WAVE2 is required for directed cell migration and cardiovascular development

WAVE2, a protein related to Wiskott-Aldrich syndrome protein, is crucial for Rac-induced membrane ruffling, which is important in cell motility. Cell movement is essential for morphogenesis, but it is unclear how cell movement is regulated or related to morphogenesis. Here we show the physiological functions of WAVE2 by disruption of the WAVE2 gene in mice. WAVE2 was expressed predominantly in vascular endothelial cells during embryogenesis. WAVE2-/- embryos showed haemorrhages and died at about embryonic day 10. Deficiency in WAVE2 had no significant effect on vasculogenesis, but it decreased sprouting and branching of endothelial cells from existing vessels during angiogenesis. In WAVE2-/- endothelial cells, cell polarity formed in response to vascular endothelial growth factor, but the formation of lamellipodia at leading edges and capillaries was severely impaired. These findings indicate that WAVE2-regulated actin reorganization might be required for proper cell movement and that a lack of functional WAVE2 impairs angiogenesis in vivo.     

Impairment of angiogenesis and cell migration by targeted aquaporin-1 gene disruption

Aquaporin-1 (AQP1) is a water channel protein expressed widely in vascular endothelia, where it increases cell membrane water permeability. The role of AQP1 in endothelial cell function is unknown. Here we show remarkably impaired tumour growth in AQP1-null mice after subcutaneous or intracranial tumour cell implantation, with reduced tumour vascularity and extensive necrosis. A new mechanism for the impaired angiogenesis was established from cell culture studies. Although adhesion and proliferation were similar in primary cultures of aortic endothelia from wild-type and from AQP1-null mice, cell migration was greatly impaired in AQP1-deficient cells, with abnormal vessel formation in vitro. Stable transfection of non-endothelial cells with AQP1 or with a structurally different water-selective transporter (AQP4) accelerated cell migration and wound healing in vitro. Motile AQP1-expressing cells had prominent membrane ruffles at the leading edge with polarization of AQP1 protein to lamellipodia, where rapid water fluxes occur. Our findings support a fundamental role of water channels in cell migration, which is central to diverse biological phenomena including angiogenesis, wound healing, tumour spread and organ regeneration.     

Actin microfilament dynamics in locomoting cells

The dynamic behaviour of actin filaments has been directly observed in living, motile cells using fluorescence photoactivation. In goldfish epithelial keratocytes, the actin microfilaments in the lamellipodium remain approximately fixed relative to the substrate as the cell moves over them, regardless of cell speed. The rate of turnover of actin subunits in the lamellipodium is remarkably rapid. Cell movement is directly and tightly coupled to the formation of new actin filaments at the leading edge.     

Reversible stress softening of actin networks

The mechanical properties of cells play an essential role in numerous physiological processes. Organized networks of semiflexible actin filaments determine cell stiffness and transmit force during mechanotransduction, cytokinesis, cell motility and other cellular shape changes. Although numerous actin-binding proteins have been identified that organize networks, the mechanical properties of actin networks with physiological architectures and concentrations have been difficult to measure quantitatively. Studies of mechanical properties in vitro have found that crosslinked networks of actin filaments formed in solution exhibit stress stiffening arising from the entropic elasticity of individual filaments or crosslinkers resisting extension. Here we report reversible stress-softening behaviour in actin networks reconstituted in vitro that suggests a critical role for filaments resisting compression. Using a modified atomic force microscope to probe dendritic actin networks (like those formed in the lamellipodia of motile cells), we observe stress stiffening followed by a regime of reversible stress softening at higher loads. This softening behaviour can be explained by elastic buckling of individual filaments under compression that avoids catastrophic fracture of the network. The observation of both stress stiffening and softening suggests a complex interplay between entropic and enthalpic elasticity in determining the mechanical properties of actin networks.     

Myosin I is located at the leading edges of locomoting Dictyostelium amoebae

Movement of a eukaryotic cell along a substrate occurs by extension of lamellipodia and pseudopodia at the anterior and retraction at the posterior of the cell. The molecular and structural mechanisms of these movements are uncertain. Dictyostelium discoideum contains two forms of myosin. Here we show by immunofluorescence microscopy that non-filamentous myosin I occurs at the leading edges of the lamellipodial projections of migrating Dictyostelium amoebae, which are devoid of myosin II, whereas filamentous myosin II is concentrated in the posterior of the cells. On the basis of these locations of the two forms of myosin and their known biochemical and biophysical properties, we suggest that actomyosin I may contribute to the forces that cause extension at the leading edge of a motile cell, while the contraction of actomyosin II at the rear squeezes the cell mass forward. Myosin I isozymes might have similar roles in metazoan cells, for example at the leading edges of neuronal growth cones, and in the extension of lamellipodia and pseudopodia of leukocytes, macrophages and fibroblasts.     

湿式多片摩擦离合器对偶钢片热机耦合分析

针对湿式多片摩擦离合器对偶钢片会发生翘曲、裂纹等导致动力传递失效的问题,以某船用湿式多片摩擦离合器为研究对象,从摩擦热流生成和分配模型、温度场与耦合应力场的数值计算等方面提出了湿式多片摩擦离合器对偶钢片热机耦合问题的分析方法,揭示了对偶钢片发生热失效的机理。研究结果表明：在接合过程中,对偶钢片温度从内沿向外沿依次递增,在3 s的接合时间中摩擦表面温度在2.6 s达到最高点;热应力分布规律为内沿产生周向拉应力,外沿产生周向压应力,摩擦表面产生径向压应力,内部产生径向拉应力。为解决对偶钢片热失效问题提供了理论依据。     

An unconventional myosin in Drosophila reverses the default handedness in visceral organs

The internal organs of animals often have left-right asymmetry. Although the formation of the anterior-posterior and dorsal-ventral axes in Drosophila is well understood, left-right asymmetry has not been extensively studied. Here we find that the handedness of the embryonic gut and the adult gut and testes is reversed (not randomized) in viable and fertile homozygous Myo31DF mutants. Myo31DF encodes an unconventional myosin, Drosophila MyoIA (also referred to as MyoID in mammals; refs 3, 4), and is the first actin-based motor protein to be implicated in left-right patterning. We find that Myo31DF is required in the hindgut epithelium for normal embryonic handedness. Disruption of actin filaments in the hindgut epithelium randomizes the handedness of the embryonic gut, suggesting that Myo31DF function requires the actin cytoskeleton. Consistent with this, we find that Myo31DF colocalizes with the cytoskeleton. Overexpression of Myo61F, another myosin I (ref. 4), reverses the handedness of the embryonic gut, and its knockdown also causes a left-right patterning defect. These two unconventional myosin I proteins may have antagonistic functions in left-right patterning. We suggest that the actin cytoskeleton and myosin I proteins may be crucial for generating left-right asymmetry in invertebrates.     

Lyn is a redox sensor that mediates leukocyte wound attraction in vivo

Tissue wounding induces the rapid recruitment of leukocytes. Wounds and tumours--a type of 'unhealed wound'--generate hydrogen peroxide (H(2)O(2)) through an NADPH oxidase (NOX). This extracellular H(2)O(2) mediates recruitment of leukocytes, particularly the first responders of innate immunity, neutrophils, to injured tissue. However, the sensor that neutrophils use to detect the redox state at wounds is unknown. Here we identify the Src family kinase (SFK) Lyn as a redox sensor that mediates initial neutrophil recruitment to wounds in zebrafish larvae. Lyn activation in neutrophils is dependent on wound-derived H(2)O(2) after tissue injury, and inhibition of Lyn attenuates neutrophil wound recruitment. Inhibition of SFKs also disrupted H(2)O(2)-mediated chemotaxis of primary human neutrophils. In vitro analysis identified a single cysteine residue, C466, as being responsible for direct oxidation-mediated activation of Lyn. Furthermore, transgenic-tissue-specific reconstitution with wild-type Lyn and a cysteine mutant revealed that Lyn C466 is important for the neutrophil wound response and downstream signalling in vivo. This is the first identification, to our knowledge, of a physiological redox sensor that mediates leukocyte wound attraction in multicellular organisms.     

沙枣(Elaeagnus angustifolia L.)体内、外胚胎发育的比较研究

本文应用经典制片法和离体培养法。对沙枣体内、外胚胎发育的各阶段做比较研究。主要区别于原胚期:1)、形态发生:体内只有一种方式,即两极分化方式。而离体的有二种方式,即器官发生和胚状体发生途径。2)、胚性细胞起源:体内只一种起源(即起源于受精卵),离体的胚性细胞的起源有三种方式:a由紧邻表皮细胞的单个薄壁细胞产生;b由表皮细胞横分裂产生和c由表皮及其下的薄璧细胞共同参与产生。3)胚性细胞的细胞学特征:体内发生的合子具明显的极性分化,细胞质、淀粉粒和细胞核集中在合点端。它第一次分裂后,顶、基细胞在细胞学特征上具明显区别。而离体条件下的胚性细胞第一次分裂后无典型的顶、基细胞之分。故也缺乏典型的胚柄细胞。胚分化和成熟期、二者在形态学特征上基本相同     

Effect of ATP on actin filament stiffness

Actin is an adenine nucleotide-binding protein and an ATPase. The bound adenine nucleotide stabilizes the protein against denaturation and the ATPase activity, although not required for actin polymerization, affects the kinetics of this assembly Here we provide evidence for another effect of adenine nucleotides. We find that actin filaments made from ATP-containing monomers, the ATPase activity of which hydrolyses ATP to ADP following polymerization, are stiff rods, whereas filaments prepared from ADP-monomers are flexible. ATP exchanges with ADP in such filaments and stiffens them. Because both kinds of actin filaments contain mainly ADP, we suggest the alignment of actin monomers in filaments that have bound and hydrolysed ATP traps them conformationally and stores elastic energy. This energy would be available for release by actin-binding proteins that transduce force or sever actin filaments. These data support earlier proposals that actin is not merely a passive cable, but has an active mechanochemical role in cell function.     

基于DSP和图像识别的拉索表面缺陷检测技术

针对国内对拉索表面保护材料层的两种检测方法的不足,搭建以嵌入式DSP为核心处理器,结合CCD、视频解码芯片、SDRAM、FLASH ROM等外围资源的采集和检测系统,提出了一套快速识别拉索表面缺陷的检测识别算法,包括:确定图像区域,改进中值滤波,SOBEL边缘检测和动态阈值分割,形态学闭合运算,缺陷面积计算和存储.实验结果表明该方法实现了桥梁拉索表面缺陷的实时、非接触的智能化检测,并给出了该系统所能达到的指标.该系统结构简单、成本较低、操作简便、具有重要价值.     

烟株不同叶位及接种方式对TMV传播的影响

为进一步弄清烟草普通花叶病毒病的传毒规律.试验以烟草品种K326为材料,连续3a以不同接种方式对健康烟株进行TMV接种试验.结果表明:烟草普通花叶病不通过烟叶气孔传毒,而是通过微伤口、大伤口和叶面与叶面接触渠道传播病毒,而且病毒人口离生长中心越近,病毒传播表现的速度更快,病毒的潜伏期为15～30 d,且在接种30～45d内,烟叶的发病率有一高峰值;烟草普通花叶病毒在烟株的幼嫩叶片上更易传播,症状表现在接种以上的叶片上,带病症的老叶片随着烟株的生长,症状会慢慢消失;在20～35℃的范围内,高温高湿有利于病毒的侵染和症状的表现.杜绝烟草幼嫩叶片摩擦伤口和TMV接触,是防治烟株上TMV传播的有效途径.     

比较烫伤和烧伤致小型猪皮肤深二度损伤的异同

目的研究五指山小型猪的深二度皮肤损伤模型的制备方法,并比较烫伤和烧伤两种不同途径所致五指山小型猪的深二度皮肤损伤存在的差异。方法使用烫伤仪于92℃下,持续接触12 s在五指山小型猪皮肤上烫伤8个创面,同时使用含有无水乙醇的4 cm×5 cm纱布贴敷在去毛位置,点火燃烧18 s,烧伤8个创面,计算创面愈合率并进行病理检测,比较两种造模方法对深二度皮肤烧伤的异同。结果观察烧烫伤部位在临床观察、愈合率和病理检查方面的动态变化过程。结论实验结果表明烫伤法和烧伤法均可在五指山小型猪皮肤上制备深二度烧烫伤动物模型。     

Spatial control of actin organization at adherens junctions by a synaptotagmin-like protein Btsz

Epithelial tissues maintain a robust architecture during development. This fundamental property relies on intercellular adhesion through the formation of adherens junctions containing E-cadherin molecules. Localization of E-cadherin is stabilized through a pathway involving the recruitment of actin filaments by E-cadherin. Here we identify an additional pathway that organizes actin filaments in the apical junctional region (AJR) where adherens junctions form in embryonic epithelia. This pathway is controlled by Bitesize (Btsz), a synaptotagmin-like protein that is recruited in the AJR independently of E-cadherin and is required for epithelial stability in Drosophila embryos. On loss of btsz, E-cadherin is recruited normally to the AJR, but is not stabilized properly and actin filaments fail to form a stable continuous network. In the absence of E-cadherin, actin filaments are stable for a longer time than they are in btsz mutants. We identify two polarized cues that localize Btsz: phosphatidylinositol (4,5)-bisphosphate, to which Btsz binds; and Par-3. We show that Btsz binds to the Ezrin-Radixin-Moesin protein Moesin, an F-actin-binding protein that is localized apically and is recruited in the AJR in a btsz-dependent manner. Expression of a dominant-negative form of Ezrin that does not bind F-actin phenocopies the loss of btsz. Thus, our data indicate that, through their interaction, Btsz and Moesin may mediate the proper organization of actin in a local domain, which in turn stabilizes E-cadherin. These results provide a mechanism for the spatial order of actin organization underlying junction stabilization in primary embryonic epithelia.     

Reconstitution of actin-based motility of Listeria and Shigella using pure proteins.

Actin polymerization is essential for cell locomotion and is thought to generate the force responsible for cellular protrusions. The Arp2/3 complex is required to stimulate actin assembly at the leading edge in response to signalling. The bacteria Listeria and Shigella bypass the signalling pathway and harness the Arp2/3 complex to induce actin assembly and to propel themselves in living cells. However, the Arp2/3 complex alone is insufficient to promote movement. Here we have used pure components of the actin cytoskeleton to reconstitute sustained movement in Listeria and Shigella in vitro. Actin-based propulsion is driven by the free energy released by ATP hydrolysis linked to actin polymerization, and does not require myosin. In addition to actin and activated Arp2/3 complex, actin depolymerizing factor (ADF, or cofilin) and capping protein are also required for motility as they maintain a high steady-state level of G-actin, which controls the rate of unidirectional growth of actin filaments at the surface of the bacterium. The movement is more effective when profilin, alpha-actinin and VASP (for Listeria) are also included. These results have implications for our understanding of the mechanism of actin-based motility in cells.     

Cell type-specific activation of actin genes in the early amphibian embryo

Muscle actin genes are the earliest yet described to show cell type-specific activation in amphibian embryos. Gene-specific probes show that alpha-skeletal and alpha-cardiac actin genes start to be transcribed simultaneously at the end of gastrulation, but only in those regions of the mesoderm that subsequently form embryonic muscle. Their expression provides a molecular marker for early cell determination.     

杂草稻的分类地位和利用途径探讨

对海南岛杂草稻和亚洲栽培稻及其近缘野生种的形态特征和生长习性作了对比观察,表明杂草稻虽然易落粒和种子休眠性较强,但它们与伴生的栽培稻如蕊稻（深水稻）在外部形态和叶表皮微形态等上很相似．结合前人研究结果,探讨了杂草稻的来源,指出杂草稻应归入栽培稻籼粳二亚种,作为变种,同时,观察到杂草稻与杂交稻Ｆ１等一样,在叶片远轴面脉间两气孔带之间的几行长细胞中零星分布较多气孔,简称“中气孔”,指出这种异常现象可作为杂合程度的量化指标之一,在选育杂种性品种中有应用价值,杂草稻的杂种性繁殖机制和特异基因值得鉴定、研究和利用．     

钢丝绳安全诊断与应用

根据可靠性理论 ,对矿用钢丝绳由于断丝而影响其使用寿命的计算方法进行了数学建模 ,得出了钢丝绳安全诊断的计算公式。经试验证明 ,该计算方法具有一定的可靠性     

随机荷载下索梁结构拉索参数振动分析

采用拉索参数振动和索-梁-塔相互振动的有限元方法,以1993年Fujino进行的索梁结构试验模型为对象,进行随机荷载下拉索参数振动计算和分析.结果表明,当随机荷载强度达到一定水平时拉索发生参数振动,横向振动位移远高于主梁位移;三自由度的理论解析法只适用于主梁竖向一阶频率与拉索横向一阶频率之比为2∶1的索梁结构,对于主梁竖向二阶频率与拉索横向一阶频率之比为2∶1的索梁结构,该方法求得的主梁竖向位移偏小.     

Wnt-dependent de novo hair follicle regeneration in adult mouse skin after wounding

The mammalian hair follicle is a complex 'mini-organ' thought to form only during development; loss of an adult follicle is considered permanent. However, the possibility that hair follicles develop de novo following wounding was raised in studies on rabbits, mice and even humans fifty years ago. Subsequently, these observations were generally discounted because definitive evidence for follicular neogenesis was not presented. Here we show that, after wounding, hair follicles form de novo in genetically normal adult mice. The regenerated hair follicles establish a stem cell population, express known molecular markers of follicle differentiation, produce a hair shaft and progress through all stages of the hair follicle cycle. Lineage analysis demonstrated that the nascent follicles arise from epithelial cells outside of the hair follicle stem cell niche, suggesting that epidermal cells in the wound assume a hair follicle stem cell phenotype. Inhibition of Wnt signalling after re-epithelialization completely abrogates this wounding-induced folliculogenesis, whereas overexpression of Wnt ligand in the epidermis increases the number of regenerated hair follicles. These remarkable regenerative capabilities of the adult support the notion that wounding induces an embryonic phenotype in skin, and that this provides a window for manipulation of hair follicle neogenesis by Wnt proteins. These findings suggest treatments for wounds, hair loss and other degenerative skin disorders.