Gated regulation of CRAC channel ion selectivity by STIM1

Two defining functional features of ion channels are ion selectivity and channel gating. Ion selectivity is generally considered an immutable property of the open channel structure, whereas gating involves transitions between open and closed channel states, typically without changes in ion selectivity. In store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels, the molecular mechanism of channel gating by the CRAC channel activator, stromal interaction molecule 1 (STIM1), remains unknown. CRAC channels are distinguished by a very high Ca(2+) selectivity and are instrumental in generating sustained intracellular calcium concentration elevations that are necessary for gene expression and effector function in many eukaryotic cells. Here we probe the central features of the STIM1 gating mechanism in the human CRAC channel protein, ORAI1, and identify V102, a residue located in the extracellular region of the pore, as a candidate for the channel gate. Mutations at V102 produce constitutively active CRAC channels that are open even in the absence of STIM1. Unexpectedly, although STIM1-free V102 mutant channels are not Ca(2+)-selective, their Ca(2+) selectivity is dose-dependently boosted by interactions with STIM1. Similar enhancement of Ca(2+) selectivity is also seen in wild-type ORAI1 channels by increasing the number of STIM1 activation domains that are directly tethered to ORAI1 channels, or by increasing the relative expression of full-length STIM1. Thus, exquisite Ca(2+) selectivity is not an intrinsic property of CRAC channels but rather a tuneable feature that is bestowed on otherwise non-selective ORAI1 channels by STIM1. Our results demonstrate that STIM1-mediated gating of CRAC channels occurs through an unusual mechanism in which permeation and gating are closely coupled.     

RNAi-mediated gene silencing in non-human primates

The opportunity to harness the RNA interference (RNAi) pathway to silence disease-causing genes holds great promise for the development of therapeutics directed against targets that are otherwise not addressable with current medicines. Although there are numerous examples of in vivo silencing of target genes after local delivery of small interfering RNAs (siRNAs), there remain only a few reports of RNAi-mediated silencing in response to systemic delivery of siRNA, and there are no reports of systemic efficacy in non-rodent species. Here we show that siRNAs, when delivered systemically in a liposomal formulation, can silence the disease target apolipoprotein B (ApoB) in non-human primates. APOB-specific siRNAs were encapsulated in stable nucleic acid lipid particles (SNALP) and administered by intravenous injection to cynomolgus monkeys at doses of 1 or 2.5 mg kg(-1). A single siRNA injection resulted in dose-dependent silencing of APOB messenger RNA expression in the liver 48 h after administration, with maximal silencing of >90%. This silencing effect occurred as a result of APOB mRNA cleavage at precisely the site predicted for the RNAi mechanism. Significant reductions in ApoB protein, serum cholesterol and low-density lipoprotein levels were observed as early as 24 h after treatment and lasted for 11 days at the highest siRNA dose, thus demonstrating an immediate, potent and lasting biological effect of siRNA treatment. Our findings show clinically relevant RNAi-mediated gene silencing in non-human primates, supporting RNAi therapeutics as a potential new class of drugs.     

Dynamic Analysis of Cable Roofs Under Transient Wind:A Comparison Between Time Domain and Frequency Domain Approaches

At present, high-speed computing capabilities and advanced nonlinear dynamic finite element procedures enable detailed dynamic analysis of cable structures. Although deterministic approaches require considerable analysis time and effort in relation to modeling, running, and data processing, they seem to be the only alternative to obtain high accuracy. Detailed dynamic analysis of cable roof networks is sophisticated and requires advanced modeling expertise. This paper presents a comparison between detailed nonlinear dynamic analysis and a simplified frequency domain approach to estimate the maximum probable response of weakly nonlinear cable roofs. The approach can be considered as alternative to detailed time-domain analysis in the preliminary design phase, or can be used to validate results obtained from more elaborated numerical models. The proposed method is illustrated with two examples of cable net roofs that were also analysed in the time domain.     

钢筋受压黏结滑移模型

为研究钢筋的受压黏结滑移关系,采用分辨率较高的激光位移计,对一批短锚长试件进行系列推出试验研究,得到精确度较高的黏结滑移值及完整的试验黏结滑移关系曲线,描述钢筋在混凝土中的受压黏结滑移破坏全过程:弹性阶段、局部滑移阶段、滑移上升段、滑移下降段和残余段.在对试验得到的较短锚长试件推出试验结果分析的基础上,经统计回归和分析,提出钢筋的受压黏结滑移曲线模型,并与试验结果进行对比.     

The ELF3 zeitnehmer regulates light signalling to the circadian clock

The circadian system regulates 24-hour biological rhythms and seasonal rhythms, such as flowering. Long-day flowering plants like Arabidopsis thaliana, measure day length with a rhythm that is not reset at lights-off, whereas short-day plants measure night length on the basis of circadian rhythm of light sensitivity that is set from dusk, early flowering 3 (elf3) mutants of Arabidopsis are aphotoperiodic and exhibit light-conditional arrhythmias. Here we show that the elf3-7 mutant retains oscillator function in the light but blunts circadian gating of CAB gene activation, indicating that deregulated phototransduction may mask rhythmicity. Furthermore, elf3 mutations confer the resetting pattern of short-day photoperiodism, indicating that gating of phototransduction may control resetting. Temperature entrainment can bypass the requirement for normal ELF3 function for the oscillator and partially restore rhythmic CAB expression. Therefore, ELF3 specifically affects light input to the oscillator, similar to its function in gating CAB activation, allowing oscillator progression past a light-sensitive phase in the subjective evening. ELF3 provides experimental demonstration of the zeitnehmer ('time-taker') concept.     

Prion-like behaviour and tau-dependent cytotoxicity of pyroglutamylated amyloid-β

Extracellular plaques of amyloid-β and intraneuronal neurofibrillary tangles made from tau are the histopathological signatures of Alzheimer's disease. Plaques comprise amyloid-β fibrils that assemble from monomeric and oligomeric intermediates, and are prognostic indicators of Alzheimer's disease. Despite the importance of plaques to Alzheimer's disease, oligomers are considered to be the principal toxic forms of amyloid-β. Interestingly, many adverse responses to amyloid-β, such as cytotoxicity, microtubule loss, impaired memory and learning, and neuritic degeneration, are greatly amplified by tau expression. Amino-terminally truncated, pyroglutamylated (pE) forms of amyloid-β are strongly associated with Alzheimer's disease, are more toxic than amyloid-β, residues 1-42 (Aβ(1-42)) and Aβ(1-40), and have been proposed as initiators of Alzheimer's disease pathogenesis. Here we report a mechanism by which pE-Aβ may trigger Alzheimer's disease. Aβ(3(pE)-42) co-oligomerizes with excess Aβ(1-42) to form metastable low-n oligomers (LNOs) that are structurally distinct and far more cytotoxic to cultured neurons than comparable LNOs made from Aβ(1-42) alone. Tau is required for cytotoxicity, and LNOs comprising 5% Aβ(3(pE)-42) plus 95% Aβ(1-42) (5% pE-Aβ) seed new cytotoxic LNOs through multiple serial dilutions into Aβ(1-42) monomers in the absence of additional Aβ(3(pE)-42). LNOs isolated from human Alzheimer's disease brain contained Aβ(3(pE)-42), and enhanced Aβ(3(pE)-42) formation in mice triggered neuron loss and gliosis at 3 months, but not in a tau-null background. We conclude that Aβ(3(pE)-42) confers tau-dependent neuronal death and causes template-induced misfolding of Aβ(1-42) into structurally distinct LNOs that propagate by a prion-like mechanism. Our results raise the possibility that Aβ(3(pE)-42) acts similarly at a primary step in Alzheimer's disease pathogenesis.     

Bone marrow cells regenerate infarcted myocardium

Myocardial infarction leads to loss of tissue and impairment of cardiac performance. The remaining myocytes are unable to reconstitute the necrotic tissue, and the post-infarcted heart deteriorates with time. Injury to a target organ is sensed by distant stem cells, which migrate to the site of damage and undergo alternate stem cell differentiation; these events promote structural and functional repair. This high degree of stem cell plasticity prompted us to test whether dead myocardium could be restored by transplanting bone marrow cells in infarcted mice. We sorted lineage-negative (Lin-) bone marrow cells from transgenic mice expressing enhanced green fluorescent protein by fluorescence-activated cell sorting on the basis of c-kit expression. Shortly after coronary ligation, Lin- c-kitPOS cells were injected in the contracting wall bordering the infarct. Here we report that newly formed myocardium occupied 68% of the infarcted portion of the ventricle 9 days after transplanting the bone marrow cells. The developing tissue comprised proliferating myocytes and vascular structures. Our studies indicate that locally delivered bone marrow cells can generate de novo myocardium, ameliorating the outcome of coronary artery disease.     

Genome sequencing in microfabricated high-density picolitre reactors

The proliferation of large-scale DNA-sequencing projects in recent years has driven a search for alternative methods to reduce time and cost. Here we describe a scalable, highly parallel sequencing system with raw throughput significantly greater than that of state-of-the-art capillary electrophoresis instruments. The apparatus uses a novel fibre-optic slide of individual wells and is able to sequence 25 million bases, at 99% or better accuracy, in one four-hour run. To achieve an approximately 100-fold increase in throughput over current Sanger sequencing technology, we have developed an emulsion method for DNA amplification and an instrument for sequencing by synthesis using a pyrosequencing protocol optimized for solid support and picolitre-scale volumes. Here we show the utility, throughput, accuracy and robustness of this system by shotgun sequencing and de novo assembly of the Mycoplasma genitalium genome with 96% coverage at 99.96% accuracy in one run of the machine.     

聚焦光束钎焊接头的力学性能及变形行为

研究了光束钎焊获得的对接和搭接钎焊接头的力学性能及其在拉伸载荷作用下的变形行为。光束钎焊对接接头的断裂强度σb、相对延伸率δ、断面收缩率ψ均低于被钎焊母材。同质接头的弹性极限σ0.01、屈服极限σ0.2与母材相当，而异质接头的σ0.01、σ0.2值仅取决于低屈服极限的母材，与高屈服极限的母材无关。对接接头在拉伸载荷作用下的变形是非均匀的，同质接头中的钎缝和近缝区的塑性变形量最小，而异质接头中屈服极限较高的母材一侧几乎无塑性变形。搭接接头在拉伸载荷作用下下会产生“折弯效应”，折弯程度随被钎焊母材屈服极限的增加而减小。对接接头的断裂是由纯拉应力导致的，而搭接接头的断裂是剪应力和拉应力综合作用的结果。     

二十一世纪的碳氢化合物——洛克碳氢化合物研究所的工作

碳氢化合物来源于石油、天然气或煤 ,它在许多方面是现代生活所必需的。全球的碳氢化合物主要用作燃料、发电和供热。化学工业、石化工业、塑料和橡胶工业也都依赖碳氢化合物作为原材料来生产其产品。确实 ,绝大多数化工行业的重要合成化学品都是源于石油产品。今天 ,世界上每天石油的使用总量已经超过 1 0 0 0万吨。很显然 ,不断增长的世界人口和能源消耗 ,与有限的不可再生的石油资源处于一个不断冲突的过程中 ,而且后者还将日益减少。认识到在碳氢化合物化学领域需要广泛的基础研究和研究生教育 ,南加利福尼亚大学于 1 977年成立了“洛克…