功能多样性和功能冗余对高寒草甸群落稳定性的影响

功能多样性和功能冗余是影响群落稳定性的重要因素,但它们对稳定性影响的相对强弱尚有争论。通过在青藏高原高寒矮嵩草(Kobresia humilis)草甸为期6a的刈割(不刈割、留茬3cm、留茬1cm)和施肥(施肥、不施肥)控制实验对此进行了探讨。研究结果显示,群落稳定性随着功能多样性和功能冗余的增大而单调增加,但由于功能多样性的变异性大于功能冗余的变异性,功能多样性与物种多样性间的相关性强于功能冗余与物种多样性间的相关性,功能多样性与群落稳定性间的相关性也强于功能冗余与群落稳定性间的相关性,因此,尽管功能冗余产生的保险效应对维持群落稳定性具有促进作用,但功能多样性的互补效应对维持群落稳定性的作用更大。结果表明,功能多样性和功能冗余对群落稳定性的相对影响与其变化程度正相关,功能多样性与群落稳定性的变化具有更紧密的联系,能更好地预测生态系统稳定性的变化。研究为草原生态系统的可持续管理提供了重要启示。     

获得多能性干细胞的方法

胚胎干细胞系的获得为细胞和器官损伤及病变的治疗提供了新的途径,但是治疗用细胞和受体病人之间免疫不相容问题妨碍了干细胞临床应用.近年来对分化细胞重编程研究使研究人员可以获得多能性干细胞,这为解决这一难题带来了新的希望.对获得多能性干细胞所涉及的机制以及方法进行了综述.     

乳脂球表皮生长因子8在心血管系统疾病中的作用研究进展

乳脂球表皮生长因子8(milk fat globule-epidermal growth factor 8,MFG-E8)是一种由巨噬细胞、树突状细胞、成纤维细胞等多种细胞分泌的蛋白.MFG-E8在凋亡细胞和吞噬细胞之间发挥桥接作用,增强吞噬细胞的吞噬功能,促进组织中死亡细胞的清除,从而影响各种疾病的进展.近年来的研究...     

治疗性克隆研究进展

核移植来源的胚胎干细胞 (ES) 细胞在动物疾病模型上的成功治疗作用以及核移植来源的患者特异的ES细胞研究进展有望将这一技术即治疗性克隆应用于人类疾病治疗.本文对治疗性克隆的研究进展、治疗性克隆研究中存在的问题以及治疗性克隆的应用前景作一综述和讨论.     

吞噬凋亡细胞的机制

被吞噬细胞吞噬是多数凋亡细胞的命运.凋亡细胞表面膜磷脂酰丝氨酸的暴露、膜碳水化合物的改变及表面糖蛋白的重新分布和聚集导致被吞噬细胞识别与摄取.吞噬细胞的多种受体参与吞噬过程,有些受体参与栓系凋亡细胞,有些激发巨吞饮的摄取机制.吞噬的摄取过程因吞噬细胞和凋亡细胞的类型差异而不同.至少有7种线虫吞噬基因及其哺乳动物同源物组成两条部分重叠而又平行的摄取信息传导通路.吞噬基因的突变可以改变凋亡细胞的进程.吞噬功能的缺陷将影响机体正常的免疫应答.     

细胞信号网络功能鲁棒的简并性拓扑特征

细胞信号网络对于外界环境的干扰表现出优良的鲁棒性,但是其维持功能鲁棒的内在机制尚未明确,本文研究了细胞信号网络功能鲁棒性的拓扑特征。选择布尔网络模型模拟细胞网络的动态行为,利用网络节点状态的扰动模拟外界环境干扰。基于演化策略探寻不同网络拓扑的功能并分析其在干扰环境下的鲁棒性,采用埃德尔曼提出的基于信息论的计算方法评估网络拓扑的简并度、冗余度和复杂度等拓扑属性,对比分析它们与功能鲁棒度的相关性及作用机理。结果显示,在网络模型的演化过程中,其拓扑简并度与功能鲁棒度显著正相关,相关性水平高于拓扑冗余度与鲁棒度的相关性。并且,随着鲁棒度的提升,网络的节点数和复杂度也随之升高,同样简并度与网络的节点数和复杂度的相关性高于拓扑冗余度与网络的节点数和复杂度的相关性。这说明增加的网络节点以简并的方式同时提高了网络拓扑的鲁棒度和复杂度。因此,细胞网络功能鲁棒性的拓扑特征是简并而不是冗余,简并为解决生物系统的复杂问题提供了有效手段,为人工系统的可靠性设计提供有益的借鉴。     

Functional diversity and redundancy of subalpine meadows subjected to anthropogenic disturbances

人为干扰下的亚高山草甸功能多样性和功能冗余 人为干扰程度的加剧会引起植物群落物种多样性和功能多样性的改变,并降低生态系统的稳定性。较高水平的功能冗余对于物种损失引起的生态系统功能和稳定性的改变起到了重要的缓冲作用。然而,关于亚高山草甸植物群落功能冗余对干扰的响应的研究相对较少。本研究的目的是,确定人为干扰下不同退化程度的亚高山草甸,其植物群落功能多样性和功能冗余对干扰的响应特征,及不同物种对功能冗余的贡献程度及其在干扰梯度上的变化规律。研究区位于青藏高原东南缘玉龙雪山上的亚高山草甸。本研究识别出4类干扰强度(无干扰、弱干扰、中度干扰和重度干扰),测定了干扰梯度上的植物物种组成、土壤性质和5个关键的植物功能性状等指标,进一步计算了Simpson多样性指数、功能多样性指数(RaoQ)、功能冗余度、群落的植物功能性状加权平均值(CWM)以及物种水平的功能冗余等指数。研究结果表明,功能多样性和功能冗余在干扰梯度上呈现单峰变化规律,即二者分别在中度干扰、弱干扰下达到最大值。物种多样性在干扰梯度上整体呈下降趋势。随着干扰程度的增加,采取保守生长策略并具有相关性状特征(如较低比叶面积和较高的干物质含量)的物种的丰富度降低,采取资源获取策略并具有相关性状(如低矮植株、较高的比叶面积和较低的干物质含量)的物种增加。不同物种的功能冗余程度存在差异。值得注意的是,一些物种在群落中扮演着独特的功能角色,如无干扰梯度下的网脉橐吾(Ligularia dictyoneura)以及中度和重度干扰梯度下的滇西委陵菜(Potentilla delavayi)。     

胚胎干细胞特异性分子标志

胚胎干细胞(embryonic stem cells,ES细胞)特异性分子标志是指ES细胞胞内或胞膜上特异表达的分子.已报道的包括转录因子、信号通路受体、黏附因子在内的ES细胞特异性标志与ES细胞的自我更新和全能性具有密切关系.ES细胞特异性分子标志的研究,有助于ES细胞的鉴定、分离纯化、质量控制,加快ES细胞的基础研究和临床应用.现对目前已经发现的ES细胞特异性分子标志及其研究方法和常用ES细胞分子标志的功能进行综述.     

血液检测中白细胞下降的病因及对飞行学员的影响

白细胞是血液中体具有保护和防御作用的有核血细胞。根据其免疫功能不同分为吞噬细胞和免疫细胞。吞噬细胞具有非特异性的免疫功能,能够吞噬各种异物,包括粒细胞和单核细胞两种。免疫细胞具有特异性的免疫功能,参与体液性和细胞性免疫,即淋巴细胞[1]。虽然白细胞的形态结构和生理功能多样化,但是彼此在机体的防护、免疫和创伤愈治过程中起协同作用,而不是相互孤立。     

新收集燕麦种质的遗传多样性和冗余性鉴定

从青海省4个县收集的60份燕麦样本中鉴别可能的重复材料,为编目和入库保存提供依据。通过名称与来源分析、形态变异性与相似性评价以及分子标记遗传多样性与冗余性鉴定,初步认为这些材料的来源不同,特性明显,遗传多样性丰富,具有一定的保存和利用潜力。但从中也发现同名材料较多,个别材料间遗传相似性较高,存在一定遗传冗余性,并鉴别出可能的重复材料,如白燕麦(1083)与白燕麦(1093)、燕麦(1225)与大燕麦(1226)等。本研究为资源工作者有效鉴别种质收集品中的重复材料、提高保种效率提供参考依据。     

土壤含水量与N2O产生途径研究

土壤含水量变化对N₂O产生和排放影响的研究表明,不同含水量情况下,N₂O排放也不相同。特别是用乙炔抑制技术证明了在播种前后,气候干燥而土壤含水量较低的情况下,N₂O产生主要来自于硝化过程;降雨后,土壤含水量较高时,N₂O主要是通过反硝化过程产生;而在农田中等含水量情况下,土壤微生物的硝化和反硝化作用产生的N₂O大约各占一半。指出旱作农田N₂O产生途径主要取决于土壤水分的控制和调节。     

基因的功能冗余

1　冗余的定义对于特定的一个系统以及该系统的各种组成部件 ,其寿命总是有限的 ,不可避免地会发生故障。为了确保系统的正常运转 ,必须为系统配制一定数量的备用零件 ,即构成所谓的冗余[3 ] 。没有冗余的系统是脆弱的 ,经不起外界随机事件的干扰 ,必须具有足够的冗余 ,它才能维持其结构和功能的正常进行。冗余 (ｒｅｄｕｎｄａｎｃｅ)这一概念来源于自动控制系统可靠性理论[1] 。系统是由不同的元件 (成分 )组成的 ,元件的组合方式与系统的可靠性关系十分密切。按元件组合方式可把系统分为串联系统和并联系统。在串联系统中 ,当系统的元件…     

Repair and regeneration: opportunities for carcinogenesis from tissue stem cells

This review will discuss the mechanisms of repair and regeneration in various tissue types and how dysregulation of these mechanisms may lead to cancer. Normal tissue homeostasis involves a careful balance between cell loss and cell renewal. Stem and progenitor cells perform these biologic processes as the functional units of regeneration during both tissue homeostasis and repair. The concept of tissue stem cells capable of giving rise to all differentiated cells within a given tissue led to the concept of a cellular hierarchy in tissues and in tumors. Thus, only a few cells may be necessary and sufficient for tissue repair or tumor regeneration. This is known as the hierarchical model of tumorigenesis. This report will compare this model with the stochastic model of tumorigenesis. Under normal circumstances, the processes of tissue regeneration or homeostasis are tightly regulated by several morphogen pathways to prevent excessive or inappropriate cell growth. This review presents the recent evidence that dysregulation of these processes may provide opportunities for carcinogenesis for the long-lived, highly proliferative tissue stem cell population. New findings of cancer initiating tissue stem cells identified in several solid and circulating cancers including breast, brain and hematopoietic tumors will also be reviewed. Finally, this report reviews the cellular biology of cancer and its relevance to the development of more effective cancer treatment protocols.     

冗余理论及其在农业生态系统管理中的应用

冗余理论是20世纪90年代发展起来的一个生态学理论.本文扼要介绍了冗余的概念、冗余假说和冗余度的含义,对近年来国内外物种冗余、层次冗余、基因冗余和生长冗余等有关冗余理论和方法的研究进展作了简要回顾和分析.在此基础上,提出了农作物最佳生长冗余度假说：在一定的栽培管理条件下,农作物存在着一个与最高产量相对应的生长冗余度（最佳生长冗余度）,在生产中,如果能通过各种栽培管理措施使农作物的生长冗余度达到最佳值,就能获得高产.用水稻高产栽培实例,对这一假说作了分析和验证.     

The malignant social network: Cell-cell adhesion and communication in cancer stem cells

Tumors contain a vastly complicated cellular network that relies on local communication to execute malignant programs. The molecular cues that are involved in cell-cell adhesion orchestrate large-scale tumor behaviors such as proliferation and invasion. We have recently begun to appreciate that many tumors contain a high degree of cellular heterogeneity and are organized in a cellular hierarchy, with a cancer stem cell (CSC) population identified at the apex in multiple cancer types. CSCs reside in unique microenvironments or niches that are responsible for directing their behavior through cellular interactions between CSCs and stromal cells, generating a malignant social network. Identifying cell-cell adhesion mechanisms in this network has implications for the basic understanding of tumorigenesis and the development of more effective therapies. In this review, we will discuss our current understanding of cell-cell adhesion mechanisms used by CSCs and how these local interactions have global consequences for tumor biology.     

The malignant social network

Tumors contain a vastly complicated cellular network that relies on local communication to execute malignant programs. The molecular cues that are involved in cell-cell adhesion orchestrate large-scale tumor behaviors such as proliferation and invasion. We have recently begun to appreciate that many tumors contain a high degree of cellular heterogeneity and are organized in a cellular hierarchy, with a cancer stem cell (CSC) population identified at the apex in multiple cancer types. CSCs reside in unique microenvironments or niches that are responsible for directing their behavior through cellular interactions between CSCs and stromal cells, generating a malignant social network. Identifying cell-cell adhesion mechanisms in this network has implications for the basic understanding of tumorigenesis and the development of more effective therapies. In this review, we will discuss our current understanding of cell-cell adhesion mechanisms used by CSCs and how these local interactions have global consequences for tumor biology.     

The role of domain redundancy in genetic robustness against null mutations

A key question in molecular genetics is why severe gene mutations often do not result in a detectable abnormal phenotype. Alternative networks are known to be a gene compensation mechanism. Gene redundancy, i.e. the presence of a duplicate gene (or paralog) elsewhere in the genome, also underpins many cases of gene dispensability. Here, we investigated the role of partial duplicate genes on dispensability, where a partial duplicate is defined as a gene that has no paralog but which codes for a protein made of domains, each of which belongs to at least another protein. The rationale behind this investigation is that, as a partial duplicate codes for a domain redundant protein, we hypothesised that its deletion might have a less severe phenotypic effect than the deletion of other genes. This prompted us to (re)address the topic of gene dispensability by focusing on domain redundancy rather than on gene redundancy. Using fitness data of single-gene deletion mutants of Saccharomyces cerevisiae, we will show that domain redundancy is a compensation mechanism, the strength of which is lower than that of gene redundancy. Finally, we shall discuss the molecular basis of this new compensation mechanism.     

干细胞理论及研究进展

干细胞是目前细胞工程研究最活跃的领域,通过对各种干细胞的界定,胚胎干细胞和成体干细胞的比较研究、以及干细胞的技术应用,揭示出干细胞尤其是胚胎干细胞在医学以及整个生命科学中的巨大潜势,乃至于引发医学领域的重大变革。     

More to learn from gene knockouts

Gene targeting by homologous recombination in mouse embryonic stem cells is a powerful technique to determine the physiological function of any gene product in embryonic and postnatal development and in molecular pathogenesis. Although the technique is very demanding and still in its developing stage several knockout mice carrying disrupted genes, which were once thought important for the development or molecular pathogenesis of certain tissues, have given unexpected results. A gene/function redundancy or superfluous and on-functional theory has been advanced by many investigatiors to explain the unexpected results. These surprising results may teach us a new lesson and lead to a revision of the strongly held view that highly conserved and abundantly expressed genes have a prominent role and function in cell physiology and development Additional, they may also support the notion that molecular cross-talk among the genes may play an important role in determining the minimal phenotype.