bluuebunny/crossref_metadata_2025_split huggingface dataset:
High yields from microcarrier cultures by medium perfusion
Authors: Butler M. , Imamura T. , Thomas J. , Thilly W. G. 
Published: April 2021

ABSTRACT
A culture perfusion system is described for the growth of anchorage-dependent cells on microcarriers. The critical component of this system is a column separator, which removes medium while allowing the microcarriers to remain in the culture. Amino acids and ammonia were analysed during cell growth of the perfusion culture. None of the amino acids was completely utilized. The accumulation of ammonia to 2·3 mM was observed and may be responsible for, or coincident with, events limiting further cell growth. It is suggested that oxygen deprivation and growth inhibitor accumulation, rather than nutrient depletion, are the major factors in limiting even higher cell yields.
Neuronal motility: The ultrastructure of veils and microspikes correlates with their motile activities
Authors: Tosney K. W. , Wessells N. K. 
Published: April 2021

ABSTRACTWe have documented the ultrastructural characteristics that correlate with protrusion, adhesion and retraction of neuronal veils and microspikes, by filming individual neurons of the chick ciliary ganglion and examining the same cells with high-voltage electron microscopy.We find that new veils invariably contain only a cortical meshwork of filaments and are devoid of microtubules, groups of vesicles and other organelles. At sites of recent veil retraction a cortical meshwork on the substratum side underlies a filament-free space containing vesicle clusters and a complexly folded upper membrane. Areas without veil activity are smooth-surfaced and contain a three-dimensional lattice of filaments. We discuss the implications of these observations for the mechanisms of surface recruitment and retrieval during motile activity.We also find that the ultrastructure of moving and attached extensions of the cell surface differs dramatically. Unattached microspikes and actively extending veils have an open, criss-cross array of filaments, whereas attached microspikes contain more aligned filaments, which extend as a small bundle into the growth cone. These results suggest that cell surface protrusion is mediated by meshworks of loosely packed filaments. More compact bundles of filaments are probably generated only at adhesion points.
Action Spectrum For Changes In Spindle Fibre Birefringence After Ultraviolet Microbeam Irradiations Of Single Chromosomal Spindle Fibres In Crane-Fly Spermatocytes
Authors: Sillers Peggy J. , Forer Arthur 
Published: April 2021

ABSTRACT
Single chromosomal spindle fibres in Nephrotoma suturalis (crane-fly) spermatocytes in metaphase and anaphase were irradiated with monochromatic ultraviolet light focussed to a 2μm spot. In cells in both metaphase and anaphase either the birefringence of the irradiated spindle fibre was altered in the irradiated region, or there was no change, depending on the dose and wavelength of ultraviolet light used for the irradiation. When there was an area of reduced birefringence (ARB), it moved poleward regardless of whether the associated chromosome moved poleward. When cells were irradiated in early metaphase they remained in metaphase until the ARB reached the pole. In some cells irradiated in late metaphase the chromosomes began anaphase before the ARB reached the pole ; in many such cells anaphase was abnormal in that all six half-bivalents separated at the start of anaphase but none moved polewards.
In all cases the ARB moved poleward at the same speed as subsequent chromosome movement; that is, at about 0·8μm/min.
In cells irradiated in anaphase, spindle fibre birefringence was reduced independently of blockage of chromosome movement. Because birefringence and movement were altered independently there were four classes of results: (1) in some cases there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (2) In some cases, primarily with 260 nm wavelength light, there was no effect on the movement of the chromosome associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre. (3) In some cases, primarily with 290 nm wavelength light, there was an effect on the movement of the chromosome associated with the irradiated spindle fibre and no effect on the birefringence of the irradiated spindle fibre. (4) In some cases, primarily with 270 nm and 280 nm wavelength light, there was an effect on the movement of the chromosomes associated with the irradiated spindle fibre and there was an effect on the birefringence of the irradiated spindle fibre.
The action spectrum for reducing spindle fibre birefringence in crane-fly spermatocytes had two peaks, one at 260 nm and the other, less sensitive, at 280 nm. For irradiations at 270 nm, 280 nm and 290 nm, five to fifty times more energy was needed to reduce spindle fibre birefringence than to stop chromosome movement, but for irradiations at 260 nm five times less energy was needed to reduce spindle fibre birefringence than to stop chromosome movement. The action spectrum for reducing spindle fibre birefringence is quite different from that for stopping chromosome movement.
Feulgen Banding Of Heterochromatin In Plant Chromosomes
Authors: Marks G. E. 
Published: April 2021

ABSTRACT
Feulgen bands can be obtained at the sites of constitutive heterochromatin in the chromosomes of Anemone blanda, Fritillaria lanceolata and Scilla siberica, simply by means of a short or extended acid hydrolysis. Extended hydrolysis gives positive bands in A. blanda and F. lanceolata and negative bands in S. siberica. Short hydrolysis gives no bands in A. blanda and S. siberica but gives negative bands in F. lanceolata. The kind of Feulgen banding obtained is not correlated with the type of base richness of the heterochromatin DNA; rather, it is probably due to differences in the associated nucleoproteins.
Attachment Of Paramecium To Polystyrene Surfaces : II. Induction Of The Attachment By Hydrophobic Reagents Or Immune Immunoglobulin G
Authors: Kitamura Akio , Steers Edward 
Published: April 2021

ABSTRACT
Mating-reactive cells of Paramecium multimicronucleatum attach to a polystyrene surface (Falcon 1007 culture dishes) irrespective of extracellular ion concentration and swimming velocity. This attachment is induced in cells that are not mating-reactive by treatment with purified immunoglobulin G from antiserum, which blocks cells from mating or from antiserum prepared against the surface-localized immobilization antigens. Treatment with certain hydrophobic reagents such as phenethylamine, benzylamine, amphetamine or phenylethylamine also strongly induces attachment. Similar results are obtained with P. caudatum. Micronuclear activation, which normally occurs in the conjugation process, does not occur, however, in cells that are induced to attach to the polystyrene surface.
X-Ray Microanalysis Of Proximal And Distal Tubule Cells In The Mouse Kidney, And The Influence Of Cadmium On The Concentration Of Natural Intracellular Elements
Authors: Kendall Marion D. , Warley Alice , Nicholson J. K. , Appleton T. C. 
Published: April 2021

ABSTRACT
Quantitative X-ray microanalysis of frozen freeze-dried sections of mouse cortex have been used to determine the concentrations of Na, Mg, P, S, Cl, K, Ca and Cd in normal mice and those subjected to 0·7 μmol of cadmium chloride in two subcutaneous injections. These injections result in tissue levels of approximately 100 mg Cd/kg dry weight (&lt;1 mM) in whole kidney when analysed by atomic absorption spectrometry.
There were distinct and characteristic differences – ‘fingerprints’ – in the elemental composition of both cytoplasm and mitochondria in proximal and distal tubules of normal mice that were disturbed by the cadmium treatment.
The most significant effect of the cadmium injections was a highly significant increase in the sulphur content of the cytoplasm and mitochondria of distal tubules and a loss in concentration of Mg, P, Cl, K, and particularly Na, from the mitochondria. These results are discussed in the light of current concepts of metallothionein induction (metallothionein is a sulphur-rich protein that acts to bind, amongst other metals, cadmium) and the lack of damage observed in the distal tubules.
Serotonin-Binding Glycoprotein Of Rat Platelets
Authors: Tamir H. , Kupsky W. J. , Huang Y. L. , Gershon M. D. 
Published: April 2021

ABSTRACT
Platelets, because of their ability to take up serotonin, are often considered as models of serotonergic neurons. We have purified a glycoprotein from rat platelets that specifically binds serotonin (KD = 10 nM) but not [3H]imipramine (up to 0·2 μM). This protein is distinct from fibronectin. Antiserum raised against this protein was shown to be monospecific by double diffusion, rocket immunoelectrophoresis and immunoreactivity of protein transferred from slab gels to nitrocellulose sheets. We have called this protein serotonectin. Serotonectin-like material was localized by light- and electron-microscopic immunocytochemistry in rat platelets, using the unlabelled peroxidaseantiperoxidase complex bridge technique. All serotonectin immunoreactivity was found to be associated with the plasma membrane but no immunoreactivity was found in the surface connecting system. Washing platelets with Krebs solution removed 75% of the extractable serotonectin, indicating that it is a peripheral protein. Serotonectin was found to be circulating in the plasma, as the ease of its removal from platelet membranes suggests it must do; however, none was found in brain synaptosomes. Serotonectin was found to be synthesized in blood-forming organs (spleen, bone marrow) but not in the liver or the mucosa of the gut. Antibodies to serotonectin (4·5 mg/ml) inhibited the uptake of [3H]serotonin (0·2 μM) by rat platelets but not by synaptosomes. Serotonectin did not bind [3H]imipramine and washing the protein off platelet membranes did not impede the binding of [3H]imipramine to the membranes. Thus an action on serotonectin does not seem to be responsible for the antagonism by tricyclic antidepressants of serotonin uptake. These data suggest that serotonectin is present on the external surface of platelet plasma membranes, that it is excluded from the plasma membrane of the surface connecting system, and that it may be in equilibrium with free material in plasma.
Higher-Order Structure Of Chromatin From Resting Cells : I. Electron Microscopy Of Chromatin From Calf Thymus
Authors: Cavazza B. , Trefiletti V. , Pioli F. , Ricci E. , Patrone E. 
Published: April 2021

ABSTRACT
Extremely large domains of the genome of resting cells (calf thymus) have been visualized in the electron microscope by combining mild extraction procedures with a non-artifactual method of mounting the sample (the phospholipid monolayer technique). The observed chromatin strands, free from distortion, reach contour lengths up to 60μm.
After lysis of the nuclei, four classes of fibres may be identified on the basis of their diameters (30, 24, 18 and 11 nm, respectively). The morphology of giant chromatin strands is strikingly regular; long trains of equally sized, arc-shaped segments are observed, their length being, in many cases, multiples of a fixed value. The inflection points delimiting contiguous segments are often associated with laminar fragments of the nuclear envelope or, less frequently, linked to fibrillar elements. It appears that higher-order structures of chromatin in resting cells conform, to a large extent, to a so called ‘drapery-like’ model, according to which a continuous strand runs between contiguous an-chorage sites placed on the nuclear envelope. Because of the presence of regularly spaced inflection points, this organization is much more ordered than expected.
Spontaneous unwinding of the fibres at low ionic strength, limited nuclease digestion, and relaxation in the presence of ethidium bromide, have been used as probes of the conformation. All these experiments rule out its identification with a single-strand helix. The final ordered state is attained by folding the basic 11 nm strand and by winding up this configuration on itself. This leads to a coiled-coil or ‘rope-like’ model. The 11 nm strand is ‘punctuated’ by sharp kinks. Roughly, it may be assimilated to a chain of semirigid, freely joined elements. As a consequence, local flexibility is greatly enhanced, so allowing the assembly mode described.
Ultrastructural analysis of crystalloid endoplasmic reticulum in ut-1 cells and its disappearance in response to cholesterol
Authors: Anderson Richard G. W. , Orci Lelio , Brown Michael S. , Garcia-Segura Luis M. , Goldstein Joseph L. 
Published: April 2021

ABSTRACT
The crystalloid endoplasmic reticulum (ER) consists of hexagonally packed membrane tubules that contain 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase), an intrinsic membrane protein that catalyses the rate-limiting step in cholesterol synthesis. The crystalloid ER appears in a clone of Chinese hamster ovary cells, designated UT-1, that contain high levels of HMG CoA reductase as a result of growth in the presence of compactin, a competitive inhibitor of the reductase. In the present studies, we have used ultrastructural morphometry to estimate that the crystalloid ER: (1) occupies about 15% of the volume of UT-1 cells; (2) contains 3·4-fold more membrane area than the plasma membrane; and (3) contains less than 700 subunits of HMG CoA reductase per μm2 of membrane surface. The crystalloid ER tubules contain 2000 intramembrane particles per μm2 with a mean diameter of 10·4 nm, as determined by freeze-fracture. The crystalloid ER membranes are low in cholesterol, as indicated by the small number of filipin-cholesterol complexes in freeze-fracture images after treatment with filipin. The addition of cholesterol or related sterols to UT-1 cells promoted a rapid and stepwise disappearance of the crystalloid ER. Initially, the crystalloid ER fragmented into randomly arranged vesicles and tubules. Subsequently, membrane-bound structures disappeared from the cell so that after incubation with cholesterol for 24—72h, the cells appeared completely normal. We found no morphological evidence that autophagic vacuoles participate in the degradation. We conclude: (1) that the crystalloid ER is more extensive than necessary merely to support HMG CoA reductase; and (2) that upon exposure to cholesterol the crystalloid ER is degraded by a process that does not involve autophagy.
Ultrastructure and development of the flagellar apparatus and flagellar motion in the colonial green alga Astrephomene guberna culifera
Authors: Hoops Harold J. , Floyd Gary L. 
Published: April 2021

ABSTRACT
Immediately following embryonic cleavage, the cells of Astrephomene have four equal-sized basal bodies, two of which are connected by a striated distal fibre and two striated proximal fibres. The four microtubular rootlets, which alternate between having 3/1 and 2 members, are arranged cruciately. The two basal bodies that are connected by the striated fibres then extend into flagella, while the two accessory basal bodies are now markedly shorter. At this stage the flagellar apparatus has 180° rotational symmetry and is very similar to the flagellar apparatus of the unicellular Chlamydomonas and related algae. Development proceeds with a number of concurrent events. The basal bodies begin to separate at their proximal ends and become nearly parallel. Each striated proximal fibre detaches at one end from one of the basal bodies. Each half of the flagellar apparatus, which consists of a flagellum and attached basal body, an accessory basal body, two rootlets and a striated fibre (formerly one of the proximal striated fibres), rotates about 90 °, the two halves rotating in opposite directions. An electron-dense strut forms near one two-membered rootlet and grows past both basal bodies. During this time a fine, fibrous component appears between newly developed spade-like structures and associated amorphous material connected to each basal body. The basal bodies continue to separate as the distal fibre stretches and finally detaches from one of them. These processes result in the loss of the 180° rotational symmetry present in previous stages. Although the flagella continue to separate, there is no further reorganization of the components of the flagellar apparatus. In the mature cell of Astrephomene, the two flagella are inserted separately and are parallel. The four microtubular rootlets are no longer arranged cruciately. Three of the rootlets are nearly parallel, while the fourth is approximately perpendicular to the other three. A striated fibre connects each basal body to the underside of the strut. These fibres run in the direction of the effective stroke of the flagella and might be important either in anchoring the basal bodies or in the initiation of flagellar motion. Unlike the case in the unicellular Chlamydomonas, the two flagella beat in the same direction and in parallel planes. The flagella of a given cell may or may not beat in synchrony. The combination of this type of flagellar motion and the parallel, separate flagella appears to be suited to the motion of this colonial organism.
Ultrastructure of the dinoflagellate polykrikos : I. development of the nematocyst–taeniocyst complex and morphology of the site for extrusion
Authors: Westfall Jane A. , Bradbury Phyllis C. , Townsend J. W. 
Published: April 2021

ABSTRACT
Development of the nematocyst-taeniocyst complex in the four-zooid stage of a dinoflagellate, Polykrikos kofoidi, was studied by electron microscopy. We observed the following stages: formation of large spherical bodies in islets of cytoplasm containing extensive rough endoplasmic reticulum and Golgi complexes; differentiation of an anlage of first the nematocyst and then the taeniocyst into a tandem pair; and, maturation of the complex into a nematocyst with operculum and capsule, and a taeniocyst with head, neck and body. In the intermediate stages of dinoflagellate cnidogenesis the structurally elaborate pattern of development differed from that of coelenterate nematocysts but in certain features the mature organelles of both groups were similar. Nematocyst-taeniocyst complexes migrated into chutes on zooids two and four near the junction of the annulus and sulcus at the flagellar bases. The specialized chute was partially lined by thimble-shaped organelles of unknown function. The taeniocyst protruded from the surface in association with a striated fibre whose structure and position were those of a trigger to discharge the two organelles. We found no cytostome in this holozoic colony; the structure of the chute suggested that it might also function as a cytostome.
Limited and unlimited growth of sv40-transformed cells from human diploid mrc-5 fibroblasts
Authors: Huschtscha L. I. , Holliday R. 
Published: April 2021

ABSTRACT
Human foetal lung strain, MRC-5, was treated with simian virus 40 and cultures were obtained that had many of the properties of transformed populations. In 10 experiments, only two produced permanent lines, designated MRC-5V1 and MRC-5V2, which have grown to passage 750 and 650, respectively. In all cases, the SV40-treated cultures acquired many of the features of transformation, including production of T-antigen, loss of contact-inhibition, and ability to grow in low concentrations of serum. The presence or absence of other transformed characteristics, such as altered morphology, abnormal karyotype or ability to grow in soft agar, can be used to distinguish between individual newly infected cultures. However, the cells invariably entered a period of slow growth, or crisis, and in eight experiments the cultures subsequently died without the emergence of a permanent line. The report that late-passage diploid cultures are more easily transformed to permanent lines than young cultures has not been confirmed. MRC-5V1 initially had a sub-diploid chromosome number, but during serial passaging this gradually increased. MRC-5V2, which has a more extreme transformed phenotype than MRC-5V1, had a hyper-diploid chromosome number, which also increased during long-term growth. MRC-5V1 became polymorphic for glucose-6-phosphate dehydrogenase, as judged by the heat-lability and electrophoretic mobility of the enzyme. Fusions between MRC-5V1 and Lesch-Nyhan fibroblasts yielded hybrids with a limited lifespan, and certain sub-lines of MRC-5V1 also slowed down, exhibited characteristic signs of senescence and ceased to grow.
Transitions in Dictyostelium discoideum behaviour: Influence of calcium and fluoride on slug phototaxis and thermotaxis
Authors: Dohrmann Ulrike , Fisher Paul R. , Brüderleln Martina , Williams Keith L. 
Published: April 2021

ABSTRACT
Phototaxis and thermotaxis by slugs of Dictyostelium discoideum show transitions that result in bimodality in phototaxis and temperature-dependent orientation up or down temperature gradients. New steps in the sensory transduction chain for these kinds of behaviour are elucidated from studies using inorganic salts (Ca2+, EGTA, KF) and several mutants. KF enhances bimodality of phototaxis, improves the accuracy of thermotaxis, and affects the transition temperatures from positive to negative thermotaxis. Changing the Ca2+ concentration has effects on both phototaxis and thermotaxis. At low Ca2+ concentrations phototaxis and thermotaxis are enhanced. In the presence of EGTA or high concentrations of Ca2+ phototaxis becomes bimodal, thermotaxis is impaired and spontaneous turning is suppressed. These results obtained by changing Ca2+ concentrations are analogous to those obtained previously with sensory transduction mutations, which coordinately affect phototaxis and thermotaxis.
Manganese-dependent cell - substratum adhesion
Authors: Grinnell Frederick 
Published: April 2021

ABSTRACT
I n the presence of manganese, baby hamster kidney cells attached and spread on substrata without added adhesion factors (e.g., fibronectin, lectins). This Mn-dependent adhesion occurred even when the substratum was coated with proteins, such as albumin, haemoglobin, immunoglobulin or ovalbumin, or a dried collagen film. Under similar conditions, cells without Mn in Mg/Ca-containing medium attached poorly and did not spread. Other divalent cations, including Mg, Ca, Fc, Co and Ni, could not replace Mn. Cell surface sites required for Mn-dependent adhesion were destroyed by brief proteolytic treatment of the cells with trypsin or Pronase under conditions where the fibronectin-receptor was unaffected. Also, addition to the incubations of antibodies that inhibited ligand-mediated cell adhesion (e.g., by fibronectin or lectins) inhibited adhesion of cells in Mn-containing medium and caused rounding of cells previously attached and spread in the presence of Mn. The continuous presence of Mn was required for adhesion. That is, cells that were attached and spread in Mn-containing medium and then switched to Mg/Ca-containing medium (which permitted cytoskeletal function) were found to round up and detach. In marked contrast, cells that were allowed to attach and spread on fibronectin-coated substrata in the presence of Mn did not round up when they were switched to Mg/Ca containing medium. Possible explanations for Mn-dependent cell adhesion are discussed.