bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and regrowth of actin bundles in Chara: bundle assembly by mechanisms differing in sensitivity to cytochalasin
Authors: Williamson Richard E. , Hurley Ursula A. 
Published: April 2021

ABSTRACT
Cytochalasin is known to inhibit cytoplasmic streaming rapidly in characean cells without disassembling their actin bundles. Lower cytochalasin concentrations than those needed for streaming inhibition are now shown to disrupt bundle assembly and, over longer periods, assembled bundles. After local wounding, cytochalasin limited bundle regeneration to the production of polygons and straight, discontinuous bundles that rarely connected to bundles outside the wound. The regenerated bundles supported only scattered organelle movements, whereas long, oriented bundles of control cells were connected to those outside the wound and supported bulk endoplasmic streaming. Unwounded Chara plants cultured for up to 2 weeks in 1 μM-cytochalasin maintained normal bundle orientation and rapid cytoplasmic streaming, but the mean number of bundles per file of chloroplasts fell from 5·2 in controls to 2·0 in growing cells and 3·4 in nongrowing cells. These structural effects seem more likely than the streaming inhibition to reflect cytochalasin’s in vitro effect of blocking extension at the barbed but not the pointed end of F-actin. In particular, cytochalasin inhibited the extension into the wound of bundles in which only the barbed ends of filaments would be exposed. However, short lengths of isolated bundles grew within the wound and bundle growth in the intact cell continued, albeit in modified form. It is suggested that these examples of continuing bundle growth involve cytochalasin-resistant mechanisms that are not wholly dependent on barbed-end filament growth.
Role of cell adhesion in contact-dependent transfer of a lysosomal enzyme from lymphocytes to fibroblasts
Authors: Olsen I. , Oliver T. , Muir H. , Smith R. , Partridge T. 
Published: April 2021

ABSTRACT
Normal lymphocytes were found to adhere strongly to monolayer cultures of fibroblasts deficient in the lysosomal enzyme, j3-glucuronidase. During this co-culture, the fibroblasts acquired from the lymphocytes substantial amounts of this enzyme, which often accumulated at sites of contact between the two types of cell. Enzyme transfer was prevented by addition to the co-cultures either of purified lymphocyte plasma membranes or of antibody raised against such plasma membranes, but it was not inhibited by the addition of antibody raised against lymphocyte-derived β-glucuronidase. An active role for the lymphocyte in this contact-dependent process was suggested by interference contrast, immunofluorescence and scanning electron-microscopic studies. These revealed extensive arrays of projections of the lymphocyte that ramified over the fibroblast cell surface. By transmission electron microscopy, conspicuous clusters of micropinocytotic vesicles were evident in the cytoplasm of the ‘recipient’ fibroblasts, subjacent to the surface in regions closely apposed to adherent lymphocytes. Such high frequencies of these vesicles were restricted to sites of lymphocyte-fibroblast contact, suggesting that they may play an important part in the transfer of enzyme between these two types of cell.
Sporidesmin and gliotoxin induce cell detachment and perturb microfilament structure in cultured liver cells
Authors: Jordan T. W. , Pedersen J. S. 
Published: April 2021

ABSTRACT
Changes in cell morphology and cell adhesion occurred when cultured cells from the rat liver cell strain C3 were exposed to the fungal toxins, sporidesmin or gliotoxin. Both toxins caused loss of attachment of the cells to the plastic of tissue culture plates and this effect was preceded by loss of actin cables. Other changes included cytoplasmic vacuolation and blocked entry into S-phase of the cell cycle. Under these conditions [3H]thymidine incorporation into the cells was also diminished but changes were not detected in the amount of cellular actin, or in the accessibility of cell surface proteins to iodination carried out by the Bolton and Hunter method. The observations suggest that disruption of microfilaments is one of the earliest effects of these toxins on eukaryotic cells.
Evidence for the persistence of a decondensed chromosome scaffold in the interphase nucleus
Authors: Bekers AD G. M. , Pieck Anna C. M. , Rijken Antonia A. M. , Wanka Friedrich 
Published: April 2021

ABSTRACTNuclei of in vitro cultured bovine liver cells, deprived of the membranes by Triton X-100, were treated with 2 M-NaCl and DNase. Changes in ultrastructure and protein composition were studied at successive steps during treatment. Electron micrographs of nuclei treated with 2 M-NaCl showed a peripheral lamina and an internal system of randomly coiled filaments embedded in a mass of DNA fibres. After partial removal of the DNA the filaments could be seen to serve as backbones for the DNA attachment. Artificial redistribution occurring during fixation with glutaraldehyde suggests that the salt-resistant filaments are not stably cross-bridged into a three-dimensional network. The existence of reversible cross-bridges in vivo cannot be excluded, however. From the available data it is inferred that the filaments represent a decondensed from of the chromosome scaffolds and play a basic role in the organization of the genome throughout the nuclear cycle.
Conditions for fibroblast adhesion without fibronectin
Authors: Curtis A. S. G. , Mcmurray Heather 
Published: April 2021

ABSTRACT
Conditions that permit the adhesion of BHK fibroblasts to a variety of surfaces after inhibition of protein synthesis and competition of any adsorbed fibronectin or vitronectin with the fibronectin cell-binding tetrapeptide, Arg-Gly-Asp-Ser (RGDS), are defined. Exposure of the cells to serum components at any stage in the preparation prevents cell attachment if cycloheximide or fibronectin tetrapeptide is present. If leupeptin is used cell adhesion and spreading occur even when all fibronectin synthesis is suppressed by cycloheximide inhibition, or fibronectin binding by tetrapeptide competition. The adhesions formed under these conditions appear by interferencereflection microscopy and by general properties to be identical to those formed by cells under normal culture conditions. The cell suspensions produced in the presence of leupeptin rather than other trypsin inhibitors show good adhesion at low temperatures, though the cells hardly spread at all. The results suggest that the role of fibronectin in cell adhesion should be reinterpreted in terms of its possible action as an activator rather than as a bonding molecule.
The role of the micronucleus in stomatogenesis in sexual reproduction of Paramecium tetraurelia: Laser microbeam irradiation of the micronucleus
Authors: Tam Lai-Wa , Ng Stephen F. 
Published: April 2021

ABSTRACT
Fifteen amicronucleate cell lines and 22 cell lines with defective micronuclei were obtained following selective laser microbeam irradiation of the micronucleus. The amicronucleate cell lines showed reduced growth rate and formed abnormal oral apparatuses in asexual reproduction, and failed to produce any oral apparatus in autogamy, in agreement with previous observations on amicronucleate cells obtained by micropipetting. The 22 cell lines with defective micronucleus exhibited various abnormalities of the oral apparatus newly formed during autogamy. These abnormalities included the arrest of membranelle assembly, reduction in the length of the buccal cavity and oral membranelles, disruption of the organization of the membranelles, quadrulation of the dorsal peniculus, and failure of addition of membranellar basal body rows. Hence the micronucleus plays multiple roles in sexual stomatogenesis, deciding early steps of oral membranelle assembly and affecting their subsequent patterning. Our results agree with the notion that the micronucleus acts during a critical period between the second meiotic division and up to the formation of the zygotic nucleus to control the early stage of oral membranelle assembly. Laser microbeam irradiation might have created recessive mutations and/or chromosomal aberrations, which were expressed during this critical period with the formation of abnormal postmeiotic nuclei.
Affinity binding of non-histone chromatin proteins to the X chromosome of Drosophila by in situ chromatin reconstitution and its significance
Authors: Ukil Mitali , Chatterjee Kaberi , Dey Anup , Ghosh Saswati , Mukherjee A. S. 
Published: April 2021

ABSTRACT
Cytophotometric analysis of the in situ binding affinity of non-histone chromosomal protein (NHCP) to the polytenic X chromosome and autosome of Drosophila melanogaster has been carried out using Feulgen-Napthol Yellow S staining technique. The results reveal that the mean transformed absorbance ratio (male:female) with a 547nm interference band filter for the two specific segments of the X chromosome is close to 0·5, while for a specific segment of an autosome it is close to 1·0, in the two sets of control; namely, the positive control (no treatment) and the negative control (treated with 1 M-urea+2M-NaCl) as well as in the reconstituted chromosomal preparations, which received 1 M-urea+2M-NaCl and the NHCP isolated from D. melanogaster. In contrast, the transformed absorbance ratios (male:female) with a 433 nm interference band filter yielded an interestingly different result. The ratios with a 433 nm filter for the X chromosome segments are significantly greater than 0·5 in all three sets of experiments. This finding by itself suggests that the NHCP binding affinity is dissimilar for the X chromosomes of male and female. When the 433 to 547 nm absorbance ratios were compared among the three sets, the data clearly revealed that in both positive control and NHCP reconstituted samples, the absorbance ratios (i.e. 433:547 nm) are significantly different between X chromosomes from males and those from females, while they are different between autosomes from males and females. The ratios are also not significantly different between male and female, either for the X chromosome or for the autosome in the negative control. These findings, therefore, suggest that there is a stronger binding affinity of NHCP for the male X chromosome of Drosophila, and reinstate the view that the X-chromosomal hyperactivity in male Drosophila is the consequence of a regulated organizational change in the DNA template.
Dissociation and reassociation of trichocyst proteins: Biochemical and ultrastructural studies
Authors: Peterson Joan B. , Heuser John E. , Nelson David L. 
Published: April 2021

ABSTRACT
Trichocysts, the crystalline exocytotic organelles in Paramecium tetraurelia, are composed of small, acidic proteins existing primarily as disulphide-linked dimers. We have disaggregated trichocyst proteins with heat, simultaneously observing the changes in morphology and protein composition. The tip matrix was most heat-labile; its subunits progressively broke away from the distal end. During this process, breakdown of the cylindrical shaft began. Shafts first became flattened and torn lengthwise, yielding smaller, interconnected pieces still having the crystalline arrangement of their 5nm thick fibres. Ultimately this pattern became disordered, and discrete fibrils of the same thickness disengaged from the meshwork. In freeze-etched preparations these fibrils were composed of thinner filaments in side-by-side association. Disaggregation of the tip sheath began from the distal end before shaft dissociation was complete. Trichocysts broke down to thin fibrils, but probably not to monomeric subunits. At least three proteins were preferentially released in the initial phase of dissociation. Disulphide-reducing agent present during heating increased the rate of dissociation without altering the sequence of morphological changes or the order of release of individual proteins. The rate and extent of heat-induced dissociation were strongly dependent on pH and cation concentration. The stabilizing effects of low pH and of cations were additive.
A cooled suspension of fully dissociated trichocysts reassociated into sedimentable aggregates with discernible filamentous order, but without the crystalline structure of intact trichocysts. Reassociation was dependent upon time, temperature and protein concentration. All but one of the trichocyst proteins re-entered the sedimentable aggregate during reassociation.
Reassociation was faster and more complete at pH 6 than at pH 8 and was stimulated by Ca2+, Mg2+ and La3+. Trichocyst proteins dissociated in the presence of dithiothreitol did not reassociate, even after removal of the reducing agent.
Trichocysts from mutants defective to varying degrees in trichocyst formation were subjected to similar experimental protocols. Heat-dissociated trichocysts of the mutants scc6 and ptA1 reassociated at rates similar to those of wildtype; ftA3 showed slower reassociation, and tam38 showed little or no reassociation. Reassociation of wild-type trichocyst proteins was blocked by the addition of an equal amount of tam38 trichocyst proteins. Despite the variant structure, the main detectable difference in the protein complements of different strains was the relative prominence of common bands, rather than the presence of unique bands or the absence of common bands.
Effect of cell shape on proteinase secretion by epithelial cells
Authors: Hong H. L. , Brunette D. M. 
Published: April 2021

ABSTRACT
Cell proliferation has been found to correlate with increased secretion of proteinases, such as plasminogen activator, in several different cell populations. In addition, the shape of the cell may also play a role in regulating proteinase secretion. However, the relationship between cell proliferation, cell shape and proteinase secretion has not been studied in diploid epithelial (E) cells cultured from porcine periodontal ligament (PL). We have modified PLE cell shape by physical means, such as growth on less-adhesive substrata and mechanical stretching, and by exposure to cholera toxin and 12-O-tetradecanoylphorbol-13-acetate (TPA). Neutral proteinase and plasminogen activator secretion were found to correlate with cell shape, the more round the cells, the greater the amount of proteinase secreted. PLE cells, stimulated to proliferate by cholera toxin or dibutyryl cyclic AMP, were more spread than control cells, but secreted less neutral proteinase and plasminogen activator. TPA stimulated cell proliferation slightly but, in contrast to cholera toxin, increased cell rounding and the secretion of neutral proteinase and plasminogen activator. Thus proteinase secretion was related more to cell shape than to cell proliferation.
Genotypic control of centromere positions of parental genomes in Hordeum × Secale hybrid metaphases
Authors: Schwarzacher-Robinson Trude , Finch R. A. , Smith J. B. , Bennett M. D. 
Published: April 2021

ABSTRACT
The spatial disposition at metaphase of centromeres from Hordeum and Secale in root tip cells of H. chilense × S. africanum is described and compared with corresponding results for H. vulgare × S. africanum obtained previously. In both of these F1 sexual hybrids (2n = 2x = 14) each of the seven chromosome types from Secale was easily distinguished by its large size from any of the seven from Hordeum.
In H. chilense × S. africanum, centromeres of Secale chromosomes tended to be nearer the centre of the metaphase plate than did centromeres of Hordeum chromosomes in both squash preparations seen by light microscopy and unsquashed cells examined using electron microscope three-dimensional serial thin section reconstructions. This difference was significant in some individual cells, and highly significant for pooled data for reconstructed cells and separately for squashed metaphases. In no cell were Hordeum centromeres on average significantly nearer the centre of the metaphase plate than Secale centromeres.
These results agreed with those previously obtained for H. vulgare × S. africanum in that: (1) centromeres of the two parental haploid sets tended to be spatially separate; and (2) centromeres from one particular parent usually tended to be in the peripheral region of the metaphase plate that surrounded the central region containing the centromeres from the other parent. However, these results contrasted completely with those obtained previously in that Secale centromeres tended to be more central than Hordeum centromeres in H. chilense × S. africanum, but more peripheral than Hordeum centromeres in H. vulgare × S. africanum.
As centromeres of the parental set with the larger chromosomes (i.e. Secale) can be either inside, or outside, centromeres from the parental genome with the smaller chromosomes (i.e. Hordeum), then clearly, a tendency for a concentric separation of parental genomes is not a packing phenomenon determined by chromosome size perse, but is presumably under genotypic control.
Association of calmodulin with lysosomes
Authors: Nielsen Thor B. , Field James B. , Dedman John R. 
Published: April 2021

ABSTRACT
We examined the subcellular localization of calmodulin in several cultured cells (primary thyroid follicular cells, thyroid C-cell tumour cells (TT), kidney cells (PtK2-L23) and peritoneal macrophages) by indirect immunofluorescence using affinity-purified antibody to calmodulin. When cells were fixed with 3 % formaldehyde for 15 min prior to lysis with 0·5% Triton X-100, spindle fibres in mitotic cells were fluorescent and a diffuse cytoplasmic localization of calmodulin was observed in resting cells. However, when cells were lysed with 0·5% Triton X-100 for 90s prior to fixation for 30min with 3% formaldehyde, three effects were observed. One: there was little diffuse cytoplasmic staining. Two: discrete vesicles were stained. Three: spindle fibres in mitotic cells were fluorescent. The stained vesicles were phase-dense and ranged from 0·1 to 0·5μm in primary thyroid follicular cells but were smaller in PtK2 and TT cells. The thyroid follicular cells retained vesicular staining after exposure to thyrotropin and isobutyl-methylxanthine, but the number of labelled vesicles decreased by almost 80%. Phase-dense vesicles were identified as lysosomes or other acidic vesicles by vital staining with Acridine Orange. After differential centrifugation of thyroid homogenates, calmodulin was measured by radioimmunoassay (RIA) and found in both cytosolic (89 %) and membrane vesicle fractions (11 %). The vesicular calmodulin was not eluted by washing with 5 mM-EGTA. The thyroid fractions were subjected to SDS–polyacrylamide gel electrophoresis and the gels incubated with 125I-labelled calmodulin to reveal calmodulin acceptor proteins (CAPs). The vesicle fraction contained quantitatively major CAPs with Mr of 200000, 140000, 89000, 38000 and 34000, and minor CAPs of 60 000 and 50 000. Washing the pellet with 5 mM-EGTA did not reduce the content of CAPs. Thus, calmodulin and CAPs are present both in the cytoplasm and in a membrane vesicle fraction. The lysosomal locale of calmodulin and the effect of thyrotropin on vesicle number suggest a role for calcium in the regulation of lysosome function.
The suppression of malignancy by terminal differentiation: Evidence from hybrids between tumour cells and keratinocytes
Authors: Harris Henry , Bramwell Michael E. 
Published: April 2021

ABSTRACT
When malignant human cells are crossed with diploid human keratinocytes, malignancy, as defined by progressive growth in vivo, is suppressed so long as the hybrid cells continue to produce involucrin, a protein that characterizes terminal differentiation in the kératinocyte. When, on continued cultivation in vitro, the cells lose the ability to produce involucrin, they reacquire the ability to grow progressively in the animal.
Dissection of the bovine epidermal desmosome into cytoplasmic protein and membrane glycoprotein domains
Authors: Skerrow Christine J. , Hunter Irene , Skerrow David 
Published: April 2021

ABSTRACT
Epidermal desmosomes contain two main regions. The core consists of a pair of membranes, one on either side of a cross-striated intercellular space bisected by a denser midline. The cytoplasmic compartment comprises a dense plaque deposited on the cytoplasmic surface of each membrane and a diffuse layer occupying the zone between the plaque and attached cr-keratin filaments. Analysis of isolated desmosomes by SDS-PAGE has shown the presence of four major protein (dpl-4) and three major glycoprotein (dgl-3) bands, which have been allocated to the cytoplasmic and core compartments, respectively.
In the present paper, we report the use of urea to fractionate this complex structure, both in situ and following isolation with citrate buffer, pH2’6. Extraction of the living layers of bovine epidermis with 9M-urea, pH 7 · 5, resulted in rapid removal of the dense desmosomal plaques, followed by separation and vésiculation of desmosomal membranes. The resistance of the plaque to urea increased abruptly at the transition between living epidermis and dead, dehydrated horny layer. A similar sequence of morphological changes accompanied the extraction of isolated desmosomes with urea. Analysis of residues and extracts of isolated desmosomes by SDS-PAGE confirmed the selectivity of 9M-urea, pH 7 · 5, for the cytoplasmic compartment. The four major desmosomal proteins, dpl-4 (Mr240, 215, 90 and 83 (× 103), respectively) predominated in the extracts. Desmosomal membranes, both paired and vesiculated, consisted almost entirely of the three desmosomal glycoproteins dgl-3 (Mr 150, 120 and 110 (× 103), respectively).
These results provide evidence that all three desmosomal glycoproteins are integral membrane proteins. The separation of desmosomal membranes by urea, which is not accompanied by additional loss of proteins, further suggests that desmosomal adhesion is based on interactions between membrane components with no separate extracellular molecules being involved. The dissection of the desmosome by urea into two topographically and biochemically distinct domains should facilitate further studies on the molecular basis of desmosomal adhesion and a- keratin filament binding.
Characterization of Pales spermatocyte spindles, with reference to an mtoc-associated protein
Authors: Bastmeyer Martin , Russell David G. 
Published: April 2021

ABSTRACT
Pales ferruginea spermatocytes, because of their high proportion of dividing cells, offer many advantages in the study of the meiotic spindle. In the present study we have combined ultrastructural and immunofluorescence techniques with biochemical analysis of constituent spindle components. Using a centrosome-reactive serum, which recognizes an antigen in the centrosomal and midbody regions of dividing cells, we have identified an MTOC-associated polypeptide of 112000Mr with a pl of 5·6. The relative abundance of this protein in cells and isolated cytoskeletons indicates that it is present in other regions of the cell and is either more abundant, or is only recognized by the antibody in association with MTOCs.