17‐β estradiol attenuates the pro‐oxidant activity of corticotropin‐releasing hormone in macroendothelial cells

Corticotropin‐releasing hormone, which is the predominant regulator of neuroendocrine responses to stress, attenuates inflammation through stimulation of glucocorticoid release. Enhanced corticotropin‐releasing hormone expression has been detected in inflammatory cells of the vascular endothelium, where it acts as a local regulator of endothelial redox homeostasis. Estrogens have beneficial effects on endothelial integrity and function, though the mechanism underlying their antioxidative effect remains as yet largely unknown. We therefore investigated the effect of 17β‐estradiol on pro‐oxidant action of corticotropin‐releasing hormone in vitro in macroendothelial cells, and, more specifically, the role of 17β‐estradiol on corticotropin‐releasing hormone‐induced activities/release of the antioxidant enzymes namely, endothelial nitric oxide synthase, superoxide dismutase, catalase, and glutathione. We observed that 17β‐estradiol abolished the stimulatory effect of corticotropin‐releasing hormone on intracellular reactive oxygen species levels and counteracted its inhibitory effect on endothelial nitric oxide synthase activity and nitric oxide release. In addition, 17β‐estradiol significantly induced superoxide dismutase and catalase activity, an effect that was not significantly influenced by corticotropin‐releasing hormone. Finally, 17β‐estradiol significantly increased glutathione levels and the glutathione/glutathione + glutathione disulfide ratio, an action that was partially blocked by corticotropin‐releasing hormone. Our results reveal that 17β‐estradiol counterbalances corticotropin‐releasing hormone‐mediated pro‐inflammatory action and thereby maintains the physiological threshold of the endothelial cell redox environment. These observations may be of importance, considering the protective role of estrogen in the development of atherosclerosis.     

A highly resolved food web for insect seed predators in a species‐rich tropical forest

The top‐down and indirect effects of insects on plant communities depend on patterns of host use, which are often poorly documented, particularly in species‐rich tropical forests. At Barro Colorado Island, Panama, we compiled the first food web quantifying trophic interactions between the majority of co‐occurring woody plant species and their internally feeding insect seed predators. Our study is based on more than 200 000 fruits representing 478 plant species, associated with 369 insect species. Insect host‐specificity was remarkably high: only 20% of seed predator species were associated with more than one plant species, while each tree species experienced seed predation from a median of two insect species. Phylogeny, but not plant traits, explained patterns of seed predator attack. These data suggest that seed predators are unlikely to mediate indirect interactions such as apparent competition between plant species, but are consistent with their proposed contribution to maintaining plant diversity via the Janzen–Connell mechanism.     

Exposure–Response of Wheat Cultivars to TiO2 Nanoparticles in Contrasted Soils

Unprecedent usage of nanoparticles (NPs) over very large scale has raised concerns about their release into agro-environments. The effects of these emerging pollutants on staple food crops and contrasted soils are not very well documented. The main aim of present work was to investigate the exposure–response of 10 wheat cultivars to titanium dioxide (TiO₂) NPs (0–1000 mg kg^?1) in terms of early growth parameters followed by evaluation of the selected cultivar for complete growth cycle cultivated on contrasted soils in terms of various physicochemical characteristics. Among all the 10 tested wheat cultivars, only Galaxy cultivar sustained to the whole TiO₂ NPs exposure range. TiO₂ NPs exposure at 1000 mg kg^?1 adversely affected the early growth response parameters in MH, Ujala, Uqab, Shafaq and FSD wheat cultivars which clearly indicated the toxic effects induced by NPs. Pot studies were performed using Galaxy cultivar cultivated in different textured soils (loam and sandy loam). At the highest tested concentration of TiO₂ NPs, plant growth, biomass and phosphorus (P) concentration along with other tested parameters were not improved in both types of soils compared to their respective control groups. These results suggested the controlled use of NPs to avoid the NPs contamination in soil–plant ecosystems in the longer run.     

Ecological communities are vulnerable to realistic extinction sequences

Loss of species will directly change the structure and potentially the dynamics of ecological communities, which in turn may lead to additional species loss (secondary extinctions) due to direct and/or indirect effects (e.g. loss of resources or altered population dynamics). Furthermore, the vulnerability of food webs to repeated species loss is expected to be affected by food web topology, species interactions, as well as the order in which species go extinct. Species traits such as body size, abundance and connectivity might determine a species’ vulnerability to extinction and, thus, the order in which species go primarily extinct. Yet, the sequence of primary extinctions, and their effects on the vulnerability of food webs to secondary extinctions, when species abundances are allowed to respond dynamically, has only recently become the focus of attention. Here, we analyse and compare topological and dynamical robustness to secondary extinctions of model food webs, in the face of 34 extinction sequences based on species traits. Although secondary extinctions are frequent in the dynamical approach and rare in the topological approach, topological and dynamical robustness tends to be correlated for many bottom–up directed, but not for top–down directed deletion sequences. Furthermore, removing species based on traits that are strongly positively correlated to the trophic position of species (such as large body size, low abundance, high net effect) is, under the dynamical approach, found to be as destructive as removing primary producers. Such top–down oriented removal of species are often considered to correspond to realistic extinction scenarios, but earlier studies, based on topological approaches, have found such extinction sequences to have only moderate effects on the remaining community. Thus, our result suggests that the structure of ecological communities, and therefore the integrity of important ecosystem processes could be more vulnerable to realistic extinction sequences than previously believed.     

Non‐native plant species benefit from disturbance: a meta‐analysis

Disturbances, such as fire and grazing, are often claimed to facilitate plant species richness and plant invasions in particular, although empirical evidence is contradictory. We conducted a meta‐analysis to synthesize the literature on how non‐native plant species are affected by disturbances. We explored whether the observed impact of disturbance on non‐native plant communities is related to its type and frequency, to habitat type, study approach (observational or experimental), and to the temporal and spatial scales of the study. To put the results in a broader context, we also conducted a set of parallel analyses on a data set involving native plant species. The diversity and abundance of non‐native plant species were significantly higher at disturbed sites than at undisturbed sites, while the diversity and abundance of native plant species did not differ between the two types of sites. The effect of disturbance on non‐native plant species depended on the measure used to evaluate the impact (species diversity or abundance) and on disturbance type, with grazing and anthropogenic disturbances leading to higher diversity and abundance of non‐native plant species than other disturbance types examined. The impact of disturbance on non‐natives was also associated with study approach, habitat type and temporal scale, but these factors covaried with disturbance type, complicating the interpretation of the results. Overall, our results indicate that disturbance has a positive impact particularly on non‐native plant species (at least when they are already present in the community), and that the strength of this impact depends primarily on the disturbance type. Synthesis Empirical evidence of the effect of disturbances on plant species richness is contradictory. Here we use a meta‐analysis to synthesize the published literature on how different types of disturbances influence the diversity and abundance of plant species, focusing in particular on non‐native plants. Our study supports the hypothesis that disturbances generally facilitate the diversity and abundance of non‐native plant species, although the strength of this facilitation depends primarily on the disturbance type.     

The Sm protein methyltransferase PRMT5 is not required for primordial germ cell specification in mice

PRMT5 is a type II protein arginine methyltransferase with roles in stem cell biology, reprograming, cancer and neurogenesis. During embryogenesis in the mouse, it was hypothesized that PRMT5 functions with the master germline determinant BLIMP1 to promote primordial germ cell (PGC) specification. Using a Blimp1‐Cre germline conditional knockout, we discovered that Prmt5 has no major role in murine germline specification, or the first global epigenetic reprograming event involving depletion of cytosine methylation from DNA and histone H3 lysine 9 dimethylation from chromatin. Instead, we discovered that PRMT5 functions at the conclusion of PGC reprograming I to promote proliferation, survival and expression of the gonadal germline program as marked by MVH. We show that PRMT5 regulates gene expression by promoting methylation of the Sm spliceosomal proteins and significantly altering the spliced repertoire of RNAs in mammalian embryonic cells and primordial cells.     

Foreign DNA acquisition by the I-F?CRISPR–Cas system requires all components of the interference machinery

CRISPR immunity depends on acquisition of fragments of foreign DNA into CRISPR arrays. For type I-E CRISPR–Cas systems two modes of spacer acquisition, naïve and primed adaptation, were described. Naïve adaptation requires just two most conserved Cas1 and Cas2 proteins; it leads to spacer acquisition from both foreign and bacterial DNA and results in multiple spacers incapable of immune response. Primed adaptation requires all Cas proteins and a CRISPR RNA recognizing a partially matching target. It leads to selective acquisition of spacers from DNA molecules recognized by priming CRISPR RNA, with most spacers capable of protecting the host. Here, we studied spacer acquisition by a type I-F CRISPR–Cas system. We observe both naïve and primed adaptation. Both processes require not just Cas1 and Cas2, but also intact Csy complex and CRISPR RNA. Primed adaptation shows a gradient of acquisition efficiency as a function of distance from the priming site and a strand bias that is consistent with existence of single-stranded adaption intermediates. The results provide new insights into the mechanism of spacer acquisition and illustrate surprising mechanistic diversity of related CRISPR–Cas systems.