bluuebunny/crossref_metadata_2025_split huggingface dataset:
An intracellular pool of a cell-surface ligand which inhibits lectin-induced capping
Authors: McDonough James , Rutz Richard , Lilien Jack 
Published: April 2021

ABSTRACT
It has previously been established that cells dissociated from embryonic chick neural retina tissues redistribute their cell surface Concanavalin A receptors into patches and caps upon treatment with the lectin. During 4 h in continuous culture the cell population progressively loses the capacity to cap Con A receptors. In the presence of cycloheximide this decrease occurs for only the first 2 h of incubation. Concomitant with this loss in the ability to redistribute Con A receptors, cells become agglutinable by a tissue-specific component first described in 1975.
The results of our experiments assaying inhibition of capping by tissue culture supernatant solutions and loss of capping ability through cellular repair processes are interpreted in terms of an endogenous pool of one or more species, which, when displaced to the cell surface, inhibit the capping of Con-A receptors and permit tissue-specific cell agglutination. Once present at the cell surface, these species are released into the culture medium, either during continuous culture or during an incubation in fresh medium containing cycloheximide. Subsequent to release of these species, the cells regain their capacity for cap formation and lose agglutinability. In addition, the components released from the cells inhibit capping of Con A receptors when added to freshly dissociated cells.
The assay methods were also used to determine parameters governing mobilization of the pool of capping inhibitors to the cell surface.
Distribution of anionic sites on surface of b cell granule and plasma membranes: a study using cationic ferritin
Authors: Howell S. L. , Tyhurst Margaret 
Published: April 2021

ABSTRACT
The distribution of anionic sites on the membranes of rat pancreatic B cells and of their storage granules has been studied by the use of a visual probe of cationic ferritin. Membranes of isolated storage granules possessed a net negative charge which was apparently evenly distributed; the number of anionic sites was not markedly altered by prior incubation of the granules with neuraminidase or with 10−6 to 2 × 10−3 M calcium chloride. Distribution of charges along B cell plasma membranes was less uniform but was similarly unaffected by alterations of calcium concentration, or by neuraminidase treatment. However, during the fusion of plasma membrane and granule membrane which occurs in exocytosis, the emerging granule membrane was found to be devoid of anionic sites. The implications of these findings for the regulation of insulin secretion by exocytosis are discussed.
Endotoxin-induced platelet aggregation and secretion I. morphological changes and pharmacological effects
Authors: Macintyre D. Euan , Allen Anthony P. , Thorne Kareen J. I. , Glauert Audrey M. , Gordon John L. 
Published: April 2021

ABSTRACT
Endotoxin lipopolysaccharide (LPS) from Acinetobacter 199 A induced aggregation of blood platelets from immune adherence-positive species (rat, rabbit) but not from immune adherencenegative species such as pig and man. Aggregation occurred in 2 phases: the first was not accompanied by secretion of platelet constituents, was apparently a consequence of C3 activation, and was selectively inhibited by EGTA. The second phase of aggregation was associated with secretion of platelet granule contents, and with a lesser amount of cytoplasmic leakage. Secondary aggregation was abolished by the sulphydryl alkylating agent N-ethyl maleimide, and by agents which increased the level of cyclic AMP in platelets, such as prostaglandin Et (a stimulator of adenylate cyclase) and methyl xanthines (inhibitors of phosphodiesterase). Secondary aggregation was partly inhibited by agents which block platelet prostaglandin biosynthesis (e.g. aspirin, indomethacin). Primary aggregation was unaffected by these inhibitors at concentrations which blocked secondary aggregation.
Endotoxin-induced platelet aggregation and secretion. II. changes in plasma membrane proteins
Authors: Thorne Kareen J. I. , Oliver Rhonda C. , Macintyre D. Euan , Gordon John L. 
Published: April 2021

ABSTRACT
Responses of blood platelets to bacterial endotoxin lipopolysaccharide (LPS) have been correlated with changes in the molecular organization and composition of the platelet plasma membrane proteins. Binding of LPS, which occurred in the absence of Ca2+, was distinguished from platelet aggregation and degranulation, which required Ca2+ and plasma proteins.
Changes in membrane organization were detected by double-labelling with [l25I] and [131I] iodide, mediated by lactoperoxidase and hydrogen peroxide. Changes in total membrane composition were detected by gel electrophoresis of isolated membranes. Binding of LPS was associated with increased accessibility of a protein of mol. wt. 80000 to iodination. After aggregation and degranulation there was, in addition, increased accessibility of proteins of mol. wt. 68000 and 48000. Isolated membranes from LPS-stimulated platelets contained more of a protein of mol. wt. 200000 and less of a protein of mol. wt. 220000 than control membranes prepared from unstimulated platelets in the presence of cAMP and aminophylline.
The relationship of the modified plasma membrane proteins to the contractile proteins of the platelet and their possible redistribution in the cell during aggregation and secretion is discussed.
Interaction of glycosaminoglycan and adenylate cyclase at the surface of cultured human diploid fibroblasts (HLM15)
Authors: Kelley Robert O. , Palmer Gene C. , Crissman Harry A. , Nilson John H. 
Published: April 2021

ABSTRACT
To determine whether glycosaminoglycan-containing (GAG) components of embryonic cell surfaces are associated with adenylate cyclase, human limb mesenchymal cells (HLM15) in exponential and stationary conditions were incubated in testicular hyaluronidase (300 lU/mg) prior to analysis of enzyme activity (stimulated with 10−4 M norepinephrine, NE). Treatment with NaF revealed an active catalytic component of the adenylate cyclase system. However, little activity of adenylate cyclase was observed after incubation of exponential growth control groups with NE. Removal of GAG increased enzyme activation by NE over that of controls, suggesting the presence of a developed but masked receptor component. Untreated, stationary cells after incubation in NE showed enzyme activity similar to that of hyaluronidase-treated cells in exponential growth. Patterns of distribution in G1S and G2+ M after enzyme treatment were identical to controls. In addition, cells incubated for 4 h in growth medium containing NE had normal cell cycle distributions. HLM15 cells incubated in medium containing dibutyryl cyclic AMP (dbcAMP: 10−5 to 10−8 M) had population doubling times of 40 + h (in contrast to a 24-h generation time for controls) and exhibited a consistent perturbation of S. Cells incubated in hyaluronidase and cultured for 4 additional hours in NE show a pattern of perturbation in S identical to that of cells cultured in dbcAMP. Furthermore, these cells exhibit increased incorporation of [3H]uridine into RNA when compared to untreated cells. We conclude that HLM15 cells have developed both receptor and catalytic components of the adenylate cyclase system and that enzyme receptivity to hormone stimulation is enhanced when cell-surface GAG is reduced.
Association of membrane cisternae and macrotubules in vinblastine-treated histiocytes
Authors: Schliwa Manfred 
Published: April 2021

ABSTRACT
Resting histiocytes within the dermis and epidermis of the cichlid fish Pterophyllum scalare exhibit an unusual association between stacks of lamellar cistemae and tubular structures greater in diameter than ordinary microtubules (macrotubules) after treatment with 2 × 10−4 M vinblastine. Macrotubules are found in the intercistemal spaces in a regular side-by-side orientation and extend the entire length of the cisternae. The lamellae seem to be formed as a result of increased membrane proliferation of the outer nuclear membrane; in some instances, cistemae have been observed to be continuous with the nuclear envelope. Since blebbing of the outer nuclear membrane is also observed in untreated histiocytes, lamellae formation is envisaged as hypertrophy of a normally occurring process. The association of lamellae with macrotubules possibly indicates a relationship between membranes and microtubule proteins.
Cell contact-induced inhibition of division in Dictyostelium
*
Authors: Kopachik Will J. , Gregg James H. 
Published: April 2021

ABSTRACT
The developmental stage at which Dictyostelium discoideum strain v12/M2 cells was inhibited in resuming cell division was monitored by a Coulter counter. Neither vegetative nor preaggregating v12/M2 amoebae used as inocula in liquid growth cultures exhibited a delay in recommencing cell division. Inocula prepared from aggregates were delayed for 3 h before the onset of division. Although cyclic AMP had no effect upon vegetative or preaggregating stages the aggregating amoebae were inhibited for 9 h before resuming division. Following the onset of division by both controls and cyclic AMP-treated cells the normal growth rate of vegetative amoebae (3·2 h/generation) was attained. Aggregateless mutant vegetative amoebae and those of comparable ages to v12/M2 aggregates were not inhibited in the rate of cell division by cyclic AMP.
Cyclic AMP sustains the delay in cell division only among amoebae derived from aggregates. Cyclic AMP induces structural components in the plasma membranes which may be necessary in cell adhesion and interactions. Consequently interactions between the membranes of apposing cells may transmit stimuli intracellularly to inhibit cell division.
Fluorescent staining of fungal nuclei with a benzimidazol derivative
Authors: Lemke Paul A. , Kugelman Bertha , Morimoto Hideo , Jacobs Ernest C. , Ellison John R. 
Published: April 2021

ABSTRACT
A direct staining procedure is described for fluorescence microscopy of fungal nuclei, chromosomes and mitochondria. The fluorochrome is a benzimidazol derivative (33258 Hoechst) known to bind selectively to deoxyribonucleic acid at neutral pH. The advantages of 33258 Hoechst relative to Feulgen compounds used previously to stain these structures include a greater intensity of fluorescence, the absence of fading or rapid quenching of the fluorescence, and the omission of acid hydrolysis from the procedure for removal of ribonucleic acid. 33258 Hoechst has been evaluated as a nuclear stain with a yeast (Saccharomyces cerevisiae) and a filamentous fungus (Agaricus bisporus) and appears to penetrate easily vegetative cells and spores of both fungi.
Studies on the incorporation of dna into Paramecium Aurelia
Authors: Gibson I. 
Published: April 2021

ABSTRACT
Attempts have been made to transform the cell Paramecium aurelia with DNA preparations. No success was achieved for the genes concerned with maintenance of killer particles or surface antigens. Using radioautography, density gradient ultracentrifugation and nucleic acid hybridization it was shown that extracellular DNA was taken up by paramecia and remained as long nucleotide sequences. Possible reasons for the failure of transformation in the face of such observations are given.
Sarcomere length during post-natal growth of mammalian muscle fibres
Authors: Goldspink G. 
Published: April 2021

ABSTRACT
The length of the sarcomeres, the A- and the I-filaments and their percentage overlap were measured in the fibres of the biceps brachii muscle from mice of different ages. The sarcomere length with the limb in the fully extended position was found to increase from 2·3 μ in the newborn animal to 2·8 μ in the adult. This increase was due to a decrease in the percentage overlap of the filaments and not to any change in the filament lengths. The sarcomeres at the ends of the fibres were found to be shorter than those in the middle of the muscle, at all ages. When the muscles were stretched beyond their resting length, only about the middle 60 % of the sarcomeres in the young muscles increased in length. Length/tension plots were obtained for young and old muscles and the difference in the shape of these plots could be explained as being due to the non-functional terminal sarcomeres of the young muscles. The maximum tension developed by the young muscles was found to be attained at an initial muscle length about 10 % greater than their length at maximum limb extension. The adult muscles developed maximum tension at their length at maximum limb extension.
The response of human cultured lymphocytes to cytochalasin b
Authors: Ridler M. A. C. , Smith G. F. 
Published: April 2021

ABSTRACT
The cytochalasins are a new group of compounds which have been recently isolated from moulds. Some of their properties are of interest in the study of cytoplasmic and nuclear division since they have been shown to inhibit motility, produce nuclear extrusion and prevent cytoplasmic cleavage with the production of multinucleated cells. The present study is a report of the effects of cytochalasin B on cultured human lymphocytes.
After exposure to cytochalasin B, a proportion of the cultured human lymphocytes became multinucleate. The magnitude of this effect was related to the concentration and the length of time of exposure to the compound. Cells with from one to eight nuclei were identified. Progressive variation in nuclear morphology became apparent as the number of nuclei in a cell increased. Examination of the chromosomes showed only diploid, tetraploid and a few octa-ploid cells. No obvious chromosomal abnormalities were detected, except in octaploid cells. It is suggested that in multinucleated cells there may be a failure of mitotic control leading to variations in size and shape of interphase nuclei.
The effect of antrycide on patterns of rna synthesis in Amoeba discoides
Authors: Summers Julie M. , Hawkins Shirley E. 
Published: April 2021

ABSTRACT
Antrycide is an aminoquinaldine whose inhibitory action on the growth of Trypanosoma and Crithidia is not fully understood at the cellular level. The growth of Amoeba discoides in concentrations of antrycide between 0·5 and 2 was reduced considerably, while cells failed to divide in 4 μg/ml. The effects on growth rate were reversible at least up until 7 days in antrycide.
In order to assess the action of this synthetic drug on RNA synthesis in amoebae, the pattern of synthesis in normal cells was investigated using polyacrylamide gel electrophoresis. The profile of high molecular weight RNAs observed depended on the length of time in [3H]uridine, and was only fully developed after 66 h, when 5 peaks could be seen. The relative molecular weights of these peaks (I-V) were 2·45, 1·55, 1·13, 0·8 and 0·52×106 Daltons respectively. Those of 1·55 and 0·8 × 106 corresponded to ribosomal RNAs, the identity of the other peaks is unknown.
After growth in 2 μg/ml antrycide for 4 days, no high molecular weight RNA was found. Use of [14C]adenine/[3H]uridine showed that after 17 h in antrycide there was a loss of ribo-somal RNA and increased levels of low molecular weight RNAs, due either to lack of synthesis or to degradation of newly synthesized material. Incorporation of [3H]leucine into hot acid-precipitable protein was inhibited in antrycide-treated cells by at least 50%. A possible explanation of the effect of antrycide on A. discoides was the inhibition of mRNA synthesis for ribosomal proteins, leading to degradation of newly synthesized rRNA. Reduced growth would continue on pre-existing ribosomes and previously synthesized long-lived mRNAs.
Membrane junctions in the myelin sheath of goldfish lateral nerve
Authors: Bertaud W. S. 
Published: April 2021

ABSTRACT
The myelin sheath of the goldfish lateral line nerve has been studied by means of the freezeetch technique. Fracture faces of the myelin lamellae reveal linear structural elements which in some respects resemble those of tight junctions. In unfixed myelin rows of particles on the ef face are matched by narrow grooves on the pf face. Fixation with glutaraldehyde produces a partitioning of junctional particles between the 2 fracture faces. These elements are observed most frequently in the outer layers of the sheath where their arrangement is predominantly more or less parallel and longitudinal, merging in places into a more reticulate organization. They also occur at other levels in the myelin and in association with Schmidt-Lantermann clefts. Orientation in these cases appears to be predominantly longitudinal, though circumferentially running elements have been observed. The possible functional significance of these structures and their implications for tissue development, maintenance and growth are discussed.
Direct visualization of the 10-nm (100- Å)-filament network in whole and enucleated cultured cells
Authors: Small J. V. , Celist J. E. 
Published: April 2021

ABSTRACT
Following extraction of actomyosin and tubulin from cultured cells treated with Triton X-100, a cytoskeleton remains which is composed predominantly of the cell nucleus encompassed by a network of 10-nm filaments. After negative staining the dense perinuclear region appears as a densely woven filament net punctuated by patches of high electron density. Enucleation of 3T3cells with cytochalasin B gives rise to karyoplasts surrounded by 10-nm filaments and cytoplasts in which 10-nm filaments remain situated in the central region of the cytoplasm. While the 10-nm filaments occurred mainly as single filaments in human skin fibroblasts and 3T3cells, in epithelioid PtKi and PtK2 cells they were commonly associated in prominent meandering bundles. In addition, in these latter cells after Triton extraction the remaining ribosomes were bound specifically to the 10-nm-filament net.
After exposure of 3T3cells to cytochalasin B the 10-nm filaments formed branches that radiated from the perinuclear region into the immobile cell extensions. Concavalin A had no marked effect on the distribution of the 10-nm-filament net.
The results suggest that the 10-nm filaments act primarily as structural elements, serving, in particular, to support and constrain the nucleus in its position in the cell.
The induction of the acrosome reaction in guinea-pig sperm by the divalent metal cation ionophore a23187
Authors: Green D. P. L. 
Published: April 2021

ABSTRACT
The divalent metal cation, ionophore A23187 induces an acrosome reaction in guinea-pig sperm which is dependent on external calcium. Examination of this acrosome reaction by electron microscopy shows that it is morphologically normal. The known properties of A23187 and the morphological similarity between the acrosome reaction and the secretory discharges of other secretory cells suggests that the immediate cause of the acrosome reaction is an increase in the cytoplasmic free calcium concentration.
Macrotubules induced by halothane: in vitro assembly
Authors: Hinkley Robert E. 
Published: April 2021

ABSTRACT
The formation of macrotubules by the volatile anaesthetic halothane was investigated in vitro using microtubule-enriched fractions of crayfish nerve cords. Sequential studies showed that macro tubules assemble from helical ribbons of 18 –20 laterally associated microtubule protofilaments which fold upon themselves to form intact macrotubules averaging 48 nm in diameter. The initial rate of macrotubule assembly is dependent on the concentration of halothane employed and is stimulated by calcium. Glycerol pretreatment blocked macrotubule formation by halothane and caused preformed macrotubules to reassemble rapidly into typical microtubules. These experiments show that microtubules and macrotubules require different conditions for assembly and support the contention that macrotubule formation by halothane is due to a direct interaction between the anaesthetic molecule and the microtubule subunit.
IgG receptors on foetal chick yolk sac
Authors: Linden Carol D. , Roth Thomas F. 
Published: April 2021

ABSTRACT
In the chicken, maternal IgG is deposited in the oocyte yolk and subsequently transported intact by the foetal chick yolk sac into the chick circulation. Such transport appears to require a specific membrane-localized IgG receptor.
Using the assay of 125I-yolk IgG binding, we have investigated the existence and properties of such receptors in yolk sac tissue disks. We find that: (1) There are specific 125I-IgG binding sites on yolk sac tissue; (2) specific yolk 125I-IgG binding has a distinct pH optimum at pH 6·0–6·3; (3) the apparent equilibrium dissociation constant of specific 125I-IgG binding is 2·3×10−6 M; and (4) heterologous proteins compete less efficiently than yolk IgG for 125I-IgG binding.
Intercellular bridges between follicle cells and oocyte during the differentiation of follicular epithelium in Lacerta sicula Raf
Authors: Andreuccetti P. , Taddei C. , Filosa S. 
Published: April 2021

ABSTRACT
Intercellular bridges first appear during lizard oogenesis when follicles are rather small (150 pm in diameter); at this stage they form connecting links between the oocyte and follicle cells, which have not yet differentiated into pyriform cells. Later on, when the follicles have become larger (1 mm) and the follicular epithelium appears constituted by 3 types of cells (small, intermediate and pyriform cells) they form connecting links between the oocyte and both intermediate and pyriform cells. The establishment of intercellular bridges between pyriform cells and the oocyte precedes the complete differentiation of the former, which excludes the possibility that the fusion between pyriform cells and oocyte occurs only after these cells are completely differentiated.
In still larger follicles (up to 2 mm in diameter), during the degeneration of the pyriform cells, the occurrence, inside the bridges, of mitochondria and other cytoplasmic material suggests that these cells at the end of their function transfer their contents into the oocyte.
Cell motility in fibroblast aggregates
Authors: Armstrong Margaret T. , Armstrong Peter B. 
Published: April 2021

ABSTRACT
The stable arrangements of cells in tissues and organs require that most tissue cells, whatever their inherent abilities for active pseudopod-directed locomotion, remain confined to the boundaries of their parent tissues and organs for the lifetime of the organism. Contact inhibition of motility represents a potential mechanism for immobilizing cells in tissues and thus in promoting positional stability. In order to assess the effectiveness of contact inhibition in immobilizing cells in 3-dimensional tissue-like masses, spherical aggregates of chick heart, sclera and skin fibroblasts were fused with tritiated thymidine-labelled aggregates of the identical cell type. After being placed in contact, the 2 aggregates cohere and broaden the area of mutual contact to form a single aggregate with a planar interface between the two. Mobility of cells was detected by the migration of labelled cells across the interface and into the unlabelled aggregate. Based on measurements of distances moved in day-old aggregate pairs, it was found that fibroblasts moved up to 17 cell diameters and up to 36 % as far in solid tissue masses as in monolayer culture under optimal conditions for directed migration.