p85alpha regulates osteoblast differentiation by cross-talking with the MAPK pathway

Class IA phosphoinositide 3-kinase (PI3K) is involved in regulating many cellular functions including cell growth, proliferation, cell survival, and differentiation. The p85 regulatory subunit is a critical component of the PI3K signaling pathway. Mesenchymal stem cells (MSC) are multipotent cells that can be differentiated into osteoblasts (OBs), adipocytes, and chondrocytes under defined culture conditions. To determine whether p85α subunit of PI3K affects biological functions of MSCs, bone marrow-derived wild type (WT) and p85α-deficient (p85α(-/-)) cells were employed in this study. Increased cell growth, higher proliferation rate and reduced number of senescent cells were observed in MSCs lacking p85α compare with WT MSCs as evaluated by CFU-F assay, thymidine incorporation assay, and β-galactosidase staining, respectively. These functional changes are associated with the increased cell cycle, increased expression of cyclin D, cyclin E, and reduced expression of p16 and p19 in p85α(-/-) MSCs. In addition, a time-dependent reduction in alkaline phosphatase (ALP) activity and osteocalcin mRNA expression was observed in p85α(-/-) MSCs compared with WT MSCs, suggesting impaired osteoblast differentiation due to p85α deficiency in MSCs. The impaired p85α(-/-) osteoblast differentiation was associated with increased activation of Akt and MAPK. Importantly, bone morphogenic protein 2 (BMP2) was able to intensify the differentiation of osteoblasts derived from WT MSCs, whereas this process was significantly impaired as a result of p85α deficiency. Addition of LY294002, a PI3K inhibitor, did not alter the differentiation of osteoblasts in either genotype. However, application of PD98059, a Mek/MAPK inhibitor, significantly enhanced osteoblast differentiation in WT and p85α(-/-) MSCs. These results suggest that p85α plays an essential role in osteoblast differentiation from MSCs by repressing the activation of MAPK pathway.     

高脂饲料诱导的肥胖大鼠网膜素水平的实验研究

人群调查发现肥胖人群网膜素水平较正常人群低,而正常及肥胖大鼠血清网膜素水平及其基因表达情况尚不清楚.将SD大鼠随机分为正常组(n=10)和高脂组(n=30),分别喂养普通饲料和高脂饲料.6 w后从高脂组选取体重增长最快的20只,再从中随机抽取10只继续喂养高脂饲料,12 w后两组各剩9只,采用全自动生化仪ADVIA2400测定血糖及血脂、ELISA检测血清胰岛素及网膜素水平、RT-PCR检测网膜脂肪组织网膜素mRNA表达水平.结果显示高脂组大鼠体重、体重增加值、肥胖指数、低密度脂蛋白、胰岛素、血清网膜素水平及网膜脂肪组织网膜素mRNA表达水平均高于正常组(P<0.05).首次发现肥胖大鼠血清网膜素水平及网膜脂肪组织中网膜素mRNA表达水平较正常大鼠显著增高,与人群调查结果不一致.     

云南哀牢山地区森林附生维管植物多样性及区系特征

附生植物作为山地森林生态系统中重要的结构性成分,在维持森林生态系统生物多样性格局、水分和养分循环等方面发挥着重要作用。本文通过野外调查、标本查阅并结合相关文献,对云南哀牢山地区附生维管植物物种组成及分布进行了系统研究。结果显示,哀牢山地区附生维管植物共有23科83属218种,其中附生蕨类和兰科植物最丰富。附生蕨类有34属93种,以附生-石生蕨类生活型占优势,其中水龙骨科17属62种,占附生蕨类的66.67%,瓦韦属(Lepisorus)和石韦属(Pyrrosia)分别有13种和10种。附生兰科植物有26属65种,其中石斛属(Dendrobium)和石豆兰属(Bulbophyllum)分别有12种和8种。该地区附生维管植物属的分布具有明显的热带性质并以热带亚洲分布居多。附生植物生长于生境因子变化剧烈、资源有限的林冠,对环境变化敏感,极易遭受破坏且破坏后难以恢复,不少附生植物具有很高的药用、观赏等价值。因此,应加强对附生维管植物这一特殊类群的保护。     

植物SUMO化修饰及其生物学功能

SUMO化修饰是细胞内蛋白质功能调节的重要方式之一。植物中的SUMO化修饰途径由SUMO分子和SUMO化酶系组成。SUMO化修饰是一个可逆的动态过程。SUMO前体蛋白在SUMO特异性蛋白酶的作用下成熟,随后通过SUMO活化酶、SUMO结合酶和SUMO连接酶将靶蛋白SUMO化,最后SUMO特异性蛋白酶将SUMO与靶蛋白分离,重新进入SUMO化循环。初步研究表明,植物SUMO化修饰参与植物花期调控、激素信号转导、抗病防御以及逆境应答等生理过程。     

Periplasmic proteins of Escherichia coli are highly resistant to aggregation: reappraisal for roles of molecular chaperones in periplasm

Periplasmic proteins of Gram-negative bacteria like Escherichia coli are subjected to immediate affect of environmental fluctuation that may unfold proteins, due to the permeability of the outer membrane to small molecules. They are thus supposedly protected by certain molecular chaperones. Nevertheless, no homologues of typical molecular chaperones have so far been found in periplasm, and the recently reported chaperone activities of periplasmic protein disulfide isomerase (PDI) and peptidyl prolyl isomerase (PPI) seem to be too weak to satisfy such assumed needs. In an attempt to reveal whether periplasmic proteins exhibit certain unusual properties, we discovered that such proteins as a whole are highly resistant to aggregation under a wide variety of denaturing conditions. Furthermore, in an effort to unveil the nature behind this phenomenon we purified and examined four prominent periplasmic proteins. Our results demonstrate that these proteins unfold at rather mild denaturing conditions and expose hydrophobic surfaces during such unfolding process, but hardly form complexes with a typical molecular chaperone. Based on these observations, we propose that the periplasmic proteins have been evolved to resist the formation of aggregates when subjected to various denaturing conditions and molecular chaperones may thus not be needed in periplasm.     

Soil respiration in Tibetan alpine grasslands: belowground biomass and soil moisture, but not soil temperature, best explain the large-scale patterns

The Tibetan Plateau is an essential area to study the potential feedback effects of soils to climate change due to the rapid rise in its air temperature in the past several decades and the large amounts of soil organic carbon (SOC) stocks, particularly in the permafrost. Yet it is one of the most under-investigated regions in soil respiration (Rs) studies. Here, Rs rates were measured at 42 sites in alpine grasslands (including alpine steppes and meadows) along a transect across the Tibetan Plateau during the peak growing season of 2006 and 2007 in order to test whether: (1) belowground biomass (BGB) is most closely related to spatial variation in Rs due to high root biomass density, and (2) soil temperature significantly influences spatial pattern of Rs owing to metabolic limitation from the low temperature in cold, high-altitude ecosystems. The average daily mean Rs of the alpine grasslands at peak growing season was 3.92 μmol CO(2) m(-2) s(-1), ranging from 0.39 to 12.88 μmol CO(2) m(-2) s(-1), with average daily mean Rs of 2.01 and 5.49 μmol CO(2) m(-2) s(-1) for steppes and meadows, respectively. By regression tree analysis, BGB, aboveground biomass (AGB), SOC, soil moisture (SM), and vegetation type were selected out of 15 variables examined, as the factors influencing large-scale variation in Rs. With a structural equation modelling approach, we found only BGB and SM had direct effects on Rs, while other factors indirectly affecting Rs through BGB or SM. Most (80%) of the variation in Rs could be attributed to the difference in BGB among sites. BGB and SM together accounted for the majority (82%) of spatial patterns of Rs. Our results only support the first hypothesis, suggesting that models incorporating BGB and SM can improve Rs estimation at regional scale.     

欧美杂种山杨体细胞无性系变异的分析

以成年欧美杂种山杨(Populustremula×P.tremuloides)优良无性系为材料,通过组织培养方法获得体细胞无性系,利用细胞学和分子生物学方法对其发生的变异进行研究。结果表明:用3.0mg.L-12,4-D诱导的再生植株的细胞染色体稳定性较差,所检测的144个细胞中,变异的细胞中多数发生了染色体加倍,二倍体细胞数仅占36.81%。有些染色体还发生了形态变异,染色体加长,形成带有随体或长臂较长的大型染色体。用1.0mg.L-16-BA诱导再生植株中染色体数量稳定性介于对照和3.0mg.L-12,4-D诱导的再生植株之间,在观察的142个细胞中二倍体细胞占54.93%。再生植株的AFLP分析表明,由激素诱导的再生植株中,AFLP谱带发生了变化,表明发生了体细胞无性系分子水平变异。     

Overexpression of fucosyltransferase IV in A431 cell line increases cell proliferation

Fucosyltransferase IV is an essential enzyme that catalyzes the synthesis of fucosylated oligosaccharides by transferring GDP-fucose to the terminal N-acetylglucosamine with the alpha1,3-linkage. Lewis Y oligosaccharide has a terminal alpha1,3-linked fucose residue and elevation of Lewis Y level is seen in many epithelial cancers. The mechanism of Lewis Y elevation in neoplastic cells is still largely unknown. To study the impact of fucosyltransferase IV on Lewis Y expression and its role on neoplastic cell proliferation, a pEGFP-N1-FUT4 recombinant plasmid was developed and stably transfected into A431 cells. We found that fucosyltransferase IV overexpression promoted cell proliferation and increased the expression of proliferating cell nuclear antigen that correlated with Lewis Y augmentation. Cell cycle analysis demonstrated that fucosyltransferase IV overexpression facilitated cell cycle progression. In conclusion, fucosyltransferase IV overexpression augments Lewis Y expression to trigger neoplastic cell proliferation. These studies suggest that fucosyltransferase IV may serve as a potential therapeutic target for the treatment of Lewis Y-positive epithelial cancers.     

Functions of poly-gamma-glutamic acid (γ-PGA) degradation genes in γ-PGA synthesis and cell morphology maintenance

Poly-γ-glutamic acid (γ-PGA) is an important biopolymer with greatly potential in industrial and medical applications. In the present study, we constructed a metabolically engineered glutamate-independent Bacillus amyloliquefaciens LL3 strain with considerable γ-PGA production, which was carried out by single, double, and triple markerless deletions of three degradation genes pgdS, ggt, and cwlO. The highest γ-PGA production (7.12 g/L) was obtained from the pgdS and cwlO double-deletion strain NK-pc, which was 93 % higher than that of wild-type LL3 strain (3.69 g/L). The triple-gene-deletion strain NK-pgc showed a 28 % decrease in γ-PGA production, leading to a yield of 2.69 g/L. Furthermore, the cell morphologies of the mutant strains were also characterized. The cell length of cwlO deletion strains NK-c and NK-pc was shorter than that of the wild-type strain, while the ggt deletion strains NK-g, NK-pg, NK-gc, and NK-pgc showed longer cell lengths. This is the first report concerning the markerless deletion of γ-PGA degradation genes to improve γ-PGA production in a glutamate-independent strain and the first observation that γ-glutamyltranspeptidase (encoded by ggt) could be involved in the inhibition of cell elongation.     

Structure-based interpretation of missense mutations in Y-family DNA polymerases and their implications for polymerase function and lesion bypass

Our understanding of the molecular mechanisms of error-prone lesion bypass has changed dramatically in the past few years. The concept that the key participants in the mutagenic process were accessory proteins that somehow modified the ability of the cell's main replicase to facilitate bypass of normally blocking lesions has been replaced with one in which the replicase is displaced by a polymerase specialized in lesion bypass. The participants in this process remain the same, only their function has been reassigned. What was once known as the UmuC/DinB/Rev1/Rad30 superfamily of mutagenesis proteins, is now known as the Y-family of DNA polymerases. Quite remarkably, within the space of 3 years, the field has advanced from the initial discovery of intrinsic polymerase function, to the determination of the tertiary structures of several Y-family DNA polymerases.A key to determining the biochemical properties of each DNA polymerase is through structure-function studies that result in the site-specific substitution of particular amino acids at critical sites within each DNA polymerase. However, we should not forget the power of genetic selection that allows us to identify residues within each polymerase that are generated by "random mutagenesis" and which are important for both a gain or loss of function in vivo. In this review, we discuss the structural ramifications of several missense mutations previously identified in various Y-family DNA polymerase and speculate on how each amino acid substitution might modify the enzymatic activity of the respective polymerase or possibly perturb protein-protein interactions necessary for efficient translesion replication in vivo.