bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of In Vivo Cell Movement Using Transparent Tissue Systems
Authors: Thorogood Peter , Wood Andrew 
Published: May 2013

ABSTRACT
The embryos of certain teleost species are transparent and cell behaviour within the intact embryo can be observed and recorded using Nomarski microscopy coupled with time-lapse video recording or time-lapse cine filming. In this report we review some of our recent analyses of cell behaviour patterns underlying key morphogenetic events. (1) Contact-guided cell migration through a structurally ordered extracellular matrix during fin development; (2) movement of tissue layers during epibolic overgrowth; and (3) cell ‘social’ behaviour during the establishment of the body axis (i.e. notochord formation and somitogenesis).
These results, on cell behaviour correlated with normal morphogenesis, provide a baseline for further work in which hypotheses concerning subcellular and molecular controls of cell behaviour can be tested by experimental perturbation in vivo.
Early Functional Differentiation in the Chick Embryonic Disc: Interaction between Mechanical Activity and Extracellular Matrix
Authors: Kučera Pavel , Monnet-Tschudi Florianne 
Published: May 2013

ABSTRACT
The mechanical behaviour of ectodermal cells in the area opaca and the supracellular organization of fibronectin in the adjacent extracellular matrix were studied in whole chick blastoderms developing in vitro. The pattern of spontaneous mechanical activity and its modification by immunoglobulins against fibronectin were determined using a real-time image-analysis system. The pattern of fibronectin was studied using immunocytochemical techniques.
It was found that the ectodermal cells in the area opaca actively develop a radially oriented contraction, which leads to a distension of the area pellucida from which the embryo develops. Abnormally increased tension resulted in perturbations of gastrulation and neurulation. An optimized mechanical equilibrium within the blastoderm seems to be necessary for normal development. Anti-fibronectin antibodies applied to the basal side of the blastoderm led rapidly and reversibly to an increase of tension in the contracted cells. This observation indicates that modifications of the extracellular matrix can be transmitted to cytoskeletal elements within adjacent cells.
The extracellular matrix of the area opaca contains fibronectin arranged in radially oriented fibrils. This orientation corresponds to the direction of migration of the mesodermal cells. Interestingly, the radial pattern of fibronectin is found in the regions where the ectodermal cells are contracted and develop radially oriented forces. This observation suggests that the supracellular assembly of the extracellular materials could be influenced by the mechanical activity of adjacent cells. Possible modulations of the supracellular organization of extracellular matrix by other factors, e.g. diffusible metabolites, is also discussed.
The presence of characteristically organized extracellular matrix components, of spatially differentiated cell activities and of reciprocal interactions between them makes the young chick blastoderm an excellent system for physiological studies of the coordinated cellular activities that lead to changes in form, complexity and function.
Léucocyte Locomotion: Behavioural Mechanisms for Accumulation
Authors: Wilkinson P. C. 
Published: May 2013

ABSTRACT
The behavioural mechanisms that may contribute to the accumulation of leucocytes (e.g. in inflammatory sites) are reviewed. Almost all of the neutrophils and monocytes of blood are motile and capable of migrating into tissues, but many blood lymphocytes are non-motile. They can however be induced to acquire locomotor capacity by culture with growth activators such as anti-CD3 antibodies. Resting lymphocytes become motile after entering the G1 phase of the cell cycle. Chemotaxis is well-studied in neutrophil leucocytes and is an efficient mechanism for cell accumulation. Possible mechanisms by which leucocytes respond to attractant gradients are discussed. Non-chemotactic mechanisms may also lead to cell accumulation, and evidence is reviewed that shows that an adhesive trapping mechanism causes leucocytes that cross an adhesion boundary to accumulate in the absence of a chemotactic gradient. Leucocytes migrating through aligned connective tissue show contact guidance in the axis of alignment of the tissue. Contact guidance can reinforce or hinder the response of neutrophils to chemotactic gradients.
Qualitative and Quantitative Analysis of Tumour Invasion in vivo and in vitro
Authors: Mareel Marc M. , Roy Frans M. Van , Messiaen Ludwine M. , Boghaert Erwin R. , Bruyneel Erik A. 
Published: May 2013

ABSTRACT
Qualitative and quantitative methods for the analysis of invasion in ‘natural’ and in experimental tumours in vivo and in vitro are reviewed. In human tumours the functional consequences of invasion were evaluated histologically through staging on the basis of depths of invasion and through the presence of tumour cells inside vessels. Antibodies against components of the basement membrane have facilitated the definition of minimal invasion. With new probes derived from oncogene research the search for molecular differences between invasive and non-invasive parts of the tumour has begun. Since the same methods as those used for analysis of natural tumours also apply to experimental tumours in vivo, the major advantage of the latter is the possibility of manipulation. We have described a new mesenterium assay that may permit the selection of invasive cells from non-invasive ones in transfection experiments. Invasion relative to growth as a function of time was quantified in the kidney invasion test. In three-dimensional confrontations between embryonic chick heart fragments and invasive cells, we have used both a subjective grading and a qualitative computer-assisted image analysis of serial histological sections to score invasion. In two-dimensional confrontations supplementary methods could be applied, since such confrontations permitted direct observations on living cultures. In a variety of natural and experimental tumours, ultrastructural analysis, transmigration in two-compartment chambers, and release of metabolic label have demonstrated the role of motility and of lytic activity in tumour invasion.
Tumour suppressor genes
Authors: Klein George 
Published: May 2013

ABSTRACT
Genes that can inhibit the expression of the tumorigenic phenotype have been detected by the fusion of normal and malignant cells, the phenotypic reversion of in vitro transformants, the induction of terminal differentiation of malignant cell lineages, the loss of ‘recessive cancer genes’, the discovery of regulatory sequences in the immediate vicinity of certain oncogenes, and the inhibition of tumour growth by normal cell products. Such tumour suppressor genes will probably turn out to be as, if not more, diversified as the oncogenes. Consideration of both kinds of genes may reveal common or interrelated functional properties.
Feedback regulators in normal and tumour tissues
Authors: Lord B. I. 
Published: May 2013

ABSTRACT
Regulation of cell behaviour and population size is presumed to be not unlike classical regulation in non-biological systems, i.e. it is controlled by the cybernetic principle of negative feedback whereby the performance of progenitor cells depends inversely on a signal from their product, the size of which is proportional to the mass of the product. This signal may be inhibitory, acting directly on the progenitor cells. Alternatively, it may operate via an indirect and integrated inhibitor/stimulator feedback loop in which the one influences the production of the other. Illustrations taken from the various phases of haemopoietic development show the operation of these loops. Haemopoietic stem cells are under the direct influence of both inhibitor and stimulator but it is a feedback signal from the stem cell population that dictates the production of the one rather than the other. A second inhibitor acting at the stem cell level is a low molecular weight tetrapeptide which blocks the entry of cells into DNA synthesis, thus protecting them during a regimen of treatment with an S-phase cytotoxic drug. Proliferation of the maturing cells is also inhibited by feedback products of their fully mature descendants. Here, the effect is one of cell cycle modulation, whereas in the stem cell population the inhibitor and stimulator effect an on/off switch.
Attempts to characterize the molecules involved have been limited. A series of tri-to penta-peptides has been described for haemopoietic or epithelial cell inhibitors. A common feature of several is a pGlu-Glu end though whether this has any significance is not known.
In tumours it has been shown that some ascites are self-limiting and treatment of small tumours with cell-free fluid from a mature growth blocks their further growth. It appears that many tumour cells produce the feedback signals characteristic of their normal counterparts but are themselves less sensitive to it. The same is true of transforming growth factor-β which is produced and detected by virtually all cell types. In this case, the factor, inhibiting in most cases, is produced in inactive form and achieves its target specificity by a localized capacity to activate it. Some tumours, while responding to exogenous active TGF-/ β are incapable of activating the latent molecule.
It is concluded that the differential sensitivity of normal and neoplastic tissues to physiological feedback regulators is a potentially exploitable property in cancer therapy.
Regulatory factors of embryonic stem cells
Authors: Heath John K. , Smith Austin G. 
Published: May 2013

ABSTRACT
The analysis of factors which regulate cell proliferation and differentiation in early mammalian development has been facilitated by the existence of cell lines derived from pluripotential stem cells of the early embryo; embryonal carcinoma (EC) cells and embryonic stem (ES) cells. EC cells have proved to be a useful source of embryonic growth factors. A potent mitogen, ECDGF has been isolated from EC cell conditioned medium. ECDGF appears to be a novel member of the heparin binding growth factor family. A remarkable feature of heparin binding growth factors is their ability to induce mesodermal differentiation in Xenopus laevis animal pole expiants. ES cell differentiation in vitro is controlled by exogenous factors, in particular a novel differentiation inhibitory factor DIA. Controlled bipotential differentiation of ES cells can be achieved by exposing ES cells to different combinations of regulatory signals.
Multi-lineage ‘stem’ cells in the mammalian embryo
Authors: Gardner R. L. , Beddington R. S. P. 
Published: May 2013

ABSTRACT
The term ‘stem’ cell has acquired a rather more restricted meaning in cell biology than in embryology as a result of studies on the growth kinetics of renewing tissues in mature organisms. It is normally used in an embryological context as a synonym for ‘progenitor’ cell.
Methods of establishing the existence of multi-lineage progenitor cells in mammals are examined briefly before the occurrence and properties of such cells in both embryonic and extra-embryonic tissues of the mouse conceptus are reviewed. Various attributes of ‘stem’ cells that can be obtained from outgrowths of blastocysts in vitro are also discussed.
Early haemopoietic stem cells in the avian embryo
Authors: Dieterlen-Lievre Françoise , Pardanaud Luc , Yassine Fouzia , Cormier FranÇoise 
Published: May 2013

ABSTRACT
Using ‘yolk sac chimaeras’, we have previously demonstrated that stem cells, destined to colonize haemopoietic organs other than the yolk sac, arise in the embryo proper. We have now investigated the emergence and potentialities of these cells in vivo and in vitro.
The in vivo approach consisted of interspecies grafting between quail and chick embryos. The cell progeny from the grafts was detected by means of QH1, a monoclonal antibody specific for the quail haemangioblastic lineage. When grafted into the dorsal mesentery of the chick embryo, which is a haemopoietic microenvironment, the region of the aorta from E3-E4 quail embryos generated large haemopoietic foci. When associated with a chick attractive thymic rudiment, cells left the quail aorta, entered this rudiment and underwent lymphopoiesis.
Cell suspensions prepared from 40-50 chick aortae, seeded in appropriate semi-solid media, yielded macrophage, granulocyte or erythrocyte clones. These colony forming cells were two to eight times more frequent than in cell preparations from hatchling bone marrow. By contrast, cells prepared from the whole embryonic body deprived of the aorta were not clonogenic.
By interspecies grafting of somatopleural (ectoderm + mesoderm, e.g. limb bud) or splanchnopleural rudiments (endoderm + mesoderm, e.g. lung, pancreas, intestine), the endothelial lining of blood vessels was shown to arise by two entirely different processes according to the rudiment considered: angiogenesis, i.e. invasion by extrinsic endothelial cells, in the limb bud, and vasculogenesis, i.e. in situ emergence of endothelial cells, in internal organs. The spleen, which first develops as a continuum to the pancreatic mesoderm, acquires its endothelial network by vasculogenesis, and is colonized by extrinsic haemopoietic stem cells. Granulopoietic cells in the pancreas and accessory cells in the lung are also extrinsic. Thus, in the case of endomesodermal rudiments, interspecies grafting reveals separate origins of endothelial and haemopoietic cells.
Identification of immunoglobulin heavy chain binding protein as glucose-regulated protein 78 on the basis of amino acid sequence, immunological cross-reactivity, and functional activity
Authors: Kozutsumi Yasunori , Normington Karl , Press Eileen , Slaughter Clive , Sambrook Joe , Gething Mary-Jane 
Published: May 2013

ABSTRACT
Immunoglobulin heavy chain binding protein (BiP) associates transiently with various proteins destined for the secretory pathway. To investigate the relationship between BiP and the 78K (K=103Mr) glucose-regulated protein (GRP78), we have determined a partial amino acid sequence of purified mouse BiP and isolated and sequenced a full-length cDNA clone encoding mouse GRP78. The 26 amino-terminal residues of the mature BiP protein are identical to a sequence of amino acids located near the start of the open reading frame encoding GRP78. A polyclonal antiserum raised against mouse GRP78 protein expressed in bacteria from the cloned GRP78 cDNA could immunoprecipitate complexes consisting of BiP and unfolded forms of immunoglobulin heavy chains. Furthermore, a monoclonal antibody raised against mouse BiP immunoprecipitated mouse GRP78 expressed in monkey CV-1 cells from an SV40-GRP78 recombinant vector. Finally, like the endogenous BiP of simian cells, mouse GRP78 associated with malfolded, non-glycosylated forms of influenza hemagglutinin (HA) when GRP78 and HA were co-expressed from SV40 vectors in CV-1 cells. These studies confirm that BiP is identical to GRP78. Comparison of the nucleic acid and deduced amino acid sequence of mouse GRP78 with those of other rodent and human GRP78s revealed an extremely high degree of sequence identity. BiP/GRP78 is closely related (∼60% identity) to the cytoplasmic 70K heat-shock proteins. Surprisingly, the carboxy-terminal 29 amino acids of BÌP/GRP78, which are not conserved in HSP70 proteins, are almost identical in sequence to the steroidogenesis activator peptide found in the cytoplasm of rat Leydig tumor cells. Possible relationships between these polypeptides are discussed.
Import of proteins into the chloroplast lumen
Authors: Weisbeek Peter , Hageman Johan , Boer Douwe De , Pilon Rien , Smeekens Sjef 
Published: May 2013

ABSTRACT
Plastocyanin is a nuclear-encoded protein that is functional in the thylakoid lumen of the chloroplast. It is synthesized in the cytoplasm as a precursor with an N-terminal transit peptide of 66 amino acids. Its transport route involves two steps, import into the chloroplasts and subsequent routing over the thylakoid membrane into the lumen. Concomitant with the transport, the transit peptide is removed in two successive steps. The transit peptide consists of two functionally different domains. In this study we examine to what extent each domain is involved in import and routing and how far these two processes are linked. For this purpose we made deletions in the N- terminal and C-terminal part of the transit peptide and fusion proteins which only contain one of these parts. The results show that the N-terminal part of the transit peptide is responsible for import into the chloroplast. The N-terminal 43 amino acids are sufficient to direct other proteins into the stroma. The C-terminal part of the transit peptide is a prerequisite for routing inside the chloroplast but not for import. When deletions are made in this part, the transport of plastocyanin stops after import and the intermediate accumulates in the stroma or on the outside of the thylakoids.
Transgenic tomato plants that constitutively express a foreign plastocyanin gene were used to study protein transport in different tissues. Normally, expression of endogenous plastocyanin genes in plants is restricted to photosynthetic tissues only. However, in the transgenic plants this foreign plastocyanin protein is found in all tissues examined. The protein is transported into the local plastids of these tissues and it is processed to the mature size. We conclude that plastids of developmentally different tissues are capable of importing precursor proteins that are normally not found in these tissues. Most likely such plastids, though functionally and morphologically differentiated, have similar or identical protein import mechanisms when compared to the chloroplasts in green tissue.
The precursor of ferredoxin was expressed in Escherichia coli. Surprisingly the precursor interacts with the cytoplasmic membrane and is translocated across this membrane. The unprocessed precursor accumulates in the periplasm.
Involvement of membrane lipids in protein export in Escherichia coli
Authors: Tommassen Jan , Vrije Truus de , Cock Hans De , Bosch Dirk , Kruijff Ben De 
Published: May 2013

ABSTRACT
Several models for the transport of proteins across membranes predict a role for lipids. If these models are correct, then alterations in lipid metabolism may affect protein export and vice versa. We are investigating this possibility by studying Escherichia coli K-12 mutants with defects in protein export or phospholipid metabolism. A temperature-sensitive secA mutant, which is defective in protein export at 42°C, exhibited severe pleiotropic effects on membrane biogenesis. Incubation of this strain at 42°C resulted in the appearance of intracytoplasmic membranes, in alterations in lipopolysaccharide structure and in decreased cardiolipin and C18:1 fatty acid content. On the other hand, a pgsA mutant which is defective in the synthesis of acidic phospholipids, exhibited a protein export defect when studied in vivo or in vitro. These results are in agreement with a postulated role of membrane lipids in protein export.
Positioning of gene products during Caulobacter cell differentiation
Authors: Shapiro Lucy , Gober James W. 
Published: May 2013

ABSTRACT
Caulobacter crescentus has one of the simplest known developmental programs that exhibits both temporal and spatial organization. A hallmark of the Caulobacter cell cycle is that the progeny cells that result from each cell division differ from one another with respect to structure and developmental program. The process of establishing asymmetry prior to cell division requires that a number of gene products be targeted to a pole of the predivisional cell and consequently segregated to one of the two progeny. Several products involved in flagellar biogenesis and the chemotaxis machinery are segregated to the swarmer cell. Evidence suggests that the protein product of somefla and che genes is targeted to the incipient swarmer cell pole. In the case of other flagellar genes, it is the mRNA that is apparently segregated to the swarmer cell. Two heat shock proteins, DnaK and Lon are specifically segregated to the progeny stalked cell.
Passage of Salmonella through polarized epithelial cells: role of the host and bacterium
Authors: Finlay B. Brett , Fry Jennifer , Rock Edwin P. , Falkow Stanley 
Published: May 2013

ABSTRACT
Salmonella are intracellular parasites which enter their hosts by penetrating the intestinal epithelial barrier. We examined the interaction of .S’. choleraesuis and .S’. typhimurium with Madin Darby canine kidney (MDCK) and human larynx (HEp-2) epithelial cells to characterize bacterial adherence, invasion and penetration through epithelial monolayers. Epithelial cell microfilaments were required for bacterial internalization and surrounded the bacteria as they were internalized. The bacteria entered membrane-bound vacuoles inside epithelial cells where they replicated. When polarized MDCK cell monolayers were infected, we found that Salmonella could pass through this barrier and enter medium bathing the opposite surface, although most bacteria remained within the monolayer. Synthesis of several Salmonella proteins was induced by the presence of epithelial cell surfaces, and these proteins were required for bacterial adherence and invasion. This induction was stimulated by trypsin- and neuraminidase-sensitive structures on epithelial cells.
Regulation of the cell cycle timing of mitosis
Authors: Moreno Sergio , Hayles Jacqueline , Nurse Paul 
Published: May 2013

ABSTRACT
Considerable advances have been made recently in our understanding of how the cell cycle timing of mitosis is regulated. This has come about because links have been established between two independent areas of research, one based on a genetic approach using the fission yeast Schizosaccharomyces pombe and the second based on a biochemical approach using Xenopus and starfish oocytes. In this chapter we review work that has identified a number of the mitotic regulating genes in fission yeast and has established links with controls operative in multicellular eukaryotes.
Further characterization of a size control gene in Saccharomyces cerevisiae
Authors: Cross Frederick R. 
Published: May 2013

ABSTRACT
The DAF1-1 mutation reduces cell size and reduces or eliminates Gj phase in Saccharomyces cerevisiae, and results in a-factor resistance. DAF1-1 cells transferred into low cycloheximide express an increased G1 phase in their cycle, suggesting that Gj regulation is present but cryptic in the DAF1-1 cycle in rich medium. DAF1-1 reduces cell size by the criterion of RNA content per cell as well as cell volume. The α-factor resistance of DAF1-1 cannot be suppressed by bypassing the pheromone-receptor interaction with ‘signalling-constitutive’ mutations, suggesting that pheromone binding and initial signalling is normal in DAF1-1 strains, but that division arrest in response to the signal is specifically defective. Consistent with this idea, the cdc28–3 mutation significantly suppresses DAF1-1 α -factor resistance at permissive temperature; CDC28 is a gene required specifically for START and the G1/S transition, and does not affect pheromone response. Genetic results additional to those previously reported confirm that the wild-type dafl + /WHI1 gene is non-essential; this result may be surprising since the gene product is apparently ratelimiting for the G1/S transition: its deletion increases cell size, and multiple copies decrease cell size.