bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light-induced colour changes by the iridophores of the neon tetra, Paracheirodon Innesi
Authors: Clothier Jennifer , Lythgoe J. N. 
Published: April 2021

ABSTRACT
The iridophores of the Neon tetra Paracheirodon innesi consist of alternating layers of guanine and cytoplasm. In the dark-adapted state the reflected light from constructive interference is in the ultraviolet or blue. When exposed to light the cytoplasm layers increase in thickness and as a result the reflections shift to longer wavelengths and the iridophores appear green. The iridophores are thought to contain a rhodopsin-like molecule and we suggest that the colour-change mechanism involves the light-induced opening of sodium channels in the plasma membrane, leading osmotically to an increase in thickness of the cytoplasm layers. Experimental support for this suggestion was obtained by the substitution of choline chloride for sodium chloride in the perfusing medium, which can be done without altering the osmotic strength of the perfusing medium. This procedure almost abolished the light response and makes it seem likely that sodium ions are necessary for the light response to take place.
Induction of cybrid strains of Tetrahymena thermophila by electrofusion
Authors: Gaertig Jacek , Kiersnowska Mauryla , Iftode Francine 
Published: April 2021

ABSTRACT
In this paper, the electrofusion of the ciliated protozoan, Tetrahymena thermophila, is described. Deciliated cells were brought into close membrane contact by dielectrophoresis in a weakly conductive medium. Then cell fusion was induced by application of repeated electric pulses. Up to 20 prestarved, logarithmic or stationary phase cells of the same or different mating types may form a single giant cell. The polykaryons are fully able to regenerate cilia and became motile. After an initial process of partial integration the polykaryons yield viable clones by separation of components. Cytoplasmic exchange between fused components occurs before separation. Cytoplasmically inherited chloramphenicol resistance was transmitted from one strain to another by electrofusion and drug-resistant cybrid strains were generated.
Cloning of a gene encoding an antigen associated with the centrosome in Drosophila
Authors: Whitfield W. G. F. , Millar S. E. , Saumweber H. , Frasch M. , Glover D. M. 
Published: April 2021

ABSTRACT
The monoclonal antibody Bx63 recognizes a centrosomal antigen of Drosophila melanogaster by indirect immunofluorescence and identifies two proteins, with apparent molecular weights of 185 ×103 and 66×103, on Western blots. We have used this antibody to isolate five clones (λcsl, -2, -3, -4 and λj63) from λgtll expression libraries of Drosophila DNA. Using polyclonal anti-centro- somal sera raised against both immunoaffinity- purified Bx63 antigen and electrophoretically purified fusion protein from clone λcs3, we have demonstrated that the fusion proteins encoded by four of these clones (λcsl-4) share at least two epitopes with the 185×103Mr centrosomal antigen. This indicates that clones λcsl-4 contain DNA from the gene coding for this protein. The four clones are independent isolates from a single chromosomal site, which we show by in situ hybridization to correspond with salivary gland chromosome region 88E 4—8. A low-abundance transcript of approximately 4·0×103 bases corresponding to the cloned gene is detected in all stages of the Drosophila life-cycle.
The mechanism of secretion of the milk fat globule
Authors: Wooding F. B. P. 
Published: April 2021

ABSTRACT
The morphology of secretion of the fat globule is identical in goat, guinea-pig and cow. The smallest fat droplets, which are found in the basal cytoplasm of the secretory cell, have no membrane separating the lipid from the cytoplasm and no direct association with rough endoplasmic reticulum. In the apex of the cell, fat droplets have numerous peripheral vesicles, most of which appear to be derived from the Golgi body. The progressive fusion of these vesicles results in the extrusion of the fat droplet surrounded by a unit membrane originating partly from the originally peripheral vesicles and partly from the plasmalemma. This membrane bears on its inner surface a zone of dense material which appears to be derived from the cytoplasm, and this is also seen around fat globules in secreted milk. Thus the term apocrine secretion is considered a valid description of the process.
Two populations of mast cells on fibroblast monolayers: Correlation of quantitative microscopy and functional activity
Authors: Hammel I. , Shiloh-Rabinovich H. , Nir I. 
Published: April 2021

ABSTRACTWe have previously shown that a confluent layer of mature mast cells is obtained when lymph node cells are grown on embryonic flbroblast monolayers. Two populations of mast cells may be observed, depending on treatment of the mice from which the lymph node cells are derived. We report now on the morphometric evaluation of these two mast cell entities, and we correlate this with cellular biochemistry and secretory behaviour. The first type of mast cell is small (265 ± 20 μm3). It arises from the embryonic monolayer and the cells have feathers resembling those of connective tissue mast cells. These cultured cells are filled with about 1000 homogeneous electron-dense granules, which usually range in diameter from 0·05 to 0·2 μm. The second type of mast cell arises from precursors originating from the lymph node and they have feathers of mucosal mast cells. These cells are larger (480 ± 40 μm3) and contain about 300 heterogeneous granules, which range from 0·1 to 0·8; μm. Both cell entities contain about equal amounts of histamine, serotonin and chymase. Biologically, the two cell entities secrete soluble mediators (histamine and serotonin) at different rates compared to the rate at which they secrete chymase. We suggest that such a pattern of secretion exhibits a form of degranulation that permits the release of freely diffusible mediators that are loosely bound to granules, but only partially permits the secretion of insoluble mediators, which are stored in the granules. Alternatively, there might be a mechanism that rapidly inactivates or binds chymase so that only the vasoamines will be free.
The formation of siliceous scales by Raphidiophrys ambigua (protista, centroheliozoa)
Authors: Patterson David J. , Dürrschmidt Monika 
Published: April 2021

ABSTRACT
Ultrastructural aspects of the formation of siliceous scales by the protozoon Raphidiophrys ambigua are described. Cells in culture become scale-free in silicon-impoverished medium. Scales may be seen adhering to the cell surface within four to six hours of the addition of silicon to the medium. Silica scale formation occurs within deposition vesicles (SDVs) near the periphery of the cell. Many scales are formed at the same time; each may be in a different phase of scale formation. The source of the SDV membrane is not known. Silicification proceeds centrifugally from two pattern centres. The first parts of the forming scale are two opposed sterna,which establish the longitudinal axis of the scale. One sternum develops from each pattern centre. The scale develops outwards by formation of fairly evenly spaced lateral ribs from each central sternum. Distally, the ribs branch to form a reticulate pattern. A thin continuous sheet of silicon is added to the periphery of the scale, curving inwards to form a rim. The development of this pattern may be described in terms of a small number of morphogenetic processes.
High frequencies of preprophase bands in soybean protoplast cultures
Authors: Wang Hong , Cutler Adrian J. , Fowke Larry C. 
Published: April 2021

ABSTRACT
Protoplasts derived from a non-regenerable soybean cell line provide an excellent experimental system for studying plant preprophase bands (PPBs). Cultured protoplasts developed PPBs in high frequencies, permitting a detailed analysis of PPB development. From observations of thousands of PPBs, six distinct developmental stages were identified. This classification should prove useful in recognizing developmental stages of PPBs and in comparing results among different tissues and species. Perinuclear fluorescence appeared when PPBs were well developed. It consisted of microtubule strands radiating from the nuclear surface at its early stages and more extensive arrays on the surface at later stages.
All protoplast cultures from O·5 day to 5 days had a PPB index (ratio between number of PPBs and number of phragmoplasts) greater than unity, suggesting that in this cell line a high frequency of PPBs is apparently not related to the potential for organized growth (e.g. embryogenesis). Different methods of quantifying the occurrence of PPBs were evaluated. The PPB value (ratio between % of cells with PPB and the mitotic index) was compared with the PPB index and results indicate that it is a useful new parameter for studies of the distribution of PPBs in plant cells.
Ductal epithelial cells cultured from human foetal epididymis and vas deferens: relevance to sterility in cystic fibrosis
Authors: Harris Ann , Coleman Lindsay 
Published: April 2021

ABSTRACT
A tissue culture System for epithelial cells derived from male human foetal genital ducts has been established. The cells show morphological and biochemical characteristics of ductal epithelial cells, and can be passaged and maintained in culture for considerable periods of time. These cells will provide a suitable System for investigating, by electrophysiological, biochemical and molecular biological methods, the cause of sterility in cystic fibrosis.
Red cell membrane protein distribution during malarial invasion
Authors: Dluzewski A. R. , Fryer P. R. , Griffiths S. , Wilson R. J. M. , Gratzer W. B. 
Published: April 2021

ABSTRACT
Immuno-gold labelling electron microscopy of thin sections was used to determine the distribution of red cell membrane and membrane skeleton proteins in the vicinity of internalized malaria parasites. When examined immediately after invasion (young ring-stage parasites), the parasitophorous vacuole membranes of both Plasmodium falciparum and P. knowlesi were found to be characterized by the essentially complete absence of spectrin, ankyrin and the most abundant transmembrane protein, band 3. P. knowlesi merozoites were trapped in the attached but not internalized state by pretreatment with cytochalasin B. In this merozoitered cell complex antibody labelling showed that band 3 had been eliminated from the region of the host cell membrane in contact with the parasite. Internal vesicles, originating apparently from the site of attachment, were often observed in the red cell. Opposite the attached parasite a cavity was also sometimes seen in the host cell, presumably representing an incipient internal vesicle. The membrane was intact, as judged by the absence of protein (haemoglobin) in the cavity, and, like the membranes surrounding the internal vesicles, was devoid of membrane proteins. A large multilamellar body was sometimes seen in the merozoite close to its point of attachment. The lamellar spacing was about 50 nm. The electron microscope images suggest a diffusion of electron-dense material from the lamellar body into the cavity in the host cell.
Internalization and recycling to serotonin-containing granules of the 80K intégral membrane protein exposed on the surface of secreting rat basophilie leukaemia cells
Authors: Bonifacino Juan S. , Yuan Lydia , Sandoval Ignacio V. 
Published: April 2021

ABSTRACT
The 80K (80x103Mr) integra! membrane protein, first described in the secretory granules of rat basophilie leukaemia (RBL) cells, is also localized to lysosomes in these cells. The protein displays the same distribution in natural killer lymphocytes (RNK-7), wherein it codistributes with cytolysin in secretory granules. In contrast, the protein is absent from the endocrine and exocrine secretory granules of rat pancreatic acinar and pituitary cells, respectively, where it is confined to lysosomes. The protein colocalizes with lysosomal intégral membrane proteins in ail the cells studied, indicating that is largely restricted to secretory granules with lysosomal properties (LSG) and lysosomes. The protein expressed on the surface of secreting RBL cells is internalized by endocytosis via coated pits, and found in coated vesicles, endosomes, multivesicular bodies and Golgi System, before being recycled to LSG and partly delivered to lysosomes. The recycled protein is re-expressed on the surface of cells stimulated to secrete a second time.
Brain dynein crossbridges microtubules into bundles
Authors: Amos Linda A. 
Published: April 2021

ABSTRACT
Cytoplasmic dynein was purified from pig brain, using a modified version of published procedures, in order to study its interaction with microtubules. Since the preparation produces ATP-dependent sliding of taxol-stabilized purified microtubules over glass and runs on SDS-containing gels as a major band exceeding 300 000 Mr plus a medium chain band at about 75 000Mr, it is assumed to be identical to the mammalian brain dynein (MAP 1C) purified by Vallee and colleagues.
When viewed by electron microscopy in negative stain, individual particles show two distinct configurations. Some are clearly similar to the twoheaded bouquet structure already shown for MAP 1C. A larger number of molecules in the present preparation appear to have the two heads fused together, forming a dimeric globular particle with two separate tails. They are referred to as phi-particles, because of their resemblance to the greek letterϕ.
A model for the structural relationship between the two molecular forms is presented. The stems of two associated dynein subunits may separate beyond the base, to form a bouquet, or they may remain fused to form the larger tail of a phi-particle. The smaller tail probably represents a combined pair of features equivalent to the ‘stalks’ shown to emanate from axonemal dynein heads by Goodenough and colleagues. Both tails of a phi-particle can bind to microtubules, even in the presence of ATP, and cause microtubule bundling. These results suggest a complete structural homology between axonemal and cytoplasmic dynein.
The organization of tip-growth-related organelles and microtubules revealed by quantitative analysis of freeze-substituted oomycete hyphae
Authors: Heath I. Brent , Kaminskyj Susan G. W. 
Published: April 2021

ABSTRACT
The distribution of organelles and microtubules in hyphal tips of the oomycete, Saprolegnia feras, were quantitatively determined at high resolution from serial-section electron microscopy of freeze-substituted cells. All the organelles and the microtubules were non-uniformly distributed, each showing a characteristic longitudinal gradient starting at a different point behind the tip. In addition, when the cytoplasmic cross-sectional area was divided into radial regions, all organelles occurred preferentially in either the central (mitochondria and Golgi bodies) or the peripheral (microtubules, wall vesicles and spherical vesicles) region. The nuclei were so large as to span both regions but were always oriented with their centrioles facing the plasmalemma. Microtubules occurred in the extreme tips, became more abundant sub-apically, were predominantly short but increased in mean length with distance from the tip. The correlated patterns of organelle and cytoskeleton organization from this and previous work show that neither the microtubules nor the detected arrays of actin are sufficient to account for most organelle arrangements. However, on the basis of the distribution and orientation of the predominantly elongated wall vesicles, we suggest that the wall vesicles travel radially from their origin at the centrally located Golgi bodies to the cell periphery where they are transported longitudinally to the hyphal tip in conjunction with the plasmalemma-associated actin cables. Our data also suggest that the hyphae contain a cortical ectoplasm with which the nuclei interact, at least in part, via their centrioles and centriole-associated microtubules, and whose mechanical integrity is increased by both the peripheral actin cables and a high density of microtubules. We suggest that the endoplasm is less strong and has physiological properties that enhance the differentiation of endoplasmic reticulum and nuclear envelope into Golgi body production.
A Ca2+-sensitive glycoprotein, GP90, associated with the cytoskeleton from brain and gizzard
Authors: Moss Diana J. , White Carol A. 
Published: April 2021

ABSTRACT
We describe here the expression during development, tissue distribution and molecular properties of GP90: a major concanavalin A (ConA)-binding glycoprotein present in the neuronal membrane skeleton from chicken brain. GP90 is co-isolated with, and has a similar developmental profile to contactin (previously called GP130). In whole brain, GP90 undergoes rapid synthesis between embryonic days 10 and 12. Unlike contactin, it is not restricted to nervous tissue and is quite abundant in gizzard, where there are two antigenically related proteins of 100K and 90K (K = 103Mr). In both brain and gizzard GP90 and (GP100) are enriched in the membrane skeleton fraction. Trypsinization of live cells suggests that GP90 from gizzard is related to GP100 by the removal of a polypeptide chain. GP90 from both neurones and gizzard cells is protected from proteolysis by the presence of extracellular Ca2+. In the absence of Ca2+ a soluble fragment of approximately 70K can be released from the surface of cells indicating that a large fraction of GP90 is extracellular. Deglycosylation of GP90 from brain using endoglycosidase F demonstrates the presence of at least five carbohydrate chains and a polypeptide chain of approximately 80K. Immunofluorescence studies show that GP90 is exposed on the surface of cultured neurones, gizzard cells and most glial cells with the exception of Schwann cells. It is observed in clusters or patches even when cells are prefixed, suggesting this may be the normal distribution of GP90.
Genetic Elements in Escherichia coli
Authors: Sharpe Colin R. 
Published: April 2021

Abstract
This book is directed toward the teaching of advanced undergraduate courses and covers the genetics and, in part, the molecular biology of plasmids and phage in Escherichia coli. It will appeal, however, to a wider audience, that is to anyone whose research concerns plasmids and phage either directly or superficially as ‘reagents’ in molecular biology. Within the scope of this book lie such topics as gene mapping, recombination, DNA repair and transposition. The section on phage lambda provides a good if somewhat limited introduction to this important system, which is a fault that may be excused given the excellent concise nature of the book, which conforms to the aim of the Series to provide ‘authoritative texts of a manageable size’.
Fibroblast contractility and actin organization are stimulated by microtubule inhibitors
Authors: Danowski Barbara A. 
Published: April 2021

ABSTRACT
Despite considerable evidence that cytoplasmic microtubules play some role in guiding or controlling the locomotion of tissue cells, the nature of this control is not understood. In particular, little is known about the role of microtubules in the exertion of propulsive ‘traction’ forces, or about microtubule effects on the organization of the cytoplasmic actin stress fibers. In this study, the silicone rubber substratum technique was used in combination with fluorescence microscopy in order to observe the effects of microtubule-depolymerizing drugs on the contractile strength and organization of cytoplasmic actin networks.
Perfusion with a variety of microtubule poisons (either colcemid, nocodazole or vinblastine) was found to cause a rapid and substantial strengthening of fibroblast contractility. This was demonstrated in two established fibroblast cell lines, as well as in primary cultures of rat gingival fibroblasts and embryonic chick heart fibroblasts. Treatment with the drug taxol, which promotes microtubule assembly, was found to prevent the strengthening effects of the microtubule inhibitors. It was also found that the disruption of actin stress fibers by the phorbol ester tumor promoter, TPA, is reversed by microtubule poisons: stress fibers reform within 30 min of the addition of the microtubule drugs, despite the continued presence and activity of the TPA.
Several possible mechanisms are considered, including the idea that microtubule assembly normally exerts a pushing force, which counterbalances part of the contractile force exerted by the actin stress fibers. However, the mechanism that seems best to account for the observations is that microtubules modulate, in an inhibitory fashion, the contractility and the state of organization of cytoplasmic actin.
Sertoli cell ectoplasmic specializations: a type of actin-associated adhesion junction?
Authors: Grove B. D. , Vogl A. W. 
Published: April 2021

ABSTRACT
In this paper we provide evidence that ectoplasmic specializations are a form of intercellular adhesion junction. Ectoplasmic specializations, found at basal junctions between adjacent Sertoli cells and at sites of adhesion between Sertoli cells and germ cells, consist of actin filament bundles sandwiched between the plasma membrane and a cistern of endoplasmic reticulum. The actin filaments in each bundle are unipolar and are hexagonally packed. The bundles are coupled to the adjacent membranes and to each other. Because ectoplasmic specializations are associated with junctional sites, they may play a role in intercellular adhesion. In this study, we report a procedure for obtaining samples enriched for ectoplasmic specializations and identify polypeptides that may be associated with ectoplasmic specializations. On SDS-poly-acrylamide gels, an 83K (K = 103 Mr) polypeptide is specific to the ectoplasmic specialization-enriched sample, sμggesting that it may be a component of ectoplasmic specializations. Other polypeptides at 38, 53, 56 and 69K also may be associated with ectoplasmic specializations. Immunoblots further indicate that fimbrin and vinculin are present in the ectoplasmic specialization-enriched fraction. In addition, immunofluorescence indicates that vinculin is associated with spermatid-Sertoli cell and Sertoli-Sertoli cell junctions. We suspect that fimbrin, an actin-bundling protein, may be involved in cross-linking the hexagonally packed actin filaments in ectoplasmic specializations while vinculin may be associated with actin—membrane linkages. If so, ectoplasmic specializations may be a new class of actin-associated junctional site. Moreover, the presence of vinculin in testicular fractions enriched for ectoplasmic specializations and at junctional sites supports the view that these structures may play a role in intercellular adhesion, possibly by stabilizing an adhesive membrane domain.
Evidence for a second class of membrane glycoprotein involved in cell adhesion
Authors: Norris Wendie E. 
Published: April 2021

ABSTRACT
It is believed that transmembrane relationships exist between the cytoskeleton and the extracellular matrix through integral membrane proteins, almost certainly glycoproteins, which would act as transmembrane receptors. Such receptors would include those involved in cell adhesion. I have been able to isolate a detergent-soluble fraction from chick embryo fibroblasts that is enriched in these integral membrane proteins by making use of their amphipathic character to phase-separate them in the detergent Triton X-114. Antisera raised to this fraction had biological activities interfering with cell adhesion and motility. A 45×103Mr glycoprotein unique to this fraction appears to be responsible for this biological activity and is a candidate for a transmembrane receptor involved in cell adhesion.