bluuebunny/crossref_metadata_2025_split huggingface dataset:
Roles of calcium in aggregation of rat ascites hepatoma cells by cell surface-associated adhesive factor
Authors: Kurano Shinya , Ishida Mitsugu , Ishimaru Yasuji 
Published: April 2021

ABSTRACT
Our previous studies have shown that a cell surface-associated adhesive factor (AF), separated from rat ascites hepatoma AH136B cells of a differentiated type and highly purified by chromatography, induces not only aggregation of dissociated AH136B cells or rat ascites hepatoma AH 109 A cells of an undifferentiated type but also adhesiveness characterized by the development of junctional complexes; the AF-induced aggregation of the cells was Ca2+-dependent.
Further analysis of the roles of Ca2+ in cell aggregation was performed using AH109A cells (present as single cells in vivo). (1) AF clearly enhanced 45 Ca uptake by the cells; (2) calmodulin was isolated from the cells; (3) calmodulin inhibitor, W-7 (iV-(6-amino-hexyl)-5-chloro-l-naphthalenesulphonamide), strongly inhibited aggregation of the cells; (4) W-7 also inhibited the clustering or capping of AF-binding sites on the cell surface; (5) binding of 125 I-labelled AF to the cells was independent of Ca2+ concentration; (6) binding of 125 I-labelled AF to AF-conjugated beads was not observed, independently of the presence of Ca2+. These findings suggest that Ca2+ and Ca2+-activated calmodulin may play a key role in the process of aggregation of the cells by controlling the microfilament components and that Ca2+ may not be involved either in the interactions between AF and its cellular receptor or in linkages of AF molecules.
Effect Of Altered Oligosaccharide Structure On The Cell Surface Number, Distribution And Turnover Of The High Molecular Weight Acidic Glycoproteins Of CHO Cells
Authors: Fitzgerald L. A. , Denny J. B. , Baumbach G. A. , Ketcham C. M. , Roberts R. M. 
Published: April 2021

ABSTRACT
The influence of altered carbohydrate structure on the surface number, distribution and turnover of plasma membrane glycoproteins has been studied in Chinese hamster ovary (CHO) cells by comparing three lines that are resistant to the cytotoxic effects of wheat germ agglutinin (WGA) with parental CHO cells. The glycoproteins investigated were members of a group of high molecular weight acidic glycoproteins (HMWAG). On parental cells these represent the major surface components that become labelled by lactoperoxidase-catalysed iodination. They are the only plasma membrane glycoproteins that bind WGA. The mutant lines also possess iodinatable surface polypeptides of high molecular weight, but these were less acidic and electrophoretically less diffuse than those from parental cells. These polypeptides in general did not bind [l25I]WGA when two dimensional polyacrylamide gels were overlaid with iodinated lectin. Mutant cells treated with fluorescein-conjugated WGA showed low surface fluorescence. However, the nuclear envelope and a small region in the perinuclear zone fluoresced strongly. Together, these results confirm that the surface glycoproteins of mutant cells had altered carbohydrate structure. Mouse antiserum prepared against the HMWAG, however, bound equally effectively to the mutant lines as to the parental lines. Indirect immunofluorescence experiments showed that the HMWAG had a fairly uniform distribution over the surface, and that internalization induced by second antibody occurred at a similar rate and in a similar manner in all lines, including the mutants. Electron microscopic observations using immunoperoxidase procedures confirmed the similarities in glycoprotein distribution on mutant and parental cells. Two mouse monoclonal antibodies raised against the HMWAG also revealed no difference in the number or topography of surface glycoproteins. Finally, the half-lives of several HMWAG in a parental and a mutant line (15B) maintained on low-serum medium were compared by means of a 121I /1311 double-label technique. Half-lives of HMWAG from the former averaged 12 h and from the latter 11 h. It is concluded that the lack of complex termini on oligosaccharides of this particular group of CHO plasma membrane glycoproteins has no effect on their number, distribution or turnover.
Ultrastructure Of The Flagellar Roots In Chlamydomonas Gametes
Authors: Weiss Richard L. 
Published: April 2021

ABSTRACT
The cytoskeleton of Chlamydomonas reinhardtii gametes has been studied by electron microscopy. The microtubular system, consisting of four flagellar roots inserted into the basal apparatus, is shown to include two daughter basal bodies and two striated fibres, newly described in this report. One new fibre associates with the 3-over-l root and is similar to its counterpart, the striated fibre of the 2-membcr root. These similar root fibres connect each daughter basal body to the V-shaped microtubular root pair. The other new striated fibre joins the daughter basal body to both flagellar roots and is similar to the proximal striated fibre. In mt+ gametes, the conventional root microtubules make direct contact with the doublet zone of the non-activated mating structure. During activation, doublet zone microfilaments associate with the daughter basal body and the finely striated fibre of the 3-over-l root. These observations suggest that the cytoskeleton acts as a scaffolding for membrane extension by the mt+ mating structure microfilaments.
Nucleolar Nomenclature
Authors: Jordan E. G. 
Published: April 2021

ABSTRACT
At the 8th European Nucleolar Workshop, which was organized by M. Bouteille and colleagues at Banyuls-sur-mer in June 1983, a discussion was held on nucleolar nomenclature. The terms that are italicized in the following report were agreed upon. The short descriptions following each term were written to convey the consensus of opinion that emerged. After the discussion a report was displayed for approval. The following account is the approved, amended report of the meeting, incorporating a few minor points made in later comments.
The Major 67 000 Molecular Weight Protein Of The Clam Oocyte Nuclear Envelope Is Lamin-Like
Authors: Maul Gerd G. , Baglia Frank A. , Newmeyer Donald D. , Ohlsson-Wilhelm Betsy M. 
Published: April 2021

ABSTRACT
Nuclear envelopes of somatic cells have at least two different major proteins in the 60—70(×103) molecular weight range (1amins A(C) and B) that seem to be involved in chromatin attachment. In contrast, nuclear envelopes from clam germinal vesicles have only a single major protein of the same size class (∽67×103Mr) and have no chromatin attached to them. The data presented in this report show that this 67×103μ, clam protein shares a variety of physical properties with lamins A(C) and B, derived from rat liver nuclei. These properties include similar size, although different isoelectric points; phosphorylated forms; strong tendencies to cross-link by disulphide bonds; presence of carbohydrates, demonstrated by direct incorporation of mannose and labelling with borohydride; and shared epitopes, demonstrated using both monoclonal and polyclonal antibodies. Taken together, these observations identify the clam 67× 10Mr protein, the major structural protein of a nuclear envelope that lacks attached chromatin, as being lamin-like and demonstrate that it is more closely related to lamin A(C) than to lamin B.
Chemoattractant-mediated changes in cytoskeletal actin of cellular slime moulds
Authors: Mcrobbie S. J. , Newell P. C. 
Published: April 2021

ABSTRACTWe report changes in actin associated with the Triton-insoluble cytoskeleton following chemotactic stimulation in five species of cellular slime moatd, Dictyostelium discoideum, D. mucoroitSes, D. purpureurn, D. lacteum and Polysphondylium violaceum. Stimulation of amoebae with the chemoattractant specific for each species elicits at rapid increase in cytoskeletal actin content with a peak at 5 s, probably corresponding to pseudopodium formation. Subsequent changes consist of a second discrete peak of actin accumulation and, in at least two species, D. discoideum and P. vtolaceum, a third peak. We correlate these later changes in actin content with the changes in amoebal shape that have been reported to be a consequence of chemotactic stimulation.We have also investigated species variation in actin content and find D. purpureum to have a remarkably low cytoskeletal actin content in comparison to other species.Whole cell and cytoskeletal actin levels during the first 12 h of D. discoideum development have also been analysed. While little change is found in total protein content, whole cell actin shows an abrupt decline during aggregation and this is accompanied by an increase in cytoskeletal actin, amounting to 100% over 0—12h of development.These results are discussed in the Light of a possible changing role for actin during the course of development, from being involved in the dynamic events of chemotaxis to assuming a more structural role in the multicellular aggregate.
Ectodermal fragments from normal frog gastrulae condition substrata to support normal and hybrid mesodermal cell migration in vitro
Authors: Nakatsuji Norio , Johnson Kurt E. 
Published: April 2021

ABSTRACT
Using time-lapse cinemicrography and scanning electron microscopy, we have shown that normal Rana embryos and gastrulating hybrid embryos have extracellular fibrils on the inner surface of the ectodermal layer. These fibrils are absent prior to gastrulation and appear in increasing numbers during gastrulation. They can also be deposited in vitro where they condition substrata in such a way that normal presumptive mesodermal cells placed on them show extensive attachment and unoriented cell movement. These fibrils are also present in some arrested hybrid embryos, but in reduced numbers, or are lacking in other arrested hybrid embryos. Explanted ectodermal fragments from arrested hybrid embryos fail both to condition culture substrata by the deposition of fibrils and to promote cell attachment and translocation. In contrast, ectodermal fragments from normal embryos can condition culture substrata so as to promote moderate cell attachment and, for one particular gamete combination, even cell translocation of presumptive mesodermal cells taken from arrested hybrid embryos. These results provide new evidence to support the hypothesis that extracellular fibrils represent a system that promotes mesodermal cell migration in amphibian embryos. Differences in the fibrillar system in urodele and anuran embryos are discussed in relation to fundamental differences in the mode of mesodermal cell migration in these two classes of Amphibia.
Membrane-substrate contact under the spermatozoon of Caenorhabditis elegans, a crawling cell that lacks filamentous actin
Authors: Roberts Thomas M. , Streitmatter Gloria 
Published: April 2021

ABSTRACT
Caenorhabditis elegans spermatozoa use a single, persistent pseudopod to crawl at about 20μm/min but, unlike other types of crawling cells, sperm lack both filamentous actin and myosin. Interference reflection microscopy has revealed that sperm form broad grey areas of contact, analogous to the close contacts that have been described underneath other crawling eukaryotic cells, between their pseudopods and their substrate. Individual sperm change the size, shape and pattern of their substrate attachments as they crawl but we found no correlation between the extent of underside of the cell in contact with the substrate and the velocity of locomotion. Two predominant attachment patterns were observed: (1) a single broad contact extending from the front of the pseudopod nearly to the rear of the cell; and (2) two separate contact sites, one under the front of the pseudopod and one under the cell body. Occasionally, under cells exhibiting the second type of attachment pattern, portions of the anterior contact separated and remained stationary relative to the substrate while the cell moved forward. This observation, as well as the continuous change in shape of the contact areas, suggests that sperm continually form new contacts near the tip of the pseudopod and release these contacts backwards. In extreme cases, sperm were able to crawl with only the front of the pseudopod in contact with the substrate. Therefore, we propose that sperm locomotion depends on the interaction of several key events (traction, propulsion, membrane insertion) occurring at the leading edge of the pseudopod.
Ultrastructural morphometry of gap junctions during differentiation of stratified squamous epithelium
Authors: White F. H. , Thompson D. A. , Gohari K. 
Published: April 2021

ABSTRACT
The presence of gap junctions in stratified epithelia has now been extensively documented, but there have been few attempts to quantify them. In the present report, samples of hamster cheek pouch mucosa were processed for electron microscopy and electron micrographs from defined basal, spinous and granular layers were obtained. Using a combination of direct measurement and stereological intersection counting techniques, the relative surface areas of peripheral gap junctions (i.e. those in direct contact with the epithelial plasma membrane) and annular gap junctions (i.e. those present as complete, approximately circular profiles within the epithelial cell cytoplasm) were determined. Following estimation of the plasma membrane surface area of ‘average’ epithelial cells from each of the defined strata, relative values were transformed into absolute data. Data from peripheral and annular junctions were pooled to provide an estimate of total gap junctional area.
Relative surface area estimates were similar for peripheral, annular and total gap junctions, in that values were invariably highest in the spinous layer and lowest in the granular layer. Absolute data indicate that there is more than a threefold increase in the area of membrane differentiated into gap junctions in the average spinous cell when compared with the average basal cell. Values for total gap-junctional areas in the average granular cell are reduced somewhat with respect to the average spinous cell and this is effected by a decrease in the area of peripheral gap junctions. We conclude that there is synthesis of gap junctions between basal and spinous cells, which is followed by evidence of degradation between spinous and granular cells. The magnitude of the estimates of area is comparable to those obtained from other stratified and non-stratified epithelia and it would thus appear that gap junctions may play a significant role in cellular control processes in all viable epithelial strata.
Lanthanum staining of neurotubules in axons from cockroach ganglia
Authors: Lane Nancy J. , Treherne J. E. 
Published: April 2021

ABSTRACT
The axoplasm of the neurons of Penplaneta amencana contains numerous neurotubules which are morphologically similar to the microtubules found in non-nervous tissues after sectioning or negative staining. In cross-sections of fixed material such tubules usually appear as electron-dense circles containing a less dense core and surrounded by a non-opaque ‘clear zone’. However, when cockroach ganglia are fixed and incubated in lanthanum hydroxide, the lanthanum is taken up intracellularly by the axoplasm of certain of the neurons and in these is found to stain the entire core of the neurotubules, as well as the clear zone. At least part of the wall of the tubules remains unstained and appears as a ring of non-opaque subunits against an electron-dense, lanthanum-stained background. Since lanthanum staining, under the conditions used here, is sometimes considered to demonstrate the presence of acid muco polysacchandes, its uptake by the neurotubules may indicate that they contain carbohydrate as well as the protein that is generally considered to form part of the microtubular wall. Alter natively, the lanthanum could indicate the location of other anionic molecules, possibly under going extra- or intratubular translocation. The extent to which neurotubules could mediate movements of relatively small water-soluble ions and molecules is considered in relation to their diffusion through the polyamon matrix represented by the core of the tubules.
The origin of flimmer inSaprolegnia, Dictyuchus, synuraandCryptomonas
Authors: Heath I. B. , Greenwood A. D. , Griffiths H.B. 
Published: April 2021

ABSTRACTThe endoplasmic reticulum of Saprolegnia, Dictyuchus, Synura and Cryptomonas may contain tubules less than 20 nm in diameter. In Saprolegnia these tubules have a maximum length of 1·6μm, a wall of a single layer of colchicine-resistant, osmiophilic subunits, and a tapering end-piece. Flimmer hairs (flagellar hairs) are morphologically similar and are attached to the flagellum sheath by a tapering end-piece. It is suggested that Flimmer hairs are produced in cisternae of the endoplasmic reticulum of the above organisms. Cryptomonas bears 2 rows of Flimmer hairs on one flagellum and a single row of shorter ones on the other.
The effect of inhalational anaesthetics on the microtubular system in Actinosphaerium nucleofilum
Authors: Allison A. C. , Hulands G. H. , Nunn J. F. , Kitching J. A. , Macdonald A. C. 
Published: April 2021

ABSTRACT
Six different anaesthetic agents were found to cause reversible collapse of the axopods of Actinosphaerium nucleofilum. The effect occurred at concentrations proportional to those required to anaesthetize man. Electron microscopy showed dispersal of the microtubular system and disaggregation of the microtubules of the axonemes, and expanded microtubules without interlinkage were seen in the related heliozoon Actinophrys sol under treatment with halothane. In both genera there was a rapid reassembly during the recovery period. Diethyl ether, an inhalational anaesthetic with a particularly large molecule, was ineffective except at relatively very high concentrations, and with this agent cytolysis often occurred with little or no shortening of axopods.
Some physiological and morphological effects of polylysine on Amoeba proteus
Authors: Sanders E. J. , Bell L. G. E. 
Published: April 2021

ABSTRACT
The effect of polylysine on pinocytosis and the cell surface of Amoeba proteus was investigated. The intensity of the pinocytotic response was evaluated by a channel counting method, and the surface was examined by means of transmission and scanning electron microscopy.
Cells treated with polylysine and then immersed in a protein pinocytosis inducer showed a higher intensity of channel formation during the initial stages of the cycle than cells not pre- treated. This was considered to be an additive effect of the protein and the polymer, since the latter alone was demonstrated to induce pinocytosis. No influence of molecular weight of the basic polymer on this reaction could be demonstrated.
As well as normal pinocytotic channels electron micrographs revealed the presence of fine channels, 20–50 nm in width, in the cytoplasm as a result of polylysine treatment. The polymer was visualized as dense surface aggregates, about 25·0 nm in diameter, associated with the extracellular material. This deposit was not seen on Amoeba dubia, which lacked a well-developed extracellular covering, and micro-channels failed to develop in this case. It has been demonstrated that when polylysine and a protein pinocytosis inducer were applied to the cell sequentially both compounds occupied the same channels. In view of the lack of effect of metabolic inhibitors on the formation of channels by polylysine it was concluded that this phenomenon is distinct from pinocytosis. It is proposed that this kind of channel formation can be explained in terms of the bridging of areas of membrane by the polymer–polysaccharide complex.
Heterochromatin, the synaptonemal complex and crossing over
Authors: Stack Stephen M. 
Published: April 2021

ABSTRACT
A combined light- and electron-microscopic examination of chromosomes from two angiospermous plants, Plantago ovata and Lycopersicon esculentum, and a mammal, Mus musculus, was performed. From this investigation three observations have been made that may be relevant to the observed lack of crossing over in heterochromatin. (1) Differential staining indicates that heterochromatin represents a smaller fraction of the length of pachytene chromosomes than it represents in the length of mitotic metaphase chromosomes. Since the synaptonemal complex (SC) runs throughout the length of these pachytene chromosomes, it is under-represented in heterochromatin. Considering the evidence for a rough correlation between the length of SC and the amount of crossing over, this could result in less crossing over in heterochromatin than expected on the basis of its length in mitotic metaphase chromosomes. (2) Electron microscopy indicates that, unlike the SC in euchromatin, the SC in heterochromatin is densely ensheathed in highly compact chromatin. If crossing over occurs in the SC or even in the surrounding chromatin, the compaction of the chromatin may prevent the penetration of enzymes needed in recombination. (3) Finally, a difference in the structure of SCs in euchromatin versus heterochromatin was observed that could be associated with the lack of crossing over in heterochromatin.
Effects of sulphydryl reagents on the structure of dehistonized metaphase chromosomes
Authors: Jeppesen Peter , Morten Helen 
Published: April 2021

ABSTRACT
Dehistonized metaphase chromosomes lose their apparent axial organization (the ‘scaffold’) and sediment more slowly following exposure to β-mercaptoethanol (BME). We have subsequently treated BME chromosomes with reagents that oxidize protein sulphydryls to disulphides, and found that if calcium is also present during the oxidation an apparently similar axial structure is restored following dehistonization, as seen by microscopic examination. In general, however, we do not find that oxidation restores the higher sedimentation rate of dehistonized control chromosomes. Analysis of residual core protein in dehistonized chromosomes by sodium dodecyl sulphate/polyacrylamide gel electrophoresis fails to detect any differences in polypeptide composition related to the state of oxidation or to the presence or absence of visible axial organization. Combining our results with those of other workers, we conclude that the axial structure evident in dehistonized metaphase chromosomes is maintained, at least partially, by inter-protein cross-linking, although in vivo this may not be via simple disulphide bridges. Additional factors, which we have not yet characterized, but which possibly include heavy metal ions, appear to be involved in the axial organization existing in vivo.