Prokaryotic cells: structural organisation of the cytoskeleton and organelles

For many years, prokaryotic cells were distinguished from eukaryotic cells based on the simplicity of their cytoplasm, in which the presence of organelles and cytoskeletal structures had not been discovered. Based on current knowledge, this review describes the complex components of the prokaryotic cell cytoskeleton, including (i) tubulin homologues composed of FtsZ, BtuA, BtuB and several associated proteins, which play a fundamental role in cell division, (ii) actin-like homologues, such as MreB and Mb1, which are involved in controlling cell width and cell length, and (iii) intermediate filament homologues, including crescentin and CfpA, which localise on the concave side of a bacterium and along its inner curvature and associate with its membrane. Some prokaryotes exhibit specialised membrane-bound organelles in the cytoplasm, such as magnetosomes and acidocalcisomes, as well as protein complexes, such as carboxysomes. This review also examines recent data on the presence of nanotubes, which are structures that are well characterised in mammalian cells that allow direct contact and communication between cells.

The actin filament network associated to Sertoli cell ectoplasmic specializations

Junctional devices in Sertoli cells conform the blood-testis barrier and play a key role in maturation and differentiation of germ cells. The spacial distribution of ectoplasmic specializations of Sertoli cells was studied by beta-actin immunolabelling, using laser confocal and transmission electron microscopy. For confocal microscopy, beta-actin immunolabelling of ectoplasmic specializations was studied over the background of either prosaposin or glutaredoxin immunolabelling of the Sertoli cytoplasm. Labelling was found near the basal lamina, surrounding early spermatocytes (presumably in leptotene-zygotene) or at one of two levels in the seminiferous epithelium: (1) around deep infoldings of the Sertoli cell cytoplasm, in tubular stages before spermiation, and (2) in the superficial part of the seminiferous epithelium, in tubular stages after or during spermiation. For transmission electron microscopy, beta-actin immunolabelling of ectoplasmic specializations was also used. Ectoplasmic specializations were found at two different levels of the seminiferous epithelium. We also used freeze fracture to analyze the characteristics of tubulo-bulbar complexes, a known component of apical ectoplasmic specializations. Also, these different approaches allowed us to study the complex arrangement of the actin cytoskeleton of Sertoli cells branches, which surround germ cells in different stages of the spermatogenic cycle. Our results show a consistent labelling for beta-actin before, during and after the release of spermatozoa in the tubular lumen (spermiation) suggesting a significant role of the actin network in spermatic cell differentiation. In conclusion, significant interrelations among the beta-actin network, the junctional complexes of the blood-testis barrier and the ectoplasmic specializations were detected at different stages of the seminiferous cycle.

Trypanosoma cruzi trypomastigotes induce cytoskeleton modifications during HeLa cell invasion

It has been recently shown that Trypanosoma cruzi trypomastigotes subvert a constitutive membrane repair mechanism to invade HeLa cells. Using a membrane extraction protocol and high-resolution microscopy, the HeLa cytoskeleton and T. cruzi parasites were imaged during the invasion process after 15 min and 45 min. Parasites were initially found under cells and were later observed in the cytoplasm. At later stages, parasite-driven protrusions with parallel filaments were observed, with trypomastigotes at their tips. We conclude that T. cruzi trypomastigotes induce deformations of the cortical actin cytoskeleton shortly after invasion, leading to the formation of pseudopod-like structures.

Toxoplasma gondii: further studies on the subpellicular network

The association of the pellicle with cytoskeletal elements in Toxoplasma gondii allows this parasite to maintain its mechanical integrity and makes possible its gliding motility and cell invasion. The inner membrane complex (IMC) resembles the flattened membrane sacs observed in free-living protozoa and these sacs have been found to associate with cytoskeletal proteins such as articulins. We used immunofluorescence microscopy to characterise the presence and distribution of plateins, a sub-family of articulins, in T. gondii tachyzoites. A dispersed labelling of the whole protozoan body was observed. Electron microscopy of detergent-extracted cells revealed the presence of a network of 10 nm filaments distributed throughout the parasite. These filaments were labelled with anti-platein antibodies. Screening the sequenced T. gondii genome, we obtained the sequence of an IMC predicted protein with 25 percent identity and 42 percent similarity to the platein isoform alpha 1 present in Euplotes aediculatus, but with 42 percent identity and 55 percent similarity to that found in Euglena gracilis, suggesting strong resemblance to articulins.

Biliary Hamartoma / 대한간학회지

No abstract available.

Light and electron microscopic examination of human subungual tissue Glomus and lamellated bodies

There is only limited data related to the subungual glomus body. We therefore studied the structure of this organ, aiming to obtain further evidence. Additionally, we encountered undefined receptor like structures in close association with these glomus cells, named them as lamellated bodies and examined both of the structures at light and electron microscopic levels. This study was carried out at the Faculty of Medicine, Hacettepe University, Ankara, Turkey, during the time period May 2001 to March 2002. In this study, the subungual tissues of 4 patients were examined. Within subungual tissue, 2 groups of morphologically significant structures were determined by light microscopy. The first structure was described as glomus body. It was characterized as an encapsulated structure, rich in rounded clear cells filling its central compartment. The latter structure having a lamellated appearance was described as lamellated body. In the electron microscopic examination, lamellated bodies were characterized by central filament rich large cells and surrounding cytoplasmic processes of ensheathing cells, some of which were vacuolated. Glomus bodies were surrounded by a capsule and centrally located numerous rounded cells which reflected the structural features of an active cell. The lamellated bodies are very unusual structures and they are not found in any other part of the body. The structural organization of the ensheathing cells in the lamellated bodies greatly resembles many skin associate receptors. Therefore, we planned future studies by using immunohistochemistry, to reveal nervous elements for structural contribution

Cytoskeletal changes during poliovirus infection in an intestinal cell line.

BACKGROUND & OBJECTIVES: Although polioviral replication has been extensively studied, cytoskeletal changes in the host cell during poliovirus replication have not been extensively investigated. We studied the ultrastructural and cytoskeletal changes in host cells during poliovirus infection. METHODS: Fluorescence staining of filamentous actin with a fluorescein-isothiocynate labelled mycotoxin, in the absence and presence of microfilament inhibitors cytochalasins B and D, and electron microscopy were used to investigate the role and fate of actin microfilaments during poliovirus infection, morphogenesis and release in an intestinal cell line, HRT-18. RESULTS: At 10 h post-infection, fluorescence staining of actin showed focal areas of fluorescence in the cytoplasm. By 16 h, these became more prominent and increased in number, and by 18-22 h they coalesced to enclose areas of the cytoplasm. These changes in the actin profile were confirmed by electron microscopy, where small actin bundles appeared in association with vesicles, increased in size, number and thickness, enclosed areas of cytoplasm with numerous vesicles and were finally seen in association with crystalline arrays of virus near the periphery of the cells. The addition of microfilament inhibitors cytochalasins B and D, after the initial period of adsorption resulted in complete inhibition of changes in the actin profile and of viral release, indicating that microfilament inhibitors prevented both polymerization of actin and movement of the virus within the cell. INTERPRETATION & CONCLUSION: In poliovirus infection, both intracellular movement and release of virus appear to be related to cytoskeletal changes, particularly involving actin microfilaments.

The cytoskeleton of the electric tissue of Electrophorus electricus, L

The electric eel Electrophorus electricus is a fresh water teleost showing an electrogenic tissue that produces electric discharges. This electrogenic tissue is distributed in three well-defined electric organs which may be found symmetrically along both sides of the eel. These electric organs develop from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolema. This review examines the contribution of the cytoskeletal meshwork to the maintenance of the polarized organization of the electrocyte, the cell that contains all electric properties of each electric organ. The cytoskeletal filaments display an important role in the establishment and maintenance of the highly specialized membrane model system of the electrocyte. As a muscular tissue, these electric organs expresses actin and desmin. The studies that characterized these cytoskeletal proteins and their implications on the electrophysiology of the electric tissues are revisited.

Keratinas: biología celular y significado funcional normal y patológico / Keratins: cell biology and it normal and pathological functional significance

Las Keratinas (Ks), son filamentos intermedios que forman parte del citoesqueleto de las células epiteliales. Pueden expresarse en los epitelios simples (Ks. 7, 8, 19 y 20) y en epitelios estratificados (Ks. 1, 2, 5, 9, 10, 11, 16). La diferente expresión de estas proteínas multigénicas del citoesqueleto está ligada a programas de diferenciación celular específicos (OSBORN & WEBER, 1983; NAGLE, 1988); por ello, el estuio de las Ks. tiene singular importancia en el conocimiento de nuevos aspectos de la Histología e Histopatología, como también de la Biología del Desarrollo. Además, la evaluación de las Ks. mediante técnicas de inmunofluorescencia o inmunohistoquímicas es útil en la correcta identificación y caracterización de las células normales, displásicas y neoplásicas (OSBORN & WEBER, NAGLE). Los distintos patrones de expresión de las Ks. se correlacionan con el grado de diferenciación de células epiteliales inmaduras, y, pór ello, con el grado de diferenciación de los tumores malignos. (FUCHS & GREEN, 1980; FRANKE et al. 1981b; MOLL et. al. 1892a; SCHAAFSMA & RAMAEKERS, 1994). Por último, la valoración de los cambios de inmunoexpresión de Ks. es útil para el diagnóstico diferencial entre metaplasias escamosas típicas y atípicas, incluyendo las displasias epiteliales moderadas y severas y las neoplasias intraepiteliales anteriormente denominadas carcinomas in situ (MOLL et. al., 1982a; TSENG et. al., 1982; QUINLAN et. al., 1985; HUSZAR et. al., 1986; GIGI-LEITNER et. al., 1986; HEID et. al., 1988)

Participación del citoesqueleto en la fisiología del endometrio / Cytoskeleton participation in endometrium physiology

En el endometrio el citoesqueleto participa en todas las funciones mecánicas de la célula, en el movimiento y reacomodo de organelos y proteínas solubles y en el metabolismo en general. El epitelio endometrial por su morfología y aparente homogeneidad celular, se ha estudiado más que el estroma. Se sabe que los filamentos intermedios muestran un patrón característico típico de la clase celular. Durante la preñez y la pseudopreñez, en la región apical de las células epiteliales tanto luminales como glandulares predomina la queratina sobre la región basolateral, en tanto que la vimetina solo se encuentra en las células epiteliales luminales, y se incrementa el día de la implantación. En humanos y roedores, la desmina solo se expresa en la decidua. Se piensa que los filamentos intermedios, participan en la difusión de proteínas de membrana cambiando la polaridad. Los microfilamentos intervienen en la regulación de la forma y movilidad celular. En el epitelio luminal participan en las transformaciones de la superficie uterina, como son las microvellosidades. Al sistema de microtúbulos (MT) en el endometrio y otros órganos se le ha relacionado con la psisción y movimiento de orgánulos como son los lisosomas, mitocondrias o aparato de Golgio; además se ha demostrado que los MT también intervienen en la síntesis de DNA, ya que drogas como la colchicina impiden estos fenómenos

Estudo de células cultivadas do adenoma pleomórfico humano: análise do fenótipo celular frente à açäo de proteínas da matriz extra-celular, análise da distribuiçäo citoesqueletal do filamento intermediário vimentina / Study of cells cultivated from human pleomorphic adenoma: analysis of cellular phenotype under the action of proteins from the extracellular matrix, analysis of cytoskeletal distribution of vimentine intermediary filaments

Cultura primária de células derivadas do adenoma pleomórfico humano (AP2) foi estabelecida e utilizada em estudos de resposta à açäo de proteínas da matriz extra-celular (MEC). As células cultivadas foram caracterizadas como mio-epitelial símile por imunocitoquímica e microscopia eletrônica de transmissäo (MET). Células AP2 cresceram em contato com as seguintes proteínas da MEC: lamina, colágeno I, colágeno IV e membrana basal reconstituída (Matrigel). Laminina e colágenos tipos I e IV, quando aplicados individualmente, näo causaram efeito no fenótipo das células AP2. No entanto, células crescidas em Matrigel mostraram importantes alteraçöes fenotípicas, dependendo do modo de aplicaçäo do substrato. Células crescidas sobre finas camadas de Matrigel desenvolveram fenótipo estrelado, com prolongamentos delicados, longos e intercomunicantes, lembrando as células mio-epiteliais normais. Células crescidas dentro de massas de Matrigel formaram agrupamentos tri-dimensionais. Ao microscópio confocal e MET esses agrupamentos apresentaram dupla camada de células epitelióides delimitando espaços luminais. As células próximas aos lúmens eram cubóides, com vilosidades apicais e complexo juncional. Nosso trabalho forneceu uma evidência direta demonstrando que a formaçäo de estruturas luminais do adenoma pleomórfico somente ocorre quando suas células säo tri-dimensionalmente envoltas por membrana basal. Paralelamente a esse estudo, foi analisada a distribuiçäo do filamento intermediário vimentina no citoplasma de células AP2. Nessa célula, a vimentina distribui-se como filamentos pequenos, completamente segregados da rede principal. A maioria desses filamentos näo co-localiza com microtúbulos. Análise da relaçäo vimentina-microtúbulos nas células AP2 mostrou que essas estruturas somente interagem quando os filamentos de vimentina se estendem em direçäo à periferia da célula

Parietal cells contain most of the myosin, filamin and actin present in rat gastric glands

The association of myosin and a filamin-like protein to the F-actin cytoskeleton of parietal cells was studied in the rat gastric mucosa. Myosin and the filamin-like protein were localized by indirect immunofluorescence microscopy while the distribution of actin was established by using FITC-phalloidin. These cytoskeletal proteins, concentrated in the parietal cells, changed their distribution in correlation with the hydrochloric acid (HCl) secretory state of the cells and the appearance of a developed intracellular canaliculus. Thus,in resting parietal cells, actin showed a patchy distribution, delimiting the poorly developed secretory canaliculi, while myosin and the filamin-like protein distributed diffusely over the cytoplasm. In secreting cells, F-actin was concentrated in the cytoplasmic projections filling the canalicular lumen, while myosin and the filamin-like protein were excluded from this region, concentrating in the adjoining cytoplasm. The present results show that myosin and the filamin-like protein change their association with the secretory membranes in relation to the development of the secretory canaliculus of parietal cells. In resting cells, both proteins associate with the endocellular secretory membranes. In secreting cells, the microvillar projections of the canalicular surface formed by these membranes bind F-actin, but exclude myosin and the filamin-like protein

Further studies on the cytoskeleton of resident, stimulated and activated macrophages

A organizaçäo tri-dimensional do citoesqueleto de macrófagos residentes, estimulados e ativados fou estudada por microscopia eletrônica de transmissäo e imunofluorescência indireta. O exame de réplicas de platina e carbono mostrou com grande clareza a organizaçäo de filamentos e microtúbulos citoplasmáticos. Preparaçöes de citoesqueleto revelaram estructuras filamentosas em torno aos centríolos, bem como grânulos densos dispersos na rede filamentosa de macrófagos ativados. A microanálise de raios-X mostrou que eles concentram ósmio. Foi revelada a apresença de tubulina, actina, vimentina e miosina dispersas e/ou associada a estruturas filamentosas em macrófagos nas três situaçöes de ativaçäo, através da imunofluorescência indirecta

Analysis of the ultrastructure of the platelets during the process of aggregation, with emphasis in the cytoskeleton and membranous changes

In this paper we presetn our findings in relation to the ultrastructural changes that are produced in the platelets during the hemostatic activation process. When the platelets are in the resting stage they have a discoid form with are a peripheral microtubular structure that encloses numerous granules, showing an open canalicular system spreading throughout the cytoplasm. Once they are activated, sequential morphological changes take place. First of all, the microtubular structure desintegrates and is replaced by a membranous pseudotubular membranous complex which fuses itself to the granules enhancing the open canalicular system which grows until it takes a sacular-canalicular appearance. Degranulation takes place at the same time. The from of the platelets becomes spherical and irregular. Later on, a microfilament organization appears, specially in the peripheral zozne projecting into the pseudopodical prolongations which are formed in the surface, giving the platelets a very irregular filopoidal form. Finally they loose all their structure becoming hyaline and vacuolated. We believe that the pseudopodical stage is the last step of the activation, prvious to the final vacuolization and destruction

The biology of neurofilaments and the degenerative disorders of the central nervous system

Los neurofilamentos son uno de los más importantes componentes de las redes estructurales del citoplasma neuronal. Ellos contienen tres polipeptidos con pesos moleculares de 68.000, 160.000 y 200.000. En esta revisión nosotros discutimos su purificación, propiedades químicas, interacciones moleculares, distribución celular y transporte axonal, como también la posible relación de esta estructura con ciertas enfermedades del sistema nervioso central. En este contexto es interesante mencionar que pacientes con encefalopatías espongiformes y Enfermedad de Alzheimer familiar, presentan títulos altos de autoanticuerpos dirigidos a la subunidad de 200.000 del neurofilamento