bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the template activity of ‘isolated’ Xenopus erythrocyte nuclei: I. the effects of ions
Authors: H1Lder V. A. , Maclean N. 
Published: April 2021

ABSTRACT
The isolation and characterization of nuclei from Xenopus erythrocytes is described. Such nuclei are freely permeable to ions and large molecules. They have an extremely low basal rate of RNA synthesis which can be increased by the addition of Escherichia coli RNA polymerase and by alteration in the ionic strength of the incubation medium within physiological limits. The results are discussed in terms of the mechanisms which control gene activity in these cells.
Binding of radiolabelled collagen to blood platelets
Authors: Gordon J. L. , Dingle J. T. 
Published: April 2021

ABSTRACT
Purified, soluble collagen was prepared from rat skin, and the tyrosine residues were labelled with 125I by the chloramine T method. The collagen was added to platelet-rich plasma from rats or rabbits, and then layered on 23 % w/v Ficoll. After centrifugation at 3900 g for 20 min, the platelets were recovered from beneath the Ficoll, and the radioactivity associated with them was measured. This represented the platelet-bound collagen, since very little collagen penetrated the Ficoll if platelets were absent.
The amount of platelet-bound collagen paralleled the extent of collagen microfibril formation, which in turn increased with the time the collagen was preincubated at 36 °C before being added to the plasma.
The amount of binding in each sample was reproducible within groups of rats or rabbits, but the amount of collagen bound per platelet was about 3 times greater in samples from rabbits than from rats.
The aggregation of rabbit polymorphonuclear leucocytes: Effects of antimitotic agents, cyclic nucleotides and methyl xanthines
Authors: Lackie J. M. 
Published: April 2021

ABSTRACT
The aggregation of rabbit peritoneal exudate polymorphonuclear leucocytes (PMNs) was investigated by following total particle number with time, in a shaken suspension. Aggregation was rapid and essentially complete by 30 min, but could be inhibited by microtubule-blocking agents, adenosine and methyl xanthines. The addition of cyclic adenosine 3’:s’-mono-phosphate (cAMP), or its dibutyryl derivative, also inhibited aggregation slightly, but guanosine nucleotides had no significant effect. By consideration of the maximum inhibition brought about by colchicine or theophylline alone, or the two in combination, it appears that they act at different sites to inhibit aggregation, though the effects of either were partially reversed by the addition of adenine. Adenine, lumicolchicine and high concentrations of vinblastine sulphate (10−4 M), enhanced aggregation.
Release from density-dependent inhibition of growth in the absence of cell locomotion
Authors: Yarnell Margaret M. , Schnebli H. P. 
Published: April 2021

ABSTRACT
3T3 mouse fibroblasts are released from density-dependent inhibition of growth by treatment with insulin. The same insulin treatment stimulates cell locomotion several hours before any new mitoses become visible. Inhibition of cell locomotion by colcemid does not affect the overgrowth stimulation due to insulin. From this it is concluded that cellular locomotion is not a prerequisite for the release from density-dependent inhibition of growth.
Effects of dmso on vacuole formation, contractile vacuole function, and nuclear division in Tetrahymena Pyriformis GL
Authors: Nilsson J. R. 
Published: April 2021

ABSTRACT
Increasing concentrations of dimethyl sulphoxide (DMSO) affect vacuole formation in Tetrahymena, as measured quantitatively by the uptake of carmine particles. The rate of vacuole formation decreased to about 50% of the control value in 5·0% DMSO (v/v) and to zero in 7·5%. At the latter concentration, the inhibition was expressed immediately; however, the effect of t-h exposure was reversible after removal of DMSO by washing. In vivo observations revealed abnormal function of the contractile vacuole in 7·5% DMSO, while cell motility and cell division appeared to be unaffected. Although cell division occurred there was little or no increase in cell number, as studied over a cell generation time. Feulgen preparations showed that nuclear division was inhibited and that cell division resulted in one anucleate and one nucleate daughter cell. This effect was also observed in some dividing cells at lower concentrations of DMSO. The effect of DMSO on Tetrahymena was dependent not only on the concentration of the compound but also on the physiological state of the cells.
Transcription and translation of the sex message in the smut fungus Ustilago Violacea: II. the effects of inhibitors
Authors: Cummins J. E. , Day A. W. 
Published: April 2021

ABSTRACT
In Ustilago violacea conjugation involves a period of courtship followed by the cooperative assembly of a conjugation tube between paired sporidia of opposite mating type. During courtship information is exchanged between the paired sporidia directing transcription and translation of a ‘sex message’. This information exchange is completed even though the plasma membranes and walls of the mating sporidia remain intact until after the sex message has been translated. Once translation is completed the copulatory organelle is assembled.
Inhibitor studies show that translation of specific mRNA species (sex message) is essential during the 3–4 h period of courtship prio1 to assembly and that transcription of this sex message is completed 15–30 min prior to the completion of translation. Amino acid incorporation studies show that even though the cellular protein levels remain constant during courtship there is extensive amino acid turnover as the sporidia adjust to mating conditions. However, an enhancement of amino acid turnover by mating, in contrast to unmixed sporidia, is not detectable. Prototrophic strains continue to synthesize stable RNA during courtship while amino acid auxotrophs discontinue stable RNA synthesis immediately on transfer to mating conditions. Both prototrophs and auxotrophs show extensive RNA turnover during courtship but a specific enhancement of turnover due to mating activity is not detectable from the labelling pattern alone. A round of DNA replication may be completed during courtship but mating activity does not influence the gross pattern of DNA replication in either of the mating types.
Evidence for the association of rna with the ciliary basal bodies ofTetrahymena
Authors: Hartman H. , Puma J. P. , Gurney T. 
Published: April 2021

ABSTRACTA new procedure for isolating pellicles from TetraJiymena yields stable whole pellicles in good yield. Electron microscopy of fixed pellicles showed inner membranes and basal bodies but no mitochondria. Sucrose gradient sedimentation of pellicle extracts labelled with [sH]uridine showed an increase in the ratio 17 s RNA to 25 s RNA and little 4 s RNA. The method of long term labelling presumably excluded messenger RNA. The technique of RNA/DNA hybridization in the presence of competing RNA showed that 35 % of the pellicle RNA which could hybridize (Cot 2–3) to DNA did not contain sequences in common with ribosomal RNA. It is proposed that a stable RNA which is not mitochondrial RNA, transfer RNA or ribosomal RNA is associated with the pellicle. Fixed pellicles stained with acridine orange showed brilliant yellow-green fluorescence at the basal bodies. RNase reduced or abolished fluorescence; DNase, histone, and lysozyme had no effect. Mercaptoethanol changed the colour of the fluorescence of basal bodies from yellow-green to orange, while not changing yellow nuclear fluorescence. Fluorescence of basal bodies was seen in pellicles isolated from log-phase cells and also in synchronized cells. It is proposed that basal bodies contain, or are associated with, single-stranded RNA held in a rigid configuration by protein. The implications of this proposal are discussed.
Cell cycle kinetics and development of Hydra attenuata: II. interstitial cells
Authors: Campbell R. D. , David C. N. 
Published: April 2021

ABSTRACT
The cell cycle parameters of interstitial cells in Hydra attenuata have been determined. Interstitial cells were classified according to cluster size in which they occur (1,2,4, 8 or 16 cells) and morphology using maceration preparations and histological sections. The lengths of G1, S, G2 and M were determined by standard methods of cell cycle analysis using pulse-chase and continuous labelling with [3H]- and [14C]thymidine. Nuclear DNA contents were measured microfluorimetrically. All classes of interstitial cells proliferate but the cell cycle of large interstitial cells occurring singly 01 in pairs is longer than that of interstitial cells occurring in clusters of 4, 8 and 16 cells. The S-phase is 11-12 h long and G1 is less than 1 h for all classes of interstitial cells. G2, is 3-4 h long for interstitial cells in clusters of 4, 8 and 16 cells giving these cells a total cell cycle duration of 16—17 h. In contrast, large interstitial cells occurring as singles and in clusters of 2 have G2, durations ranging from 4 to 22 h. Two subpopulations can be discerned among these cells, one having a G1 of about 6 h and a total cell cycle of about 19 h, the other having an average G2 of 14 h and a total cell cycle of about 27 h. The differences in cell cycle duration appear to be associated with interstitial cell function. Cells having a short cell cycle are probably committed to nematocyte differentiation, while large interstitial cells having long and variable cell cycles appear to be undetermined stem cells responsible for pro-liferating further interstitial cells. The variable length of G2 in these cells suggest it as a possible control point.
Acetylcholine receptors of cultured muscle cells demonstrated with ferritin-α-bungarotoxin conjugates
Authors: Hourani B. T. , Torain B. F. , Henkart M. P. , Carter R. L. , Marchesi V. T. , Fischbach G. D. 
Published: April 2021

ABSTRACT
α-Bungarotoxin-ferritin conjugates were used to visualize by freeze-fracture and thin-section electron microscopy toxin-binding sites, presumably acetylcholine (ACh) receptors, in membranes of muscle cells grown in tissue culture. Toxin conjugated to ferritin by a glutaraldehyde reaction and purified by column chromatography in a buffer of high ionic strength remains active in blocking the effect of iontophoretically applied ACh. The potency of the conjugates was decreased 5–10 times compared to native α-bungarotoxin. Toxin-ferritin conjugates were identified in small clusters which were not uniformly distributed over the surface membrane. Binding was inhibited by preincubation in D-tubocurare or unconjugated toxin. The relation of the clusters to the non-uniform distribution of ACh sensitivity and α-bungarotoxin binding on cultured muscle fibres is discussed.
Cytoplasmic cleavage during zoosporogenesis in Thraustochytrium sp.: Ultrastructure and the effects of colchicine and D2O
Authors: Kazama F. Y. 
Published: April 2021

ABSTRACT
Subplasmalemma microtubules were present in the cleavage furrows during zoosporogenesis in Thraustochytrium sp. The microtubules transversed the furrows but were not at right angles to nor circumferentially arranged in the plane of cleavage. Evidence of microtubuleplasmalemma bridges was found. Colchicine and deuterium oxide inhibited cleavage. The data suggested that microtubules had a motive rather than a structural function.
Junctional structures in the midgut cells of lepidopteran caterpillars
Authors: Flower N. E. , Filshie B. K. 
Published: April 2021

ABSTRACT
The junctional structures present between the midgut cells of 2 lepidopteran caterpillars have been examined using freeze-etching, conventional staining and lanthanum tracer techniques. The bonding junction present in this type of tissue is the so-called continuous junction. Septa have only occasionally been reported in conventionally stained cross-sections of these junctions. During the present study septa have been observed in such sections but were more readily located in tissue treated with lanthanum tracer. Tangential sections of lanthanum-impregnated tissue show that these septa are parallel-sided, in contrast to the honeycomb appearance of the septa in septate junctions. The septa in freeze-etch replicas of glutaraldehyde-fixed tissue often show continuous rods on one membrane face, suggesting that the continuous junction may be more akin to the tight junction than to the normal septate junction. However, freeze-etch replicas of unfixed tissue appear much more like replicas of normal septate junctions. The main differences between septate and continuous junctions appear to be that the intermembrane septa of the continuous junction are parallel-sided in tangential section, as against the honeycomb appearance of the septate junction, and that the particles which delineate the septa in freeze-etched preparations appear to be both somewhat differently bonded and closer together in the continuous junction. A diagram is presented showing the internal and intermembrane structures of the 2 types of junction based on the present study, and suggesting a possible explanation of the fact that septa are more readily seen in cross-sections of septate junctions than in continuous junctions. As septa are present in both types of junction, and because their freeze-etch appearances are not very different, it is suggested that the two types of septate junction be called ‘smooth septate’ and ‘pleated septate’ junctions, to indicate their characteristic appearances in tangential section.
Changes in dna synthesis during cell growth and chloroplast replication in greening spinach leaf disks
Authors: Rose R. J. , Cran D. G. , Csiro J. V. Possingham 
Published: April 2021

ABSTRACT
Spinach leaf disks grown initially in the dark, show increased cell expansion and chloroplast replication when transferred to the light. These changes are accompanied by increases in the total amount of DNA and the incorporation of [3H]thymidine (3H-TdR). Autoradiography of EDTA-separated cells dried on to glass slides was used to follow changes in 3H-TdR incorporation in both chloroplasts and nuclei. Specificity of incorporation was confirmed by nuclease studies. DNA synthesis occurs in both the chloroplasts and nuclei, and is highest just prior to, and during the period of most rapid cell growth and chloroplast replication which occurs shortly after the transfer to the light. Light, however, appears to have a greater and more immediate effect on nuclear DNA synthesis. Though nuclear and chloroplast DNA syntheses follow similar patterns during disk growth, in a given cell, chloroplast DNA synthesis can be separate in time from nuclear DNA synthesis. The increased nuclear DNA synthesis is possibly required to support the increased population of chloroplasts, while chloroplast DNA synthesis is associated with chloroplast division. If the disks are not transferred to the light but kept in darkness, chloroplast 3H-TdR incorporation remains high, though chloroplast division is reduced. Epidermal cells in light-grown tissue also show 3H-TdR incorporation but low rates of chloroplast division. It would appear that chloroplast DNA synthesis in mesophyll cells from light-grown tissue shows a general relation to chloroplast division, but there does not appear to be an obligatory close coupling between the 2 processes.
Adhesion of Phytophthora palmivora zoospores: Electron microscopy of cell attachment and cyst wall fibril formation
Authors: Sing V. O. , Bartnicki-Garcia S. 
Published: April 2021

ABSTRACT
Zoospores of Phytophthora palmivora adhered to a plastic film surface were examined by electron microscopy. Three stages of adhesion were compared: (1) non-adhesive, unencysted zoospores, (2) adhered incipient cysts, and (3) adhered mature cysts. Thin sections of incipient cysts revealed cells attached to the film surface through the partially discharged contents of the so-called peripheral vesicles; this seems to be the first step in cell adhesion. In mature cysts, the adhesive appeared to have been compacted into an electron-dense deposit binding the cyst wall to the plastic surface. The adhesion zone was also examined in face view after lysing attached incipient cysts with sodium dodecyl sulphate. Cyst wall microfibrils were seen together with an amorphous substance (presumably the adhesive material). The microfibrils were in various stages of formation. Seemingly, adhesion and microfibril formation take place concurrently. The possibility was considered that the material contained in the peripheral vesicles serves in both cell adhesion and microfibril elaboration.
The giemsa-staining centromeres of Nigella damascena
Authors: Marks G. E. 
Published: April 2021

ABSTRACT
The centromere regions of each chromosome in the complement of Nigella damascena (2n = 2x = 12) stain differentially with Giemsa at interphase and throughout all the principal stages of mitosis and meiosis. Each centromere is seen to consist of a pair of sister half-centromeres which appear as 2 differentially stained dots. The appearance and behaviour of these dots indicates that they are kinetochores. The technique used does not stain centromeres in other plant species investigated, a fact which shows that the centromeres of Nigella are in some way different. The implications of this observation in relation to centromere polymorphism are discussed.
Affinity chromatography of dna-binding proteins from human, murine and man-mouse hybrid cell lines
Authors: Jost E. , Lennox R. , Harris H. 
Published: April 2021

ABSTRACT
About 60 proteins from human and murine cell lines were isolated by their ability to bind to different preparations of DNA. In the intact cell, the majority of these proteins are to be found in the cell nucleus. The electrophoretic mobilities of the DNA-binding proteins from human, murine and man-mouse hybrid cell lines were compared in two-dimensional acrylamide gels. Few, if any, species-specific differences were found. These observations suggest that the structures of the vast majority of the proteins that interact with DNA are conserved through evolution. A molecular basis is thus provided for the intracellular compatibility of hybrid cells derived from different animal species.
Cell surface lipids and adhesion: I. the effects of lysophosphatidyl compounds, phospholipase a2 and aggregation-inhibiting protein
Authors: Curtis A. S. G. , Campbell J. , Shaw Felicity M. 
Published: April 2021

ABSTRACT
Aggregation-inhibiting protein (AIP: Curtis & Greaves, 1965), which diminishes the adhesiveness of cells, particularly at low temperatures, is identified in the present paper as phospholipase A2 (EC. 3.1.1.4). Our reasons for this identification are because phospholipase activity parallels AIP activity during purification of AIP, because pure phospholipase A2 acts in the same manner as AIP on cell adhesion, and because various inhibitors and sera act in a parallel manner on adhesion in the presence of AIP or phospholipase. We suggest that the enzyme acts on adhesion by producing lysolecithin and other lysolipids in the plasmalemma. Addition of lysolipids diminishes cell adhesion in a manner similar to phospholipase A. Incubation of cells in Hanks’ medium at 37 °C has a parallel effect.
Conditions which would be expected to stimulate reacylation of lysolipids in the plasma-lemma, i.e. incubation of cells in the external presence of CoA, ATP and a fatty acid, lead to a recovery or maintenance of adhesion after or during Hanks’ incubation at 37 °C. All these results suggest that lipid components of the cell, probably in the plasmalemma, are of importance in adhesion. The results are discussed in relation to the long-standing controversy about the effects of low temperatures and trypsinization on cell adhesion, for phospholipase treatment of cells affects adhesion in a manner similar to trypsinization.
The organization of genetic units in chromosomes
Authors: Callan H. G. 
Published: April 2021

ABSTRACT
In the genomes of chromosomal organisms, cytological evidence from disparate sources suggests that each unit of information encoded as a DNA base sequence is serially repeated. Further cytological and genetical evidence suggests that among such serially repeated sequences a terminal unit serves as the ‘master’ sequence, within which recombinational events can occur, followed by ‘slave’ sequences which are not directly involved in recombination but which are made congruent to the master sequence once per life-cycle. The formation of lateral ‘lampbrush’ loops in meiotic prophase, after synapsis, is claimed to represent the outcome of the master/slave matching process.
Observations on the distribution of the proteinpolysaccharide complex and collagen in bovine articular cartilage
Authors: Smith J. W. , Peters T. J. , Serafini-Fracassini A. 
Published: April 2021

ABSTRACT
The contents of collagen and chondroitin sulphate in bovine articular and nasal cartilage were determined by chemical analysis, and the distributions of collagen and proteinpolysac-charide in articular cartilage were studied by electron microscopy. Collagen was visualized, after osmium fixation, in Araldite sections stained with uranyl acetate or phosphotungstic acid (PTA), while the proteinpolysaccharide distribution was observed in Araldite sections of tissue which had been bulk stained with bismuth nitrate at low pH.
The intercellular tissue is divisible into a pericellular zone and a main matrix. The pericellular zone exhibits fine fibres which are less than 250 Å in diameter : although they do not stain typically with PTA, they are probably collagenous in nature. The main matrix contains native collagen fibres which vary in diameter from 250–900 Å. Proteinpolysaccharide exists in the intercellular tissue in two states, namely, as free and randomly oriented macromolecules, and as macromolecules which are attached transversely over the a and b1 bands of each 640-Å period of the collagen fibres. The concentration of free proteinpolysaccharide is high throughout the pericellular zone, but diminishes practically to zero from the margin of the pericellular zone to the central part of the main matrix. No attached proteinpolysaccharide is present in the pericellular zone whereas a large amount is evident throughout the whole of the main matrix.
It is suggested that this distribution conforms to the concept that the pericellular zone is a pool from which the proteinpolysaccharide, which has been synthesized by the neighbouring chondrocyte, migrates into the main matrix to effect the metabolic turnover of this tissue component.