bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and biochemical differentiation of the mammalian small intestine during foetal development
Authors: Bailey David S. , Cook Alastair , Mcallister George , Moss Margaret , Mian Nasi 
Published: April 2021

ABSTRACT
Microscopical studies showed that initial differentiation of the guinea-pig small intestine occurs between days 35 and 55 of foetal development. Changes observed at this time include formation of villi (by day 42), elaboration of submucosal duodenal Brunner’s glands (by day 49) and the appearance of a well-developed microvillus membrane (by day 56).
Different microvillus membrane-associated hydrolases appear at different stages of foetal and postnatal development. The ‘early’ enzymes such as aminopeptidase, alkaline phosphatase and sucrase show a sharp increase and reach their maximal levels between days 35 and 50, whereas the late enzymes such as dipeptidyl peptidase IV and lactase increase gradually between days 35 and 50, and reach maximal activity between days 50 and 60.
A combination of techniques involving precipitation with Mg2 + followed by fractionation on sucrose density gradients has enabled us to prepare, for the first time, a 21-fold enriched microvillus membrane fraction from the foetal intestine.
Polypeptide analysis of this membrane fraction by sodium dodecyl sulphate/polyacrylamide gel electrophoresis showed the presence of developmentally specific polypeptides at different stages of foetal and postnatal development. Three polypeptides of molecular weights 205 000, 80 000 and 47 000 are major microvillus membrane components at the 40-day foetal stage. Two other polypeptides of molecular weights 60 000 and 131 000 are major microvillar components at 56-day and older foetal stages as well as at the 3-day neonatal stage. The adult microvillus membrane contained 112 000 and 122 000 Mr polypeptides as major components. The above results were confirmed using two-dimensional isoelectric focussing-sodium dodecyl sulphate/polyacrylamide gel electrophoretic techniques.
Dna replication and repair in Tilapia cells i. the effect of ultraviolet radiation
Authors: Yew F. H. , Chang L. M. 
Published: April 2021

ABSTRACT
The effect of ultraviolet radiation on a cell line established from the warm water fish Tilapia has been assessed by measuring the rate of DNA synthesis, excision repair, post-replication repair and cell survival. The cells tolerate ultraviolet radiation better than mammalian cells with respect to DNA synthesis, post-replication repair and cell survival. They are also efficient in excision repair, which in other fish cell lines has been found to be at a low level or absent. Their response to the inhibitors hydroxyurea and 1-β-D-arabinofuranosylcytosine is less sensitive than that of other cell lines, yet the cells seem to have very small pools of DNA precursor.
Biochemical and ultrastructural studies of human eccrine sweat glands isolated by shearing and maintained for seven days
Authors: Lee Catherine M. , Jones Christopher J. , Kealey Terence 
Published: April 2021

ABSTRACT
A new method of isolating human eccrine sweat glands by the repeated dissection of skin biopsies with scissors is described. The success of the technique is attributed to a potential line of weakness between the investing capsule and the surrounding connective tissue, which parts under shear forces. The yield is 20-50 glands per biopsy (5 cm×O·5 cm). The glands are judged to be viable by: (i) light and electron microscopy; (ii) ATP, ADP and AMP contents of 81 ·0 ± 12 ·7, 13 ·8 ± 3 ·3 and 3 ·8 ± 1 ·0pmol/gland, respectively (mean ± S.E.M.), which gave an energy charge of 0 ·90; (iii) the 28-fold rise in cyclic GMP content and the sevenfold rise in cyclic AMP content effected by treatment for 2min with 10−5 M-acetylcholine and for 10min with 10−5 M-isoprenaline, respectively; (iv) the rate of [3H]leucine uptake into protein; and (v) the concentration of Neutral Red by the collecting duct. Glands were maintained for 7 days on polycarbonate filters floating on RPMI 1640 tissue-culture medium. After this time the ATP, ADP and AMP contents were 63 ·2 ±7 ·3, 8 ·5 ± 2 ·2 and 3 ·5 ± 0 ·8 pmol/gland, respectively (mean ±S.E.M.), which gave an energy charge of 0’90. During maintenance a dilatation of the intercellular spaces developed in both secretory coil and collecting duct. Following maintenance there was a significant rise in the rate of [3H]leucine uptake into protein. Maintained glands demonstrated a fivefold greater accumulation of cyclic AMP in response to isoprenaline than did freshly isolated glands, but there was no comparable maintenance hypersensitivity of cyclic GMP to acetylcholine. This pattern of adrenergic, but not cholinergic, maintenance hypersensitivity matches the known lack of denervation hypersensitivity of human eccrine sweat glands to acetylcholine in vivo.
Studies on the cytoskeletal and nuclear architecture of Xenopus erythrocytes
Authors: Gambino John , Weatherbee James A. , Gavin R. H. , Eckhardt Ronald A. 
Published: April 2021

ABSTRACT
A proteinaceous cytoskeletal network is present in nucleated erythrocytes, which is obscured ultrastructurally in whole cells due to the presence of haemoglobin. Lysis of Xenopus erythrocytes in solutions containing Triton X-100 reveals a cytoskeleton that contains a centrally positioned nucleus, which is linked to the cell surface-associated cytoskeleton by intermediate filaments. The marginal band microtubules are also preserved in these structures. In addition, a single or a pair of perinuclear centrioles is frequently observed in thin sections. These structures are surrounded by a mass of intermediate filaments and fibrogranular material. In contrast to the centrioles in invertebrate erythrocytes those in Xenopus erythrocytes are not associated with the marginal band.
Cytonuclear skeletons were obtained by DNase I digestion and subsequent high-salt extraction of cytoskeletons. The resulting structures were chromatin-depleted and consisted of a nuclear lamina that was maintained in the same overall shape and position as that of intact nuclei. With the exception of the marginal band, the remaining cytoskeletal elements persisted after these treatments. Although marginal bands were not detectable by electron microscopy, the cytonuclear skeletons contained roughly the same amount of tubulin as cytoskeletons, as indicated by immunoblotting with affinity-purified anti-tubulin antibodies.
When intact erythrocytes were exposed to the ionophore A23187 in the presence of calcium, the cell shape and centric nuclear position were altered. Nuclear dislodgement may be attributable to the disruption of intermediate filament associations with the subsurface cytoskeletal shell. Indirect immunofluorescent staining of cytoskeletons lysed in buffers containing either EGTA or calcium indicates that in the absence of calcium, the intermediate filament network extends to the cell periphery. In structures lysed in calcium, however, the filaments are restricted to the vicinity of the nucleus.
The subcellular concentration of ions and elements in thin cryosections of onion root meristem cells an electron-probe eds study
Authors: Cameron Ivan L. , Hunter Keithley E. , Smith Nancy K. R. 
Published: April 2021

ABSTRACT
Quantitative electron-probe energy dispersive X-ray microanalysis has, for the first time, been accomplished at a subcellular level in plant tissue using cryofixed and thin freeze-dried cryosections. The subcellular concentrations of Na+, Cl−, K+, P, S, Mg2+ and Ca2+ were measured in mol/kg dry weight in two types of root meristematic cells of the onion, Allium cepa. The cell wall of the meristematic cells had much higher concentrations of K+ and Ca2+ than was found in the intracellular compartments. Storage granules in the protoderm cells were about 6-12 times lower in P and were about four times higher in S as compared to other intracellular compartments. Comparison between the concentrations of ions and other elements in meristematic plant cells and in mouse cardiac myocytes confirms that major differences in cytoplasmic Na+ and Cl− concentrations do indeed exist between these cell types.
Ultrastructure of the fusion cell inFaucheocolax attenuatasetch. (rhodophyta, rhodymeniales)
Authors: Delivopoulos Stylianos G. , Kugrens Paul 
Published: April 2021

ABSTRACTThe fusion cell in Faucheocolax attenuata Setch. is a highly lobed, thicSk-walled, multinucleate and irregularly shaped cell originating from the basal cell of the auxiliary cell branch. The formation of the fusion cell occurs by an incorporation of vegetative cells into the basal cell, after dissolution of septal plugs between these cell types. Thus the fusion cell is a syncytium containing only haploid nuclei, as well as unusual mitochondria and plastids. Mitochondria lack cristae and instead contain a tubular helical structure. Plastids are atypical with regard to thylakoid organization in red algae, because they lack the peripheral thylakoid and their photosynthetic thylakoids are aggregated to one side. In addition, they contain large osmiophilic bodies. Nuclear envelopes appear to produce large quantities of membrane cisternae. Floridean starch is absent and the cytoplasm contains few ribosomes. The plasma membrane is irregular and endoplasmic reticulum cisternae are situated parallel to it. Bundles of putative microfilaments were commonly found in nuclei and the cytoplasm. Structural evidence does not support any meristematic, nutritive or secretory functions previously ascribed to fusion cells in other genera.
Xeroderma pigmentosum d-hela hybrids with low and high ultraviolet sensitivity associated with normal and diminished dna repair ability, respectively
Authors: Johnson R. T. , Squires Shoshana , Elliott G. C. , Koch G. L. E. , Rainbow A. J. 
Published: April 2021

ABSTRACT
Fusion between HeLa and fibroblasts from complementation group D xeroderma pigmentosum (XPD) followed by challenge with small doses of ultraviolet light (u.v.) results in the production of hybrid cells expressing either HeLa (HD1) or XPn-like (HD2) sensitivity to u.v. and related repair capacity. Assays used include unscheduled DNA synthesis (UDS), DNA break accumulation in the presence of inhibitors of DNA repair synthesis and host cell reactivation of irradiated adenovirus. Complementation assay in heterokaryons reveals limited ability of HD2 to restore UDS in XPD nuclei. We believe this complementation is more apparent than real since proliferating hybrids of HD2 and XPD parentage are without exception u.v.-sensitive and express limited excision repair. On the other hand hybrids between HD2 and XPc, XPE or XPR fibroblasts show true complementation resulting in a return to normal u.v. sensitivity and elevated repair ability.
Bone cells predispose bone surfaces to resorption by exposure of mineral to osteoclastic contact
Authors: Chambers T. J. , Fuller K. 
Published: April 2021

ABSTRACT
The cell-free endocranial surface of young adult rat parietal bones was used as a substrate for osteoclastic bone resorption, either without prior treatment, or after incubation of the parietal bones with collagenase or neonatal rat calvarial cells. Untreated, the endocranial surface consisted of unmineralized organic fibres; incubation with calvarial cells or collagenase caused disruption and removal of these fibres, with extensive exposure of bone mineral on the endocranial surface, without morphologically detectable mineral dissolution. Neonatal rabbit osteoclasts resorbed bone to a greater extent from parietal bones pre-incubated with calvarial cells or collagenase than from untreated bones; mineral exposure and subsequent osteoclastic resorption were both increased if calvarial cells were incubated with parathyroid hormone ; removal of bone mineral after incubation with calvarial cells removed the predisposition to osteoclastic resorption. These experiments demonstrate that calvarial cells are capable of osteoid destruction, and indicate that one mechanism by which osteoblasts induce osteoclastic bone resorption may be through digestion of the un-mineralized organic material that covers bone surfaces, to expose the underlying resorptionstimulating bone mineral to osteoclastic contact.
Infection and maintenance of Holospora obtusa, A macronucleus-specific bacterium of the ciliate Paramecium caudatum
Authors: Fujishima Masahiro , Fujita Miho 
Published: April 2021

ABSTRACT
The gram-negative bacterium Holospora obtusa is a macronucleus-specific symbiont of the ciliate Paramecium caudatum, which invades the host cell via a food vacuole, infects its macronucleus and grows exclusively in the nucleus. From infection experiments, we showed that a property of the macronucleus that is necessary for it to be recognized and infected by H. obtusa is commonly provided by P. caudatum, P. multimicronucleatum and 14 species of the P. aurelia complex, but not by P. jenningsi, P. burearia, P. trichium, P. duboscqui, Didinium nasutum, Blepharisma japonicum, Pseudourostyla levis, seven species of Euplotes or Tetrahymena thermophila. Further-more, it was also shown that the bacteria that infect the macronuclei of P. multimicronucleatum and the P. aurelia species complex always disappear from the nuclei within 5 days and the infected bacteria are maintained stably in the host nuclei in only 13 out of 22 strains of P. caudatum. The results indicate that the species specificity of the habitat of H. obtusa is not simply a matter of its ability to penetrate the host nuclear membrane but depends on unknown factors that exist only in certain strains of P. caudatum.
Divergent expression of laminin and fibronectin in non-tumorigenic and transformed liver epithelial cells
Authors: Junker J. L. , Wilson M. J. 
Published: April 2021

ABSTRACT
The immunocytochemical expression of laminin and fibronectin by non-transformed liver epithelial cells and by transformed cells derived from the same cell line, TRL1215, was examined in ethionine-transformed cells (ETC), untreated control cells at the same high passage level (HPC), and untreated, low passage cells (LPC). At confluence, a divergent expression of laminin and fibronectin was observed in the three sublines. In flat areas of polygonal cells, LPC showed abundant laminin staining and sparse fibronectin staining; HPC had intermediate expression of both; and ETC had sparse laminin staining and abundant fibronectin. Specifically, the laminin network was often found at intercellular junctions, outlining individual LPC, outlining groups of HPC, and having a focal expression in ETC. A fine reticulum of laminin was seen in large areas of LPC, in relatively small areas of HPC, and in multilayered areas of ETC. Fibronectin was visible as thick, matted fibrils, which were sparse in LPC, loosely arranged in HPC and dense in ETC. Prior studies had shown that the increased fibronectin expression in the transformed cells was associated with increased expression of actin stress fibres, increased cell spreading and increased numbers of focal contacts between cell and substrate. The divergent expression of laminin and fibronectin shown here indicates that these two matrix proteins need not be expressed in a parallel manner during trans-formation, and that increased fibronectin, but not laminin, is associated with maximal cell spreading and adhesion.
Duchenne muscular dystrophy: studies of cell motility in vitro
Authors: Witkowski J. A. , Dubowitz V. 
Published: April 2021

ABSTRACT
Duchenne muscular dystrophy (DMD) is a severe degenerative disorder of skeletal muscle. It has been suggested that an abnormality of the plasma membrane may be responsible for the pathogenesis of DMD, and a number of cell surface changes have been described in DMD muscle fibres and other cell types. Alterations in cell-to-cell and cell-to-substratum adhesiveness have been reported for DMD cells and we have determined whether these alterations in cell adhesiveness affect migration of cells from DMD muscle explants. DMD cells move more rapidly and spend less time at rest than do normal or DMD carrier cells, although the differences were statistically significant only for the latter cells. An inverse relationship between cell speed and contact with surrounding cells was not observed. All cells tended to persist in their direction of movement, and there were no differences between the types of cells studied. Our results support the view that there may be a cell surface defect in DMD.
Nifedipine-sensitive calcium channels are involved in polar growth of lily pollen tubes
Authors: Reiss Hans-Dieter , Herth Werner 
Published: April 2021

ABSTRACT
Pollen germination and tube growth of Liliunt longiflorwn in vitro are affected by 10−5 M-nifedipine. Germinating ‘tubes’ form broad protuberances along the whole colpus. Short tubes show a high tendency to grow ‘amoeboid-like’ and to branch; or a second tube emerges in another region of the colpus. Longer tubes (≧ 100 μm) broaden irregularly or swell at their tips. The diameter of the tube can vary drastically within the same tube. With increasing time of treatment many tubes burst. Normal tip growth stops within 10min, but protoplasmic streaming continues even after 15 h. More or less regularly, wall thickenings are formed along the whole tube or on the flanks of the germinating region after some hours. The internal calcium gradient, visualized by chlorotetracycline (CTC) fluorescence, is also disturbed. Nifedipine treatment results in uniform or irregular CTC fluorescence. Branching tubes temporarily show a new subapical CTC gradient. After 6–8 h of nifedipine treatment many cells are no longer stainable with CTC. The results indicate the presence of nifedipine-sensitive calcium channels in pollen tubes.
Actin synthesis in tumorigenic and non-tumorigenic human hybrid cells
Authors: Gowing Linda R. , Tellam Ross L. , Banyard M. R. C. 
Published: April 2021

ABSTRACT
We have previously shown that the total actin content of tumorigenic HeLa/fibroblast somatic cell hybrids is significantly lower than that of the non-tumorigenic hybrid cells. A measure of actin synthesis, relative to total protein synthesis, was obtained for these cells to determine whether the reduced actin content of the tumorigenic cells is due to specific suppression of actin synthesis. Actin synthesis was measured in cells labelled with [35S]methionine using DNase I affinity chroma-tography to isolate the actin quantitatively. The results show that actin synthesis is not specifically suppressed, since the relative amount of actin synthesized is constant for the tumorigenic and non-tumorigenic cell lines. The reduced actin content of the tumorigenic cells is therefore most likely to be the result of increased degradation of actin.
The effect of partial protein synthesis inhibition on cell proliferation in higher plants
Authors: Cuadrado Antonio , Navarrete Matilde H. , Cánovas José L. 
Published: April 2021

ABSTRACT
Meristematic cells from Allium cepa L. roots can attain a steady state of growth in the presence of anisomycin at concentrations that effectively reduce the rate of protein synthesis. Under these conditions the lengths of cell cycle periods increase but not in the same proportion as the generation time (t). Mitosis is hardly affected and S period is slightly lengthened. G2 increases less in proportion to t, while G1 is extended much higher in proportion to t. Natural synchronous populations have been used to study cell cycle parameters during transition from the physiological steady state to the new one created by the presence of the drug. G2 was the same during transition as during steady-state growth. G1 was much shorter during transition. Average cell mass at division was reduced, and a negative correlation was observed between the length of G2 and the size of the cell at termination of DNA synthesis. We propose that in higher plants, G2 length is regulated by cell mass at completion of DNA synthesis (G2 being shorter in big cells than in small cells), though there is no cell size requirement for mitosis.
Synchronous exocytosis in Paramecium cells. VI. ultrastructural analysis of membrane resealing and retrieval
Authors: Plattner H. , Pape R. , Haacke B. , Olbricht K. , Westphal C. , Kersken H. 
Published: April 2021

ABSTRACT
After the synchronous induction of exocytosis of secretory organelles (trichocysts) in Paramecium tetraurelia cells the process of membrane resealing and retrieval could be followed under synchronous conditions. The characteristic aggregates of membrane intercalated particles (MIPs) contained within the freeze-fractured cell membrane (rings and rosettes) and trichocyst membranes (annulus MIPs), in addition to collar striations on the top of trichocyst membranes, served as endogenous ultrastructural markers. This allowed us to follow the re-arrangement of membrane constituents during and after exocytosis with high temporal and spatial precision. Membrane specificity is maintained to a considerable extent (∼ 99·5%), as judged from the rare occurrence of aberrant resealing (according to freeze-fracture data) and from the rather minute shift of glycocalyx components (according to electron staining experiments) during normal membrane resealing. Coated pits are not involved in membrane retrieval (155 ghosts analysed); since the membrane regions involved in exocytotic fusion are backed by apposed materials, probably proteins, this may restrain membrane constituents from intermixing. Another factor for maintaining membrane specificity is the fact that resealing of the exocytotic opening occurs much more rapidly than in most other systems. The retrieval operates with a half-life of 3 (strain 7S) to 9 min (K401), the involvement of cortical microtubules in the retrieval can be largely excluded, since only two microtubules (of unidentified origin) were seen to approach ghost structures in 4074 cases analysed during this period of intense ghost retrieval. Phalloidin microinjected at a dose that blocked all cytoplasmic streaming (before synchronous exocytosis was induced) did not abolish membrane resealing and retrieval, which, therefore, may be passive processes.
Light and scanning electron microscopy of the same human metaphase chromosomes
Authors: Harrison Christine J. , Jack Elspeth M. , Allen Terence D. , Harris Rodney 
Published: April 2021

ABSTRACT
A technique has been developed to examine the same G-banded human metaphase chromosomes, first in the light microscope and then in the scanning electron microscope (SEM). A structural involvement in chromosome banding was confirmed by a positional correlation between the G-positive bands observed in the light microscope and the circumferential grooves between the quaternary coils of the metaphase chromosomes, observed in the SEM. In further support of this the regions between the grooves showed a positional relationship with the G-negative or reverse (R) bands.
The examination of slightly extended metaphase chromosomes in the light microscope demonstrated that the G-banding pattern corresponded to that described by the Paris nomenclature for metaphase chromosomes. The arrangement of the circumferential grooves of the same chromosomes, observed in the SEM, was shown to relate to that described by the Paris nomenclature for prometaphase chromosomes. Therefore, using the SEM it is possible to demonstrate the details of prometaphase banding in metaphase chromosomes.