bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cytoskeletal Changes During Oogenesis And Early Development Of Xenopus Laevis
Authors: Wylie C. C. , Heasman Janet , Parke Judy M. , Anderton Brian , Tang Peter 
Published: May 2013

ABSTRACT
The frog oocyte is well known for studies on the control of gene expression, but has been used much less in studies on the cytoskeleton. However, frog oocytes are very large single cells, whose cytoplasmic movements and asymmetries are fundamental to the correct development of the subsequent embryo. One particular example of asymmetrically distributed cytoplasm is germ plasm, thought to be important in the formation of the germ line. Data are presented that show that germ plasm is a highly concentrated mass of cytoskeletal elements, which include tubulin, and an intermediate filament protein of molecular weight 55 × 103. The distribution of these molecules has been studied during oogenesis and during early post-fertilization development. The implications of these findings are discussed.
Enzyme systems initiating replication at the origin of the ESCHERICHIA COLI chromosome
Authors: Kornberg Arthur 
Published: May 2013

ABSTRACT
More than ten proteins are known to participate in replication of plasmids bearing the unique origin of the Escherichia coli chromosome (onC). Initiation of replication of oriC plasmids has been resolved into five separable stages. An initial complex formation (Stage I) requires an oriC plasmid, dnaA protein and HU protein. In the presence of ATP at a temperature of &gt;28°C, a dnaB-C protein complex interacts to form a prepriming complex (Stage II). This is followed by extensive unwinding of the template that depends on the further addition of gyrase and singlestrand binding protein (SSB) (Stage III). Hydrolysis of an rNTP by dnaB protein (a helicase action) and of ATP by gyrase (a swivelling action) drives the extreme unwinding of the template. This unwound template-protein complex is the substrate for priming by primase (Stage IV) and elongation by DNA polymerase III holoenzyme (Stage V). Priming of all DNA chains is done by primase; RNA polymerase functions in template activation rather than priming. DNA polymerase III holoenzyme, composed of at least seven subunits, synthesizes the DNA chains. The α subunit is the polymerase, the ε subunit is the 3′ →5′exonuclease; α+ε is the proofreading activity. Following the synthesis of new DNA chains, DNA polymerase I and ribonuclease H remove the RNA primers, polymerase I fills the gaps, and ligase seals the daughter strands (Stage VI). Replication produces plasmids identical in structure and sequence to the initial template.
Mechanisms of Tumour Cell Metastasis
Authors: Parish Roger W. , Schmidhauser Christian , Schmidt Thomas , Dudler Robert K. 
Published: May 2013

ABSTRACT
Abercrombie and his colleagues have accumulated evidence that changes in the heterotypic contact-inhibition response are largely responsible for the invasiveness of cells, at least in culture. We have identified a 37 000Mr protein on the surface of mouse fibrosarcoma cells that is involved in their in vitro invasion. Blocking this protein with specific antibodies inhibits the invasion of chicken heart fibroblasts by the tumour cells and normal heterotypic contact inhibition is restored. These results are presented in the general framework of metastatic mechanisms and we review a selection of more recent studies aimed at describing the metastatic phenotype in molecular terms.
Integrin, A Transmembrane Glycoprotein Complex Mediating Cell-Substratum Adhesion
Authors: Buck Clayton A. , Horwitz A. F. 
Published: May 2013

ABSTRACT
A monoclonal antibody, CSAT, which inhibits the adhesion of chick cells to substrata coated with fibronectin, laminin and vitronectin, has been used to identify a cell surface receptor required for cell—substratum adhesion. This receptor, termed integrin, is found on the ventral surface of cells in close contact adhesion sites, at the periphery of adhesion plaques and beneath stress fibres. It is a heterodimer consisting of non-covalently linked alpha and beta subunits. Integrin binds directly to laminin, fibronectin and vitronectin with dissociation constants in the micromolar range. The binding of integrin to matrix molecules is sensitive to peptides carrying the cell-binding sequence Arg-Gly-Asp and requires heteromeric integrity. Integrin also binds directly to the cytoskeleton-associated protein talin. Thus, integrin has the properties of a transmembrane molecule capable of bringing extracellular matrix and cytoskeleton-associated molecules in proper juxtaposition to form adhesion structures. The integrin beta subunit is phosphorylated following Rous sarcoma virus transformation. Phosphorylation alters the ability of the receptor to bind extracellular matrix molecules as well as talin, suggesting a mechanism for the alteration of cellular adhesive and morphological properties following malignant transformation. A major phosphorylation site is on the cytoplasmic domain of the beta subunit. Synthetic peptides homologous with this region of integrin inhibit integrin-talin binding. The gene for the beta subunit of integrin has been sequenced. Its structure is consistent with the membrane-spanning properties of the receptor. Integrin is structurally and serologically related to adhesion receptors from mammalian tumour cells, fibroblasts, platelets and lymphocytes. It appears to be a member of a supergene family of receptors involved in cellular adhesive interactions. Antibody and peptide inhibition experiments have suggested a role for integrin and integrin-like molecules in cell migration, neurite extension, •neural differentiation, histogenesis and embryonic development in Drosophila. Thus, integrin appears representative of a set of evolutionarily conserved, biologically important adhesive molecules.
The Influence of Extracellular Matrix on Gene Expression: Is Structure The Message?
Authors: Bissell Mina J. , Barcellos-Hoff Mary Helen 
Published: May 2013

ABSTRACT
The study of the regulation of gene expression in cultured cells, particularly in epithelial cells, has been both hampered and facilitated by the loss of function that accompanies culture on traditional plastic substrata. Initially, investigations of differentiated function were thwarted by the inadequacy of tissue culture methods developed to support growth of mesenchvmal cells. However, with the recognition that the unit of function in higher organisms is larger than the cell itself, and that gene expression is dependent upon cell interactions with hormones, substrata and other cells, came the understanding that the epithelial cell phenotype is profoundly influenced by the extra-cellular environment. In the last decade research on epithelial cells has centred on culture conditions that recreate the appropriate environment for function with very promising and important results. The investigations into the modulation of phenotype in culture produced not only a better model, J&gt;ut also contributed to a better understanding of the regulation of normal function. Using cultured mammary gland epithelial cells as a primary model of these interactions, our studies of gene expression are based on three premises.
That the extracellular matrix (ECM) on which the cells sit is an extension of the cells and an active participant in the regulation of cellular function; i.e. the ECM is an ‘informational’ entity in the sense that it receives, imparts and integrates structural and functional signals. That ECM-induced functional differentiation in the mammary gland is mediated through changes in cell shape, i.e. that the structure is in large part ‘the message’ required to maintain differentiated gene expression. That the unit of function includes the cell plus its extracellular matrix; in a larger context, the unit is the organ itself.
These tenets and the data presented below are consistent with a model of ‘Dvnamic Reciprocity’, where the ECM is postulated to exert an influence on gene expression via transmembrane proteins and cytoskeletal components. In turn, cytoskeletal association with polvribosomes affects mRNA stability and rates of protein synthesis, while its interaction with the nuclear matrix could affect mRNA processing and, possibly, rates of transcription.
Epithelial Cell Polarization In Culture: Orientation of Cell Polarity and Expression of Specific Functions, Studied With Cultured Thyroid Cells
Authors: Mauchamp Jean , Chambard Marianne , Verrier Bernard , Gabrion Jacqueline , Chabaud Odile , Gerard Corinne , Penel Claude , Pialat Bernard , Anfosso Francine 
Published: May 2013

ABSTRACT
Isolated porcine thyroid cells reorganize in culture into various types of multicellular structure, which differ in the orientation of cell polarity and in the surface of the cell layer accessible to molecules present in the culture medium. The types of structure are: (1) follicles-, the basal pole is oriented toward the medium; (2) inside-out follicles or monolayers: the apical pole is facing the culture medium; (3) monolayers on a permeable substratum: both sides of the cell layer are accessible to the medium. Follicles can be transformed into inside-out follicles or monolayers and vice versa by manipulation of the external cell environment and without dissociating the cells. Cells concentrate iodide and respond to acute stimulation by thyroid-stimulating hormone (TSH) when the basal pole is accessible, and organification occurs only when cells form a closed follicular lumen.
In porous-bottomed culture chambers monolayers are formed with the basal surface accessible to the medium and the apical compartment separated from the medium. Under these conditions 85–95% of the thyroglobulin produced is secreted apically and 5–15% basally. Thyrotropin stimulates (×3) apical accumulation without modifying secretion in the basal compartment.
Sodium transport across the cell layer has been characterized. An amiloride-sensitive influx occurs at the apical pole whereas the Na+/K+-ATPase, localized in the basolateral membrane, mediates ouabain-sensitive efflux at the basal pole. The thyroid epithelium in culture appears therefore as a Na+-absorbing epithelium. The role of this transport in the stabilization of cell polarity is discussed.
The genetics of protein targeting in Escherichia coli K12
Authors: Trun Nancy J. , Silhavy Thomas J. 
Published: May 2013

ABSTRACT
Genetic analysis of protein targeting in Escherichia coli has been facilitated by the use of lacZ gene fusions. Strains which contain a fusion between a gene specifying a noncytoplasmic protein and lacZ exhibit novel phenotypes that can be exploited to obtain export-defective mutations. Analysis of these mutations has demonstrated the importance of the signal sequence and provided some insight into the functions performed by this complex intragenic export signal. In addition, genes that specify components of the cellular protein export machinery have been identified. Three of these genes, secA, secB, and prlA/secY have been studied in some detail and results indicate that the protein products function in the translocation of exported proteins across the cytoplasmic membrane.
Regulation of transforming growth factor-β subtypes by members of the steroid hormone superfamily
Authors: Wakefield Lalage , Kim Seong-Jin , Glick Adam , Winokur Thomas , Colletta Anthony , Sporn Michael 
Published: May 2013

ABSTRACT
Transforming growth factor-/fe (TGF-βs) are potent regulators of cell growth and differentiation. Expression of the closely related TGF-β subtypes in vivo is differentially regulated both temporally and spatially. Members of the steroid hormone superfamily may play an important role in this gene- and tissue-specific regulation. We have shown that anti-estrogens induce the production of TGF-β1 in mammary carcinoma cells and fetal fibroblasts, whereas retinoic acid specifically induces TGF-β2 in primary epidermal kératinocytes. The induction of TGF-β2 by retinoids is accompanied by an increase in TGF-β2 mRNAs, but little change in transcription rates, suggesting an effect of retinoids on message stability or processing. In contrast, TGF-β1 mRNA levels are unchanged by anti-estrogen treatment, suggesting these compounds may regulate the translatability of the TGF-β1 message or some post-translational processing event. We have identified a stable stem-loop structure in the 5′ untranslated region (UTR) of the TGF-β mRNA that inhibits translation of a heterologous reporter gene, and we are investigating the possibility that anti-estrogens may regulate the activity of this element, and hence the translatability of the TGF-β1 message. A significant fraction (25–90%) of the TGF-β induced by retinoids and anti-estrogens is in the biologically active rather than the latent form. We have shown that active TGF-β has a much shorter in vivo half-life than latent TGF-β, suggesting that the TGF-β induced by retinoids and steroids may act locally at the site of production. Since many tumor cells retain sensitivity to the growth inhibitory effects of active TGF-β, the use of members of the steroid hormone superfamily for inducing this potent growth inhibitor locally at the tumor site may have therapeutic potential.
Kinetic analysis of regulated myosin ATPase activity using single and limited turnover assays
Authors: Ankrett R. J. , Walmsley A. R. , Bagshaw C. R. 
Published: May 2013

ABSTRACT
Myosin from molluscan adductor muscle is regulated directly by Ca2+ binding. In the absence of Ca2+ the ATPase activity is greatly inhibited. We review the application of transient kinetic methods to this system and show how they can be simple to perform and less ambiguous than steady-state methods.
Molecular basis of myosin assembly: coiled-coil interactions and the role of charge periodicities
Authors: Atkinson Simon J. , Stewart Murray 
Published: May 2013

ABSTRACT
Complementation of alternating zones of positive and negative charge in the myosin rod enables molecules to interact in a number of ways. This accounts for the complexity of the molecular organisation of thick filaments. However, directed mutagenesis of expressed LMM cDNA indicated that charge zone complementation is not a major driving force in myosin polymerisation. Instead, it probably serves to prevent unfavourable interaction geometries.
A model for kinesin movement from nanometer-level movements of kinesin and cytoplasmic dynein and force measurements
Authors: Kuo Scot C. , Gelles Jeff , Steuer Eric , Sheetz Michael P. 
Published: May 2013

ABSTRACT
Our detailed measurements of the movements of kinesin- and dynein-coated latex beads have revealed several important features of the motors which underlie basic mechanical aspects of the mechanisms of motor movements. Kinesin-coated beads will move along the paths of individual microtubule protofilaments with high fidelity and will pause at 4nm intervals along the microtubule axis under low ATP conditions. In contrast, cytoplasmic dynein-coated beads move laterally across many protofilaments as they travel along the microtubule, without any regular pauses, suggesting that the movements of kinesin-coated beads are not an artefact of the method. These kinesin bead movements suggest a model for kinesin movement in which the two heads walk along an individual protofilament in a hand-over-hand fashion. A free head would only be able to bind to the next forward tubulin subunit on the protofilament and its binding would pull off the trailing head to start the cycle again. This model is consistent with the observed cooperativity between the heads and with the movement by single dimeric molecules. Several testable predictions of the model are that kinesin should be able to bind to both alpha and beta tubulin and that the length of the neck region of the molecule should control the off-axis motility. In this article, we describe the technology for measuring nanometerlevel movements and the force generated by the kinesin molecule.
Characteristics of the motor responsible for the gliding of native microtubules from squid axoplasm
Authors: Weiss Dieter G. , Seitz-Tutter Dieter , Langford George M. 
Published: May 2013

ABSTRACT
Nucleotide-dependent movement of native microtubules (nMTs) in squid axoplasm has biochemical and biophysical characteristics of kinesin-driven motility. However, the high vanadate and N-ethylmaleimide sensitivity and the velocity demonstrate that the properties of the native motile system differ considerably from those of purified kinesin preparations.
Antibodies against vertebrate microfilament proteins in the analysis of cellular motility and adhesion
Authors: Jockusch Brigitte M. , Zurek Barbara , Zahn Ralph , Westmeyer Annette , Füchtbauer Annette 
Published: May 2013

ABSTRACT
Microinjection of specific antibodies can be an alternative and a supplement to genetic engineering in dissecting the function of individual cytoskeletal components. In this report, we describe some of the requirements for using this technique, its potential application in conjunction with morphological and biochemical analyses, and its limitations. Examples are given for the injection of antibodies to "-actinin, vinculin and myosin, and the effects of such treatment on adhesion, motility and cytokinesis of the recipient cells.
Tau protein and the establishment of an axonal morphology
Authors: Kosik Kenneth S. , Caceres Alfredo 
Published: May 2013

ABSTRACT
Dissociated neuronal cultures from several regions of the nervous system elaborate two populations of neurites which have features of axons and dendrites. The microtubule-associated protein tau appears to segregate to the axon in some of these culture systems, however it does not do so until after the development of morphological polarity. Despite this observation, tau very likely has some role in the development of polarity because in cultured cerebellar macroneurons taken from the rat embryonic day 15 primordial cerebellum, the inhibition of tau expression by antisense techniques resulted in the failure of a single minor neurite to elongate and form an axon-like neurite. Tau antisense given continuously for up to 72 h kept neurons locked in a stage with minor neurites only; however when released from the effects of the antisense they fully recovered. The administration of tau antisense after the development of polarity resulted in the loss of the axonlike neurite, while dendrite-like neurites continued to grow. Together these results suggest that dendritic differentiation in cerebellar macroneurons requires the prior elaboration of an axon-like structure.
Intracellular organization of hippocampal neurons during the development of neuronal polarity
Authors: Dotti Carlos G. , Banker Gary 
Published: May 2013

ABSTRACT
In culture, hippocampal neurons initially establish several short, apparently identical processes; of these, only one acquires axonal characteristics, the remainder becoming dendrites. We examined the organization of cytoplasmic constituents that might influence which of the initial processes becomes the axon. The Golgi complex was visualized using either fluorescent wheat germ agglutinin or a specific antibody. Presumptive microtubule-organizing centers were identified by depolymerizing microtubules with nocodazole, then allowing them to repolymerize for brief periods. As judged by light microscopy, hippocampal neurons contained a single Golgi region and a single microtubule-organizing center, which were frequently localized together adjacent to a shallow indentation in the nucleus. In cells fixed shortly after the axons had emerged, there was no correlation between the position of the Golgi complex or the microtubule organizing center and the site of origin of the axon. Based on nuclear shape, the position of the Golgi complex and microtubuleorganizing center could also be inferred in living cells. When axonal outgrowth was followed in individual cells by time-lapse microscopy, so that the location of the Golgi complex and microtubuleorganizing center could be determined at the exact moment when the axon emerged, no correlation was apparent. Antibodies that recognize specific post-translational modifications of a-tubulin-acetylation and de-tyrosination-were used to assess the distribution of arrays of stable microtubules. Stable microtubules were present in all processes, both before and after the emergence of the axon. They were not confined to the axon. Thus the localization of these cellular constituents does not play a major role in determining which of the processes initially extended by hippocampal neurons becomes the definitive axon.
Regulation of expression of glial filament acidic protein
Authors: Sarkar Srijata , Cowan Nicholas J. 
Published: May 2013

ABSTRACT
The regulation of cell type-specific expression of the gene encoding glial filament acidic protein (GFAP) was examined by introducing various deletion mutants of the gene into GFAP-expressing (U251 human astrocytoma) and non-expressing (HeLa) cell lines, and measuring their transcriptional activity in an RNAase protection assay. The expression of GFAP is influenced by a number of cis-acting elements. A domain that resides between nucleotides-1631 and — 1479 can confer cell type-specific expression when coupled to a heterologous gene. We also present evidence for the existence of a negative regulatory element that resides within the first intron of the GFAP gene.
The expression and distribution of laminin in the developing nervous system
Authors: Edgar David 
Published: May 2013

ABSTRACT
The extracellular matrix glycoprotein laminin exerts profound effects on the survival and differentiation of neurons in vitro. Although principally confined to the basement membranes of the adult extracellular matrix, during development laminin immunoreactivity may be found both within the interstitial extracellular matrix and on the membranes of neural cells, in which location it may be expected to affect their development in vivo. To investigate the reasons for the occurrence of laminin outside basement membranes, the expression of genes coding for laminin subunits has been analysed in mouse sciatic nerves at different postnatal ages. The results show that the expression of genes coding for laminin subunits decreases from high levels at birth, very low steady state levels of the individual mRNAs being found in the adult. Thus, the predicted high rate of laminin synthesis during development might exceed the rate at which it may be incorporated into basement membranes. The effective change in distribution of laminin into the basement membrane is therefore likely to be simply a consequence of the down-regulation of gene expression, rather than being caused, for example, by the differential expression of laminin variants.
Microtubule-associated proteins and neuronal morphogenesis
Authors: Matus Andrew 
Published: May 2013

ABSTRACT
The microtubule-associated proteins (MAPs) are a set of structural proteins that bind to microtubules in vitro. Several of them occur at high levels in neurons where their expression is under strong developmental regulation, suggesting that they are involved in neuronal morphogenesis. Recently cDNAs for several of them have been cloned and sequenced revealing their primary structures and opening the way for genetic manipulation experiments aimed at determining their functions. Such experiments have shown that there are at least two classes of MAPs that are distinguished by the amino acid sequence motifs by which they bind to tubulin. One of these classes contains three known genes, two of which have been expressed in non-neuronal cells where the proteins cause bundling of microtubules and their rearrangement within the cytoplasm. The mechanism of this rearrangement is at present controversial. Another significant feature of these proteins is that several of them are differentially distributed within the neuronal cytoplasm; for example, some forms of MAP2 are selectively located in dendrites while in many situations MAP tau is limited to axons. In the case of MAP2, the mRNA that encodes the protein is also located in dendrites. This suggests that synthesis of MAP2 may be regulated locally in the dendritic cytoplasm. The molecular mechanism underlying the sorting of these proteins within neurons is unknown at present.