bluuebunny/crossref_metadata_2025_split huggingface dataset:
The extracellular matrix ofVolvox: A comparative study and proposed system of nomenclature
Authors: Kirk David L. , Birchem Regina , King Nancy 
Published: April 2021

ABSTRACTThe structure of the extracellular matrix (ECM) of representatives of all four sections of the genus Volvox was examined by a combination of light- and electron-microscopic methods. On the basis of these observations, plus published descriptions of aspects of ECM organization in other members of the order Volvocales, a system of nomenclature is proposed, to facilitate discussion of comparative morphology and phylogeny of the ECM in the order. In this system the ECM is divided into four main zones: the flagellar zone (FZ), which consists of attachments to and specializations of the ECM around the flagella; the boundary zone (BZ), which consists of portions of the ECM that (except in periflagellar regions) are continuous over the surface of the organism and are not structurally continuous with deeper layers; the cellular zone (CZ), which consists of specializations, other than those of the FZ, around individual cells; and the deep zone (DZ), which consists of components that fill the central region of the organism, internal to CZ. An empirically based set of hierarchical subdivisions of these zones is then proposed that permits specific identification of most morphologically distinct ECM components. The fact that not all zones and subzones are present in all members of the order means that this system permits identification of those ECM structures that have been gained or lost during Volvocalean evolution.Species-specific differences in the structure of virtually all aspects of the ECM were seen among the Volvox species examined in this study. However, the fact that such differences cannot always be used as diagnostic characters for the four divisions of the genus was demonstrated by the observation that in certain ECM features two members of the samedivision (V. carteri f. nagariensis and V. carteri f. weismannia) differ markedly in structure from one another, with one member of the pair resembling a member of another division. Thus many details of ECM organization appear to be under separate control, and capable of independent evolution.
Actin cytoskeleton of spread fibroblasts appears to assemble at the cell edges
Authors: Svitkina Tatjana M. , Neyfakh Alexander A. , Bershadsky Alexander D. 
Published: April 2021

ABSTRACT
The action of metabolic inhibitors on actin cytoskeleton of cultured quail embryo fibroblasts has been studied using electron microscopy of platinum replicas and immunofluorescence microscopy. Sodium azide as well as other inhibitors (oligomycin and dinitrophenol) caused the disassembly of all types of actin structures: actin meshwork at the cell active edges, microfilament sheath underlying the cell surface, and microfilament bundles. Studying the time- and dose-dependence of the destruction process we have found that the active edge meshwork and microfilament sheath are much more labile than microfilament bundles. After the removal of metabolic inhibitors actin cytoskeleton restoration begins at the cell edges. The first sign of this process is the formation of actin meshwork along the whole cell perimeter (l-10min of recovery). Sometimes fragments of this meshwork bend upwards forming ruffles. Later (10-20 min of recovery) the microfilament sheath appears at the cell periphery as a narrow band. The sheath seems to be formed from the edge meshwork, since ruffles in the process of transformation to sheath could be seen. During the following restoration the microfilament sheath gradually expands towards the cell centre. The last step of actin cytoskeleton restoration (60-120 min of recovery) is the formation of bundles.
We suggest that the actin in spread fibroblasts polymerizes predominantly at the cell edges and then moves centripetally, forming the microfilament sheath and bundles.
Three-dimensional electron microscopy of the internal nucleolus-associated chromatin and of the nucleolar vacuoles during early germination of Sinapis alba
Authors: Deltour R. , Mosen H. , Bronchart R. 
Published: April 2021

ABSTRACT
Spatial relationships between the internal nucleolus-associated chromatin (NAC) and the numerous nucleolar vacuoles that appear during early germination have been studied in nucleoli of quiescent (non-germinated) and early germinating embryos of Sinapis using serial sections. In quiescent non-vacuolated nucleoli, the transcriptionally inactive internal NAC is a short strand about 900 nm thick that in cross-section appears as heterogeneous fibrillar centres (FCs). At 4 and 6 h after germination one or several large networks of interconnected nucleolar vacuoles develop around the dispersing internal NAC. Clumps of dense chromatin are still present within the nucleolar vacuoles and are probably unfolding into deoxyribonucleoprotein (DNP) fibres (about llOnm thick), which rapidly intrude within the nucleolar body and form thin chromatin threads. At 24 h after germination the internal NAC is more dispersed and forms, for its greatest part, a long thread (about 240 nm in diameter) wrapped up with a few dense fibrillar component, the whole forming the first outline of a nucleolonema. In cross-section most of the internal NAC appears as homogeneous FCs but short portions remain more condensed and appear as heterogeneous FCs always associated with a nucleolar vacuole. From 48 h the internal NAC is a longer thinner strand (about 160 nm in diameter), probably continuous and surrounded entirely by a homogeneous muff of dense fibrillar component, the whole forming a typical nucleolonema (about 950 nm thick) meandering throughout the nucleolus. Small amounts of the internal NAC still remain undispersed in the form of heterogeneous FCs associated with a nucleolar vacuole. The repeated association of nucleolar vacuoles and dispersing internal NAC suggests that they could play a role in chromatin dispersion and, or, activation by creating a favourable microenvironment.
Control of cell proliferation in the human embryonic cornea: An autoradiographic analysis of the effect of growth factors on dna synthesis in endothelial and stromal cells in organ culture and after explantation In Vitro
Authors: Hyldahl Louise 
Published: April 2021

ABSTRACT
A novel technique for studying the growth properties of human embryonic corneal endothelial and stromal cells in organ culture was devised. Human embryonic eye globes were microdissected so that a passage was opened between the outer environment and the anterior chamber, which rendered free access of tissue culture medium to the endothelial cell monolayer. The dissected eye globes were maintained in organ culture for 24 h in the continuous presence of tritiated thymidine. Cross-sections were cut through the whole eye globes and subjected to autoradiographic analysis in order to estimate the mitogenic response of each corneal cell type to externally supplied growth factors and hormones.
It was found that the corneal endothelial cells could be stimulated to initiate DNA synthesis by exposure to epidermal growth factor (EGF). The stimulatory effect of this growth factor could be enhanced if either insulin-like growth factor I (IGF I) or a combination of insulin, transferrin and high density lipoprotein (HDL) was simultaneously added. Similar results were obtained by adding growth factors and hormones to primary cell cultures from human embryonic corneas. It was also found that the stromal cell could be stimulated to initiate DNA synthesis by the addition of EGF and IGF I or a combination of insulin, transferrin and HDL.
Taken together, these results suggest that the proliferation of corneal endothelial cells and stromal cells is dependent on EGF-like factors as well as on some insulin-like substance during embryogenesis.
Characterization of early compartments in fluid phase pinocytosis: a cell fractionation study
Authors: Casey Kimberly A. , Maurey Karen M. , Storrie Brian 
Published: April 2021

ABSTRACT
Flotation through a 5·6% Percoll gradient of pinosomes from Chinese hamster ovary (CHO) cells labelled during a 10min internalization period with horseradish peroxidase (HRP), a solute, revealed two pinosomal populations, the expected low-buoyancy population and an unexpected buoyant population. The buoyant pinosomes that sedimented similarly to plasma membrane were not an artifact of HRP trapping during homogenization or of cell surface-adherent HRP. No trapping or cell surface adherence of HRP could be detected by biochemical or cytochemical assays, even after internalization periods as short as 15 s to 1 min. With short uptake times, the buoyant pinosome population was the major HRP positive vesicle population, suggesting a precursor-to-product relationship between the two populations. In pulse-chase experiments, the buoyant pinosome population was shown to be highly exocytic and the precursor to later pinosomes. By electron-microscope cytochemistry, rapidly labelled, HRP positive pinosomes (15 s to 1 min uptake) were typically smooth vesicles with a median diameter of ≈0·30 μm and a size range from ≈0·10 μm to greater than 1·0 μm in diameter. We suggest that these rapidly labelled structures are a very early stage in the intracellular processing of pinocytic vesicles.
Differential redistribution of lectin receptor classes on clonal rat myotubes and myoblasts
Authors: Sawyer James T. , Akeson Richard A. 
Published: April 2021

ABSTRACT
To evaluate the relative mobilities of cell surface glycoconjugates during myogenesis we have studied the redistribution of fluorescein-conjugated plant lectins on L6 rat myogenic cells. Previous experiments had demonstrated that the receptors for the lectins soybean agglutinin (SBA), wheat germ agglutinin, concanavalin A and Lens culinaris agglutinin all were relatively uniformly distributed on both myoblasts and myotubes, and that SBA receptors were capable of rapid redistribution on myotubes but not myoblasts at 4°C (Sawyer & Akeson, 1983). Here we show that when SBA-labelled myoblasts are incubated at 37°C, or for extended times at 4°C, the lectin aggregates as on myotubes. So it appears that SBA-binding components show a quantitative rather than qualitative change in their mobility during L6 differentiation. In addition, the redistribution of the three other lectins on myoblasts and myotubes was either less prominent (i.e. showing fewer apparent surface clusters) or occurred less rapidly than with SBA. None of these three lectins showed striking differences in mobility between myoblasts and myotubes. Thus, it appears that SBA binds to a subset of surface glycoconjugates that is relatively highly mobile, and that this mobility is specifically enhanced with differentiation.
Cellulose microfibril orientation in Oocystis solitaria: Proof that microtubules control the alignment of the terminal complexes
Authors: Quader H. 
Published: April 2021

ABSTRACT
In the green alga Oocystis solitaria microtubules control the regular deposition of cellulose microfibrils. Although it has frequently been suggested that the influence of the cortical microtubules is mediated through the alignment of structures in the plasma membrane, e.g. the cellulose-synthesizing enzymes, experimental proof is lacking. In Oocystis the putative cellulose-synthesizing units, the so-called terminal complexes, can be visualized following freeze-fracture. With respect to the synthesis of a given layer of microfibrils two distinct situations are observable: terminal complex doublets occur before the start of cellulose formation, but are subsequently separated into single terminal complexes by pressure exerted by the crystallizing microfibrils. In order to investigate the effect of anti-microtubular substances on the orientation of the terminal complexes, the state of cellulose deposition at the time of drug application was marked by short (15–30 min) treatment with Congo Red, which causes a morphological change in the terminal complexes. The characteristic alignment of the terminal complexes, both doublets and fragmented single ones, is severely disturbed in cells treated with the herbicide amiprophosmethyl, which is known to interfere with the action of microtubules. The results provide strong evidence that microtubules control the alignment of the putative cellulose-forming units in Oocystis. The observed pattern of interference indicates that the microtubules most probably achieve their control by imposing fluidity channels on the membrane and not via direct links with the terminal complexes.
A gradient in the density of intramembrane particles is formed during capping induced by concana valin a
Authors: Bennett Holly , Condeelis John 
Published: April 2021

ABSTRACT
During capping of concanavalin A (ConA) by amoebae of Dictyostelium discoideum, each cell becomes polarized, with the ConA at one end and newly extended pseudopodia at the opposite end of the cell. This new polarity is stable until the cap is shed or internalized.
Intramembrane particles (IMPs) are widely believed to represent large integral membrane proteins, many of which are ion pumps and channels. Since asymmetric ion currents have been implicated in the development of cell polarity, we have used morphological landmarks associated with the capped cell in freeze-fracture to make a morphometric analysis of the IMP distribution relative to the axis of polarization of the capped cell.
Untreated cells in suspension extend pseudopodia randomly from their surfaces. In these cells the numerical density of IMPs is random. However, capped cells demonstrate a density gradient of IMPs with the lowest density usually in the pseudopodia and the highest in the cap. The difference in density between the cap and other regions of the cell is two- to threefold for all IMPs, but can be as much as sevenfold for &gt;12 nm IMPs.
This study is the first to document that the numerical density of IMPs is altered in response to ligand-induced capping and demonstrates that the distribution of IMPs in a capped cell is related to the axis of polarization of the cell. These results suggest that the development of cell polarity during capping in Dictyostelium amoebae may be due to the asymmetric distribution of IMPs, which may cause asymmetric ion currents across the cell.
Characterization and partial purification of a plasma membrane receptor for Bacillus thuringiensis var. kurstaki lepidopteran-specific δ-endotoxin
Authors: Knowles Barbara H. , Ellar David J. 
Published: April 2021

ABSTRACT
The lepidopteran-specific Pl ô-endotoxin of Bacillus thuringiensis var. kurstaki HD-1 was activated in vitro using insect gut proteases and found to be highly specific for the lepidopteran cell line Choristoneura fumiferana CF1 among a wide range of lepidopteran and dipteran cell lines tested. The toxicity of Pl against CF1 cells is inhibited by.’V-acetylgalactosamine (GalNAc), and the lectins soybean agglutinin (SBA) and wheat-germ agglutinin. Protein blotting was used to identify a glycoprotein of 146×103Mr in the plasma membrane of CF1 cells, capable of binding both the toxin and SBA, which is specific for GalNAc. This glycoprotein was labelled using galactose oxidase and sodium boro-[3H] hydride and solubilized in Triton X-100 before partial purification by affinity chromatography on SBA-agarose. We propose that this glycoprotein is a good candidate for the cellular receptor of the lepidopteran-specific Pl δ-endotoxin of B. thuringiensis var. kurstaki HD-1.
Nuclear matrix generation during reactivation of avian erythrocyte nuclei: An analysis of the protein traffic in cybrids
Authors: Woodcock Christopher L. F. , Woodcock Hilary 
Published: April 2021

ABSTRACT
It has previously been shown that an internal nuclear matrix is generated during the reactivation of the chick erythrocyte nucleus in mouse L-cell cytoplasts. This experimental system has now been used to identify the major polypeptides that migrate into the nucleus during the reactivation process. Mouse L-cells were prelabelled with [35S]methionine, enucleated using cytochalasin B, and fused with 14-to 17-day embryonic chick erythrocytes. Sixteen hours post-fusion, the redistribution of the labelled proteins was examined by electron microscopic autoradiography, and two-dimensional polyacrylamide gel fluorography of the isolated nuclei was used to identify the major imported species. After allowing for cytoplasmic contamination, 15 nucleus-associated polypeptides were identified, two of which also matched with counterparts in the L-cell nuclear preparation. Five of the nucleus-associated polypeptides were tentatively identified (on the basis of one-dimensional gel matches) as nuclear matrix proteins; these five included the two that had counterparts in L-cell nuclei. The autoradiographic results showed that 16 h post-fusion, the specific activity (silver grains/unit area) of the reactivated nucleus was about half that of the cytoplasm, with no evidence for an accumulation of labelled protein at the nuclear periphery. When well-reactivated nuclei were distinguished from poorly reactivated nuclei on the basis of the extent of chromatin decondensation, it was found that their specific activities were quite similar, but because of the difference in size, the well-reactivated nuclei contained about twice as much labelled protein. Estimates of the protein traffic based upon the autoradiographic data indicated that the nuclei had increased in mass by 10·20% during the 16 h reactivation period.
Effect of taxol on first and second meiotic spindle formation in oocytes of the surf clam, Spisula solidissima
Authors: Kuriyama Ryoko 
Published: April 2021

ABSTRACT
The effect of taxol on first and second meiotic spindle formation was examined in oocytes of the surf clam, Spisula solidissima, by immunofluorescence staining with anti-tubulin antibody. The first meiotic spindle appeared to form as in untreated control cells. However, the spindle did not migrate toward the periphery of taxol-activated oocytes, resulting in blockage of the formation of the first polar body. In spite of inhibited microtubule depolymerization and failure of spindle disappearance, the pole separation in telophase that is typical of this material began at the same time as in untreated cells. Polymerization of the second spindle microtubules onto the spindle persisting from the first meiosis led to the formation of a triple form of spindle connected at the poles of each other. The subsequent emergence of ring-shaped microtubule-containing structures in mature activated eggs was not affected by taxol. The mechanism of meiotic spindle formation thus seemsto be different from that in mitosis, where taxol has been shown to block spindle formation completely.
Selection of kidney cell types in primary glomerular explant outgrowths by in vitro culture conditions
Authors: Oberley Terry D. , Yang An-Hang , Gould-Kostka Jeanine 
Published: April 2021

ABSTRACT
Adult guinea pig glomeruli were grown in vitro either in serum or in a chemically defined medium. Glomeruli were plated either directly into plastic flasks or into plastic flasks that had been coated with the extracellular matrix produced by the PF-HR-9 mouse teratocarcinoma endodermal cell line. Both the composition of the medium and the nature of the culture substrate affected whole glomerular attachment and the type of cells produced in culture. Quantitative studies demonstrated selection of cell types by different culture conditions. Three colony types, each composed of distinctive cell types, could be identified by morphological features. The cells constituting two of these colony types were epithelial in nature, but they were identified as different epithelial types by both histochemical and ultrastructural criteria. Previous studies suggested that one epithelial cell type was derived from the glomerular visceral epithelial cell. This study demonstrates that this cell type could be selectively grown in defined medium on plastic. A second cell type showed several features of renal tubular epithelial cells, including histochemical staining for catalase, cell surface microvilli and cilia, and formation of hemicysts and structures that resembled tubules after prolonged periods in culture. To demonstrate that the ‘glomerulus-derived’ tubular cells were indeed tubular epithelium, we isolated purified renal cortical tubules (&gt;99% pure) and cultured them on the HR-9 matrix in a serum-free chemically defined medium. The resultant outgrowths had morphological properties identical to those of the glomerulus-derived tubular cells. It seems likely that small tubular fragments attached to a minority of the glomeruli are the source of these glomerulus-derived tubular cells. Neither epithelial cell type could be subcultured on plastic, but both could be passaged on the HR-9 matrix. A third cell type, the spindle-shaped cell, was easily propagated on both plastic and the HR-9 matrix. The origin of this cell type is not clear. Our results demonstrate the important effect of culture conditions on the selection, growth and differentiation of kidney cell types in vitro.
Phorbol esters activate protein kinase c and glucose transport and can replace the requirement for growth factor in interleukin-3-dependent multipotent stem cells
Authors: Whetton A. D. , Heyworth C. M. , Dexter T. M. 
Published: April 2021

ABSTRACT
Interleukin 3 (IL-3) promotes the survival, proliferation and development of progenitor cells from several distinct haemopoietic lineages and can also stimulate the self-renewal of stem cells. We have explored the mode of action of this growth factor in promoting survival and proliferation, using a multipotent haemopoietic stem cell line FDC-Mix 1. In the absence of IL-3 these cells died within 16–48 h. However, this requirement for IL-3 could be replaced by 12-O-tetradecanoyl-phorbol-13-acetate (TPA) plus Ca2+ ionophore, which promoted not only survival but also DNA synthesis with no concomitant loss of the multipotential nature of these cells. TPA and Ca2+ ionophore, respectively, could also interact synergistically with IL-3 to promote DNA synthesis. Both IL-3 and TPA stimulated the translocation of protein kinase C (PK-C) from the cytosol to a membrane-bound form in FDC-Mix 1 cells. Previously we suggested that IL-3 can activate the primary metabolism of IL-3-dependent cells so that increased glucose transport and glycolysis lead to maintenance of ATP levels and cellular survival. To investigate whether TPA and, or, Ca2+ ionophore could also influence cellular survival via an activation of glucose uptake we assessed the effects of these agents on hexose transport. TPA ± Ca2+ ionophore activated hexose transport to the same degree as does IL-3 but these agents cannot superstimulate FDC-Mix 1 hexose transport in cells that already exhibit an activated transport system from preincubation with IL-3. We conclude that IL-3 maintains FDC-Mix 1 cells via its ability to activate PK-C and increase cytosolic levels of Ca2+, and that an IL-3-mediated activation of PK-C may promote cellular survival via its ability to enhance hexose uptake by phosphorylating the glucose transport protein.