bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclic amp stimulates accumulation of inositol trisphosphate in Dictyostelium
Authors: Europe-Finner G. Nicholas , Newell Peter C. 
Published: April 2021

ABSTRACT
Previous studies indicated that in Dictyostelium amoebae signal transmission from cell surface cyclic AMP receptors to intracellular events concerned with chemotaxis involves inositol 1,4,5-trisphosphate (1,4,5-IP3): micromolar amounts of 1,4,5-IP3 or Ca2+ were found to mimic the effects of chemoattractants and 1,4,5-IP3 triggered release of Ca2+ from non-mitochondrial stores. Here we report a more direct test of the involvement of inositol phosphates. Intact amoebae were labelled with high specific activity [3H]inositol, then stimulated with the chemoattractant cyclic AMP at 22 °C and rapidly assayed for phosphorylated inositol products formed. Labelled IP3 was found to accumulate transiently after a pulse of 50nM-cyclic AMP, with a peak at 15 s after stimulation and some (inconclusive) evidence for a more rapidly formed peak at 5 8 or less. Inositol bisphosphate (IP2) showed a transient shallow peak at about 20 s. When the events of signal transmission were slowed down by incubation at 4°C, the rapidly formed IP3 peak could be consistently seen at 5 s after stimulation and the second peak at 25–30 s. Further resolution of the IP3 peaks indicated the presence of IP4, which represented a major fraction of the peak accumulated at 5 s (4°C). The results provide an important link in the chain of evidence connecting the cell surface cyclic AMP receptors, vía IP3, with the Ca2+-activated events of chemotaxis.
Extracellular matrix and cell migration: locomotory characteristics of mos-11 cells within a three-dimensional hydrated collagen lattice
Authors: Noble P. B. 
Published: April 2021

ABSTRACT
The locomotory trajectories of MOS-11 cells migrating in a three-dimensional hydrated collagen lattice have been determined using a computer-assisted optical sectioning unit. The trajectories have been quantified using a three-dimensional continuous-time Markov probability theory consisting of eight directional states and one stationary state; in the latter the cells are not locomoting. Markov analysis shows that these cells are locomoting in a random manner with regard to direction and remain stationary for about three times as long as they are locomoting. Analysis of persistence also implies random locomotion. Compilation of the distribution of angles between steps reveals that the cells exhibit a predilection for turns around 30° and 150° on either side of the previous step. Time-lapse video recordings show that the cells are bi-polar with ruffling membranes at opposite poles. Ruffling, and hence locomotion, occurs alternately at one pole and then the other, which would account for the distribution of angles encountered. The mean speed of the cells was of the order of 3 μm min−1 including the time stopped and approximately twice this if the time stopped (state 0) is not included. The results obtained provide base-line data on the locomotory characteristics of MOS-11 cells locomoting in a 1·2 mg ml−1 collagen gel. It is now possible to study the role of various matrix components in cell locomotion. Such studies are of importance to embryology, wound healing, host defence mechanisms and the invasion of cancer cells.
Deficiency of density-dependent regulation of cell growth in the culture of skin fibroblasts from patients with mucolipidosis iii
Authors: Oohira Atsuhiko , Matsui Fumiko , Oki Takashi , Nogami Hiroshi 
Published: April 2021

ABSTRACT
Cultured skin fibroblast cells were prepared from two patients with mucolipidosis HI (ML HI), which is a genetic disorder characterized by low activities of multiple lysosomal enzymes in fibro-blasts. Genetic complementation analysis of fused fibroblast hybrids revealed that the patients were classified in different complementation groups. Growth curves of fibroblasts of ML HI patients in culture were compared with those of fibroblasts of Sanfilippo’s syndrome patients as well as of the normal fibroblasts. Normal and Sanfilippo fibroblasts gave essentially the same sigmoid curve of cell growth. However, although both ML m cell lines grew at the normal rate in the initial logarithmic phase, they continued to proliferate actively even after the cultures reached confluency. This is the first report to demonstrate the deficiency of density-dependent regulation of cell growth in the culture of non-transformed cell types. Therefore, the culture of skin fibroblasts of ML HI patients may serve as a useful experimental model for investigating the regulation of cell proliferation in vitro.
Identification of calmodulin in Acetabularia: its distribution and physiological significance
Authors: Cotton Geneviève , Driessche Thérèse Vanden 
Published: April 2021

ABSTRACT
In order to test whether calmodulin is present in Acetabularia, material was isolated from this alga, using the chlorpromazine affinity method. This resulted in the purification of a protein with the correct mobility on SDS–polyacrylamide gels. This protein reacted with anti-calmodulin in dot blots, using an immunogold, silver-enhanced method, so we conclude that calmodulin is present in the alga, although at a very low concentration (200–450 pg per gram wet weight).
The localization of calmodulin was studied, using fluphenazine fluorescence. The pattern is described; the chief feature being the concentration of fluorescence towards the tip during both the slow and the rapid growth phases. Fluorescence is also observed at the insertion points of hairs on the stalk and decreases in intensity between hairs of successive order. The apical fluorescence vanishes when cap formation begins. The localization of calmodulin parallels that of calcium studied by means of chlorotetra-cycline and aequorin.
Expecting inhibitors of calmodulin to produce physiological effects, we studied the growth of whole and anucleate Acetabularia in the presence of trifluoperazine (TFP). TFP severely inhibited growth and cap formation, as did lanthanum. A circadian rhythm of sensitivity to these inhibitors was found. The hypothesis is put forward that calcium and calmodulin are important during a critical photosensitive phase of the circadian cycle.
An actin-related protein inside pea chloroplasts
Authors: Mccurdy David W. , Williamson Richard E. 
Published: April 2021

ABSTRACT
A pea chloroplast protein resembles vertebrate and algal actins by several chemical and immunological criteria. On two-dimensional polyacrylamide gels it migrated with a slightly lower relative molecular mass (Mr = 41 000) and slightly more basic isoelectric point than rabbit skeletal muscle actin. A monoclonal antibody to chicken gizzard actin reacted on immunoblots with rabbit skeletal actin, with Chara actin and with a 41000Mr band from pea chloroplasts. Pea and Chara bands of approximately 58 000Mr were also stained. A DNase I-affinity column that bound muscle actin also bound 41 000 and 58 000Mr chloroplast polypeptides. Similarities existed between enzymically and chemically generated fragments of the 41000Mr chloroplast polypeptide and rabbit muscle actin. The 41000 Mr protein was protected from degradation by thermolysin only in preparations of intact, but not ruptured, isolated chloroplasts, indicating that this protein resides within the outer envelope membrane of these organelles. It is concluded that a 41 000 Mr protein with major similarities to actin occurs inside pea chloroplasts, and that a 58000Mr protein with some similarities to actin also probably exists within chloroplasts.
Surface membrane clearing of receptor–ligand complexes in human blood platelets
Authors: Behnke O. 
Published: April 2021

ABSTRACT
Human blood platelets were challenged sequentially in vitro with polyclonal anti-platelet antibodies and cationized ferritin. Both ligands bound to the surface membrane and were sequestered by internalization into a surface-connected membrane system (SCS) with a cleared surface membrane as the eventual result. Patching and capping of bound antibody preceded internalization, and platelets cooperated in the clearing process by adhering to each other at capped areas and by mutual covering up, a process dubbed platelet hugging. The internalization process was repeated upon challenge with the second ligand, the two ligands being sequestered as separate deposits in the SCS, mirroring the two cycles of internalization. Platelets were activated during the internalization process and tended to aggregate. In aggregates, surfaces exposed to the medium were cleared of ligand, which accumulated in the intercellular spaces and within the SCS of the aggregated platelets. Aggregation but not internalization and hugging was prevented by adenosine and adenosine monophosphate.
The role of reactive oxygen metabolites in lymphocyte-mediated cytolysis
Authors: Bishop C. J. , Rzepczyk C. M. , Stenzel D. , Anderson K. 
Published: April 2021

ABSTRACT
To examine the possible role of reactive oxygen metabolites in lymphocyte-mediated cytolysis, the morphology of cell death following the exposure of cells to reactive oxygen metabolites in vitro was compared with the morphology of cell-mediated killing in vitro of tumour cells by natural killer (NK) cells. Ultrastructural examination of human tumour cells that were dying following incubation for 60 min with the oxygen metabolite generating systems, xanthine-xanthine oxidase or t-butylhydroperoxide, showed that cell death in both instances was exclusively by necrosis. It was unclear which oxygen metabolites were involved in killing. Cell death was not decreased by the addition of superoxide dismutase, a scavenger of the superoxide anion, to the xanthinexanthine oxidase mixture. Although the cells were not killed by incubation with 1 mM-hydro-gen peroxide, the addition of catalase, a scavenger of hydrogen peroxide, to the xanthinexanthine oxidase mixture significantly reduced cell death. The addition of scavengers for the hydroxyl radical to either the xanthine-xanthine oxidase mixture or t-butylhydroperoxide gave inconsistent protection.
In contrast, tumour cell killing mediated by natural killer cells was by apoptosis, a morphologically distinct mode of cell death with a different basic mechanism, indicating that reactive oxygen metabolites are not directly involved in lymphocyte-mediated cytolysis.
Isolation of an endocytic compartment from A431 cells using a density modification procedure employing a receptor-specific monoclonal antibody complexed with colloidal gold
Authors: Beardmore Julia , Howell Kathryn E. , Miller Karen , Hopkins Colin R. 
Published: April 2021

ABSTRACT
Our objective was to isolate a prelysosomal compartment involved in receptor-mediated endo-cytosis in human epidermoid carcinoma (A431) cells. The isolation protocol involves density modification of endosome elements in A431 cells, caused by the receptor-dependent binding and internalization at 20 °C of colloidal gold-transferrin receptor antibody (B3/25) particles. The use of 125I-labelled gold–B3/25 provides a radioactive marker for the endosome compartment, the major peak being recovered at the bottom of a continuous sucrose gradient at a density of 1·23 g ml−1. Enzyme markers characteristic of other cytoplasmic compartments are present only in negligible amounts in this fraction and L-[35S]methionine-labelling of the cells indicates approximately a 200-fold enrichment of bilabelled gold–B3/25 versus protein. Electron microscopy of the endosome-rich fraction reveals that we have isolated a highly purified population of small gold-containing vesicles and tubules from which the transferrin receptor can be immunoprecipitated using the B3/25 antibody. Gel electrophoresis and fluorography of L-[35S]-methionine-labelled cells suggests that these elements contain a characteristic profile of approximately 10 major proteins of which three appear to be specifically enriched. In cells incubated with [125I]transferrin, 12% of the ligand sediments with the gold-labelled elements. We conclude, therefore, that the components we have isolated play a role in the intracellular processing of the transferrin-transferrin receptor complexes.
Quiescence and increased adhesion after mammalian DNA transfection of human fibrosarcoma cells
Authors: Nagy Adam , Baker Robert F. 
Published: April 2021

ABSTRACT
When a population of human fibrosarcoma HT1080 cells was transfected with a mammalian expression vector and DNA pieces representing either the human whole genome or mouse bulk cDNA, there was a transient increase in the number of adhesive cells in the population. The number of cells with increased adhesion was proportional to the amount of transfected DNA; the increase occurred at a maximal frequency of between 10−4 and 10−5 per cell. Increased adhesion in these cells persisted for 9–12 days, corresponding to the period of highly efficienttransient transfection, and was accompanied by arrest in cell division. Transfection of non-mam-malian DNAs, reduction of transfected mammalian sequence length by restriction enzyme digestion, or omission of expression vector DNA did not permit these shifts in phenotype. The effects seen suggest that expression of specific transfected mammalian DNA sequences suppresses certain phenotypic characteristics in these transformed mammalian cells.
A monoclonal antibody recognizes a human nuclear protein resembling Xenopus oocyte nucleoplasmin
Authors: Lord Janet , Brown Geoffrey , Bunce Christopher , Nathan Paul 
Published: April 2021

ABSTRACT
The monoclonal antibody 10BG2 (IgG3) was derived from a mouse immunized with human pre B cells. In immunofluorescence studies the antibody revealed a human nuclear-associated determinant, which in interphase cells was entirely restricted to the nucleus. In metaphase cells 10BG2 antigen was detected throughout the cytoplasm with intensified staining at the periphery of chromosomes. 10BG2 antibody stained all human normal and transformed cells tested. In contrast, the antibody did not stain mouse 3T3 cells or Chinese hamster ovary (CHO) cells. Electrophoresis under denaturing and non-denaturing conditions revealed the 10BG2 antigen to be a 130 ×103 to 140×103Mr protein with a subunit molecular weight of 29·5×103. This suggests the protein is at least a tetramer. On two-dimensional gels the 10BG2 antigen had a streaked appearance and separated into two isoelectric variants (pl 5·2, 5·4). The protein was also shown to be phosphorylated and thermostable, and remained in solution at pH 3·6. 10BG2 antigen was highly soluble in aqueous buffers and co-migrated on non-denaturing gels with the nucleosome-assembly protein, nucleoplasmin, purified from Xenopus oocytes. The similarity of 10BG2 antigen to nucleoplasmin is discussed.
Hydration, volume changes and nuclear magnetic resonance proton relaxation times of HeLa S-3 cells in M-phase and the subsequent cell cycle
Authors: Wheatley Denys N. , Inglis Marget S. , Foster Margaret A. , Rimington J. Ewen 
Published: April 2021

ABSTRACT
Most mitotic HeLa cells divided into two daughter cells with half the volume of the parent; no additional reduction in volume was detectable during late telophase or the early part of G1. Synchronous growth throughout the next generation cycle was exponential, without an additional and sudden rise in volume being detectable as cells entered M-phase. Since the wet weight / dry weight ratio and the protein per unit mass of cells remained constant throughout the cycle, measurements based on volume changes accurately reflected growth parameters and cell water content.
Nuclear magnetic resonance (n.m.r.) t1 (spinlattice) proton relaxation times for intracellular water for M-phase cells measured at both 32 MHz (25°C) and 80MHz (37°C) in a Bruker spectrometer had the same values as normal interphase cells. Furthermore, cells arrested in metaphase by nitrous oxide or alkaloids gave the same t1 values. Artificial manipulation of cell hydration by adjustment of the tonicity of the external medium led to t1 values that correlated well with the level of intracellular water. On this basis, a 40% increase in hydration raised t1values by a factor of 1 ·29 at 32 MHz and 1 ·5 at 80MHz. This is considerably less than the increase by a factor of 1 ·9 in t1 time reported with the 40% rise in cell water accompanying mitosis, measured at 30 MHz and 25 °C under isotonic conditions by others. The protein-synthesizing ability of hydrated cells was reduced to only half the normal level after a doubling of intracellular water.
The data from these several different analyses, taken together, strongly indicate that the water content of mitotic cells is very similar to that of interphase cells, and that certain features unique to the mitotic phase of the cell cycle cannot be ascribed to an elevated (free) water content.
The microtubule-organizing complex and the Golgi apparatus are co-localized around the entire nuclear envelope of interphase cardiac myocytes
Authors: Kronebusch Paul J. , Singer S. J. 
Published: April 2021

ABSTRACT
In most animal cells, the microtubule-organizing centre (MTOC) and the Golgi apparatus (GA) are co-localized on one side of the nucleus, an arrangement that allows these cells to acquire a functional polarity. An exception has been reported in the skeletal muscle myotube, where the MTOC and GA exhibit a circumnuclear distribution. We wished to determine if this unusual distribution of the MTOC and GA was peculiar to syncytial myotubes or reflected a pattern found in muscle cells generally. Immunofluorescence microscopic studies of cultured chicken skeletal muscle, cardiac muscle and gizzard smooth muscle cells were carried out using preimmune sera that recognized the pericentriolar material, anti-tubulin antibodies to label the MTOC, and fluorescent wheat-germ agglutinin to label the GA. These studies have shown that cardiac myocytes possess a circumnuclear distribution of their MTOC and GA as do skeletal myotubes, but smooth muscle cells exhibit the centrosomal MTOC and GA distribution found in most other cells. The circumnuclear MTOC/GA distribution therefore is associated with striated muscle cells. We also found that as embryonic cardiac myocytes pass through the cell cycle the microtubuleorganizing activity in these cells switches from a circumnuclear distribution in interphase to the conventional centrosomal location during mitosis. Thus, cardiac myocytes provide a rare example of mononucleated animal cells that do not display a centrosomal MTOC or a polarized GA, and also reveal a system in which the MTOC structure can be reversibly altered in a cell cycledependent manner.
Isolation and characterization of a mutant of Tetrahymena thermophila blocked in secretion of lysosomal enzymes
Authors: Hünseler Peter , Scheidgen-Kleyboldt Gerda , Tiedtke Arno 
Published: April 2021

ABSTRACT
The development of a sensitive screening procedure for mutants of Tetrahymena thermophila blocked in secretion of lysosomal enzymes is described.
By means of this procedure a mutant blocked in secretion of lysosomal enzymes has been isolated. This sec− mutant, MS-1, is constitutively blocked in release of at least six lysosomal enzymes, under both nutrient and non-nutrient conditions. MS-1 possesses, bound within the cell, the same amount of active lysosomal enzymes as the wild type. During starvation in media of low ionic strengh MS-1 develops a highly vacuolated phenotype. This phenotype is caused by the sec− allele. It is reversed to a normal cell shape when the mutant is transferred to isotonic medium.
The sec− mutant MS-1 contains mucocysts and is capable of inducing exocytosis of these secretory organelles, suggesting that Tetrahymena possesses at least two independent protein-secreting organelles.
Key words: Tetrahymena thermophila, lysosomal enzymes, protein secretion, secretory mutants.
Analysis of the temperature-sensitive period of the short-1 mutation affecting stomatogenesis in Paramecium tetraurelia
Authors: Tam Lai-Wa , Ng Stephen F. 
Published: April 2021

ABSTRACT
Reduction in the length of the oral apparatus produced by the temperature-sensitive mutation short-1 (shl) involved suppressed growth of the oral primordium in all stages of development. Temperature shift-up and heat-shock experiments revealed that the temperature-sensitive period of this mutation coincided with nearly the entire stomatogenic phase (stages 1–6) in sexual reproduction. Low- and high-sensitivity phases were noted, corresponding to the periods of slow (stages 1 and 2) and rapid (stage 3 to stage 6) elongation of the oral primordium, respectively. The action of shl is thus concentrated after stage 2. The mutation hypothetically results in defective membrane growth and extension in the oral primordium, leading to restriction in incorporation of basal bodies into the developing membranelies.
A glycoprotein rapidly labelled with [14C]glucose present in a murine melanoma cell line
Authors: Bramwell M. E. 
Published: April 2021

ABSTRACT
If a murine melanoma cell line PG19 is metabolically labelled with [14C]glucose for a short time, one particular membrane component incorporates more radioactivity than the rest. This is a glycoprotein of about Mr 100 000, which is not preferentially labelled in non-malignant variants of the melanoma or in suppressed hybrid cells formed between PG 19 and mouse fibroblasts.
Organization of the boar spermatozoan plasma membrane: Evidence for separate domains (subdomains) of integral membrane proteins in the plasma membrane overlying the principal segment of the acrosome
Authors: Peterson R. N. , Gillott M. , Hunt W. , Russell L. D. 
Published: April 2021

ABSTRACT
Indirect immunofluorescence microscopy and freeze-fracture have been used to identify over-lapping subdomains at the peripheral rim of the sperm-head plasma membrane (PM) and the margin of the outer acrosomal membrane (OAM) comprising the principal segment of the acrosome of the boar spermatozoon. An array of ridge-like structures (spaced 12–16 nm centre-to-centre), originally observed on the OAM by Aguas & Pinto da Silva, lies just beneath an area of the PM that is sparsely populated with large intra-membranous particles compared to that of other regions of the head PM. This region has a high specificity for the lectin aracbis hypogaea (peanut agglutinin). We suggest that the OAM at the rim of the sperm head may be rich in acidic phospholipids and that the close apposition of this membrane with a region of the PM relatively poor in integral membrane proteins may provide sites for initiating the acrosome reaction.
Formation, distribution and dissociation of intercellular junctions in the lens
Authors: Gruijters W. T. M. , Kistler J. , Bullivant S. 
Published: April 2021

ABSTRACT
A 70000 Mr membrane protein (MP70) has previously been identified as a specific component of lens intercellular junctions. In this paper we use anti-MP70 immunofluorescence microscopy of dissected fibre bundles to study the formation, distribution and dissociation of junctional plaques in the outer cortex region of the sheep lens. Abundant, small junctional plaques are assembled de novo in the broad sides of the elongating fibres near the equatorial lens periphery. In fully elongated, pole-to-pole fibres, junctional plaques are generally larger, and while dispersed on the broad sides of the fibres in the equatorial lens plane, these junctions line up in the middle of the broad and narrow sides of the fibres in the lens polar regions. This precisely defined positioning is independent of junction size and hence cannot solely be explained by the constraints of fibre width. Junctional plaques fragment to smaller sizes and MP70 is cleaved to MP38 in mature, enucleated fibres located in the deeper portions of the lens outer cortex. These results demonstrate a dynamic aspect of lens intercellular junctions and show that they are positioned in a precise fashion, possibly in association with other membrane or cytoskeletal components.