Transmembrane mechanisms in the assembly of the postsynaptic apparatus at the neuromuscular junction

The vertebrate neuromuscular junction (NMJ) is marked by molecular specializations that include postsynaptic clusters of acetylcholine receptor (AChR) and acetylcholinesterase (AChE). Whereas AChRs are aggregated in the postsynaptic muscle membrane to a density of 10,000/mum(2), AChE is concentrated, also to a high density, in the synaptic basement membrane (BM). In recent years considerable progress has been made in understanding the cellular and molecular mechanisms of AChR clustering. It is known that during the early stages of motoneuron-muscle interaction, the nerve-secreted proteoglycan agrin activates the muscle-specific kinase MuSK, which leads to the formation of a postsynaptic cytoskeletal scaffold that immobilizes and concentrates AChRs through a process generally accepted to involve diffusion-mediated trapping of the receptors. We have recently tested this diffusion-trap model at the single molecule level for the first time by using quantum-dot labeling to track individual AChRs during NMJ development. Our results showed that single AChRs exhibit Brownian-type movement, with diffusion coefficients of 10(-11) to 10(-9)cm(2)/s, until they become immobilized at "traps" assembled in response to synaptogenic stimuli. Thus, free diffusion of AChRs is an integral part of their clustering mechanism. What is the mechanism for AChE clustering? We previously showed that the A(12) asymmetric form of AChE binds to perlecan, a heparan-sulfate proteoglycan which in turn interacts with the transmembrane dystroglycan complex. Through this linkage AChE becomes bound to the muscle membrane and, like AChRs, may exhibit lateral mobility along the membrane. Consistent with this idea, pre-existent AChE at the cell surface becomes clustered together with AChRs following synaptogenic stimulation. Future studies testing diffusion-mediated trapping of AChE should provide insights into the synaptic localization of BM-bound molecules at the NMJ.     

Functional differentiation of the anterior pituitary cells in the fetal pig

Summary The fetal porcine pituitary was investigated by means of ultrastructural immunocytochemistry (1) to identify the first cells synthesizing the adenohypophyseal hormones, (2) to follow their differentiation during fetal development, and (3) to compare their ultrastructural characteristics with those of mature adult cells.The first ACTH-cells, which produced and stored ACTH, -LPH, -MSH, and - and -endorphin in the same granules, were very numerous at day 34 and displayed a uniform morphology. At day 50 and thereafter, until the end of gestation, the ACTH-cells differed in their appearance probably reflecting various stages of differentiation of one cell type. The GH-cells gained rapidly ultrastructural features comparable to those of mature GH-cells. In contrast, in the case of PRL-cells, which appeared only at the end of the gestation period as immature elements containing very small secretory granules, the morphological maturation seemed to take place only after birth. The first cells synthesizing the glycoprotein hormones (LH, LH, FSH and TSH) displayed ultrastructural features of immature cells. At day 50, their ultrastructural organization started to show a different pattern. At the end of gestation, the TSH-cells and the gonadotropic cells displayed the ultrastructural features of mature cells.     

HLA-DRB1基因多态性与新疆哈萨克族人群结核病易感性的研究

目的:研究HLA-DRB1基因多态性与新疆哈萨克族人群结核病(TB)的相关性。方法:采用病例-对照的研究方法,应用聚合酶链反应-序列特异性引物(PCR-SSP)技术对231例新疆哈萨克族肺结核患者和230例新疆哈萨克族健康对照者的13个HLA-DRB1等位基因进行分型,比较其等位基因频率(GF)并计算其比值比(OR)。结果:与新疆哈萨克族人群对照组相比,新疆哈萨克族人群结核病例组中HLA-DRB1*04显著增高(11.72%比6.75%,p0.05,OR=1.889),HLA-DRB1*10也增高(2.86%比1.09%),但统计学上无显著性差异(Pc0.05)。结论:HLA-DRB1*04可能是新疆哈萨克族人群结核病的易感基因。     

Reorientation of Microfibrils and Microtubules at the Outer Epidermal Wall of Maize Coleoptiles During Auxin-Mediated Growth

Auxin-mediated elongation growth of isolated subapical coleoptile segments of maize (Zea mays L.) is controlled by the extensibility of the outer cell wall of the outer epidermis (Kutschera et al., 1987). Here we investigate the hypothesis that auxin controls the extensibility of this wall by changing the orientation of newly deposited microfibrils through a corresponding change in the orientation of cortical microtubules. On the basis of electron micrographs it is shown that cessation of growth after removal of the endogenous source of auxin is correlated with a relative increase of longitudinally orientated microfibrils and microtubules at the inner wall surface. Conversely, reinduction of growth by exogenous auxin is correlated with a relative increase of transversely orientated microfibrils and microtubules at the inner wall surface. These changes can be detected 30–60 min after the removal and addition of auxin, respectively. The functional significance of directional changes of newly desposited wall microfibrils for the control of elongation growth is discussed.     

Coccidia of the Leporidae*

Thirty-six species of coccidia, all members of the genus Eimeria, have been described from 3 of the 9 genera and 11 of the more than 48 species in the lagomorph family Leporidae. All these are described briefly in the present paper and their synonymies are given. Coccidia have been described from the single species of Oryctolagus, from 4 of the 13 species of Sylvilagus and from 6 of the 26 species of Lepus. These genera have 12, 12, and 14 known species of Eimeria, of which only 2 are shared by Oryctolagus and Sylvilagus. Lepus has none of the coccidia of these genera. One species is known to occur in the bile ducts of the liver, 13 in the intestine, and the location of 22 is unknown. Life cycles have been determined for 9 of the species, of which 8 have been worked out in the domestic rabbit Oryctolagus and 1 in the cottontail Sylvilagus.     

邻苯二甲酸二丁酯对翡翠贻贝抗氧化酶及脂质过氧化水平的影响

实验室条件下,研究了不同浓度邻苯二甲酸二丁酯(DBP)长期胁迫(15 d)对翡翠贻贝内脏团和外套膜抗氧化酶(超氧化物歧化酶SOD、过氧化氢酶CAT)及脂质过氧化(LPO)水平(以MDA含量表示)的影响,以及受胁迫翡翠贻贝在清洁海水中恢复阶段上述生化指标的变化特征.结果表明:胁迫阶段,0.5和2.5 mg.L-1DBP下翡翠贻贝内脏团SOD活性表现为先抑制后逐渐恢复,12.5和62.5 mg.L-1下则持续受到显著抑制;不同浓度组CAT活性均明显被抑制.LPO水平明显升高.外套膜中,2.5 mg.L-1下SOD活性受到持续诱导,其他浓度组则先被抑制,后随曝露时间延长逐渐被诱导;各浓度组CAT的变化波动较大,没有明显规律;而LPO水平明显升高.净化恢复阶段,12.5和62.5 mg.L-1DBP胁迫下的内脏团SOD和CAT活性恢复较慢,其LPO水平随时间延长逐渐恢复至对照组水平;外套膜中SOD活性呈持续升高趋势,CAT活性和LPO水平则随时间延长恢复到对照组水平.     

Modeling the spontaneous initiation of the polymerization of methyl methacrylate

The mechanism of the spontaneous initiation of the polymerization of methyl methacrylate (MMA) was investigated theoretically. The six minimum energy paths (MEP) of the possible reactions were calculated using the density functional theory (DFT) in conjunction with the B3LYP functional and 6-31G* basis set. The Diels-Alder initiation mechanism (path (I) and path (II)) with remarkably high energy barriers is not applicable to MMA. Four favorable paths were found (path (III), path (IV), path (V) and path (VI)), which are supporting the Flory mechanism. Path (V) has the lowest active energy. Therefore this path is considered as the main path for the spontaneous polymerization of MMA. Figure The mechanism of the spontaneous initiation of the polymerization of methyl methacrylate (MMA) was investigated theoretically. The six minimum energy paths (MEP) of the possible reactions were calculated using the density functional theory (DFT) in conjunction with the B3LYP functional and 6-31G* basis set.     

RNA干扰作用(RNAi)研究进展

RNA干扰作用 (RNAi)是生物界一种古老而且进化上高度保守的现象 ,是基因转录后沉默作用 (PTGS)的重要机制之一 .RNAi主要通过dsRNA被核酸酶切割成 2 1～ 2 5nt的干扰性小RNA即siRNA ,由siRNA介导识别并靶向切割同源性靶mRNA分子而实现 .RNAi要有多种蛋白因子以及ATP参与 ,而且具有生物催化反应特征 .RNAi是新发现的一种通过dsRNA介导的特异性高效抑制基因表达途径 ,在后基因组时代的基因功能研究和药物开发中具有广阔应用前景     

In vitro studies of the rabbit immune system. IV. Differential mitogen responses of isolated T and B cells.

The mitogenic responses of separated rabbit lymphocyte populations functionally analogous to mouse T and B cells have been tested in vitro. Purified T cells were prepared by passage over nylon wool (NW) and purified B cells prepared by treatment with antithymocyte serum and complement (ATS + C). ATS + C kills 70% of peripheral blood lymphocytes (PBL's) and 50% of the spleen cells while passage over NW yields 40% of the applied PBL's and 5–23% of the applied spleen cells. NW-purified T cells from the spleen or PBL's respond fully to concanavalin A (Con A) but have a reduced response to phytohemaglutinin (PHA) and little or no response to goat anti-rabbit immunoglobulin (anti-Ig). PBL's that survive ATS + C (B cells) are stimulated by anti-Ig but not by Con A or PHA. B cells purified from spleen do not respond to Con A or PHA but will respond to anti-Ig under appropriate conditions. A full spleen B-cell response to anti-Ig required removal of Ig produced by the cultures that blocked anti-Ig stimulation. It is concluded that, for rabbit lymphocytes, Con A and PHA are primarily T-cell mitogens and that anti-Ig is primarily a B-cell mitogen. However, the mitogen response of unfractionated PBL or spleen cell populations indicates an overlap in reactivity. This could be due to cells sharing T and B properties, alteration of cell populations by the fractionation procedures used, or recruitment of one population in the presence of a mitogenic response of the other population.     

Genetic variations of TLRs and their association with HPV/EBV,co-infection along with nicotine exposure in the development of premalignant/malignant lesions of the oral cavity in Indian population

Background: Despite being most preventable malignancies associated with smoked and smokeless tobacco products, squamous cell carcinoma of oral cavity is one of the most common malignancy in India. The aim of the present study was to evaluate the role of TLRs in oral pre-cancerous, cancerous cases and their genotypic correlation with HPV/EBV, co-infection & lifestyle habits in Indian population.Methods: The present study was conducted on 300 subjects (100 OSCC, 50 pre-cancer & 150 controls). The amplification of TLRs gene and HPV/EBV co-infection was assessed by Nested PCR, PCR–RFLP and further confirmation by direct sequencing.Results: The TLR 9(−1486 T/C), revealed that the TT vs. CT + CC genotype had a ˜5-fold increased risk for the development of pre-cancerous lesions as compared to controls (p = 0.0001). Further analysis showed that the risk of cancer was extremely pronounced in HPV/EBV, co-infection (p = 0.0141), implicating the possible interaction between TLR 9(−1486T/C) genotype and HPV infection in increasing cancer/pre-cancer risk. The ‘G’ allele of TLR 4(+896A/G) was also a higher risk of developing pre-cancerous lesions with 4.5 fold and statistically significant (p = 0.0001). The genotypic association of TLR 9(-1486T/C) in OSMF cases showed ˜8 fold increased risk and TLR 4(+896A/G) showed fourteen fold higher risk for leukoplakia (p < 0.0001, OR = 14.000).Conclusion: Genetic polymorphism of TLR 9(−1486 T/C) and TLR 4(+896A/G) may influence the effects of HPV/EBV, co-infection and play the significant role in development of the disease. The significance of these TLRs seemed to be enhanced by tobacco chewing and smoking habits also, which act as an important etiological risk factor for OSCC.     

线粒体渗透性转变孔结构和功能的研究进展

非正常生理浓度的Ca^2 和氧化应激等刺激线粒体渗透性转变孔(mitochondria permeability transition pore,MPTP)开放,使线粒体形态功能发生改变,被释放的细胞色素c和凋亡诱导因子(apoptosisinducing factor,AIF)等参与到caspase信号通路中,诱导细胞发生凋亡。本文在MPTP的主要组成成分、两种不同的结构功能模型、抑制剂对MPTP的抑制机制和缺血,再灌注及缺血预适应对MPTP开放的影响等方面的研究进展作一综述。     

LptB-LptF coupling mediates the closure of the substrate-binding cavity in the LptB2FGC transporter through a rigid-body mechanism to extract LPS

Lipopolysaccharides (LPS) are essential envelope components in many Gram-negative bacteria and provide intrinsic resistance to antibiotics. LPS molecules are synthesized in the inner membrane and then transported to the cell surface by the LPS transport (Lpt) machinery. In this system, the ATP-binding cassette (ABC) transporter LptB₂FGC extracts LPS from the inner membrane and places it onto a periplasmic protein bridge through a poorly understood mechanism. Here, we show that residue E86 of LptB is essential for coupling the function of this ATPase to that of its partners LptFG, specifically at the step where ATP binding drives the closure of the LptB dimer and the collapse of the LPS-binding cavity in LptFG that moves LPS to the Lpt periplasmic bridge. We also show that defects caused by changing residue E86 are suppressed by mutations altering either LPS structure or transmembrane helices in LptG. Furthermore, these suppressors also fix defects in the coupling helix of LptF, but not of LptG. Together, these results support a transport mechanism in which the ATP-driven movements of LptB and those of the substrate-binding cavity in LptFG are bi-directionally coordinated through the rigid-body coupling, with LptF’s coupling helix being important in coordinating cavity collapse with LptB dimerization.     

The role of the supramammillary area of the hypothalamus in cognitive functions

The supramammillary area (SUM) of the hypothalamus has wide spread connection with numerous brain structures. It is known that the SUM can control the frequency of the hippocampal theta rhythm, which plays a role in the cognitive functions of the hippocampal formation. In order to examine the role of the specific cells of the SUM in learning and memory, selective cholinergic neurotoxic or excitotoxic lesioned rats of the SUM were tested for spatial memory on the Morris water maze (MWM) test. After the behavior tests, the expression of acetylcholinesterase (AChE) in the hippocampus was studied using the immunohistochemistry. In the MWM test, both lesion of the SUM with 192 IgG-saporin or ibotenic acid produced the impairment of spatial learning and memory. The expression of AChE immunreactive neurons in the hippocampal CA3 region was decreased after injections of 192 IgG-saporin into the SUM. These findings suggest that cholinoceptive cells of the SUM area may play a critical role in the process of learning and memory.     

Removal of Cr6+ from groundwater using zero-valence iron in the laboratory

Abstract

In this paper, we describe a series of laboratory experiments which quantify the rate of Cr⁶⁺ reduction by Fe⁰. The main goal of these experiments was to determine the removal efficiency of Cr⁶⁺ by iron. The results indicate that Fe⁰ reduces Cr⁶⁺ to Cr³⁺ under alkaline and slightly acidic conditions. The removal efficiency rises with an increase of the initial concentration of Cr⁶⁺ (1 mg/L to 10 mg/L) when the quantity of Fe⁰ is stable. The removal efficiency increases as the quantity of Fe⁰ is raised when other conditions are constant. The removal efficiency would not be affected by other inorganic ions unless they were present at very high concentrations. When the initial concentration Cr⁶⁺ is 10mg/L and pH is 6.5–7.7, the final concentration of Cr⁶⁺ in effluent is less than 0.05 mg/L and the total Fe is less than 0.3 mg/L in effluent.     

哺乳动物胚胎发育极性的研究进展

哺乳动物胚胎的早期发育,可依据环境变化进行自我调控。胚胎是何时具有自我调控能力的,一直有两种说法:其一,胚胎刚形成时,细胞质成分空间分布均衡,胚胎具有发育全能性,经几次卵裂后,卵裂球间开始分化发育,另外一种观点认为,胚胎形成时就具有极性,具备了分化发育的特异性,随着不断卵裂、细胞质的分离,这种发育差异表现得更加明显。近年的研究多倾向于第二种观点,认为卵裂的顺序及方位,对着床前胚胎的极性发育有影响。     

Photoinhibition of photosynthesis represents a mechanism for the long-term regulation of photosystem II

The obligate shade plant, Tradescantia albiflora Kunth grown at 50 mol photons · m^–2 s^–1 and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 mol · m^–2 · s^–1, were exposed to photoinhibitory light conditions of 1700 mol · m^–2 · s^–1 for 4 h at 22° C. Photosynthesis was assayed by measurement of CO₂-saturated O₂ evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 mol · m^–2 · s^–1 was most resistant, with pea grown at 50 mol · m^–2 · s^–1 showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (q_p) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F_vF_m, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81–92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F_vF_m, since q_p at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid pH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to q_p, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.Abbreviations F_o and F_o minimal fluorescence when all PSII reaction centres are open in darkness and steady-state light, respectively - F_m and F_m maximal fluorescence when all PSII reaction centres are closed in darkand light-acclimated leaves, respectively - F_v variable fluorescence - (F_m-F_o) under steady-state light con-ditions - F_s steady-state fluorescence in light - Q_A the primary,stable quinone acceptor of PSII - q_Ne non-photochemical quench-ing of fluorescence due to high energy state - (pH); q_Ni non-photochemical quenching of fluorescence due to photoinhibition - q_p photochemical quenching of fluorescence To whom correspondence should be addressedThis work was supported by the Swedish Natural Science Research Council (G.Ö.) and the award of a National Research Fellowship to J.M.A and W.S.C. We thank Dr. Paul Kriedemann, Division of Forestry and Forest Products, CSIRO, Canberra, Australia, for helpful discussions.     

Sulfmyoglobin conformational change: A role in the decrease of oxy-myoglobin functionality

This work is focused at understanding the interaction of H₂S with Myoglobin (Mb), in particular the Sulfmyoglobin (SMb) product, whose physiological role is controversial and not well understood. The scattering curves, Guinier, Kratky, Porod and P(r) plots were analyzed for oxy-Mb and oxy-Hemoglobin I (oxyHbI) in the absence and presence of H₂S, using Small and Wide Angle X-ray Scattering (SAXS/WAXS) technique. Three dimensional models were also generated from the SAXS/WAXS data. The results show that SMb formation, produced by oxyMb and H₂S interaction, induces a change in the protein conformation where its envelope has a very small cleft and the protein is more flexible, less rigid and compact. Based on the direct relationship between Mb's structural conformation and its functionality, we suggest that the conformational change observed upon SMb formation plays a contribution to the protein decrease in O₂ affinity and, therefore, on its functionality.     

离心液相色谱法快速分离纯化神经节苷脂

神经节苷脂在脊椎动物的神经组织细胞膜上含量丰富,除有受体的功能外,还有许多其它功能。采用离心液相色谱法,以国产硅胶Ｇ－６０为填料,分离纯化神经节苷脂,取得了满意的效果。经分离后产物的脂结合唾液酸（ＬＢＳＡ）含量,由１４．３％提高到２４．１％。以蛋白质含量为代表的含氮化合物由２２．０％降至９．６％。回收率为９０．２５％。特点是操作简便、周期短、成本低、效果好。优于ｌａｔｒｏｂｅａｄｓ柱层析法。