Protein phosphatase 5 is required for ATR-mediated checkpoint activation

In response to DNA damage or replication stress, the protein kinase ATR is activated and subsequently transduces genotoxic signals to cell cycle control and DNA repair machinery through phosphorylation of a number of downstream substrates. Very little is known about the molecular mechanism by which ATR is activated in response to genotoxic insults. In this report, we demonstrate that protein phosphatase 5 (PP5) is required for the ATR-mediated checkpoint activation. PP5 forms a complex with ATR in a genotoxic stress-inducible manner. Interference with the expression or the activity of PP5 leads to impairment of the ATR-mediated phosphorylation of hRad17 and Chk1 after UV or hydroxyurea treatment. Similar results are obtained in ATM-deficient cells, suggesting that the observed defect in checkpoint signaling is the consequence of impaired functional interaction between ATR and PP5. In cells exposed to UV irradiation, PP5 is required to elicit an appropriate S-phase checkpoint response. In addition, loss of PP5 leads to premature mitosis after hydroxyurea treatment. Interestingly, reduced PP5 activity exerts differential effects on the formation of intranuclear foci by ATR and replication protein A, implicating a functional role for PP5 in a specific stage of the checkpoint signaling pathway. Taken together, our results suggest that PP5 plays a critical role in the ATR-mediated checkpoint activation.     

Topological constraints in nucleic acid hybridization kinetics

A theoretical examination of kinetic mechanisms for forming knots and links in nucleic acid structures suggests that molecules involving base pairs between loops are likely to become topologically trapped in persistent frustrated states through the mechanism of ‘helix-driven wrapping’. Augmentation of the state space to include both secondary structure and topology in describing the free energy landscape illustrates the potential for topological effects to influence the kinetics and function of nucleic acid strands. An experimental study of metastable complementary ‘kissing hairpins’ demonstrates that the topological constraint of zero linking number between the loops effectively prevents conversion to the minimum free energy helical state. Introduction of short catalyst strands that break the topological constraint causes rapid conversion to full duplex.     

Integrated soil and plant phosphorus management for crop and environment in China. A review

In semi-arid grassland ecosystems, soil biogeochemical processes are controlled by seasonal and inter-annual rainfall variation and temperature, which may override the long-term impact of grazers on N availability and N dynamics. In a three-year (2004?C2006) case study of an Inner Mongolian grassland, we analysed time-integrated (ion-exchange resins) and instantaneous (soil mineral N extractions) inorganic N availability at three sites of varying grazing intensities and combined these data with information on soil water content (SWC), aboveground net primary productivity (ANPP) and plant N uptake. Additionally, the effects of rainfall and grazing on N-form availability (NO ₃ ^? -N, NH ₄ ⁺ -N) were considered. Grazing had less impact on N availability compared to seasonal and annual rainfall distribution. One of the three study years (2004) showed a grazing effect with higher resin-N availability at the ungrazed site compared to the heavily grazed site. Inorganic N availability was low in the driest year (2005) and highest in a year of average rainfall amount and favourable distribution (2004). In general, we found a positive relationship between inorganic N availability and both plant productivity and plant N uptake. Rainfall also controlled the plant available NO ₃ ^? -N and NH ₄ ⁺ -N pools; NH ₄ ⁺ -N dominated the available inorganic N-form in times of low SWC, while the available NO ₃ ^? -N increased with SWC. We observed N availability and plant productivity in a temporal synchronized pattern. Increased rainfall variability and land-use practices affecting SWC will likely alter N availability dynamics (and the relation of N-forms) and, therefore, important processes of semi-arid natural grassland carbon and N cycling.     

CD40 signal expression in gastric cancer tissue and its correlation with prognosis of gastric cancer patients

CD40 signaling plays a critical role in the survival rate of gastric cancer patients. Tumour samples were collected from 73 patients with who were diagnosed as gastric cancer in general surgery department in the 1st affiliated hospital of Suzhou University between September 2002 and July 2003. All patients had not received radiotherapy and chemotherapy before operation. These patients include 46 male and 27 female. Here we show that CD40 is constitutively expressed in the human gastric carcinoma tissues, and CD40 protein and mRNA positive expression in gastric cancer tissues closely correlated with lymph node metastasis and tumour TNM stage. CD40 positive expression in gastric cancer patients with lymph node metastasis was markedly higher than that in gastric cancer patients without lymph node metastasis. CD40 positive expression in stage III-IV gastric cancer patients was markedly higher than that in stage I-II gastric cancer patients. Moreover, CD40 expression closely correlated with prognosis of gastric cancer patients. Therefore, CD40 was taken as grouping variable, and lymph node metastasis and clinical staging were taken as stratification variables, respectively, further analysis showed that prognosis in gastric cancer patients with lymph node metastasis and CD40 positive expression was markedly worse than that in gastric cancer patients without lymph node metastasis and CD40 negative expression (P = 0.0076). These results suggest that CD40 signaling plays a critical role in the survival of gastric cancer patients.     

不同覆盖方式对底泥内源营养盐释放的控制效果

通过底泥内源营养盐释放控制室内模拟试验,考察了塑料包被、斜发沸石、方解石、石英砂和硝酸钙5种覆盖材料对底泥氮磷释放效率的影响,系统分析了各自优劣程度,为实际环境中不同污染背景水体选择适宜的控制技术提供科学依据.结果表明: 不同覆盖材料对底泥总磷释放的控制效果依次为:塑料包被>硝酸钙>斜发沸石>方解石>石英砂;不同覆盖材料对底泥总氮释放的控制效果依次为:斜发沸石>塑料包被>方解石>石英砂>硝酸钙;不同覆盖材料对底泥硝态氮释放的控制效果依次为:塑料包被>斜发沸石>方解石>石英砂>硝酸钙;不同覆盖材料对底泥铵态氮释放的控制效果依次为:硝酸钙>石英砂>斜发沸石>方解石>塑料包被;温度和底泥内源营养盐释放有对应关系,水样中总磷、总氮和硝态氮浓度会随着温度上升而增加,而铵态氮浓度呈下降趋势.     

利用假型反转录病毒对大部分胰腺切除后再生细胞的世系追踪

胰腺是一个重要的内外分泌混合腺, 胰腺发生损伤后能够再生。为了探讨胰腺活体细胞世系追踪的方法和胰腺损伤后再生细胞的来源,分别通过胰腺伤口涂抹并胰内注射、尾静脉注射及腹腔注射三种方法, 利用假型反转录病毒对成体小鼠大部分切除后胰腺的细胞进行世系追踪。结果发现在活体条件下, 与尾静脉注射及腹腔注射法相比, 胰腺伤口涂抹并胰腺内注射反转录病毒的方法能够更有效的标记胰腺细胞; 而且, 通过对标记细胞的世系追踪研究证明, 在胰腺损伤后, 胰腺腺泡细胞能够接受损伤信号刺激发生再生。为今后进一步利用反转录假病毒对活体胰腺进行细胞命运追踪研究奠定基础, 为利用反转录病毒载体进行胰腺疾病的基因治疗提供线索。     

Transgenic animal production and animal biotechnology

Considerable progress has been made in methods for production of transgenic livestock; beginning with pronuclear microinjection over 20 years ago. New methods, including the use of viral vectors, sperm-mediated gene transfer and somatic cell cloning, have overcome many of the limitations of pronuclear microinjection. It is now possible to not only readily make simple insertional genetic modifications, but also to accomplish, more complex, homozygous gene targeting and artificial chromosome transfer in livestock.     

Enzyme-substrate interactions revealed by the crystal structures of the archaeal Sulfolobus PTP-fold phosphatase and its phosphopeptide complexes

The P-loop-containing protein phos-phatases are important regulators in signal transduction. These enzymes have structural and functional similarity with a conserved sequence of Dx(25-41)HCxxGxxR(T/S) essential for catalysis. The singular protein tyrosine phosphatase (PTP) from archaeal Sulfolobus solfataricus is one of the smallest known PTPs with extreme thermostability. Here, we report the crystal structure of this phosphatase and its complexes with two tyrosyl phosphopeptides A-(p)Y-R and N-K-(p)Y-G-N. The structure suggests the minimal structural motif of the PTP family, having two variable sequences inserted between the beta2-beta3 and beta3-beta4 strands, respectively. The phosphate of both phosphopeptide substrates is bound to the P-loop through several hydrogen bonds. Comparison of several phosphatase-substrate complexes revealed that Gln135 on the Q-loop has different modes of recognition toward phosphopeptides. The substrate specificity of SsoPTP is primarily localized at the phosphotyrosine, suggesting that this phosphatase may be a prototypical PTP.