bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of a spindle-associated protein in ciliate micronuclei
Authors: Keryer Guy , Loubresse Nicole Garreau De , Bordes Nicole , Bornens Michel 
Published: April 2021

ABSTRACTCiliated protozoa display a nuclear dualism, with germinal micronuclei and a somatic macronucleus. During mitosis, which proceeds without disruption of the nuclear envelope, a spindle is organized within the micronucleus from, presumably, intranuclear microtubule-organizing centres (MTOCs). In order to characterize these MTOCs, monoclonal antibodies generated against human centrosomes were screened on several ciliates and particularly on Paramecium tetraurelia. In this ciliate, the monoclonal antibody CTR 532, which decorates centrosomal and spindle-associated components in mammalian cells, specifically labelled the micronuclei during interphase. At the electron-microscope level, it stained a fibrous material surrounding microtubules localized on the inner face of the nuclear envelope. During mitosis this decoration extended all over the metaphase spindle. At all stages of the cell cycle, the decoration remained specific to the micronucleus and was absent not only from all of the various cytoplasmic and cortical microtubule arrays but also from the macronuclei, even at early stages of their development from the zygotic nucleus. CTR 532 recognizes a single 170xl(rMr polypeptide in the cytoskeletal fraction that contains micronuclei and this polypeptide is absent in the cytoskeletal fraction of amicro-nucleate cells.
Digital image processing of optical density wave propagation in Dictyostelium discoideum and analysis of the effects of caffeine and ammonia
Authors: Siegert Florian , Weijer Cornelis 
Published: April 2021

ABSTRACT
Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum were analyzed by digital image processing in a manner that immediately shows the following parameters: wave propagation velocity, period length, wave amplitude und wave shape. We have characterized the aggregation of AX-2 and the streamer F mutant NP 377 in terms of these parameters and investigated the influence of caffeine and ammonia. It was found that during normal aggregation oscillation frequency increases while at the same time wave propagation velocity decreases. Caffeine, a known inhibitor of cyclic AMP relay, reduces oscillation frequency and wave propagation velocity in a dose-dependent manner but most notably leads to the appearance of bimodal (harmonic) oscillations. These bimodal waves are also found in streamer F mutants without caffeine during early aggregation.
The effect of caffeine is interpreted as an increase in the average chemotactic deadaptation time due to elevated cyclic GMP levels after a cyclic AMP stimulus. This increased deadaptation time results in some cells responding to every chemotactic signal, while others respond only to every second signal, leading to mixed population behavior and hence biphasic optical density waves. Ammonia has no significant influence on oscillation frequency and wave propagation velocity but shows a clear increase in the amplitude of the optical density waves. This may indicate a more vigorous chemotactic response by individual cells or a better synchronization of the responding cell populations due to shortened chemotactic deadaptation times.
The disruption of dictyosomal integrity by caffeine in the green algal flagellate, Gloeomonas Kupfferi
Authors: Domozych David S. 
Published: April 2021

ABSTRACT
The endomembrane system of the green algal flagellate, Gloeomonas kupfferi, is a highly ordered complex of endoplasmic reticulum sheets, 14–18 dictyosomes, vesicles and 8–12 peripheral vacuoles centered around a large nucleus. Each dictyosome is a highly polar cisternal stack with distinct cis and trans faces and an assortment of different-sized vesicles. The methylxanthine, caffeine, in concentrations of 1–2 mM, has been shown to be an effective disrupting agent of dictyosome integrity. For short treatments (1 h), caffeine causes an inhibition of typical trans-face vesiculation. Dictyosomes expand laterally and trans-face cisternal edges fuse. The resultant morphological products includeexaggerated circular profiles and multidictyosomal masses. During longer treatment times (3–4 h), cisface cistemae swell and ultimately disintegrate into large vesicles. Trans-face cistemae also vesiculate but do so into masses of tiny vesicles. The caffeine effects are reversible for up to 12 h, after which time cytological changes result in cell death. Phosphatase cytochemistry was also employed in this study to help reveal localized effects of caffeine. A putative explanation of the action of caffeine is presented.
Diacylglycerols and PMA induce actin polymerization and distinct shape changes in lymphocytes: relation to fluid pinocytosis and locomotion
Authors: Keller H. U. , Niggli V. , Zimmermann A. 
Published: April 2021

ABSTRACT
Shape changes have been determined in human blood lymphocytes stimulated with OAG, diC8, PMA, colchicine or the hexapeptide fNLPNTL in short-term assays (30 min). Distinct types of shapechange responses were observed. Colchicine was active in generating a relatively small proportion of polarized lymphocytes (front-tail polarity). OAG, diC8 and PMA produced different types of shape change (non-polar cells with surface projections), and these were closely associated with an increase in actin polymerization and a shift of F-actin into the projections at the cell periphery. The diacylglycerols OAG and diC8 produced biphasic dose-response curves leading to rounding up of cells at very high stimulant concentrations. PMA produced no comparable biphasic response when tested over a much wider concentration range. Though the nonpolar cells with surface projections generated by OAG, diC8 or PMA showed vigorous shape changes, they lacked significant locomotor activity. α-Phorbol, 4α-PDD, lumicolchicine or fNLPNTL were inactive. Small blood lymphocytes stimulated by OAG, diC8 or PMA showed a very small increase in the net uptake of FITC-dextran by fluid pinocytosis. Unlike neutrophils, which show a high net uptake, lymphocytes did not concentrate FITC-dextran in large granules, indicating that they do not develop a ‘storage’ compartment in the form of large vesicles. However, small fluorescent spots were consistently found in at least a fraction of blood lymphocytes. The results indicate that stimulated surface movement may be instrumental in fluid pinocytosis. Diacylglycerols may act as second messengers to induce pinocytosis, shape changes and altered actin polymerization in lymphocytes.
The translaminal fibrils of the human amnion basement membrane
Authors: Campbell S. , Allen T. D. , Moser B. B. , Aplin J. D. 
Published: April 2021

ABSTRACT
The organisation of extracellular matrix beneath the human amniotic epithelium was investigated in order that the co-ordinate synthesis of basal lamina and stroma by these cells could be better understood. Transmission electron microscopy of intact tissue confirmed that stromal matrix fibrils are located between the cell surface and the basal lamina, and also penetrate the lamina. The distribution of the supralaminal fibrils and their association with the lamina was further investigated by scanning electron microscopy (SEM) after removal of the overlying epithelium. Five complementary procedures were used to remove the cells from the underlying lamina. Trypsin–EDTA treatment caused the epithelial cells to retract or detach from the lamina. SDS or ammonium hydroxide was used to extract the epithelium, which was then removed by physical shearing. Transmission electron microscopy (TEM) confirmed that the lamina densa and supralaminal fibres were present after extraction by these agents. Incubation in CHAPS, a zwit terionic detergent, did not remove the epithelium but permitted exposure of the basal lamina by mechanical scoring. Extraction with boric acid followed by osmium tetroxide produced epithelial disruption and revealed the lamina and stroma in different areas. Although the extraction pattern was different in each case, all of the five methods confirmed that individual fibrils and fibril bundles are present on the apical surface of, and enter, the lamina densa. Examination of the stromal surface of the basal lamina after fracture revealed fibrils passing from the stroma into the lamina densa. We therefore suggest that, in this tissue, newly synthesised stromal matrix components appear in an assembled fibrillar form between the basal cell surface and the basal lamina before becoming associated with the sublaminal stroma.
Onset of expression of peanut lectin-binding glycoproteins is correlated with stratification of keratinocytes during human epidermal development in vivo and in vitro
Authors: Watt Fiona M. , Keeble Stella , Fisher Chris , Hudson David L. , Codd Jane , Salisbury Jonathan R. 
Published: April 2021

ABSTRACT
During gestation the epidermis develops from a single layer of ectoderm into a layer of keratinocytes overlaid by a layer of periderm; this is followed by a progressive increase in the number of layers of keratinocytes, until finally the distinct granular and cornified layers characteristic of mature epidermis are formed. As part of our investigation into the function of the peanut lectin-binding glycoproteins of cultured human keratinocytes, we have examined their expression at different stages of human epidermal development. We found that the onset of expression of the glycoproteins coincided with the transition from a two-to a threelayered epidermis, both in vivo and in organ culture. In adult epidermis, the patterns of binding of peanut lectin and Limax flavus lectin are complementary, with peanut binding more strongly to suprabasal keratinocytes and Limax βavus lectin binding more strongly to cells in the basal layer. We found that the complementary pattern of binding of the two lectins was established at, or shortly after, the onset of stratification and retained throughout development. In contrast, expression by keratinocytes of involucrin, a protein precursor of the cornified envelope, occurred after stratification had begun. Finally, we identified the peanut lectin-binding glycoproteins of adult epidermis by immunoblotting with an antiserum raised against the glycoproteins of cultured neonatal keratinocytes. In conclusion, expression of the peanut lectin-binding glycoproteins is an early eve&gt;Summarynt in epidermal development, and this would be consistent with a role for the glycoproteins in stratification.
Commentary how is microtubule-based organelle translocation regulated?
Authors: STEBBINGS HOWARD 
Published: April 2021

ABSTRACT
It has long been appreciated from light-microscopical studies that components move in a directed fashion within cells, and this is particularly obvious in cells showing high degrees of asymmetry. The correlation between such movements and the presence of orientated aggregations of microtubules, first observed by electron microscopy and subsequently at the light-microscopic level using immunological techniques, pointed to the involvement of these linear organelles in this intracellular translocation (see Hyams and Stebbings, 1979). Many different cellular organelles, including endosomes, lysosomes, mitochondria and various types of secretory vesicles, show directed translocation along microtubules, and their movement is clearly crucial to normal cell physiological function. The most extensively studied example has been the axonal processes of neurones, but various protozoa, fish pigment cells and insect ovaries also show exaggerated forms of intracellular translocation, and have proved valuable in studying the phenomenon.
Serum enhancement of human endothelial cell attachment to and spreading on collagens I and IV does not require serum fibronectin or vitronectin
Authors: Norris William D. , Steele John G. , Johnson Graham , Underwood P. Anne 
Published: April 2021

ABSTRACT
The initial attachment and spreading of endothelial cells from human umbilical artery onto type i collagen, type IV collagen or gelatin substrata was shown to be enhanced by inclusion of serum in the culture medium. To test whether this serum effect was mediated by adsorption of serum fibronectin or vitronectin onto the collagen, these adhesive glycoproteins were selectively removed from the serum prior to addition to the culture medium. The stimulatory effect of serum on human endothelial cell spreading on collagens I and IV was also observed with serum from which either fibronectin or vitronectin, or both, had been selectively removed. The stimulatory effect for cell spreading on gelatin was diminished by selective removal of serum fibronectin, but unaffected by removal of vitronectin. Hu man endothelial cell attachment and spreading onto tissue culture plastic was abolished by removal of vitronectin from the serum in the culture medium. These results emphasize that the native structure of collagens is required for serum-enhancement of human endothelial cell attachment and spreading on native collagen types I and TV, and show that on these substrata the stimulated adhesion and spreading are not dependent upon adsorption of serum fibronectin or vitronectin onto the collagen substratum.
Contact activation in Chlamydomonas gametes by increased binding capacity of sexual agglutinins
Authors: Tomson A. M. , Demets R. , Musgrave A. , Kooijman R. , Stegwee D. , Ende H. Van Den 
Published: April 2021

ABSTRACT
When the flagella of compatible gametes of Chlamydomonas eugametos contact one another, the capacity for sexual adhesion is rapidly increased. It is shown that during this so-called contact activation the amount of adhesion molecules, or agglutinins, on the flagellar surface remains relatively constant, indicating that the increase in sexual adhesiveness is mainly the result of an enhancement in binding capacity of the agglutinins. Contact activation coincides with an apparent aggregation of agglutinins in association with a weakening of the agglutinin binding to the membrane. Artificial clustering of the agglutinins, using the lectin wheat germ agglutinin, also leads to an increase in sexual adhesiveness. In the presence of anti-tubulin drugs compatible gametes make contact with one another but fail to increase their adhesiveness. It is proposed that micro-aggregation of agglutinin molecules, mediated by tubulin, underlies the enhancement of sexual binding capacity.
The circadian bioluminescence rhythm of Gonyaulax is related to daily variations in the number of light-emitting organelles
Authors: Fritz Lawrence , Morse David , Hastings J. W. 
Published: April 2021

ABSTRACT
The number of scintillons, which are cellular organelles responsible for light emission in the marine alga Gonyaulax, were counted by both immunofluorescence and electron microscopic methods and found to vary tenfold between subjective day and subjective night. The number of scintillons peaks during the subjective night, as does stimulated bioluminescence (flashing). Furthermore, the number drops sharply at the time of the maximal spontaneous bioluminescence (glow), which occurs at the end of the night phase, suggesting that the breakdown of scintillons may be responsible for this mode of emission.
In situanalyses reveal that the two nuclei ofGiardia lambliaare equivalent
Authors: Kabnick Karen S. , Peattie Debra A. 
Published: April 2021

ABSTRACTThe protozoan parasite Giardia lamblia has the unusual morphology of bearing two equalsized nuclei. This organism probably represents the earliest diverging lineage of eukaryotes, suggesting that its biological tactics may be transitional. To begin to understand the role played by the two equalsized nuclei in this organism, and perhaps the role this organism has played along the path to higher eukaryotes, we have analyzed the structure and function of these two nuclei. We show that the two nuclei are equivalent with respect to the amount of DNA harbored in each nucleus, the presence of ribosomal DNA sequences, and the transcriptional activity. We begin also to address the question of how these bilaterally symmetrical ancestors divide, by illustrating the mitotic plane of division.
Telomere cloning and mammalian chromosome analysis
Authors: Brown William R. A. , Dobson Melanie J. , Mackinnon Philip 
Published: April 2021

ABSTRACT
Although eucaryotic chromosomes vary in size over five orders of magnitude and are constituents of diverse genetic systems the fundamental features of their telomeres appear to be almost completely conserved. This can be exploited to enable molecular cloning of human telomeres in yeast and suggests that many of the ideas that will arise from studies of telomeres in the experimentally tractable ciliates and yeasts will hold true of mammalian telomeres. The particular value of cloned mammalian telomeres is that they contribute reagents for mapping mammalian chromosomes and that they provide one set of elements for the construction of artificial mammalian chromosomes.
Cell proliferation in the repairing adult insect central nervous system: incorporation of the thymidine analogue 5-bromo-2-deoxyuridine in vivo
Authors: Smith P. J. S. , Howes E. A. , Treherne J. E. 
Published: April 2021

ABSTRACT
Uptake of the thymidine analogue 5-bromo-2-deoxyuridine into non-neuronal cells of the insect central nervous system has been examined following a controlled lesioning of the glial elements. The pattern of BUdR labelling along the penultimate abdominal connective was examined over a period of 17 days. Cell proliferation occurred in and immediately around the site of damage in both perineurial and subperineurial glial cells but at different times post-lesion for the two regions. Proliferation in the perineurial zone was maximal at 6-8 days post-lesion but continued for at least 17 days. Subperineurial proliferation was less dramatic and peaked between days 8-11 post-lesion. In both areas division appears to be confined to the reactive glial cells. These results are discussed in the context of past research on this system, particularly with regard to the restoration of the bloodbrain barrier.
Pseudo-self-compatibility in ultraviolet-irradiated plants of Primula acaulis (‘pin’ morph)
Authors: Carraro Luisa , Gerola P. D. , Lombardo Giuliana , Gerola F. M. 
Published: April 2021

ABSTRACT
Apoplastic peroxidase distribution in transmitting tissue of the stylar ‘neck’ was investigated using the DAB cytochemical reaction applied to electron microscopy in non-, self- and cross-pollinated pistils of Primula acaulis (‘pin’ morph) exposed or not to ultraviolet (u.v.) irradiation. In non-irradiated flowers, apoplastic peroxidase activity, which is present in non-pollinated pistils, is increased by self-pollination, whereas cross-pollination causes its disappearance from the central portion of the transmitting tissue. Apoplastic peroxidases localized in the central portion of the transmitting tissue are supposed to play a role in the predisposition of the pistil to reject incompatible pollen tubes and in the rejection mechanism itself. Pistil irradiation with u.v., which induces pseudo-self-compatibility, modified the aforementioned apoplastic peroxidase distribution. Shortly after u.v. irradiation of nonpollinated styles, apoplastic peroxidase activity was absent from the central portion of the transmitting tissue; some hours later peroxidase activity was restored, and 40 h after treatment, the ‘normal’ peroxidase distribution was observed. Our data suggest an u.v.-induced temporary removal of the ‘predisposition’ for incompatible pollen tube rejection. Moreover, soon after irradiation, the usually observed peroxidase production due to self-pollination was inhibited. Pseudo-self-compatibility, observed when self-pollination was carried out immediately after u.v. irradiation, was due to incompatible pollen tube elongation in a transmitting tissue devoid of apoplastic peroxidases and hindered in the rejection mechanism. However, pseudo-self-compatible pollen tube growth was not accompanied by the dramatic changes in transmitting tissue ultrastructure observed after compatible cross-pollination. The data indicate that, even if incompatible pollen tubes are not ‘rejected’, they are still ‘recognized’ and hindered in their absorption of cellular reserves from the transmitting tissue.
Polarity of endogenous and exogenous glycosyl-phosphatidylinositol-anchored membrane proteins in madin-darby canine kidney cells
Authors: Wilson Jean M. , Fasel Nicolas , Kraehenbuhl Jean-Pierre 
Published: April 2021

ABSTRACT
Madin-Darby canine kidney cells (MDCK) were transfected with a cDNA encoding the glycosyl-phosphatidylinositol (GPD-anchored protein mouse Thy-1 in order to study the steady-state surface distribution of exogenous and endogenous GPI-linked proteins. Immunofluorescence of transfected cells grown on collagen-coated coverslips showed that expression of Thy-1 was variable throughout the epithelium, with some cells expressing large amounts of Thy-1 adjacent to very faintly staining cells. Selective surface iodination of cells grown on collagen-coated or uncoated transwell filters followed by immunoprecipitation of Thy-1 demonstrated that all the Thy-1 was present exclusively in the apical plasma membrane. Although cells grown on uncoated filters had much smaller amounts of Thy-1, it was consistently localized on the apical surfaces. Immunofluorescent localization of Thy-1 on 1 pm frozen sections of filter-grown cells demonstrated that all the Thy-1 was on the apical surface and there was no detectable intracellular pool. Phosphatidylinositolrspecific phospholipase C digestion of intact iodinated monolayers released Thy-1 only into the apical medium, indicating that Thy-1 was processed normally in transfected cells and was anchored by a GPI-tail. In agreement with previous findings, endogenous GPI-linked proteins were found only on the apical plasma membrane. These results suggest that there is a common mechanism for sorting and targeting of GPI-linked proteins in polarized epithelial cells.
Commentary How mobile are active RNA polymerases?
Authors: Cook P. R. 
Published: April 2021

ABSTRACT
The photographs of ‘genes in action’ taken by Miller et al. (1970) are some of the most evocative in molecular biology. When bacteria are burst osmotically to spread their DNA, RNA polymerases can be seen frozen in the act of transcription as they processed along the template; the resulting nascent transcripts are covered with ribosomes, which are also caught in the synthetic act. These beautiful images adorn standard texts and we are all familiar with the model for transcription that they apparently confirm so powerfully. The model underlies our terminology - the ‘processivity’ of polymerases, nuclear ‘run-ons’, ‘upstream’ and ‘downstream’. But this model is usually a two-dimensional one. I will argue that recent data on the three-dimensional organisation of DNA ill-fit this accepted model and can be accommodated by an alternative model derived from studies on eukaryotes. The essential element of the alternative is the immobilisation of the polymerase so that the DNA moves past the fixed polymerase, rather than vice versa.