bluuebunny/crossref_metadata_2025_split huggingface dataset:
Yolk transport in the ovarian follicle of the hen (Gallus domesticus): Lipoprotein-like particles at the periphery of the oocyte in the rapid growth phase
Authors: Perry M. M. , Gilbert A. B. 
Published: April 2021

ABSTRACT
Thin sections of the oocyte periphery and surrounding granulosa layer from 1–5-day preovulatory follicles were examined by transmission electron microscopy. With the use of certain procedures in tissue preparation, notably the tannic acid method, numerous particles in the range of 15–40 nm with a mean diameter of 27 nm were observed both extra- and intracellularly. The particles were abundant in the granulosa basal lamina, in the spaces between the granulosa cells and in the perivitelline space. They appeared to adhere to the oolemma as a continuous double layer which was also observed to line the coated vesicles, 200–350 nm in diameter, invaginating from the oolemma. The layer of particles was not found on the plasma membranes of the granulosa cells, nor were particles present within the cells. In the peripheral cytoplasm of the oocyte the yolk spheres, ranging upwards from 250 nm diameter, were membrane-bound and contained tightly packed particles similar to those on the oolemma. Bodies displaying features intermediate between coated vesicles and yolk spheres suggested that, on entry into the cell, loss of the cytoplasmic coat and obliteration of the vesicular lumen gave rise to nascent yolk spheres which then fused together to form the larger spheres. The extracellular layer, coated vesicles and smaller yolk spheres were absent in oocytes fixed after a 10-min delay.
The evidence indicated that 27-nm particles were transferred from the basal lamina to the oocyte surface via the intergranulosa cell channels, incorporated into the cell by adsorptive endocytosis and then transferred to the yolk spheres with little morphological alteration. The identity of the particles with very low density lipoproteins, the major components of the yolk solids, was discussed.
Pseudopodium induction by the action of quaternary ammonium ions on Amoeba proteus
Authors: Brewer J. E. , Bell L. G. E. 
Published: April 2021

ABSTRACT
Some aliphatic long-chain quaternary ammonium compounds and choline derivatives have been examined for their ability to induce pseudopodia from Amoeba proteus. The reaction involved in pseudopodium induction is believed to be between the quaternary nitrogen cations and polysaccharides on the cell surface. Not all of the carboxyl groups of the polysaccharide are involved in this reaction. The mechanism of pseudopodium induction is discussed in terms of changes in the surface charge and the permeability of the cell membrane.
The effect of dissolved oxygen partial pressure on the growth and carbohydrate metabolism of mouse LS cells
Authors: Kilburn D. G. , Lilly M. D. , Self Daphne A. , Webb F. C. 
Published: April 2021

ABSTRACT
Batch cultures of mouse LS cells were grown in suspension at controlled dissolved oxygen partial pressures (pO2). At low pO2 (1·6 mmHg) the growth and respiration rates and the final cell population were all limited. At high pO2 (320 mmHg), cell division was inhibited after an initial doubling of the cell number. At intermediate values of pO2, the growth rate was constant but the final cell population varied. Within the pO2 range of 40 –100 mmHg, the final cell population was constant and maximal at 1·2 × 106 viable cells/ml. Except at 320 mmHg pO2, about 90 % of the glucose consumed served as an energy source and could be accounted for as lactate and CO,. In the culture at 320 mmHg, only 60 % of the glucose consumed could be accounted for in this way. During growth the production of lactate and pyruvate was highest at low pO2. A sharp increase in lactate production was observed as logarithmic growth ceased in each culture, except at high pO2 (160 mmHg). These observations indicate that pO2 markedly influences cell growth and carbohydrate metabolism in these cells.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: I. general introduction and histological effects
Authors: Fell Honor B. , Dingle J. T. 
Published: April 2021

ABSTRACT
The addition of sucrose to a chemically denned culture medium caused intense cytoplasmic vacuolation of the perichondrial, oesteogenic and articular cartilage cells of limb-bone rudiments from day embryonic chicks grown in organ culture. The rest of the cartilage appeared unaffected by the sugar. The osteocytes were intensely vacuolated; the bone matrix was much less dense than that of the controls and had an abnormal fibrillar structure. When the explants were transferred to medium without sucrose, after 6 days vacuolation had almost disappeared.
The effect of the sucrose was dose-dependent; at a concentration of 0·32M the sugar was highly toxic; at 0·16M the explants survived and vacuolation of the chondrocytes extended further into the cartilage than at 0·08M. A similar vacuolation of the cells in response to sucrose was seen in the isolated shafts of the limb-bones and in the mandibular rami from 11- to 13-day embryos; in the sucrose-treated explants osteogenesis was arrested and in places the bone showed osteolytic changes.
In the absence of glucose, day limb-bone rudiments failed to grow and rapidly degenerated in medium containing 0·08 M sucrose, indicating that sucrose was very little if at all metabolized. Explants of day rudiments grown for 8 days in the presence of 0·08M glucose showed no vacuolation; dextran had some effect, and both mannitol and sorbitol caused vacuolation.
Studies on the fine structure of muscle fibres and contained crystalloids in basal socket muscle of the entoproct, Barentsia gracilis
Authors: Reger J. F. 
Published: April 2021

ABSTRACT
Basal socket muscle fibres of Barentsia gracilis are morphologically similar to invertebrate muscles classified as slow, tonic-type muscles. They are divisible into a non-contractile bulbous and a contractile myofilamentous portion, are innervated on their non-contractile surface, and are obliquely striated. The electron density and myofilament packing vary from fibre to fibre. Some muscle fibres appear degenerate in that they contain disorganized-appearing myofilaments and electron-dense bodies morphologically reminiscent of autophagosomes found in cells undergoing cytolysis.
A distinguishing feature of muscle fibres observed in B. gracilis is the presence of crystalloids, morphologically reminiscent of protein storage crystalloids found in other cell types. These crystalloids are seen to be composed of 30—70 A thick, helically shaped filaments arranged in a hexagonal lattice. Filaments have a pitch of 130—150 A and a tilt-angle of 35–45 degrees. Crosslinks occur between adjacent filaments at regular intervals. Crystalloids appear to be formed in the bulbous portion of muscle cells. Constituent, 30–70 A filaments appear to branch from crystalloids and are found free in the myofilamentous area of muscle fibres.
The above evidence, coupled with evidence elsewhere in the literature, suggests that the crystalloids may be a storage form of myofilament precursor which relate either to myogenesis or to cyclic regenerative and degenerative phenomena known to occur in Entoprocts, including B. gracilis.
Muscle attachment related to cuticle architecture in apterygota
Authors: Caveney S. 
Published: April 2021

ABSTRACT
In Apterygota muscles are attached to the cuticle by a series of discrete structures. The junction of the muscle and epidermal cells is demarcated by regular interdigitations of the two tissues, with desmosomes lining these processes. Within the epidermal cells, microtubules link up the desmosomes of the interdigitated region with dense material associated with cone-like depressions in the apical plasma membranes of the epidermal cells. Each of these ‘conical hemidesmosomes’ is situated opposite a pore canal. From within each cone, an electron-dense ‘muscle attachment fibre ‘extends up the corresponding pore canal through the procuticle and is inserted on the epicuticle. There is no direct link between the microtubules and the muscle attachment fibres. The muscle attachment fibres are slightly elliptical in cross-section, and are twisted, this twist being in phase with the orientation of the chitinprotein microfibrils forming the lamellae of the procuticle. The attachment fibres are straight, and not helically arranged; patterns obtained in oblique sections of procuticle including these structures support the twisted ribbon model of pore canal shape. The cuticle, particularly in Thysanu?an and Dipluran intersegmental membrane, displays the parabolic patterning typical of softer insect procuticle and procuticle deposition zones. The epicuticular insertion of the muscle attachment fibre is characterized by a pit in the cuticulin layer, the fibre passing through the middle of this pit.
The microtubule-associated conical hemidesmosomes appear to be cytoskeletal in function. The muscle attachment fibres are rigid structures which are not digested by the moulting fluid enzymes. New muscle attachment fibres may only become attached to the epicuticle during its formation. The structures described in regions of muscle attachment in Apterygota are similar to those recorded for other arthropods.
Nuclear ultrastructure of the transforming lymphocyte during inhibition of deoxyribonucleic acid synthesis with hydroxyurea
Authors: Milner Gillian R. 
Published: April 2021

ABSTRACT
The pattern of decondensation of heterochromatin in the transforming lymphocyte was found to be unaffected by hydroxyurea although DNA synthesis, which normally accompanies the latter part of this decondensation, was greatly inhibited. It is suggested that metabolic inhibition of DNA synthesis may result in atypical sites of DNA synthesis when the inhibitor is removed, since such sites are normally partly governed by an ordered sequence of decondensation of heterochromatin.
The nutritional relationship of Anemonia Sulcata (pennant) and its dinoflagellate symbiont
Authors: Taylor D. L. 
Published: April 2021

ABSTRACT
High resolution autoradiography in the optical and electron microscopes has been used to define the nature of the nutritional relationship between Anemonia sulcata and its algal symbiont. Grain counts from these autoradiographs have been examined quantitatively, and the results compared with those obtained from an in vitro analysis of the excreted products of the symbionts. These investigations clearly indicate that a system of carbon translocation between the alga and the host does exist in situ, and that over 60 % of the carbon fixed in photosynthesis is transferred to the host under the conditions of these experiments.
Mitochondrial associations with specific microtubular components of the cortex of Tetrahymena thermophila : II. response of the mitochondrial pattern to changes in the microtubule pattern
Authors: Aufderheide Karl J. 
Published: April 2021

ABSTRACT
Mitochondria in Tetrahymena thermophila are known to associate with the cell cortex in asymmetrical patterns corresponding to the asymmetrical organization of the microtubular components of the cortex. Specific mitochondrion-microtubule associations are seen at the light-microscope and ultrastructural levels. The hypothesis that the mitochondrial pattern is determined by the microtubular pattern was tested. Using the phenotypes of various mutations to generate changes in the organization of the cortex, the response of the mitochondrial pattern to the cortical change was assayed. The results consistently show that changes in the local organization of the cortical microtubule systems are followed by a corresponding change in the cortical mitochondrial pattern. However, the mitochondrial pattern is unaffected by a mutation which changes the ‘long-distance’ patterning of certain organelles, but which does not influence the local microtubular organization. Thus, the data support the hypothesis that there is a causal relationship between the arrangement of the cortical microtubules and the corresponding mitochondrial pattern.
Formation of cell-to-substrate contacts during fibroblast motility: An interference-reflexion study
Authors: Izzard Colin S. , Lochner Linda R. 
Published: April 2021

ABSTRACT
The formation of close contacts and focal contacts (co. 30 nm and 10–15 nm separation distance respectively) has been studied during the movement of chick heart fibroblasts on planar substrates using interference-reflexion microscopy, and evaluated in the context of spreading and net movement. During spreading the overall advance of the margin of the close contact is steady, punctuated by periods in which it remains stationary, and only 5% of the time is spent withdrawing in contrast to the extreme leading edge. The close contact advances only where a lamellipodium has first extended free of the substrate (⩾100 nm separation distance) ahead of the existing close contact. The new close contact is formed by the lamellipodium lowering to the substrate either progressively from its base forward or distally in patches which later join with the main close contact. New focal contacts are formed successively ahead of existing ones, either by microspikes or lamellipodia contacting the substrate locally ahead of the close contact, or within the close contact usually immediately, but not more than 1–2 μm, behind its margin. Examining the cell margin alternately with interference-reflexion and differentialinterference contrast showed that the formation of the focal contact was preceded in 90% of the cases by the development of a linear structure in the form of a microspike (as expected), a short projection (&lt;2 μm long) of the lamellipodium, or a fibre within the lamellipodium, each of which could be traced to the cytoplasmic fibre typically associated with the focal contact. Stress fibres subsequently developed centripetally from these initial fibres. The different forms of the linear structure which preceded the focal contact were interchangeable, giving rise to one another, and we have evaluated that the structure common to each is probably a short bundle of microfilaments.
The following features indicate that the close contact plays a primary role in marginal spreading: it is lost when spreading ceases; it is reformed when spreading resumes but only under the newly spread area; the advance of the margin of the thicker leading lamella closely follows that of the close contact; the advance of both can occur ahead of and is thus independent of existing focal contacts and associated stress fibres. We propose that the close contact provides the adhesion required to transmit to the substrate the forces involved in the forward movement of the marginal cytoplasm. The continual formation of focal contacts and stress fibres at the margin is consistent with their role, suggested by others, in drawing the bulk of the cell forward. These evaluations are discussed in the context of the form and distribution of contractile proteins in the cell margin. A primary role of the lamellipodia and microspikes in extending the cell margin and forming new adhesions, preparatory to further cytoplasmic movement, is established by this work.
The ultrastructure of prokaryotic-eukaryotic cell junctions
Authors: Tamm Sidney L. 
Published: April 2021

ABSTRACT
Freeze-fracture and thin-section electron microscopy were used to describe the sites of attachment of 2 kinds of ectosymbiotic bacteria to a devescovinid flagellate from termites. In each case, surface specializations in both partners occur at the junctional complexes. Rod bacteria lie in pockets of the eukaryotic membrane which are coated by dense material and contain high densities of intramembrane particles. A double row of closely spaced particles circumscribes the edges of the pockets on the P face. The surface of the rod bacteria which is exposed to the external medium bears a thick glycocalyx and flagella. Fusiform bacteria are attached along ridges of the protozoon surface. Dense material underlies the ridges, and particles are aggregated on both P and E faces of the ridge membrane. The outer layer of the fusiform bacteria is grooved to match the host ridge. The bacterial—devescovinid junctions are considered to serve mainly as attachment sites, and the membrane specializations at the sites of contact are discussed in this respect. Control of junction assembly by the cortical bacteria is suggested by the parallel patterns of junctional replication and bacterial reproduction.
Orientation of calvaria and periodontal ligament cells in vitro by pairs of demineralized dentine particles
Authors: Bellows C. G. , Melcher A. H. , Brunette D. M. 
Published: April 2021

ABSTRACT
Rat calvaria cells (RC cells) and monkey periodontal ligament fibroblasts (MPL cells) were cultured for 4–6 days with demineralized dentine, acid-washed glass particles or untreated glass particles to determine whether the presence of these particles can affect the orientation of the cells. Encapsulation of dentine particles began as early as the first day in culture and occasional cells were attached to, and oriented between adjacent particles. Multilayers of cells formed along the periphery of the dentine particles and the more superficial of these cells projected outwards in a radial fashion. Oriented cell sheets were evident between dentine particles after 3 days in culture. Finally, the cell sheets tore away from the surface of the culture dish to give rise to thick multilayered cellular bridges between dentine particles. The nuclear orientation index (ratio of L/W) for each RC cell lying between 15 randomly selected pairs of each particle type in 4-day cultures was measured along 2 axes; the length represented by the shortest distance between the 2 particles and the width perpendicular to this axis. The nuclear orientation index was 1·52 for cells between dentine, 1·13 between acid-washed glass and 1·06 between untreated glass. Control measurements of cells associated with single particles were 1·06, 1·09 and 1·06 respectively. The frequency of cellular orientation occurring between dentine particles was significantly greater than that occurring between acid-washed glass particles (χ2 &gt; 0·001) which in turn was significantly greater than that for untreated glass particles (χ2 &gt; 0·001). The observations and results suggest that the development and maintenance of the observed cell orientation depends upon development and maintenance in the cell sheet of tensional forces oriented parallel to the axis between the dentine particles, and that this is related directly to the capacity of the cells to attach to the particles.
The effects of fibronectin on the migration of human foreskin fibroblasts and syrian hamster melanoma cells into three-dimensional gels of native collagen fibres
Authors: Schor Seth L. , Schor Ana M. , Bazill George W. 
Published: April 2021

ABSTRACTThe effects of fibronectin on the migration of human, skin fibroblasts and Syrian hamster melanoma cells into 3-dimensional gels of native collagen fibres have been examined. Cell migration into the 3-dimensional gel was measured by plating cells on the gel surface and then determining the percentage of cells within the gel at various times thereafter by direct microscopic examination. We find that fibronectin bound to collagen inhibits the migration of human skin fibrobroblasts and stimulates the migration of melanoma cells into the gel matrix. Fibronectin had no apparent effect on cell adhesion to the collagen gels, proliferation or morphology under the conditions studied.
Phagocytosis by macrophages I. kinetics of adhesion between particles and phagocytes
Authors: Ueda Masamichi J. , Ito Tadanao , Ohnishi Shun-Ichi , Okada T. S. 
Published: April 2021

ABSTRACT
A quantitative method for measuring the initial rate of adhesion of foreign particles to mouse peritoneal macrophages, using protein-coated paraffin oil particles, is described. It was performed to measure the rate of adhesion, which is the first step of phagocytosis, separately from the other phagocytic activities. Kinetic studies showed that the cell-substrate adhesion was a Michaelis-Menten type reaction, which has two rate indices, Km and V. The effects of various reagents on the adhesion rate were analysed. KCN and NaN3 change the rate by affecting V, while the changes in the rate brought about by chlorpromazine and filipin are due to their effect on the Km. Cytochalasin B decreased the adhesion rate, but colchicine did not. The initial rate of adhesion decreased with decreasing temperature. An Arrhenius plot of the initial rate showed a break at 30 °C, and gave an activation enthalpy of 14-8 kcal for the process at the physiological temperature. No characteristic change in membrane fluidity was found at 30 °C using electron spin resonance spectroscopy.
Polypeptide synthesis in cell cycle mutants of fission yeast
Authors: Dickinson D. P. 
Published: April 2021

ABSTRACT
The cell cycle of a growing cell is characterized by 3 main periodic events: DNA synthesis, mitosis and cell division. These events generally lie in a dependent sequence, in which one event cannot occur unless preceding events have occurred. The existence of dependent sequences of events raises the possibility that at least some of the gene products involved in the events are synthesized in a dependent sequence parallel to the observable events. To test this hypothesis, the patterns of polypeptide synthesis were investigated in 2 types of cell cycle mutant of the fission yeast Schizosaccharomyces pombe: temperature-sensitive cell cycle (ts cdc) mutants, which become blocked in cell cycle progress at the restrictive temperature; and wee 1 mutants, which are defective in size control over nuclear division, and which divide at a small size. Cells of mutants and wild-type cells were labelled with [35S]sulphate under conditions designed to maximize any differences between the labelling patterns of wild-type and mutant cell polypeptides. The polypeptides were then separated by O’Farrell z-dimensional gel electrophoresis, and the patterns compared.
Although both types of mutation affect cell cycle control, and cause a considerable alteration in the relative proportions of cellular components, an examination of over 700 polypeptides detected on gels revealed no qualitative differences between wild-type and mutant cell polypeptides. These results suggest that a large majority of the more abundant polypeptides in the growing cell are synthesized independently of cell cycle controls directly related to DNA synthesis and division, and that the synthesis of these polypeptides can occur in the absence of normal progress through the cell cycle. Dependent sequences of gene expression do not appear to make a significant contribution to total polypeptide synthesis during the cell cycle, or to the occurrence of periodic cell cycle events such as mitosis. It is suggested that such cell cycle events may result largely through the reorganization of existing cellular components, rather than by the synthesis of new ones.
An unsuccesful attempt was made to detect the wee 1 gene product on gels by surveying a range of mutants for changes in an individual spot. The limitations of gel electrophoresis for this type of survey, and other cell cycle experiments, are discussed.