bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of endosomal pH evolution in Dictyostelium discoideum amoebae Study by fluorescence spectroscopy
Authors: Aubry Laurence , Klein Gérard , Martiel Jean-Louis , Satre Michel 
Published: April 2021

ABSTRACT
The evolution of endo-lysosomal pH in Dictyostelium dis -coideum amoebae was examined during fluid-phase endocytosis. Pulse-chase experiments were conducted in nutritive medium or in non-nutritive medium using fluorescein labelled dextran (FITC-dextran) as fluid-phase marker and pH probe. In both conditions, efflux kinetics were characterized by an extended lag phase lasting for 45-60 min and corresponding to intracellular transit of FITC-dextran cohort. During the chase period, endosomal pH decreased during ∼20 min from extracellular pH down to pH 4.6-5.0, then, it increased within the next 20-40 min to reach pH 6.0-6.2. It was only at this stage that FITC-dextran was released back into the medium with pseudo first- order kinetics. A vacuolar H+-ATPase is involved in endosomal acidification as the acidification process was markedly reduced in mutant strain HGR8, partially defective in vacuolar H+-ATPase and in parent type strain AX2 by bafilomycin A1, a selective inhibitor of this enzyme. Our data suggest that endocytic cargo is channeled from endosomes to secondary lysosomes that are actively linked to the plasma membrane via recycling vesicles.
α Melanocyte stimulating hormone (αmsh) stimulates normal human melanocyte growth by binding to high-affinity receptors
Authors: Luca Michele De , Siegrist Walter , Bondanza Sergio , Mathor Monica , Cancedda Ranieri , Eberle Alex N. 
Published: April 2021

ABSTRACT
The combined action of cholera toxin (CT)-dependent activation of the adenylate cyclase signaling pathway, stimulation of protein kinase C, and activation of the tyrosine kinase activity of cell surface receptors and proto-oncogene products, have been shown to stimulate melanocyte proliferation. However, natural factors responsible for the optimal stimulation of normal human melanocyte growth, either isolated or co-cultured with keratinocytes, remain largely unknown. aMSH (α melanocyte stimulating hormone) has previously been shown to bind to murine and human melanoma cells and to stimulate their adenylate cyclase and tyrosinase activity. In contrast, very little is known about the presence and function of αMSH receptors in normal human melanocytes. We now report that aMSH: (i) binds to normal human melanocytes through a single class of high-affinity receptors; (ii) does not induce per se melanocytes to enter the S-phase of the cell cycle; (iii) does indeed stimulate melanocyte proliferation in a dose-dependent fashion; but its stimulatory effect requires bFGF and/or the activation of protein kinase C.
Six git genes encode a glucose-induced adenylate cyclase activation pathway in the fission yeast Schizosaccharomyces pombe
Authors: Byrne Susan M. , Hoffman Charles S. 
Published: April 2021

ABSTRACT
An important eukaryotic signal transduction pathway involves the regulation of the effector enzyme adenylate cyclase, which produces the second messenger, cAMP. Previous genetic analyses demonstrated that glucose repression of transcription of the Schizosaccharomyces pombe fbp1 gene requires the function of adenylate cyclase, encoded by the git2 gene. As mutations in git2 and in six additional git genes are suppressed by exogenous cAMP, these ‘upstream’ git genes were proposed to act to produce a glucose-induced cAMP signal. We report here that assays of cAMP levels in wild-type and various mutant S. pombe cells, before and after exposure to glucose, show that this is the case. The data suggest that the cAMP signal results from the activation of adenylate cyclase. Therefore these ‘upstream’ git genes appear to encode a glucose-induced adenylate cyclase activation pathway. Assays of cAMP on a strain carrying a mutation in the git6 gene, which acts downstream of adenylate cyclase, indicate that git6 may function to feedback regulate adenylate cyclase activity. Thus git6 may encode a cAMP-dependent protein kinase.
Transcriptionally active minichromosomes are attached transiently in nuclei through transcription units
Authors: Jackson D. A. , Cook P. R. 
Published: April 2021

ABSTRACT
Viral minichromosomes provide simple models for chromatin domains. The sequences attaching them to larger nuclear structures were mapped; attachments were defined operationally by their ability to prevent chromatin fragments electroeluting from nuclei. Cells encapsulated in agarose microbeads were lysed and analysed subsequently in a ‘physiological’ buffer. Non-transcribed minichromosomes eluted from nuclei but transcriptionally active ones did not. Cutting attached minichromosomes with HaeIII enabled most of the resulting ∼400 bp fragments to elute. Analysis of residual fragments showed that no single sequence was responsible for attachment; rather, minichromosomes were attached at only one or two points through a promoter or part of a transcription unit. This suggests that RNA polymerases mediate attachments that change dynamically as the template slides past the attached enzyme. As, under optimal conditions, polymerases continue to elongate roughly at the rate found in vivo, these attachments are unlikely to be generated artifactually.
Detection of dna in the nucleoids of chloroplasts and mitochondria in Euglena gracilis by immunoelectron microscopy
Authors: Hayashi-Isimaru Yasuko , Ueda Katsumi , Nonaka Mitsuko 
Published: April 2021

ABSTRACT
DNA in the nucleoids of chloroplasts and of mitochondria in Euglena gracilis was detected with anti-DNA antibodies by immunoelectron microscopy. After treatment with the antibodies, DNA in these organelles combined with gold particles that had been coated with anti-IgM antibodies such that it was possible to trace the outlines of the nucleoids. Nucleoids in chloroplasts appeared to be composed of twisted threads 50-70 nm in diameter. The twisted threads were entangled to form thicker nodes of 100-200 nm diameter. Most nucleoids in mitochondria were spherical or ovoid, 70-130 nm in diameter. Nucleoids both in chloroplasts and in mitochondria contained cores with which DNA threads were in tight contact. The structure of the nucleoids was very different from those previously observed by conventional electron microscopy.
Identification and preliminary characterization of a 65 kDa higher-plant microtubule-associated protein
Authors: Chang-Jie Jiang , Sonobe Seiji 
Published: April 2021

ABSTRACT
Microtubules in plant cells, as in animal cells, are dynamic structures. However, our lack of knowledge about the constituents of microtubules in plant cells has prevented us from understanding the mechanisms that control microtubule dynamics. To characterize some of these constituents, a cytoplasmic extract was prepared from evacuolated protoplasts (miniprotoplasts) of tobacco BY-2 cells, and microtubules were assembled in the presence of taxol and disassembled by cold treatment in the presence of Ca2+ and a high concentration of NaCl. SDS-PAGE analysis of triplecycled microtubule protein revealed the presence of 120 kDa, 110 kDa and a group of 60-65 kDa polypeptides in addition to tubulin. Since these polypeptides had copolymerized with tubulin, through the three cycles of assembly and disassembly, and they bundle microtubules, we tentatively identified the three polypeptides as microtubule-associated proteins (MAPs).
To characterize these factors further, triple-cycled microtubule protein was fractionated by Mono-Q anion-exchange chromatography and the microtubulebundling activity of each fraction was examined. Fractions having microtubule-bundling activity contained only the 65 kDa MAP, an indication that the 65 kDa MAP is responsible for the bundling of microtubules. Purified 65 kDa MAP formed cross-bridge structures between adjacent microtubules in vitro.
Polyclonal antibodies were raised in mice against the 65 kDa MAP. Immunofluorescence microscopy revealed that the 65 kDa MAP colocalized with microtubules in BY-2 cells throughout the cell cycle. Western blotting analysis of extracts from several species of plants suggested that the 65 kDa MAP and/or related peptides are widely distributed in the plant kingdom.
Vcam-1 is a cs1 peptide-inhibitable adhesion molecule expressed by lymph node high endothelium
Authors: May Michael J. , Entwistle Gillian , Humphries Martin J. , Ager Ann 
Published: April 2021

ABSTRACT
Previous studies have shown that unactivated lymphocytes bind to CS1 peptide and that the adhesion of these cells to high endothelium is inhibited by CS1 peptide. These results suggest that lymphocyte binding occurs via recognition of the CS1-containing splice variant of fibronectin expressed on the high endothelial surface. We have now extended these studies by determining the role of the CS1 receptor, α4β1 (VLA-4) and the alternative VLA-4 ligand, VCAM-1 in a rat model of lymphocyte-high endothelial cell interaction. Anti-VLA-4 antibody, HP2/1, blocked lymphocyte adhesion to resting and IFN-γ (interferon-γ) pretreated cultured high endothelial cells (HEC) in a dose-dependent manner with maximal inhibition of 60%. HP2/1 completely blocked the adhesion of rat lymphocytes to immobilized CS1 peptide and to a recombinant soluble (rs) form of human VCAM-1. Lymphocyte binding to rsVCAM-1 was also completely blocked by CS1 peptide. Anti-rat VCAM-1 monoclonal antibody 5F10 inhibited adhesion to untreated and IFN-γ-treated HEC equally and its effect at 50% inhibition was slightly less than that of HP2/1. These findings suggest that a CS1 peptideinhibitable ligand expressed by high endothelium is VCAM-1. The majority of cultured HEC expressed significant levels of VCAM-1 under basal conditions, as did HEV in peripheral lymph nodes. VCAM-1 expression by HEC was upregulated by cytokine pretreatment and the effects were ordered: IFN-γ &gt; TNF-α &gt; IL-1 β.
The results described here demonstrate that rat peripheral lymph node HEC express VCAM-1, its expression is upregulated by cytokines, in particular IFN-γ, and it supports the adhesion of unactivated lymphocytes. They also suggest that the VLA-4/VCAM-1 adhesion pathway may operate during the constitutive migration of lymphocytes into lymphoid organs. Although the mechanism of CS1 peptide inhibition was not determined, these results show that VCAM-1 is a CS1 peptide-inhibitable ligand and therefore CS1, on its own, cannot be used as a specific indicator of fibronectin activity.
Internucleosomal dna fragmentation and programmed cell death (apoptosis) in the interdigital tissue of the embryonic chick leg bud
Authors: Garcia-Martinez V. , Macias D. , Gañan Y. , Garcia-Lobo J. M. , Francia M. V. , Fernandez-Teran M. A. , Hurle J. M. 
Published: April 2021

ABSTRACT
In this work we have attempted to characterize the programmed cell death process in the chick embryonic interdigital tissue. Interdigital cell death is a prominent phenomenon during limb development and has the role of sculpturing the digits. Morphological changes in the regressing interdigital tissue studied by light, transmission and scanning electron microscopy were correlated with the occurrence of internucleosomal DNA fragmentation, evaluated using agarose gels. Programming of the cell death process was also analyzed by testing the chondrogenic potential of the interdigital mesenchyme, in high density cultures. Our results reveal a progressive loss of the chondrogenic potential of the interdigital mesenchyme, detectable 36 hours before the onset of the degenerative process. Internucleosomal DNA fragmentation was only detected concomitant with the appearance of cells dying with the morphology of apoptosis, but unspecific DNA fragmentation was also present at the same time. This unspecific DNA fragmentation was explained by a precocious activation of the phagocytic removal of the dying cells, confirmed in the tissue sections. From our observations it is suggested that programming of cell death involves changes before endonuclease activation. Further, cell surface changes involved in the phagocytic uptake of the dying cells appear to be as precocious as endonuclease activation.
The nuclear pore complex: three-dimensional surface structure revealed by field emission, in-lens scanning electron microscopy, with underlying structure uncovered by proteolysis
Authors: Goldberg M. W. , Allen T. D. 
Published: April 2021

ABSTRACT
The structure of the nuclear pore complex (NPC) has been previously studied by many different electron microscopic techniques. Recently, scanning electron microscopes have been developed that can visualise biologically relevant structural detail at the same level of resolution as transmission electron microscopes and have been used to study NPC structure. We have used such an instrument to visualise directly the structure of both cytoplasmic and nucleoplasmic surfaces of the NPC of manually isolated amphibian oocyte nuclear envelopes that have been spread, fixed, critical point dried and coated with a thin fine-grained film of chromium or tantalum. We present images that directly show features of the NPC that are visible at each surface, including coaxial rings, cytoplasmic particles, plug/spoke complexes and the nucleoplasmic basket or fishtrap. Some cytoplasmic particles are rod-shaped or possibly “T”-shaped, can be quite long structures extending into the cytoplasm and may be joined to the coaxial ring at a position between each subunit. Both coaxial rings, which are proud of the membranes, can be exposed by light proteolytic digestion, revealing eight equal subunits each of which may be bipartite. We have determined that the nucleoplasmic filaments that make up the baskets are attached to the outer periphery of the coaxial ring at a position between each of its subunits. These filaments extend into the nucleoplasm and insert at the distal end to the smaller basket ring. The space left between adjacent basket filaments would exclude particles bigger than about 25 nm, which is consistent with the exclusion limit previously found for NPC-transported molecules.
Nuclei that lack a lamina accumulate karyophilic proteins and assemble a nuclear matrix
Authors: Jenkins Hazel , Hölman Thomas , Lyon Carol , Lane Birgitte , Stick Reimer , Hutchison Christopher 
Published: April 2021

ABSTRACT
Xenopus egg extracts, which support nuclear assembly and DNA replication in vitro, were physically depleted of lamin B3 using monoclonal antibodies linked to magnetic beads. Depleted extracts were still able to support nuclear envelope assembly around demembranated sperm heads but the resulting pronuclei lacked a lamina and were unable to initiate semiconservative DNA replication or to assemble replicases, confirming previous data. Immunoblotting analysis of isolated nuclei and nuclear matrix fractions indicated that lamin-depleted nuclei still accumulated nucleoporins and PCNA. Furthermore, the rate of PCNA uptake was identical in lamin-depleted and control nuclei. However, neither the nucleoporins nor the PCNA was associated with nuclear matrix fractions. The major protein components of sperm pronuclear matrix fractions were characterized by two-dimensional gel electrophoresis. Of these proteins only three out of 22 species, other than the lamins, were significantly reduced in lamin-depleted nuclei, indicating that these nuclei do assemble a nuclear matrix.
Selective killing induced by an inhibitor of n-linked glycosylation
Authors: Larsson Olle , Carlberg Magdalena , Zetterberg Anders 
Published: April 2021

ABSTRACT
Treatment with a low dose (0.5 μg/ml) of tunicamycin (an inhibitor of N-linked glycosylation) blocked the cell cycle progression of both normal Balb/c 3T3 cells (A31) and their SV40-transformed derivatives (SVA31) specifically in early G1 (0-3 h after mitosis). Upon release after an 8-h treatment the A31 cells returned to the cell cycle via a 9-h recovery phase, indicating that they were arrested in G0. The A31 cells were fully viable after this treatment. In contrast, the postmitotic SVA31 cells, which were unable to arrest in G0, did not divide after the removal of tunicamycin. Instead, these cells died but this did not occur until 22-34 h after release from the treatment. SVA31 cells that had passed the postmitotic phase of G1 survived during the parental generation and divided normally. However, a large portion of these cells died during the next cycle, and in total during a 48-h period approximately 50% of the cells were killed as a consequence of an 8-h exposure to tunicamycin. In contrast, treatment with inhibitors of protein synthesis and HMG CoA reductase activity as well as inhibitors of modification of N-linked oligosaccharide chains did not result in cell death.
Internalization of hyaluronan by chondrocytes occurs via receptor-mediated endocytosis
Authors: Hua Qiang , Knudson Cheryl B. , Knudson Warren 
Published: April 2021

ABSTRACT
Several studies have suggested that chondrocytes must have the capacity to internalize and degrade extracellular hyaluronan. In the present study we show direct evidence that hyaluronan is, in fact, endocytosed by chondrocytes and that the endocytosis is mediated via cell surface CD44/hyaluronan receptors. Cultures of bovine articular chondrocytes as well as rat chondrosarcoma chondrocytes were incubated with either fluoresceinor 3H-labeled hyaluronan. Intense binding and accumulation of labeled hyaluronan was visualized by fluorescence microscopy or bright-field/dark-field microscopy following autoradiography. Cell surface hyaluronan was removed with either trypsin or Streptomyces hyaluronidase in order to distinguish and quantify intracellular endocytosed hyaluronan. Labeled hyaluronan was visualized within small discrete intracellular vesicles distributed throughout the cytoplasm. Binding and endocytosis of fluoresceinor 3H-labeled hyaluronan was totally blocked by the addition of excess unlabeled hyaluronan or hyaluronan hexasaccharides, competitive inhibitors of hyaluronan/hyaluronan receptor interactions. Binding and endocytosis was also blocked by the addition of anti-CD44 monoclonal antibodies. Characterization of endocytosed 3H-labeled hyaluronan demonstrated that a significant portion of the hyaluronan was degraded by both the bovine articular and rat chondrosarcoma chondrocytes. Interestingly, a higher proportion of bound hyaluronan was internalized by the bovine chondrocytes. Therefore, hyaluronan receptormediated endocytosis and degradation of hyaluronan may provide a critical link to the maintenance and homeostasis of cartilage tissue.
Endothelial cells adhere to the rgd domain and the fibrinogen-like terminal knob of tenascin
Authors: Joshi Paritosh , Chung Chang-Y. , Aukhil Ikramuddin , Erickson Harold P. 
Published: April 2021

ABSTRACT
We have found that endothelial cells adhere much more strongly than fibroblasts to domains of tenascin and fibronectin. Endothelial cells adhered weakly, without spreading, to bacterial expression proteins corresponding to the tenth fibronectin type III (FN-III) domain of fibronectin, which contains the RGD. A larger fibronectin protein, containing this domain and the three amino-terminal ‘synergy’ domains gave strong adhesion and spreading. Two widely separated domains of tenascin gave adhesion. The third FN-III domain, TNfn3, which contains an RGD sequence in human and chicken tenascin, gave very strong adhesion and spreading of endothelial cells when tested as an isolated domain. Larger segments containing TNfn3 and the adjacent TNfn2 gave weaker adhesion, probably because the RGD sequence is partially blocked. Adhesion to this domain required divalent cations, was exquisitely sensitive to soluble GRGDSP peptide, and was blocked by antisera to the integrin αvβ3. The second tenascin adhesion domain was the fibrinogen-like C-terminal knob, TNfbg. Cells adhered to but did not spread on this domain. This adhesion required divalent cations and was also sensitive to GRGDSP peptide, so it may be mediated by an integrin receptor.
We have explored a range of conditions for preparing the adhesion substratum, and our results may resolve the controversy over whether tenascin can act as a substratum adhesion molecule. When coated for short times (1-2 hours) on plastic, tenascin had no adhesion activity, in contrast to fibronectin and the expression proteins, which gave strong adhesion under these conditions. When coated for longer times (12-24 hours) on plastic, the tenascin substratum supported good adhesion, but not spreading, of endothelial cells. Tenascin coated on nitrocellulose gave substantially stronger adhesion than on plastic, but still required long coating times for maximal activity. Adhesion of endothelial cells to native TN was inhibited by GRDGSP peptide. The cell adhesion activity demonstrates the presence on endothelial cells of tenascin receptors, which may play a supportive role in angiogenesis, in the structure of blood vessels, or in binding tenascin to the cell surface to elicit or enhance a signalling function.
Commitment of the teratocarcinoma-derived mesodermal clone c1 towards terminal osteogenic differentiation
Authors: Poliard A. , Lamblin D. , Marie P. J. , Buc-Caron M. H. , Kellermann O. 
Published: April 2021

ABSTRACT
The mesodermal clone C1 was derived from the multipotent embryonal carcinoma 1003 cell line transformed with the plasmid pK4 carrying SV40 oncogenes under the control of the adenovirus E1A promoter. We have shown that the C1 clone becomes committed to the osteogenic pathway when cultured in aggregates in the presence of mediators of the osteogenic differentiation. To further validate C1 as a model with which to study osteogenesis in vitro the kinetics of its differentiation was studied, focusing on the histology of the aggregates and on the expression of a set of genes corresponding to representative bone matrix proteins. The presence of ascorbic acid and - glycerophosphate specifically leads to mineralization in almost 100% of the aggregates. Transcription of the above genes, silent in exponentially growing cells, specifically occurred with the establishment of cell-cell contacts independently of the presence of ascorbic acid and inorganic phosphate. The latter, however, were absolutely required for matrix deposition and mineralization. In their presence, one observed an overall decline in type I collagen and alkaline phos-phatase transcripts while osteocalcin and osteopontin transcripts preferentially accumulated in cells lining the mineralizing foci. Concomitantly, type I collagen and osteocalcin became extracellularly deposited. The osteogenic differentiation of C1 occurred while cells were still proliferating. The C1 clone thus behaves as a mesodermal stem cell, becoming committed to the osteogenic pathway upon: firstly, establishment of cel-lular contacts; and secondly, addition of ascorbate and β-glycerophosphate. It therefore appears to be a promis-ing in vitro system for deciphering the molecular basis of osteoblast ontogeny. More generally it emphasizes the potential of the pK4-immortalized cell lines for the study of lineage specification.