bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of high hydrostatic pressure on the mechanical properties of the surface of the sea-urchin egg
Authors: Wolpert L. , Marsland D. , Hirshfield M. 
Published: April 2021

ABSTRACT
There is evidence that high hydrostatic pressure can solate and weaken gel-like structures within cells. It was thus of interest to determine its effect on the mechanical properties of the cell surface since it has been suggested that there is a gel-like cortex beneath the plasma mem brane which makes a significant contribution to its mechanical properties. The mechanical property measured was the resistance to deformation when the eggs were compressed mechanic ally. The eggs of Arbacia were compressed by placing a small plate made either from a fragment of coverslip or Melinex plastic sheet on a small group of eggs (20–100) so that the eggs sup ported the plate. The deformation of the eggs was determined by measuring their increased diameter. The mechanical properties of the cell membrane of unfertilized eggs appear to be unaffected by high hydrostatic pressure. When compressed fertilized eggs, from which the fertilization membrane had been, removed by urea treatment, were subjected to pressure of about 7 × 104 kN m−2 (10000 lb/in.2), there was a significant increase in cell diameter. This increase was such that it appeared as if the resistance to deformation of the membrane were about quartered. Surprisingly after a few minutes the diameter decreased again indicating a contraction at the membrane even while under high hydrostatic pressure. Release of the hydrostatic pressure resulted in a further reduction in diameter and thus contraction at the surface, the final diameter sometimes being less than that before the hydrostatic pressure was applied.
A biological system producing a self-assembling cholesteric protein liquid crystal
Authors: Neville A. C. , Luke B. M. 
Published: April 2021

ABSTRACT
The protein in the oothecal glands of praying mantids (Sphodromantis tenuidentata, Mio mantis monacha) exists in the form of lamellar liquid crystalline spherulites, which coalesce asthey flow out of a punctured gland tubule. Electron micrographs of sections of these spherulites after fixation show parabolic patterns of an electron-light component, set in a continuous matrix of protein. Such patterns arisein helicoidal systems (e.g. arthropod cuticle) and microdensito metric scans of the matrix show a rhythmical electron-density variation consistent with helicoidal structure. Double spiral patterns identical to those seen in liquid crystal spherulites are illustrated. These properties resemble those of cholesteric liquid crystals. The constructional units appear to be molecular rather than fibrillar as described by previous authors. The helicoidal architecture arises by self-assembly in the gland lumen. Lamellar surface structures self-assembled spontaneously on glass coverslips when the protein was left to stand for several days. When heated to 55 °C, the birefringent liquid crystalline protein abruptly changes to an isotropic gel, with associated loss of parabolic patterning in electron micrographs and of the rhythmical electron-density variation on microdensitometric scans. This behaviour is compared to the formation of gelatin from collagen, in terms of the randomization of an originally ordered secondary structure.
On the function and fate of phage progeny rna in infected bacteria
Authors: Fenwick M. L. 
Published: April 2021

ABSTRACT
Spheroplasts of Escherichia coli infected with RNA phage R17 were treated with actinomycin D to inhibit the synthesis of host RNA and protein. Ribosomes occurred predominantly as monomers, dimers and trimers which were active in viral protein synthesis. Partly finished strands of viral RNA in lysates sedimented at a rate characteristic of groups of 6–12 ribosomes and their buoyant density suggested that they were in fact attached to ribosomes. Newly completed strands were associated with single (70-s) ribosomes, forming a 75-S complex, and with ribosome dimers and trimers. Some were probably loosely bound to 30-s ribosomal subunits.
Newly made RNA began to accumulate in mature virions after a lag of about 5 min and rose to 16 % of the total labelled viral RNA by the end of the growth cycle, either with continuous labelling or after a 5-min pulse followed by a non-radioactive chase. It is suggested that most, if not all, new viral RNA forms a rather stable association with ribosomes and that a small proportion of this RNA may subsequently pass into progeny virus.
Calcium ions initiate the selective depolymerization of the pellicular microtubules in bloodstream forms of Trypanosoma brucei
Authors: Dolan Michael T. , Reid Colin G. , Voorheis H. Paul 
Published: April 2021

ABSTRACT
Calcium ions (100μM) were found to initiate the selective and complete depolymerization of the pellicular microtubules of Trypanosoma brucei. The Ca2+-dependent release of tubulin was found to occur without the detectable mediation of calmodulin. The released, depolymerized, pellicular tubulin from T. brucei cross-reacted with a monoclonal antibody raised against yeast tubulin. The pellicular tubulin was found to be composed of two alpha isotypes (apparently equal amounts) and one beta isotype. No other proteins were released from the plasma membrane-microtubule complexes during treatment with Ca2+. The released pellicular tubulin was capable of reassembly into microtubules with normal ultrastructure. The observations reported here suggestthat a special process may be required to accommodate the cleavage furrow during cytokinesis. Thia process would either be the Ca2+-dependent depolymerization of at least two of the cross-linked pellicular microtubules or the detachment of the cross-bridges between two pairs of pellicular microtubules on opposite sides of the cell.
Pollen-stigma interactions in Brassica: IV. Structural reorganization in the pollen grains during hydration
Authors: Elleman Carole J. , Dickinson H.G. 
Published: April 2021

ABSTRACT
With the aid of osmium tetroxide vapour, dry pollen and pollen at various stages of hydration has been fixed anhydrously for examination with the transmission electron microscope (TEM). In addition to establishing features characteristic of grains at different states of hydration, this technique has enabled the detection of a superficial layer investing both the exine and the pollen coating. This layer, some 10 nm in depth, binds both lanthanum and Alcian Blue and is shown to be the first component of the pollen grain to make contact with the stigmatic pellicle. The use of vapour fixation has also rendered it possible to chart the passage of water into the pollen grains with great accuracy, for each level of hydration displays a strikingly different cytoplasmic organization. For example, dry pollen is characterized by the presence of unusual structures at the protoplast surface and large numbers of spherical fibrillar bodies, whilst the protoplast of hydrating pollen is conspicuously stratified and contains a peripheral layer of membranous cisternae, subjacent to which is a fibrillar matrix derived from the spherical bodies found in the dry grains. Vapour-fixed, fully hydrated pollen resembles conventionally fixed grains.
The pollen coating appears electron-translucent after anhydrous fixation and contains discrete, slightly rounded bodies some 50 nm in diameter. The uptake of water by grains on the stigma is accompanied by conspicuous structural changes in this layer for, after a short period in contact with the papillar surface, the spherical bodies rapidly disappear and the coat becomes electron-opaque. Close examination of this ‘converted’ coating reveals the presence of membranous vesicles and other structural components.
The synaptonemal complexes of Caenorhabditis elegans: Pachytene karyotype analysis of hermaphrodites from the recessive him-5 and him-7 mutants
Authors: Goldstein Paul 
Published: April 2021

ABSTRACT
The him-5 and him-7 mutants (high incidence of males) of Caenorhabditis elegans both showed increased rates of X chromosome non-disjunction (16% and 3%, respectively) but him-7 also had a high frequency of autosomal non-disjunction (34%). Synaptonemal complex (SC) karyotype analysis revealed a haploid chromosome number of six in each strain. Alterations in him-7 nuclear morphology were observed but there were no aberrations in SC structure that could account for the increased frequency of autosomal non-disjunction. However, the frequency of X-chromosome nondisjunction occurred at predicted rates on the basis of the number of disjunction regulator regions (DRRs) present on the SCs. The observation that the levels of X-chromosome non-disjunction were not influenced by the increase in the frequency of autosomal non-disjunction supports the notion that the X chromosome is subject to separate controls during meiosis. The him-7 mutant is nested within the rad-4 map region on linkage group V, however, SC analysis did not reveal the physical position on the chromosome because of synaptic adjustment.
Comparison of the relative importance of tyrosine-specific vinculin phosphorylation and the loss of surface-associated fibronectin in the morphology of cells transformed by rous sarcoma virus
Authors: Kellie S. , Patel B. , Mitchell A. , Critchley D. R. , Wigglesworth N. M. , Wyke J. A. 
Published: April 2021

ABSTRACT
We have investigated the relative importance of tyrosine-specific phosphorylation of vinculin and the loss of surface-associated fibronectin in the maintenance of the rounded morphology characteristic of chick embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSV). To address this question we have examined the interaction of CEF and RSV-CEF in vitro with exogenously added fibronectin in both 3-day culture experiments and short-term, 3-h spreading experiments. We report that the addition of human plasma fibronectin to cultures of RSV-CEF results in the restoration of a near-normal morphology, as has been described previously, with the added fibronectin incorporated into an extracellular matrix. However, the phosphotyrosine content of vinculin in these cells was unchanged from that of control, untreated RSV-CEF despite the change in morphology. In short-term spreading experiments RSV-CEF were unable to adopt a fully spread morphology on fibronectin substrates, with defects in the formation of adhesion plaques and microfilament bundles compared with untransformed CEF. pp60v-src was present in the newly formed adhesion plaques of RSV-CEF spreading on fibronectin substrates. The relevance of these results to the maintenance of the transformed phenotype is discussed.
Organization of stigma surface components inBrassica:A cytochemical study
Authors: Gaude T. , Dumas C. 
Published: April 2021

ABSTRACTThe nature of secretion products forming the pellicle of the dry-type stigma surface has been investigated in Brassica by an electron-microscopic cytochemical study. In order to determine whether the pellicle is organized like a membrane, we used a series of cytochemical methods to visualize cell membranes. Three groups of techniques presenting different degrees of specificity in terms of cell surface markers have been used: non-specific labelling of cell-surface components, characterization of glycoconjugates and localization of enzymic activities. We demonstrated that the pellicle of Brassica stigmas, although not possessing a trilamellar structure, presents numerous characteristics encountered in biological membranes. In particular, it possesses cytochemically demonstrable enzyme activities, including ATPase and adenylate cyclase, whose role remains to be elucidated in relation to the pollen-stigma interactions.
Structure of dictyosomes in Scenedesmus acuminatus observed by the freezesubstitution method
Authors: Ueda Katsumi , Noguchi Tetsuko 
Published: April 2021

ABSTRACT
The ultrastructure of dictyosomes in Scenedesmus acuminatus was studied by the freezesubstitution method. The cisternal membranes of dictyosomes clearly exhibited three-layered structures. Electron-dense particles were visible on or in the proximal cisternal membranes. The upper and lower membranes of the distal cisternae were in close contact with each other at the cisternal centre. The electron density of transfer vesicles, secretory vesicles and cisternal margins was very high. These findings differ considerably from those obtained by conventional chemical fixation, and suggest that freeze-substitution is superior to chemical fixation for preserving structures, without distortion and preventing dissolution of constituent substances.
Contraction of collagen lattice by peritubular cells from rat testis
Authors: Ehrlich H. P. , Borland K. M. , Muffly K. E. , Hall P. F. 
Published: April 2021

ABSTRACT
Peritubular cells from 15- and 25-day-old rat testis trapped in collagen lattices caused those lattices to contract. Contraction proceeded more rapidly and to a greater extent using cells from younger rats. When 36000 cells from 15- and 25-day-old rats were trapped in 800 mm2 lattices, the areas were reduced to 28 mm2 and 170 mm2, respectively, within 24h. The cells from older rats were less effective at contracting the lattice than cells from younger rats. Cytochalasin B (5μg ml−1) inhibited lattice contraction and caused disruption of actin filaments as seen by fluorescent staining with Rh-phalloidin. Cholera toxin (10μgml−1), and 1 mM-dibutyryl cAMP inhibited lattice contraction, as did 10 μM-trifluoperazine, commonly an inhibitor of calmodulin. The total intracellular concentration of cAMP was greater in peritubular cells from 25-day-old rats than in those from 15-day-old rats: 427 ± 34 and 120 ± 16pmolmg−1 cell protein, respectively. When peritubular cells in monolayer were permeabilized with glycerol, the addition of ATP caused the cells to contract. Cell contraction was greater in cells from 15-day-old rats than 25-day-old rats. When cells were grown on silicone rubber, they caused that surface to wrinkle. Peritubular cells from 15-day-old rats caused the onset of wrinkling at 4 h. At the same time, no wrinkling was observed with cells from 25-day-old rats. Studies of lattice contraction and cell contraction were also made using cells from 20-day-old rats. In each case, contraction was intermediate between that of cells from 15- and 25-day-old rats. The possibility exists that lattice contraction, cell contraction and wrinkling of silicone film result from a mechanism of actin filament sliding, generated by myosin ATPase activity, and is inhibited by cAMP. The reduced rate of contraction in cells from 25-day-old rats may be related to their higher intracellular levels of cAMP. Evidence exists to show that cAMP blocks myosin ATPase activity by inhibiting the phosphorylation of its regulatory peptide, myosin light chain.
Increase in the concentration of major boar sperm surface proteins during maturation in the epididymis
Authors: Saxena N. K. , Saxena N. , Hunt W. , Peterson R. N. , Henry L. , Russell L. D. 
Published: April 2021

ABSTRACT
High-resolution two-dimensional polyacrylamide gel electrophoresis analyses have indicated that several major boar sperm plasma membrane polypeptides (PMPs) increased in concentration during maturation in the epididymis. To investigate this further,monoclonal antibodies (MAbs) to two of these PMPs/glycoproteins referenced as 4·85 and 5·0 and polyclonal antisera (PCA) raised against PMP 5·0 were used to quantify these changes. ELISA assays for both PMPs, using solubilized plasma membrane (PM) and intact PM as antigens, indicated that both PMPs were present in greater concentration in cauda PM than in caput PM. ELISA assay using PCA against 5·0 and whole sperm from the cauda and caput epididymis also showed an increase in the concentration of this protein during transit through the epididymis. Indirect FITC fluorescence microscopy showed that MAbs reacted specifically with the luminal aspect of secretory cells of the corpus epididymis and, with greater intensity, with secretory cells of the cauda segment. When MAb tags were used the fluorescence technique indicated that PMP 5·0 was restricted to a narrow area of PM overlying the principal segment of the head of caput sperm but fluorescence extended further into the principal segment and into the flagellum of cauda PM. Since MAb binding sites appear to be partially masked, PCA were also used to localize antigenic sites. PCA to PMP 5·0 showed antigen localization in both head and flagellar PM of cauda and caput sperm. The fluorescence of cauda sperm PM, however, was significantly more intense than that of caput sperm PM. MAb to PMP 4·85 also bound to antigen more extensively on cauda sperm. The sum of these analyses suggests that major sperm PMPs are secreted by the epididymis and absorbed by sperm. The magnitude of surface protein changes occurring during epididymal transit in boar sperm appears to be greater than heretofore recognized.
Characterization of cystathionine synthase as a selectable, liver-specific trait in rat hepatomas
Authors: Goss S. J. 
Published: April 2021

ABSTRACT
Cell growth using homocysteine as a source of cysteine-sulphur requires two enzymes, cystathionine synthase (CS) and γ-cystathionase (CT). The second of these enzymes, CT, is apparently present in most cell lines regardless of their tissues of origin, since most cells can grow m vitro in the absence of cystine if they are provided with cystathionine, the intermediate in the pathway. Likewise, homocysteine will support the growth of many human cells. However, of a wide range of rodent cells, only well-differentiated rat hepatoma cells were found to grow using homocysteine in place of cystine. It is shown that cell growth in homocysteine-medium correlates well with the presence in the cells of detectable levels of CS. Furthermore, in cells able to grow in homocysteine-medium, it is possible to demonstrate the homocysteine-dependent transsulphuration of serine to cysteine. Growth in homocysteine-medium is not dependent on the release of preformed cysteine from disulphide complexes with serum proteins. In cell hybrids, and in ‘dedifferentiated’ variants of rat hepatomas, CS, but not CT, is subject to extinction coordinately with well-characterized liver-specific traits. For rodent cells, homocysteine-medium thus acts as a selective medium requiring the expression of a single liver-specific trait, CS. In addition it is shown that, in certain hepatoma variants, CS is regulated co-ordinately with a urea-cycle enzyme (carbamoyl phosphate synthetase I) by glucocorticoids and cyclic-AMP.
Cell death through cysteine starvation is briefly considered. The immediate cause of death is apparently an insufficient supply of reduced glutathione. Selenium and vitamin E assist cell growth when the supply of cysteine is limiting.
The primary culture of epithelia from the secretory coil and collecting duct of normal human and cystic fibrotic eccrine sweat glands
Authors: Lee C. M. , Carpenter F. , Coaker T. , Kealey T. 
Published: April 2021

ABSTRACT
Isolated human eccrine sweat glands have been microdissected into their secretory and reabsorptive components. Complete separation of these epithelia was confirmed by differential uptake of Neutral Red stain by an intermediate section of gland containing the junction between the secretory coil and the collecting duct. Primary cultures were obtained from explants of both tissues in medium RPMI-1640 or Williams E supplemented with foetal calf serum, insulin, transferrin, epidermal growth factor and hydrocortisone. The cells in the initial coil cultures had an elongated morphology while those of ductal origin were polyhedral. After 10 days both cultures were composed of polyhedral cells of varying diameter. All these morphological types were of epithelial lineage, as demonstrated by the binding of a monoclonal antibody to cytokeratin, the intermediate filament specific for epithelial cells.
Outgrowth from both secretory and reabsorptive epithelia were multilayered, with plentiful desmosomal connections and an underlying basal lamina. Ultrastructural features typical of the epithelial cell types present in intact eccrine sweat glands were absent in a high proportion of the proliferating cells but domes, indicative of transepithelial active ion transport, were present in dense cultures from the reabsorptive duct.
Outgrowth was also obtained from the secretory and reabsorptive epithelia of sweat glands from two cystic fibrotic patients. Since the most characteristic malfunction of cystic fibrosis is the impaired ion transport in the eccrine sweat gland, the availability of cultured epithelia should provide a useful model for study of the disease.
Basal body loss during fungal zoospore encystment: evidence against centriole autonomy
Authors: Heath I. Brent , Kaminskyj Susan G. W. , Bauchop Tom 
Published: April 2021

ABSTRACT
The controversial question of the possible autonomy of centrioles, as shown by the persistence of all or part of them in the generative cell line throughout the life cycle of organisms, remains unresolved. All previous reports on shedding or withdrawal of cilia and flagella showed that their basal bodies (= centrioles) were retained in the cells where they may, or may not, subsequently disassemble. We show that in the fungusNeocallimastix sp. the basal bodies are discarded with the flagella when zoospores encyst. This shedding of basal bodies argues against centriolar persistence in any form and thus against their autonomy and endosymbiotic origin.
Pattern of dna increase in macronuclear anlagen of Tetrahymena
Authors: Roth Joachim , Cleffmann Günter 
Published: April 2021

ABSTRACT
By combining cytophotometry with autoradiography, five stages of macronuclear anlagen can be discriminated by their DNA content until the end of the first cell cycle after conjugation in Tetrahymena. DNA increases from 2C to about 32C. Each S-phase is followed by a non-synthetic period. Comparing the mean nuclear DNA content after and before each S-phase revealed that 16C anlagen contain significantly less DNA than twice the amount of 8C anlagen. This is unlike the situation in other S-phases during which the amount of DNA is precisely doubled. In the second cell cycle after conjugation some of the cells increase their macronuclear G2 DNA content beyond the 64C stage, while the majority show a mean G2 content of about 64C.
Rectilinear particle arrays in freeze-fracture replicas of the surface membrane of Paramecium tetraurelia
Authors: Preston Robin R. , Newman T. M. 
Published: April 2021

ABSTRACT
Freeze-fracture replicas of the plasma membrane of unfixed, uncryoprotected Paramecium tetraurelia bear large rectilinear arrays of 11 nm particles arranged in 7–11 parallel rows. The arrays are of sufficient size to leave impressions in replicas of the underlying outer alveolar membrane, and are apparent as parallel ridges in replicas of the surface coat of deep-etched cells.
By noting the location of arrays in replicas of identified portions of the cortex of P. tetraurelia, it has been possible to map the distribution of arrays over the cell surface. The arrays are found primarily over the anterior surfaces of the cell, covering an area that extends from the preoral suture over the left adoral field and a large portion of the anterior dorsal surface.
Freeze-fracture analyses of cells taken from a number of different stages of a culture cycle suggest that the particle arrays are not replicated as an integral part of the cortex during cell division, but are assembled and oriented in the membrane as the cells mature. The appearance of small intramembranous particle complexes in the plasma membrane of cells in logarithmic growth phase supports this hypothesis, possibly representing an assembly stage in the formation of the larger particle arrays.
The facts that the particle arrays are apparent in replicas of the surface coat of cells, are found primarily at the anterior of the cell body, and have a highly specific orientation with respect to the cell surface, strongly suggest that they function as chemoreceptors in P. tetraurelia.