Página 9 dos resultados de 6914 itens digitais encontrados em 0.019 segundos

‣ Cellular aproaches and tailor-made 3D starch-based scaffolds for improved vascularization in bone tissue engineering strategies; Estratégias celulares e adequação de suportes 3d à base de amido para a melhoria da vascularização em engenharia de tecidos ósseos

Santos, Marina I.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 27/03/2009 Português
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Tese de doutoramento em Engenharia Biológica; The establishment of a vascular supply in bone grafts is presently identified as the main pitfall in bone tissue engineering and the major hurdle for the clinical application of the engineered constructs. Granted the importance of intraosseous vasculature in bone physiological processes, the existence of a microcirculation is not only essential to assure cell survival in strategies that involve cell seeding but also on all the other approaches aimed at bone tissue formation. This is particularly critical in the regeneration of large bone defects because in these cases diffusion can not assure the metabolic demands of the cells and post-implantation vascularization is a slow and insufficient process to assure the success of the implant. The recognition of the aforementioned problem urged the development of strategies to induce and accelerate the formation of a blood vessel network to simultaneously supply the implant and functionally connect to the host vasculature. The research work described in this thesis addresses strategies to augment vascularization on different formulations of starch poly(I-caprolactone) (SPCL) fiber-mesh scaffold, a biodegradable material previously proposed for bone regeneration. Endothelial cells (ECs) are the key element in angiogenesis. Vascularization strategies either directly or indirectly target this cell type. Thus...

‣ The human T-cell leukemia virus type 1 transactivator protein Tax colocalizes in unique nuclear structures with NF-kappaB proteins.

Bex, F; McDowall, A; Burny, A; Gaynor, R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1997 Português
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The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) is a potent activator of viral transcription. Tax also activates the expression of specific cellular genes involved in the control of T-lymphocyte growth via effects on cellular transcription factors, including members of the NF-kappaB/cRel family. Immunocytochemistry and electron microscopy were used to characterize the intracellular localization of Tax and identify cellular factors which are the potential targets for its transcriptional activity. These studies indicated that Tax localizes in discrete nuclear foci in T lymphocytes transformed by HTLV-1 and in cells transduced with Tax expression vectors. The Tax-containing foci are complex nuclear structures comprising a central core in which Tax colocalizes with splicing factor Sm. In addition to splicing factors Sm and SC-35, the Tax-containing nuclear structures also contain transcriptional components, including the largest subunit of RNA polymerase II and cyclin-dependent kinase CDK8. The inclusion of the two subunits of NF-kappaB, p50 and RelA, and the presence of the mRNA from a gene specifically activated by Tax through NF-kappaB binding sites suggest that these unique nuclear structures participate in Tax-mediated activation of gene expression via the NF-kappaB pathway.

‣ Predicted alpha-helix/beta-sheet secondary structures for the zinc-binding motifs of human papillomavirus E7 and E6 proteins by consensus prediction averaging and spectroscopic studies of E7.

Ullman, C G; Haris, P I; Galloway, D A; Emery, V C; Perkins, S J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/10/1996 Português
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The E7 and E6 proteins are the main oncoproteins of human papillomavirus types 16 and 18 (HPV-16 and HPV-18), and possess unknown protein structures. E7 interacts with the cellular tumour-suppressor protein pRB and contains a zinc-binding site with two Cys-Xaa2-Cys motifs spaced 29 or 30 residues apart. E6 interacts with another cellular tumour-suppressor protein p53 and contains two zinc-binding sites, each with two Cys-Xaa2-Cys motifs at a similar spacing of 29 or 30 residues. By using the GOR I/III, Chou-Fasman, SAPIENS and PHD methods, the effectiveness of consensus secondary structure predictions on zinc-finger proteins was first tested with sequences for 160 transcription factors and 72 nuclear hormone receptors. These contain Cys2His2 and Cys2Cys2 zinc-binding regions respectively, and possess known atomic structures. Despite the zinc- and DNA-binding properties of these protein folds, the major alpha-helix structures in both zinc-binding regions were correctly identified. Thus validated, the use of these prediction methods with 47 E7 sequences indicated four well-defined alpha-helix (alpha) and beta-sheet (beta) secondary structure elements in the order beta beta alpha beta in the zinc-binding region of E7 at its C-terminus. The prediction was tested by Fourier transform infrared spectroscopy of recombinant HPV-16 E7 in H2O and 2H2O buffers. Quantitative integration showed that E7 contained similar amounts of alpha-helix and beta-sheet structures...

‣ Genotoxic Stress and Cellular Stress Alter the Subcellular Distribution of Human T-Cell Leukemia Virus Type 1 Tax through a CRM1-Dependent Mechanism

Gatza, Michael L.; Marriott, Susan J.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /07/2006 Português
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Human T-cell leukemia virus type 1 Tax is a predominantly nuclear viral oncoprotein that colocalizes with cellular proteins in nuclear foci known as Tax speckled structures (TSS). Tax is also diffusely distributed throughout the cytoplasm, where it interacts with and affects the functions of cytoplasmic cellular proteins. Mechanisms that regulate the distribution of Tax between the cytoplasm and nucleus remain to be identified. Since Tax has been shown to promote genome instability by perturbing cell cycle progression and DNA repair mechanisms following DNA damage, we examined the effect of genotoxic stress on the subcellular distribution and interacting partners of Tax. Tax localization was altered in response to various forms of cellular stress, resulting in an increase in cytoplasmic Tax and a decrease in Tax speckled structures. Concomitantly, colocalization of Tax with sc35 (a TSS protein) decreased following stress. Tax translocation required the CRM1 nuclear export pathway, and a transient interaction between Tax and CRM1 was observed following stress. These results suggest that the subcellular distribution of Tax and the interactions between Tax and cellular proteins respond dynamically to cellular stress. Changes in Tax distribution and interacting partners are likely to affect cellular processes that regulate cellular transformation.

‣ Radiation induced CNS toxicity – molecular and cellular mechanisms

Belka, C; Budach, W; Kortmann, R D; Bamberg, M
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
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Radiotherapy of tumours proximal to normal CNS structures is limited by the sensitivity of the normal tissue. Prior to the development of prophylactic strategies or treatment protocols a detailed understanding of the mechanisms of radiation induced CNS toxicity is mandatory. Histological analysis of irradiated CNS specimens defines possible target structures prior to a delineation of cellular and molecular mechanisms. Several lesions can be distinguished: Demyelination, proliferative and degenerative glial reactions, endothelial cell loss and capillary occlusion. All changes are likely to result from complex alterations within several functional CNS compartments. Thus, a single mechanism responsible cannot be separated. At least four factors contribute to the development of CNS toxicity: (1) damage to vessel structures; (2) deletion of oligodendrocyte-2 astrocyte progenitors (O-2A) and mature oligodendrocytes; (3) deletion of neural stem cell populations in the hippocampus, cerebellum and cortex; (4) generalized alterations of cytokine expression. Several underlying cellular and molecular mechanisms involved in radiation induced CNS toxicity have been identified. The article reviews the currently available data on the cellular and molecular basis of radiation induced CNS side effects.   http://www.bjcancer.com © 2001 Cancer Research Campaign

‣ Light Scattering Measurements of Subcellular Structure Provide Noninvasive Early Detection of Chemotherapy-induced Apoptosis1

Chalut, Kevin J.; Ostrander, Julie Hanson; Giacomelli, Michael G.; Wax, Adam
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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We present a light scattering study using angle-resolved low coherence interferometry (a/LCI) to assess nuclear morphology and sub-cellular structure within MCF-7 cells at several timepoints following treatment with chemotherapeutic agents. While the nuclear diameter and eccentricity are not observed to change, the light scattering signal reveals a change in the organization of sub-cellular structures that we interpret using fractal dimension (FD). The FD of sub-cellular structures in cells treated with paclitaxel and doxorubicin is observed to increase significantly compared to that of control cells as early as 1.5 and 3 hrs after application, respectively. The FD is then found to decrease slightly at 6 hrs post application for both agents only to increase again from 12 to 24 hrs post treatment when the observations ceased. The changes in structure appear over two time scales, suggesting that multiple mechanisms are evident in these early apoptotic stages. Indeed, quantitative image analysis of fluorescence micrographs of cells undergoing apoptosis verify that the FD of DAPI stained nuclear structures does not change significantly in cells until 12 hrs after treatment while that of MitoTracker stained mitochondria is seen to modulate as early as 3 hrs after treatment. In contrast...

‣ Cellular Scaling Rules for the Brains of an Extended Number of Primate Species

Gabi, Mariana; Collins, Christine E.; Wong, Peiyan; Torres, Laila B.; Kaas, Jon H.; Herculano-Houzel, Suzana
Fonte: S. Karger AG Publicador: S. Karger AG
Tipo: Artigo de Revista Científica
Português
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What are the rules relating the size of the brain and its structures to the number of cells that compose them and their average sizes? We have shown previously that the cerebral cortex, cerebellum and the remaining brain structures increase in size as a linear function of their numbers of neurons and non-neuronal cells across 6 species of primates. Here we describe that the cellular composition of the same brain structures of 5 other primate species, as well as humans, conform to the scaling rules identified previously, and that the updated power functions for the extended sample are similar to those determined earlier. Accounting for phylogenetic relatedness in the combined dataset does not affect the scaling slopes that apply to the cerebral cortex and cerebellum, but alters the slope for the remaining brain structures to a value that is similar to that observed in rodents, which raises the possibility that the neuronal scaling rules for these structures are shared among rodents and primates. The conformity of the new set of primate species to the previous rules strongly suggests that the cellular scaling rules we have identified apply to primates in general, including humans, and not only to particular subgroups of primate species. In contrast...

‣ The critical protein interactions and structures that elicit growth deregulation in cancer and viral replication

Ou, Horng D.; May, Andrew P.; O’Shea, Clodagh C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2011 Português
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One of the greatest challenges in biomedicine is to define the critical targets and network interactions that are subverted to elicit growth deregulation in human cells. Understanding and developing rational treatments for cancer requires a definition of the key molecular targets and how they interact to elicit the complex growth deregulation phenotype. Viral proteins provide discerning and powerful probes to understand both how cells work and how they can be manipulated using a minimal number of components. The small DNA viruses have evolved to target inherent weaknesses in cellular protein interaction networks to hijack the cellular DNA and protein replication machinery. In the battle to escape the inevitability of senescence and programmed cell death, cancers have converged on similar mechanisms, through the acquisition and selection of somatic mutations that drive unchecked cellular replication in tumors. Understanding the dynamic mechanisms through which a minimal number of viral proteins promote host cells to undergo unscheduled and pathological replication is a powerful strategy to identify critical targets that are also disrupted in cancer. Viruses can therefore be used as tools to probe the system-wide protein-protein interactions and structures that drive growth deregulation in human cells. Ultimately this can provide a path for developing system context-dependent therapeutics. This review will describe ongoing experimental approaches using viruses to study pathways deregulated in cancer...

‣ Accurate Construction of Photoactivated Localization Microscopy (PALM) Images for Quantitative Measurements

Coltharp, Carla; Kessler, Rene P.; Xiao, Jie
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 12/12/2012 Português
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Localization-based superresolution microscopy techniques such as Photoactivated Localization Microscopy (PALM) and Stochastic Optical Reconstruction Microscopy (STORM) have allowed investigations of cellular structures with unprecedented optical resolutions. One major obstacle to interpreting superresolution images, however, is the overcounting of molecule numbers caused by fluorophore photoblinking. Using both experimental and simulated images, we determined the effects of photoblinking on the accurate reconstruction of superresolution images and on quantitative measurements of structural dimension and molecule density made from those images. We found that structural dimension and relative density measurements can be made reliably from images that contain photoblinking-related overcounting, but accurate absolute density measurements, and consequently faithful representations of molecule counts and positions in cellular structures, require the application of a clustering algorithm to group localizations that originate from the same molecule. We analyzed how applying a simple algorithm with different clustering thresholds (tThresh and dThresh) affects the accuracy of reconstructed images, and developed an easy method to select optimal thresholds. We also identified an empirical criterion to evaluate whether an imaging condition is appropriate for accurate superresolution image reconstruction with the clustering algorithm. Both the threshold selection method and imaging condition criterion are easy to implement within existing PALM clustering algorithms and experimental conditions. The main advantage of our method is that it generates a superresolution image and molecule position list that faithfully represents molecule counts and positions within a cellular structure...

‣ In Situ Gelation for Cell Immobilization and Culture in Alginate Foam Scaffolds

Andersen, Therese; Markussen, Christine; Dornish, Michael; Heier-Baardson, Helene; Melvik, Jan Egil; Alsberg, Eben; Christensen, Bjørn E.
Fonte: Mary Ann Liebert, Inc. Publicador: Mary Ann Liebert, Inc.
Tipo: Artigo de Revista Científica
Português
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Essential cellular functions are often lost under culture in traditional two-dimensional (2D) systems. Therefore, biologically more realistic three-dimensional (3D) cell culture systems are needed that provide mechanical and biochemical cues which may otherwise be unavailable in 2D. For the present study, an alginate-based hydrogel system was used in which cells in an alginate solution were seeded onto dried alginate foams. A uniform distribution of NIH:3T3 and NHIK 3025 cells entrapped within the foam was achieved by in situ gelation induced by calcium ions integrated in the foam. The seeding efficiency of the cells was about 100% for cells added in a seeding solution containing 0.1–1.0% alginate compared with 18% when seeded without alginate. The NHIK 3025 cells were allowed to proliferate and form multi-cellular structures inside the transparent gel that were later vital stained and evaluated by confocal microcopy. Gels were de-gelled at different time points to isolate the multi-cellular structures and to determine the spheroid growth rate. It was also demonstrated that the mechanical properties of the gel could largely be varied through selection of type and concentration of the applied alginate and by immersing the already gelled disks in solutions providing additional gel-forming ions. Cells can efficiently be incorporated into the gel...

‣ Modest Interference with Actin Dynamics in Primary T Cell Activation by Antigen Presenting Cells Preferentially Affects Lamellal Signaling

Roybal, Kole T.; Mace, Emily M.; Clark, Danielle J.; Leard, Alan D.; Herman, Andrew; Verkade, Paul; Orange, Jordan S.; Wülfing, Christoph
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 03/08/2015 Português
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Dynamic subcellular distributions of signaling system components are critical regulators of cellular signal transduction through their control of molecular interactions. Understanding how signaling activity depends on such distributions and the cellular structures driving them is required for comprehensive insight into signal transduction. In the activation of primary murine T cells by antigen presenting cells (APC) signaling intermediates associate with various subcellular structures, prominently a transient, wide, and actin-associated lamellum extending from an interdigitated T cell:APC interface several micrometers into the T cell. While actin dynamics are well established as general regulators of cellular organization, their role in controlling signaling organization in primary T cell:APC couples and the specific cellular structures driving it is unresolved. Using modest interference with actin dynamics with a low concentration of Jasplakinolide as corroborated by costimulation blockade we show that T cell actin preferentially controls lamellal signaling localization and activity leading downstream to calcium signaling. Lamellal localization repeatedly related to efficient T cell function. This suggests that the transient lamellal actin matrix regulates T cell signaling associations that facilitate T cell activation.

‣ Ultrastructural Studies by Correlative Stochastic Optical Reconstruction Microscopy and Electron Microscopy

Kim, Doory
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
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Fluorescence light microscopy (LM) and electron microscopy (EM) are two of the most widely used imaging modalities for probing cellular structures. In this dissertation I present our works in both developing methods of several correlative super-resolution fluorescence light microscopy (LM) and electron microscopy (EM) assays by combining stochastic optical reconstruction microscopy (STORM), a super-resolution imaging technique with several different EM imaging modalities and applying super-resolution microscopy to investigate the distributions and interactions of purine biosynthetic enzymes organization complex called purinosomes within the cell. The first work contained in this dissertation is to develop Correlative fluorescence light microscopy and electron microscopy allows the imaging of spatial distributions of specific biomolecules in the context of cellular ultrastructure. Recent development of super-resolution fluorescence microscopy allows the location of molecules to be determined with nanometer-scale spatial resolution. However, correlative super-resolution fluorescence microscopy and electron microscopy (EM) still remains challenging because the optimal specimen preparation and imaging conditions for super-resolution fluorescence microscopy and EM are often not compatible. Here...

‣ BONE REMODELING PROCESS AS AN OPTIMAL STRUCTURAL DESIGN

COLLOCA, MICHELE
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
Português
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The functional adaptation of bone to mechanical usage implies the existence of a physiological control process: once the structure has sufficiently adapted, the feedback signal is diminished and further changes to shape and properties are stopped. In bone tissue it has been widely accepted that mineral component is resorbed in regions exposed to low mechanical stimulus, whereas new bone is deposited where the stimulus is high. This process of functional adaptation is thought to enable bone to perform its mechanical functions with a minimum of mass and with the strength necessary to support mechanical loads associated with daily activity and to protect internal organs. This premise can be expressed as a global, multi-objective optimization problem in which stiffness and mass are conflicting goals. Maximizing stiffness is equivalent to minimize the compliance or minimize the strain energy in the bone. From this point of view, the bone remodeling process is analogous to the topology optimization in structural design including the cellular automaton (CA) technique and the solid isotropic material with penalization (SIMP) approach. The process of bone remodeling can be analytically described, integrated with the finite element method and numerically simulated. With a proper control strategy...

‣ Effect of Flightless protein on skin architecture, cellular responses and Epidermolysis Bullosa.

Kopecki, Zlatko
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2011 Português
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Wound healing is an area of largely unmet medical need with patients often relying on wound management practice rather than specific therapies. Recent research in our laboratory has identified a cytoskeletal protein Flightless (Flii) as a negative regulator of wound healing. This highly conserved protein is important in development and has a unique structure allowing it to act as a multifunctional protein. Flii expression increases in response to wounding, inhibiting cellular migration and proliferation while its deficiency improves wound healing. The aim of this study was to investigate the effect of differential Flii expression on skin architecture, cellular responses during wound healing, adhesionmediated cell signaling and skin blistering associated with the genetic skin disorder Epidermolysis Bullosa (EB). Chapter 3 of this thesis describes the effect of differential Flii expression on skin architecture and formation of hemidesmosomes which anchor the skin layers. Using primary fibroblasts and keratinocytes with varying Flii expression this study investigated the effect of Flii expression on cellular adhesion, spreading and migration on different extracellular matrix substrates. The results presented in Chapter 3 also describe the effect of Flii neutralising antibodies on primary keratinocyte proliferation illustrating improved proliferation in response to decreased Flii expression. In Chapter 4 an incisional wound healing model was used to investigate the effect of differential Flii expression on different components of hemidesmosomes. Flightless was shown to regulate hemidesmosome formation through its effects on integrin-mediated cellular adhesion and migration. Using immunoprecipitation studies...

‣ Untersuchungen zur RNA-Rekombination beim Virus der bovinen viralen Diarrhö – Einfluss einer zellulären Insertion auf die virale Polyproteinprozessierung und Zytopathogenität; RNA-recombination in the bovine viral diarrhea virus : influence of a cellular insertion onto the processing of the viral polyprotein and the cytopathogenity

Fricke, Jens G.
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
Português
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BVDV ist dafür bekannt, dass zythopathogene Virusvarianten durch Integration zellulärer Sequenzen in das virale RNA-Genom entstehen. Die zellulären Insertionen induzieren nach Translation eine zusätzliche Spaltung des viralen Polyproteins. In der vorliegenden Arbeit wurden die Genome von verschiedenen BVDV Isolaten charakterisiert, die alle aus einem erkrankten Tier stammen. Analysen von cDNA-Klonen und RT-PCR Fragmenten erlaubten es, die Genomstrukturen einer Reihe von Viren zu rekonstruieren. Alle enthielten die gleiche zelluläre Sequenz, flankiert von unterschiedlich rearrangierten viralen Sequenzen. Die gefundenen Genomstrukturen lassen sich auf eine Grundstruktur zurückführen. Da die Entstehung solcher Virusvarianten mit weitgehend übereinstimmenden Genomstrukturen in unabhängigen Rekombinationsereignissen unwahrscheinlich ist, deuten diese Ergebnisse auf einen evolutionären Prozess hin, in dem eine Primärrekombinante gebildet und anschliessend durch weitere Rekombinationen verändert wurde. Bei der zellulären Insertion handelt es sich um ein Fragment des LC3 („light chain 3“), einem Bestandteil von Mikrotubuli assoziierten Proteinen. Aufgrund früherer Befunde war zu erwarten, dass das LC3 im viralen Polyprotein als Signal für eine proteolytische Prozessierung dient. Dies konnte in proteinbiochemischen Analysen bestätigt werden. Mutageneseexperimente erlaubten die Charakterisierung der Spaltstelle...

‣ Precision Assembly of Complex Cellular Microenvironments using Holographic Optical Tweezers

Kirkham, Glen R.; Britchford, Emily; Upton, Thomas; Ware, James; Gibson, Graham M.; Devaud, Yannick; Ehrbar, Martin; Padgett, Miles; Allen, Stephanie; Buttery, Lee D.; Shakesheff, Kevin
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 26/02/2015 Português
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The accurate study of cellular microenvironments is limited by the lack of technologies that can manipulate cells in 3D at a sufficiently small length scale. The ability to build and manipulate multicellular microscopic structures will facilitate a more detailed understanding of cellular function in fields such as developmental and stem cell biology. We present a holographic optical tweezers based technology to accurately generate bespoke cellular micro-architectures. Using embryonic stem cells, 3D structures of varying geometries were created and stabilized using hydrogels and cell-cell adhesion methods. Control of chemical microenvironments was achieved by the temporal release of specific factors from polymer microparticles positioned within these constructs. Complex co-culture micro-environmental analogues were also generated to reproduce structures found within adult stem cell niches. The application of holographic optical tweezers-based micromanipulation will enable novel insights into biological microenvironments by allowing researchers to form complex architectures with sub-micron precision of cells, matrices and molecules.

‣ Calcification and Silicification: Fossilization Potential of Cyanobacteria from Stromatolites of Niuafo‘ou's Caldera Lakes (Tonga) and Implications for the Early Fossil Record

Kremer, Barbara; Kazmierczak, Józef; Łukomska-Kowalczyk, Maja; Kempe, Stephan
Fonte: Mary Ann Liebert, Inc. Publicador: Mary Ann Liebert, Inc.
Tipo: Artigo de Revista Científica
Publicado em /06/2012 Português
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Calcification and silicification processes of cyanobacterial mats that form stromatolites in two caldera lakes of Niuafo‘ou Island (Vai Lahi and Vai Si‘i) were evaluated, and their importance as analogues for interpreting the early fossil record are discussed. It has been shown that the potential for morphological preservation of Niuafo‘ou cyanobacteria is highly dependent on the timing and type of mineral phase involved in the fossilization process. Four main modes of mineralization of cyanobacteria organic parts have been recognized: (i) primary early postmortem calcification by aragonite nanograins that transform quickly into larger needle-like crystals and almost totally destroy the cellular structures, (ii) primary early postmortem silicification of almost intact cyanobacterial cells that leave a record of spectacularly well-preserved cellular structures, (iii) replacement by silica of primary aragonite that has already recrystallized and obliterated the cellular structures, (iv) occasional replacement of primary aragonite precipitated in the mucopolysaccharide sheaths and extracellular polymeric substances by Al-Mg-Fe silicates. These observations suggest that the extremely scarce earliest fossil record may, in part, be the result of (a) secondary replacement by silica of primary carbonate minerals (aragonite...

‣ Modeling of time dependent localized flow shear stress and its impact on cellular growth within additive manufactured titanium implants

Zhang, Ziyu; Yuan, Lang; Lee, Peter D; Jones, Eric; Jones, Julian R
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
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Bone augmentation implants are porous to allow cellular growth, bone formation and fixation. However, the design of the pores is currently based on simple empirical rules, such as minimum pore and interconnects sizes. We present a three-dimensional (3D) transient model of cellular growth based on the Navier–Stokes equations that simulates the body fluid flow and stimulation of bone precursor cellular growth, attachment, and proliferation as a function of local flow shear stress. The model's effectiveness is demonstrated for two additive manufactured (AM) titanium scaffold architectures. The results demonstrate that there is a complex interaction of flow rate and strut architecture, resulting in partially randomized structures having a preferential impact on stimulating cell migration in 3D porous structures for higher flow rates. This novel result demonstrates the potential new insights that can be gained via the modeling tool developed, and how the model can be used to perform what-if simulations to design AM structures to specific functional requirements.

‣ Determination of the secondary structure of and cellular protein binding to the 3'-untranslated region of the hepatitis C virus RNA genome.

Ito, T; Lai, M M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1997 Português
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Hepatitis C virus (HCV) contains a positive-stranded RNA genome of approximately 9.5 kb. Despite the overall sequence diversity among individual HCV isolates, the 3'-end 98 nucleotides (nt) of the HCV RNA, which constitute part of the 3'-untranslated region (3'-UTR), are highly conserved. This conserved region may contain the cis-acting signals for RNA replication involving possibly both viral and cellular proteins. We carried out RNase digestion studies, which revealed that this 98-nt region contains three stem-loops but may also assume alternative structures. We further performed UV cross-linking experiments to detect cellular proteins that bound to this region. A 58-kDa cellular protein (p58) was detected. Its binding site was mapped to the stem-loops 2 and 3, which are the most conserved region of the 3'-UTR. Site-directed mutagenesis studies revealed that both stem structures and specific nucleotide sequence within the two loops are important for p58 binding. Mutations that disrupted stem structures abolished protein binding, while the compensatory mutations restored its binding. This region also contains partial sequence similarity to the reported consensus binding sequence for polypyrimidine tract-binding protein (PTB) (a 57-kDa protein). The UV-cross-linked protein could be immunoprecipitated with the anti-PTB antibody...

‣ On Decidability Properties of One-Dimensional Cellular Automata

Finkel, Olivier
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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In a recent paper Sutner proved that the first-order theory of the phase-space $\mathcal{S}_\mathcal{A}=(Q^\mathbb{Z}, \longrightarrow)$ of a one-dimensional cellular automaton $\mathcal{A}$ whose configurations are elements of $Q^\mathbb{Z}$, for a finite set of states $Q$, and where $\longrightarrow$ is the "next configuration relation", is decidable. He asked whether this result could be extended to a more expressive logic. We prove in this paper that this is actuallly the case. We first show that, for each one-dimensional cellular automaton $\mathcal{A}$, the phase-space $\mathcal{S}_\mathcal{A}$ is an omega-automatic structure. Then, applying recent results of Kuske and Lohrey on omega-automatic structures, it follows that the first-order theory, extended with some counting and cardinality quantifiers, of the structure $\mathcal{S}_\mathcal{A}$, is decidable. We give some examples of new decidable properties for one-dimensional cellular automata. In the case of surjective cellular automata, some more efficient algorithms can be deduced from results of Kuske and Lohrey on structures of bounded degree. On the other hand we show that the case of cellular automata give new results on automatic graphs.; Comment: Final version; to appear in the Journal of Cellular Automata