bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mitochondrial extensions associated with microtubules in outgrowing processes from chick spinal cord In Vitro
Authors: Grainger Felicity , James D.W. 
Published: April 2021

ABSTRACT
Electron-microscopic examination of processes growing out from chick spinal cord cultivated in vitro raises the possibility that mitochondria may be continuous with a system of membrane-bound profiles ramifying within the cytoplasm. These profiles are distinctive in appearance, and appear to establish a particular spatial relationship with microtubules. In this, dense material extends from the profiles to constitute a meshwork within whose interstices tubules lie. The suggestion is made that these appearances may reflect the utilization of the products of mitochondrial activity for transport by microtubules.
Membrane alterations and other morphological features associated with polyethylene glycol-induced cell fusion
Authors: Robinson J. M. , Roos D. S. , Davidson R. L. , Karnovsky M. J. 
Published: April 2021

ABSTRACT
Polyethylene glycol (PEG) induces rapid fusion of LM cells. Membrane fusion, as detected by formation of pentalaminar membrane arrays, occurs as early as 1 min after PEG treatment. The entire cell surface appears to be capable of fusion since fusion occurs in regions where pseudopodia make contact with each other or with a neighbouring cell body and also in areas where cells are in contact along their entire periphery. Cytoskeletal components showed no apparent deleterious effect from PEG treatment or subsequent cell fusion as determined by thin-section EM. Freeze-fracture of monolayer cultures reveals a thermotropic rearrangement of intramembranous particles following PEG treatment.
A reliable method for obtaining matched replicas of freeze-fractured cell suspensions
Authors: Wilkinson M. J. , Northcote D. H. 
Published: April 2021

ABSTRACT
A method that overcomes the majority of practical problems involved in performing matched freeze-fracture replication of cell suspensions is described. Specimens are rapidly frozen between copper support plates. The prior attachment of gold grids to the plates using Formvar ensures the exact alignment of corresponding grid squares and the production of a central fissure running through the specimen upon fracturing. Grids, with replicas permanently attached, are removed from the support plates by dissolving the Formvar. Sample digestion and rinsing of replicas is by a gentle procedure employing glass capillaries as a means of handling the grids. Matched replication of plant and animal cells has been achieved by this method. Apart from the excellent preservation of the membrane ultrastructure of unfixed cells and the capacity for matching both membrane halves this technique also enhances the fracture characteristics of certain specimens, notably isolated protoplasts, providing larger fracture faces than are obtained by the knife-splintering method.
Plasma membrane ultrastructure during plant protoplast plasmolysis, isolation and wall regeneration: A freeze-fracture study
Authors: Wilkinson M. J. , Northcote D. H. 
Published: April 2021

ABSTRACT
The freeze-fracture morphology of the plasma membrane of cells and isolated protoplasts of plant callus suspensions has been investigated. Plasmolysis of suspension cells leads to the formation of 2 types of hexagonal arrays of intramembrane particles situated on the inner fracture face (PF). These arrays are interpreted as proteins that have ‘crystallized ‘in the plane of the membrane as the area of surrounding lipid bilayer is reduced during protoplast retraction from the cell wall. Time-course studies have revealed no positive relationship between the distribution of hexagonal arrays and the occurrence of microfibrils regenerated around isolated protoplasts during periods of culture. No evidence for the specialized transport functions attributed to hexagonal arrays of plant cells by previous workers has been found.
Two new septate junctions in the phylum coelenterata
Authors: Green C. R. , Flower N. E. 
Published: April 2021

ABSTRACT
Freeze-fracture of fixed and unfixed tissue, lanthanum tracer and conventional thin-section studies have revealed 2 new types of septate junction in the class Anthozoa, phylum Coelenterata. These new junctions have the 15−18-nm intercellular spacing of all other described septate junctions and are found around the apical circumference of cells lining a lumen or outside edge. However, in freeze-fracture replicas and tangential views of lanthanum-impregnated tissue, they are seen to be quite different from other known septate junction types. One of the new junctions is found in endothelial tissue such as that lining the gut or the inside of the tentacles. In tangential view it is seen to consist of relatively short, straight, double septa, again with lateral projections. Tn freeze-fracture of unfixed tissue, the junction consists of double rows of particles on the P face, the particles of one row being rounded, those of the other being elongated at right angles to the line of the septum. This dichotomy in particle size is unexpected, as the 2 halves of the septa as seen in tangential view are symmetrical. In freeze-fracture of fixed material the particle arrays remain on the P face and appear similar to those of unfixed material, but never as clear. In fixed tissue, some distortion has occurred and in extreme cases septa appear as a single broad jumbled row of particles. In this double septa junction, the rows of particles seen in freeze-fracture are occasionally seen to anastomose with a septum dividing into 2 and a third row of particles aligning with the 2 new septa to form their double particle rows. In both fixed and unfixed tissues, the E face of the junction consists of wide, shallow grooves.
The second of the new junctions occurs in epithelial tissue, such as around the outer edge of sea-anemone tentacles, and consists of long wavy septa with lateral projections. In views where these projections appear longest, they arise predominantly from one side of the septa. In freeze-fracture of both fixed and unfixed tissue, this junction appears as rows of closely spaced particles on the P face. Occasionally rows of particles are seen on the E face, but usually this face is characterized by shallow grooves. In some aspects these 2 new junctions have features in common with the Hydra type junction also found in the Coelenterata. In all 3 types septa are relatively straight, rather than pleated, and there are lateral projections on the septa.
Characteristics of pollen diffusates and pollen wall cytochemistry in poplars
Authors: Ashford A. E. , Knox R. B. 
Published: April 2021

ABSTRACT
Pollen diffusates, known to be important in pollen-stigma interactions controlling inter-specific incompatibility between Populus deltoides and Populus alba, have been partly characterized and shown to contain more than 20 protein bands by polyacrylamide gel electro-phoresis, at least 4 of these being glycoproteins. Seven fractions had antigenic activity in rabbits and several enzyme activities were also present. Peroxidase and leucine aminopeptidase isoenzymes were detected in the diffusates, demonstrating the extracellular location of these 2 enzymes. Isoenzyme patterns of peroxidase, esterase and acid phosphatase were complex, with some bands common to both species. Localization of acid phosphatase in the intine and esterase in the exine was demonstrated after brief aldehyde fixation and low-temperature embedding in glycol methacrylate. The in tine and exine sites were distinguished by their chemical and structural features. Calcofluor white M2R new proved to be an excellent stain for differentiating the intine. Aniline blue-positive material, probably β-1,3-glucan, is present associated with the intine of many ungerminated as well as germinating grains: production of this material may be a response to damage.
Adhesive and non-adhesive membrane domains of amphibian embryo cells
Authors: Roberson Marie , Armstrong Jon , Armstrong Peter 
Published: April 2021

ABSTRACT
Superficial blastomeres of mid-cleavage stage amphibian embryos (32- and 64-cell stage) display regional cell-surface differences in adhesiveness. The cells are adhesive on the lateral and basal cell surfaces and non-adhesive on the apical surface. These adhesive differences are maintained by single cells which have been dissociated from the intact embryo. Pigmentation differences afford a means of distinguishing apical surface from basal/lateral surface in dissociated cells. The apical surface is underlain by melanin granules and so appears dark, whereas the lateral and basal surfaces lack pigment and are white. Scanning electron-micrograph observations of isolated superficial cells reveal striking morphological differences between the adhesive and non-adhesive regions. The apical (non-adhesive) portion of the cell surface has a convoluted appearance and is almost entirely devoid of microvilli. The lateral and basal (adhesive) surfaces lack the convolutions of the apical surface and bear scattered microvilli.
The isolated superficial cells continue to divide in culture. The cells display a unilateral or one-sided furrow which begins in the basal surface and progresses toward the apical surface. The plane of cleavage of most of the cells is oriented such that the pigmented cap is bisected, with very few cells having the plane of the furrow pass parallel to the apical surface. The direction of furrowing in the isolated cells from the 32-to 64-cell embryo represents a direction of furrow progression in the intact embryo from the interior to the surface. Since the early cleavages are initiated at the surface and progress into the interior, it is suggested that a reversal in direction of furrowing occurs by mid-cleavage stages.
Human β-globulin factors affecting growth of human lymphocytes and mouse fibroblasts
Authors: Thomou H. , Koussoulakos S. , Stathakos D. 
Published: April 2021

ABSTRACT
Evidence is presented to show the existence in human β-globulin (Cohn fraction III) of 2 growth-promoting factors that stimulate DNA synthesis and cell division in human lympho-cytes and 3T3 B mouse fibroblasts.
After extraction of human β-globulins at pH 3·0 in 0·1 M NaCl followed by sieve chromatography on Sephadex, 2 distinct fractions were obtained containing the biological activity; one of polypeptide nature and molecular weight of approx. 10000 Daltons and the other consisting of a homogeneous ribonucleic acid, as revealed by polyacrylamide gel electrophoresis.
The above-mentioned factors appear to lack both cell and species specificity, since they are mitogenic agents for cells as diverse as mouse fibroblasts and human lymphocytes.
Investigations on ploidy levels of haploid and diploid callus and cell suspension cultures of Datura innoxia mill
Authors: Kibler R. , Blaschke J. , Forche E. , Neumann K.-H. 
Published: April 2021

ABSTRACT
Using haploid and diploid Datura innoxia Mill, callus cultures and cell suspensions it was shown that meristematic material usually attains the lowest possible C-value of a given ploidy level. Parenchyma material of callus cultures, however, indicates a broad scattering of C-values up to 16 C, which is paralleled by C-value distribution of the free cell fraction in actively dividing cell suspensions. In these suspensions, cell division activity seems to be restricted to small meristem-like clusters.
The development of lampbrush chromosome-type transcription in the early diplotene oocytes of Xenopus laevis: an electron-microscope analysis
Authors: Hill R. S. , Macgregor H. C. 
Published: April 2021

ABSTRACT
Oocytes of Xenopus laevis in pachytene and early diplotene of meiosis have been studied using the Miller spreading technique. Transcription first appears in germinal vesicles 25–40μm in diameter, when the oocyte is in early diplotene. Transcription at this stage consists of arrays of short RNF transcripts, irregularly distributed along the DNP axis. Linear regression analysis has shown that many of these arrays are transcription units (Type 1) with the transcripts having a common point of origin. The lengths of these early transcription units (mean = 7·06 ± 5 06/tm), calculated from the linear regression data, are comparable to the lengths of transcription units from later stages, including Dumont stage 3. The polymerase granules of Type 1 transcription units are widely and irregularly spaced, having a mean spacing of 5051748 nm. More advanced transcription units (Type II, mean length = 8·72 ± 3·77μm) are usually found in the same chromosome set as the Type I units. Type II transcription units have closer and more regularly spaced polymerase granules than Type I transcription units (mean spacing = 92±49nm). Both Type I and II transcription units have comparatively short RNP transcripts, the mean values for the slopes of their regression lines being 0-1336 and 0·1440 respectively. By the time the germinal vesicles are about 50–60μm in diameter the transcription units have a quite different morphology (Type III). The lengths of the Type III transcription units are comparable to the Type I and II units, the mean length being 6-3414-03 /tm. The spacing of the polymerase granules in the Type III units is closer and more regular than the earlier stages (70±40nm). Another significant difference between Type III and Types I and II transcription units is a decrease in the foreshortening of the Type III RNP transcripts. The mean slope of the regression lines for Type III transcription units is 0 2439. The morphological appearance of the Type III transcription unit is virtually identical to that of the transcription units from Dumont stage 3 oocytes, both with respect to the length and the spacing of the polymerase granules. However, the transcripts in Type III transcription units are still more foreshortened than those of Dumont stage 3 oocytes, having mean regression slopes of 0–4728. From the data obtained in the present study, it has been concluded that the pattern of lampbrush-type transcription is virtually fully established by the time most germinal vesicles are about 50 μm in diameter.
Motile apparatus in Vallisneria leaf cells. I. organization of microfilaments
Authors: Yamaguchi Yasuo , Nagai Reiko 
Published: April 2021

ABSTRACT
The organization of the microfilaments in epidermal cells of Vallisneria leaves was investigated with respect to the induction of cytoplasmic streaming (secondary streaming).
In many of the epidermal cells, cytoplasm exhibited rotational streaming along the anticlinal wall of the cell after exposure to intense light. In these cells, many bundles of 6–7 nm microfilaments were observed in the cortex around the anticlinal wall. The bundles were arrayed in parallel to the streaming direction. They were recognized usually as 10–40 closely packed dense dots in cross-section. The spacing between bundles was not even. Bundles tended to form groups of 4 to 5 in which the spacing between bundles was usually 0·3 and 0·5 μm.
The microfilaments were identified as F-actin. Together with the fact that rotational streaming in Vallisneria cells was inhibited by cytochalasin B, the motile mechanism of secondary streaming was concluded to be similar in its essential features to the cytoplasmic streaming seen in Characean cells (primary streaming).
In epidermal cells that had been kept under low-intensity light the cytoplasm and the chloroplasts were mostly localized along the wall facing the exterior (the periclinal wall). No cytoplasmic streaming occurred in these cells. The bundles of microfilaments remained in the very thin layer of cytoplasm lining the anticlinal wall, although they were fewer and somewhat loosely packed.
EGTA at appropriate concentration could induce cytoplasmic streaming in these cells. The mechanism of the induction is discussed on the basis of the effectiveness of EGTA and the requirement of a low concentration of free Ca2+ for cytoplasmic streaming in Characean cells.
Commitment during nematocyte differentiation in Hydra
Authors: Fujisawa Toshitaka , David Charles N. 
Published: April 2021

ABSTRACT
Nematocytes in Hydra differentiate from interstitial stem cells. Desmonemes differentiate mainly in the distal half of the body column while stenoteles differentiate predominantly in the proximal half. This difference was used to determine the timing of nematocyte-type commitment in the differentiation pathway. Cells were transferred from distal or proximal regions to all positions in the body column to test when the proportion of stenotele and desmoneme differentiation changed to reflect the new environment. In the first experiment, the distal region of the body column was isolated and permitted to regenerate a whole Hydra. In the second experiment, dissociated cells from distal or proximal regions were transplanted into regenerating aggregates of Hydra tissue. Both experiments effectively transferred cells from distal or proximal positions to positions throughout the body column. By comparing the kinetics of stenotele and desmoneme differentiation with the time required for distal or proximal cells to differentiate stenoteles and desmonemes in accord with their new environment, it was possible to conclude that stenotele and desmoneme commitment occurs during the terminal cell cycle prior to nematocyte differentiation and not at the stem cell. Additional experiments indicated that the number of rounds of cell division preceding differentiation is fixed at the time stem cells enter the nematocyte pathway.
Effects of steroids and different culture media on cell cycle of the androgen-sensitive human cell line NHIK3025
Authors: Østgaard Kjetill , Wibe Einar , Lindmo Tore , Eik-Nes Kristen B. 
Published: April 2021

ABSTRACT
The median cell cycle of synchronized NHIK3025 cells grown in Eagle’s MEM with 10 % foetal calf serum was 23·6 h, compared to 18 h observed earlier in Puck’s Eza medium with 30 % serum (20 % human and 10 % horse). This difference is due to a prolongation of both G1 and G2 in the MEM type medium.
Testosterone and 4-androstene-3β,17β-diol reduced the cell cycle of synchronized populations of NHIK3025 cultured in MEM type medium. Dexamethasone gave cell cycle prolongation while estradiol had no effect. These results are in accordance with steroid-induced changes in growth of asynchronous cell populations observed earlier. The androgen growth stimulation was partly due to a shortening of G2 but was not exclusively located in one particular phase of the cell cycle.
Ultrastructural analysis of hyphal tip cell growth in fungi: Spitzenkörper, cytoskeleton and endomembranes after freeze substitution
Authors: Howard Richard J. 
Published: April 2021

ABSTRACT
The ultrastructure of freeze-substituted tip cells of Fusarium acuminatum was analysed by conventional and high-voltage transmission electron microscopy (HVEM). At least 2 morphologically distinct types of Golgi-like endomembrane cisternae were observed, each existing as single, fenestrated sheets and tubular elements that were often, very closely associated with mitochondria. From HVEM observations of thick (0 · 25 and 0 · 5 µ m) sections, the Spitzenkdrper appeared to correspond to an apical mass of vesicles. A network of microfilamenis was identified among component vesicles of the Spitzenkörper and adjacent to developing septa. Microtubules were oriented primarily parallel to the direction of hyphal growth and were located in all areas of the cytoplasm, including the tip cell apex. Cytoplasmic vesicles were closely associated with these microtubules. From these observations it is suggested that cytoskeletal elements play important roles in localized cell wall formation. The filasome, a previously unreported type of coated vesicle in fungi, might also be involved in wall synthesis.
Adhesive properties of mdck cell membranes: possible role in epithelial histogenesis
Authors: Whitesell Luke , Edwardson J. Michael , Cuthbert Alan W. 
Published: April 2021

ABSTRACT
MDCK cells in culture form a functional transporting epithelium. Apical surfaces of MDCK monolayers are not adhesive to free MDCK cells that fail to grow attached to existing monolayers. In contrast, when plated at high density (10 6 cm -1) MDCK cells form multilayered structures in which only the outermost layer shows a typical apical surface (microvilli, tight junctions, etc.). In the lower layers cell-cell contacts (desmosomes, etc.) are made, suggesting that the basolateral surfaces remain adhesive.
Using a novel, quantitative, heterotypic cell adhesion reaction with aged human red cells, we have measured the adhesive properties of the apical surfaces of MDCK cells in a variety of conditions. It is found that the adhesion of red cells is dependent on cell density in the monolayer and falls to a low value at confluence. The reaction is considerably stronger at 6 °C compared to 22 °C (the temperature of most studies), while at 37 °C the reaction is expressed less strongly. MDCK cells with adherent red cells fail to divide, suggesting that the cell surface receptors involved might mediate growth inhibition by a similar homotypic reaction at confluence. The expression of the adhesive property is associated with cell division. This was shown by inducing synchrony in cultures either by refeeding starved cultures or by removal of a thymidine ‘block’. Peaks in adhesiveness were related to peaks in thymidine incorporation in synchronized cultures.
Because of the precise quantitative way in which adhesion can be measured it is considered that this is an ideal system in which to identify the membrane components responsible for the reaction. Furthermore, it may prove possible to identify signals that arise as an immediate consequence of the adhesion reaction.
Cytoskeletal and transmembrane interactions in the expression of tumourigenicity in human cell hybrids
Authors: Der Channing J. , Ash J. F. , Stanbridge Eric J. 
Published: April 2021

ABSTRACT
The cytoplasmic cytoskeletal organization was examined by immunofluorescence analysis in a series of paired non-tumourigenic and tumourigenic HeLa/fibroblast hybrids. The microfilament and microtubule complexity in tumourigenic hybrids was compared to that of the corresponding transformed, non-tumourigenic hybrids from which they were derived. Since both the non-tumourigenic and tumourigenic hybrids displayed well-organized microtubules, the disruption of these cytoskeletal elements is not required for transformation or tumourigenicity. In contrast, the microfilament organization was drastically altered in association with the re-expression of tumourigenicity. However, treatment of these tumourigenic segregant lines with sodium butyrate or dexamethasone resulted in a more flattened morphology and the appearance of well-developed microfilament bundles. This indicated that microfilament complexity was related to cellular morphology and not to tumourigenic potential. Finally, results of double immunofluorescence analyses for microfilaments and fibronectin staining in these hybrids agree with the existence of a transmembrane association between these 2 systems. In both normal fibroblasts and non-tumourigenic hybrids a close, but not identical, distribution was seen for surface fibronectin and cytoplasmic microfilaments. In the tumourigenic hybrids the lack of a well-organized miciofilament system was associated with a much reduced stitched-like pattern for fibronectin. The antibody-induced redistribution of surface β2-microglobulin reflected this loss of a transmembrane influence on the organization of surface components. Unlike the non-tumourigenic hybrids, the tumourigenic segregants possessed an altered extracellular matrix, rounded morphology, and reduced adhesion capabilities. The corresponding reduction in microfilament organization in these hybrids suggests that there is a close interrelationship between these cellular parameters. The exact contribution of these alterations to tumourigenic potential is unclear but the apparent loss of the transmembrane interaction with the cell surface organization may well represent a crucial alteration central to in vivo growth potential.