Negative feedback regulation of Wnt signaling by G�¦�-mediated reduction of Dishevelled

Wnt signaling is known to be important for diverse embryonic and post-natal cellular events and be regulated by the proteins Dishevelled and Axin. Although Dishevelled is activated by Wnt and involved in signal transduction, it is not clear how Dishevelled-mediated signaling is turned off. We report that guanine nucleotide binding protein beta 2 (Gnb2; Gβ₂) bound to Axin and Gβ₂ inhibited Wnt mediated reporter activity. The inhibition involved reduction of the level of Dishevelled, and the Gβ₂γ₂ mediated reduction of Dishevelled was countered by increased expression of Axin. Consistent with these effects in HEK293T cells, injection of Gβ₂γ₂ into Xenopus embryos inhibited the formation of secondary axes induced either by XWnt8 or Dishevelled, but not by β-catenin. The DEP domain of Dishevelled is necessary for both interaction with Gβ_2γ2 and subsequent degradation of Dishevelled via the lysosomal pathway. Signaling induced by Gβ_2γ2 is required because a mutant of Gβ₂, Gβ₂ (W332A) with lower signaling activity, had reduced ability to downregulate the level of Dishevelled. Activation of Wnt signaling by either of two methods, increased Frizzled signaling or transient transfection of Wnt, also led to increased degradation of Dishevelled and the induced Dishevelled loss is dependent on Gβ₁ and Gβ₂. Other studies with agents that interfere with PLC action and calcium signaling suggested that loss of Dishevelled is mediated through the following pathway: Wnt/Frizzled→Gβγ→PLC→Ca⁺²/PKC signaling. Together the evidence suggests a novel negative feedback mechanism in which Gβ₂γ₂ inhibits Wnt signaling by degradation of Dishevelled.     

Evaluating use of ferricyanide-mediated respiration bioassays to quantify stimulatory and inhibitory effects on Escherichia coli populations

A number of recent studies have utilised ferricyanide as a respiratory mediator for microbial-based assays for determining water quality parameters such as biochemical oxygen demand (BOD) and toxicity. The majority of assays published to date obtain a result by determining the difference in ferrocyanide accumulation between a test sample and one or more control samples. However, a validation of the relationship between ferrocyanide accumulation and standard measures of cell density or viability has not yet been performed. To this end, a rapid microbially catalysed ferricyanide-mediated respiration (FM-RES) assay was compared with standard plate count (SPC) and spectrophotometer (OD₆₀₀) measurements on a growing batch culture of Escherichia coli. Good agreement was observed between all techniques, with predictable deviations noted in different phases of the growth curves. Standardised FM-RES assays showed excellent correlations with the SPC method under controlled conditions, indicating that short-term changes in microbial activity are due to a change in per-cell respiration, rather than changes in cell numbers. The FM-RES assay was then used to observe the changes in the respiration of E. coli induced by the addition of a glucose-glutamic acid (GGA) mixture, 3,5-dichlorophenol (3,5-DCP) and Ag⁺ in various combinations and concentrations. Stimulation of respiration was pronounced in the presence of GGA while both 3,5-DCP and, in particular, Ag⁺ demonstrated inhibitory respiratory effects. The results highlight the validity and suitability of ferricyanide-mediated respiration bioassays, with appropriate modification, to monitor either stimulatory effects on microbial populations, such as occurs with BOD, or inhibitory effects, such as occurs with toxicity assays.     

铜中毒对SD大鼠肝的影响研究

将36只雄性大鼠80~100 g随机分为3组,分别喂以对照日粮(Cu质量分数13.15mg/kg)和高铜日粮(Cu质量分数650、850 mg/kg),实验期为9周,进行了铜中毒对大鼠肝脏影响的病理学研究。结果表明,与对照组比较,高铜Ⅰ、Ⅱ组大鼠肝脏出现不同程度的病理损害;大鼠肝脏脏器系数有增高趋势,但差异无显著(P0.05)。同时,乳酸脱氢酶、谷草转氨酶活性显著升高(P0.01),血清铜含量上升,SOD含量下降。提示日粮铜质量分数650~850 mg/kg即可引起大鼠肝脏的病理损伤,功能降低。     

近红外无创生化检测中不同光程的光谱校正模型研究

近红外无创生化检测中采用不同血流容积光谱相减的方法理论上能够消除人体组织产生的强背景干扰,但人体光谱相减后得到的血液光谱的光程是未知的,这给校正模型的建立带来了困难。通过设计模拟实验并采用正交信号校正的方法对光程信息进行校正,提高不同光程的光谱建立校正模型的预测精度。分别建立了光程校正前后的模型,模型的交叉验证标准偏差从90.17mg.dL-1下降到31.62mg.dL-1,相关系数从0.978 7提高到0.996 8。实验结果表明,采用正交信号校正的方法能够有效抑制光程信息的干扰,提高模型的预测精度,这为不同血流容积光谱相减法的实际应用提供了基础。     

Controlled immobilization of peptide nanotube-templated metallic wires on Au surfaces

Peptide nanotubes were immobilized on Au substrates functionalized with self-assembled monolayers of 4-mercaptobenzoic acid in a pH 6 citric acid solution via hydrogen bonds between the peptide nanotubes and the monolayers. Subsequently, the immobilized nanotubes were metallized by nickel via the electroless coating process. Received 30 November 2000     

Vectorial photoinduced electron transfer in phospholipid vesicles and LB bilayers

Summary Photoinduced electron transfer (PET) was studied in phospholipid vesicles and in Langmuir-Blodgett bilayers in the attempt to produce a model for electron transfer processes in biological media. Spatial organization of the reaction centers in lipid membranes needs to be controlled in order to provide high efficiency of light-to-chemical energy conversion. We designed a phospholipid system where the donor is localized in the inner bilayer whereas the acceptor is at the polar groups-water interface. We used dipalmitoylphosphatidic acid vesicles containing low molar fractions of dipalmitoylphosphatidylcholine with pyrene (donor) bound to one of the alkyl chains. Methylviologen (acceptor) was added to the external aqueous phase; upon photoexcitation of the donor we observed the electron transfer to take place in a unidirectional manner from the inside of the bilayer to the interface. Information about the location of the donor was obtained studying the photophysical properties of the pyrene chromophore in vesicles and in LB layers. The photoinduced electron transfer reaction was evidenced by quenching of pyrene fluorescence in the presence of increasing concentrations of acceptor, the process was studied both with steady-state and time-resolved fluorescence emission. Fluorescence intensity was found to decrease with increasing concentration of methylviologen, similar results were obtained for vesicles and LB layers of analog composition immersed in a methylviologen solution. Lifetimes of the excited species were found to be of the same order of magnitude in vesicle and LB-layer systems. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

超顺磁纳米颗粒弛豫时间传感技术在生化分析中的研究进展

该文介绍了基于超顺磁纳米颗粒的弛豫时间(T2)传感技术及其在生化分析应用中的研究进展.在均匀磁场中,超顺磁纳米颗粒状态的变化(分散或聚集)会改变磁场的均匀度进而引起周围水分子质子弛豫时间的改变,即磁弛豫时间传感效应.磁颗粒经表面修饰后与给体/受体偶联形成磁传感探针,当与待测物发生特异性反应后,引起介质磁颗粒聚集状态改变...     

Biophysical model for high-throughput tumor and epithelial cell co-culture in complex biochemical microenvironments

The in vivo tumor microenvironment is a complex niche that includes heterogeneous physical structures,unique biochemical gradients and multiple cell interactions.Its high-fidelity in vitro reconstruction is of fundamental importance to improve current understandings of cell behavior,efficacy predictions and drug safety.In this study,we have developed a high-throughput biochip with hundreds of composite extracellular matrix(ECM)microchambers to co-culture invasive breast cancer cells(MDA-MB-231-RFP)and normal breast epithelial cells(MCF-10 A-GFP).The composite ECM is composed of type I collagen and Matrigel which provides a heterogeneous microenvironment that is similar to that of in vivo cell growth.Additionally,the growth factors and drug gradients that involve human epidermal growth factor(EGF),discoidin domain receptor 1(DDR1)inhibitor 7 rh and matrix metalloproteinase inhibitor batimastat allow for the mimicking of the complex in vivo biochemical microenvironment to investigate their effect on the spatial-temporal dynamics of cell growth.Our results demonstrate that the MDA-MB-231-RFP cells and MCF-10 A-GFP cells exhibit different spatial proliferation behaviors under the combination of growth factors and drugs.Basing on the experimental data,we have also developed a cellular automata(CA)model that incorporated drug diffusion to describe the experimental phenomenon,as well as employed Shannon entropy(SE)to explore the effect of the drug diffusion coefficient on the spatial-temporal dynamics of cell growth.The results indicate that the uniform cell growth is related to the drug diffusion coefficient,which reveals that the pore size of the ECM plays a key role in the formation of complex biochemical gradients.Therefore,our integrated,biomimetic and high-throughput co-culture platforms,as well as the computational model can be used as an effective tool for investigating cancer pathogenesis and drug development.     

基于回声状态网络的BOD在线软测量模型

针对污水处理过程的BOD建模问题,提出了一种基于回声状态网络的BOD在线软测量方法;基于梯度下降规则对回声状态网络的在线学习算法进行了研究;为保证学习算法的收敛性,基于Lyapunov理论对学习率范围进行了确定;实验表明,基于回声状态网络的在线BOD预测方法较常规神经网络预测精度提高约两个数量级,模型的适应性也大幅提高。     

干式生化膜片的制备及其应用

建立了一种快速检测血液中二氧化碳结合力(CO₂-CP)、葡萄糖(GLU)、尿酸(UA)含量的干式生化分析方法。筛选出合适的膜材料作为干片载体, 制备干片, 用干式生化分析仪检测干片, 建立了测定血液中CO₂-CP、GLU、UA含量的标准曲线, 对所建立的方法进行加标回收实验、稳定性实验、批间、批内重复性实验、方法学比较。 此法制备的干片颜色梯度明显、显色均匀, 测定CO₂-CP、GLU、UA的线性范围较宽;批间与批内变异系数均小于5%, 重复性良好;与临床湿化学检测相比具有良好的相关性, 相关系数大于0.99, 可应用于临床检测。