bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructural features of defective In Vitro keratinization of chick embryonic skin
Authors: Jensen H.M. , Mottet N. K. 
Published: April 2021

ABSTRACT
Thirty-four explants of epithelium and subjacent mesenchyme from the hind limb buds of 5-day chick embryos were cultured for 1 to 14 days. Controls consisted of a series of in ovo limb bud specimens from 5 day’s incubation to hatching. Both experimental and control specimens were examined by similar electron-microscopic methods.
Differentiation of epidermis was precocious and that of dermis extremely retarded in vitro, contrasting with the events in ovo where epidermal differentiation occurred later and differentiation of dermis was early and vigorous. The two types of epidermal cells developed to a different degree in vitro. Pencytes and their derivatives at times developed precociously and reached full maturity, although their pattern of differentiation was asynchronous compared with that in ovo. Basal cells and their derivatives produced filaments precociously but mature keratrnized cells were not found. Absence of keratohyaline granules in the epithelial cells appeared to be the initial defect in the keratinization process. Hyperplasia of mitochondria in basal and parabasal cells was also noted. The underlying mesenchyme, which in ovo begins to produce large amounts of collagen at an exponentially accelerating rate at 5 days, synthesized only scant collagen under the in vitro conditions employed. The hypothesis is presented that the mesenchyme alters epithelial differentiation by affecting keratohyaline synthesis which in turn controls keratinization.
The effect of neuraminidase (3:2:1:18) on the aggregation of cells dissociated from embryonic chick muscle tissue
Authors: Kemp R.B. 
Published: April 2021

ABSTRACT
Embryonic chick muscle cells were used to investigate the effect of removing cell-surface sialic acids on cell aggregation in vitro. Single cell suspensions were prepared by dissociating skeletal muscle tissue of 9-day-old chick embryos with either crystalline or crude trypsin. Cell aggregation was quantitatively estimated by turbidimetric and gyratory shaker methods.
Cells dissociated with crude trypsin and suspended in Hanks’s balanced salts solution (BSS) containing 25 u./ml neuraminidase (NANase) only aggregated for 2 h when rotated in an absorptiometer. The inhibitory effect of the enzyme was more pronounced with increasing concentration up to 25 u./ml. Cells dissociated with crystalline trypsin and treated with 100 u./ml NANase immediately exhibited a reduced aggregative competence when gyrated in Eagle’s minimum essential medium (MEM) containing 25 u./ml NANase, compared with the controls which were not exposed to NANase. The aggregation rate of muscle cells pretreated with 100 u./ml NANase and suspended in Eagle’s MEM was similar to that of the untreated controls. Cell counts showed that under all three experimental conditions cells were not added to aggregates after the 12-h stage. Aggregates formed in Eagle’s MEM (the controls) joined together to form larger aggregates after 12 h, but those rotating in the presence of NANase did not display this property.
Lissamine green viability tests showed that cells remained alive throughout the 24-h period in the presence of NANase. Determinations of oxygen uptake, protein synthesis and mitotic index confirmed that general cellular viability was not affected by NANase. Fluorescent-labelled NANase was not taken up by the cells.
Treatment of crystalline trypsin-dissociated muscle cells with 100 u./ml NANase for 30 min at 37 °C significantly reduced their negative electrophoretic mobility. This diminution closely corresponded to the removal of cell-surface sialic acids, as measured by colorimetric tests.
Interpretation of the results in the light of current theories of cell adhesion failed to give support to the concept of adhesion by physical forces. The mechanism by which cellular deformability could influence cellular adhesiveness is modified in the knowledge of the present results.
The magnitude of the extracellular space in electron micrographs of superficial and deep regions of the cerebral cortex
Authors: Harreveld A. Van , Steiner Jana 
Published: April 2021

ABSTRACT
Electron micrographs (EMs) of central nervous tissue perfused with glutaraldehyde and post-fixed with osmium tetroxide exhibit more extracellular space in superficial than in deep regions of the brain. It was postulated that this is due to the availability to the surface tissue of the cerebrospinal fluid in the subarachnoidal space. It was assumed that in addition to the extracellular material this fluid is taken up by dendritic elements in the surface layer of the cortex during the glutaraldehyde perfusion. Indeed, dendritic structures in EMs of the surface layer of glutaraldehyde-perfused and OsO4-post-fixed cortex exhibited a more pronounced swelling than similar structures in deeper cortical regions, where only extracellular material was available to the dendrites. The extracellular space in such preparations consisted of narrow slits surrounding the tissue elements. These slits were formed during the post-fixation since they were not present in freeze-substituted, glutaraldehyde-perfused tissue, which showed a paucity of extracellular material. The slits were in general wider in the superficial than in the deep cortical tissue. That this difference is related to the amount of material taken up by the dendrites during the glutaraldehyde perfusion was supported by experiments in which the exposed cortical surface was flooded with Ringer’s solution during the glutaraldehyde perfusion. This resulted in a ballooning of dendritic elements in the cortical surface due to the availability of an unlimited amount of fluid on the cortex. Post-fixed material of these flooded cortices yielded EMs with unusually wide extracellular slits around the tissue elements.
Mapping of highly ordered membrane domains in the plasma membrane of the ciliate Cyclidium glaucoma
Authors: Bardele Christian F. 
Published: April 2021

ABSTRACT
The entire cortex of Cyclidium glaucoma has been analysed in a correlated freeze-fracturing and ultrathin-scctioning study. Three types of highly ordered domains of intramembranous particles were found in the plasma membrane; owing to the many landmarks in the cortex of C. glaucoma it was possible to map their location in relation to the precisely known position of every single cilium. Eight particle plates made of parallel tripartite particle ridges have been found in precisely determined locations at the anterior pole of the cell and in the buccal cavity. It is suggested that these membrane specializations represent mechanosensitive sites. An array of three parallel rows of particles, termed a ‘simple pellicular rug’, forms a second type of membrane domain, which is closely associated with somatic dikinetids found exclusively in the anterior half of the cell. A third extremely complex array, termed a ‘complex pellicular rug’, is associated with the monokinetids in the posterior half of the cell. There is no gradient in the distribution of these domains but a sharp boundary at the level of the future fission zone. The function of the pellicular rugs is unknown, but their specific distribution will be helpful in further studies on their assembly prior to or during cell division.
The intracellular diversification of the cell surface is further augmented by the disclosure of three different aspects of the proximal part of the ciliary membrane. Beyond the double-stranded ciliary necklace, which is a common feature of all cilia, only the motile somatic cilia of C. glaucoma have typical ciliary plaques made of three rows of particles, while all oral cilia have modified plaques, which consist of four rows of particles. The single stiff caudal cilium has no plaques at all. The functional significance of the topographic differences in the plaque areas is discussed. Obviously, the plasma membrane and at least parts of the ciliary membrane form a non-fluid mosaic membrane.
Adaptation of human diploid fibroblasts in vitro to serum from different sources
Authors: Zamansky Glen B. , Arundel Carla , Nagasawa Hatsumi , Little John B. 
Published: April 2021

ABSTRACT
The growth of two human diploid skin fibroblast cell lines, originally grown in medium supplemented with foetal bovine serum and later adapted to medium supplemented with newborn bovine, bovine calf or horse serum, has been studied. Prolonged generation times, increased cell volumes and decreased plating efficiencies were observed in cultures grown in newborn bovine, bovine calf or horse serum. In general, the deleterious effects were most severe as a result of growth in bovine calf or horse serum. In the light of the present findings, we believe investigators should exert great caution in switching human fibroblast cultures from foetal bovine serum to alternative sera, even at times of scarcity and high prices.
Degeneration and regeneration of chloroplasts in Euglena gracilis grown in the presence of acetate: Ultrastructural evidence
Authors: Vannini Gian Luigi 
Published: April 2021

ABSTRACT
When green cells of Euglena gracilis, strain Z, were light-grown for several months on a solid medium containing an excess of sodium acetate (1·0% instead of the normal 0·1 %), some 30% of the cells were colourless. The ‘acetate-bleached’ organisms, isolated by plating methods and subsequently incubated in the light in a liquid medium, regained the capacity to form chlorophyll in a few days in the absence of any organic carbon source, and within 1-2 weeks in the presence of 0·1 % acetate. A number of bleached colonies, however, gave rise to populations in which the delay in pigment synthesis initiation was at least 2 months.
Besides numerous paramylum granules and lipid inclusions, the acetate-bleached cells exhibited variably shaped and sized plastids, apparently lacking in ribosomes and showing a deeply disorganized membrane system. In the alga greened in the presence of 0·1% acetate, the pattern of plastidome reorganization was altered; the thylakoids were often unpaired and vesiculated in different degrees, owing primarily to the swelling of the lumen. A complete recovery of normal chloroplast structure occurred only after several weeks of exponential growth. The entire population greened in the absence of acetate constantly showed normal chloroplasts with perfectly reassociated thylakoids and clear partitions.
Polyacrylamide Gel Electrophoretic Screening of Mammalian Cells Cultured In Vitro For The Presence Of The Intermediate Filament Protein Vimentin
Authors: Traub Ulrike E. , Nelson W. James , Traub Peter 
Published: April 2021

ABSTRACT
A total of 63 different cell lines originating from a variety of mammalian species were cultured in vitro and analysed for the presence of vimentin, employing polyacrylamide gradient slab gel electrophoresis in urea/acetic acid as buffer system. Irrespective of the cell culture conditions, and the growth potential and morphology of the cells, vimentin was expressed in all cell lines examined, with two exceptions: MPC-11 mouse myeloma and M0PC-31C mouse plasmacytoma cells. Immunoblotting with the monoclonal antibody α-IFA, which is directed against an antigenic determinant shared by all classes of intermediate filaments, did not detect any other of the known intermediate filament proteins in MPC-11 and M0PC-31C cells.
Vimentin synthesized by various cell lines was characterized by four different criteria: (1) its extractability with Triton X-100 under various ionic conditions; (2) its behaviour in (NH4)2SO4 fractionation of cellular extracts; (3) its electrophoretic mobility in polyacrylamide gel electrophoresis in urea/acetic acid ; and (4) the co-isolation of polypeptides of higher electrophoretic mobility, which, by comparison with degradation products of vimentin obtained with the Ca2+-activated proteinase specific for intermediate filament proteins in vitro, were identified as products of Ca2+-dependent proteolysis of vimentin. Although the degradation products occurred in different ratios in extracts of different cell lines, they constituted the same characteristic set of proteins whenever degradation of vimentin was observed. The formation of proteolytic breakdown products could be partially to totally suppressed when the cells were harvested, washed and processed in the presence of EGTA and proteinase inhibitors.
The experimental data show that: (1) vimentin, as well as the Ca2+-activated proteinase specific for intermediate filament proteins, is highly conserved during the evolution of mammalian species; (2) the proteolytic breakdown products of vimentin, which give rise to a characteristic ‘staircase’ in two-dimensional gel electrophoresis, are probably artefacts of isolation ; (3) the expression of vimen-tin is neither a prerequisite for nor necessarily indicative of rapid cell proliferation in vitro; and (4) the techniques described can be used for the routine identification of vimentin in cells and tissues in case vimentin-specific antibodies are not available.
Development Of Cell Junctions In Seaurchin Embryos
Authors: Spiegel E. , Howard L. 
Published: April 2021

ABSTRACT
The development of cell junctions in sea-urchin embryos has been investigated using thin sections, lanthanum-tracer and freeze-fracture techniques. Three types of desmosomes are present: belt desmosomes and spot desmosomes, which attach cells to each other, and hemi-desmosomes, which attach cells to the basement membrane. Two types of septate junctions are present: the straight, unbranched, double-septum septate, which is present in epithelial cells throughout embryogenesis, and the pleated, anastomosing, single-septum septate. The latter is formed only on cells that have invaginated to the interior of the embryo to form the digestive tract. The pleated junctions are shown to replace the straight junctions that were originally present before the cells migrated to the interior. It is suggested that these pleated septates may be specialized for digestive processes, since they are developed just prior to feeding and are retained in the adult intestine. Tricellular junctions, which join the bicellular junctions of three adjoining cells, have been identified in the embryo and in the adult intestine. Evidence for the presence of gap junctions was not obtained, but there are indications of their presence.
Conformational response of the glycocalyx to ionic strength and interaction with modified glass surfaces: Study of live red cells by interferometry
Authors: Wolf H. , Gingell D. 
Published: April 2021

ABSTRACT
We have measured separation distances between live human red blood cells and simple or modified glass surfaces, using the finite aperture technique of microscope interferometry. In general, separation increases as the ionic strength falls, in isotonic solutions. Restriction on movement parallel to the glass in all except the most dilute salt solutions, coupled with the absence of Brownian motion, indicates direct molecular contact with the substratum. Thus increased separation must be due to swelling of the glycocalyx under electrostatic forces. However, at ⪯2 mM adherent cells show a separation &gt; 100 nm, execute Brownian motion and the restriction on lateral motion is less evident. This suggests that secondary minimum adhesion by long-range forces with little or no direct molecular connection occurs at extreme dilution only.
Treatment of cells with trypsin reduces separation by up to 40 nm, but the extent to which this reflects reduced double-layer repulsion due to loss of surface charge, as opposed to the reduced opportunity for swelling in a trimmed-down glycocalyx, is unclear. Adhesion at a separation ∼ 100nm in 1 min buffer after trypsinization supports the view that adhesion can occur without very long glycoprotein connections, but does not prove it.
Adhesion to unwettable methylated glass and completely wettable unmethylated glass, with an identical ionic strength dependence of the separation, shows that hydrophilicity is not an absolute requirement. Red cells interact closely at all ionic strengths with glass made polycationic with poly-L-lysine, owing to electrostatic attraction.
The interference technique also shows that adherent cells can be spaced from the glass by an intervening layer of previously absorbed serum albumin.
Ultrastructural aspects of sporogenesis in the apogamous fern Dryopteris borreri
Authors: Sheffield E. , Laird S. , Bell P. R. 
Published: April 2021

ABSTRACT
The events that accompany sporogenesis in the apogamous fem Dryopteris borreri parallel those seen in sexually reproducing ferns. Organelles dedifferentiate and redifferentiate, and form a discrete band across the equator of dyads; nuclear vacuoles and lipid spherosomes appear during prophase, and the major part of the ribosome population is removed and subsequently replaced during meiosis. Similar events have been found to occur during sporogenesis in mosses, gymnosperms and angiosperms, and are therefore characteristic of the meiotic transition from sporophyte to gametophyte, even in the absence of a transition from diplophase to haplophase.
The novel aspects of meiosis in D. borreri are largely those connected with the restitution event that precedes meiosis I and serves to maintain the sporophytic chromosome number throughout the life cycle of this fem. Pre-meiotic cells are regularly found to be cleaved by annular wall ingrowths, which traverse the cytoplasm but not the nuclei. The significance of these ingrowths in relation to theories concerning apogamy and plant cell division are discussed.
Effect of substratum wettability and charge on adhesion in vitro and encapsulation in vivo by insect haemocytes
Authors: Lackie Ann M. 
Published: April 2021

ABSTRACT
The circulating leucocytes of insects, the haemocytes, adhere to and encapsulate foreign material that enters the insect’s body cavity. The thickness of the capsule depends not only on the insect species but also on the nature of the object concerned, a fact that is of great importance to invading parasites and pathogens. In this paper, some of the factors that may stimulate haemocyte adhesion and subsequent encapsulation of the object have been investigated using abiotic materials with surfaces of different charge and wettability. The negativity and wettability of surfaces of polystyrene beads and plates can be increased by pretreatment with acid, and adhesion of haemocytes to these modified surfaces has been examined in vivo and in vitro. A similar proportion of haemocytes of the locust Schistocerca gregaria adhere to the plates in vitro, irrespective of the changes in charge and wettability, but the adhesion of haemocytes of the cockroach Periplaneta americana is proportional to the increases in both parameters. These differences in cell behaviour are reflected in vivo: cockroach haemocytes form thicker capsules around more hydrophilic and more negatively charged polystyrene beads, while locust cells encapsulate both types of surface to the same, minimal, degree. Positively and negatively charged Sepharose beads are encapsulated more thickly than are neutral beads in cockroaches; negatively charged Sepharose beads are not encapsulated at all in locusts.
There are thus obvious differences between the two species in the ways in which their haemocytes respond to these modified abiotic surfaces. It is suggested that capsule thickness in vivo depends on the initial cell-substratum contact; different surfaces stimulate the cell to different extents, which in turn causes variations in the recruitment of other cells to the capsule.
Antibody-induced membrane fusion in Paramecium
Authors: Barnett Audrey 
Published: April 2021

ABSTRACT
Immobilization of cells by specific immune serum involves crosslinking between immunoglobulin G (IgG) and the i-antigen in the cell membrane. Globular material is seen to accumulate at the ciliary tips by phase-contrast and fluorescence microscopy in a manner analogous to ‘capping’ in more typical eukaryotes. When immobilized cells of Paramecium are examined by scanning electron microscopy, the fused ciliary tips are seen to be distended, discoidal membranes. Transmission electron microscopy often reveals several ciliary axonemes enclosed within a single, enlarged membrane that is oriented with the ferritin-labelled second antibody directed against the i-antigen antibody on the outer surface only. Fixed cells or living cells treated with immune Fab do not show membrane changes, but do bind antibody. Membrane fusion occurs only if cells are alive and the i-antigen is directly or indirectly cross-linked by intact immune IgG.
The mitotic spindle of chinese hamster ovary cells isolated in taxol-containing medium
Authors: Kuriyama Ryoko , Keryer Guy , Borisy Gary G. 
Published: April 2021

ABSTRACT
Mitotic spindles from Chinese hamster ovary (CHO) cells were isolated and purified by a one-step procedure in an isolation medium containing the microtubule-stabilizing drug, taxol. Released mitotic spindles were examined by phase-contrast, polarizing and differential-interference microscopy. They were also stained with monoclonal antibody raised against yeast tubulin and examined by epifluorescence microscopy. The spindles were free from visible cytoplasmic contaminants and the chromosomes were generally lost from the preparations. Electron microscopy showed that microtubules were the dominant structural component and sodium dodecyl sulphate/gel electrophoresis showed that tubulin was the major molecular species present, although a number of minor components, possibly representing microtubule-associated proteins (MAPs), were present. The taxol procedure was also useful in obtaining other microtubule-containing structures such as the midbody or the cytoplasmic microtubule complex in interphase cells. The taxol procedure was also used to isolate mitotic spindles from HeLa cells. The HeLa spindles stained positively with an antibody specific for the 210 × 103 Mr microtubule-associated protein, indicating that the MAP was retained by the taxol procedure. The taxol procedure appears to be of great advantage in large-scale preparations of spindles for biochemical analysis.
Intermediate filaments in the cytoskeletons of fish chromatophores
Authors: Murphy Douglas B. , Grasser William A. 
Published: April 2021

ABSTRACT
When fish pigment cells (melanophores, erythrophores) are lysed by a modified Kleinschmidt method on a buffer–air interface and examined by electron microscopy, large numbers of intermediate filaments are observed. The intermediate filament networks are distinct from actin and tubulin, and entrap the pigment as determined by stereo viewing of freeze-dried rotary-shadowed specimens. During lysis, under conditions that do not preserve actin filaments or microtubules, the area covered by dispersed pigment granules reaches a maximum size and remains stable for many minutes, suggesting that intermediate filaments are responsible for holding the pigment in position and preventing further cytoplasmic dispersion. These observations demonstrate that fish pigment cells contain large numbers of intermediate filaments and suggest that they may be important for coordinating pigment granule movement.