bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cortical endoplasmic reticulum in plants
Authors: Hepler P. K. , Palevitz B. A. , Lanceele S. A. , McCauley M. M. , Lichtscheidl I. 
Published: April 2021

ABSTRACT
Structural observations provide persuasive evidence for the existence of a cortical network of endoplasmic reticulum (ER) in a large number of plant and animal cells. The network in plants generally possesses a polygonal pattern in which smooth, tubular elements are joined by intervening lamellar segments. The individual elements of ER are often positioned extremely close to the plasma membrane (PM), and may form appositional contacts, but fusion does not occur. The network arises at cytokinesis and establishes continuity between the cortical ER of daughter cells in the form of tightly furled membranetubules that traverse the plasmodesmata. The specific function of the cortical ER complex is unknown but different possibilities seem attractive. It may serve key roles in anchoring the cytoskeleton and in facilitating secretion. The cortical ER might also participate in the communication of signals between the exterior of the cell and cytoplasm. As a consequence of its ability to release and/or sequester Ca, the ER could control the cytoplasmic activity of this ion and thus a host of physiologically and developmentally important reactions.
The composition and morphology of yeast nuclear scaffolds
Authors: Cardenas Maria E. , Laroche Thierry , Gasser Susan M. 
Published: April 2021

ABSTRACT
The yeast nuclear scaffold has been shown to bind with high affinity to genomic sequences that permit autonomous DNA replication of plasmids (ARS elements). We describe here conditions for the isolation of a histone-free nuclear substructure, the nuclear scaffold, from Saccharomyces cerevisiae. We examine the protein composition of this structure, and the conditions under which topoisomerase II, the nuclear factor RAP-1 and RNA polymerase II cofractionate with the scaffold. We find that exposure of nuclei to a combined metal and heat treatment (0.5 mM Cu2+, 37 °C) prior to detergent extraction is required for effective stabilization of these proteins with the scaffold. Electron microscopy of the residual nuclei extracted with non-ionic detergents shows the absence of a typical peripheral lamina structure.
Monoclonal antibody study of the decorated spongiome of contractile vacuole complexes of Paramecium
Authors: Allen Richard D. , Ueno Marilynn S. , Pollard Leonard W. , Fok Agnes K. 
Published: April 2021

ABSTRACT
A monoclonal antibody (mAb) has been developed and selected by immunofluorescence for the radial canals of the contractile vacuole complex (CVC) of Paramecium multimicronucleatum. By applying indirect immunogold labeling to thin frozen sections this mAb has been shown at the electron microscopic level to be specific for the decorated spongiome. We have used the mAb to study the normal interfission appearance as well as developmental stages of the decorated spongiomes. Two decorated spongiomes, presumably involved in water sequestration, radiate as 5-10 bands from unlabeled, circular, 25 μm diameter centers. Two new CVCs arise just anterior to the space occupied by the old spongiomes, the new anterior CVC appearing slightly before the posterior one. Development of the new spongiomes around a 10 gm unlabeled central zone is accompanied by a regression of old spongiome bands until the lengths of these bands in both old and new CVCs are equal just before cell division. After division both old and new spongiome bands grow at equal rates to the same length. Exceptions to the above general scheme, both in number of CVCs in interfission, as well as in position of the new relative to the old CVCs, are also observed.
An analysis of chick limb bud intercellular adhesion underlying the establishment of cartilage aggregates in suspension culture
Authors: Bee James A. , Mark Klaus von der 
Published: April 2021

ABSTRACT
To examine the mechanism of intercellular adhesion in the establishment of limb skeletal elements we have investigated the process of limb bud cell aggregation in vitro. Limb bud cells are aggregation-competent immediately after their trypsin: collagenase dissociation in the absence of calcium. This aggregation is largely Ca2+-independent (CI) and is completely and reversibly inhibited by cycloheximide. In contrast, when limb bud cells are first allowed to recover from Ca2+-free trypsin: collagenase dissociation, aggregation of the surviving population is exclusively Ca2+-dependent (CD) and completely and reversibly inhibited by cycloheximide. The presence of exogenous calcium during initial cell dissociation retains a functional CD aggregation mechanism. However, incubation of such cells with EGTA releases the CD component and converts the cells to a predominantly CI aggregation. Rabbits were immunized with limb bud cells exhibiting the recovered CD aggregation mechanism and the resulting immune sera were screened for their effect on cell aggregation. Relative to pre-immune sera, intact immune IgG agglutinated dissociated limb bud cells whilst immune Fab fragments inhibited their aggregation. The aggregation-inhibiting antiserum recognizes five major limb bud cell surface components with apparent molecular weights of 72K, 50K, 23K, 14.5K and 8.5K (K=103Mr), respectively. Limb bud cell surface plasma membranes were isolated by sucrose gradient density centrifugation and detergent-solubilized proteins coupled to Sepharose 4B with cyanogen bromide. Equivalent cell surface plasma membrane proteins were 125I-iodinated and applied to the affinity column. Limb bud cell surface protein affinity chromatography in the presence of exogenous calcium yields a single protein with an apparent molecular weight of approximately 8.5K. This protein molecule elutes at 0.6 M NaCl, indicating a high affinity, is recognized by the aggregationinhibiting antiserum, and is itself capable of inhibiting CD limb bud cell aggregation. Fab fragments prepared from rabbit antisera specifically directed against the affinity-purified material also inhibit CD limb bud cell aggregation and this inhibition is neutralized by the 8.5K protein. Our data thus demonstrate that CD limb bud cell aggregation is not mediated by fibronectin and/or collagen type I and indicate that this process is governed by a novel 8.5K cell adhesion molecule.
Physiological and structural maturation of a polarised epithelium: The Malpighian tubules of a blood-sucking insect, Rhodnius prolixus
Authors: Skaer H. le B. , Harrison J. B. , Maddrell S. H. P. 
Published: April 2021

ABSTRACT
The development of polarity in a simple epithelium, the Malpighian tubules of Rhodnius, is analysed both ultrastructurally and physiologically. The onset of physiological function, including fluid secretion and the transport of solutes, is determined in late embryos and young hatchling insects and compared with structural development in tubules over a similar period. Two phases of maturation, separated by several days, are detected. The first, during late embryogenesis, involves the development of mature intercellular contacts and the dilation of the lumen, and is associated with the ability to transport specific solutes. The second phase involves the elaboration of the apical and basal membranes and the generation of mitochondria, and is associated with the onset of fluid transport in the tubules and with feeding in 4-day-old hatchlings.
Peroxisomal assembly: Membrane proliferation precedes the induction of the abundant matrix proteins in the methylotrophic yeast Candida boidinii
Authors: Veenhuis Marten , Goodman Joel M. 
Published: April 2021

ABSTRACT
Peroxisomes are massively induced when methylotrophic yeasts are cultured in medium containing methanol. These organelles contain enzymes that catalyze the initial steps of methanol assimilation. In Candida boidinii, a methylotrophic yeast, the peroxisomal matrix (internal compartment) is composed almost exclusively of two proteins, alcohol oxidase and dihydroxyacetone synthase; catalase is present in much lower abundance. Monoclonal and polyclonal antibodies are available against peroxisomal matrix and membrane proteins. These were utilized to correlate the induction of specific proteins with the morphological changes occurring during peroxisomal proliferation. Cells cultured in glucose-containing medium contain two to five small microbodies, which are identifiable by catalase staining and immunoreactivity with a monoclonal antibody against PMP47, an integral peroxisomal membrane protein. Three stages of proliferation can be distinguished when cells are switched to methanol as the carbon source. (1) There is an early stage (within 1 h) in which several peroxisomes develop from a preexisting organelle. This is accompanied by an increase in catalase activity and an induction of PMP47, but no detectable induction of alcohol oxidase or dihydroxyacetone synthase is observed. (2) From 1 to 2.5 h there is further division of these microbodies until up to 30 small peroxisomes generally are present in each of one or two clusters per cell. Induction of alcohol oxidase, dihydroxyacetone synthase and PMP20, a protein that is distributed in the matrix and membrane, is detectable during this time. Serial sections reveal that some peroxisomes remain uninduced while others undergo proliferation. Such sections also show no obvious connections between peroxisomes within clusters. (3) After 2.5 h there is a decrease in the number of peroxisomes per cell (caused at least in part by the movement of organelles into buds) but an increase in volume per peroxisome, until a steady state is reached by 5–10 h.
Domain-specific changes of ciliary striated rootlets during the cell cycle in the hypotrich ciliate Paraurostyla weissei
Authors: Jerka-Dziadosz Maria 
Published: April 2021

ABSTRACT
The dynamics of striated ciliary rootlets (cr) during development of ciliary structures in cells of the hypotrich ciliate Paraurostyla weissei was studied by immunostaining with polyclonal antibody raised against isolated cr of Paramecium tetraurelia. Wildtype cells and two mutants: mlm showing multiple left marginal cirri and mlm/pl showing in addition a certain degree of pattern lability were used to study the boundaries of particular cortex domains.
In interphase cells, cr are attached to all left marginal and caudal cirri and to only the posterior third of the right marginal cirri, cr appear in all nonoral primordia during the first wave of basal body proliferation. After nucleation and early elongation of cr, some cr undergo site-specific regression or stabilization. The spatial deployment of these different modes of development corresponds to specific cortical domains.
In mlm/pl mutants, where specific cortical domains are broadened, changes in the cr system are characteristic for a given domain, regardless of its broadening, but boundaries between adjacent domains are weakened.
Pharmacological evidence for a role for cyclic AMP signalling in Dictyostelium discoideum slug behaviour
Authors: Darcy P. K. , Fisher P. R. 
Published: April 2021

ABSTRACT
Phototaxis and thermotaxis by Dictyostelium discoideum slugs on water agar were impaired by the presence in the agar of adenosine, which is a cyclic AMP receptor antagonist in aggregating amoebae. Caffeine, and presumably its analogue theophylline, inhibit cyclic AMP signalling in aggregating amoebae of D. discoideum. Both compounds perturbed slug behaviour in a similar manner to adenosine, as did both ammonium and sulphate ions. (NH4)3SO4 is known to perturb cyclic AMP binding to its receptor, and ammonia is an inhibitor of cyclic AMP signalling in aggregating amoebae. The receptor agonist, cyclic AMPS, disrupted slug organization and impaired phototaxis when present at concentrations high enough to saturate cyclic AMP receptors and compete effectively with endogenous cyclic AMP signals of similar magnitude to those observed during aggregation. Taken together with the considerable circumstantial evidence for cyclic AMP signalling in slugs, these results support a role for cyclic AMP signalling in slug behaviour.
Cell cycle regulation of p34 cdc2 kinase activity in Physarum polycephalum
Authors: Ducommun Bernard , Tollon Yvette , Garés Michéle , Beach David , Wright Michel 
Published: April 2021

ABSTRACT
The regulation of the mitotic histone H1 kinase activity has been analyzed during the naturally synchronous cell cycle of Physarum polycephalum plasmodia. The universal binding property of the pl3suo1Schizosaccharomyces pombe gene product was used to precipitate and assay the cdc2 histone H1 kinase activity. The kinase activity peaks at the beginning of metaphase and its decline, which requires protein synthesis, appears to be an early event during the metaphase process. Microtubular poisons, temperature shifts and DNA synthesis inhibitors were used to perturb cell cycle regulatory pathways and characterize their effects on cdc2 kinase activation. Our results suggest that the full activation of the mitotic kinase requires at least two successive triggering signals involving microtubular components and DNA synthesis.
Promotion of transendothelial neutrophil passage by human thrombin
Authors: Moser René , Groscurth Peter , Fehr Jorg 
Published: April 2021

ABSTRACT
Thrombin has been reported to elicit two temporally different effects on neutrophil-endothelial interaction, categorically described as ‘neutrophil adhesion’: one expressed within a few minutes, the other after several hours of endothelial preincubation. Prolonged activation resulted in often elongated, tightly interacting neutrophils in contact with human umbilical vein endothelial cells (HUVE) mainly at the intercellular region. In contrast, the neutrophil-endothelial interaction due to short-time priming with thrombin was dominated by round, randomly distributed neutrophils, loosely adhering on the endothelial surface. Sheer stress, introduced to characterize these morphological entities in a quantitative manner, clearly defined the neutrophil response due to short time priming as sheer stresslabile compared to the sheer stress-resistant interaction expressed after prolonged preincubation of HUVE with thrombin. Quantitative determination of neutrophil transendothelial migration served to demonstrate the relevance of such differences in neutrophil binding with respect to subsequent layer penetration. Dependent upon endothelial protein synthesis and inhibited by antithrombin-III-heparin and hirudin, neutrophil layer penetration only occurred after prolonged activation of HUVE whereas the neutrophil-endothelial interaction due to short time priming with thrombin was limited to superficial neutrophil adhesion.
We conclude that thrombin can be added to the list of activators capable of inducing the neutrophil passage-guiding principle, an effect that has recently been detected as closely related to neutrophil adhesion to endothelial ligands expressed upon activation with interleukin-1 and tumor necrosis factor. This biological activity, which can be separated from superficial attachment of polymorphonuclear leukocytes (PMN) to endothelial cells, is a catalytic sitedependent and late phase-specific effect of thrombin on HUVE.
Microgravity decreases C-fos induction and serum response element activity
Authors: groot Rolf P. de , Rijken Philip J. , Hertog Jeroen Den , Boonstra Johannes , Verkleij Arie J. , Laat Siegfried W. De , Kruijer Wiebe 
Published: April 2021

ABSTRACT
Several studies have shown that altered gravity conditions influence mammalian cell growth and differentiation. The molecular mechanisms underlying these effects, however, remain relatively obscure. In this paper we show that microgravity reached in a sounding rocket strongly decreases epidermal growth factor (EGF)-induced expression of the protooncogenes c-fos and c-jun, which are both implicated in the regulation of proliferation and differentiation. Decreased activity of the serum response element (SRE), present in the c-fos promoter-enhancer region, is probably responsible for the decrease in EGF-induced c-fos expression. In addition, we show that gravity alterations differentially modulate distinctive signal transduction pathways, indicating that gravity-dependent modulations of mammalian cell proliferation are unlikely to be caused by a nonspecific stress response of the cell.
Synthetic epidermal pentapeptide and related growth regulatory peptides inhibit proliferation and enhance differentiation in primary and regenerating cultures of human epidermal kératinocytes
Authors: Jensen Peter K. A. , Elgjo Kjell , Laerum Ole D. , Bolund Lars 
Published: April 2021

ABSTRACT
A pentapeptide that inhibits proliferation of mouse epidermal keratinocytes in vivo and in vitro has been purified from mouse skin extracts. In the present study the effect of a synthetic analog of the epidermal pentapeptide on proliferation and differentiation of cultured human epidermal kératinocytes was investigated. In young, rapidly growing primary cultures the pentapeptide caused a dramatic decrease in mitotic activity and also induced pronounced changes in the balance between kinetically defined subpopulations of proliferating cells. A dipeptide derived from the pentapeptide was found to be at least as potent A serine derivative of a hemoregula-tory peptide also seemed to be active. When tested in epidermal cultures regenerating after removal of the suprabasal cell layers, both the pentapeptide and the dipeptide were shown to cause a delay in the proliferative response. Both peptides were also able to stimulate early (increase in cell size) and late (cornified envelope formation) events in the differentiation pathway of the kératinocyte. The apparent stimulatory effect on differentiation was most clearly seen in regenerating cultures, whereas the effect on primary cultures varied with the experimental set-up. It is suggested that homologous epidermal peptide(s) may play a major role in the regulation of human epidermal homeostasis.
Desmosomal glycoproteins 2 and 3 (desmocollins) show N-terminal similarity to calcium-dependent cell-cell adhesion molecules
Authors: Holton J. L. , Kenny T. P. , Legan P. K. , Collins J. E. , Keen J. N. , Sharma R. , Garrod D. R. 
Published: April 2021

ABSTRACT
The N-terminal sequence of a mixture of desmosomal glycoproteins 2 and 3 (dg2/3, desmocollins) from bovine nasal epidermis, prepared by electro-elution from polyacrylamide gels, was determined by solidphase Edman degradation. A sequence of 23 amino acids was obtained. This showed 43% identity with that of the N terminus of the calcium-dependent cell adhesion molecule, N-cadherin. A lesser degree of identity with other members of the cadherin–uvo– morulin-L-CAM family was also found. In order to confirm that the sequence was derived from the dg2/3 molecules a rabbit antiserum was raised against a synthetic peptide corresponding to the sequence, conjugated to keyhole limpet haemocyanin (KLH). The antiserum obtained showed high (titre) activity against both the peptide and KLH in ELISA. Each activity could be specifically adsorbed with the appropriate ligand. The antiserum reacted specifically with both dg2 and dg3 of bovine nasal epidermis on immunoblots, this binding was blocked by the N-terminal peptide but was unaffected by KLH. The identity of dg2 and -3 in these preparations was confirmed by immunoblotting with two monoclonal antibodies and one polyclonal antiserum raised against the whole molecules. The N-terminal peptide antiserum was shown to bind to the intercellular space of desmosome profiles by immunoelectron microscopy on ultra-thin frozen sections. One of the two monoclonal antibodies (07–4D) also reacted with the desmosomal intercellular space. dg2 and -3 were shown by Staphylococcus aureus V8 protease digestion to have identical one-dimensional peptide maps. Both the N-terminal antiserum and 07–4D reacted with a V8 fragment of 19000Mr derived from dg2 and dg3. The other monoclonal antibody (52–3D), which has previously been shown to react with the cytoplasmic regions of dg2/3, recognised V8 fragments of lower molecular weight. These results indicate that the dg2/3 molecules of epidermal desmosomes are related to a family of calcium-dependent adhesion molecules, demonstrate that the N-termini of the molecules are located extracellularly, and support the view that they are directly implicated in desmosomal adhesion.
Differential effects of myosin-antibody complexes on contractile rings and circumferential belts in epitheloid cells
Authors: Zurek Barbara , Sanger Jean M. , Sanger Joseph W. , Jockusch Brigitte M. 
Published: April 2021

ABSTRACT
The role of myosin filaments during assembly and activity of microfilament rings was analyzed by microinjecting epitheloid cells (PtK2 and LLC-PK1 kidney cell lines) with specific anti-myosins. Six monoclonal antibodies directed against the light meromyosin (LMM) region of the myosin molecule were characterized with respect to epitope location, and their effects on actin-activated MgATPase as well as on assembly, structural integrity and stability of myosin filaments. All of these antibodies recognized LLC-PK1 myosin, but only three reacted with PtK2 myosin. The remaining three served as matching controls in experiments with this cell line. When injected in amounts sufficient to yield an excess of antibody over myosin, the reactive antibodies significantly delayed formation and constriction of the contractile ring in mitotic cells. These rings contained less myosin, but not less actin, than the controls. This indicates that the recruitment and alignment of actin in the cleavage furrow can occur independently of other components of the contractile ring.
After completion of cytokinesis, the majority of the injected cells was unable to assemble a normal circumferential belt. This resulted in defective epitheloid sheets. Approximately one third of these cells showed grossly distorted cell shapes and an increase in locomotory activity.
All these changes were fully reversible with time, suggesting that the effects of the antibodies were overcome by protein synthesis. The differential sensitivity seen between contractile rings and peripheral belts is discussed with respect to differences in their architecture, stability and proposed function.