裂球中引起受精卵质膜收缩的因子~*(简报)

根据收缩环的假设,胞质分裂是细胞膜下面的微丝收缩,使细胞膜内陷,将细胞一分为二。蛙卵第一次卵裂是动物极预定分裂沟处细胞膜下面的微丝收缩,细胞膜内陷,出现分裂沟,分裂沟二端缓慢向前伸延,再后,沟二端在植物极相遇,形成环形的分裂沟,受精卵一分为二。由此提示细胞膜的收缩与深层的细胞质无关。Sawai曾将蝾螈卵分裂沟端前面不远处靠近细胞膜的小量细胞质吸出来,注     

微丝在卵子极性产生、分裂沟形成和极体排放中的作用

小鼠生发泡（ＧＶ）期卵母细胞在１μｇ／ｍｌ细胞松弛素Ｂ（ＣＢ）中培养,部分微丝解聚,卵母细胞不 能产生极性而在细胞中部形成分裂沟（假分裂）;极泡期印在１μｇ／ｍｌ ＣＢ中,分裂沟继续收缩,排放第 一极体。假分裂的分裂沟和极泡期的极区分裂沟形成均与分裂器中体位置相关。部分微丝解聚并不影响 假分裂和第一极体排放;全部微丝解聚（１０μｇ／ｍｌ ＣＢ）将中断假分裂和胞质分裂,分裂沟消失,卵恢 复球形。由此可见,成熟过程中卵母细胞极性的产生及分裂沟的形成都依赖于微丝的聚合。胞质分裂和 第一极体排放同样需一定量的微丝存在。     

林蛙卵收缩因子的进一步纯化(简报)

大家承认动物细胞的胞质分裂是由收缩环的微丝束收缩而引起的。那么微丝束又是在什么物质作用下诱发产生的呢?两栖类卵的第一次胞质分裂是单侧卵裂(unilateral cleavage),即先在动物极出现分裂沟,沟两端逐渐向下延     

微丝在卵子极性产生,分裂沟形成和极体排放中的作用

小鼠生发泡期卵母细胞在１μｇ／ｍｌ细胞松弛素Ｂ中培养，部分微丝解聚，卵母细胞不能产生极性而在细胞中部形成分裂沟（假分裂）；极泡期卵在１μｇ／ｍｌ ＣＢ 中，分裂沟继续收缩，排和放第一极体，假分裂的分裂沟和极区分裂沟形成均与分裂器中体位置相关，部分微丝解聚并不影响假分裂和第一极体的排放，全部微丝解释（１０μｇ／ｍｌ ＣＢ）将中断假分裂和胞质分裂，分裂沟消失，卵恢复球形，由此可见，成熟过程中卵母细胞极     

荧光标记法检测不同毒物对细胞骨架的影响

细胞骨架(Cytoskeleton)主要由微管(Microtubule,MT)、微丝(Microfilament,MF)以及中间丝(Intermediate filament,IF)这三种类型组成。它们在细胞的形态维持、物质运输、信号转导、能量转换及细胞的运动和分裂等多个过程中发挥着重要的作用。其中,由肌动蛋白组成的微丝是真核细胞中含量最丰富的一种蛋白复合体,以解聚时的球状肌动蛋白G-actin(Globular actin)或聚合时的纤丝状肌动蛋白F-actin(Filamen-tous actin)形式存在。正常细胞中肌动蛋白两种形态的转换处于动态平衡,共同行使细胞的变形运动、胞质分裂、基质附着和胞间连接等多…     

大丽轮枝菌微丝荧光标记载体构建及应用

微丝在真菌生长发育、胞质分裂等生命过程中具有重要功能。通过农杆菌介导遗传转化方法,将荧光mCherry标记微丝的表达载体pSULPH-Lifeact-mCherry转入大丽轮枝菌(Verticillium dahliae Kleb.)野生型V592,获得稳定的微丝荧光标记菌株V592/Lifeact-mCherry,并检测了其生物学表型和孢子萌发、菌丝生长等过程中的微丝荧光动态变化。结果表明:微丝荧光标记菌株的菌落形态、生长速率、产孢量、萌发率等表型与野生型没有显著差异;且可以观察到微丝荧光信号在分生孢子和菌丝的顶端及隔膜都有清晰定位,同时对该菌株隔膜形成过程微丝动态观察发现,微丝参与胞质分裂进程中肌动球蛋白收缩环CAR (Contractile actomyosin ring)的形成。微丝荧光标记菌株可用于微丝在真菌发育中的动力学研究,这为深入研究微丝在真菌发育及致病过程中的作用机制提供理论与实践支撑。     

人胃癌细胞在丁酸钠的诱导下膜分子运动与膜相关骨架的关系

体外培养的人胃癌细胞,用丁酸钠处理后,显示细胞表面FN及细胞胞质微丝的变化,同时用荧光漂白恢复方法对细胞膜ConA受体复合物侧向扩散运动进行测定。结果表明,经丁酸钠处理后的细胞,胞质微丝及细胞膜表面FN均较对照组增加,而细胞膜分子侧向扩散运动减慢,说明与细胞膜相连的细胞骨架的变化对膜分子侧位运动具有牵制作用。     

植物胞质分裂发生机制

胞质分裂(cytohnesis)是指在同一细胞中在新形成的两个子核之间形成新的间隔,将母细胞一分为二的过程。胞质分裂存在于任何一种生命形式中,从单细胞的细菌到多细胞的真核生物都能进行胞质分裂。近些年由于细胞学方法的改进和研究材料增多等因素,使得对植物胞质分裂发生机制的研究取得了很大的进展。现对植物中不同类型的胞质分裂在细胞学、分子生物学方面的研究进展作一综述。     

胞质微丝改变与鼻咽癌细胞增殖和凋亡的关系

胞质微丝改变与鼻咽癌细胞增殖和凋亡的关系廖新波,孙宁,唐慰萍（广东医院病理学教研室湛江５２４０２３）本文应用激光共聚焦显微镜（ＣＬＳＭ）技术,研究鼻咽癌细胞胞质微丝骨架改变与癌细胞增殖、凋亡的关系。鼻咽癌细胞（ＣＮＥ－ＺＺ）体外培养（分诱导凋亡组和对...     

小麦胚乳细胞内,细胞间胞质骨架分布格局的超微结构观察

以小麦（ＴｒｉｔｉｃｕｍａｅｓｔｉｖｕｍＬ．）幼嫩胚乳为材料,经ＴｒｉｔｏｎＸ１００抽提、ＤＧＤ（ｄｉｅｔｈｙｌｅｎｅｇｌｙｃｏｌｄｉｓｔｅａｒａｔｅ）渗透、包埋,制备去包埋剂超薄切片,对细胞内、细胞间胞质骨架的分布格局与特征进行了电镜观察。由所获图像可见,胞质骨架呈主要由微管、微丝组成的三维网络结构;特别值得注意的是,有不少５～７ｎｍ的微丝在多处从网络表层向胞壁界面方向突出,并时而可见其横贯分界壁连接相邻骨架网络而将相邻细胞骨架联成一体。胚乳组织中微丝的跨胞分布以两种形式存在,直径达１００～２００ｎｍ微丝束的跨越和单个微丝的分散贯穿,看来这与该组织中开放态胞间通道与正常胞间连丝同时并存相吻合。初步讨论了微丝参与正常胞间连丝结构的可能性。     

Laser ablation reveals the impact of Cdc15p on the stiffness of the contractile ring

The mechanics that govern the constriction of the contractile ring remain poorly understood yet are critical to understanding the forces that drive cytokinesis. We used laser ablation in fission yeast cells to unravel these mechanics focusing on the role of Cdc15p as a putative anchoring protein. Our work shows that the severed constricting contractile ring recoils to a finite point leaving a gap that can heal if less than ∼1 µm. Severed contractile rings in Cdc15p-depleted cells exhibit an exaggerated recoil, which suggests that the recoil is limited by the anchoring of the ring to the plasma membrane. Based on a physical model of the severed contractile ring, we propose that Cdc15p impacts the stiffness of the contractile ring more than the viscous drag.     

Membrane Phospholipid Redistribution in Cytokinesis： A Theoretical Model

In cell mitosis, cytokinesis is a major deformation process, during which the site of the contractile ring is determined by the biochemical stimulus from asters of the mitotic apparatus, actin and myosin assembly is related to the motion of membrane phospholipids, and local distribution and arrangement of the microfilament cytoskeleton are different at different cytokinesis stages. Based on the Zinemanas-Nir model, a new model is proposed in this study to simulate the entire process by coupling the biochemical stimulus with the mechanical actions. There were three assumptions in this model： the movements of phospholipid proteins are driven by gradients of biochemical stimulus on the membrane surface; the local assembly of actin and myosin filament depends on the amount of phospholipid proteins at the same location; and the surface tension includes membrane tensions due to both the passive deformation of the membrane and the active contraction of actin filament, which is determined by microfilament redistribution and rearrangement. This model could explain the dynamic movement of microfilaments during cytokinesis and predict cell deformation. The calculated results from this model demonstrated that the reorientation of phospholipid proteins and the redistribution and reorientation of microfilaments may play a crucial role in cell division. This model may better represent the cytokinesis process by the introduction of biochemical stimulus.     

Modelling apical columnar epithelium mechanics from circumferential contractile fibres

Simple columnar epithelia are formed by individual epithelial cells connecting together to form single cell high sheets. They are a main component of many important body tissues and are heavily involved in both normal and cancerous cell activities. Prior experimental observations have identified a series of contractile fibres around the circumference of a cross section located in the upper (apical) region of each cell. While other potential mechanisms have been identified in both the experimental and theoretical literature, these circumferential fibres are considered to be the most likely mechanism controlling movement of this cross section. Here, we investigated the impact of circumferential contractile fibres on movement of the cross section by creating an alternate model where movement is driven from circumferential contractile fibres, without any other potential mechanisms. In this model, we utilised a circumferential contractile fibre representation based on investigations into the movement of contractile fibres as an individual system, treated circumferential fibres as a series of units, and matched our model simulation to experimental geometries. By testing against laser ablation datasets sourced from existing literature, we found that circumferential fibres can reproduce the majority of cross-sectional movements. We also investigated model predictions related to various aspects of cross-sectional movement, providing insights into epithelium mechanics and demonstrating the usefulness of our modelling approach.     

Why does a cleavage plane develop parallel to the spindle axis in conical sand dollar eggs? A key question for clarifying the mechanism of contractile ring positioning

Three types of models have been proposed about how the mitotic apparatus determines the position of the cleavage furrow in animal cells. In the first and second types, the contractile ring appears in a cortical region that least and most astral microtubules reach, respectively. The third type is that the spindle midzone positions the contractile ring. In the previous study, a new model was proposed through analyses of cytokinesis in sand dollar and sea urchin eggs. Gradients of the surface density of microtubule plus ends are assumed to drive membrane proteins whose accumulation causes the formation of contractile-ring microfilaments. In the present study, the validity of each model is examined by simulating the furrow formation in conical sand dollar eggs with the mitotic apparatus oriented perpendicular to the cone axis. The new model predicts that unilateral furrows with cleavage planes roughly parallel to the spindle axis appear between the mitotic apparatus and the vertex besides the normally positioned furrow. The predictions are consistent with the observations by Rappaport & Rappaport (1994, Dev. Biol.164, 258-266). The other three types of models do not predict the formation of the ectopic furrows. Furthermore, it is pointed out that only the new model has the ability to explain the geometrical relationship between the mitotic apparatus and the contractile ring under various experimental conditions. These results strongly suggest the real existence of the membrane proteins postulated in the model.     

Assembly and architecture of precursor nodes during fission yeast cytokinesis

The contractile ring is essential for cytokinesis in most fungal and animal cells. In fission yeast, cytokinesis nodes are precursors of the contractile ring and mark the future cleavage site. However, their assembly and architecture have not been well described. We found that nodes are assembled stoichiometrically in a hierarchical order with two modules linked by the positional marker anillin Mid1. Mid1 first recruits Cdc4 and IQGAP Rng2 to form module I. Rng2 subsequently recruits the myosin-II subunits Myo2 and Rlc1. Mid1 then independently recruits the F-BAR protein Cdc15 to form module II. Mid1, Rng2, Cdc4, and Cdc15 are stable node components that accumulate close to the plasma membrane. Both modules recruit the formin Cdc12 to nucleate actin filaments. Myo2 heads point into the cell interior, where they efficiently capture actin filaments to condense nodes into the contractile ring. Collectively, our work characterizing the assembly and architecture of precursor nodes defines important steps and molecular players for contractile ring assembly.     

Models of epidermal wound healing

The spreading of cells across the surface of an epidermal wound enables epidermal migration to be studied independently of the wound contraction that occurs in deeper wounds. In particular, the stimulus for the increase in epidermal mitosis during would healing is uncertain. Our modelling suggests that biochemical regulation of mitosis is fundamental to the process, and that a single chemical with a simple regulatory effect can account for the healing of circular epidermal wounds. The model results compare well with experimental data.     

Mutations of DMYPT cause over constriction of contractile rings and ring canals during Drosophila germline cyst formation

Ring canals, also known as stable intercellular bridges, are derived from the contractile rings of incomplete cytokinesis (IC) in most organisms. Formation of ring canals is necessary to generate functional eggs and sperm in multiple organisms including insects, birds, mammals and various plants. How the constriction of a contractile ring is arrested and how an arrested contractile ring is transformed into a ring canal is unknown. We describe here the function of the Drosophila melanogaster myosin binding subunit of myosin phosphatase (DMYPT) in both processes. We have found that DMYPT is highly enriched in the cytoplasm of cells undergoing IC during oogenesis. DMYPT mutations in germ cells, but not in somatic follicle cells, resulted in over-constriction of contractile rings and ring canals. This leads to formation of small ring canals and mis-regulation of centriole migration during female germline cyst formation. Our results suggest that there may be two parallel mechanisms to prevent the contractile rings from being completely closed, physical resistance and inhibition of myosin II activity via DMYPT.     

Cytokinesis in eukaryotes.

Cytokinesis is the final event of the cell division cycle, and its completion results in irreversible partition of a mother cell into two daughter cells. Cytokinesis was one of the first cell cycle events observed by simple cell biological techniques; however, molecular characterization of cytokinesis has been slowed by its particular resistance to in vitro biochemical approaches. In recent years, the use of genetic model organisms has greatly advanced our molecular understanding of cytokinesis. While the outcome of cytokinesis is conserved in all dividing organisms, the mechanism of division varies across the major eukaryotic kingdoms. Yeasts and animals, for instance, use a contractile ring that ingresses to the cell middle in order to divide, while plant cells build new cell wall outward to the cortex. As would be expected, there is considerable conservation of molecules involved in cytokinesis between yeast and animal cells, while at first glance, plant cells seem quite different. However, in recent years, it has become clear that some aspects of division are conserved between plant, yeast, and animal cells. In this review we discuss the major recent advances in defining cytokinesis, focusing on deciding where to divide, building the division apparatus, and dividing. In addition, we discuss the complex problem of coordinating the division cycle with the nuclear cycle, which has recently become an area of intense research. In conclusion, we discuss how certain cells have utilized cytokinesis to direct development.     

Surface viscoelastic effects in cell cleavage

The effect of passive surface traction on the cleavage of cells is incorporated in the cytokinesis hydrodynamic model of Zinemanas and Nir [Biomechanics of cell Division, pp. 281-305, Plenum Press, New York (1987)]. Different rheological behaviours were examined to model the surface tensions which arise due to the passive deformation of the cortex: a Mooney-Rivlin material, an STZC material and a viscoelastic material. The calculations show that passive surface tensions may play a significant role in determining the local surface deformations as well as in the modulation of the surface forces. Varying the rheological model has limited effect on the overall deformations. The latter appear to be affected mostly by contractile filament interactions.     

The contractile ring coordinates curvature-dependent septum assembly during fission yeast cytokinesis

The functions of the actin-myosin–based contractile ring in cytokinesis remain to be elucidated. Recent findings show that in the fission yeast Schizosaccharomyces pombe, cleavage furrow ingression is driven by polymerization of cell wall fibers outside the plasma membrane, not by the contractile ring. Here we show that one function of the ring is to spatially coordinate septum cell wall assembly. We develop an improved method for live-cell imaging of the division apparatus by orienting the rod-shaped cells vertically using microfabricated wells. We observe that the septum hole and ring are circular and centered in wild-type cells and that in the absence of a functional ring, the septum continues to ingress but in a disorganized and asymmetric manner. By manipulating the cleavage furrow into different shapes, we show that the ring promotes local septum growth in a curvature-dependent manner, allowing even a misshapen septum to grow into a more regular shape. This curvature-dependent growth suggests a model in which contractile forces of the ring shape the septum cell wall by stimulating the cell wall machinery in a mechanosensitive manner. Mechanical regulation of the cell wall assembly may have general relevance to the morphogenesis of walled cells.