Small tropical forest trees have a greater capacity to adjust carbon metabolism to long-term drought than large canopy trees

The response of small understory trees to long-term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long-term drought is, however, also likely to expose understory trees to increased light availability driven by drought-induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (J_max, V_cmax), leaf respiration (R_leaf), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world's longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased J_max, V_cmax, R_leaf and LMA (71, 29, 32, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.     

Epigenetic regulation of autophagy by the methyltransferase EZH2 through an MTOR-dependent pathway

Macroautophagy is an evolutionarily conserved cellular process involved in the clearance of proteins and organelles. Although the autophagy regulation machinery has been widely studied, the key epigenetic control of autophagy process still remains unknown. Here we report that the methyltransferase EZH2 (enhancer of zeste 2 polycomb repressive complex 2 subunit) epigenetically represses several negative regulators of the MTOR (mechanistic target of rapamycin [serine/threonine kinase]) pathway, such as TSC2, RHOA, DEPTOR, FKBP11, RGS16 and GPI. EZH2 was recruited to these genes promoters via MTA2 (metastasis associated 1 family, member 2), a component of the nucleosome remodeling and histone deacetylase (NuRD) complex. MTA2 was identified as a new chromatin binding protein whose association with chromatin facilitated the subsequent recruitment of EZH2 to silenced targeted genes, especially TSC2. Downregulation of TSC2 (tuberous sclerosis 2) by EZH2 elicited MTOR activation, which in turn modulated subsequent MTOR pathway-related events, including inhibition of autophagy. In human colorectal carcinoma (CRC) tissues, the expression of MTA2 and EZH2 correlated negatively with expression of TSC2, which reveals a novel link among epigenetic regulation, the MTOR pathway, autophagy induction, and tumorigenesis.     

Systems genetic analysis of multivariate response to iron deficiency in mice

The aim of this study was to identify genes that influence iron regulation under varying dietary iron availability. Male and female mice from 20+ BXD recombinant inbred strains were fed iron-poor or iron-adequate diets from weaning until 4 mo of age. At death, the spleen, liver, and blood were harvested for the measurement of hemoglobin, hematocrit, total iron binding capacity, transferrin saturation, and liver, spleen and plasma iron concentration. For each measure and diet, we found large, strain-related variability. A principal-components analysis (PCA) was performed on the strain means for the seven parameters under each dietary condition for each sex, followed by quantitative trait loci (QTL) analysis on the factors. Compared with the iron-adequate diet, iron deficiency altered the factor structure of the principal components. QTL analysis, combined with PosMed (a candidate gene searching system) published gene expression data and literature citations, identified seven candidate genes, Ptprd, Mdm1, Picalm, lip1, Tcerg1, Skp2, and Frzb based on PCA factor, diet, and sex. Expression of each of these is cis-regulated, significantly correlated with the corresponding PCA factor, and previously reported to regulate iron, directly or indirectly. We propose that polymorphisms in multiple genes underlie individual differences in iron regulation, especially in response to dietary iron challenge. This research shows that iron management is a highly complex trait, influenced by multiple genes. Systems genetics analysis of iron homeostasis holds promise for developing new methods for prevention and treatment of iron deficiency anemia and related diseases.     

Characterization of the in vivo and in vitro metabolic profile of PAC-1 using liquid chromatography-mass spectrometry

In the present study, the metabolic profile of PAC-1, a potential anticancer drug, was investigated using liquid chromatography-mass spectrometric (LC/MS) techniques. Two different types of mass spectrometers--a quadrupole time-of-flight (Q-TOF) mass spectrometer and an ion trap (IT) mass spectrometer--were employed to acquire structural information on PAC-1 metabolites. A gradient liquid chromatographic system composed of 0.2% formic acid in methanol and 0.2% formic acid in water was used for metabolite separation on an Agilent TC-C(18) column. A total of 16 metabolites were detected. The corresponding product ion spectra were acquired and interpreted, and structures were proposed. Accurate mass measurement using LC-Q-TOF was used to determine the elemental composition of metabolites thereby confirming the proposed structures of these metabolites. Phase I metabolic changes were predominantly observed, including debenzylation, dihydrodiol formation, hydroxylation, and dihydroxylation. The detected phase II metabolites included PAC-1 and hydroxylated PAC-1 glucuronide conjugates. Based on metabolite analysis, several PAC-1 metabolic pathways in rat were proposed.     

Protein O-Mannosyltransferases Associate with the Translocon to Modify Translocating Polypeptide Chains

O-Mannosylation and N-glycosylation are essential protein modifications that are initiated in the endoplasmic reticulum (ER). Protein translocation across the ER membrane and N-glycosylation are highly coordinated processes that take place at the translocon-oligosaccharyltransferase (OST) complex. In analogy, it was assumed that protein O-mannosyltransferases (PMTs) also act at the translocon, however, in recent years it turned out that prolonged ER residence allows O-mannosylation of un-/misfolded proteins or slow folding intermediates by Pmt1-Pmt2 complexes. Here, we reinvestigate protein O-mannosylation in the context of protein translocation. We demonstrate the association of Pmt1-Pmt2 with the OST, the trimeric Sec61, and the tetrameric Sec63 complex in vivo by co-immunoprecipitation. The coordinated interplay between PMTs and OST in vivo is further shown by a comprehensive mass spectrometry-based analysis of N-glycosylation site occupancy in pmtΔ mutants. In addition, we established a microsomal translation/translocation/O-mannosylation system. Using the serine/threonine-rich cell wall protein Ccw5 as a model, we show that PMTs efficiently mannosylate proteins during their translocation into microsomes. This in vitro system will help to unravel mechanistic differences between co- and post-translocational O-mannosylation.     

Levels of Alpha-Toxin Correlate with Distinct Phenotypic Response Profiles of Blood Mononuclear Cells and with agr Background of Community-Associated Staphylococcus aureus Isolates

Epidemiological studies of Staphylococcus aureus have shown a relation between certain clones and the presence of specific virulence genes, but how this translates into virulence-associated functional responses is not fully elucidated. Here we addressed this issue by analyses of community-acquired S. aureus strains characterized with respect to antibiotic resistance, ST types, agr types, and virulence gene profiles. Supernatants containing exotoxins were prepared from overnight bacterial cultures, and tested in proliferation assays using human peripheral blood mononuclear cells (PBMC). The strains displayed stable phenotypic response profiles, defined by either a proliferative or cytotoxic response. Although, virtually all strains elicited superantigen-mediated proliferative responses, the strains with a cytotoxic profile induced proliferation only in cultures with the most diluted supernatants. This indicated that the superantigen-response was masked by a cytotoxic effect which was also confirmed by flow cytometry analysis. The cytotoxic supernatants contained significantly higher levels of α-toxin than did the proliferative supernatants. Addition of α-toxin to supernatants characterized as proliferative switched the response into cytotoxic profiles. In contrast, no effect of Panton Valentine Leukocidin, δ-toxin or phenol soluble modulin α-3 was noted in the proliferative assay. Furthermore, a significant association between agr type and phenotypic profile was found, where agrII and agrIII strains had predominantly a proliferative profile whereas agrI and IV strains had a predominantly cytotoxic profile. The differential response profiles associated with specific S. aureus strains with varying toxin production could possibly have an impact on disease manifestations, and as such may reflect specific pathotypes.     

城市化进程中城市热岛景观格局演变的时空特征——以厦门市为例

热岛效应作为城市化过程中产生的特有环境问题,对其形成和演变规律的研究有助于人们提出有效的应对措施。以厦门市为研究对象,利用1987—2007年等时间间隔、同时相的5景Landsat TM/ETM+遥感影像数据进行地表温度反演,在此基础上使用景观格局指数分析厦门城市热岛景观格局随城市化进程演变的趋势。结果表明:随着厦门城市化进程加深,整个热岛景观在逐渐变得更加破碎化,高等级热岛景观斑块个数、类型面积和个体面积都增大;新的高等级热岛景观斑块都出现在原有高等级斑块附近,致使高等级类型的邻近度增加而各类型之间相互接触的程度也增加;景观总体的聚合度逐渐下降,而高等级热岛景观类型的聚合度则呈上升趋势;景观水平的蔓延度总体呈下降趋势,优势度高的低等级热岛景观所占的比重下降,优势度逐渐降低;多样性指数、均匀度指数总体呈上升趋势,各热岛景观面积在各类型间的分配逐渐趋于均匀;热岛景观斑块的转化方面,在20 a间低等级斑块类型(1、2、3级)向高等级斑块类型(4、5、6级)转化的面积总体上呈增加趋势,而高等级斑块类型向低等级斑块类型转化的面积总体上呈减小趋势,且等级升高的面积明显大于同期等级降低的面积;就高等级热岛景观斑块而言,他们与3级热岛景观斑块间的相互转化最容易发生,远比高等级斑块内部各类型之间的相互转化来得容易,尤其6类和5类的转化是最为困难的热岛景观变化之一;从空间上看,各高等级热岛景观斑块都经历了数量增加、面积扩大、等级升高三个方面的变化,形成了海沧、新阳、杏林、厦门岛西北港口区和机场5个高温组团。利用景观指数分析城市热环境,可探明热岛景观随城市化演变的趋势,并为有效的热岛效应减缓措施提供直接的理论依据。     

Plants Probiotics as a Tool to Produce Highly Functional Fruits: The Case of Phyllobacterium and Vitamin C in Strawberries

The increasing interest in the preservation of the environment and the health of consumers is changing production methods and food consumption habits. Functional foods are increasingly demanded by consumers because they contain bioactive compounds involved in health protection. In this sense biofertilization using plant probiotics is a reliable alternative to the use of chemical fertilizers, but there are few studies about the effects of plant probiotics on the yield of functional fruits and, especially, on the content of bioactive compounds. In the present work we reported that a strain of genus Phyllobacterium able to produce biofilms and to colonize strawberry roots is able to increase the yield and quality of strawberry plants. In addition, the fruits from plants inoculated with this strain have significantly higher content in vitamin C, one of the most interesting bioactive compounds in strawberries. Therefore the use of selected plant probiotics benefits the environment and human health without agronomical losses, allowing the production of highly functional foods.     

Induction of hepatocyte‐like cells from human umbilical cord‐derived mesenchymal stem cells by defined microRNAs

Generating functional hepatocyte‐like cells (HLCs) from mesenchymal stem cells (MSCs) is of great urgency for bio‐artificial liver support system (BALSS). Previously, we obtained HLCs from human umbilical cord‐derived MSCs by overexpressing seven microRNAs (HLC‐7) and characterized their liver functions in vitro and in vivo. Here, we aimed to screen out the optimal miRNA candidates for hepatic differentiation. We sequentially removed individual miRNAs from the pool and examined the effect of transfection with remainder using RT‐PCR, periodic acid—Schiff (PAS) staining and low‐density lipoprotein (LDL) uptake assays and by assessing their function in liver injury models. Surprisingly, miR‐30a and miR‐1290 were dispensable for hepatic differentiation. The remaining five miRNAs (miR‐122, miR‐148a, miR‐424, miR‐542‐5p and miR‐1246) are essential for this process, because omitting any one from the five‐miRNA combination prevented hepatic trans‐differentiation. We found that HLCs trans‐differentiated from five microRNAs (HLC‐5) expressed high level of hepatic markers and functioned similar to hepatocytes. Intravenous transplantation of HLC‐5 into nude mice with CCl₄‐induced fulminant liver failure and acute liver injury not only improved serum parameters and their liver histology, but also improved survival rate of mice in severe hepatic failure. These data indicated that HLC‐5 functioned similar to HLC‐7 in vitro and in vivo, which have been shown to resemble hepatocytes. Instead of using seven‐miRNA combination, a simplified five‐miRNA combination can be used to obtain functional HLCs in only 7 days. Our study demonstrated an optimized and efficient method for generating functional MSC‐derived HLCs that may serve as an attractive cell alternative for BALSS.