Cells compete for decapentaplegic survival factor to prevent apoptosis in Drosophila wing development

During the growth of Drosophila imaginal discs a process called 'cell competition' eliminates slow-proliferating but otherwise viable cells. We report here that cell competition requires the function of the brinker (brk) gene, whose expression is normally repressed by Decapentaplegic (Dpp) signalling but is upregulated in slow-growing Minute/+ cells. Excess brk expression activates the c-Jun amino-terminal kinase pathway, which in turn triggers apoptosis in these cells. We propose that slow-proliferating cells upregulate Brk levels owing to a disadvantage in competing for, or in transducing, the Dpp survival signal. This sequence of events might represent a general mechanism by which weaker cells are eliminated from a growing population, and might serve as a method of controlling cell number and optimizing tissue fitness and hence organ function.     

Axon guidance in cultured epithelial fragments of Drosophila wing

Growing axons can be guided by a number of different cues: adhesive substrates, diffusible factors, electrical fields and even factors intrinsic to the neurone itself have all been shown to affect axon orientation and outgrowth in vitro. However, in most intact systems it has proved difficult to test directly the role played by these putative guidance cues. Here, we describe a system, the developing wing of the fruitfly, in which we have tested simultaneously two putative guidance mechanisms, physical constraints to axon growth (channels) and the position of neuronal somata (guideposts), using surgical techniques. We show that pioneer sensory axons can navigate correctly and form their normal stereotyped pattern of axon bundles in wing fragments that apparently lack both physical and neural cues. This technique allows access to the surface along which neuronal pathfinding takes place, making possible a wide range of experimental manipulations on the developing system.     

Posterior-to-anterior transformation in engrailed wing imaginal disks of Drosophila

Segments in the Drosophila adult are divided into clonally distinct anterior and posterior compartments. Mutations at the engrailed locus can affect the pattern of cuticular structures in the posterior compartments of segments, but have no obvious effect on anterior structures; for example, bristles that are normally seen only on the anterior wing margin in wild-type flies can be found on the posterior margin of engrailed wings. These and clonal analysis data led to the hypothesis that engrailed causes a transformation of posterior to anterior identity in the wing cells. Despite some striking examples of this transformation, a common engrailed phenotype is the disruption or elimination of posterior pattern elements, without a clear replacement by anterior structures; this, together with indications that localized cell death can mimic some of the observed posterior-to-anterior transformations, has led some investigators to question the original engrailed hypothesis. Recently, monoclonal antibodies displaying region-specific binding patterns on the wing imaginal disk have been described, and one of these antibodies in particular provides a novel probe for the engrailed phenotype in the larval precursors of the adult wing. Here I compare the antibody binding patterns on engrailed and wild-type wing disks. The results strongly support the notion that engrailed mutations cause a posterior-to-anterior transformation in these cells.     

Dependence of Drosophila wing imaginal disc cytonemes on Decapentaplegic

The anterior/posterior (A/P) and dorsal/ventral (D/V) compartment borders that subdivide the wing imaginal discs of Drosophila third instar larvae are each associated with a developmental organizer. Decapentaplegic (Dpp), a member of the transforming growth factor-beta (TGF-beta) superfamily, embodies the activity of the A/P organizer. It is produced at the A/P organizer and distributes in a gradient of decreasing concentration to regulate target genes, functioning non-autonomously to regulate growth and patterning of both the anterior and posterior compartments. Wingless (Wg) is produced at the D/V organizer and embodies its activity. The mechanisms that distribute Dpp and Wg are not known, but proposed mechanisms include extracellular diffusion, successive transfers between neighbouring cells, vesicle-mediated movement, and direct transfer via cytonemes. Cytonemes are actin-based filopodial extensions that have been found to orient towards the A/P organizer from outlying cells. Here we show that in the wing disc, cytonemes orient towards both the A/P and D/V organizers, and that their presence and orientation correlates with Dpp signalling. We also show that the Dpp receptor, Thickveins (Tkv), is present in punctae that move along cytonemes. These observations are consistent with a role for cytonemes in signal transduction.     

Patterns of dye coupling in the imaginal wing disk of Drosophila melanogaster

Responses of developing tissues to experimental disruption demonstrate that cell interaction is important both in generating positional information and in controlling growth. However, the mechanism by which cells interact and the range over which the interactions are effective are not known. In the imaginal disks of Drosophila melanogaster, experiments on pattern regulation following surgical ablation suggest that the cell interactions are very local in nature; in fact, most of the data can be explained by assuming that cells interact only with their immediate neighbours. In contrast, studies of cell division patterns in the same tissue indicate that the "local' proliferative response to an ablation extends over a distance of up to about eight cell diameters. Still longer-range interactions have been proposed on the basis of theoretical considerations. It is possible that the interactions are mediated by the transfer of small molecules through gap junctions, as gap junctions are abundant in imaginal disks at the appropriate developmental stages. We have explored the range, timing and directionality of dye coupling between the cells of the wing disk as a test of the possible role of gap junctions in imaginal disk patterning. Our results indicate that interactions over different ranges are possible depending on the nature of the molecule being transferred.     

Dynamic control of positional information in the early Drosophila embryo

Morphogen gradients contribute to pattern formation by determining positional information in morphogenetic fields. Interpretation of positional information is thought to rely on direct, concentration-threshold-dependent mechanisms for establishing multiple differential domains of target gene expression. In Drosophila, maternal gradients establish the initial position of boundaries for zygotic gap gene expression, which in turn convey positional information to pair-rule and segment-polarity genes, the latter forming a segmental pre-pattern by the onset of gastrulation. Here we report, on the basis of quantitative gene expression data, substantial anterior shifts in the position of gap domains after their initial establishment. Using a data-driven mathematical modelling approach, we show that these shifts are based on a regulatory mechanism that relies on asymmetric gap-gap cross-repression and does not require the diffusion of gap proteins. Our analysis implies that the threshold-dependent interpretation of maternal morphogen concentration is not sufficient to determine shifting gap domain boundary positions, and suggests that establishing and interpreting positional information are not independent processes in the Drosophila blastoderm.     

对会计信息失真原因及治理对策的探讨

真实是会计信息的生命,而会计信息失真问题即屡禁不止,时时困扰人们,严重制约了国民经济的健康发展,产生这一顽疾的原因何在？作者从会计法制,会计管理体制以及知识经济对会计理论和实务的冲击与挑战等几方面进行了分析,并探究了治理会计信息真的对策。     

高校图书馆网络信息安全根源探讨

文章提出了高校图书馆网络管理与技术并重的安全策略,从技术和管理两方面对构建图书馆网络系统的安全体系作了初步论述.并提出一种安全防护体系,这样才能充分发挥高校图书馆的功能.     

高校图书馆网络信息安全根源探讨

文章提出了高校图书馆网络管理与技术并重的安全策略,从技术和管理两方面对构建图书馆网络系统的安全体系作了初步论述.并提出一种安全防护体系,这样才能充分发挥高校图书馆的功能.     

高校图书馆网络信息安全根源探讨

文章提出了高校图书馆网络管理与技术并重的安全策略,从技术和管理两方面对构建图书馆网络系统的安全体系作了初步论述。并提出一种安全防护体系,这样才能充分发挥高校图书馆的功能。     

硫酸铈诱导果蝇氧化应激及细胞凋亡的研究

本实验主要研究了稀土硫酸铈（Ce（SO4）2）对果蝇氧化应激生物标记物和细胞凋亡的影响.果蝇培养在不同质量浓度（1,4,16,64,256,1 024 mg/L）的硫酸铈培养基中,分别测定其SOD,CAT和脂质过氧化产物（即MDA含量）,同时用彗星电泳和体外切割DNA实验来检测果蝇细胞中DNA损伤程度,用DNA Laddering法和TUNEL法测定稀土元素Ce对果蝇细胞凋亡的影响.与对照组相比,当Ce（SO4）2质量浓度低于16 mg/L时,果蝇体内SOD和CAT活性显著增加,MDA含量变化不明显;而当Ce（SO4）2质量浓度高于16 mg/L时,SOD和CAT活性明显下降,MDA含量上升.彗星电泳的结果表现为随着硫酸铈剂量的递增,果蝇中肠细胞的彗星率、彗星尾长和Olive尾矩增加,并表现为明显的剂量效应关系.果蝇体外实验结果表明,硫酸铈能打断DNA,使其片段化;同时,TUNEL结果显示果蝇中肠细胞呈现凋亡细胞的特征性蓝绿色颗粒,但DNA琼脂糖电泳没有表现出细胞凋亡特征性的梯形条带图谱.硫酸铈诱导果蝇的氧化应激可以使果蝇中肠细胞SOD和CAT活性降低,MDA含量上升,使中肠细胞出现凋亡特征.由此推断,硫酸铈可诱导果蝇细胞中遗传物质的损伤,对果蝇有一定的氧化毒性和遗传毒性作用．     

昆翅在飞行中的动态形变

通过理论模化途径研究昆翅在飞行中的动态形变机制.设计翅气动力试验平台,验证翅准静态形变影响气动力的"柔性楔形效应"理论解释.探讨昆翅的变刚度特性表明,弦向刚度分布规律符合二项式函数时具有优越性和现实性,进而指出昆姻结构的变刚度特性是产生高升力的基本条件.建立了柔性翅的简化力学模型,通过坐标变换法求解在气动力和惯性力共同...     

Directional non-cell autonomy and the transmission of polarity information by the frizzled gene of Drosophila

The function of the frizzled (fz) locus is required for the development of a parallel array of bristles and hairs on the adult cuticle of Drosophila melanogaster. Marked fz mitotic clones from five alleles were generated and examined in the wing. Three alleles have a non-cell-autonomous hair polarity phenotype; wild-type cells distal to fz clones produce hairs that have an abnormal polarity. In contrast, fz clones of the other two fz alleles examined do not disrupt the polarity of neighbouring cells. These data suggest that fz has two mutably separate functions in establishing hair polarity on the wing. One function involves the transmittance and/or generation of a polarity signal along the proximal-distal axis of the wing. The second function involves the cellular interpretation of a polarity signal.     

Circadian rhythms in olfactory responses of Drosophila melanogaster.

The core mechanism of circadian timekeeping in arthropods and vertebrates consists of feedback loops involving several clock genes, including period (per) and timeless (tim). In the fruitfly Drosophila, circadian oscillations in per expression occur in chemosensory cells of the antennae, even when the antennae are excised and maintained in isolated organ culture. Here we demonstrate a robust circadian rhythm in Drosophila in electrophysiological responses to two classes of olfactory stimuli. These rhythms are observed in wild-type flies during light-dark cycles and in constant darkness, but are abolished in per or tim null-mutant flies (per01 and tim01) which lack rhythms in adult emergence and locomotor behaviour. Olfactory rhythms are also abolished in the per 7.2:2 transgenic line in which per expression is restricted to the lateral neurons of the optic lobe. Because per 7.2:2 flies do not express per in peripheral oscillators, our results provide evidence that peripheral circadian oscillators are necessary for circadian rhythms in olfactory responses. As olfaction is essential for food acquisition, social interactions and predator avoidance in many animals, circadian regulation of olfactory systems could have profound effects on the behaviour of organisms that rely on this sensory modality.     

γ相机平面成像的空间畸变校正

介绍了一种通过软件对γ相机的空间非线性畸变进行实时校正的方法.考虑到在非常小的平面内,图像的空间畸变可看成是图像的几何线性变化.产生一些校正单元,用某一校正单元对位于该校正单元的γ事件进行线性校正.各校正单元的变换参数通过最小均方差和三次样条插值来确定.     

GPS在工程变形监测中的应用

与传统的工程变形监测方法相比,GPS测量技术在连续性、实时性和自动化程度等方面有明显的优势.在分析了GPS在变形监测方面的特点的基础上,探讨了GPS在大坝、地面沉降、高层建筑物等工程变形观测中的应用.