Wnt signalling regulates adult hippocampal neurogenesis

The generation of new neurons from neural stem cells is restricted to two regions of the adult mammalian central nervous system: the subventricular zone of the lateral ventricle, and the subgranular zone of the hippocampal dentate gyrus. In both regions, signals provided by the microenvironment regulate the maintenance, proliferation and neuronal fate commitment of the local stem cell population. The identity of these signals is largely unknown. Here we show that adult hippocampal stem/progenitor cells (AHPs) express receptors and signalling components for Wnt proteins, which are key regulators of neural stem cell behaviour in embryonic development. We also show that the Wnt/beta-catenin pathway is active and that Wnt3 is expressed in the hippocampal neurogenic niche. Overexpression of Wnt3 is sufficient to increase neurogenesis from AHPs in vitro and in vivo. By contrast, blockade of Wnt signalling reduces neurogenesis from AHPs in vitro and abolishes neurogenesis almost completely in vivo. Our data show that Wnt signalling is a principal regulator of adult hippocampal neurogenesis and provide evidence that Wnt proteins have a role in adult hippocampal function.     

用随机模式和调整机制改进粒子群优化算法

提出一种改进的粒子群优化(particle swarm optimization,PSO)算法,将随机(random)概念与调整(regula-tion)机制导入PSO算法中,既可避免族群搜寻过程中陷入局部最优解,又可提高算法在最优区域局部搜寻的能力。最后用2种复杂程度不同的函数为例,比较了本算法与广被采用的PSO-CF算法的最优化能力。结果显示,算法在搜寻成功率、平均收敛时间及平均收敛代数方面的性能皆优于PSO-CF算法。     

用随机模式和调整机制改进粒子群优化算法

提出一种改进的粒子群优化(particle swarm optimization,PSO)算法,将随机(random)概念与调整(regula-tion)机制导入PSO算法中,既可避免族群搜寻过程中陷入局部最优解,又可提高算法在最优区域局部搜寻的能力.最后用2种复杂程度不同的函数为例,比较了本算法与广被采用的PSO-CF算法的最优化能力.结果显示,算法在搜寻成功率、平均收敛时间及平均收敛代数方面的性能皆优于PSO-CF算法.     

Myosin subfragment-1 is sufficient to move actin filaments in vitro

The rotating crossbridge model for muscle contraction proposes that force is produced by a change in angle of the crossbridge between the overlapping thick and thin filaments. Myosin, the major component of the thick filament, is comprised of two heavy chains and two pairs of light chains. Together they form two globular heads, which give rise to the crossbridge in muscle, and a coiled-coil rod, which forms the shaft of the thick filament. The isolated head fragment, subfragment-1 (S1), contains the ATPase and actin-binding activities of myosin (Fig. 1). Although S1 seems to have the requisite enzymatic activity, direct evidence that S1 is sufficient to drive actin movement has been lacking. It has long been recognized that in vitro movement assays are an important approach for identifying the elements in muscle responsible for force generation. Hynes et al. showed that beads coated with heavy meromyosin (HMM), a soluble proteolytic fragment of myosin consisting of a part of the rod and the two heads, can move on Nitella actin filaments. Using the myosin-coated surface assay of Kron and Spudich, Harada et al. showed that single-headed myosin filaments bound to glass support movement of actin at nearly the same speed as intact myosin filaments. These studies show that the terminal portion of the rod and the two-headed nature of myosin are not required for movement. To restrict the region responsible for movement further, we have modified the myosin-coated surface assay by replacing the glass surface with a nitrocellulose film. Here we report that myosin filaments, soluble myosin, HMM or S1, when bound to a nitrocellulose film, support actin sliding movement (Fig. 2). That S1 is sufficient to cause sliding movement of actin filaments in vitro gives strong support to models of contraction that place the site of active movement in muscle within the myosin head.     

增加农民收入的关键在于提高农民素质

农民收入问题是关系到我国全面建设社会主义小康社会能否实现的重点和难点问题；我国农民素质的现状，制约了农民收入的增加；要增加农民收入，必须要提高农民素质。     

A signal sequence is not sufficient to lead beta-galactosidase out of the cytoplasm

Escherichia coli strains have been constructed in which lacZ, the gene for the cytoplasmic enzyme beta-galactosidase, is fused to lamB, the gene for an outer membrane protein. One such strain produces a beta-galactosidase which remains cytoplasmic even though it possesses the complete signal sequence of the lamB protein precursor at the amino-terminal end.     

Auxin transport is sufficient to generate a maximum and gradient guiding root growth

The plant growth regulator auxin controls cell identity, cell division and cell expansion. Auxin efflux facilitators (PINs) are associated with auxin maxima in distal regions of both shoots and roots. Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured root layout. In our model, the stable accumulation of auxin in a distal maximum emerges from the auxin flux pattern. We have experimentally tested model predictions of robustness and self-organization. Our model explains pattern formation and morphogenesis at timescales from seconds to weeks, and can be understood by conceptualizing the root as an 'auxin capacitor'. A robust auxin gradient associated with the maximum, in combination with separable roles of auxin in cell division and cell expansion, is able to explain the formation, maintenance and growth of sharply bounded meristematic and elongation zones. Directional permeability and diffusion can fully account for stable auxin maxima and gradients that can instruct morphogenesis.     

The v-myc oncogene is sufficient to induce growth transformation of chick neuroretina cells

A number of studies have shown that full transformation of non-established rodent fibroblasts can be efficiently achieved in vitro by the concerted action of two oncogenes belonging to different complementation groups. Extension of the two-genes carcinogenesis model to other differentiated cell types, presumably endowed with different controls of growth, is desirable for a better understanding of questions such as the host cell selectivity of oncogene action. A recent report claimed that cooperation between two oncogenes, v-myc and v-mil, is required to achieve transformation of chicken embryo neuroretina cells, which are characterized by a limited growth capacity in monolayer culture. Here we present evidence that the v-myc oncogene alone is sufficient to induce growth transformation of glial and neuronal precursor cell types from chick neuroretina. We also report that induction of transformation by v-myc is accompanied by faithful preservation of some of the differentiated functions of the chick cells.     

Synapse elimination in neonatal rat muscle is sensitive to pattern of muscle use

The synaptic connections among the cells of the vertebrate nervous system undergo extensive rearrangements early in development. During their initial growth, neurones apparently form synaptic connections with an excessive number of targets, later retracting a portion of these synapses in establishing the adult neural circuits. Because of the profound effects which experience has upon the developing nervous system, a question of considerable interest has been the role which the functional use of these developing synapses might play in determining the final pattern of connectivity. At the neuromuscular junction the early changes in synaptic connections are well documented, and here questions about the importance of function can be relatively easily addressed. Mammalian skeletal muscle fibres experience a perinatal period of synapse elimination so that all but one of several synapses formed on each muscle fibre are lost. This synapse elimination is sensitive to alterations of neuromuscular use or activity. Reduction of muscle use by tenotomy or by paralysis of the muscle with drugs blocking nerve impulse conduction or neuromuscular transmission delays or even prevents synapse loss, while increased use produced by stimulation of the muscle nerve apparently accelerates the rate at which synapses are lost. I report here a further examination of the role of neuromuscular activity in synapse elimination. I show that chronic neuromuscular stimulation accelerates synapse elimination but that this acceleration is dependent on the temporal pattern in which the stimuli are presented: brief stimulus trains containing 100 Hz bursts of stimuli produce this acceleration whereas the same number of stimuli presented continuously at 1 Hz do not. Furthermore, the 100 Hz activity pattern which is effective in altering synapse elimination also alters two other muscle properties: the sensitivity of the muscle fibers to acetylcholine and the 'speed' of muscle contractions. These findings suggest that the ability of muscle fibres to maintain more than one nerve terminal, like other muscle properties, is sensitive to the pattern of muscle use rather than just the total amount of use.     

创新教学方式是提高“形势与政策”课实效性的必由之路

形势与政策课教学方式单一、陈旧,缺乏案例性、互动性、实践性,特别是没有足够重视网络发展对该课程教学方式的重大影响,成为影响教学效果的重要因素,这已严重影响大学生的学习积极性和课程的实效性,对该课程进行教学方式的改革势在必行,丰富并创新教学方式是提高形势与政策课实效性的必由之路。     

物理思维比物理公式更重要--大学物理教改探索之一

从大学物理的课程特点与教学目的出发,论证在大学物理的教学过程中,创新素质与能力的获取更多的是依赖物理思维,因而在教学过程中努力扭转重理论轻方法与重知识轻能力的倾向,强调物理思维比物理公式更重要．     

提高读者服务水平是图书馆发展的动力--文山师专学生利用图书馆情况调查报告

在调查学生利用图书馆现状的基础上，分析影响学生利用图书馆的因素并提出相应的措施，对图书馆的发展提出了意见和建议。     

A cytosolic catalase is needed to extend adult lifespan in C. elegans daf-C and clk-1 mutants.

The dauer larva is an alternative larval stage in Caenorhabditis elegans which allows animals to survive through periods of low food availability. Well-fed worms live for about three weeks, but dauer larvae can live for at least two months without affecting post-dauer lifespan. Mutations in daf-2 and age-1, which produce a dauer constitutive (Daf-C) phenotype, and in clk-1, which are believed to slow metabolism, markedly increase adult lifespan. Here we show that a ctl-1 mutation reduces adult lifespan in otherwise wild-type animals and eliminates the daf-c and clk-1-mediated extension of adult lifespan. ctl-1 encodes an unusual cytosolic catalase; a second gene, ctl-2, encodes a peroxisomal catalase. ctl-1 messenger RNA is increased in dauer larvae and adults with the daf-c mutations. We suggest that the ctl-1 catalase is needed during periods of starvation, as in the dauer larva, and that its misexpression in daf-c and clk-1 adults extends lifespan. Cytosolic catalase may have evolved to protect nematodes from oxidative damage produced during prolonged dormancy before reproductive maturity, or it may represent a general mechanism for permitting organisms to cope with the metabolic changes that accompany starvation.     

Cu3(BTC)2提高聚二甲基硅氧烷/聚醚酰亚胺复合膜气体分离性能成因的研究

将金属有机骨架化合物Cu₃(BTC)₂填充到聚二甲基硅氧烷中,制备聚二甲基硅氧烷/聚醚酰亚胺改性复合膜,用于气体分离的研究。考察了操作温度和压力对CO₂、CH₄、O₂和N₂在改性复合膜中的渗透系数、扩散系数、溶解度系数和分离系数的影响。结果表明,填充Cu₃(BTC)₂可降低气体的渗透活化能、扩散活化能和膜的压缩效应,进而提高气体的扩散性能和渗透性能;Cu₃(BTC)₂改性复合膜在低温条件下可得到较高的渗透性能和分离性能,较高压力可在不降低膜分离性能的基础上提高其渗透性能。     

GCC box in<Emphasis Type="Italic">Arabidopsis PDF1.2</Emphasis> promoter is an essential and sufficient cis-acting element in response to MeJA treatment

The expression of Arabidopsis PDF1.2 gene isregulated by jasmonic acid (JA) and ethylene (ET). It also has been well documented that GCC box is an element responsive to ET, however, the responsive mechanism of JA in such plant defense gene expression is unclear. In this paper, the authors define the essential cis-acting element in PDF1.2 promoter responsive to methyl jasmonate (MeJA) through fragment deletions and site-directed mutageneses combiningAgrobacterium-mediated transient reporter gene expression in tobacco leaves. Firstly, the MeJA inducible expression o fPDF1.2 was confirmed by using the upstream -1.86 kb fragment of PDFI.2 gene. Secondly, the upstream -300— -243 bp fragment of the promoter was evidenced to respond to MeJA. To further characterize this promoter region, three point mutations were introduced into the -300— -243 bp fragment of the promoter. This result showed that the mutation of GCC box abolished MeJA induction, whereas the mutations of the G box-like and the imperfect palindrome sequence did not significantly decrease MeJA inducible effect, indicating that GCC box in PDFI.2 is essential for MeJA induction. The sufficient responsiveness to MeJA of this GCC box was further investigated by 4xGCC fused upstream to the CaMV 35S minimal promoter. This result suggested that the fused promoter was able to activate reporter gene expression in response to MeJA. Thus these results indicate that the GCC box in PDFI.2 is an essential and sufficient element to confer MeJA induction.