Long-term landscape changes in vegetation structure: fire management in the wetlands of KwaMbonambi,South Africa

In wetlands the effects of fire on vegetation dynamics are somewhat uncertain. A change detection analysis in the herbaceous wetlands of KwaMbonambi, South Africa, which were subject to frequent fires, revealed that in 1937 the study area comprised grassland (69%), herbaceous wetland (25%), indigenous swamp forest (4%) and tree plantations (1%). However, by 1970, tree plantations occupied 78% of the landscape and grasslands and herbaceous wetlands had declined to 9% and 6%, respectively, whereas indigenous swamp forest had increased to 6%. By 2009 tree plantations had been removed from the wetland areas. Despite this opportunity for herbaceous wetlands to recover their historical extent, they decreased to only 2%, mostly changing to indigenous swamp forest or to an herbaceous/fern (Stenochlaena tenuifolia)/woodland mosaic. Fire records showed suppression of fire to be an important contributing factor, particularly in wetlands that had been disturbed by tree plantations, although subsequently removed. A pilot burning experiment revealed that S. tenuifolia did not inhibit fire. It is therefore practicable to increase fire frequency to prevent the mosaic developing into forest. A conceptual model of the influence of fire regime on wetland vegetation type is presented and priorities for further research on wetlands and fire are recommended.     

Chemoenzymatic Synthesis, Inhibition Studies, and X-ray Crystallographic Analysis of the Phosphono Analog of UDP-Galp as an Inhibitor and Mechanistic Probe for UDP-Galactopyranose Mutase

UDP (uridine diphosphate) galactopyranose mutase (UGM) is involved in the cell wall biosynthesis of many pathogenic microorganisms. UGM catalyzes the reversible conversion of UDP-α-d-galactopyranose into UDP-α-d-galactofuranose, with the latter being the precursor of galactofuranose (Galf) residues in cell walls. Glycoconjugates of Galf are essential components in the cell wall of various pathogenic bacteria, including Mycobacterium tuberculosis, the causative agent of tuberculosis. The absence of Galf in humans and its bacterial requirement make UGM a potential target for developing novel antibacterial agents. In this article, we report the synthesis, inhibitory activity, and X-ray crystallographic studies of UDP-phosphono-galactopyranose, a nonhydrolyzable C-glycosidic phosphonate. This is the first report on the synthesis of a phosphonate analog of UDP-α-d-galactopyranose by a chemoenzymatic phosphoryl coupling method. The phosphonate was evaluated against three bacterial UGMs and showed only moderate inhibition. We determined the crystal structure of the phosphonate analog bound to Deinococcus radiodurans UGM at 2.6 Å resolution. The phosphonate analog is bound in a novel conformation not observed in UGM-substrate complex structures or in other enzyme-sugar nucleotide phosphonate complexes. This complex structure provides a structural basis for the observed micromolar inhibition towards UGM. Steric clashes, loss of electrostatic stabilization between an active-site arginine (Arg305) and the phosphonate analog, and a 180° flip of the hexose moiety account for the differences in the binding orientations of the isosteric phosphonate analog and the physiological substrate. This provides new insight into the ability of a sugar-nucleotide-binding enzyme to orient a substrate analog in an unexpected geometry and should be taken into consideration in designing such enzyme inhibitors.     

Thalidomide attenuates nitric oxide mediated angiogenesis by blocking migration of endothelial cells

Background  

Thalidomide is an immunomodulatory agent, which arrests angiogenesis. The mechanism of anti-angiogenic activity of thalidomide is not fully understood. As nitric oxide is involved in angiogenesis, we speculate a cross-talk between thalidomide and nitric oxide signaling pathway to define angiogenesis. The aim of present study is to understand the mechanistic aspects of thalidomide-mediated attenuation of angiogenesis induced by nitric oxide at the cellular level.     

Site-directed mutagenesis of UDP-galactopyranose mutase reveals a critical role for the active-site, conserved arginine residues

The flavoenzyme UDP-galactopyranose mutase (UGM) is a mediator of cell wall biosynthesis in many pathogenic microorganisms. UGM catalyzes a unique ring contraction reaction that results in the conversion of UDP-galactopyranose (UDP-Galp) to UDP-galactofuranose (UDP-Galf). UDP-Galf is an essential precursor to the galactofuranose residues found in many different cell wall glycoconjugates. Due to the important consequences of UGM catalysis, structural and biochemical studies are needed to elucidate the mechanism and identify the key residues involved. Here, we report the results of site-directed mutagenesis studies on the absolutely conserved residues in the putative active site cleft. By generating variants of the UGM from Klebsiella pneumoniae, we have identified two arginine residues that play critical catalytic roles (alanine substitution abolishes detectable activity). These residues also have a profound effect on the binding of a fluorescent UDP derivative that inhibits UGM, suggesting that the Arg variants are defective in their ability to bind substrate. One of the residues, Arg280, is located in the putative active site, but, surprisingly, the structural studies conducted to date suggest that Arg174 is not. Molecular dynamics simulations indicate that closed UGM conformations can be accessed in which this residue contacts the pyrophosphoryl group of the UDP-Gal substrates. These results provide strong evidence that the mobile loop, noted in all the reported crystal structures, must move in order for UGM to bind its UDP-galactose substrate.     

High-depth sequencing of over 750 genes supports linear progression of primary tumors and metastases in most patients with liver-limited metastatic colorectal cancer

BackgroundColorectal cancer with metastases limited to the liver (liver-limited mCRC) is a distinct clinical subset characterized by possible cure with surgery. We performed high-depth sequencing of over 750 cancer-associated genes and copy number profiling in matched primary, metastasis and normal tissues to characterize genomic progression in 18 patients with liver-limited mCRC.ResultsHigh depth Illumina sequencing and use of three different variant callers enable comprehensive and accurate identification of somatic variants down to 2.5% variant allele frequency. We identify a median of 11 somatic single nucleotide variants (SNVs) per tumor. Across patients, a median of 79.3% of somatic SNVs present in the primary are present in the metastasis and 81.7% of all alterations present in the metastasis are present in the primary. Private alterations are found at lower allele frequencies; a different mutational signature characterized shared and private variants, suggesting distinct mutational processes. Using B-allele frequencies of heterozygous germline SNPs and copy number profiling, we find that broad regions of allelic imbalance and focal copy number changes, respectively, are generally shared between the primary tumor and metastasis.ConclusionsOur analyses point to high genomic concordance of primary tumor and metastasis, with a thick common trunk and smaller genomic branches in general support of the linear progression model in most patients with liver-limited mCRC. More extensive studies are warranted to further characterize genomic progression in this important clinical population.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0589-1) contains supplementary material, which is available to authorized users.     

Roles of survivin isoforms in the chemopreventive actions of NSAIDS on colon cancer cells

NSAIDs downregulate survivin (an apoptosis inhibitor), increase apoptosis and reduce growth of colon polyps and cancers. Recently, anti- and pro-apoptosis isoforms of survivin were identified. The roles of these isoforms in NSAID-induced colon cancer cell death have not been examined, and is the focus of this study. The anti-apoptosis isoforms, wild-type (WT) survivin and survivin-ΔEx3, and the pro-apoptosis isoform, survivin-2b, were present in HT-29 and RKO cells. Indomethacin treatment significantly decreased WT survivin and survivin-ΔEx3 (30.5±10.4% and 20.3±6.7%, respectively) but not survivin-2b mRNA in RKO cells. In HT-29 cells, all three isoform mRNAs were slightly decreased by indomethacin treatment. Consistently, indomethacin treatment dramatically reduced WT survivin protein in RKO but not HT-29 cells. Indomethacin treatment increased apoptosis and general cell death more significantly in RKO cells (75.7±1.1% cell death at 48 h) than in HT-29 cells (25.4±3.7% cell death at 48 h). Anti-sense suppression of survivin-2b mRNA increased resistance of both RKO and HT-29 cells to indomethacin. These data support a role for survivin isoforms in colon cancer cell apoptosis, and thus in prevention of colon cancer growth by NSAIDs.     

Neural mechanisms of context-dependent processing of CO2 avoidance behavior in fruit flies

The fruit fly, Drosophila melanogaster, innately avoids even low levels of CO₂. CO₂ is part of the so-called Drosophila stress odor produced by stressed flies, but also a byproduct of fermenting fruit, a main food source, making the strong avoidance behavior somewhat surprising. Therefore, we addressed whether feeding states might influence the fly’s behavior and processing of CO₂. In a recent report, we showed that this innate behavior is differentially processed and modified according to the feeding state of the fly. Interestingly, we found that hungry flies require the function of the mushroom body, a higher brain center required for olfactory learning and memory, but thought to be dispensable for innate olfactory behaviors. In addition, we anatomically and functionally characterized a novel bilateral projection neuron connecting the CO₂ sensory input to the mushroom body. This neuron was essential for processing of CO₂ in the starved fly but not in the fed fly. In this Extra View article, we provide evidence for the potential involvement of the neuromodulator dopamine in state-dependent CO₂ avoidance behavior. Taken together, our work demonstrates that CO₂ avoidance behavior is mediated by alternative neural pathways in a context-dependent manner. Furthermore, it shows that the mushroom body is not only involved in processing of learned olfactory behavior, as previously suggested, but also in context-dependent innate olfaction.