bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-directional pattern of movements on the cell surface of Amoeba proteus
Authors: Grebecki Andrzej 
Published: April 2021

ABSTRACT
Particles of latex, glass and precipitated Alcian Blue were studied cinematographically on the surface of migrating Amoeba proteus and in the surrounding medium. The majority of the attached and all unattached particles flow steadily forward in the direction of the endoplasmic streaming and cell locomotion. Flow on the surface is faster than in suspension. Some particles stuck on the membrane move backwards from the frontal region. This retrograde transport is slower than the anterograde flow, and the rate decreases further when the particles approach cell regions adhering to the substratum, accurately following the pattern of the withdrawal of ectoplasm in the same zone. Both movements coexist in the same region and retrograde particles may pass anterograde ones at a distance less than their diameter. Transition from forward flow to backward transport occurs just behind the frontal cap, where the new ectoplasm is formed. The anterograde movement is interpreted as reflecting the general forward flow of the laterally mobile fluid membrane components, which become added to the frontal surface of the locomoting cell; the retrograde movement as retraction of membrane components that, externally, are linked to the transported material and, on the cytoplasmic side, to the contractile microfilamentous layer, as is postulated for cap formation in tissue cells.
Dissociation of basement membrane protein deposition and cell spreading in virally transformed rat mammary myoepithelial cells
Authors: Warburton Michael J. , Ferns Sharon A. , Kimbell Rosemary , Monaghan Paul 
Published: April 2021

ABSTRACT
A myoepithelial-like cell line (Rama 401), isolated from rat mammary gland, has been transformed with a temperature-sensitive mutant of Rous sarcoma virus (tsRSV). Rama 401-tsRSV cells adopt a spindle morphology and fail to deposit basement membrane proteins when grown at the permissive temperature (35°C). When switched to the non-permissive temperature (41°C), the cells flatten (with a 5-fold increase in area), and deposit an extracellular matrix containing basement membrane proteins. When the cells are switched from 35°C to 41 °C in the presence of monensin (an ionophore that inhibits protein secretion), basement membrane proteins are no longer deposited extracellularly although the cells flatten, their area increasing by ninefold. Cells switched from 35 °C to 41 °C in the presence of cycloheximide still flatten and deposit basement membrane proteins, whereas the morphological change on switching from 41 °C to 35 °C is inhibited by cycloheximide. These experiments indicate that the ability of Rama 401-tsRSV cells to spread on a plastic substratum is not dependent on the de novo synthesis and deposition of basement membrane proteins.
Differential effects of epidermal growth factor (EGF) on cell locomotion and cell proliferation in a cloned human embryonal carcinoma-derived cell line in vitro
Authors: Engström Wilhelm 
Published: April 2021

ABSTRACT
The effects of epidermal growth factor (EGF) on clones from a human embryonal carcinoma-derived cell line (Tera-2) have been studied. Cells were plated at clonal densities, whereafter the effects of serum and EGF on cell locomotion and cell proliferation were examined. The addition of 50ngEGFml−1 resulted in increased migration, as judged by increased colony diameter in the presence of EGF. However, the effect of EGF on cell locomotion was rarely accompanied by any effect on cell proliferation. It was concluded that EGF exerts a preferential effect on cell migration in human embryonal carcinoma cells in vitro.
Inhibition of stenotele differentiation by head tissue in Hydra
Authors: Fujisawa Toshitaka 
Published: April 2021

ABSTRACT
Stenotele nematocytes in Hydra are differentiated predominantly in the proximal regions and in gradually decreasing numbers in the more distal regions of the body column. To test whether this position effect is directed by an inhibitory signal from head tissue or by a stimulatory signal from foot tissue, head or foot tissue was laterally grafted from one animal to different positions on another animal. Heads grafted to proximal positions strongly inhibited stenotele differentiation, while the foot exhibited no stimulatory effect. In addition, tissue from gastric regions showed intermediate levels of inhibition. Thus, the inhibitory signal appears to be distributed in a gradient along the body column from head to foot. During head regeneration, the inhibitory signal disappeared abruptly from the distal tip and reappeared rapidly. These results suggest that the inhibitory signal is involved in generating the regional pattern of stenotele differentiation. Head tissue from epithelial hydra, which lacks the interstitial cell lineage, also inhibited stenotele differentiation, suggesting that the inhibitory signal is localized in epithelial cells.
Type I collagen permits invasive behaviour by retinal pigmented epithelial cells in vitro
Authors: Docherty R. J. , Forrester J. V. , Lackie J. M. 
Published: April 2021

ABSTRACT
Epithelial cells cultured on type I collagen gels adopt a typical apical-basal polarity and undergo differentiation. We have compared the behaviour of chick embryo retinal pigmented epithelial (RPE) cells on collagen and on plastic with and without gelatin coats. RPE cell proliferation was similar on all three substrata, and post-confluent cultures exhibited multilayering. On plastic and gelatin-coated plastic, dome formation, typical of transporting epithelia, occurred. On type I collagen gels, however, dome formation did not occur, but rather invasion of the gel matrix by cords of epithelial cells took place. In contrast, invasive behaviour of the cells was markedly reduced on type IV coated collagen gels, particularly in the presence of laminin. These results illustrate the prominent role of the extracellular matrix on phenotypic expression by RPE cells and may represent a more general phenomenon.
Gtp Analogues Stimulate Inositol Trisphosphate Formation Transiently In Dictyostelium
Authors: Europe-Finner G. Nicholas , Newell Peter C. 
Published: April 2021

ABSTRACT
Permeabilization of amoebae of Dictyostelium discoideum with saponin was found not to uncouple the chemotactic cell surface cyclic AMP receptors from inositol trisphosphate (IP3) formation, and stimulation of permeabilized amoebae with 50 nM-cyclic AMP produced peaks of IP3 at 5, 15 and 30 s in a manner comparable to that seen previously in non-permeabilized cells. The possible involvement of a GTP-binding protein (G-protein) in this IP3 signal transduction pathway was investigated by studying the effects on such permeabilized amoebae of added GTP and non-hydrolysable GTP analogues. While GDP produced only very minor effects, stimulation of the amoebae (in the absence of added cyclic AMP) with GTP or the non-hydrolysable GTP analogues GTPγS (guanosine 5’-O-(3-thio-triphos-phate)) and Gpp(NH)p (5’-guanylylimido-diphosphate) induced transient formation of IP3 in an oscillatory manner, with peaks similar in magnitude and timing to those elicited by cyclic AMP. A dose-response curve for GTPγS indicated a concentration for half-maximal stimulation of approximately 8 μM. When tested at 300 s after addition of GTPγ, the basal level of IP3 was found to be twofold elevated with shallow (presumably asynchronous) oscillations still just discernible.
The significance of the IP3 oscillations elicited by GTP and its analogues is discussed in relation to the mechanism of signal adaptation and the presumed role of G-proteins.
Direct measurement of cell detachment force on single cells using a new electromechanical method
Authors: Francis G. W. , Fisher L. R. , Gamble R. A. , Gingell D. 
Published: April 2021

ABSTRACT
We describe a new device in which an accurately measured force is applied to individual adherent cells while the topography of the adhesion zone is simultaneously monitored. The force is applied via a flexible glass micropipette, attached by suction to the cell under study, and is calculated directly from the measured pipette deflection. Regions of close contact in the adhesion zone are observed using interference reflection microscopy. We have used the device to measure the force required to detach human red blood cells from hydrophobic and hydrophilic glass surfaces, and to detach Dictyostelium discoideum amoebae from a hydrophobic glass surface. The measured forces per unit length of contact perimeter are within an order of magnitude of the tensions required for membrane rupture.
Levels of microtubules during the meiotic maturation of the Xenopus oocyte
Authors: Jessus Catherine , Thibier Catherine , Ozon René 
Published: April 2021

ABSTRACT
The total level of tubulin and the ratio of polymeric tubulin to tubulin dimer were measured by a colchicine filter-binding assay during meiotic maturation of the Xenopus oocyte. Although the total level of tubulin remains unchanged (0·12 ± 0·03 μg/oocyte), the level of polymeric tubulin decreases during maturation (25% in prophase oocytes versus 20% in metaphase oocytes). The percentage of polymerized tubulin was estimated after drug (nocodazole and taxol) treatments and cold treatment in prophase and progesterone-matured oocytes; in all cases the microtubules present in mature oocyte are less stable than prophase microtubules. The presence of the nucleus modifies neither the level nor the stability of prophase microtubules. Our quantitative results as well as cytological arguments suggest that full-grown Xenopus oocytes may contain a cortical microtubular array.
Stimulus-response coupling in the contraction of tentacles of the suctorian protozoon Heliophrya erhardi
Authors: Butler R. D. , Mccrohan C. R. 
Published: April 2021

ABSTRACT
Experiments were carried out to determine the role of the plasma membrane in the control of tentacle contraction in Heliophrya erhardi. Intracellular recordings gave membrane potentials between −20 and −30 mV. In a Ca2+-containing medium mechanical stimulation induced tentacle contraction but no associated electrical events were recorded. Intracellular stimulation with 50 nA, 100 ms hyperpolarizing current induced contraction, but no significant changes in membrane potential, whereas up to 100 nA, 100 ms depolarizing current had no effect. In a Ca2+-free medium neither mechanical stimulation nor electrical stimulation induced contraction. Extracellular stimulation of 15 V, 100 ms induced a Ca2+-dependent, unilateral (anodal) contraction response with a threshold of 5× 10−9M-Ca2+. At concentrations above this neither latency to contraction nor contraction time showed significant variation. In a standard concentration of 10−4M-Ca2+ the sensitivity to extracellular stimulation was increased and latency to contraction was reduced in the presence of a phorbol ester (TPA), which mimics the second messenger diacylglycerol in stimulating the activity of protein kinase C. It is suggested that control of tentacle contraction is unlikely to be mediated by stimulus-activated ion channels in the plasma membrane, and the possibility that the polyphosphoinositide signalling pathway is involved is discussed.
Secretion by Toxoplasma gondii of an antigen that appears to become associated with the parasitophorous vacuole membrane upon invasion of the host cell
Authors: Kimata Isao , Tanabe Kazuyuki 
Published: April 2021

ABSTRACT
Monoclonal antibodies against Toxoplasma gondii were prepared to characterize antigens of the parasite. Immunoperoxidase staining of parasites fixed with paraformaldehyde and glutaraldehyde (PFAGA) followed by Triton X-100 treatment showed that the antibody of clone 1–63 recognized an antigen located in the anterior part of the parasite. When analysed by SDS-PAGE and immunoblotting, the antigen migrated in a 66 ×103Mr region. The parasite antigen diminished greatly in parasites after invasion of host cells, but reappeared around a time when intracellular T. gondii multiplied. Immunodetection on PFAGA-fixed T. g’ondn-infected cells, whose membranes were permeabilized by freeze-thawing in the presence of 5 % glycerol, demonstrated that, immediately after parasite invasion, the 1–63 antibody-reactive antigen appeared to become associated with the parasitophorous vacuole (PV) membrane, that had been formed mainly by invagination of the host-cell plasma membrane so as to surround an invading parasite. The antigen remained associated with the PV membrane for some time, but disappeared later when the PV increased in size after the parasites had multiplied several times. These results were strengthened by immunoelectron microscopic observations: the antigen that had been localized at the anterior part of the parasite before invasion appeared in an area of the host cell cytoplasm around the tips of penetrating parasites and, thereafter, extended throughout the surface of the PV membrane when parasites completed invasion. Thus, it appears that the I-63-reactive antigen is secreted by T. gondii upon invasion of the host cell and becomes associated with the PV membrane shortly after invasion.
Direction of sliding and relative sliding velocities within trypsinized sperm axonemes of Gallus domesticus
Authors: Woolley David M. , Brammall Andrew 
Published: April 2021

ABSTRACT
Trypsin digestion of demembranated fowl spermatozoa caused a longitudinal splitting of the distal part of the axoneme. The resulting strands, consisting of groups of doublet microtubules, formed left-handed helices. On the evidence of electron micrographs, the digestion had caused the loss of dynein arms from the outer row; it is assumed that the doublets remained linked together by dynein arms of the inner row. When such helices were mechanically detached from the proximal flagellum and reactivated with adenosine triphosphate, they lengthened in an orderly way by inter-doublet sliding. All the doublets of the axoneme could be reactivated and in all instances the direction of sliding was the same as that reported for the cilia of Tetrahymena. Within the groups of doublets the measured inter-doublet displacements were generally similar, suggesting that the rates of sliding had been equivalent. These findings are contrasted with the differential pattern of activation that is assumed to occur in vivo.
Allelic antigen and membrane-anchor epitopes of Paramecium Primaurelia surface antigens
Authors: Capdeville Yvonne , Caron Francois , Antony Claude , Deregnaucourt Christiane , Keller Anne-Marie 
Published: April 2021

ABSTRACT
Paramecium aurelia can express a repertoire of surface antigens (SAgs) according to culture conditions. These high Mr proteins are anchored in the plasma membrane by a glycolipid, and they can be isolated in two different forms, an amphiphilic membrane-bound form (mSAg) and a hydrophilic soluble form (sSAg). Endogenous or exogenous phospholipase C can convert mSAg to sSAg with unmasking of a carbohydrate antigenic determinant similar to that found in the soluble form of Trypanosoma variant surface glycoproteins and called the cross-reacting determinant. By immunizing mice with cilia from strain 156 of P. primaurelia expressing the G SAg, we obtained six monoclonal antibodies against the 156G SAg, which could be classified into two groups. Y4 and Y8, representative of each group, have been characterized by checking their reactivity in situ and in vivo towards a series of allelic G and D SAgs in P. primaurelia and the 5IB SAg in P. tetraurelia.
The monoclonal Y4 recognizes a conformational determinant, accessible in vivo and common to all the G SAgs. Thus, Y4 defines a G locus-specific epitope that corresponds to a conserved region inside a polymorphic domain. The monoclonal Y8 recognizes two homologous determinants whose detection depends on the presence or absence of the SAg membrane-anchor, and which are mutually exclusive: one is found in the reduced soluble form of all the SAgs and other surface proteins, the cross-reacting glycoproteins (CRGs); the other occurs in the unreduced membrane-bound form of the G SAgs. Thus, Y8 enables us to demonstrate that the membrane-anchor of Paramecium SAgs contains an additional hidden determinant close to the crossreacting determinant and to discriminate between the membrane-bound and soluble form of SAgs.
The in situ organization of the 156G SAg molecules is also discussed on the basis of immunogold labelling obtained using Y4 and a polyclonal antiserum.
Genetic control of plasma membrane adhesion and fusion in Chlamydomonas gametes
Authors: Forest Charlene L. 
Published: April 2021

ABSTRACT
The final stages of gamete interaction in Chlamydomonas reinhardtii occur between the specialized plasma membrane organelles (mating structures) of opposite mating-type cells. A number of mutants affecting these interactions have been obtained in several laboratories; all have been defined as fusion-defective. This paper demonstrates that there are at least two genetically definable stages of mating-structure interaction: (1) the recognition/adhesion of mating structures, and (2) gamete fusion. The possibility that these two functions, the adhesion and subsequent fusion of mating structures, may be mating-type specific is raised, since of the seven independently isolated mutants analysed, all mutants defective in fusion are of mating-type (—), and only mating type (+) mutants show defects in adhesion.
Vimentin intermediate filaments in fish melanophores
Authors: Gyoeva F. K. , Leonova E. V. , Rodionov V. I. , Gelfand V. I. 
Published: April 2021

ABSTRACT
The distribution and chemical composition of intermediate filaments in cultured melanophores of two teleost species -Gymnocorymbus ternetzi and Pterophyllum scalare -were studied by immunofluorescence staining and immunoblotting techniques. The immunofluorescence staining of the melanophores with monoclonal and polyclonal antibodies to the intermediate filament protein vimentin revealed a system of fibrils radiating from the cell centre. These fibrils were resistant to 0·6M-KCl and nocodazole treatments as has been found in other cell types. Transmission electron microscopy confirmed the presence of intermediate filaments in melanophores. Immunoblotting experiments showed the presence of the intermediate filament protein vimentin in melanophore lysates. Therefore, teleost melanophores possess a developed radial system of vimentin intermediate filaments.
Mutant RAS gene induces elevated levels of inositol tris-and hexakisphosphates in Dictyostelium
Authors: Europe-finner G. N. , Ludérus M. E. E. , Small N. V. , driel R. Van , Reymond C. D. , Firtel R. A. , Newell P. C. 
Published: April 2021

ABSTRACT
Previous studies of Europe-Finner & Newell indicated that in amoebae of Dictyostelium dis-coideum, signal transduction used for chemotaxis to cyclic AMP involved transient formation of inositol tris-and polyphosphates. Evidence was also presented for the involvement of a GTP-binding G-protein. Here we report evidence for the involvement of a ras gene product in the D. discoideum inositol phosphate pathway. Use was made of strains of Dictyostelium transformed with a wild-type D. discoideum ras gene (ras-Glyl2) or a mutant form of the gene (ras-Thrl2). Experiments using separation of soluble inositol phosphates by Dowex anion-exchange resin chromatography indicated that cells transformed with the wild-type ras-Glyl2 gene were unaffected in their basal levels of inositol polyphosphates and in the inositol phosphates formed in response to stimulation with the chemotactic agent cyclic AMP. In contrast, cells transformed with the mutant ras-Thrl2 gene showed a basal level of inositol polyphosphate that was several-fold elevated over the controls and stimulation of these cells with cyclic AMP produced only a small further elevation. When the inositol phosphates were analysed by h.p.l.c. it was found that the basal level of inositol 1,4,5-trisphosphate was raised three-to fivefold in the ras-Thrl2 strain compared to the strain transformed with ras-Glyl2, and that inositol hexakisphosphate (which was found to be present in large amounts relative to other inositol phosphates in D. discoideum cells) was also raised to a similar extent in the ras-Thrl2-transformed cells.
We propose that the Dictyostelium ras gene product codes for a regulatory protein involved in the inositol phosphate chemotactic signal-transduction pathway.
Chromosome segregation from cell hybrids IV. Movement and position of segregant set chromosomes in early-phase interspecific cell hybrids
Authors: Zelesco Paula A. , graves Jennifer A. Marshall 
Published: April 2021

ABSTRACT
We searched for evidence of aberrant movement or position of segregant set chromosomes in C-banded and G-11-banded early-phase hamster–mouse and hamster–human cell hybrids that had been prepared with minimal disruption. No evidence was obtained for an increased frequency of multipolar mitosis, delayed or precocious meta-phase congression or anaphase segregation, or for exclusion of chromosomes from the daughter nuclei. However, in hamster-human hybrids, segregant set (human) chromosomes were observed to assume a central position within a ring of hamster chromosomes on the metaphase plate. Such non-random positioning may imply that the centromeres of segregant chromosomes make aberrant, or simply less efficient, attachments to the spindle in hybrid cells. This aberrant position may perhaps result indirectly in chromosome loss by interfering with the normal processes of replication, repair or transcription.
Inositol phosphates, G-proteins and RAS genes involved in chemotactic signal transduction of Dictyostelium
Authors: Newell P. C. , Europe-Finner G. N. , Small N. V. , Liu G. 
Published: April 2021

ABSTRACT
Chemotaxis requires some form of signal transduction system (or systems) to convert extracellular messages into intracellular actions. In the amoebal organism Dictyostelium discoideum two pathways of signal transduction have been found to operate, one involves adenylate cyclase for signal relay, and the other, which forms the subject of this review, involves inositol phosphates (Fig. 1).
Characterization of a 125K glycoprotein associated with bovine epithelial desmosomes
Authors: Jones Jonathan C. R. 
Published: April 2021

ABSTRACT
An analysis of the concanavalinA binding polypeptide components of bovine tongue epithelial desmosomes reveals that in addition to the known desmosomal glycoproteins of 100/115K (the ‘desmocollins’), 140K and 160/165K (*desmoglein 1’) there is an uncharacterized glycoprotein of 125K (K = Mr× 10−3). This latter polypeptide is immunologically distinct from known desmosomal glycoproteins, as determined by Western immunoblotting, but is recognized by an antibody preparation directed against the epithelial cell adhesion molecule E-cadherin. Moreover, the cadherin antibodies recognize a polypeptide present in bovine muzzle desmosomes that co-migrates with the 125K glycoprotein component of bovine tongue epithelial desmosomes. Upon treatment of bovine tongue desmosomes with a solution containing 9·5 M-urea, the 125K polypeptide becomes enriched in a urea-insoluble, membrane-enriched pelletable desmosomal fraction. Cadherin antibodies and antibodies directed against the 100/115K and 160/165K desmosomal glycoproteins generate similar immunofluorescence staining patterns in cryostat sections of bovine tongue epithelium. However, immunoelectron microscopic analysis of bovine tongue epithelium reveals that cadherin antibodies recognize components located both along the intercellular region of the desmosome and along non-desmosomal cell surfaces whereas antibodies directed against the 100/115K and the 160/165K desmosomal glycoproteins bind specifically to desmosomes. These results suggest that a cadherin-like glycoprotein component may play a role in the adhesive properties of the desmosomes of stratified squamous epithelia.