bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphous endocytotic organelles in the receptor-mediated endocytosis of gold-labelled α2-macroglobulin complexes by human fibroblasts
Authors: Van Der Schueren B. , Gasser D. , Marynen P. , Van Leuven F. , David G. , Cassiman J.-J. , Van Den Berghe H. 
Published: April 2021

ABSTRACT
The receptor-mediated endocytosis of gold-labelled α2macroglobulin complexes with trypsin or methylamine (α2M-T-Au or α.2M-MA-Au) was studied by electron microscopy in human skin fibroblasts. The gold label was found in coated structures and very small tubules as well as in tubulovesicular structures and in multivesicular bodies/lysosomes. Thick sections (200nm), but especially serial thin sections, clearly showed the polymorphic character of the cellular structures involved in endocytosis. Numerous intercommunications were particularly obvious between the tubulovesicular structures, the larger vesicles and the multivesicular bodies (MVB). Continuities between MVBs and endoplasmic reticulum and interconnections between MVBs were also observed. The specificity of the staining reaction was confirmed by indirect labelling of intracellular α2M by polyclonal and by monoclonal antibodies on ultracryosections. These findings are discussed in relation to observations made on epithelial cells with other ligands.
Protein synthesis and uptake by isolated cecropia oocytes
Authors: Anderson Lucy M. 
Published: April 2021

ABSTRACT
A procedure has been developed for separating the oocytes and follicular epithelium-nurse cell complexes making up the vitellogenic ovarian follicle of the Cecropia moth. Both components remained viable during short-term in vitro incubation in female blood. Isolated epithelial cells were found by autoradiography to incorporate tritiated amino acids and to secrete a fixable, non-dialysable labelled material. Isolated oocytes incubated in a blood medium containing this tritiated, dialysed follicle cell product incorporated it in small cortical yolk bodies, presumably by pinocytosis. Quantitative perchloric acid-precipitation and scintillation counting indicated that the amount of labelled material incorporated by the oocytes increased with time. These results provide direct confirmation of a follicle contribution to the yolk.
Isolated oocytes were also tested for their ability to incorporate labelled amino acids. Fixable label was observed autoradiographically throughout the oocyte cytoplasm, with the greatest concentration in the cortex, but little appeared in the yolk spheres. The amount of perchloric acid-precipitable amino acid in oocytes incubated in female blood increased with time for up to 2 h and then remained constant or decreased slightly. In medium that had been previously conditioned by follicle cells and dialysed, however, incorporation of labelled amino acid continued for at least 4 h. A possible interpretation of this result is that stimulation of pinocytosis by the epithelial cell products causes increased turnover of cell membrane and demands continued synthesis of new proteins.
Labelled female blood proteins were not incorporated into yolk to an appreciable extent by isolated oocytes, even in the presence of follicle cell product. Perhaps extracellular pre-concentration, as occurs in the intact follicle, is necessary for effective accrual of blood proteins. The female blood proteins did become associated with the oocyte cortex, however, and exhibited a higher affinity for the oocyte than male blood proteins. Thus preferential adsorption to the oocyte surface may be a component of the selection process in vitellogenesis.
Shape control in the human red cell
Authors: Backman Lars 
Published: April 2021

ABSTRACT
When the human red cell consumes its ATP, the cell loses its discoid character in favour of a spiculated and eventually a spherical form. This discocyte—echinocyte transformation parallels both degradation of phosphatidylinositol 4,5-bisphosphate and phosphatidic acid but not dephosphorylation of cytoskeletal proteins. Dephosphorylation of both spectrin and band 3 lags behind metabolic crenation.
Exogenous vanadate accelerates both shape changes and lipid dephosphorylation in a parallel manner during metabolic depletion. In contrast to its effect on lipids, vanadate reduces the rate of protein dephosphorylation. These observations strongly support a shape control mechanism in the red cell, based on phosphoinositide metabolism and compatible with a bilayer-couple model.
Freeze-fracture analysis of thylakoid membranes and photosystem I and II enriched fractions from Phormidium laminosum
Authors: Glick Richard E. , Triemer Richard E. , Zilinskas Barbara A. 
Published: April 2021

ABSTRACT
Thylakoid membranes of the thermophilic cyanobacterium Phormidium laminosum have been fractionated into photosystem II and photosystem I particles. These fractions have been characterized by their partial electron transport activities, and biochemical and spectral properties. Exoplasmic fracture face and protoplasmic fracture face particles in the unfractionated thylakoid membranes were shown to correspond in size to particles in freeze-fractured photosystem II and photosystem I fractions, respectively. Differences between the histograms of the thylakoid membrane protoplasmic fracture face particles and the isolated photosystem I particles suggest that in addition to photosystem I complexes some of the particles on the thylakoid protoplasmic fracture face may be related to cytochrome b/f complexes, the hydrophobic component of the coupling factor, or respiratory complexes.
Reactivation of euglenoid movement and flagellar beating in detergent-extracted cells of Astasia longa: Different mechanisms of force generation are involved
Authors: Suzaki T. , Williamson R. E. 
Published: April 2021

ABSTRACT
Detergent-extracted cell models of the euglenoid flagellate, Astasia longa, were obtained that rounded-up on addition of calcium. Treatment with 4% Triton X-100 and Nonidet P-40 removed the flagellar membrane, all membranous structures inside the cell body and the plasma membrane at groove regions of the cell surface. Maximum rounding-up was induced when the concentration of free calcium was raised to ≥10−7M, and ATP strongly enhanced this response. The ionic requirements and sensitivity to vanadate were different from those for the reactivation of flagellar movement. The results suggest that the mechanism of force generation is different from the dynein-based system of the flagellum and that a rise in cytoplasmic free Ca2+ concentration might cause euglenoid movement in vivo. The mechanism of euglenoid movement is discussed in relation to other protozoan motile systems.
Surface contraction of dividing newt eggs induced by lowering the external ionic strength or ph, or by trypsinization
Authors: kubota Tomoyuki 
Published: April 2021

ABSTRACT
As the first cleavage progresses, newt (Cynopus pyrrhogastef) eggs deprived of their vitelline membrane grow to expose the new, unpigmented surface to a saline medium (full-strength Steinberg solution). Further exposure of these eggs to sucrose medium resulted in rapid and extensive contraction of the unpigmented surface. In the sucrose medium the contraction continued until the next cleavage, and eventually the eggs divided into many blastomeres. But partial reversal of the contraction was observed when, after brief treatment with sucrose medium, the eggs were returned to saline medium. This and other experiments indicated that the contraction was due to lowering of the extracellular ionic strength. A similar type of contraction was induced by acidification of the saline medium or by trypsinization. The contractions induced by these treatments did not absolutely require the presence of external Ca2+, had a rapid time course, and were restricted to the unpigmented region, suggesting that they had a common mechanism. Acidification of the egg cytoplasm with CO2 did not result in significant contraction. These findings, together with those of others, suggest that contraction of the unpigmented surface induced by these treatments is due to conformational changes of surface material.
Plasmalemmal vesicles and the effects of sterol-binding agents in rabbit aortic endothelium
Authors: Simons H. L. , Severs N. J. 
Published: April 2021

ABSTRACT
The rims of vesicle openings in capillary endothelium are reported to be highly sensitive to perturbation by the sterol probe filipin when this agent is administered by perfusion at 50 μM concentration in aldehyde fixative for 10 min. If, as supposed, this specific rim response reflects functionally significant aspects of membrane organization at the vesicle–plasmalemma boundary, then it would be expected to be a reproducible and universal feature of endothelial vesicles in general. In the present study, we have investigated in detail the response to filipin of rabbit and rat aortic endothelial plasmalemma. First, the effect of standard filipin treatment (150 μM, 3–20 h) was examined by freeze-fracture. The extensive generalized response observed, taken together with the effects of filipin seen by fluorescence microscopy of stripped aortic endothelial sheets, and the marked corrugation of the plasmalemma observed by freeze-fracture after tomatin treatment, indicate that substantial amounts of cholesterol are present in the membrane. Exposure of rabbit aortic endothelium to 50 μM filipin for 10, 20, 40 and 60 min enabled the progressive appearance of filipin deformations in the plasmalemma to be traced. Even at the very earliest stages of the response, there was no preferential association of filipin deformations with endothelial vesicle rims. Similar experiments in the rat gave the same result. Specific sensitivity of endothelial vesicle rims would, therefore, seem to be either non-universal in occurrence or non-reproducible, and so is unlikely to reflect any membrane property of fundamental significance to endothelial vesicle function.
Stimulation of actin synthesis by cytochalasin d is specific for the isoactins normally expressed in muscle or non-muscle cells
Authors: Tannenbaum Janet , Miranda Armand F. 
Published: April 2021

ABSTRACT
Treatment of human muscle myotube cultures with 2 μM-cytochalasin D (CD) for 6 h stimulated synthesis of both the (muscle-specific) a-actin and the (non-muscle) β and γ-actins usually expressed by these cells. In non-muscle (HEp-2) cell cultures, CD enhanced synthesis of β and γ-actin, but did not induce synthesis of α-actin, which is not normally present in these cells. Thus, synthesis of both muscle and non-muscle actins can be increased by CD, but enhancement of actin synthesis results from increases in the isoactins usually present, rather than induction of new isotypes. Comparison of CD-treated (fused) myotube cultures with (unfused) myoblast cultures indicated that β and γ-actin synthesis was similarly enhanced in both cultures, but that α-actin synthesis was stimulated to a greater extent in the myoblast cultures. Desmin synthesis was also stimulated in the myoblasts but not the myotubes, suggesting that the effect of CD on synthesis of these developmentally regulated cytoskeletal proteins (a-actin, desmin) might be modulated by fusion or the state of differentiation of the muscle cell.
Chemokinetic behaviour of insect haemocytes in vitro
Authors: Takle Garry B. , Lackie Ann M. 
Published: April 2021

ABSTRACT
Time-lapse microphotography was used to film the locomotory behaviour of cockroach haemocytes in vitro, and the cell tracks were analysed for speed and persistence; the percentage mobilization and the diffusion rate of the population were calculated. Haemocytes are either fast locomotor or spread moving cells, or non-motile spread or rounded cells; the first three types are plasmatocytes and their behaviour is interchangeable. Approximately 20% of the cells are motile under control conditions and there is no correlation between orthokinesis and klinokinesis. If activated haemocyte lysate supernatant (HLS), a source of components of the prophenoloxidase enzyme sequence, is added to the cell monolayer, up to 80 % of the cells switch to fast locomotor behaviour, rounding up and moving faster and for longer in straight lines. Neither heat-inactivated HLS nor zymosan supernatant, used to activate HLS, had any effect. If the chemokinins present in activated HLS are also released in vivo on haemocyte activation or during cuticular wounding, then they and the induced changes in haemocyte adhesion could contribute to haemocyte recruitment to sites of infection.
Distribution of the 70K U1 RNA-associated protein during interphase and mitosis: correlation with other U RNP particles and proteins of the nuclear matrix
Authors: Verheijen Ron , Kuijpers Helma , Vooijs Peter , Venrooij Walther Van , Ramaekers Frans 
Published: April 2021

ABSTRACT
Earlier studies suggested that the 70K (70 × 103Mr) polypeptide is a nuclear matrix (associated) protein since it is the only U1 RNP-associated antigen that is not released from the nucleus after treatment of the cell with, successively, detergents, DNase I and/or RNase A and high salt. The possibility that the 70K protein functions in the binding of U1 RNP to the nuclear matrix is now further substantiated by the finding that U1 RNP particles that did or did not contain the 70K protein could be isolated, depending on the method of isolation. When U1 RNP particles were obtained by means of sonic disruption of the nucleus they contained the 70K polypeptide, whereas particles that were isolated by extraction at room temperature and a slightly alkaline pH lacked the 70K protein but contained the intact U1 RNA and the other U1 RNA-associated proteins.
During interphase the localization of the 70K protein is restricted to the nucleus, giving a dotlike distribution pattern with exclusion of the nucleoli. During prophase to late anaphase the protein is dispersed throughout the entire cytoplasm with the exception of the chromatin regions. Immunofluorescence studies, using a monoclonal anti-70K antibody in combination with human autoimmune sera that react with U1 RNA-associated proteins, demonstrate that the 70K protein is localized in those areas of the cell where other U RNP proteins occur, also during mitosis. Topoisomerase I and nuclear lamins, typical nuclear matrix proteins, show completely different distribution patterns in all phases of the cell cycle.
Assembly of the nuclear envelope is attended by the re-formation of the clustered appearance of the 70K antigen. These results suggest that, although associated with the nuclear matrix fraction in interphase cells, the 70K protein remains associated with the U1 RNP particles during cell division.
Microtubules And Cell Wall Development In Differentiating Protophloem Sieve Elements Of Triticum Aestivum L
Authors: Eleftheriou E. P. 
Published: April 2021

ABSTRACT
The densities of microtubules (MTs) along the lateral walls of developing sieve elements in root protophloem of wheat have been investigated by electron microscopy. They increase gradually in the very young sieve elements to reach a maximum just before the initiation of wall thickening. During wall increment MTs remain at high densities (more than 10MTs μm−1), but their number declines abruptly when wall material deposition ceases.
Cell wall thickening is not uniform: broad ridges alternate with narrow depressions, the latter occupied by plasmodesmata. During wall material deposition MTs overlie the thickenings only, being entirely absent from the non-thick-ened areas. The orientation of MTs reflects that of the currently deposited cellulose microfibrils in the cell wall, all being perpendicular to the direction of cell expansion. Numerous vesicles, apparently of Golgi apparatus origin, are encountered amongst the cortical arrays of MTs. Though the least spacing between the contiguous MTs is much smaller than the diameter of even the smallest vesicles, the latter were seen amongst the MTs, indicating that MTs do not prevent the vesicles from passing between them towards the developing area.
All results favour the suggestion that MTs in sieve elements are involved in cell wall pattern development, cellulose microfibril orientation, and presumably in cell elongation.
Laser-induced fusion of mammalian cells and plant protoplasts
Authors: Wiegand Rosemarie , Weber Gerd , Zimmermann Karin , Monajembashi Shamci , Wolfrum Jürgen , Greulich Karl-Otto 
Published: April 2021

ABSTRACT
An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selected plant protoplasts or of B-lymphocytes with myeloma cells. The fusion took place in normal culture medium and the fusogenic condition perturbed the cells only for a fraction of a millisecond. Without manipulating the cell culture except for exposing the cells to laser light, fusion products between preselected individual pairs may be produced.
Clonal origin of chemically induced papillomas: Separate analysis of epidermal and dermal components
Authors: Deamant F. D. , Iannaccone P. M. 
Published: April 2021

ABSTRACT
A fundamental prediction of the hypothesis that critical events in tumour formation are rare is that the tumours develop by clonal expansion. This prediction has been tested by establishing the isozyme content of tumours induced in mosaic animals whose normal tissues contain two distinguishable isozyme activities. The observation that tumours contain activity associated with one or other of the two cell types present in non-neoplastic tissue has been taken to support the contention that the tumours are clonal in origin. Conversely, the presence of both isozyme activities has been taken to mean that the tumours are derived from a large number of cells. There are conflicting reports concerning the clonal origins of chemically induced epidermal tumours. In this report we present evidence that permits a critical resolution of this controversy. The neoplastic epidermal component of the tumours in mosaic animals was separated from the non-neoplastic dermal components. The neoplastic components were derived exclusively from one or other of the cell lineages present within the mosaic, while the dermal non-neoplastic tissue was shown to be derived from both cell lineages. The data support the view that, irrespective of dose or type of carcinogen, the neoplastic portion of a tumour is clonally derived and that analysis of unseparated tumours is confounded by non-neoplastic dermal tissue. The patch size (number of cells in aggregates of like cell type) was established in the target tissue, isolated epidermis. It has been previously held that the epidermal patch of chimeras is larger than that in X-chromosome-linked mosaics. We have established that this is not the case in isolated epidermis of the mouse.
Effect of phorbol myristate acetate and the chemotactic peptide fNLPNTL on shape and movement of human neutrophils
Authors: Roos F. J. , Zimmermann A. , Keller H. U. 
Published: April 2021

ABSTRACT
The results show that the distinct types of shape produced by phorbol myristate acetate (PMA) and by chemotactic peptides (fNLPNTL) are associated with distinct types of neutrophil movement. Whereas the chemotactic peptide can induce front-tail polarity characterized by an expanding front, a contracted tail and preferential unidirectional movements of intracellular organelles, PMA can only elicit non-polar movements characterized by random formation and retraction of projections all over the surface, intracellular movements of organelles being ill-defined and changing in direction. Combined stimulation of human neutrophils with PMA and fNLPNTL results in a suppression of peptide-induced polarity and the formation of non-polar motile cells resembling those stimulated with PMA alone. The results suggest that the diacyl-glycerol-protein kinase C pathway may be instrumental in transducing or modulating signals to the locomotor apparatus of the cell. PMA-treated cells are, however, still capable of developing directional responses when appropriately stimulated. The findings lead to the hypothesis that distinct types of neutrophil movements are preferentially associated with distinct functions.
Isolation of morphologically intact mitochondrial nucleoids from the yeast, Saccharomyces cerevisiae
Authors: Miyakawa Isamu , Sando Nobundo , Kawano ShigeyukI , Nakamura Soichi , Kuroiwa Tsuneyosiii 
Published: April 2021

ABSTRACT
Mitochondrial nucleoids (mt-nucleoids) of the yeast, Saccharomyces cerevisiae, were isolated from spheroplasts of stationary phase cells and their structure and organization were investigated by fluorescence microscopy, electron microscopy, and biochemical techniques. Isolated mt-nucleoids were spherical or ovoid and 0·3–0·6 μm in diameter, and were about the same size and shape as those observed in the cell by the DAPI staining technique.
Measurement of DNA content of mt-nucleoids, using a video-intensified microscope system, after DAPI staining revealed that a mt-nucleoid in spheroplasts from stationary phase cells contains, on average, 3·9 mtDNA molecules and an isolated mt-nucleoid contains, on average, 3·1.
Negatively stained electron micrographs showed that mt-nucleoids consist of particles 20–50 nm in diameter. SDS-polyacrylamide gel electrophoresis of mt-nucleoids detected 20 species of polypeptides in the molecular weight range from 10×103 to 70×103. Acid-urea/SDS two-dimensional electrophoresis of acid extract from mt-nucleoids indicated that a polypeptide of 20×103 is the only major polypeptide with basic property like histones.
Characterization of antibodies as probes for structural and biochemical studies of tektins from ciliary and flagellar microtubules
Authors: Linck R. W. , Goggin M. J. , Norrander J. M. , Steffen W. 
Published: April 2021

ABSTRACT
Rabbit antibodies raised and purified against three tektins, proteins of flagellar doublet microtubules from sea-urchin sperm (Lytechinus pictus and Strongylocentrotus purpuratus), were used to study tektin biochemistry and their structural localization. Doublet microtubules were fractionated into tektin filaments and separated by SDS-PAGE into three major tektin polypeptide bands (Mr = 47, 51 and 55 (× 103)), which were used to immunize rabbits. Antibodies against each tektin (anti-tektins) were affinity-purified and then characterized by two-dimensional isoelectric focusing/SDS-PAGE immunoblotting and by immunofluorescence microscopy. In twodimensional immunoblots of 0·5% Sarkosyl-resistant fractions of flagellar microtubules, the antibody against the 55×103Mr tektin (anti-55) stained one major polypeptide of 55 × 103Mr and pl 6·9, anti-51 stained two polypeptides of 51×103Mr and pl ≈ 6·15, and anti-47 stained one major polypeptide of 47× 103Mr and pl 615. The anti-tektins also stained several minor neighbouring polypeptides, which may be isoelectric variants, novel tektins or unrelated proteins. Furthermore, anti-47 crossreacted with the major 55×103Mr polypeptide. By immunofluorescence microscopy all three anti-tektins stained methanol-fixed echinoderm sperm flagella and embryonic cilia. In addition, anti-47 and anti-55 stained unfixed, demembranated axonemes. Besides staining axonemes, all anti-tektins labelled the basal body region, and anti-51 labelled the sperm head envelope. These results indicate that the tektins are a complex family of proteins that are components of axonemal microtubules and possibly other cytoplasmic and nuclear structures.