bluuebunny/crossref_metadata_2025_split huggingface dataset:
Attachment of Paramecium to polystyrene surfaces: A model system for the analysis of sexual cell recognition and nuclear activation
Authors: Kitamura Akio 
Published: April 2021

ABSTRACT
In the ciliate Paramecium caudatum, only mating-reactive cells can attach to the polystyrene surface of Petri dishes. The attachment of mating-reactive cells occurs exclusively at the tips of ventrally located cilia (mating-reactive cilia) and appears to involve a hydrophobic interaction. An increase in the hydrophilic nature of the polystyrene surface following treatment with sulphuric acid results in the loss of attachment of reactive cells. The presence or absence of Ca ions and varying the ionic strength of the medium have no effect upon attachment. Although attachment reactivity is closely correlated with mating reactivity, the attachment sites appear distinct from the mating recognition sites, as suggested by the following experimental results: (1) cells that lose mating reactivity following treatment with trypsin are still able to attach to the polystyrene surface; (2) the attachment of cells appears temperaturedependent over a range where mating reactivity remains uneffected; (3) mating reactivity is quickly lost as a result of attachment to the surface of the dish. While the mechanism of attachment is not the same as sexual recognition, the attachment to the polystyrene surface initiates the early stages of the conjugation process. Cells that attach show micronuclear migration while unattached cells do not. The maximum rate of micronuclear migration occurs approximately 30 min after attachment. Meiosis does not occur following migration in the attached cells as in cells that are sexually mating. The relationship between the mating substance and the attachment substance is discussed, while the utilization of the attachment phenomenon for other experimental procedures is proposed.
A cell spreading factor, abundant in human placenta, contains fibronectin and fibrinogen
Authors: Aplin J. D. , Foden L. J. 
Published: April 2021

ABSTRACT
A salt extract from human normal-term placental extracellular matrix contains material that rapidly adsorbs to glass or tissue-culture plastic and promotes the spreading of fibroblastic and epithelioid cell lines. The cellular response to placental spreading factor (PSF) is characterized and compared with the response to fibronectin. The active component is shown to contain antigenic determinants that cross-react with antibodies to fibronectin and fibrinogen. The activity is not retained on gelatin-Sepharose but another component of the extract (∼ 185000 molecular weight) is retained. Partial purification is reported, and the possible involvement of PSF in trophoblastic invasion of the uterine wall is discussed.
Nucleolar fibrillar centres in plant meristematic cells: Ultrastructure, cytochemistry and autoradiography*
Authors: Risueño M. C. , Medina F. J. , Díaz De La Espina S. Moreno 
Published: April 2021

ABSTRACT
In plant cells nucleolar fibrillar centres (FCs) undergo ultrastructural changes, depending on the nucleolar activity. We have found two types of FC structure in nucleoli with either high or low activity, to which we have given the conventional names of homogeneous and heterogeneous, respectively. The first type is characterized by the presence of fibres that we describe structurally and cytochemically as decondensed chromatin; the second type, in addition to these fibres, contains a variable number of dense cores made up of condensed chromatin. Moreover, RNA does not appear to be present in FCs, while proteins are a major component.
Autoradiography after tritiated uridine incorporation shows that FCs are not the site of transcription, but that this takes place in the fibrillar component; the same result is obtained using the lead acetate fixation technique for detecting orthophosphate ions. This fact leads us to think that FCs are not the whole interphasic counterpart of the mitotic nucleolar organizing region (NOR), as stated by other authors, but only the portion of the NOR that is temporarily inactive in transcription; the transcriptionally active part of the NOR is in the fibrillar component, bound to its earliest product of transcription. Thus, FCs and the fibrillar component constitute a functional unit.
Ultrastructural studies in the rhodophyta: I. Development of mitotic spindle poles inApoglossum ruscifolium, kylin
Authors: Dave A. J. , Godward M. B. E. 
Published: April 2021

ABSTRACTThe ultrastructure of somatic mitosis in the germlings of Apoglosrum ruscifolium, Kylin, fixed from its natural habitat, was examined to investigate spindle-pole development and the role of the ‘polar ring’. It was found that the polar ring originates from a special nuclear pore raised above a small projection of the nuclear envelope. The initiation of mitotic polarity takes the form of changes in the nuclear envelope. These are: close crowding of pores, heavy deposition of electron-opaque material and attachment of microtubules. No such phenomena are to be observed in the equatorial regions of the nuclear envelope, which persists throughout mitosis. The next stage is the development of ‘clear zones’, which become filled with microtubules excluding all other structures, notably ribosomes, at both poles. At pre-metaphase, microtubules begin to be extended from the clear zones through polar fenestrae in the nuclear envelope into the nucleus itself. With subsequent development of the intranuclear spindle, the microtubules in the clear zones show signs of degeneration. At metaphase, the polar regions of the nuclear envelope begin to return to their normal conditon. After metaphase, the polar rings degenerate. Thus it is primarily the nuclear envelope, via its polar modifications, which begins the organization of the mitotic spindle.The capabilities of nuclear pores are summarized. In the Discussion, the polar rings are compared with procentrioles; since they appear to have a passive role in spindle-pole organization, it is suggested that they may represent an evolutionary stage prior to the procentriole. The origin of the centriole ultimately from a nuclear pore is presented as an hypothesis. It is concluded to be unlikely that the polar ring is a degenerate centriole, and therefore it is proposed that the red algae never had centrioles in the course of their evolution. Thus the view of the non-flagellate ancestry of the red algae is supported.
Neutrophil granulocytes: adhesion and locomotion on collagen substrata and in collagen matrices
Authors: Brown A. F. 
Published: April 2021

ABSTRACT
Neutrophil granulocytes (PMNs) adhere poorly to and are unable to locomote on collagen-coated glass; they are able to attach to and invade three-dimensional matrices of collagen fibres. Invasion is largely independent of adhesion to the fibres, does not occur by proteolysis of the gel, and is not affected by the presence of fibronectin or chondroitin sulphate. Invasion is reduced by increasing the concentration of collagen in the gel or by the presence of hyaluronic acid. It is proposed that in both these situations there is physical obstruction of PMN movement. The ability to locomote through tissues of very variable properties in vivo is important in the role of the PMN in inflammation.
Cytoskeleton and pericellular matrix organization of pure adult human keratinocytes cultured from suction-blister roof epidermis
Authors: Kariniemi A.-L. , Lehto V.-P. , Vartio T. , Virtanen I. 
Published: April 2021

ABSTRACT
Pure adult human kératinocyte cultures were raised from suction-blister roof epidermis and cultured in MCDB-151 medium. In primary culture the epidermal cells rapidly adhered, spread and began to proliferate on collagen-coated growth substrata but not on uncoated plastic or glass substrata. A fibrillar keratin-specific fluorescence, showing a typical cell-cell arrangement, was seen in all cells in indirect immunofluorescence microscopy, whereas only some cells also showed vimentin-specific staining. A fine fibrillar fibronectin-specific surface staining was seen at the margin of attaching cells and in marginal cells of spreading cell islands, whereas no fluorescence could be seen in epidermal cells, with antibodies against type IV collagen or laminin. Interestingly, the marginal cells also showed intracellular fibronectin. The synthesis of fibronectin in epidermal cell cultures could also be revealed by metabolic labelling experiments with [35S]methionine.
In contrast to primary cultures, subcultivated kératinocytes also adhered to uncoated plastic and glass substrata. After subcultivation, keratin and surface fibronectin distribution remained unaltered but after some subcultivations, most of the cells also showed fibrillar vimentin and expressed fibronectin intracellularly.
The results show that the suction-blister method provides an easy way to obtain pure epidermal cell cultures without contaminating mesenchymal cells. Our results also suggest a direct role for fibronectin but not for collagen type IV or laminin in adhesion and spreading of epidermal cells in vitro.
Isolation and electrophoretic characterization of the plasma membrane of sea-urchin sperm
Authors: Cross Nicholas L. 
Published: April 2021

ABSTRACT
A subcellular fraction containing plasma membranes was isolated from flagella of the sperm of Strongylocentrotus purpuratus by differential centrifugation, and analysed by sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Coomassie Blue staining revealed nine major bands and 14 minor species. Five bands of apparent molecular weights ∼200 × 103, 149 × 103, 120 × 103, 75 × 103 and 59× 103 also stained with periodic acid-Schiffs reagent and so are probably glycoproteins. These five components are externally exposed, as determined by lactoperoxidase-catalysed radio-iodination. Isolation of membranes from radio-iodinated sperm results in an enrichment of about tenfold in the specific activity of 125I. Comparison of the electrophoretic patterns of labelled sperm and of the membranes isolated from 125I-labelled sperm suggests that no major labelled proteins are lost during the isolation procedure, and so to this extent the membrane fraction is representative of the entire sperm plasma membrane.
Plasma membranes, cell junctions and cuticle of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea
Authors: Kukulies J. , Komnick H. 
Published: April 2021

ABSTRACT
The cell membranes and cell junctions of the rectal chloride epithelia of the larval dragonfly Aeshna cyanea were examined in thin sections and by freeze-fracture. These epithelia function in active ion absorption and maintain a high concentration gradient between the haemolymph and the fresh-water environment. Freeze-fracturing reveals fine-structural differences in the intramembraneous particles of the luminal and contraluminal plasma membranes of these epithelia, reflecting the functional diversity of the two membranes, which are separated by the junctional complex. The particle frequency of the basolateral plasma membranes is reduced after transfer of the larvae into high concentrations of environmental salinity.
The junctional complex is located in the apical region and composed of three types of cell junctions: the zonula adhaerens, seen in freeze-fracture as a nearly particle-free zone; the extended and highly convoluted pleated septate junction and randomly interspersed gap junctions of the inverted type. Gap junctions also occur between the basolateral plasma membranes. They provide short-cuts in the diffusion pathway for direct and rapid co-ordination of the interconnected cell processes.
Colloidal and ionic lanthanum tracer solutions applied in vivo from the luminal side penetrate through the cuticle via epicuticular depressions, but invade only the apical portion of the junctional complex. This indicates that the pleated septate junction constitutes a structural control of the paracellular pathway across the chloride epithelia, which are devoid of tight junctions. The structure of the pleated septate junctions is interpreted as a device for the extension of the diffusion distance, which is inversely related to the net diffusion. A conservative estimate of the total length of the junction, and the number and extension of septa reveals that the paracellular route exceeds the transcellular route by a factor of 50.
Rate of cell cycle initiation of yeast cells when cell size is not a rate-determining factor
Authors: Lord P. G. , Wheals A. E. 
Published: April 2021

ABSTRACT
The control of cell proliferation under steady-state conditions in the budding yeast, Saccharomyces cerevisiae, is well described by either the tandem or sloppy size control models, both of which suggest that differences in cycle time between individual cells or between parents and daughters is largely due to differences in birth size. These models have been investigated further under conditions in which cell size has not been a rate-determining factor for cell cycle initiation. Two approaches have been used. The first involves the growth of cells in low concentrations of hydroxyurea (HU), which has the effect of prolonging the duration of DNA synthesis. This leads to a lengthening of the budded period, which in turn leads to daughter cells being larger at division than the normal cell cycle initiation size of daughters in steady-state populations. The second approach involves the accumulation of cells at the key control point of the cycle, called start, using the pheromone α-factor. Since growth is unaffected, all cells eventually become larger than the volume at which they would normally initiate the cell cycle. The kinetics of proliferation were followed after release from α-factor arrest. The results from both approaches were broadly consistent with the predictions of both models. However, abolition of birth-size differences between parents and daughters in the presence of HU did not lead to a complete disappearance of differences in either cycle time or proliferation kinetics. Furthermore, following release from α-factor arrest, the rate of cell cycle initiation of parent cells was slower than in steady-state culture and the daughters’ cells behaved as if comprising two separate populations. These discrepancies suggest that besides a size difference, there are additional physiological differences between parent and daughter cells.
Organization and development of the macronuclear anlage in Stylonychia Notophora stokes
Authors: Sapra G. R. , Dass C. M. S. 
Published: April 2021

ABSTRACT
The development of the macronuclear Anlage of Stylonychia notophora was studied by means of cytochemical and autoradiographic techniques. In early stages of its differentiation, the Anlage has its chromatin distributed homogeneously. Nine to ten hours later chromosomes are noticed; the nucleus is possibly diploid. Following this, the number of chromosomes increases progressively resulting in polyploidy. Later, chromosomes uncoil and polytenization follows. After consolidation and shrinkage of these chromosomes, the Anlage splits into two bodies. Five series of replication bands quickly pass through each and the vegetative macronucleus results.
Synthesis of RNA by the new macronucleus starts soon after the shrinkage stage. The old macronuclei break up into small spherical bodies which are gradually resorbed in the cytoplasm.
When [3H]thymidine is provided continuously to the exconjugants, there is little uptake into the Anlage until the old macronucleus is completely resorbed. Only after this, heavy labelling is noticed. Fate of the previously labelled macronuclei during conjugation shows that their breakdown products are re-utilized for the development of the new macronucleus.
Morphogenesis of a large micro tubular organelle and its association with basal bodies in the ciliate Nassula
Authors: Tucker J. B. 
Published: April 2021

ABSTRACT
The cytopharyngeal basket in Nassula consists largely of microtubules. During binary fission the old basket is resorbed and simultaneously two new baskets develop. Changes in basket structure occurring dunng basket development and resorption, and variations in the lengths of baskets during the interfission period have been examined using phase-contrast and electron microscopy. These examinations indicate the manner in which several different processes influence the shapes, sizes, positions, and numbers of the various basket components.
Early in development some of the microtubular basket components contact certain basal bodies from which they subsequently detach, and then, while most of them assemble into the positions they occupy in the mature organelle, they are temporarily associated with a reticulum of microtubules. Several of these components are not included in a new basket and some of them are resorbed; development of the others continues and they establish microtubular connexions to basal bodies different from those to which they were previously attached. Other basket components commence development after assembly of the microtubular components and form in contact with them, even if they have not been included in a new basket. The majority of microtubules apparently lengthen by accumulating material exclusively at one of their extremities Baskets of starving organisms gradually shorten by loss of material from their bottoms but lengthen again when the organisms feed The bulk of an old basket is not enclosed in a vacuole when it is resorbed; breakdown of tubules progresses from their extremities after loss of intertubular cross-connexions
Freeze-etch studies on fish skeletal muscle
Authors: Bertaud W. S. , Rayns D. G. , Simpson F. O. 
Published: April 2021

ABSTRACT
The results of a freeze-etch study of skeletal muscle cells of a fish, the Black Molhe (Mol lienesta sp), correlated well with published descriptions of sectioned material. The arrays of apertures of the T-tubules at the cell surface were clearly demonstrated. Numerous vesicles, communicating with the extracellular space, were also seen at the cell surface. The relation ship of the T-tubules with the adjoining sarcotubular cisternae was studied; in transverse fractures at Z-levels there was a tendency for pieces of T-tubule to adhere to the cisternae No scalloping of the sarcotubular membrane was noted where it apposed the T-tubule, but some ridges on its luminal surface were demonstrated at these regions; elsewhere the luminal surface of the sarcotubular membrane was densely covered with particles. In the myofibrils, a reversal of polarity of the structure of the thick filaments was suggested at the M-line.
Calcium and microtubule sliding in ciliary axonemes isolated from Paramecium caudatum
Authors: Mogami Yoshihiro , Takahashi Keiichi 
Published: April 2021

ABSTRACT
Microtubule sliding was induced in axonemes obtained from isolated cilia of Paramecium caudatum when they were exposed to a reactivating solution containing ATP after mild treatment with trypsin. Over a very wide range of concentrations (lnM-4mM), Ca2+ in the reactivating solution had no effect on the proportion of axonemes that disintegrated as the result of microtubule sliding. Also, the velocity of sliding, determined by cinematography, and the polarity of the direction of sliding-force generation, determined by electron microscopy with regards to the base-to-tip axis of the cilium, were not affected by Ca2+. The results indicate that the Ca sensitivity, which is responsible for the ciliary reversal response, was removed from the axoneme, possibly as the result of trypsin treatment. It is thus unlikely that Ca sensitivity is attributable to the basic sliding machinery that powers ciliary movement.
Aequorin measurements of free calcium in single mammalian cells
Authors: Cobbold Peter H. , Cuthbertson K. S. Roy , Goyns Malcolm H. , Rice Veronica 
Published: April 2021

ABSTRACT
The calcium-triggered photoprotein aequorin has been used as a sensitive indicator of cytoplasmic free calcium in cells of relatively large size. We describe here several novel modifications to the technique that make it possible to detect resting levels of free calcium in single mammalian oocytes, fibroblasts and granulosa cells. Concentrations of free calcium as low as 1 × 10−7M have been measured in single fibroblasts, corresponding to a detection limit of 10−18mol.
Morphological Changes Of The 3T3-L1 Fibroblast Plasma Membrane Upon Differentiation To The Adipocyte Form
Authors: Fan Jing Yu , Carpentier Jean-Louis , Van Obberghen Emmanuel , Grunfeld Carl , Gorden Phillip , Orci Lelio 
Published: April 2021

ABSTRACT
By quantitative evaluation carried out on freeze-fracture replicas, we have investigated the changes in plasma membrane organization as the 3T3-L1 fibroblast phenotype differentiates into the 3T3-L1 adipocyte form. As differentiation takes place there is a dramatic change in overall appearance of the cell as it acquires large lipid-laden vacuoles. On freeze-fracture replicas we find: (1) a ninefold increase in small invaginations as the cell differentiates from the fibroblast to the adipocyte phenotype; (2) virtually no quantitative change in the larger coated invaginations upon differentiation; (3) a greater density of intramembrane particles in the large invaginations as compared to the uninvaginated membrane in both the fibroblast and adipocyte form. This remains relatively constant with differentiation. By contrast, there is a marked increase of intramembrane particles in the undifferentiated membrane as the cell changes from fibroblast to adipocyte.
The functional significance of these changes in plasma membrane organization is unknown, but they significantly correlate with the onset of lipogenesis by the cell.
Microtubule-organizing centres during the cell cycle of 3T3 cells
Authors: Brooks Robert F. , Richmond Frances N. 
Published: April 2021

ABSTRACT
When Swiss 3T3 cells are treated with colcemid for 60 min (0 · 5–2 μ g/ml), although the cytoplasmic network of microtubules is considerably reduced, a significant but variable number of microtubules remain. These residual microtubules appear to converge on a single, usually ciliated, organizing centre. In contrast, on removal of the colcemid, microtubule regrowth takes place from two organizing centres in approximately 50 % of the cells. Surprisingly, whether a cell has one or two organizing centres during recovery does not depend on its position in the cell cycle, though recovery takes place earlier in serum-stimulated cells than in serum-starved quiescent ones. It seems likely that prior to colcemid treatment, cells contain two potential organizing centres only one of which is normally active, the inactive one becoming active after exposure to the drug.
Glycoproteins and glycosaminoglycans of cultured normal human epidermal keratinocytes
Authors: Brown Keith W. , Parkinson E. Kenneth 
Published: April 2021

ABSTRACT
[3H]glucosamine has been used to label metabolically kératinocyte cell-surface glycoconjugates. The major labelled bands identified on sodium dodecyl sulphate/polyacrylamide gels had apparent molecular weights of greater than 250000, and 150000–80000. Most of these components were trypsin-sensitive, indicating that the label was protein-bound. Some of the labelled components were shown to be proteoglycans and the labelled glycosaminoglycans released from them by trypsin were identified as hyaluronic acid (54%), heparan sulphate (33%) and chondroitin sulphate (13%). Specific immunological methods (immunoperoxidase staining and immunoprecipitation) showed that keratinocytes produced fibronectin. Immunoperoxidase staining showed keratinocytes produce only small ‘stitches’ of fibronectin at cell edges; no large fibrils were seen nor any staining over or between cells.