Spiraled origins

Recent studies have established that the eukaryotic actin-based cytoskeleton has prokaryotic origins. In addition to regulating cell shape and polarity, Gitai et al. (2005) provide convincing evidence that the Caulobacter actin homolog MreB also mediates the early segregation of the chromosomal origin, a typical functional role of the eukaryotic tubulin-based cytoskeleton.     

Roles of fascin in cell adhesion and motility

Many cell interactions depend on the assembly of cell protrusions; these include cell attachment and migration in the extracellular matrix, cell-cell communication, and the ability of cells to sense their local environment. Cell protrusions are extensions of the plasma membrane that are supported internally by actin-based structures that impart mechanical stiffness. Fascin is a small, globular actin-bundling protein that has emerging roles in diverse forms of cell protrusions and in cytoplasmic actin bundles. The fascin-actin interaction is under complex regulation from the extracellular matrix, peptide factors and other actin-binding proteins. Recent developments advance our understanding of the multifaceted regulation of fascin and the roles of fascin-containing structures in cell adhesion, motility and invasion in the life of vertebrate organisms.     

细胞药物的种类及生物学特性——细胞药物连载之一

细胞药物是以不同细胞为基础的用于疾病治疗的制剂、药物或产品的统称,是继放疗、化疗之后又一种临床有效的治疗手段,可实施个性化治疗。细胞药物的种类很多,按其生物学特性可分为传统体细胞、免疫细胞以及各种不同的干细胞等。经体外操作过的细胞群,如肝细胞、胰岛细胞、软骨细胞、树突状细胞、细胞因子诱导的杀伤细胞、淋巴因子激活的杀伤细胞、体外加工的骨髓或造血干细胞和体外处理的肿瘤细胞(瘤苗)等。细胞药物已在一些难治性疾病中得到应用,包括血液系统疾病、心血管系统疾病、消化系统疾病、神经系统疾病、免疫系统疾病和抗衰老等。细胞治疗涉及的细胞种类很多,且不同细胞或不同治疗方法各有特点。运用不同的细胞药物来修复病变细胞,以重建受损的功能细胞和组织,恢复其生物学功能,为细胞丢失或损伤性疾病的防治提供了崭新的思路。     

Translocation of MARCKS and reorganization of the cytoskeleton by PMA correlates with the ion selectivity,the confluence,and transformation state of kidney epithelial cell lines

The role of protein kinase C (PKC) in the regulation of the cytoskeleton of epithelial cells with tightly sealed contacts, poor contacts, and without contacts were investigated by incubating them with a protein kinase C activator phorbol myristoyl acetate (PMA). The morphology and organization of the membrane skeleton and stress fibers as well as the localization of an actin-bundling PKC substrate MARCKS in confluent MDCK cells originating from the distal tubulus of dog kidney, LLC-PK1 cells originating from the proximal tubulus of pig kidney, src-transformed MDCK cells, epidermoid carcinoma A431 cells, and MDCK cells grown in low calcium medium (LC medium) in low density were visualized with phase contrast and immunofluorescence microscopy. Four different responses to the PMA-treatment in actin-based structures of cultured epithelial cells were observed: 1) disintegration of the membrane skeleton in confluent MDCK cells; 2) depolymerization of the stress fibers in confluent MDCK and LLC-PK1 cells; 3) formation of the membrane skeleton in A431 cells, and 4) formation of the stress fibers and membrane skeleton in LC-MDCK cells. Thus, it seems that in fully confluent tightly sealed epithelium, activation of PKC has a deleterious effect on actin-based structures, whereas in cells without contacts or loose contacts, activation of PKC by PMA results in improvement of actin-based cytoskeletal structures. The main difference between the two kidney cell lines used is their selectivity to ion transport: the monolayer of LLC-PK1 cells is anion selective and MDCK cells cation selective. We propose a model where alterations in the ionic milieu within the MDCK cells by means of cation channels affect the disintegration of the membrane skeleton. The distribution of MARCKS followed the distribution of fodrin in both cell lines upon PMA-treatment, suggesting that phosphorylation of MARCKS by PKC may contribute in the regulation of the integrity of the membrane skeleton. J. Cell. Physiol. 181:83–95, 1999. © 1999 Wiley-Liss, Inc.     

Planet of the Normates

Extraordinary Bodies: Figuring Physical Disability in American Culture and Literature. Rosemarie Garland Thomson. New York: Columbia University Press, 1997. 200 pp.
Freakery: Cultural Spectacles of the Extraordinary Body. Rosemarie Garland Thomson. ed. New York: New York University Press, 1996. 400 pp.
Monster Theory: Reading Culture. Jeffrey Jerome Cohen. ed. Minneapolis: University of Minnesota Press, 1996.315pp.     

A short history of plant biotechnology

The foundations of modern plant biotechnology can be traced back to the Cell Theory of Schleiden (Arch Anat Physiol Wiss Med (J Müller) 1838:137–176, 1838) and Schwann (Mikroscopische Untersuchungen über die übereinstimmung in der Struktur und dem Wachstum des Tiere und Pflanzen. W Engelmann: Leipzig No 176, 1839), which recognized the cell as the primary unit of all living organisms. The concept of cellular totipotency, which was inherent in the Cell Theory and forms the basis of plant biotechnology, was further elaborated by Haberlandt (Sitzungsber K Preuss Akad Wiss Wien, Math-Naturwiss 111:69–92, 1902), who predicted the production of somatic embryos from vegetative cells. This brief historical account traces the development of technologies for the culture, regeneration and transformation of plants that led to the production of transgenic crops which have become central to the many applications of plant biotechnology, and celebrates the pioneering men and women whose trend-setting contributions made it all possible. Opening Plenary Address delivered at the international conference on “Plants for Human Health in the Post-Genome Era”, held August 26–29, 2007, in Helsinki, Finland.     

Auxins and Cytokinins as Antipodal Modulators of Elasticity within the Actin Network of Plant Cells

The cytoskeleton of plant and animal cells serves as a transmitter, transducer, and effector of cell signaling mechanisms. In plants, pathways for proliferation, differentiation, intracellular vesicular transport, cell-wall biosynthesis, symbiosis, secretion, and membrane recycling depend on the organization and dynamic properties of actin- and tubulin-based structures that are either associated with the plasma membrane or traverse the cytoplasm. Recently, a new in vivo cytoskeletal assay (cell optical displacement assay) was introduced to measure the tension within subdomains (cortical, transvacuolar, and perinuclear) of the actin network in living plant cells. Cell optical displacement assay measurements within soybean (Glycine max [L.]) root cells previously demonstrated that lipophilic signals, e.g. linoleic acid and arachidonic acid or changes in cytoplasmic pH gradients, could induce significant reductions in the tension within the actin network of transvacuolar strands. In contrast, enhancement of cytoplasmic free Ca2+ resulted in an increase in tension. In the present communication we have used these measurements to show that a similar antipodal pattern of activity exists for auxins and cytokinins (in their ability to modify the tension within the actin network of plant cells). It is suggested that these growth substances exert their effect on the cytoskeleton through the activation of signaling cascades, which result in the production of lipophilic and ionic second messengers, both of which have been demonstrated to directly effect the tension within the actin network of soybean root cells.     

细胞运动、细胞迁移与细胞骨架研究进展

细胞定向运动与细胞骨架的动态循环密切相关。运动细胞在其伪足前沿依靠细胞骨架的不断聚合推动细胞膜的前进,在基部靠近细胞体部位通过细胞骨架的不断解聚收缩拖拉细胞体向前运动,细胞骨架的聚合与解聚通过伪足与支撑表面的吸附与解吸附而偶连。肌动蛋白组成的微丝骨架是大多数运动细胞的主要成分。外界刺激引起微丝细胞骨架动态变化的信号通路已逐步明了。线虫精子细胞的运动行为与阿米巴变形运动相似,但是在线虫精子细胞中没有肌动蛋白,而是以精子主要蛋白为基础形成细胞骨架驱动精子细胞的运动。与肌动蛋白不同,精子主要蛋白没有分子极性、ATP结合位点和马达蛋白。通过比较研究以上两种运动体系将有助于在分子水平上进一步阐明细胞运动的机理。     

The plant cell body: a cytoskeletal tool for cellular development and morphogenesis

Summary Certain aspects of cellular behaviour in relation to growth and development of plants can be understood in terms of the cell body concept proposed by Daniel Mazia in 1993. During the interphase of the mitotic cell cycle, the plant cell body is held to consist of a nucleus and a perinuclear microtubule-organizing centre from which microtubules radiate into the cytoplasm. During mitosis and cytokinesis in meristematic cells, and also during the period of growth in post-mitotic cells immediately beyond the meristem, the plant cell body undergoes various characteristic morphological transformations, many of which are proposed as being related to changing structural connections with the actin-based component of the cytoskeleton and with specialized, plasma-membrane-associated sites at the cell periphery. In post-mitotic cells, these transformations of the plant cell body coincide with, and probably provide conditions for, the various pathways of development which such cells follow. They are also responsible, for the acquisition of new cellular polarities. Events in which the plant cell body participates include the formation of a mitotic spindle, phragmoplast, and new cell division wall, the rearrangement of a diffuse type of cell wall growth into tip growth (as occurs, e.g., during the initiation and subsequent development of root hairs), and the growth and division that occurs in reactivated vacuolate cells. If more evidence can be marshalled in support of the existence and properties of the plant cell body, then this concept could prove useful in interpreting the cytological bases of a range of developmental events in plants.Abbreviations CMT cortical microtubule - EMT endoplasmic microtubule - ER endoplasmic reticulum - MF microfilament - MT microtubule - MTOC microtubule-organizing centre - PPB preprophase band (of microtubules) - QC quiescent centre - VSC vesicle supply centre     

Asymmetric cell division of a triangular halophilic archaebacterium

Abstract The cell division of the halophilic archaebacterium, Haloarcula japonicus , which has a characteristic triangular shape in high salt concentration media, was analysed by time lapse microscopic cinematography. Cell division on an agar medium occured on average every 3.7 h. Cell plates were laid down asymmetrically, generating triangular or rhomboid shape daughter cells which then separated. Cell plate formation was clearly observed because the cells are flat and thin enough to see through using a conventional light microscope.     

Plasmodesmata in Arabidopsis thaliana suspension cells

Summary. A current challenge in plant biology is to identify the structural and functional components of plasmodesmata (PDs). The use of plant tissue as a source material for plasmodesmal characterisation has had limited success, so we have explored the frequency and features of PDs occurring in suspension cell cultures of Arabidopsis thaliana. This material has the advantages of homogeneity, quantity, and ease of disruption. Using light and electron microscopy and immunostaining for callose and calreticulin, we showed that suspension cells laid down abundant PDs in division walls, and that vestiges of these structures were retained as half PDs even when the cell-to-cell contacts were disrupted during culture growth. Although callose was a reliable marker for PD distribution, which was deposited in an organised collar around the neck of PDs, it was not abundant in unstressed cells. Calreticulin and the chemical stain 3,3-dihexyloxacarbocyanine iodide also provided useful markers when monitoring PDs in cell wall preparations by light microscopy. Purified cell walls were shown to be virtually free of contamination from cytoplasmic components, except for the presence of small amounts of cortical endoplasmic reticulum attached to PDs. Hence, clean cell walls from A. thaliana suspension cells provide a valuable resource for a proteomic approach to the analysis of plasmodesmal components.Correspondence and reprints: John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom.     

Occurrence of osteoblast necroses during ossification of long bone cortices in mouse fetuses

Previous investigations concerned with in vitro osteogenesis and mineralization have revealed some indication of a participation of cell necroses in the course of calcification. These observations were confirmed by in vivo investigations on desmoid ossification in fetal mouse calvariae, where abundant necrotic osteoblasts were found at the mineralization border and in the osteoid. In the present study, ossification of long bone cortices from fetal mice was investigated by use of electron microscopy. Specimens obtained from the collection of the Institute of Anatomy, Free University of Berlin (mouse fetuses, forearm; rat fetuses, forearm) were reinvestigated for control purposes. In all cases, mineralization of osteoid was accompanied by cell necroses. Cell degeneration was characterized by swelling of the endoplasmic reticulum and loss of the plasma membrane resulting in freely distributed vesicular structures. Cell debris was incorporated within the mineral. Initially, cell necroses in the perichondrium occurred in the region surrounding the hypertrophic cartilage and the matrix of which showed spots of endochondral mineralization. Necrotic osteoblasts occurred simultaneously with mineralization of the osteoid. During further ossification of the long bone cortices, the number of necrotic cells increased markedly. In addition to necrotic cells, healthy osteoblasts, osteocytes and perichondral tissue were present, indicating that an artifact can be excluded. The importance of cell necroses in the process of mineralization is as yet unclear. Possibly, the cells act as calcium and/or phosphate stores, which are liberated by cell death to increase the amount of mineral constituents at sites of mineralization.     

Intrinsic Response Towards Physiologic Stiffness is Cell-Type Dependent

In the continuous search for better tissue engineering scaffolds it has become increasingly clear that the substrate properties dramatically affect cell responses. Here we compared cells from a physiologically stiff tissue, melanoma, to cells isolated from a physiologically soft tissue, brain. We measured the cell line responses to laminin immobilized onto glass or polyacrylamide hydrogels tuned to have a Young’s modulus ranging from 1 to 390?kPa. Single cells were analyzed for spreading area, shape, total actin content, actin-based morphological features and modification of immobilized laminin. Both cell types exhibited stiffness- and laminin concentration-dependent responses on polyacrylamide and glass. Melanoma cells exhibited very little spreading and were rounded on soft (1, 5, and 15?kPa) hydrogels while cells on stiff (40, 100, and 390?kPa) hydrogels were spread and had a polarized cell shape with large lamellipodia. On rigid glass surfaces, spreading and actin-based morphological features were not observed until laminin concentration was much higher. Similarly, increased microglia cell spreading and presence of actin-based structures were observed on stiff hydrogels. However, responses on rigid glass surfaces were much different. Microglia cells had large spreading areas and elongated shapes on glass compared to hydrogels even when immobilized laminin density was consistent on all gels. While cell spreading and shape varied with Young’s modulus of the hydrogel, the concentration of f-actin was constant. A decrease in laminin immunofluorescence was associated with melanoma and microglia cell spreading on glass with high coating concentration of laminin, indicating modification of immobilized laminin triggered by supraphysiologic stiffness and high ligand density. These results suggest that some cell lines are more sensitive to mechanical properties matching their native tissue environment while other cell lines may require stiffness and extracellular ligand density well above physiologic tissue before saturation in cell spreading, elongation and cytoskeletal re-organization are reached.     

Actin-based motility is sufficient for bacterial membrane protrusion formation and host cell uptake

Shigella flexneri replicates in the cytoplasm of host cells, where it nucleates host cell actin filaments at one pole of the bacterial cell to form a 'comet tail' that propels the bacterium through the host's cytoplasm. To determine whether the ability to move by actin-based motility is sufficient for subsequent formation of membrane-bound protrusions and intercellular spread, we conferred the ability to nucleate actin on a heterologous bacterium, Escherichia coli . Previous work has shown that IcsA (VirG), the molecule that is necessary and sufficient for actin nucleation and actin-based motility, is distributed in a unipolar fashion on the surface of S. flexneri . Maintenance of the unipolar distribution of IcsA depends on both the S. flexneri outer membrane protease IcsP (SopA) and the structure of the lipopolysaccharide (LPS) in the outer membrane. We co-expressed IcsA and IcsP in two strains of E. coli that differed in their LPS structures. The E. coli were engineered to invade host cells by expression of invasin from Yersinia pseudotuberculosis and to escape the phagosome by incubation in purified listeriolysin O (LLO) from Listeria monocytogenes . All E. coli strains expressing IcsA replicated in host cell cytoplasm and moved by actin-based motility. Actin-based motility alone was sufficient for the formation of membrane protrusions and uptake by recipient host cells. The presence of IcsP and an elaborate LPS structure combined to enhance the ability of E. coli to form protrusions at the same frequency as S. flexneri , quantitatively reconstituting this step in pathogen intercellular spread in a heterologous organism. The frequency of membrane protrusion formation across all strains tested correlates with the efficiency of unidirectional actin-based movement, but not with bacterial speed.     

Cell growth and cell division in the rod-shaped actinomycete Corynebacterium glutamicum

Bacterial cell growth and cell division are highly complicated and diversified biological processes. In most rod-shaped bacteria, actin-like MreB homologues produce helicoidal structures along the cell that support elongation of the lateral cell wall. An exception to this rule is peptidoglycan synthesis in the rod-shaped actinomycete Corynebacterium glutamicum, which is MreB-independent. Instead, during cell elongation this bacterium synthesizes new cell-wall material at the cell poles whereas the lateral wall remains inert. Thus, the strategy employed by C. glutamicum to acquire a rod-shaped morphology is completely different from that of Escherichia coli or Bacillus subtilis. Cell division in C. glutamicum also differs profoundly by the apparent absence in its genome of homologues of spatial or temporal regulators of cell division, and its cell division apparatus seems to be simpler than those of other bacteria. Here we review recent advances in our knowledge of the C. glutamicum cell cycle in order to further understand this very different model of rod-shape acquisition.     

Looking over the edge: a new role for Ena/VASP proteins in lamellipodial dynamics

How can Ena/VASP proteins promote actin-based movement of the intracellular pathogen Listeria or rapid protrusion of lamellipodia but at the same time inhibit cell translocation? A report in the May 17(th) issue of Cell now offers a possible explanation for this conundrum. Bear et al. report that Ena/VASP proteins regulate cell motility by competing with capping proteins to control actin filament length and geometry at the leading edge of cells.     

Stimulation of fascin spikes by thrombospondin-1 is mediated by the GTPases Rac and Cdc42

Cell adhesion to extracellular matrix is an important physiological stimulus for organization of the actin-based cytoskeleton. Adhesion to the matrix glycoprotein thrombospondin-1 (TSP-1) triggers the sustained formation of F-actin microspikes that contain the actin-bundling protein fascin. These structures are also implicated in cell migration, which may be an important function of TSP-1 in tissue remodelling and wound repair. To further understand the function of fascin microspikes, we examined whether their assembly is regulated by Rho family GTPases. We report that expression of constitutively active mutants of Rac or Cdc42 triggered localization of fascin to lamellipodia, filopodia, and cell edges in fibroblasts or myoblasts. Biochemical assays demonstrated prolonged activation of Rac and Cdc42 in C2C12 cells adherent to TSP-1 and activation of the downstream kinase p21-activated kinase (PAK). Expression of dominant-negative Rac or Cdc42 in C2C12 myoblasts blocked spreading and formation of fascin spikes on TSP-1. Spreading and spike assembly were also blocked by pharmacological inhibition of F-actin turnover. Shear-loading of monospecific anti-fascin immunoglobulins, which block the binding of fascin to actin into cytoplasm, strongly inhibited spreading, actin cytoskeletal organization and migration on TSP-1 and also affected the motility of cells on fibronectin. We conclude that fascin is a critical component downstream of Rac and Cdc42 that is needed for actin cytoskeletal organization and cell migration responses to thrombospondin-1.     

Zyxin-mediated Actin Assembly Is Required for Efficient Wound Closure

Cytoskeletal regulation of cell adhesion is vital to the organization of multicellular structures. The focal adhesion protein zyxin emerged as a key regulator of actin assembly because zyxin recruits Enabled/vasodilator-stimulated phospho-proteins (Ena/VASP) to promote actin assembly. Zyxin also localizes to the sites of cell-cell adhesion and is thought to promote actin assembly with Ena/VASP. Using shRNA targeted to zyxin, we analyzed the roles of zyxin at adhesive contacts. In zyxin-deficient cells, the actin assembly at both focal adhesion and cell-cell adhesion was limited, but their migration rate was unchanged. Cell spreading on E-cadherin-coated surfaces and the formation of cell clusters were slower for zyxin-deficient cells than wild type cells. By ablating a single cell within a cell monolayer, we quantified the rate of wound closure driven by a contractile circumferential actin ring. Zyxin-deficient cells failed to recruit VASP to cell-cell junctions at the wound edge and had a slower wound closure rate than wild type cells. Our results suggest that, by recruiting VASP, zyxin regulates actin assembly at the sites of force-bearing cell-cell adhesion.