皮层蛋白介导斑马鱼(Danio rerio)原肠化细胞运动

在胚胎发育过程中, 细胞运动对指导原肠期胚胎细胞的时空定位并决定其发育命运具有核心作用, 然而活体状态下原肠化过程中细胞运动的调控机制目前并不清楚. 微丝结合蛋白皮层蛋白(cortactin)是微丝核化过程的重要调控分子, 它通过激活微丝相关蛋白2/3复合物(Arp2/3 complex)促进微丝在细胞前导缘区域迅速组装, 从而直接作用于细胞运动. 为阐明斑马鱼(Danio rerio)原肠化细胞运动的分子调控机制, 本研究首先检测了皮层蛋白在斑马鱼胚胎发育过程的表达水平. Western blotting分析证明皮层蛋白在斑马鱼原肠期胚胎中大量表达; 整装胚胎抗体染色结果表明在斑马鱼原肠化过程中, 皮层蛋白主要分布于胚胎背侧胚盾区域的细胞中, 在发生活跃运动的上皮层细胞和下皮层细胞中含量较高;在亚细胞水平, 皮层蛋白和Arp2/3复合物共同定位于运动的皮层区域, 并在细胞连接处也有大量分布. 此外, 研究还发现皮层蛋白在发育中的中枢神经系统中表达量较高. 本研究结果首次表明皮层蛋白和Arp2/3复合物介导的微丝聚合参予了斑马鱼原肠化细胞运动, 并在中枢神经系统发育中扮演重要角色.     

皮动蛋白及微丝相关蛋白2/3复合物介导的细胞运动的分子机制

皮动蛋白(cortactin)是一种含有特殊重复序列结构域的微丝肌动蛋白结合蛋白,它直接参与了细胞皮层(cortex)微丝细胞骨架的组建。它又是细胞内Src类酪氨酸蛋白激酶的主要底物之一,代表了一类高度保守的胞内皮层信号蛋白质家族。近几年来,对于细胞运动分子机制的研究取得很大进展,利用组织培养细胞进行的体外实验证明。皮动蛋白能够活化微丝相关蛋白2／3复合物(actin related protein 2／3 complex,Arp2／3 complex),调控皮层微丝细胞骨架的组装,在细胞运动过程中具有重要作用。     

微丝在卵母细胞成熟过程中的作用及调控

微丝作为细胞骨架的组成部分, 在卵母细胞成熟过程中的作用及调控近年来日益受到关注.微丝介导了卵母细胞中细胞器迁移、分散染色质收集、皮质重组、极性建立、第一极体排出等过程.现对微丝在卵母细胞的发育和成熟中作用机制的研究进展进行综述.     

果蝇羊浆膜细胞形态发生所需的Rho信号通路组分的RNAi筛选

细胞形态的形成与维持与其执行的生物学功能息息相关,其中微丝作为细胞骨架,是细胞形态的决定性因素之一。小G蛋白Rho家族是控制微丝的重要信号分子。然而Rho蛋白的不同种类,以及上游的RhoGEF和RhoGAP如何协同调控细胞形态,目前还缺乏系统研究。该研究以果蝇的羊浆膜细胞为模型,通过组织特异性表达RNAi,对Rho家族及其上游信号分子进行遗传筛选。结果显示, Rho1并未参与到羊浆膜细胞形态发生的过程中,同属Rho亚家族的RhoL、RhoBTB, Rac亚家族的Mtl,以及Cdc42是Rho活性的主要来源。通过敲降果蝇的26个RhoGEF和22个RhoGAP,进一步发现了若干重要的羊浆膜发育调控因子,其中在羊浆膜组织中敲降RhoGAP19D导致的胚胎死亡率接近100%。该研究通过RNAi遗传筛选,鉴定出一系列在羊浆膜发育过程中影响微丝的关键因子,为下一步的研究提供线索。     

蓝猪耳受精过程中中央细胞和初生胚乳细胞中微丝骨架的组装和细胞核的迁移

通过对蓝猪耳(Torenia fournieri)活体胚囊的研究,发现中央细胞和初生胚乳细胞中的微丝骨架在细胞核迁移时发生了显著的变化.授粉前,微丝在中央细胞的周质位置呈现短束状随机分布.开花两天后,它们组装成截然不同的微丝网络,在这个阶段,次生核位于中央细胞中央位置并与短束状的微丝列阵相联系.在授粉发生后不久,分布在珠孔端的微丝发生片断化,此时次生核与卵器相邻.受精后,初生胚乳细胞核从卵细胞处移开, 在初生胚乳细胞中微丝又重组形成清晰的网络结构.用latrunculin A (LAT-A)和细胞松弛素B(cytochalasin B,CB)破坏微丝骨架,得到的试验结果说明,微丝参与了中央细胞中的细胞核迁移运动.数据也表明,在受精过程中,微丝骨架的动力学特性在中央细胞和初生胚乳细胞的胞质重组中起重要作用.     

微丝的信号调控机制和体内功能

微丝是细胞骨架的主要成分之一,广泛存在于所有真核细胞中。微丝与其相关蛋白介导的信号通路几乎在所有的生物学事件中发挥重要作用,参与了细胞形态维持、细胞运动、信号转导等细胞基本生物学行为的调控。同时,微丝及其相关蛋白还在个体发育中扮演重要角色,其异常与疾病发生发展过程密切相关。该文就微丝相关蛋白、微丝相关信号通路、微丝功能及其与疾病相关的最新研究进展进行小结,并对微丝的未来研究方向进行了初步的探讨。     

肿瘤转移中E-钙粘蛋白的调控

E-钙粘蛋白是参与细胞间粘附连接的主要分子,发挥着维持细胞极性和组织结构完整性的功能.肿瘤组织中E-钙粘蛋白介导的细胞间粘附力减弱,使细胞获得浸润性和游走迁移能力.在细胞迁移到新的位置后,E-钙粘蛋白重新表达,有利于肿瘤细胞在继发部位生长增殖,形成新的病灶.E-钙粘蛋白功能调控在肿瘤转移中的作用主要涉及到以下几种机制,编码基因修饰,基因转录抑制及microRNA调节.其中microRNA通过影响E-钙粘蛋白的转录或表达在肿瘤转移过程发挥了重要作用,为肿瘤转移的临床诊断和靶向治疗开辟了新的思路.本文主要就肿瘤转移过程中E-钙粘蛋白的表达变化以及相应调控机制做一综述.     

微丝骨架调控植物特有生理活动的研究进展

微丝骨架参与了真核生物诸多重要的生理活动。真核生物的肌动蛋白均演化自同一祖先基因,在生化特性和调控机制上存在一定的相似性。动物和植物各自特异的生理活动和器官组成,动物和植物细胞中微丝骨架的存在形式、微丝结合蛋白种类及微丝动态调控机制等方面存在一定的差异。该文基于植物特有的生命活动和生理过程,重点归纳和概述了植物微丝骨架在部分植物特异生理活动中的作用机理的研究进展。     

微小RNA miR-21在皮肤创伤愈合中的研究进展

微小RNA是一类真核细胞中广泛存在的内源性转录后调控分子,其在细胞的增殖、分化、凋亡、迁移等过程中发挥了重要的调控作用。皮肤创伤修复涉及复杂的细胞与分子的相互作用网络。近年来研究表明micro RNAs在皮肤创伤修复中发挥调控作用,引人关注。miR-21作为重要的癌基因是目前研究的最多的miRNAs分子之一,其在皮肤创伤修复中的作用研究也越来越受到重视。研究表明miR-21参与了细胞增殖与迁移、炎症反应、血管生成和细胞外基质合成等重要修复相关事件的调控。因此,阐明miR-21分子在正常皮肤创伤愈合中的作用,厘清miR-21表达失调在修复不足和修复过度中的功能,将深化我们对于皮肤创伤愈合基本理论的认识,并为促进创面愈合与防治修复不足和过度提供潜在的治疗靶点。本文就miR-21分子在正常皮肤创伤修复、慢性难愈性创面和增生性瘢痕中作用的研究进展进行综述展望。     

微丝的基本性质与细胞核肌动蛋白

微丝,作为细胞骨架的重要成员,普遍存在于所有的真核细胞中。构成微丝的肌动蛋白,与肌球蛋白一起作用,使细胞产生和传导机械力,并促进细胞运动。尽管人们很早就已经认识到体细胞核中存在单体肌动蛋白,但细胞核中聚合的微丝如何动态调控及行使何种功能,仍存在争议。该文概述了微丝细胞骨架的基本性质和成核过程,并讨论细胞核内肌动蛋白的功能。     

The Contractile Proteins and Calcium Mediated Gelation and Contraction of Pollen Tube Extracts

The crude extracts of pollen tubes, like other nonmuscle ceils, showed gelation at Iow Ga2+ concentrations and ATP-dependent contraction at higher Ga2+ concentrations. The contracted cytoplasmic clots contained a lot of filaments which were mainly composed of actin, myosin, 105 kD, 67 kD, 48 kD, 38 kD, 34 kD and 28 kD proteins. It is likely that Ca2+ are able to mediate tranformation of acfin from a less ordered state to a more oriented filaments, which interact with actin-binding proteins to form the filamentous network, thus to induce the gel formation of cytoplasm, to regulate the interaction of actin and myosin which transform the chemical energy of ATP into mechanical work of contractile movement of cytoplasm.     

S100P dissociates myosin IIA filaments and focal adhesion sites to reduce cell adhesion and enhance cell migration

S100 proteins promote cancer cell migration and metastasis. To investigate their roles in the process of migration we have constructed inducible systems for S100P in rat mammary and human HeLa cells that show a linear relationship between its intracellular levels and cell migration. S100P, like S100A4, differentially interacts with the isoforms of nonmuscle myosin II (NMIIA, K(d) = 0.5 μM; IIB, K(d) = 8 μM; IIC, K(d) = 1.0 μM). Accordingly, S100P dissociates NMIIA and IIC filaments but not IIB in vitro. NMIIA knockdown increases migration in non-induced cells and there is no further increase upon induction of S100P, whereas NMIIB knockdown reduces cell migration whether or not S100P is induced. NMIIC knockdown does not affect S100P-enhanced cell migration. Further study shows that NMIIA physically interacts with S100P in living cells. In the cytoplasm, S100P occurs in discrete nodules along NMIIA-containing filaments. Induction of S100P causes more peripheral distribution of NMIIA filaments. This change is paralleled by a significant drop in vinculin-containing, actin-terminating focal adhesion sites (FAS) per cell. The induction of S100P, consequently, causes significant reduction in cellular adhesion. Addition of a focal adhesion kinase (FAK) inhibitor reduces disassembly of FAS and thereby suppresses S100P-enhanced cell migration. In conclusion, this work has demonstrated a mechanism whereby the S100P-induced dissociation of NMIIA filaments leads to a weakening of FAS, reduced cell adhesion, and enhanced cell migration, the first major step in the metastatic cascade.     

The actin cytoskeleton in normal and pathological cell motility

Cell motility is crucial for tissue formation and for development of organisms. Later on cell migration remains essential throughout the lifetime of the organism for wound healing and immune responses. The actin cytoskeleton is the cellular engine that drives cell motility downstream of a complex signal transduction cascade. The basic molecular machinery underlying the assembly and disassembly of actin filaments consists of a variety of actin binding proteins that regulate the dynamic behavior of the cytoskeleton in response to different signals. The multitude of proteins and regulatory mechanisms partaking in this system makes it vulnerable to mutations and alterations in expression levels that ultimately may cause diseases. The most familiar one is cancer that in later stages is characterized by active aberrant cell migration. Indeed tumor invasion and metastasis are increasingly being associated with deregulation of the actin system.     

Control of myofibroblast differentiation and function by cytoskeletal signaling

The cytoskeleton consists of three distinct types of protein polymer structures–microfilaments, intermediate filaments, and microtubules; each serves distinct roles in controlling cell shape, division, contraction, migration, and other processes. In addition to mechanical functions, the cytoskeleton accepts signals from outside the cell and triggers additional signals to extracellular matrix, thus playing a key role in signal transduction from extracellular stimuli through dynamic recruitment of diverse intermediates of the intracellular signaling machinery. This review summarizes current knowledge about the role of cytoskeleton in the signaling mechanism of fibroblast-to-myofibroblast differentiation–a process characterized by accumulation of contractile proteins and secretion of extracellular matrix proteins, and being critical for normal wound healing in response to tissue injury as well as for aberrant tissue remodeling in fibrotic disorders. Specifically, we discuss control of serum response factor and Hippo signaling pathways by actin and microtubule dynamics as well as regulation of collagen synthesis by intermediate filaments.     

Modulation of hyaluronan in the migratory pathway of mouse primordial germ cells

In the present report we followed the distribution of hyaluronan during the phases of separation, migration, and colonization of the primordial germ cell migratory process. Hyaluronan was detected by the use of two cytochemical methods: (1) ruthenium hexammine trichloride (RHT) associated with enzymatic treatment with hyaluronate lyase and (2) a binding specific probe for hyaluronan. After RHT treatment the proteoglycans and/or glycosaminoglycans were observed as a meshwork formed by electron-dense granules connected by thin filaments. After enzymatic digestion, no filaments could be detected in the migratory pathway. Quantitative analysis showed a close correlation between cell migration and the concentration of RHT-positive filaments. It was also shown that high amounts of hyaluronan were expressed in the separation phase and migration phases whereas during the colonization phase the amount of hyaluronan was clearly diminished. This study showed that the presence of primordial germ cells in each compartment of the migratory pathway was always accompanied by a high expression of hyaluronan. These results indicate that hyaluronan is an important molecule in the migratory process, providing the primordial germ cells with a hydrated environment that facilitates their movement toward the genital ridges.     

PI3K induced actin filament remodeling through Akt and p70S6K1: implication of essential role in cell migration

This study was designed to identify the molecular mechanisms of phosphatidylinositol 3-kinase (PI3K)-induced actin filament remodeling and cell migration. Expression of active forms of PI3K, v-P3k or Myr-P3k, was sufficient to induce actin filament remodeling to lead to an increase in cell migration, as well as the activation of Akt in chicken embryo fibroblast (CEF) cells. Either the inhibition of PI3K activity using a PI3K-specific inhibitor, LY-294002, or the disruption of Akt activity restored the integrity of actin filaments in CEF cells and inhibited PI3K-induced cell migration. We also found that expression of an activated form of Akt (Myr-Akt) was sufficient to remodel actin filaments to lead to an increase in cell migration, which was unable to be inhibited by the presence of LY-294002. Furthermore, we found that p70S6K1 kinase was a downstream molecule that can mediate the effects of both PI3K and Akt on actin filaments and cell migration. Overexpression of an active form of p70S6K1 was sufficient to induce actin filament remodeling and cell migration in CEF cells, which requires Rac activity. These results demonstrate that activation of PI3K activity alone is sufficient to remodel actin filaments to increase cell migration through the activation of Akt and p70S6K1 in CEF cells. phosphatidylinositol 3-kinase; Rac; actin filaments     

The role of Rho family proteins in controlling the migration of crawling cells

Migration of crawling cells (amoebae and some kinds of the tissue cells) is a process related to the dynamic reorganization of actomyosin cytoskeleton. That reorganization engages actin polymerization and de-polymerization, branching of actin network and interaction of myosin II with actin filaments. All those cytoskeleton changes lead to the cell progression, contraction and shifting of the uropod and the cell adhesion. Numerous external stimuli, which activate various surface receptors and signal transduction pathways, can promote migration. Rho family proteins play an important role in the regulation of actin cytoskeleton organization. The most known members of this family are Rho, Rac and Cdc42 proteins, present in all mammalian tissue cells. These proteins control three different stages of cell migration: progression of the frontal edge, adhesion which stabilizes the frontal area, and de-adhesion and shifting of the uropod. Cdc42 and Rac control cell polarization, lamellipodium formation and expansion, organization of focal complexes. Rho protein regulates contractile activity of actomyosin cytoskeleton outside the frontal area, and thus contraction and de-adhesion of the uropod.     

The coordination between actin filaments and adhesion in mesenchymal migration

Mesenchymal cell motility is characterized by a polarized distribution of actin filaments, with a network of short branched actin filaments at the leading edge, and polymers of actin filaments arranged into distinct classes of actin stress fibres behind the leading edge. Importantly, the distinct actin filaments are characteristically associated with discrete adhesion structures and both the adhesions and the actin filaments are co-ordinately regulated during cell migration. While it has long been known that these macromolecular structures are intimately linked in cells, precisely how they are co-ordinately regulated is presently unknown. Live imaging data now suggests that the focal adhesions may act as sites of actin polymerization resulting in the generation of tension-bearing actin bundles of actin filaments (stress fibres). Moreover, a picture is emerging to suggest that the tropomyosin family of proteins that can determine actin filament dynamics may also play a key role in determining the transition between adhesion states. Molecules such as the tropomyosins are therefore tantalizing candidates to orchestrate the coordination of actin and adhesion dynamics during mesenchymal cell migration.     

Navigating the cell

Changes in cell shape are associated with a variety of processes including cell migration, axon outgrowth, cell division, and vesicle trafficking. C. elegans UNC-53 and its vertebrate homologs, the Navigators, are required for the migration of cells and the outgrowth of neuronal processes. The identification of novel molecular interactions and live imaging studies have revealed that UNC-53/NAVs are signal transducers associated with actin filaments, microtubules, and intermediate filaments. In addition to modulating cytoskeletal dynamics at the leading edge of migrating or outgrowing cells, both UNC-53 and the navigators are expressed in adult cells, conspicuously those with specialized roles in endocytosis or secretion. Collectively, these results suggest that UNC-53/NAVs may be a central regulator of cytoskeletal dynamics, responsible for integrating signaling cues to multiple components of the cytoskeleton to coordinate rearrangement during cell outgrowth or trafficking.     

Spatial distribution of filament elasticity determines the migratory behaviors of a cell

Any cellular response leading to morphological changes is highly tuned to balance the force generated from structural reorganization, provided by actin cytoskeleton. Actin filaments serve as the backbone of intracellular force, and transduce external mechanical signal via focal adhesion complex into the cell. During migration, cells not only undergo molecular changes but also rapid mechanical modulation. Here we focus on determining, the role of spatial distribution of mechanical changes of actin filaments in epithelial, mesenchymal, fibrotic and cancer cells with non-migration, directional migration, and non-directional migration behaviors using the atomic force microscopy. We found 1) non-migratory cells only generated one type of filament elasticity, 2) cells generating spatially distributed two types of filament elasticity showed directional migration, and 3) pathologic cells that autonomously generated two types of filament elasticity without spatial distribution were actively migrating non-directionally. The demonstration of spatial regulation of filament elasticity of different cell types at the nano-scale highlights the coupling of cytoskeletal function with physical characters at the sub-cellular level, and provides new research directions for migration related disease.