bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental analysis of the reproduction of spindle poles
Authors: Sluder Greenfield , Begg David A. 
Published: April 2021

ABSTRACT
We have investigated the functional properties of the mechanisms that control the reproduction of spindle poles in fertilized sea-urchin eggs. By prolonging mitosis by three independent means, we show that a spindle pole can split during mitosis into two functional poles of normal appearance. However, these poles have only half the normal reproductive capacity; each daughter cell that receives a split pole, always forms a monopolar spindle at the next division. Each monopolar spindle appears to be exactly half of a spindle because two of them can come together to form a functional bipolar spindle of normal appearance. The poles of such spindles show normal reproduction in subsequent divisions.
By following the development of individual cells with monopolar spindles, we show that such a cell can stay in mitosis longer than normal, and the single pole splits into two asters, which move apart to give a functional bipolar spindle. The poles of such a spindle have only half the normal reproductive capacity, because the two daughters of the cell always form monopolar spindles at the next mitosis. This novel cycle of development is often repeated. The occurrence of such phenomena does not depend upon the method used to induce monopolar spindles. These results show that each normal pole has two polar determinants. The results also demonstrate that the reproduction of spindle poles consists of three distinct events: splitting of the polar determinants, physical separation of the two determinants, and duplication of the determinants to return the pole to a duplex state. Splitting and duplication are distinct events because they can be experimentally put out of phase with each other for several cell cycles.
Intracellular antigens associated with the cytoplasmic surface of phagolysosomes
Authors: Vaux David J. T. , Gordon Siamon 
Published: April 2021

ABSTRACT
Monoclonal antibodies were prepared to study the cytoplasmic face of latex phagolysosomes isolated from thioglycollate-elicited mouse peritoneal macrophages. Phagolysosomes obtained by sucrose flotation contained latent β-glucuronidase activity and tightly associated cellular proteins and glycoproteins. Fluorescence-activated cell sorter analysis, scanning and transmission electron microscopy showed that the particle preparation contained &gt; 98% monomers and dimers, invested with a smooth layer of membrane and minimally contaminated with cytoplasmic adhesions. Sera from immunized rats bound preferentially to isolated phagolysosomes rather than intact cells and monoclonal antibodies PL-1 and PL-4 were isolated on this basis. Indirect fluorescent, radio- and peroxidase immunobinding assays with intact and methanol-permeabilized cells confirmed that antigens PL-1 and PL-4 were exclusively intracellular and that well-washed phagolysosomes bound both antibodies. These antigens were found in a variety of cells from several species and in macrophages not fed latex. Although the PL-1 antigen could not be immunoprecipitated, intracellular staining was characteristic of intermediate filament distribution, that is, it was in the form of a fine intersecting network, which collapsed, reversibly, in a rim round the nucleus upon treatment with colcemid. The staining pattern was undetectable in cells 1 h after adherence to a substratum, but gradually appeared after 6–12 h. The PL-4 antibody has been shown elsewhere to define a Ca2+-binding protein of approximately 20000 molecular weight, which is phosphorylated during phagocytosis. This antibody stained stress fibres and revealed a widespread punctate distribution of antigen within cells at all stages after adhesion. The nature of the association between these intracellular antigens and phagolysosomes and their possible role in phagocytosis are not known.
Microtubules in immature oocytes of Xenopus laevis
Authors: Heidemann Steven R. , Hamborg Marlyn A. , Balasz Jay E. , Lindley Steven 
Published: April 2021

ABSTRACT
Previous work indicated that immature oocytes of Xenopus were incapable of assembling microtubules but that competence was achieved during maturation. We report here that small numbers of microtubules do exist in immature oocytes. Consistent with this finding, ultrastructural observations indicate that brain microtubules injected into immature oocytes persist in large numbers for at least 30 min. We report that the tubulin dimers of mature and immature oocytes are equally capable of assembling with brain tubulin in vitro. We confirmed previous results that injection of taxol into immature oocytes has no effect when assayed by light microscopy. However, ultrastructural observations suggest that some microtubule assembly is stimulated by taxol. We tested for the ability of immature oocytes to elongate microtubules from ‘seeds’ by injecting deciliated pellicles of Telrahymena. No elongation was observed either by light or electron microscopic observation. We conclude that the immature oocyte is capable of very limited microtubule assembly and that a marked increase in assembly competence occurs during maturation. Our data suggest that the change in assembly competence during maturation is due to the release, activation or synthesis of a stimulatory co-factor.
Regulation of ciliary reversal in triton-extracted Paramecium by calcium and cyclic adenosine monophosphate
Authors: Nakaoka Yasuo , Ooi Hideyuki 
Published: April 2021

ABSTRACT
A Triton-extracted model of Paramecium swims forwards when the Ca2+ concentration in the reactivation medium containing ATP is below 10−6M and swims backwards when Ca2+ concentration is above 10−6M. We found that cAMP (adenosine 3’ :5’-cyclic monophosphoric acid) inhibited Ca-induced backward swimming of the model and caused forward swimming even when the [Ca2+] was above 10−6M. This effect of cAMP was abolished by an inhibitor of cAMP-dependent protein kinase. In order to study the possible role of phosphorylation in the regulation of ciliary orientation, ATP in the reactivation medium was replaced by an ATP analogue, ARPγS (adenosine 5’-O-3-thiotriphosphate), which irreversibly thiophosphorylates proteins. In ATPγS medium, the model ceased both swimming and ciliary beating, but the orientation of cilia was dependent on [Ca2+]. At low [Ca2+], cilia were perpendicular to the cell surface and, with increase in [Ca2+], their orientation gradually changed towards the cell anterior. Such a change in ciliary orientation corresponds roughly to the change in the swimming direction observed in ATP medium. The ciliary orientation towards the anterior of the cell in ATPγS medium at high [Ca2+] was maintained when [Ca2+] was decreased. In contrast, in ATP medium, the swimming direction was reversibly changed with changes in [Ca2+]. These results suggest that the ciliary orientation is regulated not only by Ca2+ but also by cAMP, probably via protein phosphorylation.
An epithelial scatter factor released by embryo fibroblasts
Authors: Stoker Michael , Perryman Marion 
Published: April 2021

ABSTRACT
Medium conditioned by human embryo fibroblasts breaks structural junctions between several types of epithelial cells, leading to separation and scattering of the cells. An assay developed in MDCK cells shows activity up to a dilution of at least 1 in 64, equivalent to less than 100 ng of total protein. The activity is non-dialysable, heat-labile, and sensitive to trypsin, and it is assumed to be due to one or more proteins. After addition of the factor, separation of MDCK cells begins in about 15 min and is complete in 10 h. It increases migration of MDCK cells into wounds, and causes collapse of domes. Locomotion of isolated cells is not enhanced, but cell shape is affected by local membrane movement. Under the culture conditions used the factor, or an associated protein, causes a weak inhibition of cell growth without cytotoxic activity. The scattering factor has not been purified, nor has a physiological role been identified, but it might be concerned in the mobilization of epithelial cells.
The cell cycle of symbiotic Chlorella II. the effect of continuous darkness
Authors: Mcauley P. J. 
Published: April 2021

ABSTRACT
When green hydra were grown in continuous darkness the mean cell size of their symbiotic algae was smaller than when grown in light and numbers of algae per digestive cell were reduced. The former was due to a reduction in size at which the algae divided, and the latter to a loss of synchrony of algal mitosis with that of digestive cells after transfer to darkness. Eventually, algal mitosis regained synchrony with that of digestive cells. Division synchrony was not lost in reinfected hydra (with lower than normal numbers of algae per cell) transferred to darkness; this, and the observation that synchrony in normal animals transferred to darkness was regained when algal numbers per cell had fallen to a new, lower level, suggested that the initial inhibition of algal mitosis was due to competition for a limited supply of heterotrophically required metabolites.
When dark-grown hydra were returned to light there was no delay in algal division and a steady increase in the size of dividing cells, suggesting that the smaller division size in darkness was not due simply to the critical size for division being set at a lower value. In light, algal division size varied with frequency of host feeding, but this had less effect on algal division size in darkness.
It is suggested that the critical cell size that algae must attain before being able to complete the cell cycle is the same in light and darkness, but in light mitosis is restricted by some exogenous factor so that algae grow beyond the critical size without dividing. In darkness both algal cell growth and division are dependent on exogenously supplied metabolites, and cell growth rather than the division factor is limiting. The precise nature of the restriction on algal division remains unknown.
The origin of prespore vacuoles in Dictyostelium discoideum cells as analysed by electron-microscopic immunocytochemistry and radioautography
Authors: Takemoto Keiko , Yamamoto Akitsugu , Takeuchi Ikuo 
Published: April 2021

ABSTRACT
Prespore vacuoles (PSVs) are specifically formed in prespore cells of the cellular slime moulds and contain spore-specific antigens. We have examined the processes of PSV formation in Dictyostelium discoideum, using both the methods of immunoelectron microscopy with antispore serum and electron-microscopic radioautography with [3H]fucose, which is specifically incorporated into prespore cells. When prespore cells begin to differentiate at the late aggregation stages the Golgi apparatus, consisting of stacked cisternae and numerous vesicles, becomes conspicuous. Vesicles and flat sacs containing fibrous and membranous materials, respectively, are derived from Golgi cisternae. Spore antigens are found in these structures as well as in immature and mature PSVs. Fucose is incorporated into the same structures. When prespore differentiation is completed, the Golgi cisternae almost disappear and both antigens and fucose are localized in mature PSVs. The Golgi apparatus is scarcely observable in prestalk cells. Moreover, a similar pattern of changes in the Golgi apparatus and related structures occurs during the re-differentiation of prespore cells within prestalk isolates. It is concluded from these findings that PSVs are derived from the Golgi apparatus, the development of which is closely related to the differentiation of prespore cells.
Morphology and locomotion of individual epithelial cells in culture
Authors: Brown R. M. , Middleton C. A. 
Published: April 2021

ABSTRACT
The behaviour in culture of epithelial cells derived from chick embryo pigmented retina epithelium (PRE), corneal epithelium (CE) and epidermis has been studied using time-lapse cinemicrography. The analysis concentrated on the morphology and movement of individual isolated cells, lacking contacts with other cells, during a 24 h period starting 1–3 h after the cells were plated out in primary cultures.
Isolated cells from all three sources could change morphology and reversibly exhibited either a poorly spread or a well-spread morphology. While poorly spread, the different cell types all appeared similar and all blebbed vigorously. In contrast, while well spread, the cells did not bleb significantly but there were other differences between them. Well-spread CE cells were always polarized by the presence of a dominant leading lamella but well-spread PRE cells were always unpolarized. Well-spread epidermal cells exhibited both a polarized and an unpolarized morphology.
The tendency of individual isolated cells to change morphology varied with cell type. PRE cells were the most stable. Nearly 80% of them retained the same morphology throughout the period of analysis and only 1% of them showed three or more changes in morphology during this period. In contrast, 22% of CE cells and 37% of epidermal cells showed three or more changes in morphology during the period of observation. Isolated cells of all three types spent a greater proportion of the time exhibiting a poorly spread morphology than they spent exhibiting any alternative well-spread morphology.
The analysis revealed a relationship between the morphology of isolated cells and the speed of their locomotion. Only cells with a well-spread polarized morphology showed significant movement. CE and epidermal cells with this morphology moved three to four times faster than their counterparts with a poorly spread morphology or, in the case of epidermal cells, with a well-spread but unpolarized morphology. Actively moving PRE cells were not seen and this correlates with the absence of cells with a well-spread polarized morphology from cultures of this type.
These findings are discussed in the light of similar investigations of cell behaviour in other epithelial cell types and fibroblasts.
Effects of hyaluronate and hyaluronate binding proteins on cell motile and contact behaviour
Authors: Turley E. A. , Bowman P. , Kytryk M. A. 
Published: April 2021

ABSTRACT
The effects of hyaluronate on the morphology, motile and social behaviour of embryonic chick heart fibroblasts were examined in the presence or absence of hyaluronate binding proteins (HABP). HABP were inserted onto fibroblasts after treating cells with 0·2M-urea. Such treatment increased the binding of [125I]HABP to cell monolayers: at saturation, binding was increased threefold compared to untreated monolayers. Generally, the distribution of added HABP was similar to that of endogenous HABP as detected by immunochemistry. [3H] hyaluronate bound to HABP-treated monolayers in amounts that were proportional to the amount of HABP added. HABP alone reduced cell motility, decreased cell underlapping (measured as a nuclear overlap ratio) and promoted cell spreading. Hyaluronate added by itself had no significant effect on cell behaviour. However, in the presence of HABP, hyaluronate increased cell motility, reduced cell spreading, promoted the appearance of surface blebbing and ruffles, and significantly increased the nuclear overlap ratio. These biological effects were proportional to the amounts of hyaluronate and HABP that bound to heart fibroblasts. Fibronectin, bovine serum albumin or sulphated glycosaminoglycans added together with HABP did not mimic the effects of hyaluronate and had little effect additional to HABP alone. The role of HABP as a putative cell binding molecule for hyaluronate and the relationship of hyaluronate to cell social and motile behaviour are discussed in the light of these findings.
An investigation of the centriole cycle using 3t3 and cho cells
Authors: Alvey P. L. 
Published: April 2021

ABSTRACT
An investigation of the centriole cycle was based on serial-section electron microscopy of the centrioles of 790 3T3 cells and 40 CHO cells (incomplete sets of sections were excluded from the analysis). Time-course studies indicated that procentrioles first appear 4 h after the start of S-phase; evidence was obtained to suggest that they elongate progressively during the subsequent stages of the cell cycle, and that they start to separate from their parents during mitosis. An association of the structural features of the centriole cycle with the Two-transition Model of the Cell Cycle was ruled out by the finding of two centrioles in most quiescent cells, and the appearance of procentrioles in S-phase in transiently stimulated cells.
Effect of Cerophylr growth medium on exocytosis in Tetrahymena thermophila
Authors: Pesciotta Donna M. , Satir Birgit H. 
Published: April 2021

ABSTRACT
Culturing the ciliate Tetrahymena thermophila in CerophylR has provided an opportunity for studying the assembly and/or synthesis of the intramembrane particle array, the rosette, which marks the site of exocytosis in these cells. Cultures grown in this medium cease cell division after only 12 h and enter ‘stationary phase’ earlier (12 h of growth) relative to growth in standard medium (proteose peptone). In addition, the cell changes from the normally observed pear-shaped body to a thinner more ellipsoid form. Despite the initial similarities to starving cells, several differences are observed in the CerophylR-grown cells. One is that cell size remains constant for at least 72 h in contrast to starved cells. Secondly, in spite of this block in cell division, results from freeze-fracture replicas of the cell membrane of these cells show that they continue to assemble rosettes, the number of which increases approximately six times, from 0·34 rosette/^m2 to 2-1 rosettes/μm2. Addition of the protein synthesis inhibitor, cycloheximide (6 h exposure), during growth in CerophylR shows that 70% of rosettes can be assembled, despite the blockage of translation, by using pre-existing component(s) from a pool. The remaining 30% must involve de novo synthesis of one or more components; this percentage can be increased with longer exposure to the drug. Thirdly, an apparent increase in the number of mucocysts is observed by thin-section electron microscopy. At first (12–24 h) only docked mucocysts seem to accumulate in the cell. However, by 36 h a considerable increase seems to have taken place, particularly in the number of mucocysts located in the cytoplasm. In the cycloheximide-treated cells this increase in mucocysts begins to be blocked after 6 h of exposure to the drug. These observations are in agreement with the results obtained from the freeze-fracture data on the concomitant increase in number of rosettes. This system therefore offers the first possibility of exploring the biosynthesis of these components.
Cell hybridization and cell agglutination: I. enhancement of cell hybridization by lectins
Authors: Matsuya Yutaka , Yamane Isao 
Published: April 2021

ABSTRACT
A great increase in hybridization frequency of cultured rodent cells was obtained when conventional cell fusion using 50% polyethylene glycol (PEG) was combined with a cell agglutination produced by plant lectins. The rate of appearance of hybrid colonies was found to be correlated with the extent of cell agglutination by lectin, as well as with cell fusion induced by subsequent PEG treatment. Phytohemagglutinin (PHA), wheat germ agglutinin, Wistaria floribunda agglutinin and concanavalin A were all active ; the most effective was PHA. When parental cells in a monolayer were treated with PHA followed by PEG, the resuting hybridization frequency was very low because of markedly decreased viability, whereas the same cells in suspension yielded hybrid colonies at a higher rate.
These results suggest that the enhancement of hybridization by PHA/PEG treatment was brought about by the ability óf lectin to agglutinate cells.
Genesis of cilia and microvilli of rat nasal epithelia during pre-natal development: II. olfactory epithelium, a morphometric analysis
Authors: Menco Bert Ph. M. , Farbman Albert I. 
Published: April 2021

ABSTRACT
Rat foetuses from intra-uterine days E14 through E22 (day before parturition) and adults were used for a quantitative scanning electron-microscopic examination of ciliogenesis in olfactory receptor cells and microvillogenesis in olfactory supporting cells. Four developmental stages in olfactory ciliogenesis can be discerned. Two of these are characterized by the presence of primary cilia only, the other two concern outgrowth in number and length of secondary cilia. (1) Primary cilia on undifferentiated cells; this stage occurs up to E14. (2) Primary cilia on differentiating olfactory receptor and also olfactory supporting cells. This stage begins at E14 and lasts, for the olfactory receptor cells, at least up to E22. On the supporting cells primary cilia are rarely observed after E18. Virtually all primary cilia are about 1 gm long. Up to E21 dendritic endings with primary cilia occur more frequently than those with any other number of cilia; all endings have a transitional stage in which they bear primary cilia only. (3) Secondary olfactory cilia increase in number. From E16 onwards the cells become multiciliated. Beginning at this stage and continuing up to E22 an average of one cilium per day is added to the endings. At E22 the average number of cilia observed per ending is about 70% of that in adults; more than 90% of the endings are multiciliated. From E15 to E22 the exchange rate between receptor cells with only primary cilia and multiciliated cells is about 0·5 × 106 cells/cm2 per day. When considered in the light of electrophysiological data on developing rats, our data suggest that when the cells have just primary cilia, they may respond indiscriminately to all odorants, whereas multiciliated cells display odorant specificity. (4) Secondary olfactory cilia increase in length. From E14 to E19 and over the whole population of receptor cells the cilia grow at an average rate of about 0·5 μm/day. Proximal parts of olfactory cilia are longer than primary cilia; olfactory cilia begin to taper in increasing numbers around E18. At E19 the receptive membrane surface, i.e. regions of the cells facing the nasal lumen, of individual cells is about 8%, and the increase in epithelial surface due to sprouting of cilia is 5% of such values in adult animals. Concomitant with the onset of tapering of olfactory cilia, i.e. around E18, microvilli of supporting cells show a spurt in growth from about 0·4 μm to about 1·3 μm. Unlike olfactory cilia they show no growth, on average, after E19. We make a case for the involvement of modified primary cilia (insects) and secondary cilia (vertebrates) in chemosensory reception.
Direct transfer of β-glucuronidase from mouse macrophages to other types of cell
Authors: Dean M. F. , Mcnamara A. , Jenne B. M. 
Published: April 2021

ABSTRACT
Rabbit polyclonal antibodies were raised against β-glucuronidase purified from mouse liver. This antiserum immunoprecipitated the β-glucuronidase secreted by mouse fibroblasts but did not cross-react with the same enzyme isolated from human tissue. The β-glucuronidase present in mouse 3T3 fibroblasts and mouse peritoneal macrophages was clearly identified by indirect immunofluorescence, using the antiserum and an FITC-conjugated second antibody, while human fibroblasts with normal levels of β-glucuronidase activity did not fluoresce when tested with the same reagents. A range of human fibroblasts, human neuroblastoma and rat glioma cells did not fluoresce when incubated with the antibody but did fluoresce after they had been co-cultured for 24 h with mouse macrophages, showing that mouse β-glucuronidase had been transferred from adherent macrophages into adjacent recipient cells. Transfer took place even when receptor-mediated endocytosis was blocked with a suitable competitive ligand, the transferred enzyme being visible mainly as a bright punctate fluorescence with a lysosome-like distribution. Macrophages thus have the potential to act as donors of lysosomal enzymes to a wide range of recipient cells and to transfer enzymes to them during direct cell-to-cell contact.