stained giant neurons have perikarya and dendritic domains on the same side (ipsilateral giant neurons). There are also heterolateral giant neurons whose dendritic branches invade the opposite horn. Bitufted neurons are characterized by the presence of two main dendritic shafts connecting neuropil area II of both dorsal horns. At neuropil levels the major dendritic branches ramify profusely giving rise to short tortuous terminal processes. Perikarya of bitufted neurons occur in the dorsal commissure. The LCDH also contains many small and medium-sized neurons. These are oriented in two main directions: parallel or radial with respect to the dorsal horn surface. The population of horizontally oriented neurons comprises two subtypes termed here alpha and beta. Radially oriented neurons are pleomorphic, defying precise, unequivocal classification.     

Human-modified landscapes driving the global primate extinction crisis

The world's primates have been severely impacted in diverse and profound ways by anthropogenic pressures. Here, we evaluate the impact of various infrastructures and human-modified landscapes on spatial patterns of primate species richness, at both global and regional scales. We overlaid the International Union for the Conservation of Nature (IUCN) range maps of 520 primate species and applied a global 100 km² grid. We used structural equation modeling and simultaneous autoregressive models to evaluate direct and indirect effects of six human-altered landscapes variables (i.e., human footprint [HFP], croplands [CROP], road density [ROAD], pasture lands [PAST], protected areas [PAs], and Indigenous Peoples' lands [IPLs]) on global primate species richness, threatened and non-threatened species, as well as on species with decreasing and non-decreasing populations. Two-thirds of all primate species are classified as threatened (i.e., Critically Endangered, Endangered, and Vulnerable), with ~86% experiencing population declines, and ~84% impacted by domestic or international trade. We found that the expansion of PAST, HFP, CROP, and road infrastructure had the most direct negative effects on primate richness. In contrast, forested habitat within IPLs and PAs was positively associated in safeguarding primate species diversity globally, with an even stronger effect at the regional level. Our results show that IPLs and PAs play a critical role in primate species conservation, helping to prevent their extinction; in contrast, HFP growth and expansion has a dramatically negative effect on primate species worldwide. Our findings support predictions that the continued negative impact of anthropogenic pressures on natural habitats may lead to a significant decline in global primate species richness, and likely, species extirpations. We advocate for stronger national and international policy frameworks promoting alternative/sustainable livelihoods and reducing persistent anthropogenic pressures to help mitigate the extinction risk of the world's primate species.     

Evidence for the Predator Attraction Hypothesis in an amphibian predator–prey system

Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the “intended” recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues.     

Asymmetric distribution and down-regulation of the muscarinic acetylcholine receptor in rat cerebral cortex

The distribution and down-regulation of the muscarinic acetylcholine receptor (mAChR) were studied in dissociated cells from right (RCC) and left (LCC) cerebral cortex. For this purpose [³H]quinuclidinyl benzilate (QNB) and [³H]pirenzepine (Pz), two muscarinic antagonists, were used. The mAChR binding sites detected with [³H]QNB were asymmetrically distributed between the two hemispheres, the majority being found in the RCC. Asymmetry was also evident in the distribution of the mAChR subtypes (M₁ and M₂) detected with [³H]Pz. Under basal conditions the RCC had roughly 50% more M₁ subtype than the LCC. The pharmacological and kinetic parameters were similar for both antagonists in RCC and LCC, indicating that the observed lateralization was due to a different density of the receptor rather than to different kinetics of binding of the two radioligands. After sustained stimulation with the agonist carbamoylcholine, the receptor sites detected with [³H]Pz, i.e. the M₁ subtype of mAChR, decreased at a higher rate in the RCC (44%) than in the LCC (25% of controls), demonstrating that the down-regulation process is more active in the right than in the left cortex, and thus implying that there is better coupling between the stimulated mAChR and its effector system in the former.     

Influence of plant domestication on plant-pollinator interactions: Floral attributes and floral visitor communities in wild and cultivated squash plants

Premise

Domestication of plant species results in phenotypic modifications and changes in biotic interactions. Most studies have compared antagonistic plant-herbivore interactions of domesticated plants and their wild relatives, but little attention has been given to how domestication influences plant-pollinator interactions. Floral attributes and interactions of floral visitors were compared between sister taxa of the genus Cucurbita (Cucurbitaceae), the domesticated C. moschata, C. argyrosperma ssp. argyrosperma and its wild progenitor C. argyrosperma ssp. sororia in the place of origin.

Methods

We conducted univariate and multivariate analyses to compare floral morphological traits and analyzed floral reward (nectar and pollen) quantity and quality between flowers of wild and domesticated Cucurbita taxa. Staminate and pistillate flowers of all three taxa were video recorded, and visitation and behavior of floral visitors were registered and analyzed.

Results

Most floral morphological characteristics of flowers of domesticated taxa were larger in both staminate and pistillate flowers. Staminate and pistillate flowers presented distinct correlations between floral traits and integration indices between domesticated and wild species. Additionally, pollen quantity and protein to lipid ratio were greater in domesticated species. Cucurbit pollen specialists, Eucera spp., had the highest probability of visit for all Cucurbita taxa.

Conclusions

We provide evidence that floral traits of domesticated and wild Cucurbita species experienced different selection pressures. Domesticated Cucurbita species may have more resources invested towards floral traits, thereby increasing attractiveness to pollinators and potentially plant reproductive success. Wild ancestor plant populations should be conserved in their centers of origin to preserve plant-pollinator interactions.     

Begomovirus diversity in tomato crops in Costa Rica

Begomoviruses (Geminiviridae family) are characterized by their high recombination rate and a wide range of hosts, making their control difficult. In Costa Rica, various species of bipartite begomoviruses have been reported, which are Pepper golden mosaic virus (PepGMV), Tomato yellow mottle virus (ToYMoV), Tomato leaf curl Sinaloa virus (ToLCSiV) and the monopartite begomovirus Tomato yellow leaf curl virus (TYLCV). Since the TYLCV first report in Costa Rica, neither additional knowledge has been produced on how this begomovirus has spread in the country's territory nor on the distribution of the other bipartite species. A total of 429 tomato samples collected during the years 2015–2016 were used to study these aspects. Each sample was georeferenced and analysed with various techniques such as nucleic acid hybridization, polymerase chain reaction (PCR) and sequencing for the begomoviruses previously reported in Costa Rica. It was found that the presence/absence of the different species can vary, depending on the province. TYLCV is present in the six provinces analysed in this work, with a proportion from 3.7 to 86.6 per cent. Alajuela, Cartago, and Heredia are the provinces most affected by tomato-infecting begomoviruses. Fourteen different haplotypes of TYLCV were detected, but all were identified as TYLCV-IL. The distribution of TYLCV was related to the presence of the whitefly Bemisia tabaci MED, especially in the country's main tomato production areas. This information allows the phytosanitary surveillance services to develop strategies for the integrated management of the disease and to contribute data to the genetic improvement programmes of the crop.