Effects of age and distance on the composition of mixed deciduous forest fragments in an agricultural landscape

Abstract. Forest patches in central Belgium were inventoried twice for the presence or absence of forest plant species to study the effects of age and distance on species composition. All forests in the study area were subdivided based on their land use history. To avoid effects of autocorrelated environmental characteristics on species composition, habitat homogeneity was indirectly investigated using a TWINSPAN classification of the vegetation data. Two major habitats (alluvial and non‐alluvial forests) were distinguished and analysed separately. Patterns of species composition were investigated at the landscape level using Mantel tests. Species composition similarity measures were calculated between all pairs of fragments based on the floristic data. A highly significant correlation was found between species composition similarity and inter‐patch distance. Difference in age, which we used as a measure for habitat quality, was less important in explaining species composition patterns. The effects of spatial configuration became significant when difference in age was accounted for, and a partial correlation was calculated between inter‐patch distance and species composition similarity. Different results were found for alluvial and non‐alluvial forest types. Alluvial forests were more influenced by the spatial configuration than the non‐alluvial. For the non‐alluvial forest type effects measured with the difference in age between forest fragments obscured the effects of inter‐patch distance. Based on our findings we suggest that species composition is not only internally generated, but external processes such as differential colonization caused by varying degrees of isolation may be of overriding importance.     

Reduction of lamin B receptor levels by miR-340-5p disrupts chromatin,promotes cell senescence and enhances senolysis

A major stress response influenced by microRNAs (miRNAs) is senescence, a state of indefinite growth arrest triggered by sublethal cell damage. Here, through bioinformatic analysis and experimental validation, we identified miR-340-5p as a novel miRNA that foments cellular senescence. miR-340-5p was highly abundant in diverse senescence models, and miR-340-5p overexpression in proliferating cells rendered them senescent. Among the target mRNAs, miR-340-5p prominently reduced the levels of LBR mRNA, encoding lamin B receptor (LBR). Loss of LBR by ectopic overexpression of miR-340-5p derepressed heterochromatin in lamina-associated domains, promoting the expression of DNA repetitive elements characteristic of senescence. Importantly, overexpressing miR-340-5p enhanced cellular sensitivity to senolytic compounds, while antagonization of miR-340-5p reduced senescent cell markers and engendered resistance to senolytic-induced cell death. We propose that miR-340-5p can be exploited for removing senescent cells to restore tissue homeostasis and mitigate damage by senescent cells in pathologies of human aging.     

The complex biogeographic history of a widespread tropical tree species

Many tropical forest tree species have broad geographic ranges, and fossil records indicate that population disjunctions in some species were established millions of years ago. Here we relate biogeographic history to patterns of population differentiation, mutational and demographic processes in the widespread rainforest tree Symphonia globulifera using ribosomal (ITS) and chloroplast DNA sequences and nuclear microsatellite (nSSR) loci. Fossil records document sweepstakes dispersal origins of Neotropical S. globulifera populations from Africa during the Miocene. Despite historical long-distance gene flow, nSSR differentiation across 13 populations from Costa Rica, Panama, Ecuador (east and west of Andes) and French Guiana was pronounced (F(ST)= 0.14, R(ST)= 0.39, P < 0.001) and allele-size mutations contributed significantly (R(ST) > F(ST)) to the divergences between cis- and trans-Andean populations. Both DNA sequence and nSSR data reflect contrasting demographic histories in lower Mesoamerica and Amazonia. Amazon populations show weak phylogeographic structure and deviation from drift-mutation equilibrium indicating recent population expansion. In Mesoamerica, genetic drift was strong and contributed to marked differentiation among populations. The genetic structure of S. globulifera contains fingerprints of drift-dispersal processes and phylogeographic footprints of geological uplifts and sweepstakes dispersal.     

Carbohydrate metabolism is perturbed in peroxisome-deficient hepatocytes due to mitochondrial dysfunction, AMP-activated protein kinase (AMPK) activation, and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) suppression

Hepatic peroxisomes are essential for lipid conversions that include the formation of mature conjugated bile acids, the degradation of branched chain fatty acids, and the synthesis of docosahexaenoic acid. Through unresolved mechanisms, deletion of functional peroxisomes from mouse hepatocytes (L-Pex5(-/-) mice) causes severe structural and functional abnormalities at the inner mitochondrial membrane. We now demonstrate that the peroxisomal and mitochondrial anomalies trigger energy deficits, as shown by increased AMP/ATP and decreased NAD(+)/NADH ratios. This causes suppression of gluconeogenesis and glycogen synthesis and up-regulation of glycolysis. As a consequence, L-Pex5(-/-) mice combust more carbohydrates resulting in lower body weights despite increased food intake. The perturbation of carbohydrate metabolism does not require a long term adaptation to the absence of functional peroxisomes as similar metabolic changes were also rapidly induced by acute elimination of Pex5 via adenoviral administration of Cre. Despite its marked activation, peroxisome proliferator-activated receptor α (PPARα) was not causally involved in these metabolic perturbations, because all abnormalities still manifested when peroxisomes were eliminated in a peroxisome proliferator-activated receptor α null background. Instead, AMP-activated kinase activation was responsible for the down-regulation of glycogen synthesis and induction of glycolysis. Remarkably, PGC-1α was suppressed despite AMP-activated kinase activation, a paradigm not previously reported, and they jointly contributed to impaired gluconeogenesis. In conclusion, lack of functional peroxisomes from hepatocytes results in marked disturbances of carbohydrate homeostasis, which are consistent with adaptations to an energy deficit. Because this is primarily due to impaired mitochondrial ATP production, these L-Pex5-deficient livers can also be considered as a model for secondary mitochondrial hepatopathies.     

Human probiotic bacteria attenuate Pseudomonas aeruginosa biofilm and virulence by quorum-sensing inhibition

Abstract

This work investigated chloroform extracts from culture supernatants of two human probiotic bacteria, Lactobacillus casei CRL 431 and Lactobacillus acidophilus CRL 730 for the production of virulence factors and quorum sensing (QS) interference against three Pseudomonas aeruginosa strains. Both extracts inhibited biofilm biomass (up to 50%), biofilm metabolic activity (up to 39%), the production of the enzyme elastase (up to 63%) and pyocyanin (up to 77%), and decreased QS, without presenting any antibacterial acgivity. In addition, the chloroform extracts of both strains disrupted preformed biofilms of the three strains of P. aeruginosa analyzed (up to 40%). GC-MS analysis revealed that the major compounds detected in the bioactive extracts were four diketopiperazines. This study suggests that the metabolites of L. casei and L. acidophilus could be a promising alternative to combat the pathogenicity of P. aeruginosa.     

Sitting on a Sloping Seat Does Not Reduce the Strain Sustained by the Postural Chain

The objective of this study was to explore the effect of a forward sloping seat on posture and muscular activity of the trunk and lower limbs. To this aim, twelve asymptomatic participants were tested in six conditions varying seat slope (0°, 15° forward) and height (high, medium, low). Angular position of head, trunk and pelvis was assessed with an inertial orientation system, and muscular activity of 11 superficial postural muscles located in the trunk and lower limbs was estimated using normalized EMG. Results showed that a forward sloping seat, compared to a flat seat, induced a greater activity of the soleus (p<0.01), vastus lateralis (p<0.05) and vastus medialis (p<0.05), as well a lower hip flexion (p<0.01). In contrast, no significant variation of head, trunk and pelvis angular position was observed according to seat slope. It was concluded that forward sloping seats increase the load sustained by the lower limbs, without a systematic improvement of body posture.     

Characterization of new microsatellite loci isolated from Santiria trimera (Burseraceae)

? Premise of the study: To study the genetic structure among three morphotypes of an African rainforest tree species, Santiria trimera, nuclear microsatellite markers were isolated and characterized. ? Methods and Results: Seven polymorphic loci were isolated using a pyrosequencing-based protocol and successfully amplified on three different morphotypes of S. trimera. For six of the seven loci, there is at least one private allele for one of the three morphotypes. The mean effective number of alleles is about four for each of the three morphotypes. ? Conclusions: These microsatellite markers are promising to explore the genetic delimitation among sympatric morphotypes found in Gabonese forests and to study the spatial genetic structure within each gene pool.     

Na+ -D-glucose cotransporter in the kidney of Leucoraja erinacea: molecular identification and intrarenal distribution

Studies on membrane vesicles from the kidney of Leucoraja erinacea suggested the sole presence of a sodium-D-glucose cotransporter type 1 involved in renal D-glucose reabsorption. For molecular characterization of this transport system, an mRNA library was screened with primers directed against conserved regions of human sglt1. A cDNA was cloned whose nucleotide and derived amino acid sequence revealed high homology to sodium glucose cotransporter 1 (SGLT1). Xenopus laevis oocytes injected with the respective cRNA showed sodium-dependent high-affinity uptake of D-glucose. Many positions considered functionally essential for sodium glucose cotransporter 1 (SGLT1) are also found in the skate protein. High conservation preferentially in transmembrane helices and small linking loops suggests early appearance and continued preservation of these regions. Larger loops, especially loop 13, which is associated with phlorizin binding, were more variable, as is the interaction with the specific inhibitor in various species. To study the intrarenal distribution of the transporter, a skate SGLT1-specific antibody was generated. In cryosections of skate kidney, various nephron segments could be differentiated by lectin staining. Immunoreaction with the antibody was observed in the proximal tubule segments PIa and PIIa, the early distal tubule, and the collecting tubule. Thus Leucoraja, in contrast to the mammalian kidney, employs only SGLT1 to reabsorb d-glucose in the early, as well as in the late segments of the proximal tubule and probably also in the late distal tubule (LDT). Thereby, it differs also partly from the kidney of the close relative Squalus acanthias, which uses SGLT2 in more distal proximal tubule segments but shows also expression in the later nephron parts.     

Deciphering CAPTCHAs: what a Turing test reveals about human cognition

Turning Turing's logic on its head, we used widespread letter-based Turing Tests found on the internet (CAPTCHAs) to shed light on human cognition. We examined the basis of the human ability to solve CAPTCHAs, where machines fail. We asked whether this is due to our use of slow-acting inferential processes that would not be available to machines, or whether fast-acting automatic orthographic processing in humans has superior robustness to shape variations. A masked priming lexical decision experiment revealed efficient processing of CAPTCHA words in conditions that rule out the use of slow inferential processing. This shows that the human superiority in solving CAPTCHAs builds on a high degree of invariance to location and continuous transforms, which is achieved during the very early stages of visual word recognition in skilled readers.