bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preprophase bands, phragmoplasts, and spatial control of cytokinesis
Authors: Gunning B. E. S. , Wick S. M. 
Published: May 2013

ABSTRACT
Features of preprophase bands (PPBs) of microtubules (MTs), and the spatial relationship between phragmosomes, PPB sites, and developing phragmoplasts during cytokinesis, are reviewed, setting new observations in the context of current knowledge.
PPBs in onion root tip cells are present by the beginning of the G2 period of the cell cycle. They are at first wide, but later become more compact, narrower bands. MTs traverse the cytoplasm between the band at the cell cortex and the nuclear envelope. This whole assemblage of nucleus, PPB and intervening MTs remains together when the cell is ruptured during preparation for examination by immunofluorescence microscopy. Double bands are occasionally seen in early stages of PPB development, perhaps as a consequence of double induction from neighbouring cells. Calmodulin is not present in PPBs at a higher concentration than in the general cytoplasm, but it is more abundant in parts of the spindle and in the phragmoplast.
The PPB MTs disappear at prophase, but nevertheless the new cell plate fuses with the parental cell walls at the PPB site. This spatial relationship can be disrupted by treatment with CIPC. Another experimental disruption of the relationship, accomplished by making minute wounds in the PPB site of mitotic cells in Tradescantia stamen hairs, is described. In other experiments on these cells the phragmoplast is shown to become tethered to the PPB site when the cell plate is half to three-quarters developed, although the telophase nuclei are free to move. Rhodamine-labelled phalloidin reveals putative F-actin in the phragmoplast of Tradescantia, but not in the gap between the extending phragmoplast and the PPB site. Rhodamine-labelled phalloidin also stains cytoplasmic strands that exist when cytoplasmic streaming occurs before and after (but not during) mitosis. Cytochalasin B treatment blocks incorporation of actin into the phragmoplast, which, however, can still develop, though usually abnormally. The F-actin of the phragmoplast may function in consolidation of the cell plate, rather than in spatial guidance of its growth toward the PPB site at the cell surface.
Epidermal Growth Factor: Biology and Receptor Metabolism
Authors: Carpenter Graham 
Published: May 2013

ABSTRACT
Epidermal growth factor (EGF) is a small (Mr 6045) protein that stimulates cell proliferation in cell culture systems and in intact animals. This growth factor has been isolated from rodents and human material and probably exists in nearly all animal species. In humans EGF has been detected in many body fluids and receptors for the growth factor are also ubiquitous. While the mitogenic activity of EGF has been most frequently reported, it clearly has other functions, such as the inhibition of gastric acid secretion, that are unrelated to mitogenic responses. Correspondingly, receptors for EGF have been localized on cells that are rapidly proliferating and cells that are essentially non-proliferating. Nevertheless, it has not been possible to define experimentally the biological function(s) of the endogenous EGF present in the intact animal.
Studies of the mechanism of action of EGF have concentrated, to date, on the plasma membrane receptor that specifically binds this ligand. The receptor is undoubtedly the first cellular component that mediates the-eventual biological response(s) of the cell to this extracellular signal. Studies of the EGF receptor have shown that this molecule, which has no subunit structure, functions not only in ligand recognition, but also may produce an intracellular ‘second message’. The receptor contains a protein kinase activity that is activated by the binding of EGF and it is this enzymic function that may yield the critical ‘second messenger’, by phosphorylation of an intracellular protein. Although intracellular targets of this EGF-sensitive protein kinase have been identified, it has not been possible to demonstrate their relevance as regulatory mediators of EGF activity.
Early response pattern analysis of the mitogenic pathway in lymphocytes and fibroblasts
Authors: Metcalfe J. C. , Hesketh T. R. , Smith G. A. , Morris J. D. H. , Corps A. N. , Moore J. P. 
Published: May 2013

ABSTRACT
The early biochemical responses stimulated by the action of mitogens and growth factors on mouse thymocytes and 3T3 fibroblasts are analysed as part of a systematic attempt to define the mitogenic pathways from Go to S phase in these cells. Although the primary response to each mitogen can be distinguished by the pattern of secondary responses they initiate, there is substantial overlap in these responses. The aim is therefore to determine whether there is early convergence on a common mitogenic pathway, defined by a sequence of responses obligatory for progression from Go to 5 phase for different mitogens and cell types. The ‘dual-signal’ hypothesis for the mitogenic stimulation of thymocytes is a simple version of a common mitogenic pathway. It proposes that the T-cell receptor initiates the pathway via the breakdown of phosphatidylinositol (4,5)-bisphosphate to generate a Ca signal (from the release of inositol (l,4,5)-trisphosphate) and to activate protein kinase C (from the release of diacylglycerol). The rationale for this hypothesis lies in the co-mitogenic action of the Ca2+-ionophore, A23187, and the phorbol ester, 12-o-tetradecanoyl phorbol 13-acetate, which is assumed to activate specifically protein kinase C. However, detailed analysis of the coupling between some of the early responses, including the Ca and pH signals, phosphatidylinositol (4,5)-bisphosphate metabolism, c-myc gene activation and general metabolic stimulation, indicates clearly that the hypothesis is inadequate to account for the initiation of the normal mitogenic pathway in thymocytes.
The structure and biosynthesis of epidermal growth factor precursor
Authors: Scott J. , Patterson S. , Rall L. , Bell G. I. , Crawford R. , Penschow J. , Niall H. , Coghlan J. 
Published: May 2013

ABSTRACT
The structure of mouse submaxillary gland epidermal growth factor (EGF) precursor has been deduced from complementary DNAs. The mRNA is approximately 4800 bases and predicts prepro EGF to be a protein of 1217 amino acid residues (133×10Mr). EGF (53 amino acid residues) is flanked by polypeptides of 188 and 976 residues at its carboxy and amino termini, respectively. The amino terminus of the precursor contains seven cysteine-rich peptides that resemble EGF. Towards the carboxy terminus is a 20-residue hydrophobic membrane spanning domain. The mid portion of the EGF precursor shares a 33 % homology with the low density lipoprotein receptor, which extends over 400 amino acid residues. These features suggest that EGF precursor could function as a membrane-bound receptor.
RNA dot-blot analysis and in situ hybridization show EGF mRNA to be abundant in the submaxillary gland, kidney and incisor tooth buds. Lower EGF mRNA levels were found in the lactating breast, pancreas, small intestine, ovary, spleen, lung, pituitary and liver. In the kidney EGF mRNA was most abundant in the distal convoluted tubules. Analysis of EGF precursor biosynthesis in organ culture of the submaxillary gland and kidney showed differential processing of the precursor in the two tissues. In the submaxillary gland immunoreactive low molecular weight EGF was produced, but in the kidney the high molecular weight precursor was not processed. In the distal convoluted tubule of the kidney EGF precursor may act as a receptor that is involved in ion transport.
Studies Of Tektin Filaments From Flagellar Microtubules By Immunoelectron Microscopy
Authors: Amos W. B. , Amos L. A. , Linck R. W. 
Published: May 2013

ABSTRACT
Chemically resistant 2-3 nm filaments with a high α-helical content, isolated from sea-urchin sperm flagellar doublet microtubules, consist of proteins that have been named tektins. Polyclonal affinity-purified antibodies to tektins labelled sperm tails all along their lengths, as shown by indirect immunofluorescence microscopy, provided the specimens were not too well fixed. Results obtained for unfixed specimens studied by immunoelectron microscopy suggested the tektins are normally masked by tubulin. A monoclonal anti-tektin antibody labelled bare tektin filaments at longitudinal intervals of approximately 48 nm, which fits in well with the 96 nm longitudinal repeat of axonemes. We discuss a possible scheme for the regular interaction of tubulin monomers with an α-helical coiled coil.
Latent Cellular Oncogenes: The Paradox Dissolves
Authors: Duesberg Peter H. 
Published: May 2013

ABSTRACT
The 20 known transforming one genes of retroviruses are defined by sequences which are transduced from cellular genes, termed proto-one genes. Based on these sequences, viral one genes have been postulated to be transduced cellular cancer genes and proto-owc genes have been postulated to be latent cancer genes that can be activated from within the cell, to cause virusnegative tumours. The hypothesis is popular because it promises direct access to cellular cancer genes. Hpwever the existence of latent cancer genes presents a paradox since such genes would be most undesirable for eukaryotes. The hypothesis predicts (i) that viral one genes and proto-owc genes are isogenic, (ii) that expression of proto-one genes induces tumours, (iii) that activated proto-one genes transform diploid cells upon transfection, like viral one genes, and (iv) it predicts diploid tumours. As yet, none of these predictions is confirmed. Instead: (i) Structural comparisons between viral one genes, essential retroviral genes, and the proto-one genes show that all viral one genes are indeed new genes, rather than transduced cellular cancer genes. They are genetic hybrids put together from truncated viral and truncated proto-owc genes, (ii) Proto-owc genes are frequently expressed in normal cells, (iii) To date, not one activated proto-owc gene has been isolated that transforms diploid cells, (iv) Above all, no diploid tumours with activated proto owc genes have been found. Moreover the probability of spontaneous transformation in vivo is at least 109 times lower than predicted from the mechanisms thought to activate proto-owc genes. Therefore the hypothesis, that proto-owc genes are latent cellular oncogenes, appears to be an overinterpretation of sequence homology to structural and functional homology with viral owe genes. Here is is proposed that only rare truncations and recombinations, that alter the germline configuration of cellular genes, generate viral and possibly cellular cancer genes. The clonal chromosome abnormalities that are consistently found in tumour cells are microscopic evidence for rearrangements that may generate cancer genes. The clonality indicates that the tumours are initiated with, and possibly by these abnormalities as predicted by Boveri in 1914.
Tobacco mosaic virus replicase and replicative structures
Authors: Young Nevin , Forney Julie , Zaitlin Milton 
Published: May 2013

ABSTRACT
The RNA-dependent RNA polymerase (replicase) mediating the replication of tobacco mosaic virus (TMV) has been investigated in a number of laboratories over a period of 20 years. Cell-free enzyme preparations have been prepared which can continue the synthesis of nascent complementary RNA, initiated in vivo; however, the enzyme does not require, nor does it respond to, exogenous viral RNA as a template. The presence in plants of a virus-stimulated, host-encoded RNA-dependent RNA polymerase (RdRp) has added confusion to this field; it is now generally conceded, however, that this enzyme is not the TMV replicase.
Our recent studies have emphasized several aspects of TMV RNA replication. We have examined the nature of TMV replicative structures synthesized in vitro by utilizing a partially purified enzyme preparation isolated from TMV-infected tobacco tissue. Radiolabelled products of the reaction were analysed on agarose gels and fractions with the predicted electrophoretic migration and nuclease sensitivities of replicative form (RF) and replicative intermediate (RI) were isolated. These fractions were hybridized to a collection of bacteriophage M13 clones containing portions of the TMV genome of both plus and minus polarity. The nascent synthesis in the Rl-like molecules was restricted to the plus viral strand, while the new synthesis in the RF-like molecules was of both plus and minus polarity.
Solubilization of the membrane-bound replicase with the non-ionic detergent CHAPS has yielded complexes which remain in solution after high-speed centrifugation. The solubilized replication complexes have been utilized as starting material for enzyme purification by Sepharose 4B gel filtration chromatography.
The intracellular site of synthesis of TMV RNA has been reinvestigated in the light of reports suggesting a nuclear site of replication. The conclusion for nuclear synthesis has been based on fractionation of subcellular homogenates of virus-infected leaves or mesophyll protoplasts and identification of virus-related proteins associated with these fractions. In our studies, however, we conclude that these procedures can be misleading in that the 126 000 Mr TMV protein (and replicase activity) were found in all fractions of the homogenate analysed. Double-stranded TMV RNA, on the other hand, was barely detectable in preparations of purified nuclei; instead it was concentrated in the post-nuclear supernatant, suggesting that the nucleus is not the site of TMV RNA synthesis.
Genome interactions which influence dna palindrome mediated instability and inviability in Escherichia Coli
Authors: Leach David , Lindsey Janet , Okely Ewa 
Published: May 2013

ABSTRACT
The interaction of three factors determine the detrimental effect of a palindromic DNA sequence in Escherichia coli cells. The first is the nature of the palindrome (its length, extent of central asymmetry and perhaps its base sequence), the second is the genotype of the host cell and the third is the replicon within which it is located. In this paper we extend the genetic and physical characterization of lambda bacteriophages carrying a palindrome of approximately 560 base pairs. We also show that a palindrome of approximately 110 base pairs which can be cloned in a plasmid cannot be cloned in a phage M13 derivative. These observations are relevant to the choice of vectors used in the cloning of eukaryotic DNA containing palindromic sequences.
The role of sequence-specific dna-binding proteins in adenovirus dna replication
Authors: Hay Ronald T. , Barrett Perry , Clark Lilian , Harris Mark 
Published: May 2013

ABSTRACT
In prokaryotes it is well established that proteins which recognise defined DNA sequences are involved in the control of gene expression and replication. Cellular proteins in eukaryotes which may perform a similar function have been identified by their interactions with control regions of the human adenovirus genome.
Immediately after infection a small region (Ela) at the left end of the adenovirus genome is expressed. Proteins coded by the Ela region transcriptionally activate the viral early genes. The products of a number of these early genes are directly involved in replication of the viral DNA. DNA sequences which are required for efficient Ela transcription and for the initiation of DNA replication have been identified by mutational analysis. Cellular proteins which recognise these sequences were detected using a sensitive gel retention assay. The basis of this assay is that during electrophoresis DNA-protein complexes migrate more slowly through a polyacrylamide gel than free DNA. In this way a cellular protein which binds to a conserved sequence in the adenovirus enhancer has been identified and partially purified. Cellular proteins which bind to adenovirus type 2 and 4 origins of replication have also been fractionated from nuclear extracts of uninfected HeLa cells. The roles of these proteins in adenovirus replication will be discussed.
Transposable Elements in Antirrhinum Majus
Authors: Martin Cathie , Carpenter Rosemary , Robbins Tim , Hudson Andrew , Almeida Jorge , Bartlett Jeremy , MACKAY Steve , Coen Enrico 
Published: May 2013

ABSTRACT
The transposable element, Tam 3, gives rise to large-scale chromosomal rearrangements at a low frequency, when it is inserted at the nivea locus of Antirrhinum majus. Some deletions that result from imprecise excision of Tam 3 provide an allelic series for functional analysis of the nivea gene promoter. Rearrangements involving deletion, dispersion and inverted duplication of flanking sequences, where Tam 3 remains in situ, have also been identified. These rearrangements have been mapped at the molecular level, and the behaviour of Tam 3 following rearrangement has been observed. It is clear that Tam 3 has enormous potential to restructure chromosomes through successive rounds of large-scale rearrangements.
Aspects of the ac/ds transposable element system in maize
Authors: Peacock W. James , Dennis Elizabeth S. , Finnegan E. Jean , Peterson Thomas A. , Taylor Brian H. 
Published: May 2013

ABSTRACT
Studies of the Ac (Activator) transposable element provided the data which led Barbara McClintock to postulate that certain segments of chromosomes could transpose to different locations in the genome. McClintock also recognized the existence of Ds (Dissociation) elements which could transpose, but only in the presence of a trans-acting Ac element elsewhere in the genome. DNA sequences corresponding to Ds and Ac have now been identified, and an understanding of many of the properties of these transposable elements in the maize genome has been acquired in recent years.
It is known that cryptic Ac elements and members of at least two families of Ds elements occur in the genome of all maize lines examined. Ds elements also occur in Teosinte and the more distantly related Tripsacum. We discuss the possible origin of these elements and consider the mechanism of activation of cryptic Ac elements. A recent molecular analysis of a transition of an Ac-derived Ds-element back to an active Ac element suggests one molecular mechanism by which changes in the activity state of Ac may occur.
Distinctive phenotypes created by controlling elements within a target gene have been shown to be governed by the properties of the insertion element and the position of the insertion within the gene. Genetic effects include modulation of gene expression, alteration of gene products, instability of mutant phenotypes, deletion and duplication of chromosome segments and the production of chromosome rearrangements. We describe an example where a Ds insertion generates an additional intron in the Adhl gene which reduces gene expression through mRNA instability. We also discuss an Ac-dependent modulation of P gene activity in glume and pericarp tissues of maize which may be attributed to an alteration either in patterns of gene expression or the developmental biology of the flower.
The molecular consequences of Ac and Ds insertions and excisions are known at the DNA sequence level but little is known of the mechanism of transposition. An initial approach has been to analyse Ac transcription. Preliminary results showing transcription of a limited region of Ac are discussed. The corresponding upstream regions have been linked to the coding region of chloramphenicol acetyltransferase (CAT) and show promoter activity following electroporation into tobacco protoplasts.
Effect of Patterned Surfaces of Adhesive Islands on the Shape, Cytoskeleton, Adhesion and Behaviour of Swiss Mouse 3T3 Fibroblasts
Authors: Ireland G. W. , Dopping-Hepenstal P. , Jordan P. , O’neill C. 
Published: May 2013

ABSTRACT
A pattern of circular islands of adhesive substratum can be used to control cell shape and behaviour. We have shown previously that the proportion of Swiss 3T3 cells that synthesize DNA varies with the area of the island to which they are attached, within the range 500–5000 μm2. In this paper we investigate the cytoskeleton and adhesions of cells on islands using a variety of techniques including phalloidin staining and interference reflection microscopy. Islands of area 2000 μm2 or less constrain cell shape, and cause focal contacts and actin microfilament bundles to accumulate in a circle at the margin. These changes are most obvious in islands of about 1000 gm2, in which a complete ring of adhesion is sometimes formed in the periphery of the cell. This peripheral distribution is less common in cells on even smaller islands, and the focal contacts become smaller and less numerous. It is not yet clear whether any of these structural changes are associated directly with the proliferative stimulus due to contact with the substratum. However, we expect that the use of patterned substrata will contribute to the study of how cell shape and structure regulate many cell functions.
Foetal-to-Adult Transitions in Fibroblast Phenotype: Their Possible Relevance to the Pathogenesis of Cancer
Authors: Schor S. L. , Schor A. M. 
Published: May 2013

ABSTRACT
We have previously shown that the migration of foetal, adult and transformed fibroblasts into three-dimensional collagen gels is differentially affected by plating cell density. We now present data indicating that the migration of these fibroblasts is also differentially affected by local cell density in microdomains of the gel surface. In this article we discuss the possible biochemical and behavioural mechanisms that may contribute to the different migratory phenotypes expressed by foetal, adult and transformed fibroblasts; these include: (1) cell-induced alterations in the orientation and or packing density of collagen fibres in the gel; (2) deposition of specific matrix macromolecules by the fibroblasts; (3) social interactions between the cells; and (4) secretion of soluble factors affecting cell migration. We show that foetal fibroblasts secrete a migration stimulating factor (MSF) not produced by adult cells. Incubation of adult fibroblasts in the presence of MSF induces these cells to express a foetal-like migratory phenotype. Foetal fibroblasts undergo a spontaneous foetal-to-adult transition in migratory phenotype after prolonged passage in vitro ; this transition is accompanied by a cessation in MSF production. MSF appears to promote fibroblast migration at high cell density by stimulating the deposition of hyaluronic acid in the extracellular matrix.
Recent studies have indicated that skin fibroblasts from cancer, patients display certain behavioural abnormalities characteristic of transformed and/or foetal cells. In this regard, we have shown that skin fibroblasts from cancer patients commonly express a foetal-like phenotype with respect to migratory behaviour and secretion of MSF: it is of interest to note that these cancer patient fibroblasts are indistinguishable from normal adult cells in other respects, such as morphology in confluent culture. On the basis of these observations, we suggest that: (1) fibro-blasts in certain individuals fail to undergo normal foetal-to-adult transitions in a number of phenotypic characteristics; and that (2) the disruption in epithelial-mesenchymal interactions caused by the continued presence of these foetal-like fibroblasts in the adult significantly increases the risk of cancer development.