G四链体结构及其稳态

G四链体(G-quadruplex)是一种由DNA或者RNA构成的非典型核酸二级结构,广泛存在于生物体内,调节基因转录、复制等功能。然而,在生物体中,具有G四链体的核苷酸序列特征的片段并不一定能够形成由Hoogsteen键连接的G四链体结构。多种因素能够调控G四链体结构展开-折叠动态平衡:阳离子能够促进G四链体结构折叠; DNA/RNA解旋酶、转录因子能使G四链体结构展开、分子伴侣可促进G四链体结构折叠;小分子配基能够稳定G四链体结构促进其折叠;互补配对碱基序列、loop区长度也会影响G四链体结构展开-折叠过程。本综述旨在阐述影响G四链体结构展开-折叠动态平衡的因素,并为以后研究G四链体的调控机制和方向提供思路和依据。     

中心体的结构与组装

在动物细胞中,中心体是最主要的微管组织中心,对细胞运动和极性、纤毛生长以及细胞分裂都具有重要作用。该文总结了中心体的结构组成、组装过程,并具体阐述了中心体关键结构的组装等方面的研究进展,为更深入地了解中心体组装的过程及调控机制提供参考。     

水稻叶片硅体与稻壳硅体的物相和光学性质比较

研究了水稻成熟叶片和稻壳中硅体的物相、自发荧光、红外和紫外吸收特性。X-射线衍射结果和显微红外摄谱结果一致表明稻壳硅体结构单一,为典型无定型矿质S iO2。稻壳硅体在紫外激发下没有自发荧光,表明稻壳硅体不含酚类化合物,因此硅体在285 nm处的强烈吸收为稻壳硅体本身所为。叶片硅体结构变异较大,硅体与标准物质无定形硅矿质之间存在细微的差异,并且哑铃形硅体、扇形硅体和不规则硅体的红外吸收光谱也不尽相同,叶片中这3种硅体在紫外激发下都能够自发荧光,表明叶片硅体中含有酚类化合物。硅体混合物仅在290 nm处有微弱的吸收,显示出叶片硅体在结构和性质上的变异性和复杂性。     

DNA四面体纳米结构及其在生物技术领域的应用进展

DNA四面体纳米结构是一种通过精确巧妙的DNA序列设计,应用碱基互补配对的原则,由4条单链自动杂交结合而成的具有四面体形状的DNA三维纳米结构。其具有良好的生物相容性和优异的细胞膜通透性,同时制备较为简单且产率高、尺寸以及动态性均可调节,因而在微生物鉴定、医学诊断和生物传感器等领域得到了广泛的研究与应用。基于此,介绍了DNA四面体纳米结构及其功能化修饰,综述了DNA四面体纳米结构在生物技术领域的应用进展,以期为推动DNA四面体纳米结构的研究、拓宽其应用领域提供参考。     

植物油体研究进展

油体是生物体细胞中一种重要的细胞器结构,由单层磷脂酸膜包裹中性脂肪酸形成,膜上镶嵌有决定油体性质的多种膜蛋白。油体在能量储存、细胞生殖分化、抗病抗寒和发育调控等多种生命活动中起重要作用。该文对植物油体的结构、生物学功能、不同组织中油体的形成情况以及油体膜蛋白的研究进展进行了多方位概述和总结,以期为后续研究提供有益的参考。     

G-四链体DNA结合剂研究进展

富含鸟嘌呤的单链DNA序列可以缠绕折叠形成G-四链体结构。人类基因组中有36,000个以上的DNA序列有潜力生成G-四链体,如端粒末端重复序列,以及c-myc、c-kit、bcl-2等原癌基因启动子区域。G-四链体是由四个鸟嘌呤之间通过Hoogsteen氢键形成G-四分体,相邻的G-四分体再通过π-π堆积作用,由糖-磷酸骨架相连而成。G-四链体DNA的形成有着重要的生物学意义,它和相关基因表达水平密切相关,诱导和稳定G-四链体结构就有可能抑制癌基因的转录和表达,引起肿瘤细胞生物学功能的紊乱,从而抑制肿瘤细胞的增殖。G-四链体结构作为新的抗肿瘤药物靶点引起了科学家的广泛关注,能够稳定G-四链体结构的配体包括二酰胺蒽醌类、苝类、阳离子卟啉类、金属配合物和天然产物等。本文对近年来以G-四链体为靶点的配体的研究进行了综述。     

G- 四链体DNA 结合剂研究进展

富含鸟嘌呤的单链DNA序列可以缠绕折叠形成G- 四链体结构。人类基因组中有36,000 个以上的DNA 序列有潜力生成 G-四链体,如端粒末端重复序列,以及c-myc、c-kit、bcl-2 等原癌基因启动子区域。G-四链体是由四个鸟嘌呤之间通过Hoogsteen 氢键形成G-四分体,相邻的G-四分体再通过π-π 堆积作用,由糖- 磷酸骨架相连而成。G- 四链体DNA 的形成有着重要的生 物学意义,它和相关基因表达水平密切相关,诱导和稳定G- 四链体结构就有可能抑制癌基因的转录和表达,引起肿瘤细胞生物 学功能的紊乱,从而抑制肿瘤细胞的增殖。G-四链体结构作为新的抗肿瘤药物靶点引起了科学家的广泛关注,能够稳定G- 四链 体结构的配体包括二酰胺蒽醌类、苝类、阳离子卟啉类、金属配合物和天然产物等。本文对近年来以G-四链体为靶点的配体的研 究进行了综述。     

甾体激素的调节基因表达作用

由于对甾体激素受体的结构、结构与功能关系及HRE进行了许多研究,人们对甾体激素受体和HRE及多种转录因子相互作用调节基因表达的过程在分子水平上有了更深入的了解,因而对甾体激素调节基因表达的机制有了进一步的认识,本文综述了这方面的研究进展。     

不同G的四链体结构对DNAzyme活性的影响

富含鸟嘌呤的DNA序列在金属离子（通常是钠、钾离子）存在的条件下,可以形成稳定的G-四链体（G-quadruplex）。该G 四链体能够结合hemin（氯高铁血红素）形成具有过氧化物酶的活性的G四链体-hemin复合物DNAzyme。将这一原理联合滚环扩增技术可以对核酸进行可视化的检测。本研究旨在探索G-四链体-hemin复合物中,G-四链体结构以及两个G-四链体之间的链接长度与DNAzyme过氧化物酶活性之间的关系。实验分别选取了平行、反平行和混合结构的G-四链体,通过热差异光谱、紫外光谱、圆二色光谱对结构进行分析,不断加长链接序列并测定3种结构形成的DNAzyme活性,发现正平行结构的G-四链体具有更高的DNAzyme活性和更明显的可视化效果。综上所述,平行G-四链体结构可以用来满足裸眼可视化检测的需求,为无需复杂仪器的核酸检测奠定了方法基础。     

G-四链体结构的检测、功能及调控

G-四链体结构是近年来发现的特殊核酸二级结构,它在体内极易形成,分布十分广泛并且具有重要的生物学功能。研究者们已经在体外检测到G-四链体的存在并解析出其晶体结构,各种检测该结构的方法如特异性荧光探针、抗体等也不断被发现或合成。G-四链体不仅广泛分布于端粒、启动子区、外显子等具有重要功能的基因区域,在5'非编码区(5'UTR)、内含子区、3'非编码区(3'UTR)等也有广泛存在。相应区域的G-四链体参与到端粒延长、DNA复制、转录、减数分裂、基因重组等重要的生命过程,发挥抗肿瘤、抗病毒、抑制血管新生等作用。目前基于G-四链体结构的抗肿瘤药物已经进入临床试验阶段并取得了良好的疗效。G-四链体结构的内源性调节包括多种内源性蛋白以及碱基的甲基化等,维持其含量与结构的平衡状态。此外,外源性小分子也可对体内G-四链体的平衡状态发挥调节作用。本文将从化学、生物和医学的角度对G-四链体结构的检测方法及其特殊功能和调控进行系统的论述和展望。     

THE FINE STRUCTURE OF BLASTOCLADIELLA EMERSONII ZOOSPORES

The zoospore of Blastocladiella emersonii has been re-examined with the electron microscope. The following new findings were made. A double unit-membrane system surrounds all cell organelles except γ-bodies, vacuoles and a few fragments of membranes. Lipid granules on one side of the large mitochondrion alternate with vesicles. The kinetosome of the posterior flagellum does not have any central fibrils as previously reported; a small, cylindrical structure is found within its anterior end. An associated centriole is located next to the kinetosome. Three striated rootlets pass from the kinetosome by separate channels through the mitochondrion. There appears to be no connection between the striated rootlets and the mitochondrion. Microtubules originating at the anterior end of the kinetosome pass into the cytoplasm between the mitochondrion and the nuclear cap. Long, dense strands were observed in some nuclei. The axoneme is taken up into the spore during encystment and is found in the freshly encysted spore. No trace of the flagellar sheath has been found in the encysted spore.     

Coupling membranes as energy-transmitting cables. I. Filamentous mitochondria in fibroblasts and mitochondrial clusters in cardiomyocytes

An hypothesis considering mitochondria as intracellular power-transmitting protonic cables was tested in human fibroblasts where mitochondria are thin and long and in rat cardiomyocytes where they show cluster organization. Mitochondria in the cell were specifically stained with fluorescent-penetrating cation ethylrhodamine, which electrophoretically accumulates in the mitochondrial matrix. A 40-micron-long mitochondrial filament of fibroblast was illuminated by a very narrow (less than or equal to 0.5 micron) laser beam to induce local damage of the mitochondrial membranes. Such a treatment was found to induce quenching of the ethylrhodamine fluorescence in the entire filament. According to the electron microscope examination, the laser-treated filament retained its continuity after the laser illumination. Other mitochondrial filaments (some of which were localized at a distance less than 10 micron from the laser-treated one) remained fluorescent. In a cell where mitochondrial filaments seemed to be united in a network, laser illumination of one filament resulted in fluorescence quenching in the whole network, whereas fluorescence of small mitochondria not connected with the network was unaffected. The illumination of cardiomyocyte was found to result in the fluorescence quenching not only in a laser-illuminated mitochondrion but also in a large cluster of organelles composed of many mitochondria. Electron microscopy showed that all the mitochondria in the cluster change from the orthodox to the condensed state. It was also found that mitochondria in the cluster are connected to one another with specific junctions. If a mitochondrion did not form junctions with a quenched cluster, its fluorescence was not decreased even when this mitochondrion was localized close to an illuminated one. The size of the mitochondrial cluster may be as long as 50 micron. The cluster is formed by branched chains of contacting mitochondria, which may be defined as Streptio mitochondriale. In the cardiomyocyte there are several mitochondrial clusters or, alternatively, the quenched cluster is a result of decomposition of a supercluster uniting all the mitochondria of the cell. Cluster organization of mitochondria could also be revealed when a single mitochondrion was punctured in situ with a microcapillary. The obtained data are in agreement with the idea that mitochondrial junctions are H+ permeable so that, within the cluster, delta psi may be transmitted from one mitochondrion to another. The above results are consistent with the assumption that mitochondrial filaments or networks represent a united electrical system.(ABSTRACT TRUNCATED AT 400 WORDS)     

The tegumental surface of Phyllodistomum conostomum (Olsson, 1876) (Digenea), revealed by scanning electron microscopy

The external surface of P. conostomum is characterized by relatively large ridges encircling the anterior part of the worm at regular intervals. On the posterior part depressions on the ventral side at regular intervals and relatively small ridges on the dorsal side are present. Ventroposteriorally cobblestone-like protuberances observed are arranged in longitudinal rows. No corresponding arrangement was found dorsally. Only domed papillae (with and without a central knob) were observed, tentatively identified as sensory organs. The regular pattern of these papillae on the ventral and oral sucker is described, in addition to their arrangement ventrally and at the anterior end. A frontal pit anterior of oral suckers and a notch at the posterior end are figured and briefly described. No spines were observed on the body tegument.     

Mapping of two ugp genes coding for the pho regulon-dependent sn-glycerol-3-phosphate transport system of Escherichia coli.

Two genes, ugpA and ugpB, coding for a binding protein-dependent sn-glycerol-3-phosphate transport system, were mapped at 75.3 min on the Escherichia coli chromosome. A Tn10 insertion in ugpA resulted in loss of transport activity but still allowed the synthesis of the sn-glycerol-3-phosphate-binding protein. This Tn10 insertion was found to be linked by P1 transduction to pit, aroB, malA, asd, and livH with 2.5, 2.8, 25, 63.5, and 83% cotransduction frequency. An insertion of Mud (Ampr lac) in ugpB resulted in the loss of the binding protein. ugpB is closely linked to ugpA. It is either the structural gene for the binding protein or located proximal to it. The analysis of the crosses allowed the ordering of the markers in the clockwise direction as follows: aroB, malA, asd, ugpA, ugpB, livH, pit.     

Spermiogenesis in Paratomella rubra(Platyhelminthes, Acoela): Ultrastructural, Immunocytochemical, Cytochemical Studies and Phylogenetic Implications

Spermiogenesis and sperm structure of the primitive acoel Paratomella rubra from the Ligurian Sea, Italy, were investigated by several methods. During spermiogenesis, after flagellar incorporation by formation of two longitudinal lateral grooves, spermatid elongation is characterized in Paratomella by the presence of four membranes encircling each axoneme plus two membranes encircling both the axonemes and the nucleus. These structures were interpreted as being three cytoplasmic canals situated one inside the other. The filiform spermatozoon has two incorporated axonemes of 9+2 type, a nucleus almost as long as the sperm cell itself, a single elongate mitochondrion, and two types of membrane-bound granules, respectively, small and gastrula-shaped, and large. Organelles are highly ordered, the sperm is bilaterally symmetrical with a single long mitochondrion on the ventral side and a regular row of large granules, for some length embedded in the nucleus, on the dorsal side. Immunocytochemical studies and the use of fluorescent nuclear dyes reveal the spatial relationships of the axonemes with the nucleus. The granules were shown by Thiéry, PTA and enzyme digestion tests to contain glycoproteins and/or polysaccharides and very little protein. Glycogen particles were detected in the cytoplasm. Cells containing coiled spermatozoa undergoing resorption were found in the parenchyma. New apomorphies of the taxon Paratomella based on sperm structure are proposed: a very long nucleus, a highly bilaterally symmetrical pattern of organelles, a single long mitochondrion. These characters are not found in other Acoela, and particularly in Hesiolicium , sometimes considered closely related to Paratomella . © 1997 Published by Elsevier Science Ltd on behalf of The Royal Swedish Academy of Sciences.     

Surface features, sensory structures, and movement of the newly excysted juvenile Fasciola hepatica L.

Three types of presumed sensory endings were distinguished by scanning electron microscopy: a ciliated type, a domed type, and a pit. The ciliated and domed type were also serially sectioned for transmission electron microscopy. Six of the pit type were observed, a group of 3 on each side of the oral sucker. The ciliated type were found only among the tegumental spines, and on the anterior ventrolateral surfaces except for an anterodorsal pair. The domed type resembled the ciliated type in that it had a ciliary basal body and rootlet but it lacked a cilium. It was found only in the tegument above the suckers where it probably serves as a pressure or contact receptor. Movement in vitro occurred by alternate attachment and release of the suckers with a vermiform peristalsis and the rings of spines between the suckers were considered to aid this movement in vivo.     

Fertilization induced changes in sea urchin sperm: mitochondrial deformation and phosphatidylserine exposure

This study demonstrates that the single mitochondrion of the sea urchin sperm undergoes a shape change at fertilization that is linked to respiration. The mitochondrion swells and shifts to the lateral side of the sperm head on contact with the homologous egg jelly or egg surface; Mg(2+)- or Na(+)-free seawater or respiratory inhibitors also induce this change. During the mitochondrial deformation, the sperm decreases the rate of oxygen consumption and their redox-state of cytochromes is disrupted b-c(1)/c. Simultaneously, the adenine nucleotides content changes precipitously. This suggests that mitochondrial morphology is strongly associated with respiratory activities in the sea urchin sperm. These changes in mitochondrial morphology and function are similar to the mitochondrial changes in apoptotic cells such as swelling, decrease in its membrane potential, and release of cytochrome c. In apoptotic cells, the exposure of phosphatidylserine from the inner to outer leaflet of the plasma membrane is one of prominence phenomena. This change was visualized by staining the sea urchin sperm with Annexin V-Fluorescein. It is possible that mitochondrial deformation is an initial sign of sperm destruction, which like as apoptotic cells.     

Enzymes for heme biosynthesis are found in both the mitochondrion and plastid of the malaria parasite Plasmodium falciparum

All eight enzymes required for de novo heme biosynthesis have been predicted from the nuclear genome of the human malaria parasite Plasmodium falciparum. We have studied the subcellular localization of three of these using a GFP reporter in live transfected parasites. The first enzyme in the pathway d-aminolevulinic acid synthase (ALAS) is targeted to the mitochondrion, but the next two enzymes porphobilinogen synthase (PBGS) and hydroxymethylbilane synthase (HMBS) are targeted to the plastid. An enzymatically active recombinant version of PBGS from P. falciparum was over-expressed and its activity found to be stimulated by Mg²⁺(and enhanced by Mn²⁺) but not by Zn²⁺. A hypothetical scheme for the exchange of intermediates in heme biosynthesis between the mitochondrion and plastid organelle, as well as organelle attachment is discussed.     

Re-examination of the spermatozol ultrastructure of eels: observations of the external morphology of spermatozoa in three species

The nuleus of the spermatozoa in both Anguilla anguilla and A. japonica species is asymmetric on the longitudinal axis, being gently curved and elongated with a hook-shaped superior end directed inside the crescent. A single spherical mitochondrion is located at the superoanterior portion of the nucleus. Nine striae extending from the basal portion of the flagellum run along the right side of nuclear surface. These are always oriented toward the mitochondrial portion and their ends are located on the mitochondrion. These features are seen not only in both Anguilla species but also in Muraenesox cinereus and in other species including other genera of Anguilliformes. It is suggested that these features be considered as common to Anguilliformes.