bluuebunny/crossref_metadata_2025_split huggingface dataset:
The rearrangement of cytoskeletal systems in epithelial cells accompanying the transition from a stationary to a motile state at the start of epithelial spreading
Authors: Takeuchi Shigeo 
Published: April 2021

ABSTRACT
The changes in the alignment of F-actin bundles in epithelial cells were studied, mainly using NBD-phallacidin, as the isolated corneal epithelium started to spread along the surface of Millipore filter.
The epithelial cells at the margin were found to make the transition from a stationary to a motile state in two steps: first, from polygonal cells, in which F-actin was deposited along the cell border, to hemispherical cells, in which F-actin was distributed homogeneously along the inner cell surface; and second, from the hemispherical cells to spread cells in which F-actin bundles ran radially or in parallel to each other through the leading lamella from a cytocentre to the edges, as in fibroblastic cells. During the second step, an amorphous mass of F-actin was transiently accumulated at the distal end in the half-extended lamella and structured into bundles during development of the lamella. Since this proceeded only on substrata to which marginal cells could make contact firmly enough to enable the cells to extend, it was concluded that F-actin bundles were aligned within extending lamellae in relation to the tension exerted by the lamellae, and might be associated with other components to be microfilaments.
How are invertebrate epithelia made tight?
Authors: Skaer H. le B. , Maddrell S. H. P. 
Published: April 2021

ABSTRACT
Many compartments in the animal body are delineated and separated by epithelial sheets of cells. Such epithelia are described as leaky or tight depending on the extent to which the compartments on either side of them appear to be kept distinct. It has been assumed that a‘tight’ epithelium has intercellular junctions that completely seal the paracellular pathway. Indeed, in vertebrates, some tight junctions have been shown to be virtually impenetrable. However, in invertebrate tight epithelia, there is controversy over whether the paracellular pathway is sealed by a vertebrate type of tight junction or whether the septate junction, a special invertebrate junction not seen in vertebrate tissues, can fulfil the same function.
Refractile bodies (R bodies) from the macronuclear killer particle Caedibacter caryophila
Authors: Schmidt Helmut J. , Pond Finn R. , Görtz Hans-Dieter 
Published: April 2021

ABSTRACT
The macronuclei of certain isolates of Paramecium caudatum are inhabited by the bacterial endonucleobiont Caedibacter caryophila. These symbionts confer upon host paramecia a killer trait, which is clearly associated with the presence of R bodies in the endosymbionts.
R bodies are unique inclusion bodies of caedi-bacteria (which are obligate endosymbionts of Paramecium) and of certain free-living bacteria of the genus Pseudomonas. They have been grouped into four classes on the basis of morphology and behaviour. A fifth R body type, introduced in this study, is named the Cc R body to indicate its presence in bright particles of Caedibacter caryophila. Type Cc R bodies are approximately 0–8 pm in width and diameter. They unroll in a telescopic fashion from the inside and are distinguished by a tapered inner and a blunt outer terminus. They are further associated with icosahedral bacteriophages, which stick to the inner terminus. Cc R body proteins show a ladder-like pattern of stained bands on polyacrylamide gels and exhibit a certain degree of antigenic cross-reactivity with type 51 R bodies.
Interaction of plasma membrane-associated filaments and H-2 histocompatibility antigens before and after induced patching and capping
Authors: Feltkamp Constance A. , Spiele Hermina , Roos Ed 
Published: April 2021

ABSTRACT
The interaction of H-2 antigens and plasma membrane-associated filaments was studied on dry-cleaved preparations of immunogold-labelled lymphoma cells. In prefixed cells, the plasma membrane-associated network was isotropic without any prevailing direction of the filaments, and the gold-labelled H-2 antigens were preferentially localized over or at a very short distance from membrane-associated filaments. Incubation of unfixed cells with anti-H-2 antibodies followed by fixation and incubation with anti-Ig, did not induce detectable redistribution of H-2 antigens or of the filament network. Notwithstanding this apparent absence of rearrangement of H-2 antigens and filaments, a detergent-resistant linkage to the cytoskeleton was induced. Before immune incubations, virtually all H-2 antigens were solu-bilized by extraction with Triton X-100, while after incubation with anti-H-2 antibodies about 50 % of the H-2 antigens were linked to the Triton X-100-insoluble cytoskeleton. Sequential addition of anti-H-2 and anti-Ig antibodies to unfixed cells induced formation of patches and caps of H-2 antigens. Under these conditions, the majority of the H-2 antigens became linked to the detergent-resistant cytoskeleton. Redistribution into patches and caps was often accompanied by a local rearrangement of the isotropic network into bundles of parallel filaments immediately adjacent to the plasma membrane. Patches were seen to overly both isotropic networks and these parallel filaments. Large sheets of plasma membrane overlying parallel filaments were frequently devoid of gold-labelled H-2 antigens and coated pits, and thus most probably represented areas away from caps. This observation suggests that capping is accompanied by a rearrangement of filaments close to the membrane.
Sex-chromosome anaphase movements in crane-fly spermatocytes are coordinated: Ultraviolet microbeam irradiation of one kinetochore of one sex chromosome blocks the movements of both sex chromosomes
Authors: Swedak Julia A. M. , Forer Arthur 
Published: April 2021

ABSTRACT
Sex chromosomes in crane-fly spermatocytes move polewards at anaphase after the autosomes have reached the poles. In Nephrotoma abbreviate the sex chromosomes are 8 μm long by 3·5 μm wide and have two orientations when they move: the long axis of the sex chromosome is either perpendicular or parallel to the spindle axis. We assume (1) that when a sex chromosome is perpendicular to the spindle axis it has a chromosomal spindle fibre to each pole, one from each kinetochore, as in other species; and (2) that when a sex chromosome is parallel to the spindle axis each kinetochore has spindle fibres to both poles, i.e. that the latter sex chromosomes are maloriented.
We irradiated one kinetochore of one sex chromosome using an ultraviolet microbeam. When both sex chromosomes were normally oriented, irradiation of a single kinetochore permanently blocked movement of both sex chromosomes. Irradiation of non-kinetochore chromosomal regions or of spindle fibres did not block movement, or blocked movement only temporarily. We argue that ultraviolet irradiation of one kinetochore blocks movement of both sex chromosomes because of effects on a ‘signal’ system. The results were different when one sex chromosome was maloriented. Irradiation of one kinetochore of a maloriented sex chromosome did not block motion of either sex chromosome. On the other hand, irradiation of one kinetochore of a normally oriented sex chromosome permanently blocked motion of both that sex chromosome and the maloriented sex chromosome. We argue that for the signal system to allow the sex chromosomes to move to the pole each sex chromosome must have one spindle fibre to each pole.
Mapping cell–glass contacts of Dictyostelium amoebae by total internal reflection aqueous fluorescence overcomes a basic ambiguity of interference reflection microscopy
Authors: Todd I. , Mellor J. S. , Gingell D. 
Published: April 2021

ABSTRACT
The widespread ability of eukaryotic cells to produce thin cytoplasmic sheets or lamellae 100–200 nm thick can give rise to uncertainties in the interpretation of interference reflection microscopy (IRM) images when cell–substratum topography is the key interest. If allowed to spread upon a poly-L-lysine-coated surface, Dictyostelium discoideum amoebae typically form ultrathin lamellae of ≈100nm thickness by cytoplasmic retraction. Whereas the cell body is grey, the lamellae appear very dark under IRM optics. These dark areas could be misinterpreted as stemming from a closer cell–substratum apposition beneath the lamellae than the cell body. This ambiguity can be avoided if the technique of total internal reflection aqueous fluorescence (TIRAF) is used in conjunction with a high refractive index glass (n = 1·83) as substratum. Contributions to the image generated by thin cytoplasm and also variable cytoplasmic refractive index are thereby minimized due to the extremely short range of the ‘illuminating’ evanescent wave. From our comparative IRM and TIRAF study of the ultrathin lamellae of Dictyostelium amoebae it is concluded that the cell–glass gap is relatively uniform beneath the entire cell. We briefly discuss the sensitivity of several cell types to TIRAF, the generation of ultrathin lamellae and the nature of the cell–glass gap.
Localization of platelet antigens and fibrinogen on osteoclasts
Authors: Athanasou N. A. , Quinn J. , Heryet A. , O’D. Mcgee J. 
Published: April 2021

ABSTRACT
The antigenic phenotype of the human osteoclast, which is known to be derived from a circulating mononuclear precursor cell of haemopoietic origin, is controversial. Recent studies have shown that macrophage as well as megakaryocyte/platelet antigens are expressed by osteoclasts. In this study, we have sought to define, by immunohistochemistry, the nature and possible function of platelet antigens expressed by human osteoclasts in foetal and adult bone specimens. Monoclonal antibodies to platelet glycoprotein IIIa (gpllla) and CD9 antibodies stained osteoclasts in all bone specimens examined. Fibrinogen was also localized to the osteoclast membrane in foetal bone imprints. In addition, we found that CD9 and gpllla antibodies reacted weakly with monocytes in buffy coat smears. Antibodies to factor 8 and glycoproteins lb and IIb/IIIa did not react with osteoclasts. These results show that osteoclasts, monocytes, macrophages, megakaryocytes and platelets possess common antigens and that fibrinogen is present on the surface of osteoclasts. By analogy with platelets, CD9 and gpllla may play a role in fibrinogen binding by osteoclasts. Possible mechanisms by which platelet antigens and fibrinogen binding could affect osteoclast function are proposed.
Distribution of pericentriolar material in multipolar spindles induced by colcemid treatment in chinese hamster ovary cells
Authors: Sellitto Caterina , Kuriyama Ryoko 
Published: April 2021

ABSTRACT
Mitotic Chinese hamster ovary cells were obtained by treatment with microtubule drugs under various conditions, and the shape of spindles was analysed by phase-contrast microscopy of isolated spindles, and by indirect immunofluorescence staining of whole mitotic cells with anti-tubulin antibody. Bipolarity of spindles was maintained after treatment with 0·05 μM of colcemid for 3·5 h, but increased exposure to higher concentrations (0·32 μM) and for longer durations (5·5 h) led to a marked rise in multipolar spindles. Nocodazole treatment, on the other hand, failed to show a multiplicity of spindle poles even at 3·3 μM. Each pole of a multipolar spindle was associated with pericentriolar material, as shown by staining with an autoimmune serum specific for pericentriolar material. The number of locations with free pericentriolar material capable of polymerizing microtubules in vitro also increased with increasing numbers of spindle poles, suggesting that dispersion of the pericentriolar material resulted in the production of many microtubule-nucleating sites in multipolar spindles. The different efficiencies of recovery from different drugs, which have been known to be quite variable, may be partly due to the different extent of dispersion of the pericentriolar material.
Effect of seeding density on stability of the differentiated phenotype of pig articular chondrocytes in culture
Authors: Watt Fiona M. 
Published: April 2021

ABSTRACT
Articular chondrocytes are known to be pheno-typically unstable in culture. One condition that has been reported to suppress dedifferentiation is cultivation at high density on tissue-culture plasΛtic. The aim of the experiments described here was to study the effect of seeding density on chondrocyte proliferation and 35SO4 incorporΛation, and on the types of collagen and proteoglyΛcan synthesized. I found that cells seeded at low or high density reached the same final density at confluence, and that 35SO4 incorporation, while initially higher (per cell) in high-density cultures, fell under both conditions, reaching the same low level after 3 weeks. The proportion of cells expressing keratan sulphate fell in low-but not high-density cultures and the decline was not prevented by inhibition of cell division. In all the cultures cells expressing keratan sulphate tended to have a rounded morphology. After 21 days inculture, chondrocytes grown at high density exΛpressed predominantly large proteoglycans that aggregated with hyaluronic acid, whereas in low-density cultures a smaller, non-aggregating form was also present. By 21 days in culture cells at both high and low density were expressing type I collagen, although the high-density cells also had an extensive extracellular matrix of type II colΛlagen. These observations support the conclusion that high seeding density stabilizes the chondroΛcyte phenotype to a greater extent than low seedΛing density. They also suggest that enhanced dedifferentiation at low density may be due to cell spreading, rather than to selective proliferation of a phenotypically unstable subpopulation of cells.
The effect of co2 on the timing of cell cycle events in fission yeast Schizosaccharomyces pombe
Authors: Novák B. , Halbauer J. , László E. 
Published: April 2021

ABSTRACT
The effect of CO2 removal on the cell cycle phases of Schizosaccharomyces pombe has been examined in minimal, aspartate-containing and complete medium. The removal of CO2 shortened the G2 phase of the cell cycle and arrested the cells in G1 phase in minimal medium. The Gi block caused by C02 deprivation was demonstrated by transition-point and flow-cytometry analyses. The slow-down of anapleurotic CO2 fixation might be responsible for this effect, as aspartic acid could abolish the G1 block. The shortening of G2 phase in the wild-type cells was observed in every medium irrespective of whether the growth rate was changed or not. The experiments in which growth rate was not changed by CO2 shift-down suggest that this CO2 effect can be independent from its action on CO2-fixing steps in metabolism.
Therefore we propose that CO2 inhibits mitosis in fission yeast and we explain the proportionality between growth rate and cell size at mitosis found by Fantes & Nurse by this CO2 inhibition. The larger CO2 production in fast-growing cells leads to a higher CO2 concentration, which could exert a stronger inhibition of mitosis. A wee mutant, which has lost its mitotic size control, also shows the G1 block after CO2 deprivation, but its mitosis is insensitive to CO2. Comparing the respiration of wee and wild-type cells we conclude that CO2 inhibits the citric acid cycle in the wild type. The consequence of these results in the regulation of fission yeast cell cycle is discussed.
Changes in striated muscle fibres during contraction and growth with particular reference to myofibril splitting
Authors: Goldspink G. 
Published: April 2021

ABSTRACT
Ultrastructural measurements were carried out on the mouse biceps brachii and soleus muscles fixed at different states of contraction and stretch. At a sarcomere length of 2·7–2·9 μm the more peripheral actin filaments ran slightly obliquely from the Z-disk to the A-band. This is due to a mismatch between the rhombic actin lattice at the Z-disk and the hexagonal lattice at the M-line. For a perfect transformation of a rhombic lattice into a hexagonal lattice the ratio of the lattice spacings has to be 1:1·51. However, at this sarcomere length the ratio is about 1:2·0 (Z:M). During contraction the angle of the peripheral actin filaments remains approxi-mately the same because the expansion of the M lattice is compensated for, partly by an increase in the Z-lattice spacing and partly by the bowing of the peripheral myosin filaments. When the sarcomeres are stretched beyond 3·0 μm the myosin filaments straighten out and the Z:M ratio decreases. The ratio of 1:1·51 is almost attained when there is no overlap of the actin and myosin filaments.
Ultrastructural measurements were also carried out on biceps brachii muscles of different ages. The lattice spacings for a standard sarcomere length did not change during the post-natal growth period. The amount of myofibrillar material and sarcoplasmic reticulum plus transverse tubular system were estimated using linear analysis for muscles at 3 different stages of growth. It was found that the myofibrillar cross-sectional area in an individual muscle fibre may increase 40-fold during growth and that the transverse tubular and sarcoplasmic reticulum systems increase at about the same rate.
In both the biceps brachii and the soleus muscles the myosin and actin filaments are not built into a continuous mass but they are divided into numerous discrete myofibrils. Subdivision of the myofibril mass occurs because the myofibrils split once they attain a certain size. The evidence presented in this paper supports the suggestion that the longitudinal splitting of the myofibrils occurs by the ripping of the Z-disks. When tension is rapidly developed by 2 adjacent sarco-meres a stress is produced at the centre of the Z-disk resulting from the oblique pull of the actin filaments. This causes some of the Z-disk filaments to rip and the rip then extends across the disk with the direction of the weave of the lattice. Evidence for the mechanism includes electron-micrographs showing Z-disks that are apparently just commencing to split; in these cases a hole can be seen in the centre of the disk. A model experiment is described which demonstrates the importance of the rate of tension development in causing myofibril splitting. Rapid tension development produces a snatch effect which causes the Z-disk filaments to break more readily. This may explain why the myofibrils in fast muscles tend to be small and discrete whilst those in slow muscles are larger and more irregular in shape.
Pollen-wall proteins: localization, enzymic and antigenic activity during development in Gladiolus (iridaceae)
Authors: Knox R.B. 
Published: April 2021

ABSTRACT
Cytochemical methods have been used to follow the incorporation of enzymes and antigens in the cellulosic intine of the pollen grain of Gladiolus gandavensis. Acid phosphatase, esterase and ribonuclease were first detected in the developing intine during the vacuolate period, and by the end of this phase activity was present throughout the intine, especially in the area of the colpus, where this wall layer is thickened. Enzyme activity was also noted in the peripheral region of the protoplast during the period of intine growth. Succinic and NADH (reduced nicotine adeninedinucleotide) dehydrogenase activity was detected in the outer zone of the protoplast, and, at the end of pollen development, in the interbacular cavities of the exine and the pollen-coat materials, but at no time were these enzymes found in the intine.
The appearance of the antigens was traced during pollen development. Antigens were first detected in the early vacuolate period, soon after the release of the spores from the meiotic tetrads. They were found to be associated with the intine from the first deposition of poly-saccharides in this layer. As the intine thickened, so the amounts of associated antigens were found to increase, especially in the neighbourhood of the colpus.
In slurries prepared using mature pollen, enzymes and antigens were found to diffuse into the medium even with preparation times as short as 30 s. The leakage was over the whole of the exine, not only in the vicinity of the colpus; this may be related to the thinness of the exine in Gladiolus and the presence of pores in the tectum.
Electron micrographs showed the presence of vesiculate and tubular cavities in the intine, containing fibrillar or granular material. These inclusions are presumed to be the sites of the enzymes and antigens, since in a related genus, Crocus, acid phosphatase has been shown to be present in the corresponding cavities.
Gel diffusion and immunoelectrophoresis showed the presence of 4 major antigenic fractions in the leachates from mature Gladiolus pollen. Tests with the antisemm against leachates from species of the related genus, Iris, showed 1 cross-reacting fraction.
Zoospore germination in Blastocladiella emersonii: III. structural changes in relation to protein and rna synthesis
Authors: Soll D. R. , Sonneborn D. R. 
Published: April 2021

ABSTRACT
Zoospores germinate rapidly and semi-synchronously upon exposure to growth medium or an inorganic salts solution. Amino acid incorporation into protein is detected only after a characteristic lag period, the extent of which is a function of developmental, rather than absolute, time. The ‘tum-on ‘of amino acid incorporation occurs after several of the morphological events of germination have taken place -notably, retraction of the flagellum, conversion to a spheroid cell morphology, vesicle fusion with the plasma membrane, formation of the initial cell wall, and elongation of the single mitochondrion. A second group of morphological changes -release of ribosomes from the nuclear cap into the cytoplasm, appearance of multiple mitochondrial profiles, disappearance of the flagellar axoneme, and disappearance of gamma particles -takes place in the cell population during the tum-on of incorporation. Cycloheximide reversibly inhibits germination at a characteristic block point. Inhibited cells accomplish all the known morphological events of germination except the disappearance of the flagellar axoneme and the formation of the germ tube. Amino acid incorporation is inhibited to undetectable levels in growth medium and by about 80% in the inorganic salts medium. Nevertheless, the population kinetics for the morphological changes which occur in cycloheximide-inhibited cells are indistinguishable from those in untreated cells. Cycloheximide effectively enters cells prior to the characteristic block point, since the drug drastically inhibits the low level of amino acid incorporation by zoospores. ’Pools’ extractable by trichloroacetic acid (TCA) have been examined; the results do not support the possibility of extensive early protein synthesis from endogenous sources. Actinomycin D, at levels which inhibit [3H]uridine incorporation into TCA-precipitable material (nucleic acid) by over 98 %, does not affect the population kinetics of germination. The drug does not affect the lag period for amino acid incorporation. The rate of amino acid incorporation (pulse labelling) fluctuates predictably during germination. Actinomycin D only partially inhibits the first ‘round ‘of incorporation, but severely inhibits the second.
From this information, we conclude that: (a) the proteins necessary for most of the structural events of germination are preformed in the zoospore; (f&gt;) therefore, these events are controlled directly by mechanisms other than differential protein synthesis; (c) two of the known events -disappearance of the flagellar axoneme and formation of the germ tube -do appear to have a requirement for concomitant protein synthesis; (d) germination does not require de novo RNA synthesis; and (e) certain of the first proteins made during germination are evidently synthesized with preformed messages.