bluuebunny/crossref_metadata_2025_split huggingface dataset:
In vivo transcription of ribosomal rna in relation to the mitotic cycle in Physarum polycephalum*
Authors: Hunter G. J. , Turnock G. 
Published: April 2021

ABSTRACT
We have investigated the transcription of ribosomal RNA in plasmodia of Physarum polycephalum by a combination of pulse-labelling with [3H]uridine and RNA; DNA hybridization. The DNA used for the hybridization was a Hindlll restriction fragment (cloned in bacteriophage λ) of Physarum ribosomal DNA that carries a substantial fraction of the rRNA genes, enabling the ribosomal transcripts in the newly synthesized RNA to be measured. We found that ribosomal RNA constituted about 40 % of the pulse-labelled RNA at all times during the synchronous mitotic cycle.
Changes in the shape of mitochondria following osmotic stress to the unicellular green alga Chlamydomonas reinhardii
Authors: Morris G. J. , Coulson G. E. , Leeson E. A. 
Published: April 2021

ABSTRACT
The effects of various stresses on mitochondrial activity and structure within the unicellular green alga Chlamydomonas reinhardii were investigated using the fluorescent probe rhodamine 123. Within control cells, treatment with rhodamine 123 stained an intense fluorescent network, which was considered to be mitochondrial from the similarity in structure to models of mitochondria reconstructed from serial-section electron microscopy, and because this pattern of staining was abolished following the addition of metabolic inhibitors.
Following osmotic shrinkage and rehydration, fragmentation of the mitochondrial network was observed within potentially viable cells. This was reversible within 1 h of resuspension in isotonic medium. Exposure of cells to hypertonic solutions of rapidly permeating compounds did not induce similar structural alterations. These changes in the mitochondria were confirmed by thin-section electron microscopy. In the presence of higher osmolalities of non-permeating compounds, which induce a greater loss of viability, rhodamine 123 stained cells uniformly. Following the osmotic stresses induced by slow rates of freezing and subsequent thawing no fragmentation in mitochondrial staining was observed. These findings demonstrate that shrinkage and rehydration may induce alterations to the structure and function of organelles and may be factors in determining cellular viability following osmotic stress.
Defective adhesion to extracellular matrix leads to altered social behaviour in cultured fibroblasts
Authors: Aplin John D. , Foden Lynn J. 
Published: April 2021

ABSTRACT
We describe the properties of variant mouse fibroblasts selected for poor adhesion to growth substratum containing subcellular matrix accumulated by adherent cells at confluence. The variant cells adhere to virgin plastic and grow normally to confluence in the presence of serum. After subculture and reseeding onto the same surface the cells initially adhere, but after a further 2 days of growth they retract into aggregates and detach. If the aggregates are dispersed and cells reseeded onto the same surface they remain rounded. However, if the same cells are added back to virgin plastic they adhere and grow normally. The retraction can be abolished by treating the subcellular matrix-coated plastic with papain. This behaviour therefore reflects the ability of the cells to modify the composition of the underlying substratum during growth. The variant cells also exhibit retraction 2 days after seeding on a surface previously containing wild-type cells at confluence, while wild-type cells do not retract on subcellular matrix deposited by variants. This shows that the variant behaviour arises not from a deficiency in the subcellular matrix, but from an alteration in the adhesive capacity of the cells. The results are interpreted in terms of three putative adhesion mechanisms: cell–cell adhesion in confluent monolayers and aggregates; ‘early’ type cell–substratum adhesion, which occurs during culture on virgin plastic; and ‘late’ type cell–substratum adhesion occurring on surfaces containing accumulated subcellular matrix. The variant phenotype is characterized by a deficiency in the last of these. It is also associated with an increased ability to grow in suspension culture at high dilution.
Measurements of intracellular ph and its relevance to cell differentiation in Dictyostelium discoideum
Authors: Inouye Kei 
Published: April 2021

ABSTRACT
A method was developed in this study to measure the intracellular pH (pHi) of Dictyostelium discoideum cells with a pH-sensitive fluorescence dye, carboxyfluorescein dibutyrate, and the pHi values of cells on the stalk and spore pathways were compared. The pHi of prestalk cells was lower than that of prespore cells by approximately 0·3 pH unit. In monolayer cultures of sporogenous mutants, which can differentiate into stalk cells and spores without cell contact, the pHi of the amoebae depended on the medium: media in which the majority of cells eventually become stalk cells reduced the pHi while conditions favouring spore formation increased the pHi. Addition of weak acids lowered the pHi.
These results are in good accordance with the model presented by Gross and coworkers, which proposes that the choice between alternative pathways of cell differentiation is regulated via pHi and that low pHi favours stalk differentiation whereas high pHi favours spore formation.
Binding and uptake of the toxic lectin modeccin by baby hamster kidney (BHK) cells: Isolation of mutants defective in the internalization of modeccin
Authors: Gleeson Paul A. , hughes R. Colin 
Published: April 2021

ABSTRACT
The effects of the toxic lectins, ricin and modeccin, on baby hamster kidney (BHK) cells have been compared. Modeccin is about 20–50 times more toxic to BHK cells than ricin. Binding studies showed that there are 105 to 2 × 105 modeccin binding sites/cell compared with approximately 107 binding sites for ricin. Inhibition studies with galactosides indicate that both N- and O-glycans with terminal galactosyl residues are effective inhibitors of modeccin binding. Surface-bound modeccin, at O°C, was found to be very rapidly endocytosed (75–80% in 10 min) when cells were warmed to 37°C.
Two modeccin-resistant BHK cell lines have been isolated and characterized. These mutants bind normal levels of modeccin and retain sensitivity to the toxic action of ricin. Both cell lines were shown to be defective in their ability to internalize modeccin. Also, these mutants are morphologically different from parental cells as they align and elongate very prominently at low cell densities. These mutants will be very useful in understanding the mechanism of uptake and transport of modeccin.
Microtubules in root hairs
Authors: Traas Jan A. , Braat Paul , Emons Anne Mie C. , Meekes Herman , Derksen Jan 
Published: April 2021

ABSTRACT
The microtubules of root hairs of Raphanus sativus, Lepidium sativum, Equisetum hyemale, Limnoblum sloloniferum, Ceratopteris thalictroides, Allium sativum and Urtica dioica were inves-tigated using immunofluorescence and electron microscopy. Arrays of cortical microtubules were observed in all hairs. The microtubules in the hairs show net axial orientations, but in Allium and Urtica helical microtubule patterns are also present. Numerical parameters of microtubules in Raphanus, Equisetum and Limnobium were determined from dry-cleave preparations. The results are discussed with respect to cell wall deposition and cell morphogenesis.
Regulation of cell growth by vitreous humour
Authors: Lutty Gerard A. , Mello Robert J. , Chandler Carol , Fait Carolyn , Bennett Alonzo , Patz Arnall 
Published: April 2021

ABSTRACT
Extracts of normal vitreous have been found to inhibit angiogenesis in two animal models: tumour-induced neovascularization in the rabbit corneal micropocket and retinal extract-induced angiogenesis in the chick chorioallantoic membrane assay. Using in vitro assays, we have found recently that an extract of bovine vitreous, free of hyaluronic acid, inhibits proliferation of cells in the aortic wall, i.e. endothelium and smooth muscle cells, as well as capillary and corneal en-dothelium. The inhibition is dose-dependent, as determined by either cell count or [3H]thymidine incorporation, and not due to cytotoxicity, as demonstrated with a double-label thymidine assay. The inhibitor is trypsin-sensitive and heat-stable (95°C for 10 min).
Conversely, proliferation of pericytes, lens epithelium and fibroblasts (dermal and corneal) was stimulated by the vitreous extract. This mitogenic activity was heat-labile. Growth of pigment epithelium and several tumour cell lines was unaffected.
The data demonstrate that normal vitreous contains a heat-stable growth inhibitor specific for endothelium and smooth muscle cells, and a non-specific heat-labile mitogen. The paradoxical effect of this antiangiogenic factor on arterial and capillary contractile cells, smooth muscle and pericytes, suggests a basic difference in the regulation of the two vasculatures. The results suggest that a substance in normal vitreous may be important in controlling neovascularization that results from diabetic and other retinopathies, and could be useful for inhibiting tumour-induced angiogenesis.
Nucleolar activation and vacuolation in embryo radicle cells during early germination
Authors: Deltour R. , barsy T. De 
Published: April 2021

ABSTRACT
The activation of the nucleolus of primary root cells of Sinapis alba embryos during the first 72 h of germination was monitored by autoradiographic, ultrastructural and microstereological methods. Autoradiographs showed that within 48 h, the nucleolus progressively resumed the capacity to synthesize pre-rRNA molecules at a high rate. In quiescent embryos the nucleolus was small, compact and composed of mixed granular and fibrillar components. Within the first 6 h of germination a strong nucleolar vacuolation occurred, accompanied by a decrease in the volume of the nucleolus and a concomitant high loss of its ribonucleoproteins (RNPs). From 6 to 24 h, nucleolar vacuolation decreased to reach a stable level. During this last period the volume of the nucleolus increased by the accumulation of the fibrillar component resulting from a slow pre-rRNA processing. At 24 h the nucleolus presented a predominantly fibrillar texture. After 24 h, nucleolus growth continued but was due to the accumulation of the granular component, indicating that pre-rRNA processing occurred at a higher rate than during the first day of germination. F rom 48 h the nucleolus was composed of well-delineated granular and fibrillar areas. Dense nucleolus-associated chromatin as well as fibrillar centres were always observed during the whole period of observation. In addition, previous studies on the nucleolus of radicle cells of Zea mays embryo during early germination were completed by studying changes in the nucleolar volume and in the density of pre-ribosomal subunits of the granular component. On the basis of the data obtained with both species we suggest that a possible function for the nucleolar vacuoles is the increase in the nucleolus–nucleoplasm exchange interface in response to a rapid increase in the output of nucleolar RNPs. The nucleolar growth pattern during early germination is also discussed.
Gap-junctional communication in a communication-defective and in a communication-competent teratocarcinoma cell line
Authors: Lo Cecilia W. , Fang Daniel , Hooper Martin l. 
Published: April 2021

ABSTRACT
We examined the gap-junctional communication properties of a communication-defective cell line R5/3 and its communication-competent revenant H2T12. For these studies, we carried out microelectrode impalements to monitor ionic coupling and dye coupling. Our dye-injection experiments revealed that the H2T12 cells are much more efficient in dye coupling than the R5/3 cells. This latter observation is in agreement with the previous finding that the H2T12 cells are much better metabolically coupled than the R5/3 cells. With ionic coupling measurements, however, both cell lines exhibited similar levels of cell–cell coupling. The R5/3 cells demonstrated an ionic coupling coefficient of 0·19 ±0·011 (S.E.M.) and H2T12 a coupling coefficient of 0·25 ± 0·009 (S.E.M.). These results in conjunction with observations from other studies indicate that the different experimental approaches for monitoring gap-junctional communication may have different levels of sensitivity for detecting as opposed to measuring the level of cell—cell coupling.
Isolation of pure pellicles containing intact basal bodies of Tetrahymena pyriformis
Authors: Tiedtke Arno 
Published: April 2021

ABSTRACT
A new procedure for mass isolation of pure pellicles containing intact basal bodies of Tetrahymena pyriformis is reported.
The success of the procedure depends on the elimination of the sticky mucocyst contents before fractionation of the cells, which is induced by Alcian Blue 8GS. Under appropriate ionic conditions &gt; 95% of the cells are able to form a capsule by simultaneous extrusion of all mature mucocysts. About 50% of these cells are able to escape from their capsules, which are now devoid of mature mucocysts. These cells are separated from the empty capsules and encapsulated cells by passage through layers of gauze of 10 μm pore size. The fractionation of mucocyst-free cells in homogenization buffer yields pure pellicles, which are retained when the homogenate is sieved through steel sieves of 5 μm pore size.
Electron-microscopic controls show that the isolated pellicles are not contaminated with subcellular particles. Cells homogenized in the presence of low concentrations of Triton X-100 yield pellicles consisting of the known cell-surface-associated cytoskeletal elements, together with basal bodies. The cilia are detached just above the kinetosomal plate. The basal bodies of isolated pellicles are obviously undamaged, since all the known structures of native basal bodies are preserved. Even the granular matrix, a labile structure in the lumen of the basal body that probably contains RNA, is preserved.
Clonal separation of mature melanocytes from premelanocytes in a diploid human cell strain: Spontaneous and induced pigmentation of premelanocytes
Authors: Bennett Dorothy C. , Bridges Katherine , Mckay Ian A. 
Published: April 2021

ABSTRACT
Strains of pigmented melanocytes can be derived reproducibly from normal human skin. Published procedures have been modified here to yield a strain, ‘Nohm-l’, comprising many unpigmented cells as well as cells with various degrees of pigmentation observable by light microscopy. The unpigmented cells contain early melanosomes (pigment organelles) and the specific enzyme tyrosinase. They are on average smaller and less dendritic than the pigmented cells. Nohm-l cells show normal chromosomal banding patterns and normal proliferative behaviour, including senescence. They form no tumours in immunodeficient (nude) mice.
Nohm-l cells have been cloned and yield two distinct types of colony, depending on the progenitor cell. Well-pigmented melanocytes engender pure colonies of pigmented cells, but cells with little or no pigment can produce both unpigmented and pigmented progeny. Thus there is a separate cell type, or premelanocyte, which can differentiate spontaneously and stably in culture; this cell type includes both unpigmented and faintly pigmented cells. Usefully, most premelanocytes are viable after frozen storage, unlike well-pigmented melanocytes. Some components of the culture medium affect the proportion of pigmented cells in Nohm-l cultures, and hence probably the ratio of mature melanocytes to premelanocytes. Rapid pigmentation can be induced artificially and simply, by using a medium with increased extracellular pH and tyrosine concentration.
Successive asexual life cycles of starved amoebae in the cellular slime mould, Dictyostelium mucoroides var.Stoloniferum
Authors: Bonner J. T. , Joyner B. D. , Moore A. A. , Suthers H. B. , Swanson J. A. 
Published: April 2021

ABSTRACT
Dense masses of spores of Dictyostelium mucoroides var. stoloniferum have the ability to germinate and aggregate rapidly in the absence of food. This is made possible by the presence of a dominant, self-produced spore germination activator. The germination—aggregation cycle can be repeated in as many as six successive generations. In each generation the spore size is reduced so that ultimately they are only a fraction of the size of those produced by the parental, bacteria-fed amoebae.
Regulation of cell shape in Euglena gracilis. IV. localization of actin, myosin and calmodulin
Authors: Lonergan Thomas A. 
Published: April 2021

ABSTRACT
The immunofluorescence patterns for actin, myosin, calmodulin and tubulin were observed in Euglena gracilis Klebs strain Z during the biological clock-controlled shape changes observed with division-synchronized cells, and during two shock responses that induce cell rounding. The fluorescence patterns for actin, myosin, calmodulin and tubulin show a high degree of coincidence and are visualized as lines running parallel to, and having the same spacing as, the pellicle strips beneath the plasma membrane. The fluorescence patterns remain intact during the daily shape changes, implying that the shape changes do not result from cycles of polymerization and depolymerization of the microtubules and microfilaments. Resuspension of cells in Ca2+-free medium induces cell rounding of many of the cells. The actin and calmodulin patterns are partially disrupted by the Ca2+-free resuspension, while the myosin pattern is almost totally disrupted. Microtubules are unaffected by this treatment. Prior exposure of cells to the calmodulin antagonist trifluoperazine or to the microfilament-stabilizing peptide phalloidin stabilize the actin, myosin and calmodulin patterns against disruption by the Ca -free resuspension and other shock responses. The possibility of an actomyosin contractile system controlled by calmodulin is discussed.
A gradual decrease in nucleolar size with the maturation of columnar epithelial cells in the adult rat intestine under normal and various experimental conditions
Authors: Altmann G. G. 
Published: April 2021

ABSTRACT
The columnar cells, which form over 90% of the epithelium in the small intestine, undergo rapid and continuous renewal and maturation. Samples from duodenum, jejunum, upper, mid- and terminal ileum of young male rats were processed for histology. The average maximal nucleolar area was determined in 10-cell-wide bands of the basal, mid and upper levels of crypts and villi, respectively, by image analysis; in’the duodenum, it was 2·8, 2·1, 1·7, 1’5, 1·3 and 0·8 (in μm2) in the respective epithelial levels from crypt base to villus top. Although villus size jlecreased by 68% from duodenum to terminal ileum, nucleolar area was similar at each respective epithelial level along the intestine. This indicated that nucleolar size was related to cell maturity, rather than to the size of epithelium. In other groups of rats, the duodenum was examined after administering specific inhibitors. Methotrexate (within a day) and cycloheximide (within 3 h) did not significantly affect nucleolar size, indicating that the decrease in size was not under the influence of immediate synthesis of nucleic acid or protein. On the other hand, tunicamycin (within a day) delayed the decrease and actinomycin D (within 3 h) caused a maximal decrease in all nucleoli. This implied that a glycoprotein factor and some changes in DNA were involved in the decrease in nucleolar size. The rate of protein synthesis in duodenum was then measured by grain count per cell area in autoradiographs made after 1 h of injection of [3H]leucine. From crypt base to villus base, the grain count doubled while the nucleoli decreased to nearly half of their size in the crypt base. When actinomycin D injection preceded the [3H]leucine administration, all nucleoli decreased markedly and the grain counts increased by about 30% in all epithelial levels. It thus appears that the decrease in nucleolar size stimulates protein synthesis, possibly by the release of ribosomal material or some other factor. Protein synthesis in turn has been shown to be related to cell maturation. It is concluded that the nucleolus is involved in some manner in the regulation of the maturation and renewal of the epithelial cells.
Plasma membranes from adrenal cells: Purification and properties
Authors: Osawa Shoji , Hall Peter F. 
Published: April 2021

ABSTRACT
A method is reported for preparing surface (plasma) membranes from adrenal tumour (Y-l) cells. The procedure is based upon homogenization in hypotonic ZnCl2 followed by sedimentation through two sucrose density gradients. The purified membranes consist of large sheets of membrane. The identity and purity of the membranes was demonstrated by: (1) microscopy (phase contrast and electron); (2) enzyme markers; and (3) functional activities associated with plasma membranes (binding of ACTH and LDL and adenylate cyclase). Phase-contrast microscopy revealed the release of membrane ghosts free from cytoplasm and nuclei. Electron microscopy showed membranes with small fragments of cytoplasm attached to the inside. Binding of ACTH was found to be specific with KD 0·12nM and the equivalent of 2500 sites per cell. Binding of LDL was also specific with KD 0·5 nM and the equivalent of 4800 sites per cell. Specific activities of binding for ACTH and LDL were increased by 21-fold and 15-fold, respectively, relative to whole homogenate. Membranes were also prepared from beef fasciculata cells by the same method.
Competition between Chlorellae in chimeric infections of Hydra viridis: The evolution of a stable symbiosis
Authors: Rahat M. 
Published: April 2021

ABSTRACT
Aposymbiotic polyps of Hydra viridis were infected with one or two of the following strains of Chlorella : the native strain obtained from green H. viridis, and the originally non-symbiotic strains Fs and 211/8p cultured in vitro. Larvae of Artemia served as infecting vectors.
Chimeric infections were obtained with two different Chlorella strains cohabiting in the same cells and polyps. In time, the chimeric infections disappeared and mixed populations of Hydra were formed with different strains of Chlorella in different polyps.
We suggest that the Chlorella/Hydra symbiosis was initiated originally by an infection of preadapted hydra by preadapted chlorellae. Through intracellular interalgal competition and competition between dissimilar infected cells and polyps, the present-day stable symbiosis has evolved.
Enrichment of cfu-s proliferation inhibitor-producing cells based on their identification by the monoclonal antibody f4/80
Authors: Simmons P. J. , Lord B. I. 
Published: April 2021

ABSTRACT
Cells capable of synthesizing a factor that can specifically inhibit the proliferation of haemopoietic spleen colony-forming units, CFU-S, carry many of the characteristics of macrophages. The monoclonal antibody, F4/80, which is specific for murine macrophages, has therefore been used to isolate macrophages from bone marrow. These macrophages were then assayed for their ability to produce the inhibitor. Low-density bone marrow cells were first separated by a density-cut procedure and then labelled with F4/80. Fluorescence-activated cell sorting was then used to select F4/80 positive and negative cell fractions. It was found that the F4/80 positive fraction contains inhibitor cells, enriched by at least 200-fold compared to unfractionated marrow. Subsequent culture of this fraction over a period of several weeks produced a further 15-to 20-fold increase in inhibitor-producing capacity. The cultured cells producing inhibitor were virtually 100% F4/80 positive, phagocytic and exhibited histochemical properties characteristic of macrophages. The macrophage-like character of the producer cells was thus confirmed and the removal of the majority of unwanted cells means that many of the impurities in the normal crude extracts have been excluded.