Effects of water gradients on soil enzyme activity and active organic carbon composition under Carex lasiocarpa marsh

The responses of soil enzyme activity of freshwater marsh, microbial biomass carbon (MBC), dissolved organic carbon (DOC) and aboveground biomass to water gradients were studied with Carex lasiocarpa pot culture experiment. The relationships between soil enzyme activity and MBC, DOC and aboveground biomass were discussed. The water gradients were W1, 15 cm; W2, ?5 cm; W3, ?5–5 cm; W4, submerged. The results indicated that acid phosphatase, invertase and urease activities were decreased with the increase of water level, while catalase activity was increased with moisture content increasing. Drying-wetting alternation (W3) increased soil enzyme activities if compared with W1. MBC content followed the order of W3 > W1 > W2 > W4, and the activities of invertase, urease and catalase were significantly positively correlated with MBC (p < 0.05). DOC content presented the order of W4 > W1 > W3 > W2, and the activities of urease and acid phosphatase were most significantly negatively correlated with DOC (p < 0.01). In addition, drying-wetting alternation promoted the growth of Carex lasiocarpa. When water submerged plants, the growth of Carex lasiocarpa was significantly inhibited. The aboveground biomass was positively related to soil enzyme activities. There were close relationships between the activities of invertase, urease and catalase and the growth situation of Carex lasiocarpa.     

天然高分子复合人工肌腱组织细胞外基质的构建与表征

胶原与壳聚糖是2种具有较好生物相容性和一定力学强度的天然高分子,可在肌腱组织工程中用于细胞外基质的构建,但二者单独使用时各有不足.本研究利用二者性能上的互补,在一定的外力场作用下,采用EDC/NHS对2种天然高分子材料进行共价交联,获得具有一定空间取向和力学强度的多孔支架,然后引入细胞黏附因子RGD进行表面修饰,构建了具有较好组织相容性和细胞亲和性及适当降解速率的人工肌腱组织细胞外基质.对基质材料的力学性能、亲水性、体外降解速率等的检测和显微观察,结果显示:所构建的多孔支架材料柔软富有弹性,抗拉强度达:15.0Mpa,相应形变为:7.33%;孔隙率:79.4%;吸水率:772%;保水率:206%;在RPM1640培养液(含10%胎牛血清)和人血清中,3周总降解率分别为4.13%和37.2%,其降解速率可与肌腱修复周期相吻合,RGD修饰后材料对3T3-L1细胞具有较好的亲和性.有望成为理想的人工肌腱组织和人造皮肤细胞外基质,或整形手术的软组织填充材料.     

镉胁迫对拟南芥幼苗错配修复基因表达的影响

采用半定量反转录聚合酶链式反应(RT-PCR)技术研究了Cd胁迫对拟南芥(Ara-bidopsis thaliana)幼苗错配修复和增殖细胞核抗原基因表达的影响,并结合幼苗的形态和生理指标,选取Cd胁迫敏感的生物标记物.结果表明:不同浓度(0.25、0.5、1.0 mg·L1)Cd处理对拟南芥幼苗叶片数、地上部鲜质量影响不大;Cd浓度为0.25 mg·L-1时,地上部分可溶性蛋白质含量明显升高(P<0.05),Cd浓度为0.5和1.0 mg·L-1时,可溶性蛋白质含量明显降低(P<0.05);叶绿素含量随着Cd浓度的增加而微弱增加(P>0.05).Cd浓度为0.25 mg·L-1时,以18S rRNA为内参照,PCNA1、PCNA2、MSH2、MSH3、MSH6、MSH7 6个基因均出现了诱导表达,当Cd浓度增加到1.0 mg·L-1时,除了MSH6持续表达诱导及MSH3基因与对照相比表达抑制外,其他基因的表达依然出现诱导,但都低于0.5 mg·L-1Cd处理下的基因表达水平.以上结果表明,基因表达的改变可作为检测Cd污染对植物遗传毒性效应潜在有用的生物标记物.     

Trans-synaptic plasticity: presynaptic initiation, postsynaptic memory

A novel mechanism of persistent facilitation induced by serotonin at Aplysia synapses depends upon rapid postsynaptic protein synthesis and increased responsiveness to glutamate; whereas the memory for this synaptic change is postsynaptic, the initiating signal may be an increase in spontaneous release of glutamate from the presynaptic terminals.     

Structure of AscE and induced burial regions in AscE and AscG upon formation of the chaperone needle-subunit complex of type III secretion system in Aeromonas hydrophila

In the type III secretion system (T3SS) of Aeromonas hydrophila, the putative needle complex subunit AscF requires both putative chaperones AscE and AscG for formation of a ternary complex to avoid premature assembly. Here we report the crystal structure of AscE at 2.7 A resolution and the mapping of buried regions of AscE, AscG, and AscF in the AscEG and AscEFG complexes using limited protease digestion. The dimeric AscE is comprised of two helix-turn-helix monomers packed in an antiparallel fashion. The N-terminal 13 residues of AscE are buried only upon binding with AscG, but this region is found to be nonessential for the interaction. AscE functions as a monomer and can be coexpressed with AscG or with both AscG and AscF to form soluble complexes. The AscE binding region of AscG in the AscEG complex is identified to be within the N-terminal 61 residues of AscG. The exposed C-terminal substrate-binding region of AscG in the AscEG complex is induced to be buried only upon binding to AscF. However, the N-terminal 52 residues of AscF remain exposed even in the ternary AscEFG complex. On the other hand, the 35-residue C-terminal region of AscF in the complex is resistant to protease digestion in the AscEFG complex. Site-directed mutagenesis showed that two C-terminal hydrophobic residues, Ile83 and Leu84, of AscF are essential for chaperone binding.     

下行易化系统及其参与神经病理痛的机制

神经病理痛是指由中枢或外周神经系统损伤或疾病引起的疼痛综合征.神经病理痛是临床上常见的一种疾病,但是其发病机制不甚清楚,临床上也缺乏有效的治疗手段.近年来的研究除了集中于痛觉的上行传导及中枢机制,以及痛觉的下行抑制之外,也证明下行易化系统激活参与神经病理痛的发病机制.本文拟对此进行综述,希望为治疗神经病理痛提供新思路.     

Reduction of Akt2 expression inhibits chemotaxis signal transduction in human breast cancer cells

Protein kinase Cζ PKCζ mediates cancer cell chemotaxis by regulating cytoskeleton rearrangement and cell adhesion. In the research for its upstream regulator, we investigated the role of Akt2 in chemotaxis and metastasis of human breast cancer cells. Reduction of Akt2 expression by siRNA inhibited chemotaxis of MDA-MB-231, T47D, and MCF7 cells, three representative human breast cancer cells. Expression of a wild type Akt2 in siRNA transfected cells rescued the phenotype. EGF-induced integrin β1 phosphorylation was dampened, consistent with defects in adhesion. Phosphorylation of LIMK and cofilin, a critical step of cofilin recycle and actin polymerization, was also impaired. Thus, Akt2 regulates both cell adhesion and cytoskeleton rearrangement during chemotaxis. Depletion of Akt2 by siRNA impaired the activation of PKCζ while inhibition of PKCζ did not interfere with EGF induced phosphorylation of Akt. Furthermore, EGF induced co-immunoprecipitation between PKCζ and Akt2, but not Akt1, suggesting that a direct interaction between PKCζ and Akt2 in chemotaxis. Protein levels of integrin β1, LIMK, cofilin, and PKCζ didn't alter, suggesting that Akt2 does not regulate the expression of these signaling molecules. In a Severe Combine Immunodeficiency mouse model, Akt2 depleted MDA-MB-231 cells showed a marked reduction in metastasis to mouse lungs, demonstrating the biological relevancy of Akt2 in cancer metastasis in vivo. Taken together, our results suggest that Akt2 directly mediates EGF-induced chemotactic signaling pathways through PKCζ and its expression is critical during the extravasation of circulating cancer cells.     

Quantitative trait loci (QTL) analysis for rice grain width and fine mapping of an identified QTL allele gw-5 in a recombination hotspot region on chromosome 5

Rice grain width and shape play a crucial role in determining grain quality and yield. The genetic basis of rice grain width was dissected into six additive quantitative trait loci (QTL) and 11 pairs of epistatic QTL using an F(7) recombinant inbred line (RIL) population derived from a single cross between Asominori (japonica) and IR24 (indica). QTL by environment interactions were evaluated in four environments. Chromosome segment substitution lines (CSSLs) harboring the six additive effect QTL were used to evaluate gene action across eight environments. A major, stable QTL, qGW-5, consistently decreased rice grain width in both the Asominori/IR24 RIL and CSSL populations with the genetic background Asominori. By investigating the distorted segregation of phenotypic values of rice grain width and genotypes of molecular markers in BC(4)F(2) and BC(4)F(3) populations, qGW-5 was dissected into a single recessive gene, gw-5, which controlled both grain width and length-width ratio. gw-5 was narrowed down to a 49.7-kb genomic region with high recombination frequencies on chromosome 5 using 6781 BC(4)F(2) individuals and 10 newly developed simple sequence repeat markers. Our results provide a basis for map-based cloning of the gw-5 gene and for marker-aided gene/QTL pyramiding in rice quality breeding.     

结核病房医院感染与抗生素使用相关性分析

目的：探讨临床抗菌药物应用与结核病房医院感染严重程度的相关性。方法：分析3年来我院结核病房医院感染209例共计221株病原菌,细菌鉴定采用法国梅里埃ATB细菌鉴定药敏分析仪,药敏试验联合应用微量测定法与K—B纸片法。结果：在221株病原菌中革兰阴性杆菌最多为112株,占50．7％,念珠菌75株,占33．9％。主要致病菌依次为白色念珠菌61株(27．6％),铜绿假单胞菌37株(16．8％),肺炎克雷伯菌25株(10．9％)。药敏试验表明细菌耐药明显增加,大多数革兰阴性杆菌对亚胺培南、阿米卡垦、头孢他啶较敏感,金黄色葡萄球菌对万古霉素100％敏感。每例结核病患者除抗结核药物外平均使用2．67种抗菌药物。结论：结核病房医院感染主要来源于内源性感染,其严重性与抗菌药物大量、重复使用密切相关。