bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subplasmalemmal calcium-binding microregions in Acanthamoeba
Authors: Sobota A. 
Published: April 2021

ABSTRACT
Acanthamoeba cells, fixed with glutaraldehyde supplemented with calcium ions, show Ca-dependent, electron-dense deposits (CaDD) at the cytoplasmic surface of the plasma membrane. The formation of CaDD is stimulated by pre-incubation and fixation of the cells in the presence of ATP. Chemical analysis of the trichloroacetic acid extracts of CaDD-containing cells demonstrates that adenosine monophosphate, pyrophosphate and inorganic phosphate are probably the compounds involved in the formation of CaDD. Treatment of CaDD-containing cells with exogenous phosphatase evokes the disappearance of electron-dense material and a fine fibrillar network can be observed inside the ‘empty’ CaDD. The ability to restore CaDD in the presence of calcium ions with either pyrophosphate or orthophosphate confirms the suggestion that calcium/phosphate salts may be deposited in special subplasmalemmal calcium-binding microregions.
Attachment of sponge cells to collagen substrata: Effect of a collagen assembly factor
Authors: Diehl-Seifert Bärbel , Kurelec Branko , Zahn Rudolf K. , Dorn August , JeriČevic Biserka , Uhlenbruck Gerhard , Müller Werner E. G. 
Published: April 2021

ABSTRACT
Collagen, isolated from the sponge Geodia cydonium in the absence of denaturing agents, had the typical amino acid composition and was associated with the carbohydrates galactose and glucose. The resulting individual fibrils with a diameter of 23 nm, displayed a 19-5 nm periodicity with one intraperiod band. A collagen assembly factor (CAF) was identified in and partially purified from the extracellular space. The CAF reacted with antibodies against intact Geodia cells but not with antibodies against Geodia lectin and Geodia aggregation factor. In the presence of the CAF, the collagen fibrils reconstituted collagen bundles in an ordered sequence of events, which were followed by electron-microscopical and biochemical methods. Bundle formation was not dependent on the presence of the homologous lectin, glycoconjugates or aggregation factor. Homologous cells (Geodia archaeocytes) were determined to attach only to those Geodia collagen substrates that contained CAF. The attachment of these cells did not require fibronectin or Geodia lectin. Homologous glycoconjugates or NaOH-treated collagen inhibited cell attachment. Collagen from the sponge Chondrosia reniformis, even in the presence of Geodia CAF, was no appropriate substrate for Geodia cell attachment. Whether collagen is a component of cell-matrix interactions in sponge systems also in vivo is discussed.
Role of particle electrostatic charge in adhesion and ingestion in Dictyostelium discoideum amoeboid cells
Authors: Hellio Raymond , Ryter Antoinette 
Published: April 2021

ABSTRACT
The use of colloid iron hydroxide, Alcian Blue and enzymic treatments confirmed that the negative charges of Dictyostelium discoideum cell surface are mostly due to carboxylic groups. The role of electrostatic charges in adhesion and ingestion was determined by exposing cells to untreated latex beads, polylysine or polyglutamic-acid-coated beads, or carboxylated beads. This study showed that negatively charged beads presented a weaker adhesion strength than positively charged ones and that adhesion was strongest with untreated beads. This shows that hydrophobic forces are stronger than those induced by opposite electric charges between particle and cell surface. The ingestion rate was not directly related to adhesion because negatively charged beads presented the highest phagocytic rate, polylysine-coated beads had the lowest and neutral beads an intermediate one.
The treatment of cells with polylysine or polyglutamic acid before neutral bead addition generally enhanced the ingestion rate. Electron microscopic observations made on polylysine-treated cells showed, however, that this stimulating effect was not due to the presence of the polymer on the cell surface but to a membrane clearance phenomenon occurring during polymer elimination.
All these observations have led to the conclusion that the electric charges of the particle do not play a major role in D. discoideum phagocytic ability. Hydrophobic forces and probably other unknown parameters related to the cell surface properties are more important.
Studies on the mechanism of hydrated collagen gel reorganization by human skin fibroblasts
Authors: Guidry Clyde , Grinnell Frederick 
Published: April 2021

ABSTRACT
During reorganization of collagen gels by human skin fibroblasts the total protein content of the gels remained approximately constant. Only 5% of the collagen was degraded, although the volume of the gels decreased by 85% or more. It could be concluded, therefore, that gel reorganization required physical rearrangement of pre-existing collagen fibrils rather than degradation of the original collagen and resynthesis of a new matrix. Collagen molecules in the gels were not covalently crosslinked or otherwise modified enzymically during gel reorganization, as determined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and collagen re-polymerization studies. Serum was required for gel reorganization and, in the absence of serum, cell spreading was predominantly filipodial, i.e. there was little cytoplasmic reorganization. At the electron-microscopic level it was found that many more collagen fibrils became associated with the cells in the presence of serum than in its absence. Serum was also found to promote the synthesis and secretion of proteins by the cells, and conditioned medium could take the place of serum in promoting gel reorganization. The involvement of cell-secreted factors was also demonstrated by the ability of cycloheximide to inhibit gel reorganization. Finally, when gel reorganization was stopped by adding cytochalasin D to the incubations or removing cells by detergent treatment, a small but significant re-expansion of the collagen fibrils was observed. Consequently, a portion of the collagen that had been physically reorganized by the gels was unstable and could not hold its position without continued force exerted by the cells.
Suppression of malignancy in hybrid cells: The mechanism
Authors: Harris Henry 
Published: April 2021

ABSTRACT
When malignant cells, defined by their ability to grow progressively in genetically compatible hosts, are fused with diploid fibroblasts of the same species, the resulting hybrid cells, so long as they retain certain specific chromosomes donated by the diploid parent cell, are non-malignant. When these particular chromosomes are eliminated from the hybrid, the malignant phenotype reappears, and the segregant cell is again able to grow progressively in vivo. In the present experiments the histological character of the lesions produced by the inoculation of crosses between malignant and non-malignant cells was examined. It was found, in a wide range of material, and without exception, that where one or other of the parent cells in the cross was of fibroblastic lineage, malignancy was suppressed when the hybrid cells produced a’collagenous extracellular matrix in vivo; and it reappeared when genetic segregants were produced that had lost the ability to produce this matrix. These results are interpreted in terms of a general model in which it is proposed that the progressive multiplication of malignant cells in vivo is a secondary consequence of a genetically stable impairment of terminal differentiation.
Influence of vinblastine sulphate on the deployment of microtubules and ribosomes in telotrophic ovarioles
Authors: Stebbings H. 
Published: April 2021

ABSTRACT
Ovarioles of Notonecta glauca glattca have been treated with vinblastine sulphate (VBL),primarily to examine the effects of the drug on the microtubules which pack the trophic core and nutritive tubes, 10–4 M VBL had little effect on the microtubules. VBL at 10–3 M reduced the number of microtubules in nutritive tubes, while after 2 ×10–3 M VBL microtubules were rare. All 3 concentrations of VBL induced the formation of crystalline structures in the trophic coreand nutritive tubes, and to a lesser extent in the nutritive cells and follicle cells. In transverse sections crystals appeared to be composed of distinct hexagonal units and in longitudinal sections crystals showed as dark parallel lines with darker dots at regular intervals along their length. With 10–4 M VBL, the crystals were compact and close to the walls of nutritive tubes, but after treatment with stronger concentrations of VBL the crystals were web-like and scattered over cross-sections of tubes.
In addition to VBL having a destructive effect on the microtubules in the trophic core and nutritive tubes, there was also a reduction in the number of ribosomes. This overall reduction in ribosome quantity could not be attributed to the inhibition of RNA synthesis by VBL.
In regions of ovarioles where microtubules were arranged in parallel masses, as in the nutritive tubes and trophic core, the long axes of crystals were always similarly aligned. Other wise crystals were randomly oriented. The possible mode of formation, and composition, of crystals is discussed.
Microtubules in the heliozoan axopodium: iii. degradation and reformation after dilute urea treatment
Authors: Shigenaka Y. , Roth L. E. , Pihlaja D. J. 
Published: April 2021

ABSTRACT
The precise microtubule array present in the heliozoan axopodium has been studied by experimental degradation by using the protein denaturing agent urea. Since concentrations used in typical applications were found to destroy the whole organism immediately, very dilute solutions, usually 0·15 M, were used to study axopodial retraction, which was shown to occur in 2 stages: the distal half reacts immediately and is lost in very few minutes, largely by release of segments, while retraction of the proximal half may extend over an hour. Recovery of axopodial length by removal of organisms to distilled water is possible if treatment is not carried to full axopodium loss, though organisms must be treated with solutions more dilute than 0·1 M to avoid lysis. Electron-microscopic study of retracting axopodia showed degradation of micro tubules at innumerable points even in the proximal regions. Similar studies of untreated organisms showed that the typical microtubule array is found throughout the proximal portion but is progressively imprecise in the distal portion as the tip is approached. High lability to urea is therefore correlated with reduced order and reduced numbers of long linkage elements in the microtubule array. An intra-microtubule metastability is proposed and is discussed with regard to the formation of axonemes, the use of dilute urea to test microtubule stability differences, and the gradion hypothesis presented in previous work.
Studies on the structure and cellular location of various ribosome and ribosomal rna species in the green alga Chlamydomonas reinhardi
Authors: Bourque D. P. , Boynton J. E. , Gillham N. W. 
Published: April 2021

ABSTRACT
Under ionic conditions effecting little or no subunit dissociation, Chlamydomonas reinhardi contains 2 major classes of ribosomes with generic sedimentation velocities of 83 and 70s and 3 minor classes with sedimentation velocities of 66, 54, and 41 s. Ribosomal RNAs with sedimentation velocities of 25, 23, 18, 16 and 5 s have been identified. The 70-sribosomes are in the chloroplast and contain 23-, 16- and 5-s ribosomal RNA whereas the 83-s ribosomes are in the cytoplasm and contain 25-, 18- and 5-s ribosomal RNA. Numbers of chloroplast ribosome particles counted in electron micrographs of wild type C. reinhardi and the ac-20 and y mutants have been compared with relative amounts of 70-s ribosomes determined by sucrose gradient sedimentation and amounts of 23-, 16-and 5-s ribosomal RNA determined by gel electrophoresis. In response to reduced concentrations of magnesium the 70-s ribosomes of wild type are susceptible to a progressive reduction in sedimentation velocity whereas the 66-s ribosomes of the mutant ac-20 are not. Chlorophyll synthesis and the formation of the chloroplast lamellar system do not appear to be correlated with the relative amounts of chloroplast ribosomes.
Red-light stimulation of prolamellar body recrystallization and thylakoid formation in barley etioplasts
Authors: Berry D. R. , Smith H. 
Published: April 2021

ABSTRACT
The etioplasts of fully dark-grown barley leaves exhibit a relatively low frequency of crystalline prolamellar bodies (ca. 16–20%). Brief red-light treatment leads to rapid disruption of all prolamellar bodies followed by a slow reformation in the subsequent dark period. When several red-light treatments are given with intervening 3-h dark periods, a marked increase in the proportion of crystalline prolamellar bodies is seen. It is suggested that this phenomenon may be associated with the regeneration of protochlorophyll.
Red-light pretreatment stimulates the formation of granal thylakoids upon subsequent transfer to continuous white light. This response is correlated with the phytochrome-mediated shortening of the lag phase in chlorophyll-synthesis under identical conditions.
Regular arrays of hexagonal tubules 16–19 nm in diameter have been observed often in close juxtaposition to the newly forming thylakoid membranes. These may be aggregations of Fraction I protein, although their exact nature and function is at present Unknown.
Fine structure study of pollen development in Haemanthus katherinae baker: I. formation of vegetative and generative cells
Authors: Sanger Jean M. , Jackson W.T. 
Published: April 2021

ABSTRACT
When microspores of the African blood lily divide, they form pollen grains which consist of 2 cells of unequal size. This is accomplished when the microspore nucleus is displaced from the centre of the grain prior to division. The displacement is always towards the side of the grain opposite the furrow, and large vacuoles form in the cytoplasm between the furrow and the nucleus. During cell division the cell plate curves around one daughter nucleus and fuses with the pollen wall to enclose the generative cell. The cell-plate attachment always occurs with the wall that is opposite the furrow of the grain. Most of the microspore’s organelles become incorporated in the larger vegetative cell, whereas the generative cell has few, if any, plastids and only a small number of other organelles. The wall around the generative cell is composed of finely fibrillar material enclosed within 2 unit membranes. The generative cell eventually becomes detached from the pollen wall, becomes spheroidal, and moves to a position near the centre of the pollen grain. At the same time, the large vacuoles disappear from the vegetative cell and the number of organelles increases substantially.
Fine structure study of pollen development in Haemanthus katherinae baker: III. changes in organelles during development of the vegetative cell
Authors: Sanger Jean M. , Jackson W. T. 
Published: April 2021

ABSTRACT
The newly formed vegetative cell of the pollen grain of the African blood lily has a spheroidal nucleus, few dictyosomes, and a small amount of endoplasmic reticulum. Plastids are smaller than those of the microspore and usually lack starch granules. Mitochondria and lipid bodies are more numerous than they were in the microspores, but their appearance is unchanged. As the pollen grain matures, the vegetative nucleus becomes irregular in shape. There is a dramatic increase in the number of dictyosomes, starch accumulates in the plastids, and a moderately well developed system of endoplasmic reticulum appears in the form of fiat cisternae. In the developmental period immediately preceding anthesis, the vegetative nucleus becomes lobate and small nucleoli replace the large nucleoli present earlier. Plastids lose their starch, lipid bodies disappear, and the endoplasmic reticulum becomes vesicular in this final stage before germination.
The contractile mechanism in obliquely striated body wall muscle of the earthworm, Lumbricus terrestris
Authors: Knapp M. F. , Mill P. J. 
Published: April 2021

ABSTRACT
Obliquely striated muscle fibres from the longitudinal and circular layers of the body wall of the earthworm were prepared in extended and contracted states for study in the electron microscope.
Contracted fibres differ from extended ones in the following respects: (i) the I-bands are narrower, (ii) the A-bands are wider, and (iii) there are more rows of thick myofilaments in each A-band.
The arrangement of the thick and thin myofilaments in interdigitating arrays and the occurrence of cross-links between the 2 types of myofilament indicate a classical sliding-filament mechanism of contraction as in cross-striated muscle, resulting in a reduction in the I-band width.
The increase in the A-band width could be due to a moving apart of the myofilaments during contraction to preserve constant volume of the lattice.
The third change, the increase in the number of rows of thick myofilaments in the A-band, can be explained only by a shearing of these filaments past one another in such a way as to increase the amount of their overlap.
The role of the sliding-filament and shearing contraction mechanisms in bringing about the changes observed in earthworm muscle fibres is considered and the possible correlation of these mechanisms with certain physiological data is discussed. The function of the sarcoplasmic reticulum in the transmission of impulses to the interior of the fibre and/or in the control of the contraction mechanism is also discussed.
Surface features of smooth muscle cells from the mesenteric artery and vas deferens
Authors: Devine C. E. , Simpson F. O. , Bertaud W. S. 
Published: April 2021

ABSTRACT
Smooth muscle cells of small mesenteric arteries and vas deferens of guinea-pig were examined by freeze-etching. The most striking finding was that the surface vesicles lie in roughly longitudinal rows, with areas of membrane free of vesicles in between. The areas free of vesicles are believed to correspond to areas occupied by dense bodies in conventionally fixed and sectioned material. Other cell constituents which could be identified included sarcoplasmic reticulum and, probably, thick myofilaments.
The fine structure of the surface epithelium of the human ovary
Authors: Papadaki Lucienne , Beilby J. O. W. 
Published: April 2021

ABSTRACT
The surface epithelium has been studied on human adult ovarian biopsies, one foetal ovary and an ovarian biopsy from a woman 12 weeks pregnant. In the adult, the surface of the ovary is covered by a single, patchy layer of epithelium which varies from squamous, through cuboidal to columnar in shape. Cytoplasmic projections extend into the peritoneal cavity from the free surface of the cells and their lateral borders are connected by desmosomes. The nucleus is irregular and the dense cytoplasm contains many polysomes, free ribosomes and tono-filaments. Intracellular vacuoles and extracellular channels contain materials of low to moderate density. Lipid droplets and compound aggregates are present and both coated and smooth vesicles occur in the peripheral cytoplasm. Focal degenerative changes may be seen which range from loss of density in the basal cytoplasm to complete desquamation.
In pregnancy the basal surface of the epithelium is deeply infolded with an increase in cytoplasmic lipid. In the foetal ovary the entire surface is covered with an epithelium.
From these studies and the work of others, it seems clear that, although the prime function of the ovarian surface epithelium is its contribution of pregranulosa cells during foetal development, many features remain which suggest that it has an important role in transport. It may also influence follicular development in the foetus and appears to have some potential for steroid metabolism. The patchiness and degenerative changes found in the adult human ovary may be related to fluctuations in hormonal balance.
The cytoplasmic incorporation of tritiated thymidine during oogenesis in Pteridium aquilinum
Authors: Sigee D. C. , Bell P. R. 
Published: April 2021

ABSTRACT
The short-term incorporation of tritiated thymidine into the cytoplasm of cells undergoing oogenesis was investigated in Pteridium aquilinum using electron-microscope autoradiography. There was substantial uptake into the central cell and egg cell during the 6-h labelling period. The quantity and distribution of the label incorporated into the cytoplasm were closely similar in cells fixed immediately after the labelling period and in those immersed for a further 18 h in unlabelled thymidine. This suggested that incorporation was into a stable molecule, with little nucleoside turnover and no subsequent migration within the cytoplasm. Enzyme studies indicated that the tritiated thymidine was incorporated almost entirely into DNA, most probably the DNA undergoing replication.
Within the cytoplasm the label was markedly and consistently concentrated in plastids and mitochondria. This localization was not, however, complete and 5–40% was attributable to sites in the ground cytoplasm.
A gradient of incorporated label was demonstrated within the cytoplasm in both central cells and egg cells. Concentration was high adjacent to the nucleus and low at the cell periphery. This gradient could be satisfactorily explained by the distribution of the plastids and mito-chondria within the cytoplasm, the labelling of the organelles being irrespective of their position. The results of statistical examination of the frequencies of the silver grains associated with the mitochondria and plastids were considered to indicate general uptake of label directly into the DNA of these organelles without nuclear participation.
Electron stereoscopy as a means of classifying synaptic vesicles
Authors: Dennison Marion E. 
Published: April 2021

ABSTRACT
In addition to the well known ‘round’ synaptic vesicles, 2 distinct types of ‘flat’ vesicle have been found by electron stereoscopy of aldehyde-fixed central nervous tissue. In the goldfish spinal cord presynaptic terminals are found which contain cylindrical vesicles, and others which contain disk-shaped vesicles. In the rat olfactory bulb no cylindrical vesicles are found; all the flat vesicles there appear to be disk-shaped.
The distribution of electron-dense tracers in peripheral nerve fibres
Authors: Hall Susan M. , Williams P. L. 
Published: April 2021

ABSTRACT
Two electron-dense tracers, ferritin and lanthanum, have been administered to peripheral nerve fibres, and their uptake has been studied ultrastructurally. It was found that the peri-neurium was an effective barrier to ferritin in vivo, and the tracer was subsequently injected sub-perineurially. Ferritin uptake over a 120-min period was confined to occasional phagocytic vesicles in perineurial and Schwann cells, and to the nodal gap substance and paranodal peri-axonal space. No uptake was observed in the myelin sheath, incisural intraperiod line gap, or in the axoplasm. Soaking fibres in ferritin in vitro resulted in a more generalized cytoplasmic and axoplasmic uptake, although the myelin sheath and Schmidt-Lanterman incisures remained devoid of the tracer.
Lanthanum nitrate, included in the fixative solution, delineated the patent incisural intra-period line gap, and outlined the external surface of the terminal loops of nodal Schwann cell cytoplasm, and the paranodal Schwann cell-axolemmal junction. Unlike ferritin, La3+ penetrated the myelin sheath, being usually confined to the intraperiod line region of the outer lamellae, where it was associated with a widening of the lamellar unit, and an apparent splitting of the intraperiod line.
The results are discussed with regard to distribution of extracellular space in peripheral nerve fibres.