bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spreading behaviour of cultured fibroblasts from carriers of duchenne muscular dystrophy
Authors: Pizzey John A. , Witkowski Jan A. , Jones Gareth E. 
Published: April 2021

ABSTRACT
Cultured skin fibroblasts from patients with Duchenne muscular dystrophy (DMD) are more sensitive than normal cells to prolonged exposure to the ionophore monensin. In a cell spreading assay in which cells were preincubated with monensin and subsequently allowed to adhere to and spread on a glass substratum in serum-free medium for 100 min, the mean transformed cell area of normal and DMD cells was 5 ·97 ±0 ·11 and 5 ·29 ± 0 ·03, respectively. Cultured fibroblasts from carriers of DMD yielded a value of 5 ·59 ± 0 ·03, which is intermediate between, and significantly different from, the values for both normal and DMD cultures. This result would be predicted on the basis of random X-chromosome inactivation in female carriers of this disorder. However, comparison of DMD carrier cell spreading data with data obtained from pooled and summated measurements taken from separate experiments using either normal or DMD fibroblasts suggest a more complex situation. Examination of the variance of the means of cell area for the true carrier population and the summated normal and DMD population provides evidence suggesting that some form of cellular interaction may occur between the two cell genotypes in culture.
Temperature and ph govern the self-assembly of microtubules from unfertilized sea-urchin egg extracts
Authors: Suprenant Kathy A. , Marsh John C. 
Published: April 2021

ABSTRACT
A new method for microtubule purification from unfertilized sea-urchin eggs was developed in order to obtain large quantities of calcium- and cold-labile microtubules that contained microtubule-associated components important for mitosis. By taking into consideration the pH, ionic composition of egg cytoplasm, and the physiological temperature for growth of the Pacific coast sea-urchin Strongylocentrotus purpuratus, methods were developed for the assembly of intact microtubules directly from unfertilized egg extracts. The microtubules obtained by cycles of temperature-dependent assembly and disassembly are composed of tubulin and abundant microtubule-associated proteins. These microtubules are cold- and calcium-labile and assemble at a critical protein concentration of 0 ·11 mg ml−1 at 24°C. The yield of microtubule protein obtained by this new method is equivalent to that obtained with taxol (6—8mg/20ml packed eggs). Microtubules that have been fixed and prepared for electron microscopy are decorated with large, globular projections that are attached to the microtubule by thin stalks.
Monensin inhibits secretion of extracellular matrix and the spreading of mesoderm cells in the early chick embryo
Authors: Sanders E. J. , Chokka P. 
Published: April 2021

ABSTRACT
Chick embryos in culture were treated with the secretion-inhibiting ionophore monensin at the gastrulation stage of development. After treatment for 5h at a concentration of 10−5M the embryos showed a drastic reduction in the tissue space between the upper and lower epithelia, and reduced spreading of the mesoderm cells that occupied this space. The basement membrane, to which many mesoderm cells are normally attached, showed varying degrees of disruption, which permitted blebbing of the overlying epithelium. Intracellularly, the treatment caused extensive vacuolization in all tissues. These results were consistent with the effects expected by removal of hyaluronic acid from the extracellular space, and this was confirmed by demonstrating a sharp reduction in glucosamine incorporation in this region. Examination of the effects of monensin on isolated mesoderm cells in culture using interference reflection microscopy indicated that the spreading of these cells was reduced independently of the changes in the extracellular matrix of the embryo. That this was probably due to the inhibition of cell surface fibronectin secretion was shown by demonstrating severe changes in the distribution of this glycoprotein using the immunofluorescent technique. It is concluded that the effects of monensin on this intact, developing system are due primarily to the disruption of hyaluronic acid secretion, but that disrupted fibronectin synthesis contributes to the reduced spreading of mesoderm cells.
Cell activation and adhesion
Authors: Curtis Adam 
Published: April 2021

ABSTRACT
It has long been known that the adhesiveness of leucocytes and blood platelets can be changed from a state of non-adhesion to very strong adhesion to each other, and to many surfaces, in a very short time. The agents that produce such changes are prostaglandins, thromboxanes and leukotrienes (see for example, Hoover et al. 1984), agonists affecting production of these substances and also those that affect the diacyl-glycerol-inositol triphosphate pathways (see Nishizuka, 1984). Evidence has recently emerged (Dunham et al. 1983; Dunham & Weissman, 1986) showing that sponge cells can have their adhesion activated by agents that affect calcium relationships of cells through diacylglycérol—ITP pathways. Brief pulses of low levels of calcium ions activate adhesion of these cells, phorbol myristoyl acetate and a calcium ionophore act synergistically in aiding cell adhesion. The activating agents can be effective at nanomolar concentrations. It is of interest to ask whether similar activation phenomena are more widespread than suspected.
Schizosaccharomyces Pombe mutants affected in their division response to starvation
Authors: Young Paul G. , Fantes Peter A. 
Published: April 2021

ABSTRACT
Schizosaccharomyces pombe mutants have been selected on the basis of an altered response to nutritional stimulation of cell division (changed division response, cdr). Two new loci (cdr1 and cdr2) were identified and characterized. When suspended in nitrogen-free medium wild-type cells underwent stimulated rates of division and became reduced to approximately 30 % in protein content with a concomitant 3·6-fold increase in cell number after 24 h starvation, cdr cells had significantly smaller increases in cell number. The ratio of starved/unstarved protein content was higher for the cdr strains than for the wild type, cdr cells were also affected in their response to nitrogen-source shifts from proline to glutamate (or vice versa) or when shifted from serine phosphate to inorganic phosphate, showing that the alteration in division response was not restricted to nitrogen metabolism. Upon nitrogen starvation wild-type cells arrested prior to the cdc10 execution point, whereas cdr cells arrested later in the cell cycle. cdc25–22 cdr1 or cdr2 double mutants grew very slowly and were extremely elongated at all temperatures; the restrictive temperature was reduced to 27°C. wee1 was epistatic to cdr mutations with respect to cell length at the cell plate stage. cdr+ genes are postulated to play a role in the nutritional modulation of the mitotic size control.
Expression of an endogenous galactose-binding lectin in the early chick embryo
Authors: Zalik Sara E. , Thomson Lawrence W. , Ledsham Irene M. 
Published: April 2021

ABSTRACT
The gastrulating chick blastoderm contains lectin activity specific for β-D-galactoside groups. The galactose-binding lectin isolated by affinity chromatography on p-aminophenyl-β-D-lactoside separates into two bands when studied by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. One of these Ln has a relative molecular mass of 70(±2)×103 while the other L1 is a polypeptide that migrates with the dye front in 10% gels. We have prepared an antiserum against this lectin preparation and have affinity-purified antibodies against L1. When embryos at stages 3—7 were examined by immunofluorescence using the affinity-purified antibodies, lectin was expressed in cells at the lowest portions of the primitive streak as well as in cells migrating laterally from this region to form the endoderm. Lectin was also expressed by the cells of the extra-embryonic endoderm and the primordial germ cells of the proximal area opaca. In transfers of gradient gels stained with affinity-purified antibodies against LIthis lectin had an approximate molecular weight of 6·5 ×103. Our results indicate that this lectin is expressed in areas that are undergoing cell spreading.
Immunogold localization of placental lactogen and the sbu-3 antigen by cryoultramicrotomy at implantation in the sheep
Authors: Morgan G. , Wooding F. B. P. , Brandon M. R. 
Published: April 2021

ABSTRACT
In the sheep, granulated trophectodermal binucleate cells (BNC) appear at implantation 16 days post coitum (dpc) and persist throughout pregnancy. Conventional immunocytochemical techniques at both light and electron microscope levels have indicated the presence of the ovine placental lactogen (oPL) hormone in the granules but no earlier than 22 dpc, when the level was very low. Immunofluorescent studies using glycolmethacrylate sections between 15 and 55 dpc suggest a completely different distribution of oPL restricted to uninucleate cells with none in the BNC. Using the most sensitive method available, immunocytochemistry on ultrathin frozen sections, the results in this paper demonstrate that BNC granules contain oPL at their earliest appearance (16–17 dpc). No significant localization was found in any uninucleate cell. In contrast, another molecule, the SBU-3 antigen, which is demonstrated in BNC granules later in pregnancy, is not present at the earliest stages but appears between 24 and 28 dpc coincident with the development of the foetal cotyledonary villi. The significance of these results for BNC function are discussed briefly.
Evidence that tubulin forms an integral membrane skeleton in molluscan gill cilia
Authors: Stephens R. E. , Oleszko-Szuts S. , Good M. J. 
Published: April 2021

ABSTRACT
Controlled extraction of intact gill tissue, isolated cilia or reconstituted membrane vesicles with Nonidet P-40 at &gt;4 times the critical micelle concentration, or with octyl glucoside at the critical micelle concentration, delipidates the membrane, leaving a membrane remnant or skeleton of membrane tubulin and associated proteins. This skeleton consists of a disordered reticular protein network in reconstituted membrane vesicles and a similar but more compact sleeve in cilia of extracted tissue. The membrane skeleton is closely apposed to the axoneme and is attached to the outer doublets by fine radial bridges having a 20–24 nm longitudinal periodicity, supporting earlier observations made utilizing a lipophilic cross-linking agent. Higher concentrations of detergent solubilize the membrane tubulin-protein complex, producing 5–10 nm particulate material of low sedimentation coefficient. Dilution of an octyl glucoside solution to below the critical micelle concentration results in disappearance of the particles and reformation of the membrane, indicating that the particles are protein-detergent micelles and not denatured protein. Freeze-fracture electron microscopy reveals no comparablesized natural particles in the ciliary membrane proper. The reticular material of the membrane skeleton contains tubulin, demonstrated on Low-icryl K4M thin sections by a rabbit polyclonal antibody to sea-urchin egg cytoplasmic tubulin, using gold-labelled secondary antibody. Minimal cross-reactivity is detected prior to Triton-delipi-dation, suggesting that most membrane tubulin antigenic sites are buried within the bilayer and that the tubulin is not simply adsorbed to the lipid bilayer.
Chloral hydrate disrupts mitosis by increasing intracellular free calcium
Authors: Lee Greta M. , Diguiseppi Jim , Gawdi Govind M. , Herman Brian 
Published: April 2021

ABSTRACT
In examining how chloral hydrate affects mitosis, we found that extracellular application of 0·l % chloral hydrate produced an abrupt rise in cytosolic free Ca2+. Digitized fluorescence microscopy of Fura-2-loaded, mitotic and interphase PtK cells revealed that Ca2+ rose 15 s after chloral hydrate application, peaked within 1 min at a concentration two-to sevenfold above the basal level and then slowly dropped. Bathing cells in 0·l% chloral hydrate caused metaphase spindles to shorten, starting in 1–2 min, and inhibited spindle elongation without affecting chromosome-to-pole movement during anaphase, as determined by phase-contrast observation of living cells. Spindle elongation and chromosome movement were unaffected by intracellular injection of 7·5% chloral hydrate. Extensive mitotic microtubule breakdown occurred after cells were bathed for 7 min in 0·l% chloral hydrate, while interphase microtubules were unaffected as determined by immunofluorescence. The chloral hydrate-induced microtubule breakdown and metaphase spindle shortening were prevented by 10mM-CoCl2, which has previously been shown to block Ca2+ influx and to stabilize microtubules in vitro. These results imply that disruption of mitotic spindle function and structure by chloral hydrate is due to a rise in cytosolic free Ca2+, and also indicate that mitotic microtubules are more Ca2+-labile than interphase microtubules.
The translocation of mitochondria along insect ovarian microtubules from isolated nutritive tubes: a simple reactivated model
Authors: Stebbings II. , Hunt Cherryl 
Published: April 2021

ABSTRACT
Nutritive tubes, the microtubule-based translocation channels that link the trophic tissue to the developing oocytes in the ovaries of hemipteran insects, have been isolated and examined using video-enhanced differential interference contrast microscopy. When viewed in this way the nutritive tubes are seen to fray into linear strands, which, on the addition of exogenous ATP, support the translocation of particles along their lengths. The movement is also seen with GTP but not AMP-PNP. It is not affected by the addition of inhibitors of dynein or of energy metabolism. Electron microscopy shows the strands to consist of bundles of parallel microtubules of different sizes and the moving particles to be mitochondria. Comparisons are drawn between the movement of mitochondria along isolated insect ovarian microtubules and the reported translocation of vesicles along microtubules from squid axoplasm. The simplicity of the insect system is emphasized. The fact that it can be isolated easily and characterized biochemically makes it potentially valuable for investigating microtubule-based translocation.
Polo, a mitotic mutant of Drosophila displaying abnormal spindle poles
Authors: Sunkel Claudio E. , Glover David M. 
Published: April 2021

ABSTRACT
Neuroblast cells in larvae homozygous for mutant alleles of the locus polo show a high frequency of metaphases in which the chromosomes have a circular arrangement, and anaphase figures in which chromosomes appear to be randomly oriented with respect to at least one of the spindle poles. These defects appear to lead to the production of polyploid cells. Sex chromosome disjunction is affected in male meiosis, primarily in the second division, and the meiotic spindles of living cells are abnormal. One allele is a larval lethal, whereas another is semi-lethal with about 7% of homozygotes surviving as adults. Embryos from homozygous polo females have aberrant mitotic spindles that are highly branched and have broad poles. Immunofluorescence studies with an antibody that recognizes an antigen associated with the centrosome indicate that the organization of this organelle is disrupted in the mutant embryos.
Transmission of gametic nuclei through a fertilization tube during mating in a primitive dinoflagellate,Prorocentrum micansEhr
Authors: Bhaud Yvonne , Soyer-Gobillard Marie-Odile , Salmon J. M. 
Published: April 2021

ABSTRACTIn the dinoflagellate Prorocentrum micans Ehr., changing the culture medium (switching from Erdschreiber’s to Provasoli’s medium) provokes the appearance of individuals that are morphologically different from the normal vegetative forms. Observations and microspectrofluorimetric measurements made in vivo of the relative amounts of nuclear DNA show that these forms are sexual forms; unlike the situation in dinoflagellate species that are known to be sexual, the male and female gametes of P. micans do not fuse. Cells playing the role of isogametes and containing q DNA pair and form a fertilization tube by means of which a donor cell (♂) injects its nucleus into a recipient cell (♀). After conjugation, the zygote containing 2q DNA replicates and thereafter contains 4q DNA. Two successive meiotic divisions lead to the formation of a tetrad in which each nucleus contains q DNA. Cells released from the tetrad seem to be adapted to Provasoli’s medium and vegetative divisions occur again. The characteristics of sexual reproduction in those dinoflagellates in which this phenomenon has been described are reviewed and discussed.
Centriolar location during blood cell spreading and motion in vitro: An ultrastructural analysis
Authors: Gudima G. O. , Vorobjev I. A. , Chentsov Yu S. 
Published: April 2021

ABSTRACT
Different motile blood cells behave differently on a glass surface. Macrophages go through all the stages of spreading described previously for fibroblasts; granulocytes become polarized after a short stage of radial spreading, while the polarization of lymphocytes takes place immediately upon attachment. The active centrioles of the cells we have studied orient their distal ends towards the upper cell surface. The centrioles in blood cells have a different location with respect to the nucleus and the leading edge of the cell: in macrophages the centrioles are situated mostly anterior to or at the side of the nucleus; in granulocytes they lie between the nuclear segments; and in lymphocytes they are positioned strictly posterior to the nucleus, in the uropod. In each case, however, the centrioles are localized in the central region of the cytoplasm. Their alignment does not appear to be related to the blood cells’ random motion in vitro.
Positive regulation of melanin pigmentation by two key substrates of the melanogenic pathway, l-tyrosine and l-dopa
Authors: Slominski Andrzej , Moellmann Gisela , Kuklinska Elizabeth , Bomirski Andrzej , Pawelek John 
Published: April 2021

ABSTRACT
We describe results demonstrating the positive regulation of melanogenesis by two substrates of the melanogenic pathway. We have found that L-tyrosine and L-dihydroxyphenylalanine (L-dopa), whose metabolic fates are affected by the activity of that pathway, can also act as its regulators. In living pigment cells, tyrosinase (EC 1.14.18.1), a crucial and rate-limiting enzyme of melanogenesis, acts in subcellular organelles known as melanosomes. Melanin is laid down only in these organelles. We demonstrate that supplementing Ham’s F-10 medium with additional L-tyrosine or L-dopa during the culture of amelanotic Bomirski hamster melanoma cells results in a rapid increase in melanin formation, which is not simply due to greater availability of substrate. There is a rapid increase in tyrosinase activity and a large scale synthesis of melanosomes. The effects of L-tyrosine and L-dopa are prevented by the addition of cycloheximide. The actions of L-tyrosine and L-dopa are specific in that under similar conditions D-tyrosine, D-dopa, N-acetyl-L-tyrosine, L-phenylalanine, L-tryptophan and L-valine have little or no effect. The two substrates, L-tyrosine and L-dopa, appear to act through related but distinct mechanisms. Our findings provide an example of a little-known phenomenon: regulation of a differentiated eukaryotic phenotype through positive control by substrates in the pathway.
Identifying characteristics of the haematopoietic precursor cell
Authors: Murphy M. J. , Bertles J. F. , Gordon A. S. 
Published: April 2021

ABSTRACT
Studies are reported utilizing the known ability of homologous marrow cells to prevent death in otherwise lethally X-irradiated mice by ‘colonizing’ their spleens. The proportion of marrow cells functioning as progenitor cells attains a peak value during post-hypoxic polycythaemia. On the third day post-hypoxia, bone marrows of mice were harvested and prepared for density-gradient centrifugation. The relatively pure fractions of marrow cells were concentrated on the basis of their density and directly injected into the surgically exteriorized spleens of mice which had received an otherwise lethal dose of X-irradiation 48 h previously. Animals were sequentially killed from 15 min to 8 days later and spleens were prepared for examination by light and electron microscopy.
Eighty to 95 % of the light-density fraction (p = 1·0200–1·0440) was composed of large mono-nuclear cells characterized by a leptochromatic nucleus with pachychromasia at the nuclear envelope, one or more prominent nucleoli, sparse endoplasmic reticulum, a moderate number of mitochondria, a conspicuous Golgi zone and a centrosome in the region of a nuclear indenta-tion. Cells of this light fraction, devoid of erythroid elements, were competent in colonizing spleens (erythrocyte, granulocyte and megakaryocyte series) in contrast to the cells present in fractions of greater density.
The name ‘haematopoietic precursor cell’ (HPC) is tentatively used in describing this cell which is discussed in the light of some of the proposed models of haematopoiesis.
Cellular surfaces of amphibian atrial muscle
Authors: Lorber V. , Bertaud W. S. 
Published: April 2021

ABSTRACT
The cells of the amphibian atrial myocardium contain many so-called micropinocytosis vesicles, irregularly distributed along the cell membrane. In freeze-etch replicas they appear as pits when the cell membrane is seen as from an external view point, or as irregular stumps, when viewed as from an internal or cytoplasmic aspect of the membrane. In occasional specimens in which the fracture has traversed a sagittal plane the vesicles exhibit the flaskshaped appearance noted in sectioned material. In sections from tissue fixed in aldehydes and post-fixed in an osmium-lanthanum solution, the vesicles contain lanthanum whether or not they appear to be attached to the surface membrane. Since this agent is an extracellular marker, administered after cell death, this observation is taken as an indication that all the vesicles communicate with the extracellular space, and that failure to visualize the connexion is merely a consequence of the plane of sectioning. Vesicles not connected to the membrane, and free of lanthanum could not be found, suggesting that if micropinocytosis does occur, abscission is an infrequent event, and/or the vesicles are very short-lived following separation from the membrane.
The possibility that these organelles may act as an extension of the cell membrane and serve to enlarge its area has been suggested. This implies that calculations of cell membrane area based on the assumption of a smooth surface may be in error, though the magnitude of the error cannot be estimated from the present information.