bluuebunny/crossref_metadata_2025_split huggingface dataset:
Action of activated 27 000 M
r toxin from Bacillus thuringiensis var. israelensis on Malpighian tubules of the insect, Rhodnius prolixus
Authors: Maddrell S. H. P. , Overton J. A. , Ellar D. J. , Knowles B. H. 
Published: April 2021

ABSTRACT
The action of activated 27 000 Mr toxin from Bacillus thuringiensis var. israelensis (Bti toxin) on Malpighian tubules of Rhodnius prolixus has been investigated. Its binding to the tubules is slowed by low temperature but is not prevented even at 0°C. The binding is less effective at pH 10 than at pH 7. Pretreatment of the tubules with 0.1 mmol 1−1 ouabain or bumetanide or 1 μmoll−1 5-hydroxytrypt-amine did not affect the toxicity of the toxin. The toxin causes very large changes in the trans-epithelial potential difference; it changes from 40 mV, lumen negative, often to more than 100 mV, lumen positive. This reflects an initial collapse of the potential of the basal cell membrane, followed by a large positive-going potential change at the luminal cell membrane. Just prior to the effects of the toxin on rapid fluid secretion, the basal cell membrane becomes permeable to sucrose molecules. Raffinose at 170 mmol 1−1 in the bathing solution does not protect the tubules from Bti toxin action but dextran, Mr5000, at 60 mmol 1−1 significantly delayed failure of fluid secretion and, even more, the onset of staining of the tubule cells with Trypan Blue. Exposing tubules to saline that is calcium-free and/or magnesium-free, or has a composition adjusted to be similar to that of the intracellular milieu, does not affect the time course of failure of fluid secretion induced by the toxin. There is no evidence that effective aggregates of Bti toxin molecules are formed in concentrated solutions.
The time courses of failure of fluid secretion induced by Bti toxin and melittin differ. Melittin action also involves a delay before effects are observable, but its effects then develop more slowly than with Bti toxin. This is consistent with the suggestion that melittin and Bti toxin act by forming similarly sized pores but that tetramers of melittin form pores while a larger number of molecules of Bti toxin are required to form a pore.
Unique geometry of actin-membrane anchorage sites in avian gizzard smooth muscle cells
Authors: Draeger A. , Stelzer E. H. K. , Herzog M. , Small J. V. 
Published: April 2021

ABSTRACT
Adherens junctions in isolated avian gizzard smooth muscle cells appear as short longitudinal streaks or chevrons that are arranged in periodic, mainly transverse bands along the cell surface. This barrel-like geometry, revealed by antibodies to either vinculin or talin, was seen also in teased gizzard strips by confocal laser-scanning microscopy and contrasted with the rib-like surface pattern observed here and previously in other avian and mammalian smooth muscles. There were on average 67 transverse bands per gizzard cell and an estimated total of around 800 vinculin/talin sites. The longitudinal spacing between the transverse bands of vinculin streaks in the gizzard cells changed from 4–5 μm in extended cells to around Iμ m in shortened cells and the bands remained essentially transverse at all cell lengths, inconsistent with a screw-like mode of cell shortening as has been invoked for smooth muscle cells by others. The absence of rotation on shortening was confirmed by observations on isolated and bead-decorated skinned cells that were induced to contract with ATP. Counterlabelling of cells with α-actinin antibodies produced more or less exclusive staining of the cytoplasmic dense bodies, and little surface label: the total number of dense bodies per cell, estimated from confocal microscope through focal series was in the range of 3000. The data are consistent with a periodic anchorage of actin filaments to the cell surface and, in turn, with the existence of regularly spaced contractile assemblies.
Further characterization of the antigen defined by the monoclonal antibody m27
Authors: Bramwell Michael E. , Humm Susan M. 
Published: April 2021

ABSTRACT
Using immunoblotting techniques, the antigen that binds the monoclonal antibody M27 has been clearly defined in terms of apparent molecular mass and distribution. In reducing conditions it has an apparent mass of 178K (K= 103 Mr) and is present in the cytoplasm and membranes of all mammalian tissue culture cells so far examined. It is absent from lines derived from avian, piscine and amphibian sources. It is also absent from foetal liver of both rat and mouse, but subsequently appears after cultivation in vitro. Similarly, it can be detected on rat lymphocytes only after mitogenic stimulation. However, it is found on both hepatoma and lymphoma cells in vitro, and on in vivo tumours from murine sources. It thus appears to be associated with cell proliferation.
Timing of nuclear and kinetoplast DNA replication and early morphological events in the cell cycle of Trypanosoma brucei
Authors: Woodward R. , Gull K. 
Published: April 2021

ABSTRACT
We have used irnmunofluorescent detection of 5-bromo-2-deoxyuridine-substituted DNA in order to determine the timing of initiation and the duration of nuclear and kinetoplast S-phases within the procyclic stage of the Trypanosoma brucei cell cycle. Both nuclear and kinetoplast S-phases were shown to be periodic, occupying 0.18 and 0.12 of the unit cell cycle, respectively. In addition, initiation of both of these S-phases were in approximate synchrony, differing by only 0.03 of the unit cell cycle. We have also used a monoclonal antibody that recognises the basal bodies of T. brucei in order to visualise cells possessing a new pro-basal body and hence determine the time of pro-basal body formation within the cell cycle. Pro-basal body formation occurred within a few minutes of the initiation of nuclear S-phase, at 0.41 of the unit cell cycle. This provides detection of the earliest known cell cycle event in T. brucei at the level of the light microscope. Cell cycle events including initiation of nuclear and kinetoplast DNA replication and pro-basal body formation may be strictly coordinated in T. brucei in order to maintain the precise single-mitochondrion (kinetoplast), singleflagellum status of the interphase cell.
Microtubules and their protofilaments in the flagellum of an insect spermatozoon
Authors: Afzelius B. A. , Bellon P. L. , Lanzavecchia S. 
Published: April 2021

ABSTRACT
Spermatozoa of stick insects have nine accessory tubules, which surround the nine outer microtubular doublets and the two inner microtubular singlets. When fixed in a fixative that was designed to minimize protein denaturation (glutaraldehyde and tannic acid, no osmium post-fixation but block staining with uranyl acetate in water) the accessory tubules were seen to contain 17 protofilaments of the same type as those in the 9+2 microtubular doublets and singlets. The protofilaments in accessory tubules and other microtubules were roughly triangular. When studied by Markham’s photographic method a somewhat different tilt of the two longer sides was seen; this makes it possible to distinguish a polarity in the microtubules, i.e. to differentiate between a microtubule that is viewed from its (—)end to its (+)end from one that is viewed in the opposite direction. The dynein arms of the doublets can be used as an independent type of marker for the polarity. In a computer-aided analysis of the fine structure of the tail axoneme, the A-subtubules of the outer doublets were seen to be not quite equidistant; rather, there were somewhat widened electron-dense interspaces in the ring of protofilaments in four places. The locations of these widened interspaces coincide with the attachment sites for the spoke, the inner dynein arm, the outer dynein arm, and the intertubular material. It is tentatively concluded that proteins of these structures, and perhaps also other microtubule-assocIated proteins, may be anchored deep within the wall of a microtubule rather than just superficially along it.
The predicted amino acid sequence of a centrosphere protein in dividing sea urchin eggs is similar to elongation factor (EF-1a)
Authors: Kuriyama Ryoko , Savereide Paul , Lefebvre Paul , Dasgupta Santanu 
Published: April 2021

ABSTRACT
Monoclonal antibody (SU5), prepared from isolated mitotic spindles of sea urchin eggs, stained centrospheres preferentially and recognized a 5OK (K=103Mr) polypeptide on immunoblots. Three positive clones were isolated by screening a λtll cDNA expression library prepared from sea urchin egg mRNA with SU5. One clone containing a 1.8-kb (1 kb= 103 base-pairs) insert was selected for further characterization. The β-galactosidase fusion protein encoded by the cDNA clone had an apparent relative molecular mass of 150K, indicating that the inserted cDNA produced an estimated 34K of polypeptide. A single 2.2-kb RNA transcript was detected in sea urchin embryos using the cDNA clone as a probe. The cDNA fragment was sequenced and the nucleotide sequence was used to predict the amino acid sequence of the open reading frames in the clone. The putative gene product shows striking similarity to the peptide chain elongation factor (EF-lα) from yeast, fungus, shrimp, insect, mouse and human.
Binding of hexabrachion (tenascin) to the extracellular matrix and substratum and its effect on cell adhesion
Authors: Lightner Virginia A. , Erickson Harold P. 
Published: April 2021

ABSTRACT
Hexabrachion is a large glycoprotein of the extracellular matrix (ECM) that is prominent in embryogenesis, wound healing and tumorigenesis. Because of the role of extracellular matrix proteins in the regulation of cell differentiation and migration, the interaction of hexabrachion with cells as well as with other components of the ECM is of great interest. Early reports suggested that hexabrachion does not bind to fibronectin or gelatin but does bind to chondroitin sulfate proteoglycans. However, more recent reports have suggested that hexabrachion binds to fibronectin and inhibits cell adhesion as well as cell migration on fibronectin.
We have found no evidence of strong hexabrachion-fibronectin binding on either a solid-phase ELISA assay or in a fluid-phase sedimentation assay in which the reactants were allowed to dissociate. However, hexabrachion sedimentation was accelerated in a gradient containing fibronectin throughout. This demonstrates an association between hexabrachions and fibronectin, but the complex is apparently weak and readily reversible. The solid phase ELISA also shows no evidence of hexabrachion binding to gelatin, laminin or types I, III, TV or V collagen.
Hexabrachion does not support strong cell attachment of the cell lines tested. Moreover, hexabrachion can inhibit cell attachment to fibronectin. We demonstrate here that this inhibition requires the hexabrachion to be able to bind to the plastic substratum. The results suggest that hexabrachion inhibition is via a steric inhibition. When the hexabrachion molecules bind to the plastic, they cover up a significant fraction of the underlying fibronectin molecules. Antibody studies are presented that show that hexabrachion can nonspecifically block access of immunoglobulin G molecules to the underlying matrix. This steric blocking is not unique to hexabrachion.
Nerve growth in a small applied electric field and the effects of pharmacological agents on rate and orientation
Authors: McCaig Colin D. 
Published: April 2021

ABSTRACT
The rate of growth and orientation of embryonic Xenopus nerves exposed to pharmacological agents, to an applied electric field or to both simultaneously were studied. The adenyl cyclase activator forskolin (100μM) induced a threefold increase in the rate of elongation, as did an electric field alone. Together, their effect in augmenting rate of growth was additive, but only at a concentration of 50μM forskolin. The normal pattern of faster growth towards cathode than anode was not present in nerves treated with the lectin concanava lin A, which also inhibits normal turning behaviour towards the cathode. Nerve orientation towards the cathode and augmented rates of growth were found in the presence of forskolin or ganglioside GM1. It is suggested that a combined approach of drug treatment and an applied electric field may be useful in promoting nerve regeneration.
Collagen fibrillogenesis in vitro: interaction of types I and V collagen regulates fibril diameter
Authors: Birk David E. , Fitch John M. , Babiarz Joanne P. , Doane Kathleen J. , Linsenmayer Thomas F. 
Published: April 2021

ABSTRACT
The small-diameter fibrils of the chick corneal stroma are heterotypic, composed of both collagen types I and V. This tissue has a high concentration of type V collagen relative to other type I-containing tissues with larger-diameter fibrils, suggesting that heterotypic interactions may have a regulatory role in the control of fibril diameter. The interactions of collagen types I and V were studied using an in vitro self-assembly system. Collagens were purified from lathyritic chick embryos in the presence of protease inhibitors. The type V collagen preparations contained higher molecular weight forms of the α1 (V) and α2(V) chains constituting 60-70% of the total. Rotary-shadow electron micrographs showed a persistence of a small, pepsin-sensitive terminal region in an amount consistent with that seen by electrophoresis. In vitro, this purified type V collagen formed thin fibrils with no apparent periodicity, while type I collagen fibrils had a broad distribution of large diameters. However, when type I collagen was mixed with increasing amounts of type V collagen a progressive and significant decrease in both the mean fibril diameter and the variance was observed for D periodic fibrils. The amino-terminal domain of the type V collagen molecule was required for this regulatory effect and in its absence little diameter reducing activity was observed. Electron microscopy using collagen type specific monoclonal antibodies demonstrated that the fibrils formed were heterotypic, containing both collagen types I and V. These data indicate that the interaction of type V with type I collagen is one mechanism modulating fibril diameter and is at least partially responsible for the regulation of collagen fibril formation.
Monoclonal antibody analysis of the proliferating cell nuclear antigen (PCNA) structural conservation and the detection of a nucleolar form
Authors: Waseem Naushin H. , Lane David P. 
Published: April 2021

ABSTRACT
The proliferating cell nuclear antigen, PCNA, has recently been identified as the polymerase ô accessory protein. PCNA is essential for cellular DNA synthesis and is also required for the in vitro replication of simian virus 40 (SV40) DNA where it acts to coordinate leading and lagging strand synthesis at the replication fork. The cDNA for rat PCNA was cloned into a series of bacterial expression vectors and the resulting protein used to immunize mice. Eleven new monoclonal antibodies to PCNA have been isolated and characterized. Some of the antibodies recognize epitopes conserved from man to fission yeast. Immunocytochemical analysis of primate epithelial cell lines showed that the antibodies recognized antigenically distinct forms of PCNA and that these forms were localized to different compartments of the nucleus. One antibody reacted exclusively with PCNA in the nucleolus. These results suggest that the PCNA protein may fulfil several separate roles in the cell nucleus associated with changes in its antigenic structure.
Differentiation of human trophoblast cells in vitro as revealed by immunocytochemical staining of desmoplakin and nuclei
Authors: Douglas Gordon C. , King Barry F. 
Published: April 2021

ABSTRACT
The differentiation of isolated human cytotrophoblast cells has been studied by staining cells with anti-desmoplakin antibodies, to reveal cell boundaries, and with anti-nuclear antibodies, to reveal nuclei. During the first 24 h after plating in Ham’s/ Waymouth medium, mononucleated cytotrophoblast cells began to spread and aggregate, forming colonies. This was accompanied by progressive changes in the pattern of desmoplakin staining. In single cells, desmoplakin was dispersed throughout the cytoplasm. As cells aggregated, desmoplakin was redistributed and formed linear, punctate arrays at regions of cell-cell contact, consistent with desmosome formation. A pavement-like staining pattern was maintained even at 5 days. Double staining for desmoplakin and nuclei revealed that most cells within colonies were mononucleated. When plated in a growth medium originally formulated for keratinocytes, cytotrophoblast cells aggregated and formed desmosomes normally. However, after 48 h, cell diameters were increased and nuclei changed from being evenly distributed to forming clusters within large cells, consistent with syncytiotrophoblast formation. While cells grown in Ham’s/Waymouth medium for 2 days could be induced to differentiate by switching to keratinocyte growth medium, cells cultured for 5 days before switching were resistant to the differentiation-inducing effects of the keratinocyte medium. Desmosome-type junctions within colonies of trophoblast cells were unstable and, even after 5 days in culture, could be disrupted by lowering the extracellular Ca2+ concentration. While syncytiotrophoblast formation in keratinocyte growth medium (which contains epidermal growth factor, insulin and hydrocortisone) was accompanied by a 15-to 20-fold increase in chorionic gonadotropin secretion, syncytiotrophoblast formation occurred to a similar extent in keratinocyte basal medium (which does not contain these factors) but with only a twofold increase in chorionic gonadotropin release. These results support the notion that biochemical and morphological differentiation of trophoblast are independent events.
F-actin organization during the cellularization of the Drosophila embryo as revealed with a confocal laser scanning microscope
Authors: Warn R. M. , Robert-Nicoud M. 
Published: April 2021

ABSTRACT
The changes in F-actin organization during the cellularization of the Drosophila embryo have been studied with a confocal laser scanning microscope using fluorescein-phalloidin as a specific stain. Particular study has been made of the changes in the organization of the F-actin network associated with the leading edges of the growing membranes. The role of this actin network in the cellularization process is considered. Other actin-containing structures have also been examined, including the cortical actin layer and a conspicuous region of F-actin aggregates, present beneath the level of the forming cell membranes.
A filamentous network surrounding secretory granules from mast cells
Authors: Nielsen Ellen Holm 
Published: April 2021

ABSTRACT
A freezing-thawing method for rupturing mast cells has made it possible to show that each of the secretory granules is surrounded by a regular network of filaments forming a basket-like structure. The filaments attach to the membrane with hook-like structures. Immunoelectron microscopy of intact mast cells shows that actin occurs mainly in the subplasmalemmal space, whereas in ruptured cells it is seen around granules, indicating that the granule network might consist of actin.
Commentary Signal transduction by the receptors for platelet-derived growth factor
Authors: Heldin Carl-Henrik , Westermark Bengt 
Published: April 2021

ABSTRACT
Platelet-derived growth factor CPDGF) is a connective tissue cell mitogen that originally was purified from human platelets, but recently has been found to be produced by many different cell types (reviewed by Ross et al. 1986; Heldin and Westermark, 1989). The in vivo function of PDGF remains speculative, but the fact that PDGF is released by platelets and by cells involved in the inflammatory reaction and that it stimulates proliferation, chemotaxis and matrix production, suggest a role in tissue repair processes. It is also possible that PDGF is involved in regulation of cell growth and differentiation during embryonal development, since it has been found to be expressed in mouse (Rappolee et al. 1988) and Xenopus (Mercóla et al. 1988) embryos and in human placenta (Goustin et al. 1985). Such a function has been demonstrated in the developing rat optic nerve where PDGF secreted by type-1 astrocytes control the differentiation of O-2A progenitor cells into oligodendrocytes and type-2 astrocytes (Noble et al. 1988; Richardson et al. 1988; Raff et al. 1988). PDGF may also be involved in pathological processes. Thus, unscheduled production of PDGF may account for the excessive cell proliferation seen, e.g., in atherosclerosis and tissue fibrosis, as well as in malignancies. The potent transforming activity of PDGF is illustrated by the fact that the PDGF B chain gene is similar to v-sis, the transforming gene of simian sarcoma virus, and that cell transformation by this virus is exerted by auto-crine action of a PDGF-like factor (reviewed by Wester-mark et al. 1987).
Developmental expression of Drosophila melanogaster small heat-shock proteins
Authors: Haass Christian , Klein Ulrike , Kloetzel Peter-M. 
Published: April 2021

ABSTRACT
We have investigated the developmental expression of the small heat-shock proteins (hsps) during embryogenesis and in adult flies by immunocytology using an antibody that specifically identifies the small hsps. Antibody staining of unstressed early embryos reveals a predominantly cytoplasmic, homogeneous distribution of the small hsps throughout the embryo. At 6h of development small hsp expression can be identified in large, neuroblast-like cells within the extended germ band and in the brain of the embryo. During germ band contraction these cells appear to migrate to the midline where they align pairwise in a segmental pattern. After germ band contraction is complete a high level of small hsp expression can be observed in the midline glia (MECs) and in a cluster of six non-neuronal cells within the midline. In contrast to several other genes that are known to be important for embyogenesis and are expressed in the central nervous system (CNS) of embryos, CNS-specific expression of the small hsps is not restricted to the embryo but is also observed in the adult fly. In adult flies strong small hsp expression is observed in the brain, the thoracic ganglion and the leg nerves. Since the small hsps seem to be expressed predominantly in the glia of the nervous system, our data suggest a protective or stabilizing function of the small hsps within the nervous system during normal fly development, which is independent of the stress response.
Continued DNA synthesis after a mitotic block in the double mutant cut1 cdc11 of the fission yeast Schizosaccharomyces Pombe
Authors: Creanor J. , Mitchison J. M. 
Published: April 2021

ABSTRACT
DNA synthesis is normally dependent on a cell having previously gone through mitosis. Hirano et al. (1986), however, found that DNA synthesis continued at the restrictive temperature in the double mutant cut! cdcll of Schizosaccharomyces pombe even though mitosis was blocked in some of the cells. We have confirmed this result with bulk DNA assays of asynchronous cultures. Synchronous cultures of a diploid double mutant at the restrictive temperature showed two peaks of incorporation with an interval between them that was approximately the same as the doubling time in cell length. Flow cytometry showed that the cells had increased their DNA content from 4C (the diploid value) to about 16C after 7 h. The cytological appearance at this time was mixed, with uninucleate, binucleate and dead cells, but fluorescence measurements on single cells indicated that about half the population had single nuclei with about the 16 C value and had therefore gone through two rounds of DNA synthesis without mitosis.