bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of soft connective tissue in the response of pig articular cartilage in organ culture to excess of retinol
Authors: Barratt M. E. J. 
Published: April 2021

ABSTRACT
The action of excess rerinol on articular cartilage from growing pigs was studied in organ culture. Retinol had little or no effect on explants of articular cartilage alone, but if the explants were cut so as to include some of the marrow tissue in the invasion cavities, or were cultivated near or in conlact with capsular tissue, retinol caused extensive degradation of the cartilage matrix, as indicated by loss of metachromatic staining properties. Many chondrocytes were released from their capsules and assumed a fibroblast-like form. Two types of regeneration were seen. In control explants that included part of the invasion zone, cells below the explant laid down a metachromatic matrix; in similar explants cultured in the presence of retinol, a non-metachromatic osteoid-like tissue was formed at this site. There was little recovery when retinol-treated explants were transferred to normal medium, although both osteoid and chondroid tissue were sometimes regenerated.
Ultrastructural and cytochemical manifestations of protein synthesis in the peripheral sarcoplasm of denervated and newborn skeletal muscle fibres
Authors: Gauthier Geraldine F. , Schaeffer Susan F. 
Published: April 2021

ABSTRACT
In muscle fibres of the rat diaphragm, there is widespread accumulation of free ribosomes and rough-surfaced endoplasmic reticulum in the subsarcolemmal sarcoplasm at 28 days following section of the phrenic nerve. A corresponding accumulation of basophilic material is visible at the periphery of the fibres when examined with the light microscope. Both the ribosomes and the basophilic material are removed by preliminary treatment with ribonuclease. Fibres comprising the diaphragm of the newborn rat display similar aggregations of subsarcolemmal ribosomes and peripheral basophilia. These ultrastructural and cytochemical manifestations of protein synthesis correspond closely in time to the well documented ‘supersensitivity’ to acetylcholine, which occurs along the entire length of muscle fibres in the newborn and denervated rat diaphragm. It is suggested, therefore, that this protein-synthetic machinery, which is concentrated at the cell surface, is involved in the formation of new receptors.
Surface modification and electrophoresis of normal and transformed BHK21 cells
Authors: Latner A. L. , Turner G. A. 
Published: April 2021

ABSTRACT
The mean electrophoretic mobilities at pH 7·5 of virus-transformed (Py6) and normal BHK21 cells were very similar, whether they were harvested mechanically or by the use of trypsin. After formaldehyde treatment, there was significantly increased mobility in both cell types; the transformed cells showed significantly the greater change. After neuraminidase treatment, the mean electrophoretic mobility was decreased to the same extent in both types of cell. Treatment with neuraminidase and formaldehyde had no effect on the mean electrophoretic mobility of the normal cells but slowed the transformed variety. The mobility in histone solution had no relationship to histone concentration but was statistically correlated with the amount of histone per cell, calculated from total histone present divided by the total number of cells; a linear relationship being obtained with the normal cells but an initial plateau was demonstrated with the transformed cells. The normal cell line showed a similar plateau after neuraminidase treatment. The possible significance of these results is discussed.
The densities of colloidal iron hydroxide particles bound to microvilli and the spaces between them: Studies on glutaraldehyde-fixed ehrlich ascites tumour cells
Authors: Weiss L. , Subjeck J. R. 
Published: April 2021

ABSTRACT
The densities of positively charged, colloidal iron hydroxide particles binding to the surfaces of glutaraldehyde-fixed cultured Ehrlich ascites tumour cells, were determined on cells maintained in suspension and monolayer cultures. In both cases, there was a higher density of particles bound to the surfaces of microvilli than to the spaces between them. Prior treatment of the cells with ribonuclease did not significantly alter the proportions of particles binding to the 2 different surface regions, indicating that the ribonuclease-susceptible binding sites are distributed with similar mean densities over the microvilli and the regions between them. Prior treatment of the cells with neuraminidase reduced the densities of particles binding to microvilli to those of the intermicrovillous spaces, indicating that the original higher density over the microvilli is due to an increased number of sialic acid residues at their surfaces.
The findings are discussed in relationship to observed changes in the surface density of microvilli when these cells convert from suspension to monolayer cultures.
Studies on the factors affecting cellular spreading upon culture-substrate: 1. the effects of divalent cations and conditioned medium on cellular spreading
Authors: Yasuda Kunio 
Published: April 2021

ABSTRACT
The effects of various divalent cations on cellular spreading of in vitro cultured fibroblasts of chick embryos upon substrates were investigated in serum-free Eagle’s MEM. Fibroblasts spread on the surfaces of culture dishes in the presence of Mn2+, Mg2+, Ca2+ or Co2+, but not in the presence of Zn2+, Cd2+, Sr2+ or Cu2+. The minimum cation concentration for permitting cellular spreading at 37 °C is different for each cation. The values are 10−6, 5 × 10−4, 10−3 and 10−2 M for Mn2+, Mg2+, Ca2+ and Co2+, respectively. Below these concentrations the cells remain round. Mn2+ is about 1000-fold more effective in causing spreading than Ca2+. The cells do not spread at low temperature, but they do at 22 °C in the presence of 10−4 M Mn2+.
In a medium conditioned with a mass culture of fibroblasts, cell spreading occurs at one tenth of the cation concentrations given above. If conditioned medium is heated at 65 °C for 30 min or treated with trypsin, its effect is abolished; this suggests that the effective factor(s) in the conditioned medium is a protein.
Ultrastructural evidence for myosin of the smooth muscle type at the surface of trypsin-dissociated embryonic chick cells
Authors: Gwynn I. AP , Kemp R. B. , Jones B. M. , Gröschel-Stewart U. 
Published: April 2021

ABSTRACT
Cells dissociated from embryonic chick muscle tissue using trypsin were rotated in the presence of globulin-enriched rabbit antisera against both sm∞th and striated muscle actomyosins originating from chicken gizzard (GAM) and pectoralis (PAM) muscles respectively. The presence of the rabbit antibodies was demonstrated using peroxidase-labelled sheep antirabbit γ-globulins, the enzyme-antibody conjugate being located by electron-microscope histochemistry.
Anti-GAM γ-globulins reacted strongly with the plasma membrane. Judging from the complete absence of staining, γ-globulins from non-immunized rabbit serum did not interact with the membrane. When γ-globulins of sheep anti-rabbit IgG serum were applied alone, that is in the absence of pretreatment with rabbit γ-globulin, there was an observable reaction with the cell surface. Preincubation of anti-GAM with the heavy meromyosin fraction from smooth-muscle myosin inhibited the interaction of the antibodies with the membrane, as evidenced by the absence of staining. A weak positive reaction obtained with anti-PAM was due to components of the antibody preparation which were reactive with actin and not with PAM.
It was concluded that a smooth-muscle myosin-like protein is an integral part of the plasma membrane of embryonic chick muscle cells.
Configuration of flagellar microtubule subunits
Authors: Warner F. D. , Meza I. 
Published: April 2021

ABSTRACT
Microtubule protofilaments and their subunits isolated from sperm flagellar doublet tubules of the sea urchin Strongylocentrotus purpuratus were examined by analytical biochemistry and high-resolution negative staining electron microscopy. All microtubule (tubulin) fractions show 2 polypeptide bands (α and β tubulins) in an approximate 1:1 ratio on urea-polyacryl-amide gel electrophoresis. Heat (37 °C)-solubilized microtubules yield a protein fraction containing the tubulin dimer of molecular weight 115 000 Daltons. The dimeric tubulin subunit, as seen in the electron microscope, has an overall size of about 3·5 × 8 nm and appears to have the configuration of a figure 8 because of stain penetration into the centre of each of its 2 halves (figure os). Isolated protofilaments (3·5 ± 0·3 nm thick) can each be resolved into 2 subfilaments (1·7 ± 0·2 nm thick). The 2 subfilaments have periodic lateral associations resulting in the basic 4-nm subunit repeat (figure o) along the protofilament. Examination of collapsed and solubilizing protofilaments shows the figure 8 (dimeric) subunits separating at random along the proto-filaments. We conclude that the tubulin dimer must be composed of either elongated or bilobed monomers which result in the figure 8 configuration and hence the 2-stranded appearance of the protofilaments.
Characteristics of sea-urchin mitotic apparatus isolated using a dimethyl sulphoxide/glycerol medium
Authors: Forer A. , Zimmerman A. M. 
Published: April 2021

ABSTRACT
A method for isolating sea-urchin zygote mitotic apparatus (MA) is described which is based on the Filner-Behnke method of isolating brain microtubules. MA were isolated in 50% (v/v) glycerol, 10% (v/v) dimethyl sulphoxide, 5 mM MgCl2, 0·1 mM EGTA, and 5 mM Sorensen’s phosphate buffer at a final pH of 6·8. MA stored at room temperature in isolation medium had stable birefringence, stable microtubules, and stable solubility properties (in 0·5 M KC1) over a period of 10 days to 2 weeks. These MA also seem to have more dry matter per volume than do MA isolated using hexylene glycol. The biggest disadvantages of the method are that zygotes often are difficult to lyse, and that cytoplasmic debris the same size as the MA sometimes contaminates the MA pellet.
Mitochondrial dna from 4-cell stages of Ascaris lumbricoides
Authors: Tobler H. , Gut C. 
Published: April 2021

ABSTRACT
Mitochondrial DNA (mtDNA) has been isolated from 4-cell stages of Ascaris lumbricoides. This DNA amounts to about 40% of the total quantity of 4-cell-stage DNA. Its buoyant density in neutral CsCl gradients is 1·686 g cm” −3. Electron microscopy of mtDNA demonstrated the presence of circular molecules with an average contour length of 4·64 /&lt;m. About 15% of these molecules are supercoiled, covalently closed circles, whereas some 2% consist of double-forked circular molecules. The form and size of these branched molecules suggest that they are replicative intermediates.
Histotypic cell aggregation in the presence of cytochalasin b
Authors: Maslow D. E. , Mayhew E. 
Published: April 2021

ABSTRACTA study was made of the effects of cytochalasin B on (a) specific sorting of reaggregating cells; (b) redistribution of cell types after treatment of preformed aggregates; and (c) the ability of aggregates of one cell type to incorporate and sort cells of another type. Freshly disaggregated neural retina and heart cells were cultured on a gyratory shaker at 70 rev/min and the aggregates formed analysed for sorting of cell types.Cytochalasin B disrupted the sorting of forming aggregates at concentrations of 1 μg/ml and greater. The distribution of cell types in aggregates that were treated with cytochalasin after 24 h of culture was more random than the control.Untreated cultures of retinal aggregates and heart cell suspension resulted in pure retinal and pure heart aggregates, but with more than 50% mixed and sorted aggregates. Cytochalasin B treatment resulted in fewer mixed aggregates and a higher proportion of pure retina and pure heart aggregates.
The effect of prolactin on the number of membrane-associated particles in kidney cells of the euryhaline teleost Gasterosteus aculeatus during transfer from seawater to freshwater: A freeze-etch study
Authors: Bonga S. E. Wendelaar , Veenhuis M. 
Published: April 2021

ABSTRACT
The membranes of kidney cells of 3-spined sticklebacks were examined in freeze-etch replicas. The numbers of particles adhering to surfaces and fracture faces of the outer cell membranes and the membranes of the basal labyrinth were determined. The latter membranes probably are the main location of ion-transporting enzyme complexes.
The total number of particles per cell in freshwater fish exceeds that of seawater fish by about 50% for the outer cell membrane, and by almost 200% for the membranes of the basal labyrinth.
After transfer of seawater fish to freshwater, particle numbers increase and their densities approximate freshwater values after 20 h. This rise in particle numbers coincides with the increase of ion-transporting activity of the cells known to take place after transfer to freshwater.
The rate of increase of particle densities is enhanced after injection of ovine prolactin. This hormone is known to stimulate Na+/K+-ATPase activity of the basal labyrinth of teleost kidney cells.
The results indicate that the particles represent enzyme complexes. The number of particles is probably under hormonal control. The increase in particle densities after transfer to fresh water is accompanied by a rise in the number of nuclear pores, which is noticeable by 10 h.
No changes were observed in the density of the particles adhering to the fracture faces of gap junctions.
An electron-microscope study of the lampbrush chromosomes of the newt Triturus Cristatus
Authors: Mott Margaret R. , Callan H. G. 
Published: April 2021

ABSTRACT
The ultrastructure of lampbrush chromosomes has been examined in sections of endembedded spread preparations, where the nuclear sap was dispersed prior to fixation, and in oocyte nuclei fixed entire, in 60-kV and i-MV electron microscopes. In spread preparations the axial chromomeres are seen to be organized as regularly spaced, unravelled skeins of DNP, each with a skein width of some 30 nm, though in some chromomeres there are regions where the DNP is much more densely packed. In both unravelled and dense regions, the ‘ultimate’ DNP fibres, wherever they can be identified, appear to be some 5 nm wide and thrown into loose coils. The unravelled state, although it clearly reflects an orderly packaging of the non-transcribing DNP, is an artifact of preparation; in sections of entire nuclei all chromomeres are seen to consist of DNP fibrils in the more densely packed state. The interchromeric fibril is single, and some 10 nm or less wide; it shows no sign of transcriptional activity.
In sections of end-embedded preparations the RNP matrix of most lateral loops, where transcription occurs, is seen to be made up of particles, each uniformly some 30 nm in diameter and strung together in linear array. These RNP particles are equally evident in sections of whole nuclei. In many loops the strings of particles are wound back on themselves to form regularly spaced, dense aggregates, each some 200–300 nm wide or wider; the larger aggregates can be resolved in the light microscope. The RNP particles are of the same dimensions throughout the lengths of individual lateral loops, and of substantially the same dimensions in loops of different gross morphologies. It is suggested that as each successive short length of RNA is transcribed from loop axis DNA, a protein associates with this RNA and winds it up to form a ‘manageable’ package, allowing transcription to proceed.
Colchicine resistance in mammalian cell lines
Authors: Minor P. D. , Roscoe D. H. 
Published: April 2021

ABSTRACT
Colchicine-resistant variants derived from mouse and Syrian hamster lines are described. The resistant cells do not appear to be true mutants, since they appear at a high frequency, unaffected by treatment with ethyl methyl sulphonate, and are unstable in the absence of the drug. They are cross-resistant to other drugs, show a reduced rate of binding of colchicine in monolayer, and give extracts with colchicine-binding properties identical to those of the wild type. Thus the resistance is due to a permeability barrier. The naturally occurring resistance of the Syrian hamster line is specific for colchicine, and may be due to a specific permeability barrier. The Syrian hamster line is also shown to have an extra colchicine-binding pool.
Inhibition of rrna synthesis following incorporation of 5-bromodeoxyuridine into dna of Tetrahymena pyriformis
Authors: Lykkesfeldt Anne E. , Andersen H. A. 
Published: April 2021

ABSTRACT
Tetrahymena pyriformis was grown on chemically defined medium in the presence of 5-bromodeoxyuridine (BUdR). Under these growth conditions more than 60% of the thymidine sites in DNA were substituted with BUdR. It was found that RNA synthesis was strongly inhibited by the presence of BUdR in. DNA. To assure that incorporation of BUdR into DNA was a prerequisite of the effect observed, BUdR was added to synchronously dividing cells. BUdR had no effect on the cells when present outside the period of nuclear DNA replication, whereas RNA synthesis was strongly inhibited as soon as the genes coding for ribosomal RNA had replicated in the presence of BUdR.
Dna synthesis in growth and encystment of Acanthamoeba castellanii
Authors: Roti L. W. Roti , Stevens A. R. 
Published: April 2021

ABSTRACT
Differentiation of Acanthamoeba castellanii into dormant cysts occurs spontaneously in stationary phase cultures, or can be induced experimentally by starvation. Although no further increase in cell density occurred after induction in either case, incorporation of [3H]thymidine into DNA continued at a reduced rate through the period when differentiated products (cyst wall components) were formed. No net accumulation of DNA occurred during differentiation, indicating that the DNA synthesis occurring at this time was balanced by breakdown.
When either 5-fluorodeoxyuridine (FUdR) or hydroxyurea was added to exponentially growing cultures, growth was terminated and the subsequent spontaneous encystment was delayed in comparison with untreated stationary phase cultures. A similar delay was observed for experimentally induced encystment of FUdR-pretreated cells. In all cases, delay of encystment was correlated with inhibition of 32PO4 incorporation into DNA, and unexpectedly also into RNA. Addition of FUdR at zero-time of experimental induction of cells not previously exposed to FUdR, on the other hand, had no effect on encystment or on “PO4 incorporation. The delay of encystment produced by FUdR and hydroxyurea, therefore, appeared to reflect a requirement for normal synthesis of DNA and/or RNA not only during encystment, but also during the period of exponential growth just before encystment induction.
Changes in the organization of chromosomes during the cell cycle: Response to ultraviolet light
Authors: Schor S. L. , Johnson R. T. , Waldren C. A. 
Published: April 2021

ABSTRACT
Fusion between mitotic and interphase cells results in the premature condensation of the interphase chromosomes into a morphology related to the position in the cell cycle at the time of fusion. These prematurely condensed chromosomes (PCC) have been used in conjunction with u.v. irradiation to examine the interphase chromosome condensation cycle of HeLa cells. The following observations have been made:
(1) There is a progressive decondensation of the chromosomes during G1 which is accentuated by u.v. irradiation:
(2) The chromosomes become more resistant to u.v.-induced decondensation during G1 and mitosis.
(3) There is a close correlation between the degree of chromosome decondensation and the amount of unscheduled DNA synthesis induced by u.v. irradiation during G1 and mitosis:
(4) Hydroxyurea enhances the ability of u.v. irradiation to promote the decondensation of chromosomes during G1, G1 and mitosis. Hydroxyurea also potentiates the lethal action of u.v. irradiation during mitosis and G1.
These data are discussed in relation to the suggestion that chromosomes undergo a progressive decondensation during G1 and condensation during G2.
Retention of endocrine function by an insulin-secreting pancreatic islet cell tumour from syrian hamster through serial transplantation in Nude mice
Authors: Shin Seung-Il , Baum S. G. , Fleischer N. , Rosen O. M. 
Published: April 2021

ABSTRACT
An insulin-secreting islet cell tumour of the Syrian hamster has been transplanted serially in the congenitally immune-deficient nude mouse, in order to test the potential usefulness of this mouse mutant as a graft carrier of heterologous tumours with stable differentiated phenotypes. The incidence of tumour growth was very high, and the hamster tumour retained its functional and histologic characteristics during consecutive passages in nude mice. These results show that nude mice may be useful carriers of differentiated tumours from non-inbred species including man, and for the isolation of cell lines from such tumours.
Adhesion of red blood cells to charged interfaces between immiscible liquids. a new method
Authors: Gingell D. , Todd I. 
Published: April 2021

ABSTRACT
We have devised a method of making a flat oil/water interface which remains flat on inversion. Cell adhesion to the interface can be observed microscopically.
Glutaraldehyde-fixed human red blood cells adhere to the interface between physiological saline and hexadecane containing surface-active behenic acid at pH values below about 7·5. At high pH values, cells are prevented from adhering due to dissociation of the carboxyl groups of behenic acid oriented in the interface. The negative red cells are driven away electrostatically.
Adherent and non-adherent cells remain on the aqueous side of the interface and do not appreciably deform it when adherent. Cells are electrostatically attracted to a similar interface containing positively charged octadecyltrimethylammonium ions. Cells also adhere to an interface containing octadecanol, which carries no charge.
Underlying both electrostatic repulsion and attraction between red cells and oil/water interfaces is an attractive force which may be of electrodynamic (van der Waals) origin.
Cell movement and adhesion in the developing chick wing bud: studies on cultured mesenchyme cells from normal and Talpid3 mutant embryos
Authors: Ede D. A. , Flint O. P. 
Published: April 2021

ABSTRACT
Mesenchyme fragments from early wing buds of normal and talpid3 mutant chick embryos were explanted for culture in plastic Petri dishes and the behaviour of individual cells as they moved out on to the plastic surface was studied by time-lapse ciné photography, followed by statistical analysis. Two parameters of cell movement were recorded: (1) the distances moved over measured 100-s intervals and (2) the length of time each cell spent at rest before moving on. The average speed of movement over the whole path tracked for each cell, inclusive of time at rest, was significantly greater in normal than in talpid3 cells. There was no significant difference between normal and mutant cells in the average distance moved per 100-s step, equivalent to the speed over the whole path exclusive of time at rest, but the percentage of time spent at rest was significantly less in normal than in talpid3 cells. This difference appears to be related to a difference in cell morphology, since it was observed that the mutant cells were more flattened than normals, with very extensive ruffled membranes and short spiky microvilli all round the cell periphery. The relation of these differences in cell morphology and behaviour in vitro to the production of the characteristically fan-shaped limb bud outgrowth and altered pattern of cartilage elements in the developing mutant limb bud is discussed.