bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional differentiation of the membrane skeleton in Tetrahymena
Authors: Williams N. E. , Honts J. E. , Jaeckel-Williams R. F. 
Published: April 2021

ABSTRACT
Antisera have been raised in rabbits against three high molecular weight proteins that are present in Triton X-100-insoluble residues of Tetrahymena pyriformis GL cells. These proteins, called A, B and C, have apparent molecular weights of 235, 135 and 125 (×103), respectively, in SDS-polyacrylamide gels. The antisera obtained are specific for these proteins, as shown by immunoblotting. Immunolocalization studies are reported that suggest that these proteins are present throughout the epiplasmic layer beneath the cell surface (membrane skeleton). Images obtained with the fluorescence microscope, however, suggest that the membrane skeleton is modified in discrete zones: (1) around somatic basal bodies, (2) within the oral apparatus, (3) in the cytoproct, (4) in contractile vacuole pores, (5) in the fission zone in late division, and (6) at the mating junction in conjugating cells. These regions may represent areas of increased rigidity at the cell surface. The transition from pliable to rigid epiplasm in spatially delimited areas is apparently a recurring theme in cortical morphogenesis in Tetrahymena. Together, the two types of epiplasm probably allow for extensive changes in cell shape while preserving essential relationships between structural elements within the cortex.
Newt epidermal cell migration in vitro and in vivo appears to involve Arg-Gly-Asp-Ser receptors
Authors: Donaldson Donald J. , Mahan James T. , Smith Gerald N. 
Published: April 2021

ABSTRACT
The effect of a synthetic peptide consisting of Arg-Gly-Asp-Ser (RGDS), the amino acid sequence representing the fibroblast attachment site in fibronectin (FN), was tested on migrating newt epidermal cells. In one approach, skin explants were placed on the bottom of plastic dishes coated with human FN, human fibrinogen (FGN), human serum spreading factor (SF), or bovine type I collagen. The explants were then incubated overnight in serum-free medium with or without RGDS. In these experiments exposure to 50 μgml−1 of RGDS reduced migration over FN, FGN and SF to 2–7% of control levels. Two peptides structurally dissimilar to RGDS (Vai-Gly-Ser-Glu and Thr-Pro-Arg-Lys), and two that are structurally similar (Lys-Gly-Asp-Ser and Arg-Gly-Glu-Ser), had no effect on explant migration even when used at concentrations higher than 50 μgml−1. Upon removal of the RGDS peptide, inhibited explants quickly recovered. In collagen-coated dishes 50 μgml−1 of RGDS was much less effective than in dishes coated with the other substrates. Raising the RGDS concentration in collagen-coated dishes tenfold did not greatly increase the RGDS effect. When added to the medium bathing wounded limbs, 50 μg ml−1 of RGDS only moderately inhibited wound closure.
This concentration of peptide, however, severely inhibited migration from skin explants in newt-plasma-coated-dishes and migration over pieces of newt-plasma-coated plastic placed under one edge of a skin wound. Increasing the RGDS concentration to 500 μg ml−1 resulted in almost total suppression of wound closure. Wounds exposed to this same concentration of Lys-Gly-Asp-Ser closed normally.
These results indicate that newt epidermal cells possess RGDS receptors and that these receptors are involved in epidermal wound closure in vivo and in migration from skin explants onto plastic coated with FN, FGN, SF and collagen.
The relative RGDS-insensitivity of wound closure in vivo and in migration from explants onto collagen may reflect in these instances the presence of a relatively high density of RGDS receptor binding sites on the substrate; the presence of RGDS receptor binding sites of relatively high affinity; or the participation of receptors other than those involved in migration over plastic coated with FN, FGN or SF.
Visualization of the intact endoplasmic reticulum by immunofluorescence with antibodies to the major er glycoprotein, endoplasmin
Authors: Koch G. L. E. , Macer D. R. J. , Smith M. J. 
Published: April 2021

ABSTRACT
Antibodies to endoplasmin were used to examine the morphology of the endoplasmic reticulum (ER) by immunofluorescence on permeabilized plasmacytoma and fibroblastoid cells. In unfixed cells, permeabilization led to a pronounced vésiculation of the ER. Therefore cells were first fixed lightly prior to permeabilization with detergent. Fibroblastoid cells gave a characteristic reticular pattern surrounding the nucleus with clear staining of the nuclear membrane. Plasmacytoma cells, in the conventional fluorescence microscope, gave a cistemae-like pattern. Optical sectioning with a confocal scanning laser microscope gave a distinct pattern of concentric cisternae similar to those obtained with transmission electron microscopy on cell sections. The overall morphology of the ER in such cells could be revealed by serial optical sectioning. Evidence was obtained that the ER does not undergo extensive vésiculation during mitosis in plasmacytoma cells. Using anti-endoplasmin immunofluorescence monitoring, conditions were developed for the retention of ER morphology in unfixed, permeabilized cells.
These studies illustrate the value of endoplasmin as a general marker for the analysis of ER morphology in different types of cells by immunofluorescence microscopy.
Interaction In Vitro Of Non-Epithelial Intermediate Filament Proteins With Supercoiled Plasmid Dna*
Authors: KÜhn S. , Vorgias C. E. , Traub P. 
Published: April 2021

ABSTRACT
Sucrose gradient analysis of reaction products obtained from non-epithelial intermediate filament (IF) subunit proteins and a mixture of supercoiled, relaxed and linearized plasmid pBR322 DNA at low ionic strength revealed that limited amounts of these polypeptides interacted exclusively with the supercoiled form of the plasmid DNA. These results were corroborated by electron-microscopic analysis of the reaction products, which showed that only circles of supercoiled pBR322 DNA were completely and smoothly covered with vimentin. LFs reconstituted from pure vimentin reacted with supercoiled pBR322 DNA only through their physical ends. The reaction of an aged preparation of vimentin with supercoiled pBR322 DNA produced large aggregates consisting of a central, axially oriented protein scaffold to which individual loops of DNA were attached at their bases in a halo-like arrangement. The electron-microscopic appearance of such complexes was very reminiscent of that of histone-depleted metaphase chromosomes. Together with the previous observations that non-epithelial IF proteins have high affinities for single-stranded DNA and core histones and that they are structurally and functionally closely related to the nuclear lamins, these results were used to advance a novel hypothesis on the biological role of IF proteins in eukaryotic cells.
Polarized Pigment Granule Transport Occurs In The Absence Of Microtubules In Squirrelfish Erythrophores: Studies Of The Effects Of Estramustine
Authors: Stearns Mark E. , Wang Min 
Published: April 2021

ABSTRACT
We have re-examined the involvement of microtubules in the process of pigment granule transport in squirrelfish erythrophores in situ (i.e. on scales). Light-microscopic studies revealed that following exposure to 5 μM-nocodazole for 1 h at 4 °C erythrophores retained an ability to aggregate and disperse their pigment uniformly, though at reduced rates. Serial thick-section stereo high-voltage electron-microscopic studies showed that the entire microtubule population was removed by drug treatment and that the microtubules were not reassembled as a result of pigment translocation processes in the presence of reduced levels of nocodazole (0–4 μM). Immunofluorescence microscopic studies confirmed that nocodazole (0’5–1 μM) produced rapid disassembly of the microtubules. Wholemount electron-microscopic studies showed that the pigment granules were suspended in a crosslinking network of 3–10nm filaments, which appeared to support ordered pigment transport in situ in the absence of microtubules. Drug inhibition studies showed that micromolar levels of estramustine, a novel anti-MAPs (microtubule-associated proteins) drug, reversibly inhibited pigment transport. The results suggest that an estramustine-sensitive cytomatrix component might produce polarized pigment transport in intact erythrophores.
A major difference between serum and fibronectin in the divalent cation requirement for adhesion and spreading of BHK21 cells
Authors: Edwards J. G. , Robson R. T. , Campbell G. 
Published: April 2021

ABSTRACT
Adhesion and spreading of BHK21 cells on adsorbed bovine and foetal bovine serum require addition to the medium of a divalent cation. Divalent cations are effective in the order Mn2+&gt;Co2+&gt;Mg2+&gt;Ca2+, with Ca2+ ineffective below 10−4M. On purified fibronectin, however, no added divalent cation is required, since the requirement is largely met by adventitious Ca2+ (circa 10−5M) in nominally divalent cation-free saline. In such background Ca2+, adhesion and spreading on fibronectin are only slightly slower than in optimal Mg2+, and appear identical, morphologically, and in sensitivity to cytochalasin D. Cells also spread on fibronectin in response to Mg2+, when Ca2+ is buffered below 10−6M, showing that external Ca2+ is not needed as a source for an increase in internal Ca2+. Cells can be induced to spread on serum in low Ca2+ by substantially increasing the fibronectin concentration; this supports other evidence that at its unsupplemented concentration, fibronectin contributes little to the spreading of these cells on serum.
The Ca2+ requirement for spreading on preparations of vitronectin (serum spreading factor), partially purified from bovine serum, is similar to that on whole serum. Thus the difference in divalent cation requirement between serum and fibronectin may arise because, on serum, the dominant protein responsible for induction of spreading is vitronectin rather than fibronectin. We argue that such a difference in ion requirement between these surfaces points to a site of action of the ions at the cell surface, perhaps directly on binding of the adsorbed proteins by their receptors, or in receptor-specific transduction events, rather than via ion fluxes, on cyto-skeletal responses common to different surfaces.
Models are discussed to account for why the divalent cation requirement should differ for interaction of cells with different substrate-adsorbed proteins.
Establishment of a tissue culture system for epithelial cells derived from human pancreas: a model for the study of cystic fibrosis
Authors: Harris Ann , Coleman Lindsay 
Published: April 2021

ABSTRACT
A tissue culture system for epithelial cells derived from human foetal pancreas has been established. The cultured cells show many ultrastructural features of interlobular duct cells. Immunocytochemical and histochemical evidence is presented in support of the view that these cells are ductal in origin. They are likely to be one of the few cell types that express the basic defect of cystic fibrosis in vitro. The cells may be passaged and sufficient material obtained to permit biochemical and molecular biological analysis.
An endothelial cell growth factor derived from human lung carcinoma cells grown in serum-free medium
Authors: Walker C. , Mates G. , Pumford D. , Daniel M. 
Published: April 2021

ABSTRACT
A factor that stimulates the proliferation of human umbilical vein endothelial cells has been shown to be present in serum-free medium conditioned by the prior growth of a cell line (1PT) derived from a poorly differentiated bronchial carcinoma. Preliminary characterization of this factor has revealed that it is a heat-labile, acidstable proteinaceous material, the activity of which is not diminished by treatment with a reducing agent. In its partially purified state ithas been shown to be anionic and to be associated with material exhibiting a broad molecular weight range of 35×103 to 100×103. It does not bind strongly to heparin-Sepharose and its mitogenic effect on endothelial cells is not potentiated by heparin. These properties suggest that this factor may differ from other previously described tumour-derived endothelial mitogens.
Cell Movement and Cell Behaviour
Authors: Dunn G. A. 
Published: April 2021

ABSTRACT
John Lackie’s course on cell behaviour delivered to Senior Honours Cell Biology students at Glasgow University is largely responsible for the predominance of young Glaswegian scientists at British conferences on cell behaviour. Other universities have an oppor tunity to redress the balance now that this lecture course is available as a textbook. But this book, particularly the latter part, is so original in its treatment of the field that it deserves to be read by anyone with even a passing interest in the subject. It is not the first textbook to deal with cell behaviour. Others deal with the motile behaviour of embryonic cells during development, with the chemotaxis of white blood cells or with the invasiveness of malignant cells. But it is the first attempt to present a coherent survey of the whole field of cell behaviour with the emphasis on common principles. It does mainly for the metazoan cell what the now classic textbook, The Orientation of Animals by Fraenkel & Gunn (1940), did mainly for the protozoa and other small animals.
Clonal lifespan of Paramecium tetraurelia: Effect of selection on its extension and use of fissions for its determination
Authors: Takagi Yoshiomi , Nobuoka Tomoko , Doi Mayumi 
Published: April 2021

ABSTRACT
Paramecia cells, like human diploid cells cultured in vitro, provide a useful model system for understanding the mechanism that limits division potential. The reported maxima of the clonal lifespan of Paramecium tetraurelia fall into two ranges: from 220 to 258 fissions and from 310 to 325 fissions. We found that neither the selection of vigorous lines nor the cryptic occurrence of autogamy offers a plausible explanation for the much longer lifespans in the latter range. We found the sporadic occurrence of very long clonal lifespans, such as 330 fissions, without selection and autogamy. Selection, which was evaluated by using different methods to maintain lines, had little effect on the extension of the maximal clonal lifespan, whereas it did have a marked effect on the extension of the mean clonal lifespan. Autogamy, which was checked with two closely linked marker genes, was frequent, but only during the period when lines were terminating.
Statistical analysis on the mean clonal lifespans of two groups of subclones cultured at 25 and 20 °C or with rich and poor nutrition showed that the clonal lifespan that was fission-related under favourable conditions tended to dissociate from fissions under less favourable conditions. We discuss mechanisms that determine the clonal lifespan, programmed events contributing to the maximum clonal lifespan and random events contributing to the mean clonal lifespan.
Lampbrush chromosomes
Authors: Macgregor H. C. 
Published: April 2021

ABSTRACT
1986 was a celebration year for lampbrush chromosomes (LBCs), marked by the publication of Callan’s comprehensive and authoritative book on these structures. My commentary begins where Callan’s book ends, standing on tiptoe beside a large and rather neat assembly of well-established facts, principles and hypotheses, and trying hard to catch a glimpse of what lies ahead.
Calcium control of macrophage cytoplasmic gelation: Evidence for the involvement of the 70000Mr actin-bundling protein
Authors: Pacaud M. , Harricane M. C. 
Published: April 2021

ABSTRACT
Under appropriate conditions macrophage cytosolic extracts can form a three-dimensional gel network of cross-linked actin filaments. These cytoplasmic gels are mainly composed of actin, filamin, alpha-actinin, and two new proteins of about 70000 and 55 000Mr (70 and 55 K). The behaviour of 70 K protein was found to be remarkably affected by Ca2+. Ca2+ treatment of isolated cytoplasmic gels led to the selective solubilization of the 70 K protein along with a 17 K polypeptide. Half-maximal recovery in the supernatant fraction was obtained from about 0·15μM free Ca2+. The cytoplasmic gel constituents solubilized in high ionic strength buffer were able to re-assemble into an insoluble actin network when returned to near physiological ionic conditions. However, the inclusion of micromolar Ca2+ prevented the re-association of 70 K protein with actin in these complexes. As compared to the 70 K protein, alpha-actinin was fully resistant to any variations in Ca2+ concentrations. On the other hand, purified 70 K protein displayed the property of assembling actin filaments into bundles at low Ca2+ concentrations (&lt;0·15 μ M). However, the bundling activity decreased progressively at higher Ca2+, as detected by co-sedimentation and electron microscopy of the 70 K protein-actin mixtures. Half-maximal inhibition was observed at about 0·3 μM free Ca2+. Re-assembly of actin filaments into bundles occurred after chelation of Ca2+ by EGTA, indicating that the inhibitory effect of Ca2+ was reversible. Severing of actin filaments by 70 K protein was not observed in any of the solution conditions used.
The Ca2+-dependent inhibition of the ability of 70 K protein to interact with actin networks resulted in a marked distortion of the overall organization of actin filaments, as revealed by thin-section electron microscopy of cytoplasmic gels formed in the presence and absence of Ca2+. Large zones of oriented bundles of filaments were replaced by a looser mesh. When the actin gel constituents were re-assembled in the presence of Ca2+ and exogenous gelsolin, it was also observed that the filament bundles (essentially generated by alpha-actinin) collapsed into dense aggregates. Furthermore, gelsolin did not significantly affect the ability of actin to re-combine with other proteins. The data presented here and previously led us to suspect that the Ca2+ control of the functional state of 70 K protein might be one of the prime factors in the triggering of rapid assembly and disassembly of microfilaments within macrophages.
Evidence for microtubule nucleation at plasma membrane-associated sites in Drosophila
Authors: Mogensen M. M. , Tucker J. B. 
Published: April 2021

ABSTRACT
This report is concerned with the nucleation and organization of microtubule bundles that assemble after ‘conventional’ centrosomal microtubule-organizing centres have been lost. The microtubule bundles in question span the lengths of wing epidermal cells. Bundles extend between hemidesmosomes at the apical cuticlesecreting surfaces of cells and basal attachment desmosomes that unite the dorsal and ventral epidermal layers of developing wing blades. Furthermore, each bundle includes up to 1500 microtubules and most of the microtubules are composed of 15 protofilaments.
Individual cells were serially cross-sectioned at an early stage of bundle assembly. The number of microtubule profiles/cell cross-section decreased progressively by up to 59% of the most apical values in section sequences cut from fairly apical to more basal levels in the cells. The apical ends of microtubules were associated with numerous small dense plaque-like sites (diameter 0·1–0·2 gm), which were specialized regions of plasma membranes at the apical surfaces of cells. Many of the microtubules near apical plaques were not well aligned with each other; they ‘radiated away’ from cell apices. This was in contrast to the situation at more basal levels where most microtubules were oriented parallel to the longitudinal axes of cells.
These findings indicate that the relatively dispersed arrays of apical plasma membrane-associated plaques act as microtubule-nucleating sites to initiate basally directed elongation of bundle microtubules. Apical cell surfaces and their plaques seem to operate as microtubulenucleating and -organizing regions that functionally replace the centrosomal microtubule-organizing centres lost earlier in cell differentiation.
The neuron as a cell
Authors: Amos L. A. 
Published: April 2021

ABSTRACT
The neuron is a particularly useful type of cell for studying many general processes. The site of locomotion, the growth cone, is well-removed from most of the cytoplasm; thus it is possible to exclude direct involvement in locomotion for many cytoplasmic components and less of a problem to identify those that are important. The spatial separation between sites of synthesis or reprocessing in the cell body and the terminal membrane also helps in resolving the pathways of membrane-associated proteins that are recycled, degraded or exported. And, of course, the long distances that substances must travel along an axon permit studies of intracellular transport mechanisms. This volume, the proceedings of a Satellite Symposium of the 30th Congress of the International Union of Physiological Sciences, held a year ago at the University of Calgary, Alberta, brings together these various topics. A series of papers by different researchers provides much to interest cell and molecular biologists in general, as well as those scientists who are interested in the nervous system per se.
Ganglioside inhibition of attachment and differentiation of cultured rat granulosa cells: interactions with fibronectin
Authors: Morley Paul , Armstrong David T. , Gore-Langton Robert E. 
Published: April 2021

ABSTRACT
The involvement of fibronectin in the attachment and differentiation of rat granulosa cells, cultured in a chemically defined medium, was investigated using the inhibitory properties of mixed brain gangliosides (MBGs) and highly purified disialoganglioside, GD1a. MBGs inhibited cell attachment to plastic culture surfaces in a concentration-dependent manner, with 0·1 mmol 1-1 causing significantly decreased attachment between 0·5 and 24 h of incubation. Inhibition of attachment to a fibronectin-coated substratum was even greater. The inhibitory effect of MBGs was not caused by binding to the cell surface, but instead the inhibitory factor(s) were adsorbed on a surface of immobilized human plasma fibronectin, thereby preventing cell attachment to this surface. The inhibitory action of MBGs was also neutralized by the addition of soluble fibronectin. Furthermore, at least one component of MBGs, detected chemically following thin-layer chromatography, was directly shown to bind to human fibronectin.
MBGs inhibited to varying degrees the folliclestimulating hormone(FSH)-dependent responses: augmentation of cellular protein content, production of adenosine 3′,5′-cyclic monophosphate (cyclic AMP) and progestins (progesterone-1-20cv-hydroxypregn-4-en-3-one+pregnenolone), and induction of aromatase activity. These inhibitory activities of MBGs could not be eliminated by adsorption on immobilized fibronectin or reversed by addition of soluble fibronectin, thus distinguishing these actions from the early inhibition of cell attachment. FSH-dependent responses were also inhibited by GD1a, while responses to stimulation by dibutyryl cyclic AMP plus 3-isobutyl-l-methyl xanthine were less affected by this ganglioside.
These results suggest that gangliosides inhibit attachment of granulosa cells in culture by binding to fibronectin, whereas the inhibition of FSH-dependent differentiation occurs by other modes of action that are unrelated to the effects on cell adhesion.