bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surfaces and secretions in the pollen-stigma interaction: a brief review
Authors: Heslop-Harrison J. , Heslop-Harrison Y. 
Published: May 2013

ABSTRACT
Interactions between pollen and pistil are key events in angiosperm reproduction, and for this reason they have been the target of an increasing volume of research in recent years. The regulation of fertilization has proved to be remarkably complex, involving controls of various kinds imposed at several different levels. Pollen hydration, governance of germination and stigma penetration, guidance and nutrition of the pollen tube in the style -as well as various, still enigmatic, direct interactions between male and female gametophytes -may all be concerned, individually or in combination, in determining whether fertilization will or will not be effected. The controls differ in degree of efficiency and specificity. Depending largely on the taxonomic remoteness of the parents, interspecific incompatibility may result simply from lack of physiological co-adaptation between the partners, or from rejection mechanisms of a more specific kind. Intraspecific incompatibility, although generally having a deceptively simple genetic basis, has proved to be surprisingly diverse in its physiological manifestations. The paper will present a brief conspectus of the present status of research in the field, and review some recent interpretations of the nature of the specific recognition events that may be involved in some of the interactions.
Rhizobium leguminosarum genes involved in early stages of nodulation
Authors: Downie J. A. , Rossen L. , Knight C. D. , Robertson J. G. , Wells B. , Johnston A. W. B. 
Published: May 2013

ABSTRACT
Nodulation genes from Rhizobium leguminosarum have been subcloned and transferred to a strain of R. phaseoli with its symbiotic plasmid deleted (and therefore its nodulation and nitrogen fixation genes). Normal infection and nodule development occurred when these strains were added to the roots of Pisum sativum (peas) and Vicia hirsuta. The pea nodules were examined by electron microscopy; bacteroid forms were seen surrounded by peribacteroid membranes and using immuno-gold labelling it was shown that the nodule cells contained leghaemoglobin within the cytoplasm. By subcloning and analysing the nodulation region it was found that a small (3-2 × 103 bases) fragment of DNA contained three genes involved in root hair curling, the first observed step in the interaction between R. leguminosarum and the root hair cells of these legumes.
Callose biosynthesis as a ca2+-regulated process and possible relations to the induction of other metabolic changes
Authors: Kauss Heinrich 
Published: May 2013

ABSTRACT
Chitosan and poly-L-lysine induce electrolyte leakage in suspension-cultured soy bean cells due to their polycationic nature. Similar effects are caused by Polymyxin B at certain concentrations. After any of these treatments electrolyte leakage is followed by a rapid onset of callose synthesis, as studied quantitatively by its fluorescence with Aniline Blue. In addition to membrane perturbations resulting in membrane leakage callose synthesis requires the presence of external Ca2+ at μM concentrations. It is suggested that concomitant with electrolyte leakage a Ca2+ influx occurs, which leads to a local increase in Ca2+ at the cytoplasmic side of the membrane, resulting in activation of the (1→3)-β-glucan synthase.
The activity of this enzyme in microsomal preparations depends directly and reversibly on Ca2+, with half-saturation at about 5 μM. Inhibitor studies suggest that activation of the (l→3)-β-glucan synthase by Ca2+ is not mediated by calmodulin but possibly by phospholipids. The enzyme can also be activated in vitro by limited proteolysis. However, this type of activation does not appear to be involved in chitosan-elicited callose formation.
It appears of interest in regard to the function of callose in cell and tissue repair mechanisms that its formation is inhibited by unsaturated fatty acids and lysophosphatidylcholine, substances that presumably can result during membrane damage.
Callose synthesis may be regarded as an indicator of chitosan-induced increase in cytoplasmic Ca2+ concentration. It is speculated that this may also be part of the signal chain for initiation of de novo synthesis of enzymes reported to regulate phytoalexin production.
The human interleukin-2 receptor
Authors: Greene Warner C. , Depper Joel M. , KrÖnke Martin , Leonard Warren J. 
Published: May 2013

ABSTRACT
Complementary DNAs corresponding to the human receptor for interleukin-2 (IL-2) have been molecularly cloned, sequenced, and expressed in both COS-1 and L cells. The human genome appears to contain a single structural gene for this receptor located on the short arm of chromosome 10 (band 14-15). However, when transcribed, at least two families of mRNAs are produced, which vary in length due to the use of at least three different polyadenylation signals. Sequence analysis of the cloned cDNAs and Si nuclease protection assays indicate an alternative pathway of mRNA processing for this receptor whereby a 216 base-pair segment contained within the protein coding region is spliced, resulting in an mRNA unable to encode a functional IL-2 receptor. In contrast, cDNAs corresponding to mRNA retaining this 216 base-pair region code membrane receptors that bind both IL-2 and anti-Tac (monoclonal anti-IL-2 receptor antibody). Analysis of the deduced amino acid sequence reveals that the receptor is composed of 272 amino acids including a signal peptide 21 amino acids in length. Hydrophobicity analysis suggests a single, 19 amino acid transmembrane domain. A short intracytoplasmic domain composed of 13 amino acids is present and contains two potential phosphate acceptor sites (serine and threonine but not tyrosine) as well as positively charged residues presumably involved in cytoplasmic anchoring. Two sites for N-linked glycosylation sites and numerous extracytoplasmic O-linked glycosylation sites are present.
Visualization Of The Living Cytoskeleton By Video-Enhanced Microscopy And Digital Image Processing
Authors: Weiss Dieter G. 
Published: May 2013

ABSTRACT
Two steps led to our present-day view of the cytoskeleton as a highly dynamic structure that is actively involved in force generation for various kinds of cell motility and, as a result, is itself often actively moving.
The first step was the introduction of video microscopy, especially of the Allen Video Enhanced Contrast-Differential Interference Contrast Microscopy (AVEC-DIC), which allows the visualization of cellular structures in the light microscope that are up to 10 times smaller than the limit of resolution. This enables one to see images of unfixed, unstained, native or purified microtubules and actin bundles, and their interaction with membrane-bound organelles.
The second step was the discovery of a system exceptionally well-suited to study microtubule and organelle movements, namely, the extruded axoplasm of the squid giant axon. From this axon the cytoplasm can be extruded free from surrounding plasma membrane, and individual microtubules and organelles can be separated from the bulk axoplasm.
The study of these native microtubules by AVEC-DIC microscopy yielded a great number of. quite unexpected details of the dynamic behaviour of both the microtubules themselves and the motility associated with them.
Supracellular Microtubule Alignments In Cell Layers Associated With The Secretion Of Certain Fish Scales
Authors: J. Dane P. , B. Tucker J. 
Published: May 2013

ABSTRACT
Intercellularly aligned microtubule arrays are present in cell layers associated with the growth and secretion of scales in the zebra fish Brachydanio rerio and the neon tetra fish Hyphessobrycon innesi. The layers in question are: the osteoblast layer that covers the ossified outer surface of a scale, and the layer of fibroblasts that is situated immediately underneath the inner collagenous surface of a scale’s fibrillary plate.
In certain osteoblasts, the proximal portions of microtubules (with respect to centrosomes) run closely alongside the anterior margin of each cell where it flanks one of a scale’s ridge-shaped circuit. These osteoblasts and microtubule portions are arranged in aligned rows that are parallel to circuit. However, the distal portions of the microtubules curve into an orientation that is approximately at right angles to circuit and they are aligned with each other and similar microtubule portions in adjacent osteoblasts. Such microtubule alignments only occur in osteoblasts that are associated with circuit. In Hyphessobrycon osteoblasts situated elsewhere on a scale’s surface, microtubules radiate from cell centres but their distal portions curve into alignment with each other and are oriented alongside cell margins.
The proximal portions of fibroblast microtubules radiate from centrally positioned centrosomes but the distal portions curve into alignment with each other and distal microtubule portions in neighbouring fibroblasts. The overall pattern of microtubule alignment is similar to that of collagen fibres, which these fibroblasts are secreting onto the fibrillary plate.
The immunofluorescence protocol that was used to demonstrate the microtubule alignments described above did not reveal such alignments in the osteoblast and fibroblast layers associated with scales of the brown trout Salmo truttafario.
These findings are assessed in terms of intra- and inter-cellular control of microtubule alignment, and decentralized reorientation of microtubules at distances of several micrometres from centrosomal microtubule-organizing centres. The functional significance of the relationships between microtubule alignment and supracellular patterns of alignment that take place as collagen deposition and ossification proceed during scale formation is also considered.
Observations Of Microfilament Bundles In Living Cells Microinjected With Fluorescently Labelled Contractile Proteins
Authors: Sanger Jean M. , Mittal Balraj , Pochapin Mark , Sanger Joseph W. 
Published: May 2013

ABSTRACT
Fluorescently labelled contractile proteins (alpha-actinin and filamin) were used to study the dynamic nature of three types of microfilament bundles: myofibrils, stress fibres and polygonal networks. Cultured muscle and non-muscle cells that were microinjected with fluorescent alphaactinin rapidly incorporated the labelled protein into Z-bands, stress fibre densities and the polygonal foci. Living, injected cells were then observed for varying periods of time, and changes in orientation and periodicity of the myofibrils, stress fibres and polygonal networks were recorded. Permeabilized cells were also reacted with fluorescently labelled proteins and with contractile protein antibodies in order to analyse further the changes taking place in the myofibrils and stress fibres. In both living cardiac myocytes and living skeletal muscle myotubes, contractile myofibrils were present in the same cell with non-contractile nascent myofibrils. The periodicities of small Z-bodies in the nascent non-contractile myofibrils were shorter than the Z-band spacings in the contractile myofibrils, yet both types of myofibrils contained muscle myosin. Over a period of 24 h, a nascent myofibril in a living, microinjected myotube was observed to grow from Z-body spacings of 0·9–1·3µm to full sarcomere spacings (2·3um). During the same time, nascent myofibrils appeared de novo and Z-band alignment became more ordered in the fully formed myofibrils. Stress fibres were not observed to undergo the predictable type of growth seen in myofibrils, but stress fibre periodicities did change in some fibres; some shortened while others lengthened. The orientation of fibres shifted in cytoplasm of both mobile cells and stationary cells. Attachment plaques and foci also changed position and in some cases subdivided and/or disappeared. Models of stress fibres and polygonal networks are presented that suggest that the changes in the periodicities of the dense bodies in stress fibres and the distances between polygonal foci are related to the movement of the interdigitating actin and myosin filaments.
Myosin Distribution And Actin Organization In Different Areas Of Antibody-Labelled Quick-Frozen Fibroblasts
Authors: Lawson Durward 
Published: May 2013

ABSTRACT
In cortical and subcortical areas of motile non-muscle cells myosin is found only on linear actin filament bundles that are aligned with the cell’s long axis. Myosin is absent from actin filaments perpendicular to these bundles and from areas of cortical and subcortical actin, which has a complex geometrical array. These data suggest that in the non-muscle cell myosin exerts force in a unidirectional manner only, as it does in muscle. The presence of myosin up to the ends of cell processes suggests that, even in the cortex, this force transduction takes place over short-range distances. The absence of myosin rods in vivo but the presence of structures corresponding to single myosin molecules suggests that the force-generating unit for actomyosin-based movement in non-muscle cells is either a myosin dimer/small oligomer or single myosin molecule, attached to actin by their tail regions.
The structure and function of a mannose 6-phosphate receptor- enriched, pre-lysosomal compartment in animal cells
Authors: Griffiths Gareth 
Published: May 2013

ABSTRACT
The characteristics of a distinct prelysosomal compartment, evident in many animal cells, are described. The main feature of this compartment is that it is an acidic, tubulo-vesicular late endosome structure that contains high concentrations of the cation-independent mannose 6-phosphate receptor. The pathway to the lysosomes from the early endosomes, as well as that of newly synthesized lysosomal proteins from the trans-Golgi network, appear to converge in this prelysosomal compartment.
Characterisation of the nuclear location sequence of Xenopus nucleoplasmin
Authors: Dingwall Colin , Robbins Jacqueline , Dilworth Stephen M. 
Published: May 2013

ABSTRACT
Each subunit of the Xenopus nucleoplasmin polypeptide possesses a single nuclear location sequence, the boundaries of which have been determined by deletion analysis. However, the sequence identified in this analysis is unable to locate pyruvate kinase to the cell nucleus. Further investigation revealed that while this sequence element is not sufficient for nuclear localisation, it is a necessary feature of slightly longer sequences which can locate pyruvate kinase to the cell nucleus. This unusual feature of the nucleoplasmin sequence suggests testable models for the interaction of this sequence with the transport mechanism, one of which is discussed here.
Pax genes, mutants and molecular function
Authors: Chalepakis Georges , Tremblay Patrick , Gruss Peter 
Published: May 2013

ABSTRACT
The paired domain is a conserved DNA binding motif which was first found in Drosophila segmentation gene products. This paired domain is encoded by a well conserved, paired box DNA sequence, also detected in the genomes of other species. The mouse paired box-containing genes are referred to as Pax genes and are expressed in a distinct spatiotemporal pattern during embryogenesis. Pax proteins are able to bind to specific DNA sequences and modulate transcriptional activity. Interestingly, three different Pax genes have already been shown to correspond to some mouse and human mutants, emphasizing their role as developmental control genes.
The making of a tight junction
Authors: Cereijido M. , González-Mariscal L. , Contreras R. G. , Gallardo J. M. , Garcia-Villegas R. , Valdés J. 
Published: May 2013

ABSTRACT
MDCK (epithelial cells from the dog kidney) plated at confluence, establish tight junctions in 12-15 hours through a process that requires protein synthesis, formation of a ring of actin filaments in close contact with the lateral membrane of the cells, calmodulin, and a Ca2+-dependent exocytic fusion of tight junction (TJ)-associated components. Monolayers incubated in the absence Ca2+ make no TJs. Yet, if Ca2+ is added under these circumstances, TJs are made with a faster kinetics. Ca2+ is needed mainly at a site located on the outer side of the cell membrane, where it activates uvomorulin and triggers the participation of the cellular components mentioned above, via G-proteins associated with phospholipase C and protein kinase C. In principle, the sites of all these molecules and mechanisms involved in junction formation may be where a variety of agents (hormones, drugs, metabolites) act to produce epithelia with a transepithelial electrical resistance (TER) ranging from 10 to 10,000 Q.cm2. This range may be also due to a variety of substances found in serum and in urine, that increase the TER in a reversible and dose-dependent manner.
Polarity signals in epithelial cells
Authors: Rodriguez-Boulan Enrique , Zurzolot Chiara 
Published: May 2013

ABSTRACT
In simple epithelia, specialized vectorial functions such as transport and secretion are made possible by the segregation of proteins and lipids into opposite surface domains. This polarized distribution results from selective delivery to and retention at the appropriate domain. In the case of direct delivery, the sorting site for apical and basolateral proteins is the tram-Golgi network (TGN) where they are incorporated into distinct apical and basolateral vesicles that are targeted to the respective surfaces. The machinery that controls this simple process is in fact rather complicated. It involves many different steps from the recognition event (between ‘sorting signal(s)’ and ‘sorting receptor(s)’) to the formation of the vesicles, their budding, and the docking to the specialized plasma membrane domain. Here we summarize the latest developments in the sorting of apical and basolateral proteins, focusing in particular on the signals that are involved in this process and the current hypotheses about the mechanisms responsible for it, in both epithelia and in non-polarized cells.
Apical junctions and cell signalling in epithelia
Authors: Woods Daniel F. , Bryant Peter J. 
Published: May 2013

ABSTRACT
Genetic analysis in Drosophila has led to the identification of several proteins that mediate cell-cell interactions controlling the fate and proliferation of epithelial cells. These proteins are localized or enriched in the adherens and septate junctions at the apical end of the lateral membranes between cells. The proteins localized or enriched at adherens junctions include Notch, which is important for the cell interactions controlling neuroblast and bristle patterning; Boss and sevenless, which are required for the cell interaction that establishes the R7 photoreceptor cell; and Armadillo, required for the wingless-dependent cell interactions that control segment polarity and imaginai disc patterning. Proteins localized at septate junctions include the product of the tumor suppressor gene dig, which is required for septate junction formation, apical basal cell polarity, and the cell interactions that control proliferation. The results suggest that the cell signalling events important for cell fate determination and for cell proliferation control in epithelia occur at the apical junctions. The migration of the nucleus to the apical surface of the epithelium for mitosis may enable it to interact directly with the junction-associated signalling mechanisms.
Sorting of ion transport proteins in polarized cells
Authors: Gottardi Cara J. , Pietrini Grazia , Roush Denise L. , Caplan Michael J. 
Published: May 2013

ABSTRACT
The plasma membranes of polarized epithelial cells and neurons express distinct populations of ion transport proteins in their differentiated plasma membrane domains. In order to understand the mechanisms responsible for this polarity it will be necessary to elucidate the nature both of sorting signals and of the cellular machinery which recognizes and acts upon them. In our efforts to study sorting signals we have taken advantage of two closely related families of ion transport proteins whose members are concentrated in different epithelial plasmalemmal domains. The H+,K+-ATPase and the Na+,K+-ATPase are closely related members of the E1-E2 family of ion transporting ATPases. Despite their high degree of structural and functional homology, they are concentrated on different surfaces of polarized epithelial cells and pursue distinct routes to the cell surface in cells which manifest a regulated delivery pathway. We have transfected cDNAs encoding these pumps’ subunit polypeptides, as well as chimeras derived from them, in a variety of epithlial and non-epithelial cell types. Our observations suggest that these pumps encode multiple sorting signals whose relative importance and functions may depend upon the cell type in which they are expressed. Recent evidence suggests that the sorting mechanisms employed by epithelial cells may be similar to those which operate in neurons. We have examined this proposition by studying the distributions of ion pumps and neurotransmitter re-uptake cotransporters expressed endogenously and by transfection in neurons and epithelial cells, respectively. We find that one of the classes of proteins we studied obeys the correlation between neuronal and epithelial sorting while another does not. Our data are consistent with the possibility that sorting signals and sorting mechanisms are extremely plastic and can be adapted to different uses in different cell types or under different physiological conditions.
Analysis of the trk NGF receptor tyrosine kinase using recombinant fusion proteins
Authors: Horvath Curt M. , Wolven Amy , Machadeo Debbie , Huber Julie , Boter Lana , Benedetti Marta , Hempstead Barbara , Chao Moses V. 
Published: May 2013

ABSTRACT
Nerve growth factor (NGF) represents a family of structurally related trophic factors, including brain-derived neurotrophin factor (BDNF), neurotrophin-3 (NT-3), NT-4, and NT-5. These neurotrophin factors interact with two classes of receptors, the trk receptor tyrosine kinase family, and the low affinity p75 neurotrophin receptor. To study potential ligand-receptor interactions, recombinant trk fusion proteins have been constructed, and pan-Zrft polyclonal antisera directed against the cytoplasmic tyrosine kinase domain have been generated. The recombinant proteins were assessed for in vitro kinase activity and for the ability of K-252a to inhibit phosphorylation. Antibodies made against the fusion protein recognize all trk family members, and are effective in immunoprecipitation of affinity-crosslinked receptors. Comparative crosslinking indicates that NGF can recognize all trk receptor members, illustrating the large number of potential ligand-receptor interactions between neurotrophins and their receptors.
The influence of 5′ and 3′ end structures on pre-mRNA metabolism
Authors: Lewis Joe D. , Gunderson Samuel I. , Mattaj lain W. 
Published: May 2013

ABSTRACT
The 5′ cap structure of RNA polymerase II transcripts and the po?y(A) tail found at the 3′ end of most mRNAs have been demonstrated to play multiple roles in gene expression and its regulation. In the first part of this review we will concentrate on the role played by the cap in pre-mRNA splicing and how it may contribute to efficient and specific substrate recognition. In the second half, we will discuss the roles that polyadenylation has been demonstated to play in RNA metabolism and will concentrate in particular on an elegant mechanism where regulation of polyadenylation is used to control gene expression.