Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerst?tten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2-3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision--such as Anomalocaris--within the early Cambrian ecosystem probably helped to accelerate the escalatory 'arms race' that began over half a billion years ago.     

ATP-induced helicase slippage reveals highly coordinated subunits

Helicases are vital enzymes that carry out strand separation of duplex nucleic acids during replication, repair and recombination. Bacteriophage T7 gene product 4 is a model hexameric helicase that has been observed to use dTTP, but not ATP, to unwind double-stranded (ds)DNA as it translocates from 5' to 3' along single-stranded (ss)DNA. Whether and how different subunits of the helicase coordinate their chemo-mechanical activities and DNA binding during translocation is still under debate. Here we address this question using a single-molecule approach to monitor helicase unwinding. We found that T7 helicase does in fact unwind dsDNA in the presence of ATP and that the unwinding rate is even faster than that with dTTP. However, unwinding traces showed a remarkable sawtooth pattern where processive unwinding was repeatedly interrupted by sudden slippage events, ultimately preventing unwinding over a substantial distance. This behaviour was not observed with dTTP alone and was greatly reduced when ATP solution was supplemented with a small amount of dTTP. These findings presented an opportunity to use nucleotide mixtures to investigate helicase subunit coordination. We found that T7 helicase binds and hydrolyses ATP and dTTP by competitive kinetics such that the unwinding rate is dictated simply by their respective maximum rates V(max), Michaelis constants K(M) and concentrations. In contrast, processivity does not follow a simple competitive behaviour and shows a cooperative dependence on nucleotide concentrations. This does not agree with an uncoordinated mechanism where each subunit functions independently, but supports a model where nearly all subunits coordinate their chemo-mechanical activities and DNA binding. Our data indicate that only one subunit at a time can accept a nucleotide while other subunits are nucleotide-ligated and thus they interact with the DNA to ensure processivity. Such subunit coordination may be general to many ring-shaped helicases and reveals a potential mechanism for regulation of DNA unwinding during replication.     

Modular and predictable assembly of porous organic molecular crystals

Nanoporous molecular frameworks are important in applications such as separation, storage and catalysis. Empirical rules exist for their assembly but it is still challenging to place and segregate functionality in three-dimensional porous solids in a predictable way. Indeed, recent studies of mixed crystalline frameworks suggest a preference for the statistical distribution of functionalities throughout the pores rather than, for example, the functional group localization found in the reactive sites of enzymes. This is a potential limitation for 'one-pot' chemical syntheses of porous frameworks from simple starting materials. An alternative strategy is to prepare porous solids from synthetically preorganized molecular pores. In principle, functional organic pore modules could be covalently prefabricated and then assembled to produce materials with specific properties. However, this vision of mix-and-match assembly is far from being realized, not least because of the challenge in reliably predicting three-dimensional structures for molecular crystals, which lack the strong directional bonding found in networks. Here we show that highly porous crystalline solids can be produced by mixing different organic cage modules that self-assemble by means of chiral recognition. The structures of the resulting materials can be predicted computationally, allowing in silico materials design strategies. The constituent pore modules are synthesized in high yields on gram scales in a one-step reaction. Assembly of the porous co-crystals is as simple as combining the modules in solution and removing the solvent. In some cases, the chiral recognition between modules can be exploited to produce porous organic nanoparticles. We show that the method is valid for four different cage modules and can in principle be generalized in a computationally predictable manner based on a lock-and-key assembly between modules.     

Gene polymorphism in Netherton and common atopic disease.

Atopic dermatitis (AD) and asthma are characterized by IgE-mediated atopic (allergic) responses to common proteins (allergens), many of which are proteinases. Loci influencing atopy have been localized to a number of chromosomal regions, including the chromosome 5q31 cytokine cluster. Netherton disease is a rare recessive skin disorder in which atopy is a universal accompaniment. The gene underlying Netherton disease (SPINK5) encodes a 15-domain serine proteinase inhibitor (LEKTI) which is expressed in epithelial and mucosal surfaces and in the thymus. We have identified six coding polymorphisms in SPINK5 (Table 1) and found that a Glu420-->Lys variant shows significant association with atopy and AD in two independent panels of families. Our results implicate a previously unrecognized pathway for the development of common allergic illnesses.     

基于拉格朗日系统中约束力思想的编队卫星构形非线性控制方法

借鉴经典动力学中约束力的思想，提出了一种编队卫星构形精确保持的非线性控制方法．该方法首先将非线性和摄动条件下编队卫星构形保持问题转换为带有完整约束的拉格朗日动力学系统，然后将问题转换为一组微分代数方程，通过求解微分代数方程，确定编队卫星构形保持的非线性控制律．由于借鉴了约束力的思想，该方法自然地利用了编队卫星动力学系统的力学特性，具有节省能量和高精度的特点．通过对线性和非线性条件下空间圆编队卫星构形保持问题的仿真，验证了提出的非线性控制方法的这些特性．     

卫星低频电磁辐射在轨探测研究

利用地球空间探测双星计划探测一号卫星上的磁场波动分析仪的原始数据, 分析了探测一号卫星在轨电磁辐射的特性. 结果显示卫星的电磁辐射主要集中在30 Hz以下. 在30 Hz以上, 卫星的电磁辐射最多延伸到 190 Hz左右, 而且强度明显减弱. 在 190 Hz以下的卫星电磁辐射具有与卫星姿态相关的长周期变化. 在 190~830 Hz的范围的电磁辐射有不明显的长周期变化特征. 830~3990 Hz范围的电磁辐射没有长周期变化特征. 卫星电磁辐射的长周期变化是由卫星姿态变化造成的. 卫星姿态变化引起卫星太阳方位角变化. 卫星太阳方位角越大, 卫星电磁辐射越大. 卫星太阳方位角从90.6增加到93.6, 低于10 Hz以下的电磁辐射约增大为原来的9倍, 10~190 Hz范围的电磁辐射大约增加到原来的1.6倍. 卫星在＜10和10~190 Hz范围内的电磁辐射强度与卫星太阳方位角的相关系数分别达到0.90和0.91. 卫星在光照情况下的电磁辐射要比卫星在阴影情况下大. 卫星太阳能帆板电流产生的电磁辐射是卫星电磁辐射主要来源, 约占整个卫星电磁辐射的87％(低频段<150 Hz)和94％(高频段>150 Hz). 这些中国首次对卫星电磁辐射的在轨探测结果对于我国未来相关科学和应用卫星的设计方案的优化具有重要的参考价值.     

Beta-catenin/TCF4 transactivates miR-30e during intestinal cell differentiation

The Wnt/beta-catenin/TCF4 pathway plays critical roles in the maintenance of small intestinal epithelium; however, downstream targets of the beta-catenin/TCF4 complex are not extensively characterized. We identified miR-30e as an immediate target activated by the beta-catenin/TCF4 complex. miR-30e was detected in the peri-nuclear region of the intestinal crypt IEC-6 cells. Bioinformatics analysis revealed clustered beta-catenin/TCF4 binding sites within the miR-30e promoter region. This promoter region was cloned into pGL3-control luciferase reporter vector, with the enhancer region removed. Transfection of pCMV-SPORT6-beta-catenin expression vector dose-dependently increased luciferase activity, and co-transfection of pCMV-SPORT6-TCF4 expression vector further enhanced the promoter activity. Dexamethasone-induced IEC-6 cells differentiation caused a 2.5-fold increase in miR-30e expression, and upon beta-catenin siRNA transfection, miR-30e increased 1.3-fold. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay confirmed the binding between beta-catenin/TCF4 complexes from IEC-6 nuclear extracts and the putative sequences in the miR-30e promoter. These results demonstrate that beta-catenin/TCF4 transactivates miR-30e during intestinal cell differentiation.     

Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution.

Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 A resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.     

自调式镦压挤胀复合液压机的研制

从力学原理、设计原理、整机结构、关键零部件的设计和工作程序，系统地介绍了自调式镦压挤胀复合液压机．由于压机设计了顶出缸对下活动横梁调节限位结构，回程拉杆对上镦压横梁的复位结构及镦压缸和气液储能器之间的连通协调结构，这不仅使该液压机结构紧凑，同时节省了上镦压横梁的回程液压缸、下活动横梁的镦压缸，并简化了上凸模与上镦压模分设的液压系统，而且解决了直齿圆柱齿轮在塑性成形过程中齿顶难以充满、齿根易出现微裂纹，以及成形压力过大和模具寿命过低的问题．     

Role of serum components in the binding and phagocytosis of oxidatively damaged erythrocytes by autologous mouse macrophages

To investigate the role of autologous serum components in the recognition of damaged cells by macrophages, we examined the binding and phagocytosis of damage oxidatively damaged red blood cells with Cu2+ and ascorbate (oxRBCs) by autologous resident mouse peritoneal macrophages. The binding of oxRBCs by macrophages was independent of the presence of serum. However, phagocytosis by macrophages increased with serum concentration, and macrophages showed little ingestion of oxRBCs in a serum-free medium. Macrophages neither bound nor appreciably ingested native RBCs (before oxidation) in either the absence or presence of autologous serum. Mouse macrophages ingested significantly more native as well as oxRBCs in the presence of heat-inactivated fetal calf serum than in the presence of heat-inactivated mouse serum. Pretreated oxRBCs with normal serum were rarely ingested by macrophages in a serum-free medium. Phagocytosis of oxRBCs was significantly inhibited by depletion of IgG or calcium from serum, by heat inactivation of complement, or by antiserum against mouse C3. These results demonstrate that serum components such as IgG, C3, and calcium are involved in phagocytosis of oxRBCs by autologous macrophages.