bluuebunny/crossref_metadata_2025_split huggingface dataset:
The behavioural repertoire of neutrophils requires multiple signal transduction pathways
Authors: Lackie J. M. 
Published: April 2021

ABSTRACT
Signal-response transduction is usually investigated in cells that produce an easily assayed and straightforward response to a well-defined stimulus; the repertoire of the cell is often rather uninteresting. An enjoyable feature of working with neutrophil leucocytes is that their behaviour is far from simple, although at times this can be a mixed blessing. To carry out their primary defensive function in vivo, neutrophils must go through a complex sequence of activities, in the correct order, and in the right places. In an acute inflammatory response neutrophils adhere to, and move over, the luminal surface of endothelial cells, penetrate the endothelium, and move through connective tissue towards the site of damage. Having arrived, and stopped moving, neutrophils then engage in phagocytosis or secrete hydrolytic enzymes to digest large foreign objects (Lackie, 1982). The early stages require changes in adhesive and motor capacity, the late stages of the process are marked by a dramatic activation of the metabolism of the cell. Activities that are essential in the late stages would be inappropriate, and destructive of normal tissue, in the early stages.
Characterization of mutant human fibroblast cultures transformed with simian virus 40
Authors: Miranda Armand F. , Duigou Gregory J. , Hernandez Evelyn , Fisher Paul B. 
Published: April 2021

ABSTRACT
Fibroblast cell strains derived from a normal individual and from eight patients with various genetic mutations were transformed by a smallplaque variant of simian virus 40 (SV40, strain 776), cloned and studied after long-term in vitro maintenance. Seven of the cultures continued to express the mutant phenotype. Cultures derived from a patient with phosphoglycerate kinase I deficiency exhibited reappearance of normal enzyme activity after transformation. Compared to untransformed controls, all transformed cultures displayed decreased population doubling times, an increase in the relative number of cycling cells and increased saturation density on solid substrates, and did not show evidence of cellular senescence after long-term cultivation. Unlike previous studies on wild-type SV40-transformed human fibroblasts, the majority of cultures transformed by the small-plaque variant of SV40 did not exhibit signs of crisis. The cells also exhibited a decreased dependence on serum and were able to grow in semi-solid medium. The different transformed cultures expressed variable levels of SV40 large T-antigen, synthesized some infectious SV40 virus, and contained both unique arrangements and quantities of covalently integrated and episomal SV40 DNA. No correlation was observed between the rate of growth and synthesis of infectious virus in the different transformed clones. These studies indicate that this small-plaque variant of SV40 can be used effectively to generate long-lived human cultures, which generally retain their mutant phenotype. Transformation with this SV40 variant permits the generation of large quantities of clonal cell cultures for the biochemical and molecular analysis of their genetic defects.
Microtubules and microfilaments in tip growth: Evidence that microtubules impose polarity on protonemal growth in Physcomitrella patens
Authors: Doonan J. H. , Cove D. J. , Lloyd C. W. 
Published: April 2021

ABSTRACT
In this study we compare the contributions of Factin and microtubules to tip growth in filamentous cells of the moss Physcomitrella patens.
In tip growth, expansion seems to be restricted to the hemispherical apical dome. Cytoskeletal elements have been suspected, from drug studies, to be involved in this but electron microscopy has generally not confirmed the presence of an apical cytoskeleton. However, in a previous immunofluorescence study we reported that microtubules could be seen to focus upon the apical dome in tip cells of the moss P. patens. In the present investigation F-actin has also been detected at the apices of these cells. Anti-cytoskeletal drugs were therefore used to differentiate between the roles of actin filaments and microtubules in tip growth.
At high concentrations (30 μM), the herbicide cremart de-polymerized microtubules and caused tip swelling. F-actin was still present under such conditions but its fragmentation by cytochalasin D suppressed this herbicide-induced swelling. On its own, cytochalasin D arrested tip growth without causing swollen tips.
At lower concentrations, cremart disorganized microtubules rather than causing their complete depolymerization. Under these conditions, new but swollen growing points were initiated along the filament. The addition of taxol to cremart-treated filaments tended to reduce swelling and to re-polarize outgrowth. With particular combinations of these drugs, multiple lateral outgrowths were initiated in the vicinity of the nucleus.
It is concluded: (1) that F-actin is present at the tips of Physcomitrella caulonemal apical cells; (2) that unfragmented F-actin is necessary for outgrowth; (3) that even disorganized microtubules permit some degree of outgrowth but that an unperturbed distribution of axial microtubules, focussing upon an apex, is essential in order to impose tubular shape and directionality upon expansion.
The initiation, maintenance and termination of dna synthesis: a study of nuclear dna replication using Amoeba proteus as a cell model
Authors: Ord M. J. 
Published: April 2021

ABSTRACT
By means of the nuclear transfer technique for amoeba, combinations of nuclei and cytoplasms from all parts of the cell cycle were available for examining the individual roles of the nucleus and cytoplasm in nuclear DNA replication. Neither 5-phase nor division sphere cyto-plasm proved capable of initiating a new round of nuclear DNA synthesis in the G2 nucleus. There was some indication that G2 nuclei which were transferred into early prophase cells, i.e. before the formation of a regular division sphere, did incorporate more [3H]thymidine than control G, nuclei.
Positive proof of the induction of DNA synthesis in ‘immature’ nuclei was observed in only two cases. When young G2 nuclei were transplanted into late G2 amoebae, the addition of the donor nucleus generally resulted in the older nucleus being held in a late G2 phase until the younger nucleus passed through its G2. Division of 90 % of heterophasic homokaryons was synchronous, with a subsequent synchrony of DNA synthesis.
A study of variance in [3H]thymidine incorporation by S nuclei sharing the same cytoplasm – using binucleate, trinucleate and multinucleate homokaryons — showed that nuclei through the peak-5 period synthesized DNA at approximately similar rates. The large differences in PHjthymidine incorporation by nuclei of amoebae of equal age appear due to differences in endogenous precursor pools. These would vary both with differences in food intake and with the draining of remote precursor pools for simultaneous cellular activities, particularly RNA synthesis. When sharing the same cytoplasm nuclei in peak 5 incorporated similar amounts of [3H]thymidine. Though cytoplasm did not influence the progress of DNA replication by a nucleus, it did influence the use of exogenous [3H]thymidine by the cell, and in so doing caused much of the variation observed in the labelling of nuclei during S. Nuclei sharing the same cytoplasm, and so subject to the same precursor pool changes, incorporated similar amounts of exogenous thymidine.
Once DNA synthesis had been initiated it continued to completion regardless of the cyto-plasm which surrounded it. Thus neither the maintenance nor termination of DNA synthesis required a special cytoplasmic state.
Faults in the square lattice of mammalian skeletal muscle z-disks
Authors: Rowe R. W. D. , Morton D. J. 
Published: April 2021

ABSTRACT
The ordered square lattices of filaments in the Z-disk and juxtaposed I-band regions proposed by current models of Z-disk structure were compared with those observed by electron microscopy. It was commonly found that there were faults in the lattices of both the Z-disk and I-band regions. Attention is drawn to these faults and the consequences of their presence are discussed in relation to their influence on myofibril size and proliferation.
Pollen-wall proteins: the fate of intine-held antigens on the stigma in compatible and incompatible pollinations of Phalaris tuberosa l.
Authors: Knox R. B. , Heslop-Harrison J. 
Published: April 2021

ABSTRACT
By the use of an immunofluorescence technique, the main source of the antigens released by the pollen grains of Phalaris tuberosa L. (Gramineae) on leaching has been shown to be the intine. The main concentration is in the thickened zone underlying the germination pore. The intine is also the site of various hydrolytic enzymes.
The fate of the intine-held antigens has been followed in compatible and incompatible pollinations. They are lost on to the stigma within 5 – 10 min, whether or not the pollen grains germinate. Where germination does occur after a compatible pollination, the antigens remain spread on the surface of the stigma cells after the tubes have penetrated. There is no indication that antigenic material of the same type is released during the further growth of the tubes.
The possible roles of the intine-held materials as recognition substances in inter- and intra-specific compatibility reactions are discussed.
The neuropil of the glomeruli of the olfactory bulb
Authors: Pinching A. J. , Powell T. P. S. 
Published: April 2021

ABSTRACT
The neuropil of the glomeruli of the rat olfactory bulb has been studied with the electron microscope with a view to elucidating the type of processes involved - dendrites, appendages and axons - their cellular identity, and the synaptic relationships they establish. The problems encountered in defining these are considered and criteria based on the previous study of neuron types and on examination of serial sections are put forward. The glomeruli are large structures containing many thousands of processes and are the sole site of termination of the olfactory receptor axons. The terminals of the latter are characteristically electron-dense, allowing identification in normal material; they run through the glomeruli making many synapses by means of spherical vesicles and asymmetrical thickenings on to all types of dendritic profile. The glomerular dendritic arborizations of mitral and tufted cells, which are indistinguishable from each other, start as large, fairly regular, pale profiles but become increasingly varicose as they branch and diminish in size. They regularly show groups of spherical vesicles, often in association with asymmetrical synaptic thickenings directed from the dendrite; these are typically associated with return, reciprocal, synapses of the symmetrical type from profiles containing large flattened vesicles. These latter profiles are those of the dendrites and gemmules of periglomerular cells; the dendrites are of irregular outline and give rise to many appendages, mostly gemmules making synaptic contact with mitral or tufted cell dendrites. A small number of pale axon terminals containing either small or large flattened vesicles, derived from shortaxon and periglomerular cells respectively, synapse with symmetrical thickenings on to the periglomerular cell dendritic processes. Close associations of particular types of axo-dendritic and dendro-dendritic synapses on interconnecting processes, termed synaptic patterns, are described and their significance considered. The nature of the glomerular interactions is discussed and then placed in the context of other, smaller glomeruli in the central nervous system; certain common principles of glomeruli are suggested.
The intracellular origin of flagellar hairs in the dinoflagellate Woloszynskia micra leadbeater & dodge
Authors: Leadbeater B. S. C. 
Published: April 2021

ABSTRACT
The arrangement of fine hairs on the longitudinal and transverse flagella of Woloszynskia micra is illustrated and discussed. Dilations of the nuclear envelope and endoplasmic reticulum in W. micra, similar in appearance and location to those containing flagellar hairs in other algal and fungal zoids, are found to contain bundles of fibrils. These fibrils are approximately the same width and length as the flagellar hairs. For the above reasons it is now considered that the flagellar hairs in the dinoflagellate W. micra are formed intracellularly within dilations of the nuclear envelope and endoplasmic reticulum and later deposited on the flagella.
C-microtubules in isolated mitotic spindles
Authors: Cohen W. D. , Gottlieb T. 
Published: April 2021

ABSTRACT
Microtubules with incomplete cylindrical structure are present in isolated mitotic spindles of the sea urchin, Arbacia punctulata. In cross-section they appear C-shaped, and are thus similar to the ‘C-microtubules ‘or ‘C-filaments’ observed previously in other systems. The C-micro-tubules are not uniformly distributed within isolated spindles, but are typically numerous in the interzonal region of anaphase spindles and in the metaphase chromosome ‘plate’. In chromosome-to-pole regions they are seen much less frequently, and microtubules with the usual O-configuration predominate. Counts of C- and O-microtubules in anaphase spindle crosssections of known location show an inverse relationship between the number of C-microtubules present and the total number of microtubules present. The observations suggest that the C-microtubules are not simple artifacts of fixation or isolation, but rather may represent a stage of microtubule disassembly which occurs in the interzone during isolation or during anaphase in vivo. The alternate possibility of assembly is not excluded, however. The significance of C-microtubules is further discussed with respect to their occurrence in other systems, and to potential differences between mitotic microtubules.
Dna from isolated pellicles of Tetrahymena
Authors: Flavell R. A. , Jones I. G. 
Published: April 2021

ABSTRACT
Large pellicle fragments were isolated from Tetrahymena pyriformis, strain T, by 2 procedures: homogenization after treatment with 40 % ethanol at − 20 °C, or direct homogenization in a sucrose-EDTA buffer. All preparations contained entrapped mitochondria. DNA prepared from these pellicles was analysed on a CsCl gradient, and contained 3 components of buoyant densities 1·685, 1 ·688, and 1698 g cm−3 in variable proportions. The component at 1685 g cm−3 is similar in density to mitochondrial DNA and those at 1·688 and 1·698 g cm−3 to components of nuclear DNA. Most pellicle preparations contained a higher proportion of the heavy component (1·698 g cm−3) than does nuclear DNA. A similar enrichment of this component could be demonstrated in high-speed pellets from fragmented nuclei. No unique pellicle-associated component could be demonstrated. No DNA could be isolated from very pure preparations of oral plates and we conclude that there is no evidence for the presence of a specific DNA associated with the pellicle.
A comparative study of three methods for the ultrastructural demonstration of glycogen in thin sections
Authors: Vye M. V. , Fischman D. A. 
Published: April 2021

ABSTRACT
In order to evaluate 3 staining methods for demonstration of glycogen in thin sections, 2 tissues containing an abundance of this carbohydrate in β-particle form were studied. Tissues were aldehyde-fixed, postfixed in osmium tetroxide, embedded in Araldite and sectioned in the usual manner without special precautions. The first method for staining thin sections employed a sequential combination of periodic acid, thiosemicarbazide and osmium tetroxide vapour, while in the second procedure a silver protein solution was substituted for the osmium tetroxide vapour. The third technique utilized periodic acid, sodium chlorite and uranyl acetate, also in sequential combination. Each method yielded glycogen particles of greater electron density than were seen in sections stained by the usual uranyl acetate-lead citrate procedure. Under high magnification, considerable method-dependent variation in the appearance of the glycogen granules was noted. Particulate substructure, only faintly visible in routinely stained sections, was easily resolved with the periodic acid-thiosemicarbazide-silver protein technique. Conversely, periodic acid-thiosemicarbazide—osmium tetroxide completely obscured this substructure. With periodic acid—sodium chlorite—uranyl acetate, glycogen particles appeared larger, more confluent, and of a less regular outline than with the other methods. Sections were also stained by incubation in periodic acid prior to treatment with lead citrate. The alteration in appearance of the glycogen granules produced by this modification was so great that high-resolution analysis of particle size and substructure could not be undertaken. The usefulness of the procedures investigated here resides in their ability to stain glycogen in thin sections in an intense and selective manner.
Evidence that cyclic gmp regulates myosin interaction with the cytoskeleton during chemotaxis of Dictyostelium
Authors: Liu Gang , Newell Peter C. 
Published: April 2021

ABSTRACT
Amoebae of Dictyostelium discoideum respond to a chemotactic cyclic AMP stimulus within 10 s by the formation of an intracellular peak of cyclic GMP. In wild-type cells the cyclic GMP is rapidly degraded by a cyclic GMP-specific phosphodiesterase. In ‘streamer F’ mutants this enzyme is defective, due to mutation in the enzyme structural gene, and the cyclic GMP persists several times longer than the normal period, an effect that is correlated with a persistence in cell elongation during the chemotactic movement phase.
In this study we have used the streamer mutants NP368 and NP377, and their parental strain XP55, to study changes in cytoskeletal proteins during the chemotactic response. We have studied three proteins that change their association with the cytoskeleton after stimulation of amoebae with the chemoattractant cyclic AMP: (1) actin, (2) a protein with an apparent Mr of 190 ×103 and (3) myosin heavy chain. Both actin and the 190×103Mr protein were found to accumulate rapidly in the cytoskeleton after cyclic AMP stimulation, with a sharp peak at 5 s, and showed similar changes in the parental and streamer mutants. However, the cytoskeletal level of myosin heavy chain showed a different pattern of changes, which also clearly differed in the streamer mutants compared with the parental strain XP55. In XP55 myosin heavy chain showed an initial drop after cyclic AMP stimulation, with a trough at 3-10 s followed by a rapid rise to a sharp peak at 20–25 s. In contrast, the myosin heavy chain in the streamer mutants produced a broad peak that persisted several times longer than the parental strain.
We conclude that in the streamer mutants the defect in cyclic GMP phosphodiesterase that produces the broad peak of cyclic GMP is causally correlated with the broad peak of cytoskeletal myosin, and we suggest that this is connected with the observed phenotype of prolonged cell elongation during chemotaxis in these mutants.
Dynamics of membrane skeleton in fused red cell membranes
Authors: Cheng-Zhi Jin 
Published: April 2021

ABSTRACT
The dynamic nature of the red cell membrane cytoskeleton was examined by the method of fluorescence redistribution after fusion (FRAF). Ghosts, labelled at the interior membrane surface, and intact cells, labelled at the outer surface with a different fluorophore, were fused and the passage of the fluorescent label into the unlabelled part of the membrane was followed in the fluorescence microscope. To achieve specific labelling of a cytoskeletal component only, a fluorescent analogue of phalloidin was used to label the actin. It was shown that there was no dissociation of the phalloidin during the time of the experiment, and no exchange of phalloidin between labelled and unlabelled actin in unsealed mixtures of ghosts. In the fused membrane pairs at 37 °C the phalloidin-linked fluorescence diffused in the plane of the membrane and became distributed through the membrane envelope in 1–2 h. It was shown by gel electrophoretic analysis that no detectable loss of or damage to membrane proteins resulted from the fusion process. It is concluded that, at least in membrane pairs treated with fusogen, exchange of actin or actin-containing elements occurs within the cytoskeletal network.
Establishment of plastid-based quadripolarity in spore mother cells of the moss Funaria hygrometrica
Authors: Busby C. H. , Gunning B. E. S. 
Published: April 2021

ABSTRACT
Development of a tetrad of meiospores is one of the most widespread examples of geometrically precise cell morphogenesis in plants. We have studied the process in the moss Funaria hygrometrica. Changes leading to a quadripolar organization of the prophase spore mother cell (SMC) start in the archesporial cells several cell generations before meiosis. The number of plastids per cell is reduced to two and these play an increasing part in subsequent mitoses and meiosis. During meiotic prophase, the plastids elongate until they enclose the peripheral nucleus. The nucleus is then drawn back into the centre of the cell as the plastids rotate and ultimately assume a mutually perpendicular configuration. The tips of the plastids thus lie at the vertices of a tetrahedron arranged around the nucleus, which itself becomes deformed into a tetrahedral shape. Quadripolarity has now been set up in anticipation of the two meiotic divisions.
The first division spindle is also somewhat tetrahedral, with broad poles oriented perpendicular to one another along two opposite edges of the tetrahedron. As a consequence, the daughter nuclei are, from their inception, mutually perpendicular and elongated along the first spindle poles, ready for the second division, which places one haploid nucleus opposite each of the four plastid tips. Simultaneous cytokinesis then bisects the plastids and generates a tetrad of spores.
The morphological evidence thus indicates that the plastids are involved in the development of internal quadripolarity in the outwardly apolar SMCs.
Development of the quadripolar meiotic cytoskeleton in spore mother cells of the moss Funaria hygrometrica
Authors: Busby C. H. , Gunning B. E. S. 
Published: April 2021

ABSTRACT
Evidence presented in the accompanying paper that plastids function as microtubule (MT)-organizing centres for development of the quadripolar cytoskeleton of pre-meiotic spore mother cells (SMCs) in the moss Funaria hygrometrica is complemented here by observations on the MT system in these cells.
Early in meiotic prophase numerous MTs align progressively along the two plastids as they elongate. Concomitant with (and perhaps causal for) plastid rotation, new MT arrays grow from each tip of each plastid to both tips of the other plastid. The ‘along-plastid’ and ‘between-plastid’ arrays ultimately form the edges of a tetrahedron, enclosing the prophase nucleus. MT breakdown at the centre of each edge leaves four cones of MTs, one emanating from each vertex, located at the plastid tips. These partially fuse in between-plastid pairs to give a twisted spindle with broad knifeedge poles oriented at right angles to one another, i.e. a condensed form of the quadripolar precursor.
The twist causes the metaphase plate and the subsequent phragmoplast and organelle band to be saddle-shaped, and the daughter nuclei to be elongated perpendicular to one another along the two knife edges. The tetrahedral array returns during interkinesis and again breaks down into four cones of MTs centred on the plastid tips; these, however, now become individual half spindles for the two perpendicularly arranged second division spindles. When meiosis is completed the four haploid nuclei thus come to lie at the vertices of a tetrahedron that was established by MT-mediated plastid positioning during meiotic prophase.
The tetrahedral cage of MTs precedes meiosis yet predicts the planes of division, and in these two respects it is the meiotic counterpart of the preprophase band of MTs, which develops before mitosis in most higher plant cells.