bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of the RAS oncogene in the formation of tumours
Authors: Gilbert Penny X. , Harris Henry 
Published: April 2021

ABSTRACT
A c-Ha-ras 1 oncogene, cloned from the EJ human bladder carcinoma cell line, was inserted into a shuttle vector carrying the selectable marker gene gpt that encodes the enzyme xanthine-guanine phosphoribosyl transferase. This construct, pSV2gptEJ, was transfected into NIH 3T3 cells by the calcium phosphate precipitation method and cells that had incorporated the plasmid were selected by growth in the presence of mycophenolic acid to which gpt confers resistance. A number of transfectant clones were tested for tumorigenicity by inoculation into nude mice. The take incidence was variable and the tumours arose only after a prolonged latent period. Many inocula produced no tumours. These results were consistent with the view that the tumours arose by selective overgrowth of minority cell populations.
Cell lines were derived by explantation of these tumours and were back-selected in 2-thioxanthine, a cytotoxic analogue of the xanthine-guanine phosphoribosyl transferase substrate. Five clones were obtained that did not express detectable levels of the c-Ha-ras 1 oncogene product, p21ras. All of them showed a less-transformed morphology than the transfected NIH 3T3 cells from which they originated. Nonetheless three of these clones were found to be tumorigenic at all sites tested. This finding demonstrates that once tumorigenic variants have been selected from the ras-transformed cells, continued production of the p2lras protein is not necessary for the maintenance of tumorigenicity.
Cytogenetic analysis revealed that the transfection procedure itself introduced major and stable perturbations of the genome of the transfected cells and confirmed that tumours were produced by selective overgrowth of variants with a chromosome constitution palpably different from that of the majority of the cells injected. In the light of the complex background of genomic changes produced in NIH 3T3 cells by transfection with the c-Ha-ras 1 oncogene, no conclusion can be drawn in genetic terms concerning its dominance.
Fracture-Flip: New High-Resolution Images Of Cell Surfaces After Carbon Stabilization Of Freeze-Fractured Membranes
Authors: Forsman Catarina Andersson , Silva Pedro Pinto Da 
Published: April 2021

ABSTRACT
We introduce fracture-flip, a method of obtaining high-resolution views of membrane surfaces. The method, a corollary of label-fracture, is based on the stabilization of the exoplasmic halves of membranes by carbon evaporation. Inversion of these casts followed by Pt/C imaging leads to new views of the cell surface at macromolecular resolution.
Caffeine induces uncoordinated expression of cell cycle functions after ultraviolet irradiation: Accelerated cycle transit, sister chromatid exchanges and premature chromosome condensation in a transformed indian muntjac cell line
Authors: Musk S. R. R. , Downes C. S. , Johnson R. T. 
Published: April 2021

ABSTRACT
Caffeine enhances the lethal effect of DNA-damaging agents. It also affects the timing of events in the cell cycle; the enhanced cytotoxicity may be partly due to caffeine’s ability to over-come the protective damage-induced delay in S or G2 phase. When the effects of caffeine are compared in a normal Indian muntjac cell line and a simian virus 40 (SV40)-transformed, ultraviolet light (u.v.)-sensitive line in which u.v. induces many sister chromatid exchanges, different cell cycle sensitivities are seen.
In the SV40-transformed line, caffeine over-rides the delay in DNA synthesis imposed by DNA damage; it initiates late cycle events after u.v. irradiation, and in some cases it induces S-phase premature chromosome condensation, apparently by inducing mitotic factors in cells where the chromatin is still replicating. Caffeine hasbeen reported to induce similar premature chromosome condensation in cells arrested with DNA polymerase inhibitors; this is the first recognition that such events occur in response to caffeine treatment after DNA damage. Some apparent paradoxes of caffeine’s action on irradiated cells can be thus explained.
In the normal line, caffeine neither affects progression through the cycle nor induces premature chromosome condensation after irradiation. In both lines, caffeine increases killing and sister chromatid exchanges after u.v. irradiation; but these effects are more pronounced when exerted through the cell cycle-related mechanism.
DNase I Nick Translation In Situ On Meiotic Chromosomes Of The Mouse, Mus Musculus*
Authors: Raman Rajiva , Singh A. P. , Nanda Indrajit 
Published: April 2021

ABSTRACT
DNase-I-sensitive sites have been located on the meiotic chromosomes of the mouse, Mus musculus, by the in situ DNase I nick-translation method. We find that: (1) of all the cell types studied, pachytene nuclei are the most sensitive to DNase I; (2) in diplotene the nicks occur preferentially in the vicinity of chiasmata; (3) the sex chromosomes are also sensitive to the enzyme despite their transcriptional quiescence; and (4) in the sex bivalent the nicks are primarily observed in the putative region of recombination. We conclude that, in addition to discriminating between the transcriptionally active and inactive states of chromatin, DNase I identifies recombination-specific chromatin changes in meiotic prophase.
Chondrons from articular cartilage: I. Immunolocalization of type vi collagen in the pericellular capsule of isolated canine tibial chondrons
Authors: Poole C. Anthony , Ayad Shirley , Schofield Jennifer R. 
Published: April 2021

ABSTRACT
A heterogeneous population of intact chondrons extracted from low-speed homogenates of canine tibial cartilage were stained by indirect immune-fluorescence methods with a polyclonal antibody to type VI collagen. In each of the four chondron groups examined, anti-(type VI collagen) anti-serum was concentrated in the capsule immediately adjacent to the chondrocyte complex. A constant but weaker fluorescent reaction persists in ‘tail-like’ extensions common to single and double chondrons and in the medial connections between adjacent chondrons in linear columns and aggregated clusters. Frayed collagen bundles typical of chondron preparations did not react with the antibody. Similarly, chondrons reacted with normal rabbit serum, or treated by type VI collagen extraction procedures, showed no staining reaction. The differential localization of type VI collagen in the pericellular capsule is discussed in relation to the maintenance of the chondron’s integrity and to the protection of the chondrocyte during dynamic compressive loading.
Diacylglycerol-Induced Shape Changes, Movements And Altered F-Actin Distribution In Human Neutrophils
Authors: Zimmermann A. , Gehr P. , Keller H. U. 
Published: April 2021

ABSTRACT
The study shows that diacylglycerols (DAGs) as physiological activators of protein kinase C induce characteristic shape changes in human neutrophil granulocytes. In contrast to chemotactic peptides, which can induce front-tail polarity characterized by a contracted tail and an expanding front, DAGs elicit the formation of non-polar cells with surface projections. These cells exhibit a distinct type of motility characterized by vigorous and continuous shape changes without front-tail polarity and without the unidirectional movement and cytoplasmic streaming seen in polarized cells. In neutrophils exposed to DAGs, F-actin is shifted to the cell periphery and mainly into the surface projections of activated cells. DAGs induce the formation of large intracellular vacuoles in neutrophils producing surface projections, and these vacuoles persist after the cells have reacquired a spherical shape. Combinedstimulation of human neutrophils with DAG and fNLPNTL results in a suppression of peptide-induced polarity and the formation of non-polar motile cells resembling those stimulated with DAG alone. These results suggest that the diacyl-glycerol-protein kinase C pathway may be in-strumental in transducing or modulating signals to both the locomotor apparatus and the exocytotic and/or pinocytic system of the cell. Neutrophil stimulation with DAGs thus represents a useful model with which to study further the hypothesis that distinct types of neutrophil shapes and movements are preferentially associated with distinct functions and to characterize signalling pathways.
Contact Guidance On Microfabricated Substrata: The Response Of Teleost Fin Mesenchyme Cells To Repeating Topographical Patterns
Authors: Wood Andrew 
Published: April 2021

ABSTRACT
The mesenchymal tissue component of the teleost pectoral fin bud has been explanted onto microfabricated quartz discs containing patterns of regular grooves of dimensions similar to those encountered by contact-guided cells in the intact fin system. Computer-aided analysis of cell migration on five separate patterns, from 1·8 to 7·4 μm repeat spacing, revealed that migration was predominantly aligned parallel to the long axis of the grooves, with individual cells becoming highly polarized, and the highest index of alignment (3·7) produced on the widest repeat spacings. When these cells are cultured on planar quartz, which is both chemically and physically isotropic, they flatten and adopt a morphology similar to that shown by cultured fibroblastic cell types on flat surfaces, suggesting that fin mesenchymal cells are not intrinsically predisposed to adopt an arborized morphology, like that observed in the intact fin bud. These results clearly demonstrate a directional migration in response to substratum topography, from a cell type known to be contact guided in vivo, and in the complete absence of adhesive heterogeneities.
Cell surface heparan sulphate and adhesive property of sublines of rat ascites hepatoma AH7974
Authors: Kimura A. , Kawaguchi T. , Ono T. , Sakuma A. , Yokoya Y. , Kochi H. , Nakamura K. 
Published: April 2021

ABSTRACT
Two variants (74AD and 74FL) established from rat ascites hepatoma AH7974 were examined for the production of glycosaminoglycans in culture.
There was no difference between the adhesive (74AD) and the floating (74FL) variants in quantity of glycosaminoglycans produced by their cultivation in minimum essential medium supplemented with 10% foetal calf serum. However, they were distinctly different in the distribution patterns of heparan sulphate. In 74FL, about 70% of total heparan sulphate was found in the culture medium in soluble form, whereas in 74AD, only 7 % was found in the medium and the rest was in the cell-substratum complex.
In a serum-free medium, 74AD cells grew with-out adhering to the substratum. After cultivation, more than 90% of total heparan sulphate was found in the cell-associated fractions and the rest in the substratum fractions. No heparan sulphate was detected in the culture medium. On the other hand, 74FL cells released heparan sulphate to the serum-free medium as much as to the serum-containing medium.
The increase in amount of heparan sulphate in the culture medium of 74FL cells was supposed to be caused by failure of the cells to deposit heparan sulphate at the cell surface and not caused by increased production.
Cell-substratum adhesion mechanisms involving cell surface heparan sulphate (heparan sulphate proteoglycan) and some serum intermediate(s)) are discussed for 74AD cells.
Effects of suboptimal levels of extracellular calcium on the regulation of the cyclic amp phosphodiesterase-inhibitor system and membrane differentiation in Dictyostelium Discoideum
Authors: Cameron A. M. 
Published: April 2021

ABSTRACT
When starved wild-type amoebae of Dictyo-stelium discoideum were washed and incubated in 1 mM-EGTA, their ability to induce soluble cyclic AMP phosphodiesterase (PD) activity in response to either millimolar cyclic AMP or a series of nanomolar cyclic AMP pulses was reduced by 55–75 %. Supplementation of EGTA-treated cells with exogenous Ca2+ stimulated PD induction in a dose-dependent fashion (ECS0 = 100–200 nM free extracellular Ca2+), and enzyme production was maximal at about 1μM free Ca2+. Ca2+ depletion also strongly impaired production of the phosphodiesterase inhibitor (PDI). In contrast, other than delaying their appearance by about 1 h, EGTA had little effect on the induction by cyclic AMP pulses of cell surface markers such as contact sites A and membrane-bound PD activity. Similar changes in both the soluble and membrane activities were observed with strain NP368, a mutant that overproduces cyclic GMP when stimulated by cyclic AMP. Thus, Ca2+ depletion does not appear to inhibit PD and PDI production by reducing intracellular cyclic GMP. To determine whether Ca2+ depletion alters signal transduction, two mutants that produce the soluble PD activities constitutively were examined. Suboptimal concentrations of free extracellular Ca2+ were found to inhibit PD production in these cells to the same degree and with the same concentration dependence as low Ca2+ inhibited PD induction by cyclic AMP in wild-type cells. These results suggest that Ca2+ depletion by EGTA probably inhibits PD and PDI production indirectly by perturbing an intracellular Ca2+ pool(s) rather than by altering a surface cyclic AMP-receptor-mediated process.
Molecular organization of the cell wall and cell-wall crystals from Chlamydomonas eugamatos
Authors: Goodenough Ursula W. , Heuser John E. 
Published: April 2021

ABSTRACT
The unicellular green alga Chlamydomonas eugamatos is surrounded by a glycoproteinaceous cell wall. Using the quick-freeze deep-etch technique, we analyse the organization of the wall layers in situ, and delineate the structure of the outermost crystalline layer (W6). We also show the structure of the protein monomers, and propose a model for their organization in the crystalthat is similar to that deduced for the related Chlorogonium elongatum crystal by image reconstruction analysis. We also show that the C. eugamatos crystal is highly similar to the flagellar collar of Chlamydomonas reinhardtii.
Microtubule-dependent cell cycle regulation is implicated in the G2 phase of Hydra cells
Authors: Dübel Stefan , Little Melvyn 
Published: April 2021

ABSTRACT
Interstitial cells of Hydra attenuata, from which nerve cells and nematocytes (stinging cells) differentiate, were arrested in either metaphase or G2 by different concentrations of the microtubule-depolymerizing agent nocodazole. At a concentration of 1 ·4 nM-nocodazole, a large number of cells were arrested in metaphase. However, at concentrations of 2 nM-nocodazole and above most of the cells were arrested at a distinct point in G2 several hours before mitosis. After removal of the 2nM-nocod-azole block, 75% of the cells entered the next cell cycle about 10 h later. To our knowledge this is the first time that cells have been synchronized by arresting them in the G2 phase. Visualization of Hydra microtubules with a tubulin monoclonal antibody and immunofluorescent staining showed that the very low concentrations of nocodazole used for cell cycle arrest were indeed affecting microtubule structures. Spindles and stem cell microtubules disappeared at 0 ·;8-1 nM-nocodazole, followed by nerve microtubules (about 2 nM), cnidocil microtubules (10 nM) and finally by nematocyte microtubules (34 nM). Taken together, these data strongly indicate a microtubule-dependent mechanism of cell cycle regulation in the G2 phase.
Inhibition of stenotele commitment by an endogenous factor in Hydra
Authors: Fujisawa Toshitaka 
Published: April 2021

ABSTRACT
The precise timing of the inhibition of stenotele differentiation by an endogenous factor in Hydra was localized in the terminal cell cycle of the precursor cells. Animals were treated with crude extract of Hydra and the inhibition kinetics of stenotele differentiation were determined. Comparison of these results with the differentiation kinetics of stenoteles determined by using [3H] thymidine labelling indicated that an endogenous factor inhibited precursor cells from entering the stenotele pathway near the S/G2 boundary of the terminal cell cycle. Since stenotele commitment occurs during this time, these results suggest that an endogenous factor specifically blocks stenotele commitment. Precursor cells blocked by the factor appeared to choose other pathways.
Magnetic resonance imaging approaching microscopic scale: Maturation stages of Acetabularia mediterranea reproductive caps
Authors: Harrison Lionel G. , Luck S. D. , Munasinghe B. D. J. P. , Hall Laurance D. 
Published: April 2021

ABSTRACT
The reproductive cap of the giant single-celled alga Acetabularia mediterránea (or A. acetabulum) has rays tapering from a width of about 400 μm at the circumference of the cap to about 30μm at their junction with the stalk of the cell. This is ideal geometry for testing the current limits of spatial resolution of proton magnetic resonance imaging. In this work, resolution of features down to 40 μm is achieved. Maturation of the cap rays involves a major cytoplasmic reorganization, from continuous cytoplasm and a central vacuole in each ray to bundles of cysts surrounded by aqueous solution. This work shows that an intermediate stage in the change can be highlighted in images by relaxation time (T1) contrasting.
Relationship between the timing of dna replication and the developmental competence in Acanthamoeba castellanii
Authors: Jantzen Helga , Schulze Ingrid , Stöhr Michael 
Published: April 2021

ABSTRACT
In Acanthamoeba, two different cell types are known. Trophozoites are generated in the mitotic division cycle, whereas cells committed at late G2 phase of the cell cycle develop into cysts in response to starvation. In this paper we study the role of timing of DNA replication in regulating development. The investigation was performed with cultures growing in a non-defined medium (ND cells) that show a high encystation competence and with cultures that have been growing in a chemically defined medium (D cells) for several years and show a low encystation competence. Bivariate DNA/BrdUrd distributions show that ND cells progress through a cycle in which the short replication phase occurs immediately and exclusively after prior completion of mitosis. These cells arrest at late G2 phase of the cell cycle during the stationary stage. In D cells, DNA replication and mitosis seem to be uncoupled, since replication takes place before as well as after mitosis. These cells arrest within their replication phase during the stationary stage. These findings indicate that D cells do not progress into late G2 phase of the cell cycle and hence do not have the competence for commitment. The alternate timing of DNA replication and the low encystation competence of D cells can be reversed by cultivation of these cells in ND medium. Synchronization experiments reveal that late G2 phase ND cells exhibit a low capacity for BrdUrd incorporation and growth after transfer into D medium, whereas ND cells of earlier phases of the cell cycle show premitotic incorporation of BrdUrd into nuclear DNA and growth. These findings suggest on the one hand that premitotic DNA synthesis is a prerequisite for growth of cells in D medium, and that there is a dependence of the induction of premitotic DNA synthesis on the cell cycle, and on the other hand that a reciprocal relationship exists between the capacity of premitotic DNA synthesis and commitment to differentiation.
Three-dimensional organization of chromosomes of Crepis capillaris by optical tomography
Authors: Rawlins D. J. , Shaw P. J. 
Published: April 2021

ABSTRACT
The three-dimensional (3D) organization of chromosomes of Crépis capillaris (2n = 6) has been investigated. Root tips were fixed, macerated with enzymes and gently separated without squashing. The cells were then stained with DAPI and optically sectioned under computer control. Sections were stored as video images and processed to remove noise and out-of-focus information. Computer modelling was then used to trace the paths of each chromosome and to display the paths as a 3D wire diagram. In all, 88 sets of anaphase chromosomes were modelled from 47 optically sectioned cells. The models and the coordinates of the chromosomes were then analysed to detect non-random arrangements or preferential associations of particular pairs of chromosomes. The methods used have significant advantages over electron microscope tomography for the analysis of 3D chromosome arrangement; in particular, the large number of samples allowed more thorough statistical tests to be performed on the data obtained. No evidence was found for either non-random arrangements or homologous association and, moreover, the distances between the two larger pairs of homologues were larger than for other pairs of chromosomes. These results conflict with previous results for this and other plant species where the material was squashed before measurements were taken. We found no evidence of haploid genome separation.
Dissociation of lens fibre gap junctions releases MP70
Authors: Kistler Joerg , Bullivant Stanley 
Published: April 2021

ABSTRACT
MIP and MP70 are putative gap junction components in the plasma membranes of the mammalian lens fibre cells. We show now that MP70 can be solubilized separately from MIP in mild detergent solutions, and that this treatment results in the dissociation of the fibre gap junctions. Solubilized MP70 was isolated as 16’9 S particles by velocity gradient centrifugation and in the electron micro scope had the appearance of short double-membrane structures consistent with connexon-pairs. These observations open a new experimental avenue in which to characterize separately the two putative lens gap junction proteins structurally and functionally.
Parallel development of cadmium resistance and in vitro transformation in cultured indian muntjac cells
Authors: Bouffler S. D. , Ord M. J. 
Published: April 2021

ABSTRACT
The development of cadmium resistance in an Indian muntjac cell line has been investigated. The parent cell line is highly sensitive to cadmium ions. Resistance was obtained by continuous growth of cells in low levels of cadmium with stepwise increments. Four cell lines were developed with resistances of between 50- and 200-fold greater than that of the parental line. Early in the development of resistance an unstable cell line displaying extensive chromosomal rearrangement and an elevated sister chromatid exchange frequency was identified. The more stable resistant lines produced from this original cell line have normal karyotypes. Having passed through the initial period of genome rearrangement the resultant cells acquired several characteristics of morphologically transformed cells. It is concluded that long-term exposure to low levels of cadmium can transform cells in vitro concurrently with their acquiring cadmium resistance.
Ultraviolet microbeam irradiation of microtubules in vitro the action spectrum for local depolymerization of marginal band microtubules in vitro matches that for reducing birefringence of chromosomal spindle fibres in vivo
Authors: Hughes Kimberley , Forer Arthur , Wilson Paula , Leggiadro Cynthia 
Published: April 2021

ABSTRACT
Marginal bands were isolated from newt red blood cells and, using monochromatic light from an ultraviolet microbeam, the marginal band microtubules were irradiated in vitro to produce areas of reduced birefringence (ARBs). The ARBs neither moved nor changed shape after they were formed, though the marginal bands sometimes changed shape during the irradiation. Marginal band ARBs were regions in which the microtubules were locally depolymerized, as determined by electron microscopy and immunofluorescence. The action spectrum for producing ARBs on marginal band microtubules in vitro matches very closely the action spectrum for producing ARBs on crane-fly spermatocyte chromosomal spindle fibres in vivo, which indicates that ARBs in vivo are produced by the ultraviolet light acting directly on the microtubules (as opposed to an intermediate component), and confirms, without complications inherent in the fixation of living cells, that ARBs on spindle fibres in vivo are regions in which microtubules are locally depolymerized.