bluuebunny/crossref_metadata_2025_split huggingface dataset:
Common features of coated vesicles from dissimilar tissues: Composition and structure
Authors: Woods John W. , Woodward Michael P. , Roth Thomas F. 
Published: April 2021

ABSTRACT
Coated vesicles were purified and characterized from porcine brain and chicken oocyte. Electrophoresis on sodium dodecylsulphate (SDS) gels showed that coated vesicles from either source have three major proteins in common with apparent molecular weights of 180000, 120000, and 55000 Daltons. Negatively stained specimens from both sources appear to consist of a highly ordered array of short interconnected rods or ridges of material on the exterior surface of a membrane vesicle. Coated vesicles purified from porcine brain and chicken oocyte have mean external diameters of 75·0 and 85·o nm, respectively. In coated vesicles of the appropriate orientation, portions of the coat material appear to be organized into hexagons and pentagons. Based on the observed variability of size and apparent structure, it is postulated that the basic structural subunits of coated vesicles are the short rods or ridges of material observed on the exterior membrane vesicle surface. It is suggested that multiples of these sub-units can be assembled into many arrangements to yield coated vesicles of different sizes and coat structure. It is also proposed that the structural subunit is a complex of 3 proteins of molecular weight of 180000, 120000 and 55000 Daltons.
Regulation of ribosomal rna synthesis in Tetrahymena pyriformis
Authors: Keiding J. , Andersen H. A. 
Published: April 2021

ABSTRACT
Ribosomal RNA is synthesized at constant rate during most of the cell cycle in heat-shock synchronized populations of Tetrahymena pyriformis. Early in each macronuclear S-period the rate of synthesis increases abruptly, concomitant with replication of the genes coding for ribosomal RNA. The increase is prevented by inhibitors of DNA replication, added prior to the S-period. Similarly, in cultures synchronized by starvation/refeeding, inhibition of DNA replication, at the time when the rDNA is replicated, will prevent the normal increase in rate of RNA synthesis which follows refeeding.
We conclude that inhibition of rDNA replication interferes with the synthesis of rRNA, and we suggest that with respect to rRNA synthesis a gene dosis effect is operating in fastgrowing Tetrahymena cells.
Follicle cell bridges in the mosquito ovary: syncytia formation and bridge morphology
Authors: Fiil Annelise 
Published: April 2021

ABSTRACT
In the mosquito, Culex pipiens quinqefasciatus, the follicle cells enveloping the oocyte and the nurse cells are connected by intercellular bridges. The bridges are formed by incomplete cytokinesis, and they persist for more than 30 h after their formation. Reconstructions from serial sections showed that one syncytial group contained at least 32 cells; several cells continued outside the series. The cells in a syncytium divide asynchronously; this results in an irregular, branched organization. The bridges may be either embedded in the cytoplasm of the cells, or they may form an extracellular connexion.
Ouabain binding during plasma membrane biogenesis in duck salt gland
Authors: Hossler Fred E. , Sarras Michael P. , Barrnett Russell J. 
Published: April 2021

ABSTRACT
The conditions necessary for optimal ouabain binding in the avian salt gland were examined. Binding was enhanced by ATP and Mg2+ and was decreased by K+, but was unaffected by added Na+. Both maximal binding and complete inhibition of Na,K-ATPase activity were obtained at 1 × 10−6 M ouabain. Half maximal binding and half maximal inhibition of Na,K-ATPase activity were obtained at 1·7×10−7 M ouabain. Ouabain binding increased in parallel with increasing specific activity of the Na,K-ATPase during salt-induced salt gland specialization. The ratio of Na,K-ATPase activity to ouabain-binding sites remained constant during the salt stress as well as after removal of the salt diet. Autoradiography indicated binding to partially and fully differentiated secretory cells of the salt gland. The ouabain binding assay appeared to be a more useful indicator of membrane amplification than Na,K-ATPase activity since it is rapid, essentially irreversible, less sensitive to tissue fixatives, and quantitatively measured the number of enzyme molecules.
Osmoregulation in the algaVacuolaria virescens. structure of the contractile vacuole and the nature of its association with the golgi apparatus
Authors: Heywood Peter 
Published: April 2021

ABSTRACTThe contractile vacuole of the chloromonadophycean alga Vacuolaria virescens is a permanent structure that possesses a specialized membrane: subunits of this membrane have a diameter of 21—24 nm and in places are arranged in a regular hexagonal pattern. The lateral walls of these subunits form regularly spaced bristles or pegs which extend inwards from the trilaminar membrane for a distance of 13–15 nm. The contractile vacuole is situated immediately above an extensive Golgi apparatus that covers most of the anterior surface of the nucleus. Vesicles of Golgi origin give rise to subsidiary vacuoles which in turn empty into the contractile vacuole. Golgi vesicles, subsidiary vacuoles and the contractile vacuole contain similar electron-dense material. It is suggested that this material might be a highly hydrophilic substance which will attract water from the cytoplasm into the Golgi vesicles, subsidiary vacuoles and contractile vacuole from whence it is discharged from the cell. This method of osmoregulation is compared to that occurring in other algae and protozoa.
New staining method for the detection of sister-chromatid exchanges in brdu-labelled chromosomes
Authors: Alves P. , Jonasson J. 
Published: April 2021

ABSTRACT
A direct Giemsa technique is described for the selective staining of BrdU-substituted chromatin. It can advantageously be used for sister-chromatid exchange analysis and for the detailed cytological study of the mouse kinetochores. Presumptive inversions within the centromeric region of chromosomes 4 and 18 in the C57Black/6J mouse are described.
Developmental stages in the formation of inverted gap junctions during turnover in the adult horseshoe crab, Limulus
Authors: Lane Nancy J. 
Published: April 2021

ABSTRACT
Stages leading to the formation of inverted gap junctions between certain basal replacement or interstitial cells in the mid-gut of adult Limultts can be followed by freeze-fracturing. Free, 13-nm EF intramembranous particles first appear to be organized into short linear arrays or small clusters of particles, which then become transformed into anastomosing particulate networks covering a considerable surface area. These subsequently become concentrated into smaller, more nearly circular, macular plaques of EF particles or PF pits. These EF particles, both when free or assembled into macular arrays, possess a central channel or pore. Numerous formed gap junctions are present in Limulus mid-gut, which suggests that cell-to-cell communication is an important feature of the mature tissue. The results show that arthropod tissues can be used to study the development of gap junctions not only in differentiating systems but also in adult tissues during normal cell turnover.
The effects of surfactants on cell aggregation
Authors: Owen E. , Clifford J. , Marson A. 
Published: April 2021

ABSTRACT
Trypsin-dissociated HeLa and human amnion cells were employed to investigate the effects of an anionic, a cationic, and a non-ionic surfactant on cell reaggregation. All the surfactants inhibited the reaggregation process, the effect increasing with surfactant concentration, and becoming significant at concentrations of about 10−6 M for the anionic surfactant and about 10−5 M for the others. The effects of temperature and ionic strength on HeLa cell aggregation, and of surfactants on the electrophoretic mobility of HeLa cells and the release of sialic acid from their surfaces by neuraminidase, were also examined. The results indicate that although electrostatic effects occur and are likely to be of importance in cell reaggregation, the effect of surfactants cannot be accounted for on this basis alone, and it is suggested that interactions involving the cell-surface glycoproteins, possibly indirectly via effects on the fluidity of the cell membrane, are also significant in this respect.
Invasive locomotory behaviour between malignant human melanoma cells and normal fibroblasts filmed in vitro
Authors: Stephenson E. M. , Stephenson N. G. 
Published: April 2021

ABSTRACT
Explants of human malignant melanoma (MM96), normal adult human skin fibroblasts (HSF) and embryonic chick ventricle were confronted in pairs. The 2 outwandering populations in each confrontation eventually met in a situation where each could potentially invade the other. The human explants were artificially prepared from dissociated cells. The primary objective of the study was to compare the relative invasive capacities of the malignant and non-malignant human cell populations against a standard population of chick heart fibroblasts (CHF). Relative invasiveness was also compared for (a) malignant human melanoma cells against human and avian fibroblasts; (b) the 2 different fibroblast populations against MM96; and (c) the 2 fibroblast populations against each other.
Time-lapse films were prepared for each confrontation. Each cell population was also filmed in a free or unconfronted state. The films were analysed in terms of (a) cell speeds in relation to numbers of contacts; (6) the net radial outward velocity; (c) directional frequencies of movements; and (d) cell behaviour resulting from heterologous collisions. Replicate cultures were fixed and stained 24–40 h after junction. Measurements from these indicated relative distances travelled by each population towards the opposing population and towards free space. Nuclear overlap and population density measurements were also recorded.
MM96 cells invaded the standard chick fibroblast population but eventually encountered moderate obstruction. Invasion was mainly by oriented movement between successive pairs of chick cells. Contact paralysis of ruffling of MM96 was not seen. Human fibroblasts did not invade the CHF population. They were contact inhibited by chick cells and typically reversed their direction of movement. MM96 cells invaded the human fibroblast population without obstruction. They were not usually contact inhibited by HSF and several different pathways for locomotory invasion, including overlapping, were involved. Cells of both fibroblast populations were contact inhibited by leading-edge collisions with MM96 cells. Fibroblast invasion of MM96 was by underlapping of orthogonally oriented, bipolar melanocytes or dendritic processes. Human fibroblasts were less obstructed than chick fibroblasts during invasion of MM96. Initiation of invasion of HSF by chick cells was apparently orientation dependent. Invasion by CHF was assisted by the alignment, morphology and contact-mediated withdrawal of the human cells. Heterologous contact inhibition was not apparently defective for either cell type. In all confrontations involving both malignant and non-malignant cells, the extent and pattern of invasion could be related to apparent deficiencies in heterologous contact inhibition of locomotion.
SV40-transformed hamster cells resistant to 100–250 μg/ml of ethidium bromide
Authors: Wolf Gudrun , Tejmar Liana , Borell Sabine , Klietmann Wolfgang 
Published: April 2021

ABSTRACT
SV4o-transformed hamster cells were selected for resistance to ethidium bromide (EB). Several cell lines were established, which grew in the presence of up to 250 μg/ml EB. The EB resistance is genetically stable. The cloned resistant cells show no difference in morphology, with the exception of the mitochondrial ultrastructure, which exhibits condensed cristae formation. The tumorigenicity of these cells in Syrian gold hamsters is considerably reduced. Incorporation of radioactive labelled thymidine into mitochondrial DNA is not influenced by the presence of the drug. Gel electrophoresis with mitochondrial proteins from wild-type and resistant cells reveals significantly different patterns. The mechanism of EB resistance is discussed.
Directionality of microtubule assembly: an in vivo study with the ciliate Tetrahymena
Authors: Ng Stephen F. 
Published: April 2021

ABSTRACT
A temperature-sensitive mutant homozygous for the recessive gene molb in Tetrahymena thermophila offers opportunity for studying the direction of microtubule assembly in vivo. At 39 °C the mutant fails to divide properly; the 2 daughter animals remain attached and bend over each other. As revealed by protargol staining, the bending results in acute turning and breaking of some of the longitudinal microtubular bands close and parallel to the surface. Hence, 2 broken microtubular ends are available for study of the problem of directionality of microtubule assembly, by assessing which of the 2 ends regenerates. In most cases the posterior portion of the longitudinal microtubular band regenerates. The present study hence supports the conclusion based on in vitro observation in other systems that microtubule assembly is predominantly unidirectional.
The cell surface of Trypanosoma cruzi: cytochemistry and freeze-fracture
Authors: De Souza W. , Martfnez-Palomo A. , González-Robles A. 
Published: April 2021

ABSTRACT
The ultrastructure of epimastigotes of Trypanosoma cruzi, obtained from, acellular cultures, and bloodstream trypomastigotes, isolated from infected mice, were studied by thin-sectioning and freeze-fracturing techniques. Epimastigotes showed a thin (5 nm) surface coat when stained with ruthenium red, while the surface coat of trypomastigotes was more prominent (15 nm thick). Both P and E faces of the plasma membrane of T. cruzi had roughly the same number of intramembranous particles (IMP) as seen by freeze-fracture. The plasma membrane of bloodstream trypomastigotes had less IMP than epimastigotes. Several differentiations of the plasma membrane were observed. In epimastigotes a cytostome appears as a particle-poor region delimited by a pallisade-like row of adjacent IMP. Bloodstream trypomastigotes did not have a cytostome. Instead, abundant pinocytic vesicles were observed. At the base of the flagellum of epimastigotes a ciliary necklace was found. At this region, the surface coat was differentiated as long, hair-like projections after staining with ruthenium red. The flagellar membrane had less IMP than the body membrane. Clusters of IMP were present on both faces of the flagellar membrane at the flagellar-body adhesion zone of epimastigotes. Linear arrays of IMP were also seen. In bloodstream trypomastigotes clusters of particles were observed both on the flagellar and cell body membranes. Our observations demonstrate the presence of considerable structural variations of the T. cruzi plasma membrane at the two stages of the life cycle studied.
Labelling of human resting lymphocytes by continuous infusion of [3H]thymidine. I. characterization of cytoplasmic label
Authors: Schick P. , Trepel F. , Maisel K. H. , Past W. , Reisert I. , Begemann H. , Pilgrim Ch. 
Published: April 2021

ABSTRACT
After continuous 3H-TdR infusion in vivo or incubation with 3H-TdR in vitro human blood lymphocytes were examined by light-microscopic and electron-microscopic autoradiography. Using relatively long autoradiographic exposure times (50–300 days) not only nuclear but also cytoplasmic labelling was visualized, the cytoplasmic label being present in up to 96 % of the cells. The cytoplasmic label was predominantly associated with the mitochondria and was removed from the cells nearly completely by treatment with DNase but not with RNase or cold perchloric acid. It is concluded that this cytoplasmic label mainly represents 3H-TdR incorporated into mitochondrial DNA which is continuously renewed in an average turnover time of 14 days or less. This value is compatible with a turnover time of 11 days for mitochondrial DNA in mammalian cells reported in the literature.
An experimental study of the interaction between the soil amoeba Naegleria gruberi and a glass substrate during amoeboid locomotion
Authors: Preston T. M. , King C. A. 
Published: April 2021

ABSTRACT
The amoeboid locomotion of the soil protozoon Naegleria gruberi has been studied using reflexion-interference microscopy. Two types of contact are made with a planar glass substrate. One, formed at a considerable distance from the substrate in deionized water (≏100 nm) has been termed ‘associated contact’ and usually involves a considerable surface area (of the order of 100 μm1), i.e. about a third of the cell profile. From this broad platform filopodia are produced which form close contacts (‘focal contacts’). In locomotion the area of associated contact is very mobile, in contrast to the focal contacts which, once established, are stable. Focal contact sites are left behind on the glass surface (‘footprints’) when the amoeba moves away. The cell-substrate gap in the associated contact is greatly affected by the ionic strength of the medium and particularly the valency of the cation component. This suggests that long-range forces of attraction play an important role in keeping the amoeba close to a substrate and thus allow the production of filopodia from the ventral surface to form focal contacts.
Long-term maintenance of reaggregated hypothalamic cultures developed from embryonic rat hypothalamus: prostaglandin release during synaptogenesis in vitro
Authors: Gyévai Angela , Chapple Paul J. , Douglas William H. J. 
Published: April 2021

ABSTRACT
Hypothalamic aggregate cultures were developed from hypothalami taken from rat embryos at 17—19 days gestation. The aggregate cultures exhibited a prominent morphological differentiation during 3-4 weeks in culture. The fine structure of the synapses formed in the aggregates resembled synapses in the adult animal. During synaptogenesis the aggregates spontaneously released prostaglandin E2 (PGE2). The amount of PGES released in the media was reversed upon the morphological differentiation of the hypothalamic cultures. Media containing a higher PGE2 concentration increased the extracellular prolactin accumulation in monolayer cultures developed from adult rat hypophysis.
Acetylcholinesterase: A useful marker for the isolation of sarcolemma from the bivalve (Modiolus demissus demissus) myocardium
Authors: Watts John A. , Pierce Sidney K. 
Published: April 2021

ABSTRACT
The presence of cholinesterase activity in M. demissus hearts was demonstrated by light- and electron-microscopic histochemistry and by enzymic assay. The enzyme proved to be acetylcholinesterase (AChE) since acetylthiocholine was the preferred substrate, and eserine or BW284c51inhibited the enzyme activity, while isoOMPA was without effect. The AChE was localized and uniformly distributed along the cell surface membranes of the cardiac muscle cells. A fraction 8-fold enriched in AChE was isolated from pooled ventricles by a combination of differential and sucrose density gradient centrifugation. This sarcolemmal fraction contained little mitochondrial contamination as determined by electron microscopy and by succinate cytochrome c reductase activity. In addition, this fraction stained uniformly for AChE, indicating that it was free of other membrane types (for example sarcoplasmic reticulum which did not stain for ACHE). Therefore, this fraction contained purified cell surface membrane free of contamination by other membranous organelles.
Nuclear divisions with reduced numbers of microtubules in Tetrahymena
Authors: Jaeckel-Williams Ruth 
Published: April 2021

ABSTRACT
Ultrastructural observations on micronuclei of Tetrahymena thermophila, WH-6 dividing in the presence of colchicine suggest that the microtubules present at the time of drug addition persist, but no new microtubules are formed. It is suggested that the great amount of elongation seen in these drug-treated micronuclei may not be due to the persisting microtubules alone. On the basis of ultrastructural and light-microscopic observations, it is proposed that at least part of the motive force responsible for the elongation which occurs in colchicine may be due to an active sliding of the micronuclear membrane on some element of the cell cortex. In addition, the macronucleus of this species of Tetrahymena was found to be capable of dividing in colchicine in the absence of internal nuclear microtubules.
The pattern of appearance of enzymic activity during the development of the golgi apparatus in amoebae
Authors: Flickinger Charles J. 
Published: April 2021

ABSTRACT
The appearance of enzymic activity during the development of the Golgi apparatus was studied by cytochemical staining of renucleated amoebae. In cells enucleated for 4 days, there was a great decline in size and number of Golgi bodies, or dictyosomes. Subsequent renucleation by nuclear transplantation resulted in a regeneration of Golgi bodies. Samples of amoebae were fixed and incubated for cytochemical staining at intervals of 1, 6, or 24 h after renucleation. Enzymes selected for study were guanosine diphosphatase (GDPase), esterase, and thiamine pyrophosphatase (TPPase). All three were found in the Golgi apparatus of normal amoebae but they differed in their overall intracellular distribution. GDPase was normally present at the convex pole of the Golgi apparatus, in rough endoplasmic reticulum, and in the nuclear envelope. In amoebae renucleated for 1 h, light reaction product for GDPase was present throughout the small stacks of cisternae that represented the forming Golgi apparatus. By 6 h following the operation GDPase reaction product was concentrated at the convex pole of the Golgi apparatus. Esterase, which was distributed throughout the stacks of normal Golgi cisternae, displayed a similar distribution in the forming Golgi bodies as soon as they were visible. TPPase was normally present in the Golgi apparatus but was not found in the endoplasmic reticulum. In contrast to the other enzymes, TPPase reaction product was absent from the forming Golgi apparatus 1 and 6 h after renucleation, and did not appear in the Golgi apparatus until 24 h after operation. Thus, enzymes held in common between the rough endoplasmic reticulum and the Golgi apparatus were present in the forming Golgi apparatus as soon as it was detectable, but an enzyme cytochemically localized to the Golgi apparatus only appeared later in development of the organelle. It is suggested that Golgi membranes might be derived from the endoplasmic reticulum and thus immediately contain endoplasmic reticulum enzymes, while Golgi-specific enzymes are added later in development.
Action of a slowly hydrolysable cyclic amp analogue on developing cells of Dictyostelium Discoideum
Authors: Grossier C. , Gerisch G. , Malchow D. , Eckstein F. 
Published: April 2021

ABSTRACT
Adenosine 3’,5’-cyclic phosphorothioate (cAMP-S) is a cyclic AMP (cAMP) analogue which is only slowly hydrolysed by phosphodiesterases of Dictyostelium discoideum. The affinity of cAMP-S to cAMP receptors at the cell surface is only one order of magnitude lower than that of cAMP. cAMP-S can replace cAMP as a stimulant with respect to all receptor-mediated responses tested, including chemotaxis and the induction of cAMP pulses.
cAMP-S does not affect growth of D. discoideum but it blocks cell aggregation at a uniform concentration of 5 × 10−7 M in agar plate cultures of strain NC-4 as well as its axenically growing derivative, Ax-2. Another wild-type strain of D. discoideum, v-12, is able to aggregate on agar plates supplemented with 1 mM cAMP-S. The development of Polysphondylium pallidum and P. violaceum is also highly cAMP-S resistant.
In Ax-2 both differentiation from the growth phase to the aggregation-competent stage and chemotaxis are cAMP-S sensitive, whereas in v-12 only chemotaxis is inhibited, v-12 can still form streams of cohering cells and fruiting bodies when chemotaxis is inhibited by cAMP-S.
Whereas cAMP induces differentiation into stalk cells at concentrations of 10−3 or 10 −4 M, cAMP-S has the same effect in strain v-12 at the much lower concentration of 10−8 M.