bluuebunny/crossref_metadata_2025_split huggingface dataset:
The purification and immunocytochemical localization of the major iodinatable cell surface glycoproteins of chinese hamster ovary cells
Authors: Fitzgerald L. A. , Horst G. A. Baumbach, M. N. , Noonan K. D. , Roberts R. M. 
Published: April 2021

ABSTRACT
A group of high molecular weight, acidic glycoproteins (HMWAG) are enriched in a plasma membrane subfraction of low density that can be isolated from Chinese hamster ovary (CHO) cells. The HMWAG represent the major components labelled by either lactoperoxidase-catalysed iodination of whole cells or by 125I-labelled wheat germ agglutinin (WGA) overlays of the membrane fraction after it had been analysed by 2-dimensional electrophoresis. The HMWAG were solubilized from membrane in Triton X100/borate buffer and purified by affinity chromatography on WGA-Sepharose. Antisera prepared against these glycoproteins in mice bound to several CHO cell lines including the WGA-resistant line Pro-5 WGAB1. Indirect immunofluorescence experiments performed at 4 °C showed that the glycoproteins had a fairly uniform but punctate distribution over the cell edge and dorsal surface of substratum-attached cells. Filopodia projecting along the substratum were also intensely labelled. After permeabilizing the cells the HMWAG were also shown to be located in cytoplasmic vesicles and in a perinuclear zone, which is assumed to be Golgi-associated. Electron microscopic observations using indirect immunoferritin procedures confirmed that the cell surface HMWAG were heavily concentrated on microvilli. The distribution of label seen with fluorescein-conjugated WGA was similar to that noted with fluorescent antibody, except that WGA was more uniformly distributed on the cell surface and also bound to the nuclear envelope in permeabilized cells. However, if cells labelled at 4 °C were warmed to 37 °C for 30 min the patterns of internalization of WGA and antibody were distinct. With the lectin, label rapidly became concentrated in the perinuclear zone, whereas with antibody the microvilli became denuded of label, which was then internalized into cytoplasmic vacuoles just beneath the plasma membrane. These results confirm that the HMWAG are concentrated on regions of the cell surface that are likely to produce vesicles readily upon cell breakage. They also suggest that pattern of internalization of a cell surface glycoprotein may be influenced by the nature of the ligand that binds to it.
Regulation of interstitial cell differentiation in Hydra attenuata: VI. Positional pattern of nerve cell commitment is independent of local nerve cell density
Authors: Heimfeld Shelly , BODE Hans R. 
Published: April 2021

ABSTRACT
The interstitial cell of hydra is a multipotent stem cell, which produces nerve cells as one of its differentiated cell types. The amount of interstitial cell commitment to nerve differentiation varies in an axially dependent pattern along the body column. The distribution of nerve cell density has the same equivalent axial pattern. These facts have led to speculation that the regulation of nerve cell commitment is dictated by the nerve cell density.
We examined this question by assaying interstitial cell commitment behaviour in 2 cases where the normal nerve cell density of the tissue had been perturbed: (1) in epithelial hydra in which no nerve cells were present; and (2) in hydra derived from regenerating-tip isolates in which the nerve density was increased nearly 4-fold. We found no evidence of regulation of nerve cell commitment in response to the abnormal nerve cell densities. However, the typical axial pattern of nerve commitment was still obtained in both sets of experiments, which suggests that interstitial cell commitment to nerve differentiation is dependent on some parameter of axial location that is not associated directly with the local nerve cell density.
Functional differentiation of enterocytes in the follicle-associated epithelium of rat peyer’s patch
Authors: Smith Michael W. , Syme Gabrielle 
Published: April 2021

ABSTRACT
The ability of the follicle-associated epithelium (FAE) of rat Peyer’s patch to accumulate valine has been measured using a new technique of autoradiographic analysis. Maximum uptake of valine was achieved by enterocytes present in the dome region of the FAE. Valine uptake was not seen in enterocytes present on the lower slopes of the FAE or in follicle-associated crypts. The ability of the FAE to absorb valine was generally much less than that seen in enterocytes present on adjacent villi. The main reason for this discrepancy lay in the apparent inability of the FAE to develop a second phase of amino acid transport similar to that seen in villus enterocytes. It is suggested that this failure results from some unexplained interaction taking place between the FAE and its underlying lymphoid tissue.
Cell versus nuclear morphometry of serum-stimulated fibroblasts: Nuclear changes precede cell changes
Authors: Belmont Andrew S. , Nicolini Claudio A. 
Published: April 2021

ABSTRACT
Changes in the cell and nuclear morphology of sparsely plated WI38 fibroblasts were followed as a function of time after increasing the serum concentration from 0 ·3 % to 10 %. Quantitative measurements were carried out in parallel on Feulgen-stained nuclei and Wright-stained cells using the Quantimet 720-D image analysis system. We report a rapid, significant change in nuclear morphology indicative of nuclear rounding taking place within 30 min after increasing the serum concentration. In contrast, cell morphology showed only a slight change within the first 30 min but showed a significant change, also indicative of cell rounding, between 30 min and 3 h after increasing the concentration. Thus our results indicate a coupling between cell and nuclear morphology, but one in which nuclear changes precede cellular changes. As variations in both cell and nuclear morphology have been linked to the control of cell growth and transformation we also discuss briefly the implications of our results in relation to the regulation of cell growth and transformation.
Effects of temperature on the replication of chromosomal DNA of Xenopus laevis cells
Authors: Al-Saleh A. A. 
Published: April 2021

ABSTRACT
DNA fibre autoradiography has been used to study the effects of temperature on the replication of chromomosomal DNA of Xenopus laevis cells in tissue culture at 18, 23 and 28°C. Pulse/stepdown labelling shows that the DNA replicates bidirectionally. Origin-to-origin distances (initiation intervals) vary, but the range of and the mean initiation intervals at all three temperatures are much the same. The mean interval between initiation points is of the order of 60 to 66 μm. Staggering of initiation is evident at all three temperatures. Evidence against the existence of replication termini is provided. The rates of progress of DNA replication forks are 6μm/h at 18°C, 10μm/h at 23 °C and 16μm/h at 28°C.
Polysomal organization in growing and resting cultures and its relation to protein synthesis in Tetrahymena
Authors: Isberner Petra , Cleffmann Günter 
Published: April 2021

ABSTRACT
Cytosol from Tetrahymena cells growing at different rates was isolated and separated by centrifugation into polysomal and non-polysomal fractions. The RNAs of either fraction were separated chromatographically into poly(A)+ RNA and poly(A)− RNA. It was found that in resting cultures the total RNA per cell is only about half of that of rapidly growing cultures. All fractions of RNA were reduced proportionally. Thus, the percentage of polysomally bound total RNA (70 % of cytosol RNA) and polysomally bound poly(A)+ RNA (72% of cytosol poly(A)+ RNA) is the same in growing and resting cultures. Differences, however, were found in the polysomal structure. Polysomes from resting cultures contained significantly fewer ribosomes.
The amounts of RNA bound to polysomes were related to the rate of protein synthesis under different growth conditions. The decrease in cellular RNA corresponded well with the reduction in amino acid incorporation in resting cells. The rate of protein accumulation in resting cells, on the other hand, was considerably less, suggesting that polypeptides in resting cultures are less stable.
Neutrophil behaviour in the presence of protease inhibitors
Authors: Forrester J. V. , Lackie J. M. , Brown A. F. 
Published: April 2021

ABSTRACT
Neutrophil leucocytes circulate in plasma, which contains broad-spectrum antiproteases such as alpha-2-macroglobulin and alpha-1-antitrypsin, and move into environments in which antiproteases are present. Plasma antiproteases significantly reduce the adhesiveness of leucocytes in both static and dynamic adhesion assays, although their action does not seem to depend upon their anti-protease capacity. Contrary to expectation, leucocyte movement over surfaces and through both rigid and deformable three-dimensional matrices (micropore filters and collagen gels) is unaffected by antiproteases. This renders the idea that forward movement depends upon the proteolytic cleavage of redundant adhesion sites less probable. Various non-physiological antiproteases (chloromethyl ketones, soya bean trypsin inhibitor, and ε-aminocaproic acid are also ineffective in reducing locomotion, although they do cause minor changes in adhesiveness.
Formation of centriole and centriole-like structures during meiosis and mitosis in Labyrinthula sp. (rhizopodea, labyrinthulida): an electron-microscope study *
Authors: Perkins F. O. 
Published: April 2021

ABSTRACT
The fine structure of mitosis in vegetative cells of the marine protist Labyrinthida was found to involve formation of two approximately spherical, electron-dense aggregates (termed protocentrioles) 200–300 nm in diameter. Spindle microtubules were directly attached to the structures. The aggregates contained centrally located cartwheel structures but no microtubular elements in the form of a centriole-like cylinder. In non-sporulating cells the aggregates occurred only during mitosis or possibly in late interphase cells. During meiotic zoosporulation de novo centriole formation was observed. Vegetative spindle cells, which contained no centrioles, procentrioles, or centriolar plaques, aggregated then changed into approximately round or oval presporangia within sori. Two protocentrioles were formed in the cytoplasm a few hundred nanometres from each nucleus. Microtubules, oriented in astral ray patterns, were attached directly to each of the protocentrioles. Following migration to opposite sides of the nucleus, each of the protocentrioles differentiated into two centrioles attached at the cartwheel or proximal ends in a longitudinally continuous orientation. Binary fission of the paired centrioles (termed bicentrioles) and reorientation yielded a diplosome or an approximate orthogonal orientation of the organelles. Each mature centriole consisted of the usual cylinder of 9 triplet microtubular blades with a cartwheel complex at the proximal end consisting of 5 or 6 tiers of cartwheels. Further centriole replication appeared to occur by orthogonal budding from mature centrioles.
Chromocentres and the synaptinemal complex
Authors: Cour L. F. La , Wells B. 
Published: April 2021

ABSTRACT
The 1–4 chromocentres seen in nuclei of Fritillaria lanceolata, which derive from fusion of heterochromatic segments situated proximal to the centromere in all but two of the 24 chromosomes, were studied with the electron microscope in thin sections of pollen mother cells at zygotene and pachytene, in respect of the synaptinemal complex. Prophase stages of meiosis in two plants were also surveyed briefly with the light microscope.
The latter observations revealed that the timing of the separation of heterochromatic segments from chromocentres is genetically controlled. In one plant the segments were still contained in chromocentres at pachytene, whereas in the other they were free at zygotene. At this time they could be identified by a near-surface position in the nucleus and an even condensation concomitant with an absence of chromomeres.
In thin section, the fine structure of the chromocentres in zygotene nuclei was distinctive in that the chromatin fibrils were less condensed and more widely dispersed than those in euchromatic regions. The fibrillar network was also interspersed with ‘clear areas’ or channels. After further chromosome condensation, the condensation of fibrils in the chromocentres became equivalent at pachytene to those in euchromatic regions.
Synaptinemal complexes were seen at zygotene and pachytene both in euchromatic regions and chromocentres. Their presence in the chromocentres signifies that homologous chromo-somes must have been closely paired in regions extending from the centromeres to the distal ends of the heterochromatic segments already at telophase of the last pre-meiotic mitosis.
Configurations involving entangled pairs of axial cores, peculiar to zygotene and chromo-centres and parts of euchromatic regions proximal to them, are interpreted as resulting from restricted movement.
Structural analysis of basal bodies of the isolated oral apparatus of Tetrahymena Pyriformis
Authors: Wolfe J. 
Published: April 2021

ABSTRACT
The oral apparatus of Tetraliymena pyriformis was isolated using a non-ionic detergent to disrupt the cell membrane. The mouth consists largely of basal bodies and microfilaments. Each basal body is attached to the mouth by a basal plate which is integrated into the mesh work of microfilaments that confers upon the oral apparatus its structural integrity.
Each basal body is composed of 9 triplet microtubules. Two of the 3 tubules, subfibres ‘A’ and ‘B’ are composed of filamentous rows of globules with a spacing of 4·5 nm. The third tubule, subfibre ‘C’, is only one-third the length of the basal body.
The intracellular origin of flagellar hairs in the chrysophyceae and xanthophyceae
Authors: Leedale G. F. , Leadbeater B. S. C. , Massalski A. 
Published: April 2021

ABSTRACT
Cells of the chrysophycean flagellate Olisthodiscus luteus contain bundles of aligned tubes and fibres within membrane-limited vesicles. Each element in a vesicle consists of a tapering portion 0 · 25 μm long, a shaft 1 · 5 μm long and a terminal fibre 0·25μm long; the shaft is approximately 15 nm in diameter and has a helical cross-banding with a periodicity of 8 nm. The flagellar hairs of Olisthodiscus have identical morphology and dimensions to these internal elements. Zoospores of the filamentous xanthophycean algae Bumilleria sicula, Heterococcus spp. and Tribonema spp. have similar internal vesicles containing aligned tubes and fibres with precisely the same morphology and dimensions as the flagellar hairs: base plus shaft, 1· 2 μm long, two terminal fibres per hair, 0 · 5—0 · 8 μm long, shaft diameter of approximately 15 nm and a helical periodicity of the shaft of 8 nm. The aligned tubes are absent from the vegetative xanthophycean cell, appear during zoosporogenesis and disappear during early stages of zoospore settlement. It is suggested that the aligned tubes and fibres are potential flagellar hairs which are formed in the perinuclear space (and possibly other regions of the endoplasmic reticulum) and are then transported to the cell surface in vesicles of the ER for deposition on the flagella. A review of information available on the Chrysophyceae, Xanthophyceae, Phaeophyceae and Bacillario phyceae indicates that internal formation of flagellar hairs is probably the rule in the heterokont algal groups, and a similar process apparently occurs in at least the dinoflagellates, the crypto-monads and some aquatic fungi among other groups of organisms with hairy flagella.
Fine structure of degenerating and regenerating flight muscles in a bark beetle, Ips confusus: I. degeneration
Authors: Bhakthan N. M. G. , Borden J. H. , Nair K. K. 
Published: April 2021

ABSTRACT
The flight muscles of the bark beetle Ips confusus undergo a pronounced degeneration within 4 days of introducing beetles into the bark of pine logs. Numerous lysosomes develop between the myofibrils, and the fibrils become greatly reduced in size. In female beetles many of the mitochondria and most of the myofilaments disappear from the muscle, and apart from lysosomes, tracheoles and a few fine granules, little structural organization remains in the fibres. The muscles of males degenerate to a lesser extent and, unlike those of females, contain numerous lipid globules in the degenerating condition. The significance of flight muscle degeneration as a possible prerequisite for reproduction in females is discussed. In males, flight muscle degeneration may have behavioural significance in confining the flightless insect to the host tree for repetitive mating and gallery maintenance.
Seasonal changes in secretory granules and crystalloid inclusions of bat thyroid parafollicular cells
Authors: Nunez E.A. , Gould R. P. , Holt S. J. 
Published: April 2021

ABSTRACT
Parafollicular cells of active Autumn bats sometimes contain many large dense secretory granules (diameter 1–2 μm) enclosed within ribosome-studded membranes. At the same time, parafollicular cells containing small granules were often characterized by the presence of slender crystalloid rods, up to several microns in length.
Parafollicular cells with large granules become depleted of them following exposure of non-hibernating bats to cold (4 °C) for 12–48 h. This treatment causes no change in the cells containing small granules, although partial degranulation in such cells was seen in early hibernating (November) bats.
On the basis of these and previous studies it is suggested that the two types of granules in bat parafollicular cells have different fates during the animal’s annual cycle of physiological activity.
The disposition of proteinpoly-saccharide in the epiphysial plate cartilage of the young rabbit
Authors: Smith J. W. 
Published: April 2021

ABSTRACT
Although acidic bismuth nitrate stains the polysaccharide in the unfixed bovine epiphysial plate, it fails to do so in that of the rabbit. After fixation in glutaraldehyde, however, Araldite sections stained with bismuth nitrate exhibit 3-nm spots which are interpreted as polysaccharide chains in coiled conformation.
In the matrix of the proliferative zone, and in the large Golgi vesicles of the associated chondrocytes, the polysaccharide spots are arranged in closely packed groups. Lead citrate and uranyl acetate staining shows the non-fibrillar material in these situations as a continuous network of particles. The centre of each particle is translucent, and double staining with phos photungstic acid and bismuth indicates that these central regions contain the groups of polysaccharide spots.
It is suggested that in the unfixed tissue bismuth binding is prevented by screening of the polysaccharide sulphates by positively charged non-collagenous protein, and that fixation, by precipitating this protein as a network around groups of proteinpolysaccharide molecules, frees the sulphate groups to react with bismuth.
Proteinpolysaccharide molecules appear to be tangentially attached to each period of the small collagen fibrils of the matrix. Fixation precipitation of the associated protein tends to aggregate these molecules into groups which are often somewhat eccentric to their original attachment sites, and consequently the fibrillar attachment of proteinpolysaccharide usually appears to be rather irregular.
In the zone of early calcification single mineral crystals are associated with dense bodies of unknown nature and function. Many are also associated with short linear rows of polysaccharide spots. This and the similarity in the lengths of the two structures suggest that initial mineral crystals may grow along a proteinpolysaccharide molecule from one end to the other. Absence of polysaccharide spots in relation to crystal clusters suggest that these clusters are formed as a result of the seeding effect of the initial single crystals.
The midpiece of the mouse sperma tozoon: Its form and development as seen by surface replication
Authors: Woolley D. M. 
Published: April 2021

ABSTRACT
A method is described for making carbon replicas of the surface of fixed spermatozoa and spermatids. In a study of the undulations of the surface of the midpiece, it has been shown that in the mouse spermatozoon the mitochondria are arranged predominantly in two parallel helices—without exception sinistral—totalling about 87 windings around the flagellum. The variability of this number has been calculated. The origin of this arrangement in spermateleosis has been examined in replicas of spermatids, revealing a rather complicated morphogenesis. It seems that, following the migration of the terminal annulus, elongated mitochondria form a single dextral helix around the flagellum; they then divide, making an orderly arrangement of spherical units; finally, each unit elongates, pushes between the contiguous units, and, by end-to end apposition, contributes to the formation of the regular system of two sinistral helices. A detailed account of this transformation is presented. It is suggested that, for tissues of sufficient hardness, the replica technique can usefully complement the cutting of thin sections.
Kinetic analysis of cell spreading: I. Theory and modelling of curves
Authors: Bardsley William G. , Aplin John D. 
Published: April 2021

ABSTRACT
The spreading of cells on suitably treated surfaces is briefly discussed and the need to analyse this phenomenon numerically is emphasized. Possible mathematical models for fitting experimental data are classified as statistical, kinetic or empirical and examples of each of these types are given. A possible protocol for analysing cell spreading kinetics and determining goodness of fit and parameter redundancy is presented.
The Nature Of Conditioning Nutrients For Human Malignant Melanoma Cultures
Authors: Ellem K. A. O. , Kay G. F. 
Published: April 2021

ABSTRACT
From a human melanoma line (MM96), showing some dependence of its rate of growth and cell attachment on serum concentration, sublines were selected for even greater dependence on serum factors. These sublines were used to identify the production of substances by other melanoma cells in culture that would supplement or replace the requirement for serum. Most of the sublines showed higher colony-forming efficiency in medium conditioned by one of several cell types in the presence of a low concentration of serum (2·5 %) compared with fresh medium containing a high concentration of serum (10%). The conditioning factor(s) were found to be moderately heat-stable, non-lipophilic, and to be of low molecular weight (≤400).
Screening of a variety of non-essential low molecular weight nutrients, which have been reported to potentiate the growth of a variety of cell types in low-density culture, was positive for the MM96 sublines only for pyruvate. In particular, L-alanine, L-serine, putrescine and αMSH (melanocytestimulating hormone) were ineffective. Despite the problems of comparing conditioned media with fresh medium, a reasonable correlation between the stimulatory effect and the cell content of added 2-oxocarboxylates was apparent. As would be anticipated, MM96 cultures showed a population density-dependent enhancement of growth up to a cell density of 2 to 4 × 104 cells cm-2. Further increase in the initial cell density of these cultures led to a decline in growth rate.
An important additional observation was that simple dilution of the ingredients of RPMI1640 with phosphate-buffered saline or Hanks’ balanced salt solution led to a reversal of the growth inhibition accompanying a serum shift-down.