On the self-association potential of transmembrane tight junction proteins

Tight junctions seal intercellular clefts via membrane-related strands, hence, maintaining important organ functions. We investigated the self-association of strand-forming transmembrane tight junction proteins. The regulatory tight junction protein occludin was differently tagged and cotransfected in eucaryotic cells. These occludins colocalized within the plasma membrane of the same cell, coprecipitated and exhibited fluorescence resonance energy transfer. Differently tagged strand-forming claudin-5 also colocalized in the plasma membrane of the same cell and showed fluorescence resonance energy transfer. This demonstrates self-association in intact cells both of occludin and claudin-5 in one plasma membrane. In search of dimerizing regions of occludin, dimerization of its cytosolic C-terminal coiledcoil domain was identified. In claudin-5, the second extracellular loop was detected as a dimer. Since the transmembrane junctional adhesion molecule also is known to dimerize, the assumption that homodimerization of transmembrane tight junction proteins may serve as a common structural feature in tight junction assembly is supported. Received 6 October 2005; received after revision 14 December 2005; accepted 27 December 2005 †These authors contributed equally to this work.     

老采区及地表残余变形对建筑物的影响

浅部开采条件下地表残余变形分析是岩层移动领域的一个棘手问题．通过老采空区影响下地表残余变形和地基承载能力变化对地面新建建筑物的影响分析,提出了老采区上方新建建筑物地基稳定性计算公式、岩层移动参数、评价方法．应用鹤岗市和谐花园小区建筑物实例进行了验证．     

Redox-sensitivity of the dimerization of occludin

Occludin is a self-associating transmembrane tight junction protein affected in oxidative stress. However, its function is unknown. The cytosolic C-terminal tail contains a coiled coil-domain forming dimers contributing to the self-association. Studying the hypothesis that the self-association is redox-sensitive, we found that the dimerization of the domain depended on the sulfhydryl concentration of the environment in low-millimolar range. Under physiological conditions, monomers and dimers were detected. Masking the sulfhydryl residues in the domain prevented the dimerization but affected neither its helical structure nor cylindric shape. Incubation of cell extracts containing full-length occludin with sulfhydryl reagents prevented the dimerization; a cysteine/alanine exchange mutant also did not show dimer formation. This demonstrates, for the first time, that disulfide bridge formation of the domain is involved in the occludin dimerization. It is concluded that the redox-dependent dimerization of occludin may play a regulatory role in the tight junction assembly under physiological and pathological conditions.     

循环码周期分布的反问题

研究循环码周期分布的反问题,即对于给定的正整数ｎ和非负整数序列,是否存在Ｆｑ上的某个〔ｎ,ｋ〕－循环码,使得其周期分布恰好为（Ａ１,Ａ２,．．．Ａｎ）。     

Effects of Ru on microstructure stability and mechanical properties of Ni3Al single crystal alloy

The effect of Ru on microstructure stability and stress rupture properties of a Ni3Al single-crystal alloy was investigated. The experimental results showed that the addition of 2% Ru (mass fraction) improved the microstructure stability due to the res traint of harmful Y-NiMo phase formation during the thermal exposure at the high temperature above 1 000 °C. And the reason may be that the addition of Ru increased the degree of Mo supersaturation in both γ and γ′ phases, and hence suppressed the precipitation of Y-NiMo phase. The results of stress rupture tests under the testing condition of 1 100 °C, 120 MPa showed that the addition of 2% Ru in the alloy improved the stress rupture lives significantly for ther mal exposed samples. The improvement of the stress rupture properties may be attributed to the restraint of Y-NiMo phase precipitation and growth by the addition of the proper amount Ru.     

Participation of the second extracellular loop of claudin-5 in paracellular tightening against ions, small and large molecules

Tight junctions control paracellular permeability. Here, we analyzed the impact of residues in the second extracellular loop (ECL2) of mouse claudin-5 on paracellular permeability. Stable expression of claudin-5_{wild type} in MDCK-II cells—but not that of mutants R145A, Y148A, Y158A or E159Q—increased transepithelial electrical resistance and decreased fluorescein permeation. Expression of claudin-5_Y148A, _Y158A or _E159Q enhanced permeability of FITC-dextran_10 kDa, which was unchanged in cells expressing claudin-5_{wild type} or claudin-5_R145A. In contrast, targeting to tight junctions, strand morphology and tight junction assembly were unchanged. It is concluded that R145 is unessential for trans-interaction of claudin-5, but necessary for tightening against small solutes and ions. The highly conserved residues Y148, Y158 and E159 in ECL2 of claudin-5 contribute to homo- and/or heterophilic trans-interaction between classic claudins and thereby tighten the paracellular space against ions, small and large molecules. These results provide novel insights into the molecular function of tight junctions.     

Elucidating the principles of the molecular organization of heteropolymeric tight junction strands

Paracellular barrier properties of tissues are mainly determined by the composition of claudin heteropolymers. To analyze the molecular organization of tight junctions (TJ), we investigated the ability of claudins (Cld) to form homo- and heteromers. Cld1, -2, -3, -5, and -12 expressed in cerebral barriers were investigated. TJ-strands were reconstituted by claudin-transfection of HEK293-cells. cis-Interactions and/or spatial proximity were analyzed by fluorescence resonance energy transfer inside and outside of strands and ranked: Cld5/Cld5?>?Cld5/Cld1?>?Cld3/Cld1?>?Cld3/Cld3?>?Cld3/Cld5, no Cld3/Cld2. Classic Cld1, -3, and -5 but not non-classic Cld12 showed homophilic trans-interaction. Freeze-fracture electron microscopy revealed that, in contrast to classic claudins, YFP-tagged Cld12 does not form homopolymers. Heterophilic trans-interactions were analyzed in cocultures of differently monotransfected cells. trans-Interaction of Cld3/Cld5 was less pronounced than that of Cld3/Cld1, Cld5/Cld1, Cld5/Cld5 or Cld3/Cld3. The barrier function of reconstituted TJ-strands was demonstrated by a novel imaging assay. A model of the molecular organization of TJ was generated.     

Tricellulin forms homomeric and heteromeric tight junctional complexes

Sealing of the paracellular cleft by tight junctions is of central importance for epithelia and endothelia to function as efficient barriers between the extracellular space and the inner milieu. Occludin and claudins represent the major tight junction components involved in establishing this barrier function. A special situation emerges at sites where three cells join together. Tricellulin, a recently identified tetraspan protein concentrated at tricellular contacts, was reported to organize tricellular as well as bicellular tight junctions. Here we show that in MDCK cells, the tricellulin C-terminus is important for the basolateral translocation of tricellulin, whereas the N-terminal domain appears to be involved in directing tricellulin to tricellular contacts. In this respect, identification of homomeric tricellulin-tricellulin and of heteromeric tricellulin-occludin complexes extends a previously published model and suggests that tricellulin and occludin are transported together to the edges of elongating bicellular junctions and get separated when tricellular contacts are formed.     

天文大气折射与映射函数的数值模拟

为了研究天文大气折射与中性大气折射延迟之间的内在联系,利用天文大气折射表的表列数据对大气折射延迟的映射函数进行了数值模拟.计算结果表明,用天文大气折射测定值模拟映射函数是可行的;同时也表明,映射函数的形式是次要的,随着连分式项数的增加可以提高模拟的精度.该结论对于改善大气折射数据处理的归算精度,降低仪器的观测截止角,和提高仪器的使用效应具有一定的参考价值和指导意义.     

论高校图书馆与大学生素质教育

在阐述大学生素质教育的内涵及其意义的基础上，分析了高校图书馆在大学生素质教育中的地位和作用以及所具有的优势，从加强藏书建设、营造良好环境、提高馆员素质等方面提出了高校图书馆开展大学生素质教育的措施。