bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface events in polymorphonuclear leucocyte activation: insights from a hydrophobic membrane antigen that triggers the respiratory burst
Authors: Rosen H. , Gordon S. 
Published: April 2021

ABSTRACT
The rat monoclonal antibodies (Mab) 1A10.4 and IG4 were raised to a solubilized NADPH-oxidase preparation from guinea-pig polymorphonuclear neutrophils (PMN). They bind to a surface antigen restricted to guinea-pig myelomonocytic cells and on binding to the PMN surface can stimulate the respiratory burst (RB) and degranulation. This response was specific to these Mab and was not found with several other Mab restricted to myelomonocytic cells but with other antigenic epitopes. In order to understand the role of this molecule in stimulating the RB, we have characterized the antigen (Ag) by a variety of techniques. It is a hydrophobic membrane molecule with an apparent molecular weight of 8–10 (× 103) and a pI of 6·2. The Ag has been partially purified by extraction in organic solvents and high-pressure liquid chromatography on silica and is probably a proteolipid. Studies on Mab-dependent triggering of PMN secretion indicated that cross linking of the cell surface was critical. We therefore used direct immunofluorescence under triggering and non-triggering conditions to show that stimulation of the RB by Mab correlated with redistribution of the surface Ag into patches. This patching was associated with aggregation of surface Ag and transfer of Ag from a Triton X-100-extractable to a Triton X-100-inextractable membrane domain. These movements of surface Ag, which included both patching and capping resulting from aggregation of a hydrophobic membrane component, occurred at 4°C and were insensitive to inhibition by cytoskeletal inhibitors. These specific probes that control triggering of the RB have permitted the dissection of PMN stimulation into discrete membrane events by correlating the biochemical and morphological characteristics of a new PMN surface Ag as it stimulates exocytosis.
Coumarin–phalloidin: A new actin probe permitting triple immunofluorescence microscopy of the cytoskeleton
Authors: Small J. V. , Zobeley S. , Rinnerthaler G. , Faulstich H. 
Published: April 2021

ABSTRACT
7-Diethylamino-3-(4-isothiocyanotophenyl)-4-methylcoumarin (CPITC) was coupled to amino-methyldithiolanophalloidin to produce a new phalloidin derivative, coumarin–phalloidin, fluorescent in the blue region of the spectrum. Coumarin–phalloidin binds to actin with around 100-fold less affinity than unconjugated phalloidin, but with enough avidity to make it a useful stain for actin filaments. Appropriate filter combinations permit triple immunofluorescence microscopy of the cytoskeleton with fluorescein and rhodamine conjugates together with coumarin-phalloidin.
Review: Video-enhanced light microscopy and its applications in cell biology
Authors: Shotton David M. 
Published: April 2021

ABSTRACT
The combination of novel optical microscopic techniques with advanced video and digital image-processing technology now permits dramatic improvements in the quality of light-microscope images. Such video-enhanced light microscopy has lead to a renaissance in the applications of the light microscope for the study of living cells in two important areas: the intensification of faint fluorescence images, permitting observation of fluorescently labelled cells under conditions of very low illuminating intensity; and the enhancement of extremely low contrast images generated by minute cellular structures, so that these may be clearly seen and their normal intracellular movements recorded.
Application of both these aspects of video-enhanced light microscopy have recently led to major discoveries concerning the functioning of the living cell. In this review I discuss the equipment, procedures and image-processing principles employed in these applications, and describe and illustrate some of the spectacular results that have recently been obtained.
Clonality of preneoplastic liver lesions: Histological analysis in chimeric rats
Authors: Weinberg W. C. , Lannaccone P. M. 
Published: April 2021

ABSTRACT
The clonality of chemically induced altered hepatocellular foci was examined in rat liver. Chimeric rats composed of two histologically distinguishable cell lineages were placed on an initiation-promotion protocol for liver cancer induction. This resulted in multiple lesions of altered enzyme expression. These altered hepatocellular foci are generally considered to be initiated sites susceptible to cancer formation. The cellular origins of these lesions were determined by aligning sections demonstrating cell lineage with serial sections stained for altered enzyme expression. Analysis included 110 areas of deficient ATPase (EC 3.6.1.3) activity and 59 glucose-6-phosphatase (EC 3.1.3.9; G-6-Pase) deficient lesions, 744 foci of re-expression of γ- glutamyl transpeptidase (EC 2.3.2.2; γ-GT), and decreased glycogen mobilization (187 lesions). of the 1100 focal enzyme alterations, 1054 were shown to be composed entirely of cells from a single lineage of the two lineages present in the mosaic tissue. Multiple alterations occurred within given lesions. Lesions with up to four phenotypic alterations were found to consist of cells of a single lineage. These results suggest that individual enzyme-altered foci are clonal in origin and that phenotypic heterogeneity within altered hepatocellular foci is due to lesion progression within a clonal population and not to a multicellular derivation.
The preservation of specialization by dispersed steer thyroidal cells in long-term culture
Authors: Siegel E. 
Published: April 2021

ABSTRACT
Serially propagated cells derived from the steer thyroid gland preserve several specialized characteristics, some demonstrable for as long as 8 months (over 15 passes). For about 5 passes (3 months), follicular-like arrays of cells develop. Thyroid-stimulating hormone (TSH) or thyrotropin (1 and 10 mu./ml) induces the formation of supernumerary nucleoli, and promotes at the ultrastructural level the prompt (within 10 min) appearance of microvilli, pseudopodia, and intracytoplasmic droplets. These cells have a mean plating efficiency (PE) of 16·5 ±4·5 % (standard deviation) and with 3 × 104 cells as the standard inoculum, a mean doubling time (Td) of 43·7± 1·2 h. The linear variation of Td with the number of cells seeded probably signifies strong cell-cell interactions. TSH (1–50 mu./ml) influences both PE and Td, with 1 mu./ml producing the maximum stimulation. TSH (0·001–100 mu./ml) also induces the discharge of incorporated radio-iodide from the cultured thyroid cells, achieving a peak by 2–4 h, titres of 0·1–1 mu./ml being most potent. Long-acting thyroid stimulator (LATS) (0·2 u./ml) likewise effects release of 131I into growth medium (1 experiment), but over a more protracted period. After labelling with [3H]leucine, radioautographs demonstrate that the synthesis of proteins is stimulated by exposure to TSH (1 mu./ml). Precipitation with trichloro acetic acid indicates that these cells persist in synthesizing 131I-tagged iodoproteins, an activity optimally stimulated by 1 mu./ml TSH and marked by 3 h. Hence, such thyroidal cell lines afford a useful model for studying differentiation and hormonal effects.
The toxic effect of spermidine on normal and transformed cells
Authors: Otsuka H. 
Published: April 2021

ABSTRACT
The cytotoxic effect of spermidine was investigated on various tissue culture cell lines in the presence of calf serum. Cells incubated with cytotoxic concentrations remained rounded up while cells in control cultures always spread out on the surface of the Petri dish. The spermidine concentration tolerated depends on cell number, concentration of serum, the strain of cells used and the phase of the growth cycle.
The spermidine index (SI) of a cell culture is defined as the highest level of spermidine which did not show cytotoxic effect in the standard test system. The SI measures the ability of a cell culture (or line) to neutralize the cytotoxic effect of spermidine.
The SI of normal fibroblastic cells such as BHK21/C13 or mouse embryo cells alters characteristically with different phases of the cell cycle. It is highest in lag or early exponential phase, then it diminishes during the exponential growth phase reaching its lowest point after the cell culture has become confluent.
It is characteristic of polyoma virus-transformed cell lines and of other established permanent cell lines (which are probably of spontaneously transformed origin) that their SI decreases only slightly at high cell densities. There is a correlation between higher SI of transformed cells and their ability to grow in soft agar suspension.
The ultrastructure of fertilization and zygote formation in the green alga Ulva mutabilis føyn
Authors: Braten T. 
Published: April 2021

ABSTRACT
Fertilization and zygote formation in the multicellular green alga Ulva mutabilis Føyn were studied with the aid of transmission and scanning electron microscopes. The growth mutant ‘slender’ was used in this investigation. The initial contact between mating gametes is made by the flagella, whereupon cytoplasmic contact is established within a few seconds. Fusion of the cytoplasm of the 2 cells is completed in 5 min and the nuclei can be seen to fuse 30 min after the onset of copulation. The settling of the young zygotes initiates a process during which the 4 flagella are absorbed into the cell. Cell wall formation also starts when the zygotes settle. Observations indicate disintegration of one of the 2 chloroplasts in the young zygote.
The response of haemopoietic cells to growth factors: developmental implications of synergistic interactions
Authors: Heyworth Clare M. , Ponting Ian L. O. , Dexter T. Michael 
Published: April 2021

ABSTRACT
Haemopoietic cell growth factors are normally assayed using unfractionated marrow cells (NBM). However, using this population it is difficult to distinguish between direct versus indirect effects, because of the low incidence of colony forming cells (CFC) and the presence of possible accessory cells (which may themselves be acted upon by the growth factors and stimulated to produce other growth stimulatory or inhibitory molecules that influence the development of the CFC). Furthermore, NBM contain the whole spectrum of multipotent and lineage-restricted CFC and it is often difficult to determine precisely which populations are being stimulated to develop. This latter problem can be solved, in part, by using marrow from mice previously treated with 5-fluorouracil (5-FU): an agent that preferentially kills the more mature, actively cycling CFC but spares the proliferatively quiescent multipotent stem cells. Since the 5-FU-treated marrow also contains many possible accessory cells, however, it is again not clear whether or not the responses elicited by growth factors are due to direct or indirect effects upon the CFC. To circumvent this problem we have obtained a highly enriched population of multipotent stem cells (FACS-BM) that is free of accessory cells, and have compared the responses of these cells to NBM and to 5-FU-BM in the presence of a variety of growth factors. The data demonstrate that interleukin-1 (IL-1), which is not a growth factor by itself, can act synergistically with other growth factors on FACS-BM and 5-FU-BM but not on NBM. With FACS-BM, IL-1 can synergize with GM-CSF and with M-CSF but not with IL-3 or G-CSF. With 5-FU-BM, IL-1 can synergize with GM-CSF, M-CSF and IL-3. Furthermore, G-CSF, a poor growth stimulus when used alone, can synergize with GM-CSF and M-CSF, using either FACS-BM or 5-FU-BM, and can also synergize with IL-3 when using 5-FU-BM but not with FACS-BM. The data further indicate that extensive overlap occurs between the multipotential cells that respond to IL-3 alone and those that can respond to a combination of other growth-promoting stimuli such as IL-1 plus CSF-1 or G-CSF and CSF-1. This indicates that at least some multipotential cells have receptors for all the growth factors used in this study, but that combinations of growth factors sometimes need to be present in order to facilitate proliferation and development. Furthermore, the outcome of the response in terms of mature cell lineages produced is a reflection of the stimuli to which the multipotential cells are exposed. The developmental implications of these findings are discussed.
Glycosaminoglycan expression in intestinal epithelial skin-fibroblastic cell cocultures: Fibroblastic cell-mediated effects of glucocortlcoids
Authors: Bouziges Françoise , Simon-Assmann Patricia , Leberquier Cathy , Haffen Katy , Kedinger Michèle 
Published: April 2021

ABSTRACT
The nature and distribution of newly synthesized glycosaminoglycans (GAGs) were studied in foetal rat skin fibroblasts, in rat intestinal endodermal cells and in cocultures of both cell types. The data show that fibroblasts synthesize and secrete hyaluronic acid (HA), heparan sulphate (HS) and chondroitin sulphate molecules (CS). Our data focus on HA, which is found as two different molecular forms, the smallest hydrodynamic-sized species being mostly recovered within the cell or associated with the cell surface, and the largest one secreted into the medium, whatever the cell type. Endodermal cells synthesize only two types of GAGs: the low molecular weight form of HA and HS.
Cocultures of rat intestinal endodermal and skin fibroblastic cells in the presence of dexamethasone (Dx), allow optimal epithelial cytodifferentiation (Kedinger et al. 1987a). The main changes in the GAGs synthesized under these conditions as compared to skin fibroblastic cell cultures concern: (1) the enhancement of the lowest molecular weight form of HA to the detriment of the highest form in the cellular, pericellular and extracellular compartments; (2) the increase in the proportion of HS molecules associated with the cell surface. Interestingly, similar modifications are obtained by addition of Dx to the skin fibroblastic cell cultures.
The data are discussed with reference to the constitution of a basement membrane at the epithelial-fibroblast interface in the cocultures, to the fibroblastic-dependent induction of epithelial differentiation and to the glucocorticoid response.
Scanning electron microscopy of focal contacts on the substratum attachment surface of fibroblasts adherent to fibronectin
Authors: Singer Irwin I. , Kazazis Diana M. , Scott Solomon 
Published: April 2021

ABSTRACT
We have examined the cell-to-substratum attachment surface of hamster fibroblasts with scanning EM, and describe the surface ultrastructure of focal contacts and microspikes during cellular attachment and spreading on fibronectin. Nil 8 fibroblasts were seeded onto fibronectin-coated glass coverslips in serum-free medium, fixed, and the fibro-blast-fibronectin monolayer was separated from the glass and inverted for scanning electron microscopic (EM) analysis. Focal contact development was detected by interference reflection microscopy and correlated with the immunofluorescence microscopic distribution of fibronectin receptor antigens. The cell undersurface appeared smooth and featureless at 0·5 h when focal contacts were undetectable and fibronectin receptors were distributed diffusely. By 1–2 h, undersurface membrane impressions of focal contacts were detected with scanning EM; their size, shape and distribution matched that of focal contacts seen with interference reflection microscopy (IRM). These contacts had smooth external surfaces and were often arranged in chevron-shaped complexes. However, at 4–6 h, the surface texture of focal contacts became fibrous and the contact periphery was delineated with the orifices of membrane-associated vesicles. Development of this filamentous substructure is correlated with the maximum concentration of fibronectin receptors and fibronectin at focal contacts, suggesting that these molecules are involved in the maturation and stabilization of focal contacts.
Tubulin polymerization in unfertilized sea-urchin eggs induced by elevated temperature
Authors: Harris Patricia J. , Clason Elise L. , Prier Kevin R. 
Published: April 2021

ABSTRACT
Spontaneous polymerization of tubulin was induced in unfertilized eggs of the sea urchins Lytechinus pictus and Strongylocentrotus purpuratus by warming to temperatures 10–1 2deg. C above the normal environment for each species. Indirect immunofluorescence microscopy showed that over a period of several hours polymerization proceeded from a fine crystal-like precipitate to larger and fewer higher-order structures. These structures differed morphologically between the two species: L. pictus formed cytasters, while S. purpuratus most often formed flame-like arrays. Nuclear cycles were not initiated, permitting longterm observation of steady-state polymer redistribution. After several hours only a few very large cytasters remained near the surface of L. pictus eggs and these tended to constrict to form protrusions or occasionally a cleavage furrow that divided the egg into two fragments. Staining with rhodamine-labeled phalloidin showed that actin was also concentrated in the cytasters, primarily at the periphery of the centrosphere-like regions. L. pictus cytasters could be recycled by repeated cooling and rewarming, and showed an accelerated rate of polymerization with each successive cycle. Cytasters could also be isolated as long as the initial procedures were carried out at the elevated temperature. Washed preparations were stable at room temperature. From these observations we conclude that: (1) species-specific cytoplasmic factors control the temperature limits for spontaneous tubulin polymerization in unfertilized eggs, as well as the form of higher-order structures that are produced; (2) tubulin polymerized in whole eggs at elevated temperature shows characteristics similar to purified tubulin io vitro, with regard to cold recycling and steady-state polymer redistribution; (3) actin also polymerizes at the elevated temperature and is found closely associated with microtubules of the cytasters.
Aggregation of membrane-associated actin filaments following localized adherence of enteropathogenic Escherichia coli to HeLa cells
Authors: Da Silva M. Lourdes Monteiro , Mortara Renato A. , Barros Helena C. , Souza Wanderley De , Trabulsi Luiz R. 
Published: April 2021

ABSTRACT
We have previously observed that enteropathogenic Escherichia coli (EPEC) adhere to HeLa cells in a localized manner, which we designated localized adherence as opposed to the diffuse pattern of adhesion. In this paper we have examined the effects of localized adherence of EPEC on the actin microfilament system of host HeLa cells. Centrifugation of bacteria onto HeLa cells improved the localized adherence and rapid rearrangements of actin filaments were detected by immunofluorescence and electron microscopy. Aggregation of microfilaments is consistently observed at the sites of localized adherence, and is abolished by cytochalasin D and low temperatures. Scanning electron microscopy indicates that these aggregates are surface microvilli entangled with attached EPEC.
Definition of individual components within the cytoskeleton of Trypanosoma brucei by a library of monoclonal antibodies
Authors: Woods Angela , Sherwin Trevor , Sasse Rosemary , Macrae Thomas H. , Baines Anthony J. , Gull Keith 
Published: April 2021

ABSTRACT
The detergent-insoluble T. brucei cytoskeleton consists of several morphologically distinct regions and organelles, many of which are detectable only by electron microscopy. We have produced a set of monoclonal antibodies that define each structural component of this highly ordered cytoskeleton. The monoclonal antibodies were selected by cloning of hybridomas produced from mice injected with complex mixtures of proteins of either the cytoskeleton itself or salt extracts thereof. Four antibodies define particular tubulin isotypes and locate the microtubules of the axoneme and sub-pellicular array; two antibodies recognize the flagellum attachment zone; one recognizes the paraflagellar rod and another the basal bodies. Finally, one antibody defines a detergent-insoluble component of the nucleus. The antigens detected by each monoclonal antibody have been analysed by immunofluorescence microscopy, immunogold electron microscopy and Western blotting.
Reassembly of microtubules in Nitella tasmanica: assembly of cortical microtubules in branching clusters and its relevance to steady-state microtubule assembly
Authors: Wasteneys Geoffrey O. , Williamson Richard E. 
Published: April 2021

ABSTRACT
Giant internodal cells of Nitella tasmanica have cortical microtubules beneath the plasma membrane and endoplasmic microtubules associated with sub-cortical actin bundles and nuclei. We depolymerized the microtubules with oryzalin and followed their reassembly by immunofluorescence. At 18°C (the standard temperature of culture), microtubules were lost from young cells within 10 min and the first microtubules were detected in the cortex within 20 min of washing out the herbicide. Microtubules of older cells disassembled and re-formed more slowly. Continued cortical microtubule assembly was at acute angles to the first-formed microtubules, building branching clusters of microtubules. At 25°C, cortical microtubule assembly generated less extensively branched clusters and was completed more rapidly. Larger clusters but shorter MTs were generated in older cells. Reassembly of microtubules in the endoplasm only began 50 min after the removal of oryzalin. We therefore conclude that assembly proceeded independently in the cortex and endoplasm. Cortical assembly involves scattered assembly events initiating microtubules from which, as the latter elongate, further microtubules assemble as branches. We suggest that similar processes operate in steady-state cells and we explain with a simple model why branched clusters of microtubules are unusually large after microtubule depolymerization. By proposing that these processes show differential changes in activity with temperature and during cell ageing, we can account in qualitative terms for the age- and temperature-dependent differences in microtubule reassembly patterns.
Cellular asymmetry inChlamydomonas reinhardtii
Authors: Holmes Jeffrey A. , Dutcher Susan k. 
Published: April 2021

ABSTRACTAlthough largely bilaterally symmetric, the two sides of the unicellular alga Chlamydomonas rein-hardtii can be distinguished by the location of the single eyespot. When viewed from the anterior end, the eyespot is always closer to one flagellum than the other, and located at an angle of approximately 45° clockwise of the flagellar plane. This location correlates with the position of one of four acetylated microtubule bundles connected to the flagellar apparatus. Each basal body is attached to two of these microtubule rootlets. The rootlet that positions the eyespot is always attached to the same basal body, which is the daugher of the parental/daughter basal body pair. At mitosis, the replicated basal body pairs segregate in a precise orientation that maintains the asymmetry of the cell and results in mitotic poles that have an invariant handedness. The fusion of gametic cells during mating is also asymmetric. As a result of asymmetric, but dtfferent, locations of the plus and minus mating structures, mating preferentially results in quadriflagellate dikaryons with parallel flagellar pairs and both eyespots on the same side of the cell. This asymmetric fusion, as well as all the other asymmetries described, may be necessary for the proper photo-tactic behavior of these cells. The invariant handedness of the spindle pole, eyespot position, and mating structure position appears to be based on the inherent asymmetry of the basal body pair, providing an example of how an intracellular pattern can be determined and maintained.