bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of the effect of colchicine and cytochalasin b on fibroblast aggregates by the substratum
Authors: Van Der Schueren B. , Cassiman J. J. , Van Den Berghe H. 
Published: April 2021

ABSTRACT
In previous investigations, we have shown that aggregates of normal human fibroblasts displayed a remarkable number of morphogenetic properties in suspension and on a substratum. The present investigation has attempted to illustrate more clearly the role of colchicine- and cytochalasin-sensitive structures in the observed ultrastructural properties of the fibroblasts in this system.
Cytochalasin B and colchicine alter the surface ultrastructure of the cells as well as the behaviour of the cells during aggregate outgrowth. In addition, the effects of both drugs on the cells in the aggregates are modulated by the attachment of the aggregates to a substratum.
Bhk21 myosin: isolation, biochemical characterization and intracellular localization
Authors: Yerna Marie-Jeanne , Aksoy Mark O. , Hartshorne David J. , Goldman Robert D. 
Published: April 2021

ABSTRACTMyosin has been isolated from baby hamster kidney cells (BHK21/C13) in high yield and characterized biochemically and immunologically. The subunit composition consists of 2 heavy chains, approximately 2ooo∞ Daltons each, and 2 classes of light chains of approximately 16 000 and 20000 Daltons. The myosin exhibits ATPase activity in the presence of K+-EDTA or Ca2+ but very little activity with Mg2+-ATP. The Mg2+-ATPase activity is stimulated only about 2-f0ld by skeletal actin, but a much larger activation is obtained in the presence of a protein kinase isolated from chicken gizzard. The increase in actin activation is accompanied by the phosphorylation of the 20000-Dalt0n light chain. BHK21 myosin is insoluble at low ionic strength and forms typical bipolar thick filaments. A specific antiserum generated against this protein forms a single precipitin line with the antigen but does not crossreact with either skeletal or smooth muscle myosin. The antiserum also specifically stains stress fibres in BHK21 cells as shown by indirect immunofluorescence.
Effects of temperature and nutritional conditions on the mitotic cell cycle of Saccharomyces cerevisiae
Authors: Jagadish M. N. , Carter B. L. A. 
Published: April 2021

ABSTRACT
Yeast cells were cultivated at different growth rates in a chemostat by alterations in the flow of the limiting nutrient glucose and in batch cultures where variations in growth rate were achieved by alterations in the composition of nutrients. It was observed that the stage in the cycle at which S-phase was completed varied with growth rate. The faster the growth rate, the earlier the stage in the cycle in which completion of S-phase occurred. When stage in the cycle is converted into time before division it was observed that the time from completion of S-phase to cell division varied only slightly with growth rate except at extremely slow growth rates. Expansion of cell cycle transit time as the growth rate was slowed was achieved primarily by an expansion in time of the period from division to the completion of S-phase.
In contrast, when cells were grown at different rates by alterations in the temperature of cultivation, completion of S-phase occurred at approximately the same stage in the cell cycle at all growth rates.
The activation of proteolysis in the acrosome reaction of guinea-pig sperm
Authors: Green D. P. L. 
Published: April 2021

ABSTRACT
The divalent metal cation ionophore A23187 rapidly induces a normal acrosome reaction in a population of guinea-pig sperm suspended in calcium medium. In the course of the acrosome reaction, proacrosin, the zymogen precursor of the protease acrosin, is activated. Although the acrosome reaction causes exocytosis of the acrosomal contents, ‘soluble’ acrosin is not released in significant amounts until well after the sperm population as a whole has undergone an acrosome reaction. This suggests that proacrosin is stored within the acrosome in an insoluble form and that exocytosis of the acrosomal contents in the acrosome reaction is insufficient, by itself, to cause its immediate dissolution.
Electron micrographs of sperm undergoing an Az3187-induced acrosome reaction in the presence of the acrosin inhibitors benzamidine, p-amino-benzamidine and phenylmethyl-sulphonyl fluoride show that the acrosome reaction proceeds normally but that dispersal of the acrosomal contents is inhibited. These morphological changes are, for the most part, below the limit of resolution of the light microscope and using light microscopy to assess whether an acrosome reaction has taken place, it can be mistakenly inferred that the reaction itself is inhibited by the acrosin inhibitors. The inhibition of the dispersal of the acrosomal contents by acrosin inhibitors suggests that acrosin activity is important in solubilizing acrosin.
These experimental observations, taken with the evidence that the acrosome reaction is a response to an increase in intracellular free calcium, have been taken as the basis of a proposal for the mechanism of proacrosin activation in the acrosome reaction.
The osmotic properties of the acrosome of guinea-pig sperm
Authors: Green D. P. L. 
Published: April 2021

ABSTRACT
The osmotic behaviour of the acrosome in intact guinea-pig sperm has been examined by light and electron microscopy. Because the acrosome is retained within the cell, it can only experience the changes in tonicity of the cytoplasm and these have first to be related to the changes in tonicity in the external medium. Nevertheless, a qualitative description of the osmotic properties of the acrosome can be obtained. The evidence suggests that the acrosomal contents are normally close to their limit of compression. It has been proposed that a hydrostatic pressure is exerted inwards on the acrosomal membrane and that this is responsible for the maintenance of acrosomal shape. Swelling of the acrosome when sperm are suspended in hypotonic medium suggests that the acrosomal membrane does not have an abnormally low water permeability.
Two-thirds of the acrosomal volume are occupied by a single matrix which undergoes cavitation in the course of the acrosome reaction. It also undergoes cavitation when guinea-pig sperm are suspended in calcium-free medium containing the non-ionic detergent Triton X-100. This suggests that cavitation is caused by the loss of integrity of the plasma and acrosomal membranes. A mechanism for cavitation is proposed in which a colloid osmotic pressure within the acrosomal matrix is allowed expression when the crystalloids of the external medium pass into it, this internal colloid osmotic pressure forcing the matrix apart to produce a cavity.
The ultrastructure of non-membranous nuclear ghosts
Authors: Riley D. E. , Keller J. M. 
Published: April 2021

ABSTRACTNon-membranous HeLa cell nuclear ghosts, representing non-membranous nuclear envelope or ‘skeletal’ components, have been examined in whole-mount fashion by transmission electron microscopy. Major components of the ghosts include annuli with inner and outer diameters of 43 and 90 nm, respectively, which are consistent in dimensions with nuclear pore complexes. Also present are rod-like images (260 nm in length and 50 nm in width or diameter) representing either previously unobserved nuclear structures, or condensations of repeating functional units not otherwise observable. The annular and rod-like images were also observed when various steps in the ghost isolation procedure, such as the use of detergents, 0-5 M MgCl, and polylysine attachment of the ghosts to electron-microscope grids, were circumvented. The annular and rod-like images are connected into linear and polygonal arrays by strands (15-30 nm in width) that are sensitive to DNase I and DNase II but resistant to nuclease Sj. Thus, although the non-membranous ghosts from HeLa cells are composed primarily of protein, enzymic dissection indicates that their gross integrity is markedly dependent on double-stranded DNA. Nuclear ghosts prepared from a wide range of species including mammals, birds and plants, exhibited essentially the same components and organization.
Selective adhesion and impaired adhesive properties of transformed cells
Authors: Brugmans Mia , Cassiman Jean-Jacques , Van Den Berghe Herman 
Published: April 2021

ABSTRACT
Quantitative studies on the adhesive properties of transformed cells have yielded inconclusive and sometimes contradictory results. The present investigation has examined adhesive interactions between normal human fibroblasts, established as well as virus-transformed animal cell lines, and human tumour-derived cell lines by the cell–cell layer binding assay.
The results of these investigations indicate that adhesive selectivity can be observed between normal human fibroblasts and 2 human tumour-derived cell lines, providing an in vitro system to study cell surface components involved in cellular interactions between normal and malignant cells.
In addition it is demonstrated that cell layers of transformed cells form a poorly adhesive substratum for both trypsinized normal and transformed cells. Furthermore, it is confirmed that the adhesive properties of transformed cells, including adhesive selectivity, are affected by the dissociation procedure (trypsin or EDTA). In view of the observations made by other investigators, the present results suggest that transformed cells display adhesive properties which can be quantitatively and reproducibly measured but which are modulated by the dissociation procedure as well as by the configuration in which the cells are at the time of the assay.
Suppression of the transformed phenotype in somatic cell hybrids
Authors: Marshall C. J. , Dave Harsha 
Published: April 2021

ABSTRACT
Somatic cell hybrids between mouse mammary tumour cells (TA3B) and diploid rat embryo fibroblasts (REF) or between TA3B and Syrian hamster sarcoma cells (BI) were examined for the in vitro characteristics of transformed cells as soon as possible after cell fusion. Unlike the parental tumour cells three of four TA3B × REF and five BI × TA3B independent hybrid lines had low colony-forming efficiencies in agar, exhibited density-dependent inhibition of growth and did not form colonies on confluent monolayers of 3T3 cells, demonstrating that the transformed phenotype was suppressed in these hybrids. In addition tests of some of the hybrid lines for tumour production in nude mice showed that this was also suppressed. Suppression was more stable in the TA3B × REF than in the BI × TA3B hybrids, variants of the BI × TA3B hybrids with the properties of transformed cells could be readily isolated by subculturing cells that had grown in agar. Tumour growth selected for hybrids with the characteristics of transformed cells, and derivatives of the hybrids selected to show the transformed phenotype readily produced tumours. These correlations suggest that the transformed phenotype and malignancy may be under the same control in these cells. The phenomenon of suppression may be explained by the hypothesis that neoplastic transformation results from recessive mutations in genes which control the normal phenotype. On this model the finding of suppression in hybrids between two different tumour lines is interpreted as complementation and indicates that the mutations are not the same in all cell lines.
Microfilament bundles, lets protein and growth control in somatic cell hybrids
Authors: Marshall C. J. , Humphryes K. C. , Pollack R. E. 
Published: April 2021

ABSTRACT
Hybrid cell lines between normal rat embryo fibroblasts and TA3B mouse tumour cells, or between TA3B and BI hamster sarcoma cells, have been examined for the expression of the cell surface large external-transformation-sensitive (LETS) protein and the organization of microfilament bundles. LETS protein was detected by lactoperoxidase-catalysed radioiodination and microfilament bundles were visualized by indirect immunofluorescence with antibodies directed against actin or myosin. Hybrids which exhibited normal growth control characteristics had high levels of LETS protein and extensive microfilament bundles. Neoplastic transformation appears to be suppressed in these hybrids. Hybrids which had the growth control characteristics typical of transformed cells had reduced or zero levels of LETS protein and few microfilament bundles. These results confirm previous studies on the expression of the transformed phenotype in these hybrids and demonstrate that there is a good correlation between normal growth control and the presence of LETS protein and microfilament bundles. However, the changes in cell surface LETS protein and in the organization of microfilament bundles often appeared to be quantitative reductions rather than all-or-none effects. The magnitude of the alterations in levels of LETS protein and in the organization of microfilaments appeared to correlate with the range of transformed characteristics exhibited by the cells. One transformed hybrid in particular, selected for growth in agar, had some surface LETS protein, some microfilament bundles and retained density-dependent inhibition of growth.
Comparison of cell attachment and caseinolytic activities of five tumour cell types
Authors: Varani J. , Orr W. , Ward P. A. 
Published: April 2021

ABSTRACT
We have examined the ability of 5 tumour cell types to attach to plastic flasks in medium containing either 10% foetal calf serum or 10% normal human serum and compared this ability with cell-associated caseinolytic activity. The cell types used included fibrosarcoma cells which were obtained from a methylcholanthrene-induced tumour in a C57 BL/6 mouse, the SV40-transformed 3T3 (BALB/c) cells, the Walker carcinosarcoma cells and 2 lines of HeLa cells. All 5 cell types attached to the flasks and spread out efficiently in medium containing 10% foetal calf serum. The Walker carcinosarcoma cells and the 2 lines of HeLa cells also attached efficiently in medium containing 10% normal human serum and grew into monolayers in this medium. These 3 cell types had no detectable caseinolytic activity. The fibrosarcoma cells and the SV40-transformed 3T3 (BALB/c) cells did not attach in normal human serum-containing medium. These 2 cell types had readily detected caseinolytic activity. Normal human serum and foetal calf serum were compared for levels of protease-inhibitor activity. Human serum was found to have less activity than foetal calf serum against both trypsin and plasmin as well as the cell-associated caseinolytic activity. The low level of protease inhibitor activity in normal human serum may contribute to the inability of this serum to support the attachment of cells with detectable protease activity because the addition of protease inhibitors such as soybean trypsin inhibitor, lima bean trypsin inhibitor and bovine pancreas trypsin inhibitor to normal human serum dramatically enhanced cell attachment. In contrast to this, the addition of E-amino-π-caproic acid to normal human serum and the removal of plasminogen from normal human serum did not enhance its capacity to support cell attachment.
Fine-structural changes in the nucleus of primordial oocytes in immature hamsters
Authors: Habibi B. , Franchi L. L. 
Published: April 2021

ABSTRACT
This study reports observations on fine-structural changes in the nucleus of the oocyte in hamsters during the establishment of the primordial (unilaminar) follicle at 7 to 12 days after birth. Following pachytene, the nuclei at early diplotene contain simple chromosomal cores surrounded by a sheath of fibrillo-granular material symmetrically disposed in the form of lateral projections and loops. From 9 days onwards increasing numbers of the oocytes show nuclei lacking such chromosomal threads: instead, they contain randomly disposed, condensed fibrillar clumps with associated dense knots of material, and prominent aggregations of 25 – 30-nm granules. This second nuclear form is assumed by all oocytes examined at 11 and 12 days and appears to be the definitive diplotene phase. These changes in the appearance of the nuclear chromatin are discussed in the light of those found in oocytes of other species, and it is concluded that the hamster diplotene phase consists of a transitory ‘compact’ or uniform lampbrush stage, followed by a definitive dictyate condition like that in the rat, but with markedly differential condensation or extreme diffusion of lateral loops.
This conclusion is examined in relation to findings which report a marked increase in the sensitivity of hamster oocytes to X-radiation at the time that the observed changes in nuclear configuration are taking place. The combined observations support the hypothesis that the dictyate stage in rodent oocytes represents a modified diplotene phase in which the high degree of spatial diffusion of components of chromosomes of the lampbrush type results in a reduced capacity for repair following exposure to ionizing radiations.
DNA-binding properties of nuclear matrix proteins
Authors: Comings David E. , Wallack Alice S. 
Published: April 2021

ABSTRACT
Mouse nuclear matrix proteins, examined by a filter assay, were found to bind to DNA. There was no preference for homologous mouse compared to heterologous E. coli DNA. Competition assays showed a preference for AT-rich DNA and of the 4 single-stranded homopolymers there was a preference for poly(dT). These observations are consistent with the possibility that the matrix may play a role in the formation of AT-rich chromomeres (G-bands).
Regulation of interstitial cell differentiation in Hydra attenuata: IV. Nerve cell commitment in head regeneration is position-dependent
Authors: Yaross Marcia S. , Bode Hans R. 
Published: April 2021

ABSTRACT
In hydra, nerve cells are a differentiation product of the interstitial cell, a multipotent stem cell. Nerve cell commitment was examined during head regeneration in Hydra attenuata. Within 3 h of head removal there is a 10- to 20-fold increase in nerve cell commitment in the tissue which subsequently forms the new head. Nerve cell commitment is unaltered in the remainder of the gastric region. This local increase in nerve cell commitment is responsible for about one half the new nerve cells formed during head regeneration, while one half differentiate from interstitial cells that migrate into the regenerating tip.
The preparation and ultrastructure of avian erythrocyte nuclear envelope enclosed by the plasma membrane
Authors: Harris James R. 
Published: April 2021

ABSTRACT
A procedure is described for the preparation of avian erythrocyte nuclear envelope ghosts which remain enclosed by the ellipsoid plasma membrane. Haemoglobin-free nucleated chicken erythrocyte ghosts are treated in a low ionic strength buffer plus heparin which brings about decondensation of the chromatin. This is followed by solubilization of the chromatin by digestion with pancreatic deoxyribonuclease-1. When studied by light microscopy using either phase-contrast or Nomarski interference optics, the ellipsoid plasma membrane is clearly seen to remain with the collapsed nuclear envelope trapped inside. This interpretation is supported by negative-staining electron microscopy using ammonium molybdate, which in addition reveals the presence of the nuclear pore complexes. The suggestion is advanced that structural protection is provided for the fragile nuclear envelope system by the surrounding plasma membrane, which might account for the final nuclear envelope being in the form of relatively intact ghosts with well defined nuclear pore complexes. The nuclear envelope is highly fragmented when the plasma membrane is absent, the nuclear pore complexes showing appreciable breakdown. Thin sectioning supports the results of negative staining and in addition shows the nuclear envelope retained within the plasma membrane to be composed of both inner and outer nuclear membranes, but the nuclear pore complexes are not clearly defined.
Regulation of rna synthesis in Tetrahymena Pyriformis: secretion of regulatory factors
Authors: Andersen H. A. , Nielsen S. J. 
Published: April 2021

ABSTRACT
The rate of ribosomal RNA synthesis varies greatly with the population density in both exponentially and synchronously growing populations of Tetrahymena pyriforntis. Shortly after inoculation of the population —at relatively low cell densities —a gene-dose effect dominates the picture, and a doubling in the gene number is immediately followed by a doubling in the rate of RNA synthesis. However, also other mechanisms are controlling the rate of RNA synthesis. Generally one finds high rates of RNA synthesis in the lag phase of newly inoculated cells, decreasing rate of RNA synthesis during most of the exponential growth phase and very low rate of synthesis in stationary phase cells. We now have results which show that the repression of RNA synthesis in densely populated cultures is caused by a dialysable factor, which is secreted by the cells. If cells are inoculated on a medium which contains this factor the high initial rate of RNA synthesis normally observed is prevented, but the cells multiply and grow with normal generation time until normal stationary-phase population densities are reached.
Induction of autogamy by treatment with trypsin in Paramecium Caudatum
Authors: Mikami Kazuyuki , Koizumi Sadaaki 
Published: April 2021

ABSTRACT
Firmly united conjugant pairs of P. caudatum were easily separated by treatment with trypsin, 0 · 025–1 · 0 mg/ml in 2 mM phosphate buffer at pH 7 · 2. Cytological observations showed that pairs separated by this means undergo normal meiosis and subsequent prezygotic divisions. Microspectrophotometric comparisons of G1 micronuclei in the parent with those in clones derived from prematurely separated conjugants indicate usually the same DNA content in both. The stock dm-13, heterozygous for mating type gene loci, showed the definite ratio of segregation to 2 mating types in clones derived from prematurely separated conjugants. Those results suggest that the prematurely separated cells usually undergo autogamy.
Degradation of tight junctions in HT29, a human colon adenocarcinoma cell line
Authors: Polak-Charcon Sylvie , Ben-Shaul Yehuda 
Published: April 2021

ABSTRACT
The process of right junction degradation was followed in a cell line of human colon adenocarcinoma.
Tight junctions are degraded by 2 mechanisms: (1) breakdown of junctional elements to intramembrane particles; (2) bleb formation by which tight-junctional elements are internalized into the cytoplasm or excluded into the medium. It is suggested that the first mechanism allows preservation of membrane particles for re-use, whereas the second is a mechanism by which the cells eliminate unneeded junctional elements.