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991.
A method for fitting regression models to data that exhibit spatial correlation and heteroskedasticity is proposed. It is well known that ignoring a nonconstant variance does not bias least-squares estimates of regression parameters; thus, data analysts are easily lead to the false belief that moderate heteroskedasticity can generally be ignored. Unfortunately, ignoring nonconstant variance when fitting variograms can seriously bias estimated correlation functions. By modeling heteroskedasticity and standardizing by estimated standard deviations, our approach eliminates this bias in the correlations. A combination of parametric and nonparametric regression techniques is used to iteratively estimate the various components of the model. The approach is demonstrated on a large data set of predicted nitrogen runoff from agricultural lands in the Midwest and Northern Plains regions of the U.S.A. For this data set, the model comprises three main components: (1) the mean function, which includes farming practice variables, local soil and climate characteristics, and the nitrogen application treatment, is assumed to be linear in the parameters and is fitted by generalized least squares; (2) the variance function, which contains a local and a spatial component whose shapes are left unspecified, is estimated by local linear regression; and (3) the spatial correlation function is estimated by fitting a parametric variogram model to the standardized residuals, with the standardization adjusting the variogram for the presence of heteroskedasticity. The fitting of these three components is iterated until convergence. The model provides an improved fit to the data compared with a previous model that ignored the heteroskedasticity and the spatial correlation. 相似文献
992.
U. Wobus H. Bumlein R. Bassüner R. Jung K. Müntz G. Saalbach W. Weschke 《Engineering in Life Science》1986,6(1):40-41
DNA clones representing two subfamilies A and B of legum in genes and a recombinant phage containing a complete legumin B gene have been isolated and characterized by DNA sequencing. A DNA fragment harbouring the legumin B gene and adjacent sequences was used for Ti-mediated transfer into tobacco cells. 相似文献
993.
DNA translocation blockage, a general mechanism of cleavage site selection by type I restriction enzymes 下载免费PDF全文
Type I restriction enzymes bind to a specific DNA sequence and subsequently translocate DNA past the complex to reach a non-specific cleavage site. We have examined several potential blocks to DNA translocation, such as positive supercoiling or a Holliday junction, for their ability to trigger DNA cleavage by type I restriction enzymes. Introduction of positive supercoiling into plasmid DNA did not have a significant effect on the rate of DNA cleavage by EcoAI endonuclease nor on the enzyme's ability to select cleavage sites randomly throughout the DNA molecule. Thus, positive supercoiling does not prevent DNA translocation. EcoR124II endonuclease cleaved DNA at Holliday junctions present on both linear and negatively supercoiled substrates. The latter substrate was cleaved by a single enzyme molecule at two sites, one on either side of the junction, consistent with a bi-directional translocation model. Linear DNA molecules with two recognition sites for endonucleases from different type I families were cut between the sites when both enzymes were added simultaneously but not when a single enzyme was added. We propose that type I restriction enzymes can track along a DNA substrate irrespective of its topology and cleave DNA at any barrier that is able to halt the translocation process. 相似文献
994.
Krishna Saxena Ulrich Schieborr Oliver Anderka Elke Duchardt-Ferner Bettina Elshorst Santosh Lakshmi Gande Julia Janzon Denis Kudlinzki Sridhar Sreeramulu Matthias K. Dreyer K. Ulrich Wendt Corentin Herbert Philippe Duchaussoy Marc Bianciotto Pierre-Alexandre Driguez Gilbert Lassalle Pierre Savi Moosa Mohammadi Fran?oise Bono Harald Schwalbe 《The Journal of biological chemistry》2010,285(34):26628-26640
Fibroblast growth factor (FGF) signaling regulates mammalian development and metabolism, and its dysregulation is implicated in many inherited and acquired diseases, including cancer. Heparan sulfate glycosaminoglycans (HSGAGs) are essential for FGF signaling as they promote FGF·FGF receptor (FGFR) binding and dimerization. Using novel organic synthesis protocols to prepare homogeneously sulfated heparin mimetics (HM), including hexasaccharide (HM6), octasaccharide (HM8), and decasaccharide (HM10), we tested the ability of these HM to support FGF1 and FGF2 signaling through FGFR4. Biological assays show that both HM8 and HM10 are significantly more potent than HM6 in promoting FGF2-mediated FGFR4 signaling. In contrast, all three HM have comparable activity in promoting FGF1·FGFR4 signaling. To understand the molecular basis for these differential activities in FGF1/2·FGFR4 signaling, we used NMR spectroscopy, isothermal titration calorimetry, and size-exclusion chromatography to characterize binding interactions of FGF1/2 with the isolated Ig-domain 2 (D2) of FGFR4 in the presence of HM, and binary interactions of FGFs and D2 with HM. Our data confirm the existence of both a secondary FGF1·FGFR4 interaction site and a direct FGFR4·FGFR4 interaction site thus supporting the formation of the symmetric mode of FGF·FGFR dimerization in solution. Moreover, our results show that the observed higher activity of HM8 relative to HM6 in stimulating FGF2·FGFR4 signaling correlates with the higher affinity of HM8 to bind and dimerize FGF2. Notably FGF2·HM8 exhibits pronounced positive binding cooperativity. Based on our findings we propose a refined symmetric FGF·FGFR dimerization model, which incorporates the differential ability of HM to dimerize FGFs. 相似文献
995.
Pillinger MH Marjanovic N Kim SY Scher JU Izmirly P Tolani S Dinsell V Lee YC Blaser MJ Abramson SB 《The Journal of biological chemistry》2005,280(11):9973-9979
Because matrix metalloproteinases (MMPs) play roles in inflammatory tissue injury, we asked whether MMP secretion by gastric epithelial cells may contribute to gastric injury in response to signals involved in Helicobacter pylori-induced inflammation and/or cyclooxygenase inhibition. Tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and epidermal growth factor (EGF) stimulated gastric cell MMP-1 secretion, indicating that MMP-1 secretion occurs in inflammatory as well as non-inflammatory situations. MMP-1 secretion required activation of the MAPK Erk and subsequent protein synthesis but was down-regulated by the alternate MAPK, p38. In contrast, secretion of MMP-13 was stimulated by TNF-alpha/IL-1beta but not EGF and was Erk-independent and mediated by p38. MMP-13 secretion was more rapid (peak, 6 h) than MMP-1 (peak > or =30 h) and only partly depended on protein synthesis, suggesting initial release of a pre-existing MMP-13 pool. Therefore, MMP-1 and MMP-13 secretion are differentially regulated by MAPKs. MMP-1 secretion was regulated by E prostaglandins (PGEs) in an Erk-dependent manner. PGEs enhanced Erk activation and MMP-1 secretion in response to EGF but inhibited Erk and MMP-1 when TNF-alpha and IL-1beta were the stimuli, indicating that the effects of PGEs on gastric cell responses are context-dependent. These data show that secretion of MMPs is differentially regulated by MAPKs and suggest mechanisms through which H. pylori infection and/or cyclooxygenase inhibition may induce epithelial cell signaling to contribute to gastric ulcerogenesis. 相似文献
996.
Thanos Tsaktanis Heidi Kremling Miha Pav?i? Ricarda von Stackelberg Brigitte Mack Akio Fukumori Harald Steiner Franziska Vielmuth Volker Spindler Zhe Huang Jasmine Jakubowski Nikolas H. Stoecklein Elke Luxenburger Kirsten Lauber Brigita Lenar?i? Olivier Gires 《The Journal of biological chemistry》2016,291(1):425
997.
Dealing effectively with space to find important resources in a natural environment is a fundamental ability necessary for survival. Evidence has already been provided that wild gray mouse lemurs revisit stationary feeding sites regularly. In this study, we explore to what extent two sympatric mouse lemur species, Microcebus murinus and M. ravelobensis, revisited artificial feeding sites during a period of food scarcity. As the tested populations are marked with individual transponders, we built up artificial feeding platforms equipped with a transponder reader at nine different locations where mouse lemurs had been previously caught. We baited them with a liquid reward and recorded the visitors' ID, the time and frequency of their visits, as well as all encounters that occurred on the platforms. Only mouse lemurs visited platforms and a total of sixteen individuals across both species were identified. Mouse lemurs visited a platform with a frequency of 2.02 (+/-0.95, range: 1-3.4) times in a night and they revisited it on several consecutive nights following their first visit (percentage of revisits 90.6%+/-11.7, range: 73.3-100%). First visits on a platform occurred on average 44 min (+/-35; range: 13-131) after sunset. We identified encounters between mouse lemurs on platforms: all of them were agonistic and within a species. Within a dyad, chasers were significantly heavier than chasees (N=7 dyads). Our design of platform experiments offers the advantage of observing wild individually known small primates in their natural environment and of setting up controlled experiments to gain insight into their sensory and cognitive abilities. 相似文献
998.
Expression of cytokeratin 20 in urine cytology smears: a potential marker for the detection of urothelial carcinoma 总被引:1,自引:0,他引:1
A. Bhatia P. Dey Y. Kumar U. Gautam N. Kakkar R. Srinivasan R. Nijhawan 《Cytopathology》2007,18(2):84-86
BACKGROUND: Urine cytomorphology is one of the oldest methods for screening and monitoring patients with transitional cell carcinoma (TCC). Sensitivity of urine cytology is relatively low. Ancillary techniques on urine sample may increase the sensitivity. AIM: To explore the utility of cytokeratin 20 (CK20) immunostaining in identifying malignant cells in urine cytology smears. MATERIALS AND METHODS: Fourteen cases each of confirmed TCC and benign urinary cytology along with five cases of atypical cells in urine were immunostained with a monoclonal CK20 antibody. Of 14 cases of TCC, 12 showed strong positive staining with the antibody. All benign cases were negative except for a few cases in which the umbrella cells were weakly to moderately positive. In all five cases of atypical urine cytology the atypical cells stained positive with the antibody. These cases were later confirmed as TCC on histopathology of bladder wall biopsy. CONCLUSION: CK20 is an important biomarker that can be used to identify TCC in urine cytology smears. It is particularly useful in those cases where malignancy cannot be confirmed by morphology alone. 相似文献
999.
Czirr E Leuchtenberger S Dorner-Ciossek C Schneider A Jucker M Koo EH Pietrzik CU Baumann K Weggen S 《The Journal of biological chemistry》2007,282(34):24504-24513
Abeta42-lowering nonsteroidal anti-inflammatory drugs (NSAIDs) constitute the founding members of a new class of gamma-secretase modulators that avoid side effects of pan-gamma-secretase inhibitors on NOTCH processing and function, holding promise as potential disease-modifying agents for Alzheimer disease (AD). These modulators are active in cell-free gamma-secretase assays indicating that they directly target the gamma-secretase complex. Additional support for this hypothesis was provided by the observation that certain mutations in presenilin-1 (PS1) associated with early-onset familial AD (FAD) change the cellular drug response to Abeta42-lowering NSAIDs. Of particular interest is the PS1-DeltaExon9 mutation, which provokes a pathogenic increase in the Abeta42/Abeta40 ratio and dramatically reduces the cellular response to the Abeta42-lowering NSAID sulindac sulfide. This FAD PS1 mutant is unusual as a splice-site mutation results in deletion of amino acids Thr(291)-Ser(319) including the endoproteolytic cleavage site of PS1, and an additional amino acid exchange (S290C) at the exon 8/10 splice junction. By genetic dissection of the PS1-DeltaExon9 mutation, we now demonstrate that a synergistic effect of the S290C mutation and the lack of endoproteolytic cleavage is sufficient to elevate the Abeta42/Abeta40 ratio and that the attenuated response to sulindac sulfide results partially from the deficiency in endoproteolysis. Importantly, a wider screen revealed that a diminished response to Abeta42-lowering NSAIDs is common among aggressive FAD PS1 mutations. Surprisingly, these mutations were also partially unresponsive to gamma-secretase inhibitors of different structural classes. This was confirmed in a mouse model with transgenic expression of the PS1-L166P mutation, in which the potent gamma-secretase inhibitor LY-411575 failed to reduce brain levels of soluble Abeta42. In summary, these findings highlight the importance of genetic background in drug discovery efforts aimed at gamma-secretase, suggesting that certain AD mouse models harboring aggressive PS mutations may not be informative in assessing in vivo effects of gamma-secretase modulators and inhibitors. 相似文献
1000.
Amit Kumar Verma Virupaksha U. Patil Ramesh S. Bhat 《Plant Cell, Tissue and Organ Culture》2011,107(1):181-185
Six T-DNA/Ds launch pad lines (T0) previously generated by Agrobacterium-mediated transformation of M 35-1 genotype of sorghum were confirmed by PCR. T1 plants of all six lines showed 3:1 segregation when sprayed with 12 ppm Basta herbicide, indicating single copy insertion,
which was also confirmed by left border flanking sequence tag. Calli derived from pNU435-T0(1) primary transformant was co-infected with Agrobacterium-carrying iAc construct for transient expression of transposase to generate stable Ds-tagged mutants in the T0 generation. All nine regenerants were PCR-positive for Ds. However, four contained intact T-DNA/Ds launch pad, while five plants carried empty launch pad, indicating transposition of the Ds. One of these plants, IDs-T0(8), was negative for iAc PCR, indicating that it was a stable Ds-tagged mutant. Of the four plants with intact T-DNA/Ds, IDs-T0(5) carrying iAc was a double transformant and mutagenic, which can generate mutants in the subsequent generation. Hence, the transient expression
of transposase system in sorghum reported here can be employed for high throughput mutagenesis. 相似文献