Large-scale vortex lattice emerging from collectively moving microtubules

Spontaneous collective motion, as in some flocks of bird and schools of fish, is an example of an emergent phenomenon. Such phenomena are at present of great interest and physicists have put forward a number of theoretical results that so far lack experimental verification. In animal behaviour studies, large-scale data collection is now technologically possible, but data are still scarce and arise from observations rather than controlled experiments. Multicellular biological systems, such as bacterial colonies or tissues, allow more control, but may have many hidden variables and interactions, hindering proper tests of theoretical ideas. However, in systems on the subcellular scale such tests may be possible, particularly in in vitro experiments with only few purified components. Motility assays, in which protein filaments are driven by molecular motors grafted to a substrate in the presence of ATP, can show collective motion for high densities of motors and attached filaments. This was demonstrated recently for the actomyosin system, but a complete understanding of the mechanisms at work is still lacking. Here we report experiments in which microtubules are propelled by surface-bound dyneins. In this system it is possible to study the local interaction: we find that colliding microtubules align with each other with high probability. At high densities, this alignment results in self-organization of the microtubules, which are on average 15?μm long, into vortices with diameters of around 400?μm. Inside the vortices, the microtubules circulate both clockwise and anticlockwise. On longer timescales, the vortices form a lattice structure. The emergence of these structures, as verified by a mathematical model, is the result of the smooth, reptation-like motion of single microtubules in combination with local interactions (the nematic alignment due to collisions)--there is no need for long-range interactions. Apart from its potential relevance to cortical arrays in plant cells and other biological situations, our study provides evidence for the existence of previously unsuspected universality classes of collective motion phenomena.     

纤毛虫阔口游仆虫皮层微管胞器的形态及形态发生

采用荧光紫杉醇直接荧光标记,研究了腹毛类纤毛虫阔口游仆虫(Euplotes eurystomus)中由纤毛器、纤毛器附属微管和非纤毛器微管组成的皮层微管胞器.其中纤毛器、纤毛器附属微管包括口围带及小膜托架微管,波动膜及基部微管骨架网,额腹横棘毛、左缘棘毛及基部的前纵维管束、后纵微管束和横微管束,背触毛及基部的玫瑰花环附属微管等;非纤毛器皮层微管包括背腹面的细小网格状微管,背面的斜向微管层及贯穿于细胞纵长的纵微管层等.形态发生中,老口围带被前仔虫继承,前、后仔虫的额腹横棘毛发生及分化过程中老纤毛器基部微管退化,并且老棘毛及其附属微管可能具有定位和定向作用,但未见直接的物质联系.所得结果为揭示腹毛目纤毛虫皮层微管胞器建构的多样性、细胞皮层微管的分化及其细胞调控提供了基础资料.     

Identification of gamma-tubulin, a new member of the tubulin superfamily encoded by mipA gene of Aspergillus nidulans

Microtubules, which are essential for mitosis and many other cytoskeletal functions, are composed primarily of alpha- and beta-tubulin. The properties of microtubules are due, in part, to proteins other than tubulins that are part of, or interact with, microtubules and the identification and characterization of such proteins is important to understanding how microtubules function. Analyses of mutations at the mipA (microtubule interacting protein) locus of Aspergillus nidulans have suggested that the product of mipA interacts specifically, probably physically, with beta-tubulin in vivo and is involved in microtubule function. We have cloned and sequenced the wild-type mipA gene as well as complementary DNA copies of its messenger RNA. Comparisons of the predicted product of mipA with tubulins from diverse organisms reveal that mipA is a previously undiscovered member of the tubulin superfamily of genes; the only member yet discovered that does not encode alpha- or beta-tubulin. We propose that the product of mipA be called gamma-tubulin.     

Generation of GTP-bound Ran by RCC1 is required for chromatin-induced mitotic spindle formation.

Chromosomes are segregated by two antiparallel arrays of microtubules arranged to form the spindle apparatus. During cell division, the nucleation of cytosolic microtubules is prevented and spindle microtubules nucleate from centrosomes (in mitotic animal cells) or around chromosomes (in plants and some meiotic cells). The molecular mechanism by which chromosomes induce local microtubule nucleation in the absence of centrosomes is unknown, but it can be studied by adding chromatin beads to Xenopus egg extracts. The beads nucleate microtubules that eventually reorganize into a bipolar spindle. RCC1, the guanine-nucleotide-exchange factor for the GTPase protein Ran, is a component of chromatin. Using the chromatin bead assay, we show here that the activity of chromosome-associated RCC1 protein is required for spindle formation. Ran itself, when in the GTP-bound state (Ran-GTP), induces microtubule nucleation and spindle-like structures in M-phase extract. We propose that RCC1 generates a high local concentration of Ran-GTP around chromatin which in turn induces the local nucleation of microtubules.     

微管骨架在棉纤维细胞伸长中的作用

以陆地棉纤维为实验材料,研究了微管骨架在棉纤维细胞伸长阶段的功能.研究结果表明,在快速伸长期纤维细胞内,微管骨架以垂直于细胞伸长轴方向垂直排列,微纤丝的结构和分布与微管骨架保持一致,细胞壁表面平滑.经过微管阻断剂秋水仙素处理的纤维细胞内,微纤丝的结构和分布受到损坏,细胞壁表面出现颗粒状突起,纤维细胞的伸长也受到明显抑制.以上实验结果表明微管骨架在棉纤维细胞的伸长阶段具有重要的功能.     

P systems with array objects and array rewriting rules

Array P systems were introduced by Paun Gh. which is linking the two areas of membrane computing and picture grammars. Puzzle grammars were introduced by us for generating connected picture arrays in the two-dimensional plane, motivated by the problem of tiling the plane. On the other hand, incorporating into arrays the developmental type of generation used in the well-known biologically motivated L systems, Siromoney and Siromoney proposed a very general rectangular array generating model, called extended controlled tabled L array system (ECTLAS). In this paper we introduce two variations of the array P system, called BPG array P system and parallel array P system. The former has in the regions array objects and basic puzzle grammar rules (BPG), which are a specific kind of puzzle grammar rules. In the latter, the regions have rectangular array objects and tables of context-free rules. We examine these two types of P systems for their array generative power.     

P systems with array objects and array rewriting rules

Array P systems were introduced by Paun Gh. which is linking the two areas of membrane computing and picture grammars. Puzzle grammars were introduced by us for generating connected picture arrays in the two-dimensional plane, motivated by the problem of tiling the plane. On the other hand, incorporating into arrays the developmental type of generation used in the well-known biologically motivated L systems, Siromoney and Siromoney proposed a very general rectangular array generating model, called extended controlled tabled L array system (ECTLAS). In this paper we introduce two variations of the array P system, called BPG array P system and parallel array P system. The former has in the regions array objects and basic puzzle grammar rules (BPG), which are a specific kind of puzzle grammar rules. In the latter, the regions have rectangular array objects and tables of context-free rules. We examine these two types of P systems for their array generative power.     

The depolymerizing kinesin MCAK uses lattice diffusion to rapidly target microtubule ends

The microtubule cytoskeleton is a dynamic structure in which the lengths of the microtubules are tightly regulated. One regulatory mechanism is the depolymerization of microtubules by motor proteins in the kinesin-13 family. These proteins are crucial for the control of microtubule length in cell division, neuronal development and interphase microtubule dynamics. The mechanism by which kinesin-13 proteins depolymerize microtubules is poorly understood. A central question is how these proteins target to microtubule ends at rates exceeding those of standard enzyme-substrate kinetics. To address this question we developed a single-molecule microscopy assay for MCAK, the founding member of the kinesin-13 family. Here we show that MCAK moves along the microtubule lattice in a one-dimensional (1D) random walk. MCAK-microtubule interactions were transient: the average MCAK molecule diffused for 0.83 s with a diffusion coefficient of 0.38 microm2 s(-1). Although the catalytic depolymerization by MCAK requires the hydrolysis of ATP, we found that the diffusion did not. The transient transition from three-dimensional diffusion to 1D diffusion corresponds to a "reduction in dimensionality" that has been proposed as the search strategy by which DNA enzymes find specific binding sites. We show that MCAK uses this strategy to target to both microtubule ends more rapidly than direct binding from solution.     

Microtubule assembly nucleated by isolated centrosomes

Microtubules are involved in the morphogenesis of most cells and are the structural basis of the mitotic spindle. We report here that purified centrosomes nucleate the assembly of microtubules with unusual dynamic properties. This may have important implications for the mechanism by which microtubule arrays are organized and stabilized in cells.     

指环虫科三属单殖吸虫精子超微结构的研究

本文用透射电镜观察了指环虫科中黄颡四锚虫、鳙指环虫和锚盘虫的精子结构．精子呈细丝状，有一根“９十１”结构的鞭毛，一个线粒体和一个细胞核．三种不同属的单殖吸虫精子在超微结构上有所差异，本文就这些差异与半殖吸虫系统进化的关系进行探讨．     

Organization of microtubules in dendrites and axons is determined by a short hydrophobic zipper in microtubule-associated proteins MAP2 and tau

Here we report that the microtubule-associated proteins MAP2 and tau share two separable functional domains. One is the microtubule-binding site which serves to nucleate microtubule assembly; the second is a short C-terminal alpha-helical sequence which can crosslink microtubules by means of a hydrophobic zipper interaction into dense stable parallel arrays characteristic of axons or dendrites. Thus, interactions between molecules of a single type are capable of drastically reorganizing microtubules and completely suppressing their dynamic properties.     

兰州市雁儿湾污水处理厂活性污泥中纤毛虫春季群落特征

从2006年2月至2006年4月,对兰州市雁儿湾污水处理厂曝气池活性污泥中的纤毛虫群落进行了调查研究.共记录到纤毛虫57种,隶属于11目21科27属.缘毛目为优势类群.其中优势种为：小口钟虫（Vorticella microstoma）、沟钟虫（Vorticella convallaria）、八钟虫（Vorticella octava）、卑怯管叶虫（Trachelophyllum pusillum）、彩盖虫（Opercularia phryganeae）、有肋楯纤虫（Aspidisca costata）、片状漫游虫（Litonotus fasciola）.同时记录到10种常见种.与两对照样点相比较,活性污泥中纤毛虫种类数、丰度都大于两对照样点.结果表明,缘毛目优势种可以作为污水处理效果的指示生物.     

Long-term haematopoietic reconstitution by Trp53-/-p16Ink4a-/-p19Arf-/- multipotent progenitors

Haematopoiesis is maintained by a hierarchical system where haematopoietic stem cells (HSCs) give rise to multipotent progenitors, which in turn differentiate into all types of mature blood cells. HSCs maintain themselves for the lifetime of the organism because of their ability to self-renew. However, multipotent progenitors lack the ability to self-renew, therefore their mitotic capacity and expansion potential are limited and they are destined to eventually stop proliferating after a finite number of cell divisions. The molecular mechanisms that limit the proliferation capacity of multipotent progenitors and other more mature progenitors are not fully understood. Here we show that bone marrow cells from mice deficient in three genes genetically downstream of Bmi1--p16Ink4a, p19Arf and Trp53 (triple mutant mice; p16Ink4a and p19Arf are alternative reading frames of the same gene (also called Cdkn2a) that encode different proteins)--have an approximately 10-fold increase in cells able to reconstitute the blood long term. This increase is associated with the acquisition of long-term reconstitution capacity by cells of the phenotype c-kit+Sca-1+Flt3+CD150-CD48-Lin-, which defines multipotent progenitors in wild-type mice. The pattern of triple mutant multipotent progenitor response to growth factors resembles that of wild-type multipotent progenitors but not wild-type HSCs. These results demonstrate that p16Ink4a/p19Arf and Trp53 have a central role in limiting the expansion potential of multipotent progenitors. These pathways are commonly repressed in cancer, suggesting a mechanism by which early progenitor cells could gain the ability to self-renew and become malignant with further oncogenic mutations.     

MOR1 is essential for organizing cortical microtubules in plants

Microtubules orchestrate cell division and morphogenesis, but how they disassemble and reappear at different subcellular locations is unknown. Microtubule organizing centres are thought to have an important role, but in higher plants microtubules assemble in ordered configurations even though microtubule organizing centres are inconspicuous or absent. Plant cells generate highly organized microtubule arrays that coordinate mitosis, cytokinesis and expansion. Inhibiting microtubule assembly prevents chromosome separation, blocks cell division and impairs growth polarity. Microtubules are essential for the formation of cell walls, through an array of plasma-membrane-associated cortical microtubules whose control mechanisms are unknown. Using a genetic strategy to identify microtubule organizing factors in Arabidopsis thaliana, we isolated temperature-sensitive mutant alleles of the MICROTUBULE ORGANIZATION 1 (MOR1) gene. Here we show that MOR1 is the plant version of an ancient family of microtubule-associated proteins. Point mutations that substitute single amino-acid residues in an amino-terminal HEAT repeat impart reversible temperature-dependent cortical microtubule disruption, showing that MOR1 is essential for cortical microtubule organization.     

The Existence of Positive Bounded Entire Solutions of Second Order Quasilinear Elliptic Equations

In this paper we are concerned with the existence of positive entire solutions of second order quasilinear elliptic equations of the type div(|Du|p-2Du)+f(x,u)=0, x∈RN, (1) where f(x, u) is a continuous function on RN×(0,∞). This problem appears in the study of non-Newtonian fluids and non-Newtonian filtration. The quantity p is a characteristic of the madium. Media with p>2 are called dilatant fluids and those with p<2 are called pseudoplastics. If p=2, they are Newtonian fluid. In the present paper we give new sufficient conditions which ensure the existence of positive entire solutions of (1).When p=2, the related results have been obtained by [1,2]. Our theorem for existence complement and extent to the results by [1,2].     

In vitro effects on microtubule dynamics of purified Xenopus M phase-activated MAP kinase.

The protein kinase MAP kinase, also called MAP2 kinase, is a serine/threonine kinase whose activation and phosphorylation are induced by a variety of mitogens, and which is thought to have a critical role in a network of protein kinases in mitogenic signal transduction. A burst in kinase activation and protein phosphorylation may also be important in triggering the dramatic reorganization of the cell during the transition from interphase to mitosis. The interphase-metaphase transition of microtubule arrays is under the control of p34cdc2 kinase, a central control element in the G2-M transition of the cell cycle. Here we show that a Xenopus kinase, closely related to the mitogen-activated mammalian MAP kinase, is phosphorylated and activated during M phase of meiotic and mitotic cell cycles, and that the interphase-metaphase transition of microtubule arrays can be induced by the addition of purified Xenopus M phase-activated MAP kinase or mammalian mitogen-activated MAP kinase to interphase extracts in vitro.     

Global variation in copy number in the human genome

Copy number variation (CNV) of DNA sequences is functionally significant but has yet to be fully ascertained. We have constructed a first-generation CNV map of the human genome through the study of 270 individuals from four populations with ancestry in Europe, Africa or Asia (the HapMap collection). DNA from these individuals was screened for CNV using two complementary technologies: single-nucleotide polymorphism (SNP) genotyping arrays, and clone-based comparative genomic hybridization. A total of 1,447 copy number variable regions (CNVRs), which can encompass overlapping or adjacent gains or losses, covering 360 megabases (12% of the genome) were identified in these populations. These CNVRs contained hundreds of genes, disease loci, functional elements and segmental duplications. Notably, the CNVRs encompassed more nucleotide content per genome than SNPs, underscoring the importance of CNV in genetic diversity and evolution. The data obtained delineate linkage disequilibrium patterns for many CNVs, and reveal marked variation in copy number among populations. We also demonstrate the utility of this resource for genetic disease studies.     

台湾海峡微型浮游动物的摄食压力及其对营养盐再生的贡献

于2005年3月台湾海峡的5个站位采样分析了微型浮游动物的空间分布,用稀释法研究了浮游植物的生长率和微型浮游动物对浮游植物的摄食压力,同时对微型浮游动物的氨氮产生率进行了推算.结果表明,各站微型浮游动物主要为红色中缢虫(Mesodinium rubrum)和以急游虫(Strombidiumspp.)为主的无壳纤毛虫,其次为异养甲藻-螺旋环沟藻(Gy-rodinium spirale)和砂壳纤毛虫.各类群在表层呈不均匀分布:红色中缢虫A6站最低,为425个/L,E2站达最大值,为27 125个/L,且在E2,E9和E13站占绝对优势,占微型浮游动物总量的84%以上;无壳纤毛虫丰度为203-5 025个/L,E13站最低,E2站最高;异养甲藻E9站表层没有分布,A6站达最大值,为463个/L;砂壳纤毛虫丰度为0-438个/L,F1站最高.垂直分布上,除A6站外,一般表现为表层多,中层和底层逐渐减少.表层浮游植物的生长率为0.36-0.50 d-1,微型浮游动物的摄食率为0.12-0.30 d-1,相当于每天摄食浮游植物现存量的11.09%-25.67%,初级生产力的28.38%-84.04%.利用微型浮游动物的摄食率推算其氨氮产生率为0.16-2.40 mg N/m3d,达到维持现场初级生产所需氮量的8.7%-28.1%.     

Analysis of gene expression patterns with cDNA microarray during late stage of spermatogenesis in mice

The differentiation process of round spermatids to spermatozoa during the late stage of spermatogenesis is called spermiogenesis. To explore spermiogenesis-related genes, cDNA microarray was used to study expression patterns of 1176 genes in pachytene spermatocytes, round spermatids and elongating spermatids of Balb/c mice. The results showed that 208 genes were detected in all the three cell types. Most of them were down-regulated from pachytene spermatocytes to round spermatids and elongating spermatids. However, up-regulation of 7 genes expression in round spermatids and 3 genes in elongating spermatids were found. Expression of 7 differentially expressed genes in cDNA arrays was further confirmed by semi-quantitative RT-PCR study. The RT-PCR results indicated that the expression of 6 genes was consistent with that in cDNA arrays, only one gene did not show differential expression by RT-PCR. These results may provide important clues for studying of expression, regulation, and function of spermiogenesis-related genes.     

单圈图的边幻和全标号

对于图G(p,q),若存在一个映射f:V(G)∪E(G)→{1,2,…,p+q},使得任意边uv∈E(G),满足f(u)+f(v)+f(uv)=K,K为常数,则图G(p,q)为边幻和图。设计了一种算法对16个点以内的单圈图进行标号,依据得到的结果,找到了两类特殊单圈图的标号规律,定义C_nSymbolQC@〓S_m和C_nΔS_m来刻画此两类特殊单圈图,并给出其相关定理及证明。结果表明,点数小于等于16的所有单圈图均具有边幻和全标号,且其中绝大部分是超级边幻和全标号,从而猜测点数多于16的单圈图也具有边幻和全标号。