Mitotic apparatus: the selective extraction of protein with mild acid

The treatment of isolated mitotic apparatus with mild (pH 3) hydrochloric acid results in the extraction of less than 10 percent of its protein, accompanied by the selective morphological disappearance of the microtubules. The same extraction can be shown to dissolve outer doublet microtubules from sperm flagella. A protein with points of similarity to the flagellar microtubule protein is the major component of the extract from mitotic apparatus.     

The molecular architecture of axonemes revealed by cryoelectron tomography

Eukaryotic flagella and cilia are built on a 9 + 2 array of microtubules plus >250 accessory proteins, forming a biological machine called the axoneme. Here we describe the three-dimensional structure of rapidly frozen axonemes from Chlamydomonas and sea urchin sperm, using cryoelectron tomography and image processing to focus on the motor enzyme dynein. Our images suggest a model for the way dynein generates force to slide microtubules. They also reveal two dynein linkers that may provide "hard-wiring" to coordinate motor enzyme action, both circumferentially and along the axoneme. Periodic densities were also observed inside doublet microtubules; these may contribute to doublet stability.     

Flagellar movement: a sliding filament model

A sliding filament mechanism appears to provide the most satisfactory basis for a simple feedback mechanism for the control of bend propagation and bend initiation by flagella, and is supported by strong experimental evidence. A computer simulation of the movements of a flagellar model based on the sliding filament mechanism demonstrates that this mechanism offers a sufficient explanation for the automatic generation of flagellar bending waves. Further computer simulation studies may provide insight into questions such as the applicability of the sliding filament mechanism to the generation of the more complicated asymmetrical bending patterns of cilia, and the control of the bending pattern by interaction between several sliding filament systems within a flagellum.     

Cilia-like beating of active microtubule bundles

The mechanism that drives the regular beating of individual cilia and flagella, as well as dense ciliary fields, remains unclear. We describe a minimal model system, composed of microtubules and molecular motors, which self-assemble into active bundles exhibiting beating patterns reminiscent of those found in eukaryotic cilia and flagella. These observations suggest that hundreds of molecular motors, acting within an elastic microtubule bundle, spontaneously synchronize their activity to generate large-scale oscillations. Furthermore, we also demonstrate that densely packed, actively bending bundles spontaneously synchronize their beating patterns to produce collective behavior similar to metachronal waves observed in ciliary fields. The simple in vitro system described here could provide insights into beating of isolated eukaryotic cilia and flagella, as well as their synchronization in dense ciliary fields.     

Substructure of certain cytoplasmic microtubules: an electron microscopic study

egatively stained cytoplasmic microtubules of lung-fluke sperm show a helical structure that is not found in peripheral doublet tubules of axial units. In transverse sections, the wall of such microtubules appears to comprise about eight subunits.     

The kinesin Klp2 mediates polarization of interphase microtubules in fission yeast

Fission yeast (Schizosaccharomyces pombe) cells grow longitudinally in a manner dependent on a polarized distribution of their interphase microtubules. We found that this distribution required sliding of microtubules toward the cell center along preexisting microtubules. This sliding was mediated by the minus end-directed kinesin motor Klp2, which helped microtubules to become properly organized with plus ends predominantly oriented toward the cell ends and minus ends toward the cell center. Thus, interphase microtubules in the fission yeast require motor activities for their proper organization.     

似锥低颈吸虫的精子和精子形成的超微结构研究（复殖目：棘口科）

似锥低颈吸虫（Ｈｙｐｏｄｅｒａｅｕｍｃｏｎｏｉｄｅｕｍ）的成熟精子分为前段和主段。前段含两条鞭毛轴丝和一圈连续纵向排列的膜下微管；主段含两条不等长鞭毛轴丝、核、线粒体、糖原，背侧和腹侧的膜下微管。在精子形成过程中，精子细胞出现胞质突起，核与胞质突起部的质膜之间出现特殊分化区域（ＺＤ）。特殊分化区域的组成包括质膜下一排膜下微管，两个具有横纹小根的中心粒和１个中心粒间体（Ｉｎｔｅｒｃｅｎｔｒｉｏｌａｎｂｏｄｙ）。鞭毛从中心粒伸出，延伸，与中间不断伸长的胞质突起平行，核旋转，拉长，与细长的线粒体前后进入胞质突起，最后鞭毛从近端到远端（Ｐｒｏｘｉｍｉｔｏｄｉｓｔａｌｌｙ）与中间胞质突起融合，并从精子细胞群上脱落，形成成熟精子，遗留下精子细胞群的残体。残体（Ｒｅｓｉｄｕａｌｂｏｄｙ）上含弓形膜结构，线粒体，鞭毛轴丝残余以及电子致密颗粒，在一个残体上，至少有１０个以上的精子断端。     

Microtubules in spermatozoa of childia (turbellaria, acoela) revealed by negative staining

Many intact axial units, with attached basal plates, are found in spermatozoa of Childia groenlandica negatively stained with phosphotungstic acid. Electron micrographs show a total of nine doublet microtubules, confirming observations on sectioned material, where nine peripheral doublets, but no single central ones, occurred. Living spermatozoa move by waves progressing along a double undulating membrane.     

Directional switching of the kinesin Cin8 through motor coupling

Kinesin motor proteins are thought to move exclusively in either one or the other direction along microtubules. Proteins of the kinesin-5 family are tetrameric microtubule cross-linking motors important for cell division and differentiation in various organisms. Kinesin-5 motors are considered to be plus-end-directed. However, here we found that purified kinesin-5 Cin8 from budding yeast could behave as a bidirectional kinesin. On individual microtubules, single Cin8 motors were minus-end-directed motors, whereas they switched to plus-end-directed motility when working in a team of motors sliding antiparallel microtubules apart. This kinesin can thus change directionality of movement depending on whether it acts alone or in an ensemble.     

Tubular packing of spheres in biological fine structure

The symmetrical arrangements of monomers into such cylindrical structures as microfilaments of actin, flagella of bacteria, microtubules of many organisms, and the protein coats of viruses can be specified by citing the index numbers of two or three sets of contact parastichies, or helical ranks of monomers, as has been done in classical studies of phyllotaxis. This specification has the form k(m, n) or k(m, n, m+n), where m, n, and (m+n) are parastichy numbers specifying screw displacements, and k is the jugacy, or frequency of rotational symmetry. For simple structures, k = 1. This notation has the advantage of terseness and of indicating the basic isometries of these helically symmetrical structures. Theoretical models of the packing of spheres whose centers lie on the surface of a cylinder have been investigated geometrically. Their symmetry properties are discussed. Parameters of these models, such as the angular divergence, alpha, the longitudinal displacement between successive spheres, h, the radius of the cylinder, and the angles of inclination of the parastichies, have been computed for representative patterns. The ultrastructural symmetry of several biological structures of this sort has been inferred by comparison with these models. Actin, for example, has the symmetry (1, 2), Salmonella flagella, 2(2, 3, 5), the tobacco mosaic virus, (1, 16, 17) and the microtubules of many higher organisms, (6, 7, 13).     

Structures of SAS-6 suggest its organization in centrioles

Centrioles are cylindrical, ninefold symmetrical structures with peripheral triplet microtubules strictly required to template cilia and flagella. The highly conserved protein SAS-6 constitutes the center of the cartwheel assembly that scaffolds centrioles early in their biogenesis. We determined the x-ray structure of the amino-terminal domain of SAS-6 from zebrafish, and we show that recombinant SAS-6 self-associates in vitro into assemblies that resemble cartwheel centers. Point mutations are consistent with the notion that centriole formation in vivo depends on the interactions that define the self-assemblies observed here. Thus, these interactions are probably essential to the structural organization of cartwheel centers.     

微小泰泽球虫小配子发育的超微结构

采用纯种微小泰泽球虫卵囊,人工感染四日龄雏鹅,定时剖杀,取小肠组织进行超薄切片,在透射电镜下,观察微小泰泽球虫小配子体与小配子的超微结构和发育过程。小配子体由第二代裂殖子发育而来。当小配子体完成最后一次核分裂后,其核中染色质呈斑块状,核内无核仁。随后,细胞核移向小配子体边缘,并拉长成二部分,电子致密部分将发育成小配子的核,电子密度浅的另一部分则留在残体中。每个细胞核上方有一对中心粒,中心粒将进一步发育成为小配子两根鞭毛的基粒,鞭毛由此产生。成熟的小配子拥有两根鞭毛和一个体部,体部有一个长形的细胞核,核的前面嵌有一线粒体。     

Molecular sorting by electrical steering of microtubules in kinesin-coated channels

Integration of biomolecular motors in nanoengineered structures raises the intriguing possibility of manipulating materials on nanometer scales. We have managed to integrate kinesin motor proteins in closed submicron channels and to realize active electrical control of the direction of individual kinesin-propelled microtubule filaments at Y junctions. Using this technique, we demonstrate molecular sorting of differently labeled microtubules. We attribute the steering of microtubules to electric field-induced bending of the leading tip. From measurements of the orientation-dependent electrophoretic motion of individual, freely suspended microtubules, we estimate the net applied force on the tip to be in the picoNewton range and we infer an effective charge of 12 e- per tubulin dimer under physiological conditions.     

柔嫩艾美耳球虫（Eimeria ternlla）小配子发育超微结构的观察

利用透射电镜对柔嫩艾美耳球虫小配子发育的超微结构进行了观察。小配子母细胞和大配子母细胞于相邻的宿主细胞内相伴产生,系由末代裂殖子侵入后,长大变圆而形成。小配子的形成为直接分化型。首化细胞核分裂为多个,随后细胞核向周边移动,随之近核处限制膜外突,临近外限制膜下陷。中心粒在核上方形成半并发育为基粒、鞭毛中的微管和附着微管,早期形成的小配子仍与小配子母细胞的残体相连。成熟小配子与残体分离,外型呈香蕉状,外被单位膜,内有一电子结构＋分致密的细胞核,核实端侧面有一个巨大线粒体,小配子有鞭毛2根,每根鞭毛内有微管,为9＋2结构,附着微管至少6根,这些微管起始于基粒。     

柔嫩艾美耳球虫(Eimeria tenella)小配子发育超微结构的观察

利用透射电镜对柔嫩艾美耳球虫小配子发育的超微结构进行了观察 小配子母细胞和大配子母细胞于相邻的宿主细胞内相伴产生 ,系由末代裂殖子侵入后 ,长大变圆而形成 小配子的形成为直接分化型 首先细胞核分裂为多个 ,随后细胞核向周边移动 ,随之近核处限制膜外突 ,临近处限制膜下陷 中心粒在核上方形成并发育为基粒、鞭毛中的微管和附着微管 ,早期形成的小配子仍与小配子母细胞的残体相连 成熟小配子与残体分离 ,外型呈香蕉状 ,外被单位膜 ,内有一电子结构十分致密的细胞核 ,核头端侧面有一个巨大线粒体 ,小配子有鞭毛 2根 ,每根鞭毛内有微管 ,为 9+2结构 ,附着微管至少 6根 ,这些微管均起始于基粒     

中密度纤维板连续热压位置伺服系统自适应全局快速终端滑模控制

为实现中密度纤维板(MDF)连续平压热压机液压位置伺服系统在参数摄动和外负载力干扰存在条件下快速、精确地位置跟踪,提出一种自适应全局快速终端滑模控制方法。首先,设计了自适应律以估计系统中的不确定参数,增强了控制系统的鲁棒性;然后,采用全局快速终端滑模控制方法,设计了一种新型的全局快速终端滑动模态,保证系统误差能够在有限时间内收敛为零;最后,利用Lyapunov稳定性理论给出了系统渐近稳定、跟踪误差在有限时间收敛的证明。仿真结果表明:该方法在保证系统稳定性的同时,可以实现系统误差在有限时间内收敛,提高了系统的鲁棒性和快速性。     

关于Fuzzy外可加测度

Dan Butanriu引入并研究了Fuzzy可加测度。本文中,我们引入Fuzzy外可加测度并讨论其基本性质,并研究了半加类上Fuzzy测度的扩张问题,给出L(X) Fuzzy外可加测度成为Fuzzy可加测度的条件。     

基于ABAQUS有限元法的空洞树干强度分析

树木空洞可能会导致树木的死亡，同时，由于空洞树木抗风雪能力低，易在空洞处断裂，对人身和财物安全具有重大隐患。本研究通过软件Abaqus建立空心树干的三维模型进行有限元模拟分析，探索树干空洞的大小对树木强度和断裂破坏行为的影响。结果表明:1）树木发生弯曲和扭转破坏系数随载荷增加而增大，树干最外层的最大弯曲和扭转剪应力在断裂破坏前随载荷增加呈线性增加；2）当树干空洞发展到树干内外径比（α）为0.7时，随着空洞的继续增大其弯曲和扭转破坏系数会急剧增加，在α小于0.7时，弯曲和扭转破坏系数有一定的增加，但增加幅度较小；3）随着树干空洞造成内外径比的增加，树木发生扭转破坏的偏冠程度会逐渐降低。研究初步探明了树干空洞影响树木破坏行为和方式的力学机理，可为树木安全性评估提供一定的理论支持和依据。     

Modified cilia in sensory organs of juvenile stages of a parasitic nematode

Electron microscopical studies revealed the presence of dendritic nerve processes in sensory organs of the third- and fourth-stage juveniles of Haemonchus contortus, which contained structures resembling modified cilia. With few exceptions, the outer circle of fibers consisted of ten doublets, and in place of typical cilia-like central fibers were small microtubules or vesicles varying in number from zero to five.     

Evidence for retrograde lithospheric subduction on venus

Annular moats and outer rises around large Venus coronae such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On Earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronae on Venus. Accordingly, it is proposed that retrograde lithospheric subduction may be occurring on the margins of the large Venus coronae while compensating back-arc extension is occurring in the expanding coronae interiors. Similar processes may be taking place at other deep arcuate trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of eastern Aphrodite Terra.