bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhibition of cell division in amoebae: the incorporation of tritiated precursors into Amoeba proteus after the injection of non-homologous cytoplasm
Authors: Cameron J. M. , Hawkins Shirley E. 
Published: April 2021

ABSTRACT
The injection of non-homologous cytoplasm into any strain of large free-living amoebae leads to a 60 % inhibition of division amongst recipient cells. When the post-microsomal supernatant fraction of Amoeba discoides was injected into A. proteus, this inhibition of division was as high as 95 %. The incorporation of tritiated precursors, either [3H]uridine or 3H-amino acids, into these inhibited amoebae was studied at various times after the injection of the inhibitory material using autoradiography.
When cells were grown in [3H]uridine, autoradiographs indicated that RNA synthesis had ceased 2 days after the injection of non-homologous material. However, if [3H]uridine was injected into the inhibited cells, some synthesis of RNA could be detected up to 4 days after the injection of inhibitor. These results suggested that uptake of [3H]uridine was impaired and that one site of action of the inhibitory molecules was RNA synthesis for membrane components.
Experiments with a variety of 3H-amino acids suggested that protein synthesis continued for at least 9 days after the injection of non-homologous cytoplasm, and that in these cells some informational RNA molecules were long-lived. There seemed to be accumulation of material containing [3H]lysine in the nuclei of control cells taken at random from cultures, and this was seen in the nuclei of inhibited cells 1 day after injection. However, 2 days after the injection of inhibitor, no accumulation of [3H]lysine-containing material was found in the nuclei.
Similarities between platelet contraction and cellular motility during mitosis: role of platelet microtubules in clot retraction
Authors: Chao F. C. , Shepro D. , Tullis J. L. , Belamarich F. A. , Curby W. A. 
Published: April 2021

ABSTRACT
The effects of inhibitors of mitosis, energy metabolism and protein synthesis on clot retraction were investigated. The results show that (1) Incubation of colchicine (0·01–0·1 mM) with platelet-rich plasma (PRP) inhibits the subsequent retraction of clots derived from diluted PRP. (2) Inhibition of clot retraction by high concentrations of colchicine (up to 40 mM) can be overcome by increasing the platelet concentration in the system. (3) Incubation of clots in colchicine or 80 % D2O solutions inhibits their retraction. Exposure of partially retracted clots to these agents is without effect. (4) Hydrostatic pressure retards clot retraction. (5) Incubation of PRP with either 2-deoxy-D-glucose or antimycin alone does not affect clot retraction, but a combination of these agents is inhibitory. (6) Clot retraction is not inhibited by puromycin or cycloheximide. (7) Platelets in retracting clots have constricted regions containing microfilaments and pseudopods containing microtubules. Fibrin strands are progressively condensed around the constricted regions as retraction advances. (8) The development of platelet constriction, platelet pseudopods and the intracellular microfilaments are delayed in colchicinized clots, corresponding to the retardation of retraction. Following the initial delay of retraction colchicinized clots, like controls, show condensation of fibrin strands adjacent to these constricted areas of platelets containing microfilaments. The formation of pseudopods is impaired and no microtubules are found in platelets in the presence of colchicine. The above results suggest that the thrombin-induced platelet contraction during clot retraction is a coordinated movement, which, under optimal conditions involves both microtubules and microfilaments. The contraction of microfilaments produces the constriction of platelets and brings about clot retraction by reducing the angle between fibrin strands. Platelet microtubules are related to the development of pseudopods and play a supplementary role in facilitating microfilament-mediated cellular constriction. The similarities between platelet contraction and cellular motility in mitosis is discussed.
The morphology of green Hydra endosymbionts as influenced by host strain and host environment
Authors: Pardy R. L. 
Published: April 2021

ABSTRACT
The ultrastructure of Chlorella-like algal endosymbionts from the Florida and English strains of green hydra was compared under different host feeding and photoperiodic regimes. Under standard conditions (host fed daily, 12-h photoperiod) the algae from the 2 strains exhibited considerable differences. The English symbionts had a pyrenoid, compact chloroplast membranes and vesiculated polyphosphate bodies. By comparison, Florida symbionts lacked a pyrenoid, had chloroplasts with less compact membranes and exhibited spherical polyphosphate bodies.
When maintained in the dark, algae from English hydra lost their pyrenoids, showed great compaction of the chloroplast and developed large, shield-shaped, electron-dense bodies. In contrast, algae from Florida hosts did not exhibit gross ultrastructural modification.
Reciprocal cross-transfers of symbionts were made by placing Florida algae in English aposymbiotic (algal-free) hosts and vice versa. After residence in Florida hosts, English symbionts appeared to undergo ultrastructural modifications resulting in a morphology indistinguishable from the native Florida symbionts. Florida algae showed no modifications resulting from residence in English hosts. It thus appears that the English symbiont has great morphological plasticity, as its structure is greatly modified depending upon the host in which it resides and the conditions under which the host is maintained.
The results of these studies are discussed and compared with published accounts of free-living Chlorella and with reports dealing with other Chlorella symbionts.
Brittle fracture of epidermal cells by liquid shear
Authors: Gray G. M. , Yardley H. J. 
Published: April 2021

ABSTRACT
A suspension of epidermal cells obtained from pig tail skin by trypsinization was subjected to high liquid-shear forces in a French press. The material issuing from the press was examined by phase-contrast microscopy, transmission electron microscopy and scanning electron microscopy. The cytoskeleton of tonofibrils retained the shape of cell fragments, and subcellular organelles remained enmeshed in the network of tonofibrils. Examination of some cell fragments by scanning electron microscopy revealed the internal organization of the tonofibrils. The relevance of these findings to the problem of isolating subcellular fractions from epidermis is discussed.
Patterns of calcium localization in pancreatic endocrine cells
Authors: Ravazzola Mariella , Malaisse-Lagae Francine , Amherdt Myléne , Perrelet A. , Malaisse W. J. , Orci L. 
Published: April 2021

ABSTRACT
Subcellular calcium localization in the endocrine cells of rat pancreas was studied by the pyroantimonate precipitation technique. Calcium-containing electron-dense deposits in the endocrine cells were mostly found within secretory granules and along the plasma membrane, but their pattern of distribution in A-, B- and D-cells displayed qualitative and quantitative differences. In B-cells, numerous secretory granules contained deposits located in the halo surrounding the granule core. In A-cells, only few granules contained precipitates in their halo, whereas in D-cells, deposits were situated in the dense core of the secretory granules. Deposits along the plasma membrane occurred generally on the outer leaflet of the plasma membrane of B- and D-cells and on the inner leaflet of that of A-cells. In islets incubated at a high glucose concentration or in the presence of the calcium ionophore A23187, the number of beta granules containing precipitates was significantly increased. By contrast, only few deposits were observed in B-cells incubated in calcium-deprived medium enriched with EGTA. These findings indicate that: the pattern of calcium localization varies in different islet cell types; in B-cells the secretory granules represent one of the major stores of intracellular calcium; and that this store undergoes changes in conditions which alter insulin release.
Subcellular localization of diffusible ions in the yeast Saccharomyces Cerevisiae: quantitative microprobe analysis of thin freeze-dried sections
Authors: Roomans G. M. , Sevéus L. A. 
Published: April 2021

ABSTRACT
In yeast cells, of which the intracellular potassium had been partly replaced by rubidium or caesium, the intracellular ion distribution was studied by means of energy-dispersive X-ray microanalysis. The cells were rapidly frozen and thin sections were cut at low temperature on a cryo-ultramicrotome without the use of a trough liquid. By this dry cryosectioning procedure, complete retention of the diffusible ions in the cells was obtained. Unless the sections had been exposed to moisture, no signs of redistribution were apparent. For quantitative determinations a gelatin standard, containing known amounts of the elements of interest, was prepared in the same way as the cells. The concentrations of potassium, rubidium, caesium and chloride in the nucleus, the cytoplasm and the vacuole could be measured. The intracellular distributions of potassium, rubidium and caesium were very similar. The concentrations of these ions in the cytoplasm were about equal to those in the nucleus and twice those in the vacuole. The total concentration in the cytoplasm was 180–190 mmol/kg fresh weight, in the nucleus 190—200 mmol/kg fresh weight and in the vacuole 75–0 mmol/kg fresh weight. The permeability of the yeast cell for chloride is markedly lower than for the cations.
Distribution and dynamics of nematocyte populations in Hydra Attenuata
Authors: Bode H. R. , Flick Kristine M. 
Published: April 2021

ABSTRACT
The distribution and dynamics of the 4 nematocyte populations of Hydra attenuata were investigated. Ninety-seven per cent of all nematocytes, including all 4 types, are mounted in the battery cells of the tentacles. The remaining 3%, including 2 types (stenoteles and holotrichous isorhizas) are mounted in the ectoderm of the body column. Eighty-two per cent of all nematocytes are desmonemes; 11%, atrichous isorhizas; 5%, stenoteles; and 2%, holotrichous isorhizas. The density of each nematocyte population increases along the length of the tentacle towards the tip. The percentages of the total nematocytes per quarter of tentacle for each of the 4 quarters starting at the base is 15, 18, 25 and 42% respectively.
The turnover time of the nematocyte populations in the tentacles was measured with 2 methods. First, the transit time for a carbon-marked battery cell from the base to the tip of the tentacle was measured. Secondly, the time required to replace the unlabelled nematocytes in the tentacles with [3H]proline-labelled nematocytes was measured. In both cases the time was 7–9 days.
Based on these data (distribution and turnover time) a model was constructed for the dynamics of the nematocyte populations in the tentacles. The numbers of nematocytes produced daily in the body column as predicted by the model are in reasonable agreement with the measured values.
Bhk21 fibroblast aggregation inhibited by glycopeptides from the cell surface
Authors: Vicker M. G. 
Published: April 2021

ABSTRACT
Glycopeptides were removed by trypsinization from the surface of baby hamster kidney cells (line BHKzi-C13), digested by pronase and separated into 2 fractions by exclusion chromatography. The addition of small amounts of either glycopeptide fraction to shaken suspensions of lightly trypsinized cells inhibited their rapid aggregation, but one fraction was more active than the other and in higher concentrations it was able to inhibit aggregation completely. After this fraction was purified by high-voltage electrophoresis one subfraction also inhibited aggregation. The effect of the glycopeptides increased following their pretreatment with neuraminidase, but preincubation with periodiate or galactose oxidase destroyed all activity. Galactose oxidase also inhibited cell aggregation directly. Similar glycopeptides from virus-transformed BHK21 cells, oligosaccharides and intact and desialysed human urinary glycoproteins had comparatively little or no effect on BHK21 cell aggregation. The results suggest terminal β-galactosides and possibly α-galactosides, and to some extent a particular substructure of cell surface heteroglycans are necessary for their inhibitory activity. The parent, plasma membrane glycoproteins might serve as adhesive binding sites in cell cohesion, but some evidence indicates cell surface sialyl- and galactosyltransferases may not ordinarily act as their complementary binding receptors.
A highly infectious ‘mycoplasma’ that inhibits meiosis in the fungusCoprinus
Authors: Ross I. K. , Pommerville J. C. , Damm Deborah L. 
Published: April 2021

ABSTRACTWe have discovered a cytoplasmically inherited infectious agent that inhibits meiosis in a species of Coprinus, a basidiomycetous fungus. From infectivity, filtration, centrifugation and ultrastructural studies we believe the agent to be a mycoplasma. The agent is highly infectious to several strains of the host species and is capable of spreading rapidly through infected hosts. No pathological effect has been seen on any aspect of growth or differentiation of the fungus except for the inability of infected strains to undergo meiosis. The failure of meiosis results in mushrooms that do not produce the normal black spores and are therefore pale in colour. The paleness represents a simple assay for the presence and activity of the infectious agent. Infected hosts do not display any ultrastructural abnormalities in the vegetative stages, only in the cells in which meiosis should occur. In the meiotic cells, at the time when normal cells are undergoing synapsis and synaptinemal complexes are forming, the vacuoles of the infected cells become occupied with vesicular, membrane-bound bodies resembling in shape and form mycoplasmas. Extracts from infected clones may be filtered through 0·2-μm filters and retain full infectivity. The infectious material may be pelleted from such extracts at only 10000g. Migration experiments, as well as the filtration studies, rule out involvement directly of nuclei. The high rate of infection and spread of the mycoplasma through the host, combined with the anatomical simplicity of the host, make this an ideal system in which to study the basis of infection. The singularity of the pathological effect make this host-parasite association useful in studying both the underlying mechanisms of mycoplasma pathogenicity and to investigate the regulation of meiosis. This is only the second report of mycoplasmas in fungi.
Relations between the nuclear activity and the variable 3H-amino acid incorporation pattern in Amoeba Proteus
Authors: Chatterjee S. , Bell L. G. E. 
Published: April 2021

ABSTRACT
Tracer kinetic studies have revealed the existence of a variable pattern of ‘H-amino acid incorporation into amoeba proteins during the early G2 phase of the cell cycle. Two peaks of incorporation of [3H]leucine were found to occur at 19 and 22 h, whereas a single peak at 17 h was noticed in the amoebae labelled with [3H]lysine. An almost 2-fold increase of the labelled amino acid incorporation occurred during the peak periods, while the other periods showed a more or less steady state of incorporation, suggesting a basal rate of synthesis at these times.
In a detailed study involving the peaks and the basal incorporation periods of [3H]leucine, it was shown that the removal of the nucleus or Actinomycin D treatment eliminated the peaks but the base line protein synthesis was not affected. This suggests that for the peak synthetic periods, mRNA is probably transcribed concurrently, followed by immediate translation, whereas long-life mRNA accounts for the basal synthetic activity.
Organization of intramembrane particles in freeze-cleaved gap junctions of rat graafian follicles: optical-diffraction analysis
Authors: Amsterdam A. , Josephs R. , Lieberman Mara E. , Lindner H. R. 
Published: April 2021

ABSTRACT
Gap junctions were identified in the membrana granulosa and cumulus oophorus, and between cells of the internal theca, of the preovulatory rat follicle. In replicas of freeze fractured follicles, the A face presented clusters of closely packed intramembrane particles, 7—9 nm in diameter, forming a mosaic pattern, while the B face showed a similar pattern of small pits. Optical diffraction analysis of these electron micrographs revealed that both the intramembrane particles and the corresponding pits were organized in hexagonal lattices with centre-to-centre spacing of 9—10 nm. In small junctions (up to 0·4 μm in diameter), both A and B faces generally consisted of a single lattice, while large junctions (0·5–2 μm) contained multiple lattices differing in orientation. Occasionally intramembrane particles and pits were more loosely arranged throughout the junctional area and failed to show a hexagonal pattern.
Both granulosa and thecal cells often contained intracellular vesicles resembling annular junctions. These contained intramembrane particles whose assembly resembled that of the gap junctions with regard to periodicity and lattice organization. Examination of thin sections suggested that small gap junctions occur also between cytoplasmic processes of coronal cells and the oolemma. No tight junctions were detected between granulosa cells and between thecal cells.
Differentiation for aggregation in the cellular slime moulds: the emergence of autonomously signalling cells in Dictyostelium Discoideum
Authors: Raman R. K. , Hashimoto Yohichi , Cohen M. H. , Robertson A. 
Published: April 2021

ABSTRACT
The results of experiments on small populations of Dictyostelium discoideum, directed towards the measurement of the development in time of the competence of the cells to signal autonomously, are reported. This competence is quantified by Xs, the intrinsic probability that a given cell may turn autonomous. The data show an early exponential growth in time of X3, followed by saturation. The saturation value depends on the population size suggesting that the differentiation is a co-operative phenomenon. The differentiation of autonomous cells starts roughly 7 h after the removal of food and saturates within 21h.
Metabolic requirements for interactions between nuclear and cytoplasmic membranes in the repair of damaged amoeba nuclei
Authors: Flickinger Charles J. 
Published: April 2021

ABSTRACTAmoeba nuclear envelopes were damaged using microsurgery, and metabolic requirements for the steps in their repair were studied, by placing the cells in a solution containing one of several metabolic inhibitors. The first step in repair, the association of pieces of endoplasmic reticulum with holes in the nuclear membranes, appears to be a passive process since it was not affected by inhibitors of energy production, RNA synthesis, or protein synthesis. In contrast, fusion of pieces of endoplasmic reticulum with the nuclear membranes at the margins of the holes was blocked by KCN and dinitrophenol, indicating that membrane fusion requires energy derived from respiration, but RNA and protein synthesis inhibitors did not prevent fusion of pieces of endoplasmic reticulum with the nuclear membranes. The subsequent completion of repair and restoration of intact nuclear membranes was almost completely blocked by inhibitors of respiration, and it was reduced in the presence of actinomycin and emetine, suggesting that in addition to a requirement for energy, some later steps in the repair of the nuclear membranes require RNA and protein synthesis.
Electron-microscope observations on cell nuclei in various tissues of a teleost fish: the nucleolus-associated monolayer of chromatin structural units
Authors: Davies H. G. , Haynes M. E. 
Published: April 2021

ABSTRACT
Observations on stain uptake by thin sections through condensed interphase chromosomes in cells from epithelial and muscle tissue in kidney and intestine, and also in fibroblasts, show a distribution into DNA-rich and DNA-poor phases similar to that already described in cells from the connective tissue blood. In all the nuclei the nucleolus, when adjacent to the nuclear envelope, is separated from the inner membrane by a monolayer of chromatin structural units, similar to the monolayer enclosed on both sides by nuclear envelope, previously described in a wide variety of organisms. The data provide further support for the hypothesis that the condensed interphase chromosomes in eukaryotes are characterized by essentially similar structural units folded to form similar patterns. This hypothesis, regarding the higher order units, is consistent with data of others which show that histones and DNA fold to form similar repeating subunits in chromatin, irrespective of the base sequence in the DNA and the origin of the histones.
Ultrastructural site variations in mouse epidermal organization
Authors: Allen T. D. , Potten C. S. 
Published: April 2021

ABSTRACT
Mouse dorsal, ear, tail and foot epidermis are compared according to their tissue architecture and cell kinetics. Cell proliferation is expressed in terms of the daily volume of keratin replaced. The stratum corneum may be organized into vertical columns of squames, which may have minimal overlap as in dorsum and ear, or maximal overlap as in tail. Individual areas are adapted to their function both in squame fine structure and rate of cell replacement. The surface keratin loss/replacement rate is at its highest in foot and tail, and lowest in ear and dorsum. Observations on hairless mouse dorsum are also included.
The blepharoplast of Marsilea: its De Novo formation and spindle association
Authors: Hepler P. K. 
Published: April 2021

ABSTRACT
Blepharoplast formation and function has been investigated by light and electron microscopy in developing microspores of the water fern Marsilea vestita. When single-celled microspores are hydrated they undergo a series of 9 cell divisions producing 7 sterile cells plus 32 spermatids. The blepharoplast, a densely staining, spherical inclusion (0·5–1·0 μm in diameter) interpenetrated by numerous lightly stained channels, is a precursor organelle for the production of the 100—150 basal bodies of the motile sperm. During development it arises twice in the dividing spermatogenous cells; first in telophase of the second to last or 7th division, and again in telophase of the next to last or 8th division. The blepharoplast first forms on the distal side of the nucleus during telophase of the 7th division but soon degenerates as the cell enters prophase and metaphase of the 8th division. During telophase of the 8th division the blepharoplast again arises in the cytoplasm near a small indentation of the nuclear envelope. The forming blepharoplast consists of a sphere of lightly stained flocculent material within which 2 plaques separated by 40–50 nm arise. Each plaque possesses 2 dense layers (20 nm) separated by a light layer (10 nm). During subsequent development the distal layer of each plaque becomes progressively more densely stained. Light-staining channels appear within the accumulating dense material and 2 hemispherical blepharoplasts emerge. The blepharoplasts become spherical through continued growth and finally separate from each other as they move to the spindle poles during prophase of the last or 9th division.
The blepharoplast appears to act as a microtubule organizing centre during formation of the spindle apparatus in prophase of the 9th division. While it remains at the pole throughout mitosis it does not continue to serve as the focal point for the spindle tubules. During metaphase-anaphase of the 9th division the blepharoplast swells, and the channels at its surface begin transforming into procentrioles and finally basal bodies.
The results support the contention that basal bodies in Marsilea arise de novo, since no preexisting template such as a centriolar pinwheel is observed and since the intermediates which initially occur are structurally dissimilar from a procentriole.