The morphogenesis of feathers

Feathers are highly ordered, hierarchical branched structures that confer birds with the ability of flight. Discoveries of fossilized dinosaurs in China bearing 'feather-like' structures have prompted interest in the origin and evolution of feathers. However, there is uncertainty about whether the irregularly branched integumentary fibres on dinosaurs such as Sinornithosaurus are truly feathers, and whether an integumentary appendage with a major central shaft and notched edges is a non-avian feather or a proto-feather. Here, we use a developmental approach to analyse molecular mechanisms in feather-branching morphogenesis. We have used the replication-competent avian sarcoma retrovirus to deliver exogenous genes to regenerating flight feather follicles of chickens. We show that the antagonistic balance between noggin and bone morphogenetic protein 4 (BMP4) has a critical role in feather branching, with BMP4 promoting rachis formation and barb fusion, and noggin enhancing rachis and barb branching. Furthermore, we show that sonic hedgehog (Shh) is essential for inducing apoptosis of the marginal plate epithelia, which results in spaces between barbs. Our analyses identify the molecular pathways underlying the topological transformation of feathers from cylindrical epithelia to the hierarchical branched structures, and provide insights on the possible developmental mechanisms in the evolution of feather forms.     

Patterning by controlled cracking

Crack formation drives material failure and is often regarded as a process to be avoided. However, closer examination of cracking phenomena has revealed exquisitely intricate patterns such as spirals, oscillating and branched fracture paths and fractal geometries. Here we demonstrate the controlled initiation, propagation and termination of a variety of channelled crack patterns in a film/substrate system comprising a silicon nitride thin film deposited on a silicon substrate using low-pressure chemical vapour deposition. Micro-notches etched into the silicon substrate concentrated stress for crack initiation, which occurred spontaneously during deposition of the silicon nitride layer. We reproducibly created three distinct crack morphologies--straight, oscillatory and orderly bifurcated (stitchlike)--through careful selection of processing conditions and parameters. We induced direction changes by changing the system parameters, and we terminated propagation at pre-formed multi-step crack stops. We believe that our patterning technique presents new opportunities in nanofabrication and offers a starting point for atomic-scale pattern formation, which would be difficult even with current state-of-the-art nanofabrication methodologies.     

肺的组织发生与调控

概述了肺的组织发生，综述了调控或影响胎肺发育的相关基因或因子。肺的发育起始于从前肠内胚层发育而来的成对肺芽突起，肺芽以分支形态发生和肺特异性细胞分化的遗传预定模式侵入周围的中胚层间充质。内胚层上皮及其周围间充质成分相互作用，保证了肺的正常形态发生。肺的发育与相关基因或因子是否正常表达密切相关，发育基因的表达将顺次影响许多其它基因的表达。同时，胎肺周围环境因素的改变可以影响相关基因的表达，进而影响胎肺的发育。     

基于知识粗糙度的多变量决策树的构建

提出了一种基于粗糙集中知识粗糙度的构建多变量决策树的算法.基本思想是,在选择了核属性作为决策树的根节点后,将选择知识粗糙度最小的那个条件属性作为下一个分枝结点的检验属性.     

A biophysical signature of network affiliation and sensory processing in mitral cells

One defining characteristic of the mammalian brain is its neuronal diversity. For a given region, substructure, layer or even cell type, variability in neuronal morphology and connectivity persists. Although it is well known that such cellular properties vary considerably according to neuronal type, the substantial biophysical diversity of neurons of the same morphological class is typically averaged out and ignored. Here we show that the amplitude of hyperpolarization-evoked sag of membrane potential recorded in olfactory bulb mitral cells is an emergent, homotypic property of local networks and sensory information processing. Simultaneous whole-cell recordings from pairs of cells show that the amount of hyperpolarization-evoked sag potential and current (Ih) is stereotypic for mitral cells belonging to the same glomerular circuit. This is corroborated by a mosaic, glomerulus-based pattern of expression of the HCN2 (hyperpolarization-activated cyclic nucleotide-gated channel 2) subunit of the Ih channel. Furthermore, inter-glomerular differences in both membrane potential sag and HCN2 protein are diminished when sensory input to glomeruli is genetically and globally altered so that only one type of odorant receptor is universally expressed. Population diversity in this intrinsic property therefore reflects differential expression between local mitral cell networks processing distinct odour-related information.     

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.     

Dynamics of Drosophila embryonic patterning network perturbed in space and time using microfluidics

Biochemical networks are perturbed both by fluctuations in environmental conditions and genetic variation. These perturbations must be compensated for, especially when they occur during embryonic pattern formation. Complex chemical reaction networks displaying spatiotemporal dynamics have been controlled and understood by perturbing their environment in space and time. Here, we apply this approach using microfluidics to investigate the robust network in Drosophila melanogaster that compensates for variation in the Bicoid morphogen gradient. We show that the compensation system can counteract the effects of extremely unnatural environmental conditions--a temperature step--in which the anterior and posterior halves of the embryo are developing at different temperatures and thus at different rates. Embryonic patterning was normal under this condition, suggesting that a simple reciprocal gradient system is not the mechanism of compensation. Time-specific reversals of the temperature step narrowed down the critical period for compensation to between 65 and 100 min after onset of embryonic development. The microfluidic technology used here may prove useful to future studies, as it allows spatial and temporal regulation of embryonic development.     

Central inputs mask multiple adult neural networks within a single embryonic network

It is usually assumed that, after construction of basic network architecture in embryos, immature networks undergo progressive maturation to acquire their adult properties. We examine this assumption in the context of the lobster stomatogastric nervous system. In the lobster, the neuronal population that will form this system is at first orgnanized into a single embryonic network that generates a single rhythmic pattern. The system then splits into different functional adult networks controlled by central descending systems; these adult networks produce multiple motor programmes, distinctively different from the single output of the embryonic network. We show here that the single embryonic network can produce multiple adult-like programmes. This occurs after the embryonic network is silenced by removal of central inputs, then pharmacologically stimulated to restore rhythmicity. Furthermore, restoration of the flow of descending information reversed the adult-like pattern to an embryonic pattern. This indicates that the embryonic network possesses the ability to express adult-like network characteristics, but descending information prevents it from doing so. Functional adult networks may therefore not necessarily be derived from progressive ontogenetic changes in networks themselves, but may result from maturation of descending systems that unmask preexisting adult networks in an embryonic system.     

基于多模集成神经网络的蛋白质二级结构预测

为提高蛋白质二级结构预测的精度,提出了一个由5个子网络集成的多模神经网络模型,预测结果由5个子网络综合得到。对于每个子网络采用神经网络分级思想分为二级网络,一级网络采用含进化信息的profile编码蛋白质序列作为输入,二级结构作为输出。二级网络编码一级网络输出结果作为输入,并将蛋白质序列用改进正交编码方式作为另一输入来提高二级网络的预测精度,输出仍为二级结构。采用子网络差异方式进行单独训练,结果表明该方法最终的预测精度达到71.3%,较大提高了蛋白质二级结构的预测精度。     

良结构下推系统的表达能力

良结构下推系统是将状态集和栈字符集都扩展为良拟序的下推系统.研究向量加法系统及其扩展系统与良结构下推系统的关系,证明了多个模型可归约到良结构下推系统.通过树的后序遍历构造了分支向量加法系统到良结构下推系统的编码;通过显式引入栈证明递归向量加法系统是良结构下推系统的一种特例;创新地使用栈深表示向量的一维,来构造一位零测试向量加法系统到良结构下推系统的编码.通过这些编码证明了良结构下推系统的表达能力不低于这些向量加法扩展系统,进一步说明了良结构下推系统的一般性.     

缆系海底观测网远程电能监控系统

为提高缆系海底观测网的用能效率和运行可靠性,根据其物理架构特点设计了远程电能监控系统的总体结构,根据功能将该系统划分为数据采集、负载管理和网络分析三个子系统,说明了子系统的主要功能和相互关系.并研究了该系统的时间同步方案、负载供电优化策略和网络分析算法.通过理论分析,获得了分支单元节点电压向量的加权最小二乘状态估计公式,并基于电切换型分支单元的可控性,提出了海缆接地故障定位的新方法.研究内容可为未来国家海底观测网的设计和运行提供参考.     

Fibronectin requirement in branching morphogenesis

Many organs, including salivary glands, lung and kidney, are formed during embryonic development by epithelial branching. In branching morphogenesis, repetitive epithelial cleft and bud formation create the complex three-dimensional branching structures characteristic of many organs. Although the mechanisms are poorly understood, one might involve the site-specific accumulation of some regulatory protein. Here we show that the extracellular matrix protein fibronectin is essential for cleft formation during the initiation of epithelial branching. Fibronectin messenger RNA and fibrils appeared transiently and focally in forming cleft regions of submandibular salivary-gland epithelia, accompanied by an adjacent loss of cadherin localization. Decreasing the fibronectin concentration by using small interfering RNA and inhibition by anti-fibronectin or anti-integrin antibodies blocked cleft formation and branching. Exogenous fibronectin accelerated cleft formation and branching. Similar effects of fibronectin suppression and augmentation were observed in developing lung and kidney. Mechanistic studies revealed that fibrillar fibronectin can induce cell-matrix adhesions on cultured human salivary epithelial cells with a local loss of cadherins at cell-cell junctions. Thus, fibronectin expression is required for cleft formation in branching morphogenesis associated with the conversion of cell-cell adhesions to cell-matrix adhesions.     

Polarizing activity and retinoid synthesis in the floor plate of the neural tube

In many developing organisms the establishment of axial polarity and the patterning of cells depend on local signals that derive from restricted regions of the embryo. In vertebrate embryos, the origins of tissue polarity have been examined extensively in the developing limb. The anteroposterior pattern of the chick limb seems to be controlled by a morphogen, possibly retinoic acid, that is enriched in a region of the limb known as the zone of polarizing activity (ZPA). Certain tissues other than the ZPA have also shown polarizing activity experimentally in the chick limb, raising the possibility that signalling molecules involved in pattern formation in different embryonic tissues are conserved. Here we provide evidence that a similar polarizing activity is also present in a restricted region of the developing central nervous system (CNS). We show that a specialized group of neural cells termed the floor plate, but not other regions of the CNS, mimics the ZPA in respecifying the digit pattern in the developing chick limb. In addition, using an in vitro biochemical assay, we show that the floor plate can synthesize retinoic acid and 3,4-didehydroretinol, the precursor of a second morphogenetically active retinoid, 3,4-didehydroretinoic acid. These results show that the floor plate is a local source of a ZPA-like polarizing signal, possibly a retinoid, which may regulate the pattern of cell differentiation in the developing CNS.     

LEO卫星IP网络组播路由算法

为了解决低轨(low earth orbit,LEO)卫星网络中需要快速高效组播路由协议的问题,提出一种新型LEO卫星IP网络组播路由算法。在分析建立LEO卫星网络拓扑模型的基础上,该算法利用LEO卫星网络的自身特点,采用分布式迭代的计算模式,生成基于源端的组播路由树,大幅度地降低了算法的计算复杂度。仿真结果表明:与传统的LEO卫星网络组播路由算法相比,该算法具有较低的计算复杂度,生成的组播路由树具有较小的开销。相比于传统MRA算法,该算法生成的组播树中源点到组播成员节点的平均延时大约为前者的90%。     

LEO卫星IP网络组播路由算法

为了解决低轨(lowearthorbit,LEO)卫星网络中需要快速高效组播路由协议的问题,提出了一种新型LEO卫星IP网络组播路由算法。在分析建立LEO卫星网络拓扑模型的基础上,该算法利用了LEO卫星网络的自身特点,采用分布式迭代的计算模式,生成基于源端的组播路由树,大幅度地降低了算法的计算复杂度。仿真结果表明,和传统的LEO卫星网络组播路由算法相比,该算法具有较低的计算复杂度,生成的组播路由树具有较小的开销。相比于传统MRA算法,该算法生成的组播树中源点到组播成员节点的平均延时大约为前者的90%。     

基于Rough集的决策树算法

针对基于Rough集的经典分类算法值约简算法等不适合大数据集的问题，提出了基于Rough集的决策树算法。采用一个新的选择属性的测度——属性分类粗糙度作为选择属性的启发式，该测度较Rough中刻画属性相关性的测度正区域等更为全面地刻画了属性分类综合贡献能力，并且比信息增益和信息增益率的计算更为简单。采取了一种新的剪枝方法——预剪枝，即在选择属性计算前基于变精度正区域修正属性对数据的初始划分模式，以更有效地消除噪音数据对选择属性和生成叶节点的影响．采取了一种与决策树算法高度融合的简单有效的检测和处理不相容数据的方法，从而使算法对相容和不相容数据都能进行有效处理。对UCI机器学习数据库中几个数据集的挖掘结果表明，该算法生成的决策树较ID3算法小，与用信息增益率作为启发式的决策树算法生成的决策树规模相当。算法生成所有叶节点均满足给定最小置信度和支持度的决策树或分类规则，并易于利用数据库技术实现，适合大数据集。     

Specificities of heparan sulphate proteoglycans in developmental processes

Heparan sulphate proteoglycans are abundant cell-surface molecules that consist of a protein core to which heparan sulphate glycosaminoglycan chains are attached. The functions of these molecules have remained mostly underappreciated by developmental biologists; however, the actions of important signalling molecules, for example Wnt and Hedgehog, depend on them. To understand both the mechanisms by which ligands involved in development interact with their receptors and how morphogens pattern tissues, biologists need to consider the functions of heparan sulphate proteoglycans in signalling and developmental patterning.     

RSOM算法及其应用研究

神经网络以其优越的非线性拟合能力和强大的自组织模式分类能力已被用于许多模式识别问题,并取得了很好结果．但是对于大样本集分类和复杂模式识别问题,大多数常规神经网络在决定网络结构与规模、设计自学习算法和应付庞大的计算量等方面存在诸多困难．为了克服这些困难,在Kohonen自组织映射模型(SOM)的基础上,提出了两种基于类别可分性判据RSOM分类树：非结构自适应的RSOM-Ⅰ分类树与基于奇异值分解方法的结构自适应RSOM-Ⅱ分类树,这两种分类树的每个节点由拓扑有序的自组织映射网络组成．RSOM分类树的优点在于处理大样本集和复杂模式的识别问题时能够自适应地确定网络的结构和规模,最后的数据试验就是很好的佐证．