bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on isolated smooth muscle cells: the contractile apparatus
Authors: Small J. V. 
Published: April 2021

ABSTRACT
Smooth muscle cells may be isolated from the taenia coli muscle of the guinea pig which, when made permeable by treatment with Triton X-100 (0·05 %) show a sensitivity to Ca for contraction with MgATP. The rate of contraction, about 10 μm s− 1, corresponds closely to the maximum velocity of shortening of the intact muscle. Electron microscopy of such partially demembranated muscle cells shows that myosin filaments of about 16-nm diameter are present in both the rigor and the relaxed states. In addition, the actin and myosin filaments are commonly seen to be associated in groups corresponding approximately in size to the fibrils recognizable in cells in rigor in the light microscope. The dense bodies and the 10-nm filaments are found located between the actin-myosin filament groups. The thick myosin filaments may be isolated by fragmentation of the cells under relaxing conditions. These native filaments range up to about 8 μm in length and show the same structural organization as filaments assembled from purified smooth muscle myosin: there is no central bare zone and bare edges, about 0·2 μm long, occur at the filament ends. The lack of bipolarity on the native smooth muscle myosin filaments and the absence, in the contractile apparatus, of actin-associated structures equivalent to Z-lines suggests that the amount of shearing that can occur between the actin and myosin filaments is considerably greater than in skeletal muscle.
Binding of the herbicide trifluralin to Chlamydomonas flagellar tubulin
Authors: Hess F. D. , Bayer D. E. 
Published: April 2021

ABSTRACT
Colchicine-binding tubulin was isolated from the centre 2 axoneme microtubules from the flagella of the alga Chlamydomonas eugametos. Incubating this tubulin with 5·8 μM [14C]tri-fluralin resulted in significant and reproducible binding of trifluralin to tubulin. The specificity of binding was determined by demonstrating that limited or no binding occurred to flagellar membrane and matrix protein, higher plant proteins, or bovine serum albumin. It was concluded that trifluralin, at obtainable soluble concentrations, specifically inhibits microtubule-mediated processes in plants. To date no effect of trifluralin on animal microtubule systems has been reported; therefore, it is suggested that trifluralin has revealed a pharmacological difference between plant and animal tubulin.
The nucleolar cycle in man
Authors: Anastassova-Kristeva Marlen 
Published: April 2021

ABSTRACT
Tissue cultures of human embryonal kidney and ovary were examined. In the nuclei of both tissues, one to ten nucleoli have been found. The maximum number of nucleoli is connected with the gene expression of rDNA of the 10 nucleolus organizers of chromosome pairs Nos. 13, 14, 15, 21 and 22, which have secondary constrictions and are the satellite chromosomes in man. The small percentage of cells with 10, 9 and 8 nucleoli is attributed to the rapid association of 3 of the homologous acrocentrics (perhaps of group D). Two of the satellite (SAT) pairs probably associate later after mitosis. The process of fusion is dynamic, resulting in one interphase nucleolus - a manifestation of the association of all SAT chromosomes. Dissociation of the nucleolus occurs upon entering prophase, due to the condensation of the chromosomes and retreat of rDNA to the respective secondary constrictions. As a result, the nucleolar number increases again. The pattern of the nucleolar kinetics within the course of one mitotic division is described.
Comparative study of axopodial microtubule patterns and possible mechanisms of pattern control in the centrohelidian heliozoa Acanthocystis, Raphidiophrys and Heterophrys
Authors: Bardele Christian F. 
Published: April 2021

ABSTRACT
The axopodial microtubule pattern of 9 centrohelidians belonging to the genera Acanthocystis, Raphidiophrys and Heterophrys, as well as the fine structure of their microtubule organizing centre, the ccntroplast, was studied to determine the rules which govern their patterns. Microtubules capable of binding a maximum of 4 linkers are arranged in regularly distorted hexagons and equilateral triangles. The number of microtubules present in each axoneme ranges from some 140 in Acanthocystis turfacea to as few as 6 in Heterophrys marina (Stock I). In the later species each axoneme contains a single hexagon of microtubules only. In other Heterophrys species, the central hexagon is surrounded by closely packed microtubules or by microtubules arranged in pentagons; only the central hexagon is anchored in the centroplast shell, whereas additional microtubules seem to originate from secondary nucleation sites somewhat distal to the centroplast. It is argued that the distortion of the basic unit hexagon (with alternate angles close to 134°and 106°) indicates that the microtubules are composed of 13 protofilaments.
While in the larger Acanthocystis and Raphidiophrys species, the pattern may result from self-linkage, the arrays found in the Heterophrys species seem to favour a template-determined linkage. To explain the formation of the central hexagon in Heterophrys and balanced lateral growth in the larger microtubule arrays, a ‘linker-nucleation hypothesis’ is proposed. The assumption is made that graded conformational changes in the microtubule subunits not only specify the position where the next linker will bind, but that this linker, through linkage, becomes able to induce secondary microtubule nucleation, which will result in balanced lateral growth of the array. The application of this hypothesis to other microtubule systems, e.g. basal body formation, is discussed.
Differentiated regions of human placental cell surface associated with exchange of materials between maternal and foetal blood: a new organelle and the binding of iron
Authors: Ockleford C. D. , Menon G. 
Published: April 2021

ABSTRACTTo elucidate the method of uptake of a neutral iron compound into the placenta, isolated human chorionic villi were incubated in a medium containing the substance and were fixed at intervals and subsequently examined using transmission electron microscopy.None of the specimens examined showed evidence of vesicular transport in either micro- or macro-pinocytic vesicles which were either coated or smooth-surfaced. Iron uptake may involve attachment of particles to differentiated regions of the cell surface of the syncytiotrophoblast. These differentiated zones in the syncytial cell surface are composed of morphologically distinct parts and therefore probably merit classification as an organelle. Our interpretation of the organelle’s structure is that it is flattened, with a maximum distance across of about 30 nm in the plane of the membrane. It is of otherwise uncertain shape but possesses a multilaminar structure. The external layer is apparently composed of the iron compound to be taken up. Beneath this is an electron-lucent layer possibly composed of glycocalyx. The next innermost layer is continuous with the trilaminar unit membrane of the cell surface, however no trilaminar appearance is observed within the organelle. Beneath the membrane layer is an electron-dense plaque of amorphous material. Occasionally in favourable sections there is the suggestion of a thin electron-lucent strip interposed between the dense plaque and the membrane layer. The whole structure is composed therefore of 4 or 5 different regions. One possible function is that of initial binding in a process of active as opposed to passive transport of iron into the cell.
Extracellular matrix synthesis in blastula and gastrula stages of normal and hybrid frog embryos :I. toluidine blue and lanthanum staining
Authors: Johnson Kurt E. 
Published: April 2021

ABSTRACT
Four developmental stages of Rana pipiens, R. pipiens ♀ × R. catesbeiana ♂, and R. pipiens♀x R. escalenta ♂ embryos were fixed in standard electron microscopic fixatives with or without 1% lanthanum nitrate (LN) added. Embryos fixed without LN were embedded and sectioned at 0·5 μm and stained with toluidine blue. Embryos fixed with LN were embedded and sectioned at 70– 80 nm and examined in the electron microscope. Both techniques show a dramatic increase in the amount of stainable material in the extracellular matrix during development. Blastula stage embryos have a small amount of material in the extracellular matrix. Early gastrulae have more stainable material than blastulae and this increased amount appears to be due to an accumulation of material in the marginal zone of the embryo, especially near the dorsal lip of the blastopore. Late gastrulae have large amounts of stainable material in the extracellular spaces in almost all parts of the embryo. Interspecific arrested hybrid embryos do not show the same dramatic accumulation of stainable material in their extracellular matrices.
Gene transfer by means of cell fusion: II the mapping of 8 loci on human chromosome 1.by statistical analysis of gene assortment in somatic cell hybrids
Authors: Goss S. J. , Harris H. 
Published: April 2021

ABSTRACT
A method is described which should permit determination of the order and spacing of genes on all human chromosomes by the analysis of just one set of man-mouse hybrid cells. This method is used to determine the map of 8 loci on human chromosome 1. A comparison of the statistical maps of chromosome 1 and of the X-chromosome with the cytogenetic maps of these chromosomes at metaphase indicates that the statistically derived distances between genes are related to the amount of Giemsa light-band material between the genes.
Preferential inhibition of rdna transcription by 5-bromodeoxyuridine
Authors: Lykkesfeldt Anne E. , Andersen H. A. 
Published: April 2021

ABSTRACT
On a chemically defined growth medium the degree of substitution of thymidine with 5-bromodeoxyuridine (BUdR) in DNA of Tetrahymena pyriformis was controlled by the concentration of tetrahydrofolic acid, BUdR and thymidine in the medium. A correlation between the degree of BUdR substitution in DNA and the reduction in rate of total RNA synthesis has been established. It was found that the reduction of total RNA synthesis results from inhibition of transcription of all RNA species which have been measured. However, independent of the degree of BUdR substitution in DNA, a preferential inhibition of the synthesis of 25s and 17s ribosomal RNA was found. It is concluded that the various genes may respond differently to BUdR substitution with respect to transcription.
The surface of lipid droplets constitutes a barrier for endoplasmic reticulum-resident integral membrane proteins
Authors: Khaddaj Rasha , Mari Muriel , Cottier Stéphanie , Reggiori Fulvio , Schneiter Roger 
Published: April 2021

ABSTRACT
Lipid droplets (LDs) are globular subcellular structures that store neutral lipids. LDs are closely associated with the endoplasmic reticulum (ER) and are limited by a phospholipid monolayer harboring a specific set of proteins. Most of these proteins associate with LDs through either an amphipathic helix or a membrane-embedded hairpin motif. Here, we address the question of whether integral membrane proteins can localize to the surface of LDs. To test this, we fused perilipin 3 (PLIN3), a mammalian LD-targeted protein, to ER-resident proteins. The resulting fusion proteins localized to the periphery of LDs in both yeast and mammalian cells. This peripheral LD localization of the fusion proteins, however, was due to a redistribution of the ER around LDs, as revealed by bimolecular fluorescence complementation between ER- and LD-localized partners. A LD-tethering function of PLIN3-containing membrane proteins was confirmed by fusing PLIN3 to the cytoplasmic domain of an outer mitochondrial membrane protein, OM14. Expression of OM14–PLIN3 induced a close apposition between LDs and mitochondria. These data indicate that the ER–LD junction constitutes a barrier for ER-resident integral membrane proteins.
This article has an associated First Person interview with the first author of the paper.
TORC2 inhibition of α-arrestin Aly3 mediates cell surface persistence of S. pombe Ght5 glucose transporter in low glucose
Authors: Toyoda Yusuke , Soejima Saeko , Masuda Fumie , Saitoh Shigeaki 
Published: April 2021

ABSTRACT
In the fission yeast, Schizosaccharomyces pombe, the high-affinity hexose transporter, Ght5, must be transcriptionally upregulated and localized to the cell surface for cell division under limited glucose. Although cell-surface localization of Ght5 depends on Target of rapamycin complex 2 (TORC2), the molecular mechanisms by which TORC2 ensures proper localization of Ght5 remain unknown. We performed genetic screening for gene mutations that restore Ght5 localization on the cell surface in TORC2-deficient mutant cells, and identified a gene encoding an uncharacterized α-arrestin-like protein, Aly3/SPCC584.15c. α-arrestins are thought to recruit a ubiquitin ligase to membrane-associated proteins. Consistently, Ght5 is ubiquitylated in TORC2-deficient cells, and this ubiquitylation is dependent on Aly3. TORC2 supposedly enables cell-surface localization of Ght5 by preventing Aly3-dependent ubiquitylation and subsequent ubiquitylation-dependent translocation of Ght5 to vacuoles. Surprisingly, nitrogen starvation, but not glucose depletion, triggers Aly3-dependent transport of Ght5 to vacuoles in S. pombe, unlike budding yeast hexose transporters, vacuolar transport of which is initiated upon changes in hexose concentration. This study provides new insights into the molecular mechanisms controlling the subcellular localization of hexose transporters in response to extracellular stimuli.
Ultrastructural localization of acid phosphatase activity in root tips by the P-(Acetoxymercuric) aniline diazotate reagent and a comparison with a gomoriprocedure
Authors: Stewart P. , Pitt D. 
Published: April 2021

ABSTRACT
The localization of acid phosphatase was studied in root tip cells of pea and mung bean by use of a heavy metal azo-dye technique. Diazotized p-(acetoxymercuric) aniline in a postcoupling procedure, using naphthol AS-BI phosphate as substrate, yielded a fine particulate reaction product within vacuoles, intercellular spaces, multivesicular bodies and at various sites throughout the cytoplasm of pea root cells and differentiating mung bean protoxylem cells. An ultrastructural comparison with a modified Gomori lead-salt precipitation method revealed differences in the subcellular location of β-glycerophosphatase and naphthol AS-BI phosphatase. The distribution of acid phosphatases within plant meristematic cells is discussed.
Synaptonemal complex karyotyping in Melanoplus Differentialis
Authors: Solari Alberto J. , Counce S. J. 
Published: April 2021

ABSTRACT
The chromosomal axes of the spermatocytes of the grasshopper Melanoplus differentiate have been studied with a modification of the microspreading procedure used previously. The whole complement of synaptonemal complexes (SCs) and the axis of the X chromosome have been described and measured. The relative length of each SC is characteristic and constant and permits the construction of an idiogram. Relative lengths of SCs are almost equal to the relative lengths of mitotic chromosomes of spermatogonia (with the exception of the X chromosome), thus extending to an invertebrate the relationship between SCs and mitotic chromosomes that has been demonstrated in mammals. All the SCs except the 3 smallest (which are apparently telocentric) show a small short arm beyond the kinetochore. The progression of changes in the chromosomal axes during meiotic prophase has been staged by centriolar behaviour. During leptotene, axes are first formed near the nuclear envelope at a special (polar) region. SCs also begin to appear in the polar region and extend towards the nuclear interior. The beginning and completion of synapsis is not synchronous among bivalents. The X-axis is formed in midzygotene and shows a characteristic sequence of changes in shape during pachytene. Cells in post-synaptic stages show whole chromosome complements with characteristic chiasmatic configurations. Kinetochores are prominent and bipartite during diplotene-diakinesis.
Chromatin-like artifacts from nuclear sap
Authors: Skaer R. J. , Whytock Susan 
Published: April 2021

ABSTRACT
Nuclear sap, on fixation in glutaraldehyde, forms a fibrous network that resembles chromatin in its dimensions and staining properties. This artifactual network is easily confused with true chromatin fibres in sections of nuclei. With formaldehyde a homogeneous array of beads is produced. These are approximately 10 nm in diameter – the size of nucleosomes – and are interconnected by exceedingly fine fibrils. Each fixative and buffer imposes its own distinctive, reproducible pattern on nuclear sap. The structure of nuclear sap in life cannot be deduced from this range of patterns.
The induction of cytoplasmic petite mutants of Saccharomyces Cerevisiae by hydrostatic pressure
Authors: Rosin Miriam P. , Zimmerman A. M. 
Published: April 2021

ABSTRACT
This study demonstrates that hydrostatic pressure is a potent inductive agent of the petite mutation in cultures of Saccharomyces cerevisiae. The inductive capacity of this mutagen is dependent on the magnitude and the duration of the pressure treatment. Furthermore, the extent of petite induction varies with the growth stage of the culture. Induction occurs in pressure-treated (1·4×104 Ibf in.−2 or 9·66×104 kN m−2 for 4 h) log growth cultures but not in stationary or lag phase cultures. Petite induction and cell survival are also dependent on the particular strain of yeast which is pressure-treated. Tetrad analysis and complementation assays demonstrate that pressure-induced petite cells are cytoplasmic in nature. Moreover, induced petite cells show a wide range of suppressivity (2–99%) with a large proportion of the petite cells being highly suppressive.
Immunofluorescent localization of urease in the cotyledons of jack bean, Canavalia Ensiformis
Authors: Murray D. R. , Knox R. B. 
Published: April 2021

ABSTRACT
Urease has been localized in sections of cotyledons from germinating seeds of jack bean, using FITC-labelled immunoglobulin prepared from urease antiserum raised in rabbits. The complication of lectin binding to the immunoglobulins was resolved by treatment of the sections with specific glycosides. Urease is localized in 2 sites : within the cytoplasm of storage parenchyma cells in spherical granules up to 3 μm in diameter, and within the intercellular spaces in spherical granules. Although similar in size, the latter are distinguished from the cytoplasmic granules by the presence of β-lectin and appear to function as an extracellular lytic compartment or lysosome.
Oscillations and cell development in Dictyostelium discoideum stimulated by folic acid pulses
Authors: Wurster Bernd , Schubiger Katrin 
Published: April 2021

ABSTRACT
Folic acid is known to be a chemoattractant of pre-aggregation cells of Dictyostelium discoideum. When supplied in pulses, folic acid induces biochemical oscillations and stimulates the development of pre-aggregation to aggregation-competent amoebae. The continuous supply of folic acid has no stimulatory effect. Folic-acid-induced oscillations are accompanied by periodic changes in the cyclic AMP concentration. Pulses of folic acid applied with rhythms between 7 and 11 min efficiently induce oscillations. In contrast, a rhythm of 2 min neither induces oscillations nor suppresses them. Cells start to oscillate with a rhythm of about 8 min. This inherent rhythm is independent of the inducing rhythm. Oscillating cells are less sensitive to folic acid than pre-oscillating ones. They respond only to high concentrations of folic acid which also interact with the oscillating system.
Interactions between epithelial and fibroblast-like cells in cultures derived from monkey periodontal ligament
Authors: Brunette D. M. , Kanoza R. J. , Marmary Y. , Chan J. , Melcher A. H. 
Published: April 2021

ABSTRACT
Explants of adult monkey periodontal ligament produced outgrowths containing both fibro-blast-like (F) and epithelial-like (E) cells. A number of multilayers of either E or F cells, or both E and F cells were seen. Electron-microscopic examination of mixed multilayers showed that E cells could form either the superficial or deep sheet of cells. Attachments by means of desmosomes between dorsal and ventral surfaces of multilayered E cells were demonstrated. Although the membranes of E and F cells were sometimes closely apposed, no special junctional structures could be detected between them. The E cell and F cell layers were also observed in a relationship, unusual for cell culture, in which the E cell layer was sandwiched between two F cell layers. This unusual relationship may be the result of cells mimicking in vitro their relationship in vivo, since the E cells are derived from the epithelial rests of Malassez which, in vivo, are surrounded by periodontal ligament F cells. When F cells were seeded on to the surface of E cells a significant fraction of them were found to attach, but the spreading of F cells on E cells was a rare event. These observations could be interpreted as being the result of heterogeneity in the F cell populations. A further indication of the heterogeneity of F cell populations was provided by time-lapse studies of colonies of F cells obtained by culturing cell suspensions of porcine periodontal ligament. In this system, it was found that statistically significant differences existed between the different F colonies with respect to their average cellular mobility. These findings suggest that light-microscopical morphological criteria do not adequately define cell types in terms of behavioural or functional characteristics.
Thermal transitions in the adhesiveness of hela cells: effects of cell growth, trypsin treatment and calcium
Authors: Deman J. J. , Bruyneel E. A. 
Published: April 2021

ABSTRACT
The intercellular adhesiveness of density-inhibited (D.I.) and fast-growing (F.G.) HeLa cells and of trypsin-treated preparations of these, has been measured at temperatures between 37 and 6 °C.
In EDTA-containing buffer medium, F.G. cells differ from D.I. cells in that only the former display an increase in adhesiveness below 30 °C. This increase is prevented by previous treatment with trypsin.
The presence of Ca2+ in the buffer medium causes a narrowing of the thermal transition region of intact F.G. cells. On intact D.I. cells Ca+2 causes an increase in adhesiveness at temperatures below 20 °C. Previous trypsinization of F.G. cells diminishes the effect of subsequent Ca+2 addition. The adhesiveness of trypsinized D.I. cells is indifferent to changes in temperature in Ca*+-containing buffer medium.
The results are considered evidence for the occurrence of a phase transition in the glycoprotein domains of the plasma membrane of fast-growing cells. The transition is influenced by growth rate, trypsinization and Ca2+. The fluidity of the membrane glycoproteins is considered to be higher on density-inhibited cells than on fast-growing cells.
No phase transition could be detected after incorporation of the fluorescent compound 1,6-diphenyl 1,3,5-hexatriene into the lipid domain of the plasma membrane. The fluidity of the membrane lipids is lower on density-inhibited cells than on fast-growing cells.