bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adhesion of leukocytes to endothelium: Roles of divalent cations, surface charge, chemotactic agents and substrate
Authors: Hoover R. L. , Folger R. , Haering W. A. , Ware B. R. , Karnovsky M. J. 
Published: April 2021

ABSTRACT
The attachment of polymorphonuclear leukocytes (PMN) to the endothelial lining of blood vessels is an important initial event in the acute inflammatory reaction. Experiments were carried out to examine some of the parameters of this adhesive interaction and the extent to which the substrate (endothelium) plays a role in controlling the process. Using a monolayer collection assay for adhesion, we found a requirement for divalent cations. Mn’+produces maximal adhesion followed by Zn2+ &gt; Ni2+ &gt; Mg2+ &gt; Ba2+ &gt; Ca2+. Pretreatment of either the endothelium or PMN with chemotactic agents (zymosan-activated serum, a bacterial filtrate, Csa and formyl-methionyl-leucyl-phenylalanine) causes an increase in the attachment of PMN to endothelial monolayers. Modulations of net surface charge, as measured by laser Doppler electrophoresis, are not correlated to alterations in adhesion. Mn 2+, which produces maximal adhesion, reduces the net surface charge to the same extent as Ca2+, which has the smallest effect on adhesion. Similarly, reductions in net surface charge are not responsible for the increases in adhesion due to the chemotactic agents because there are no differences in electrophoretic mobilities between cells treated with either chemotactic agents or their appropriate controls. Scatchard analysis of the binding of the chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine, indicates the presence of high-affinity binding sites on the surface of the endothelium. The results suggest a role for the endothelium in mediating the adhesive interaction with the PMN.
Fine structure and behaviour of a pericentric inversion in the sand rat, Psammomys obesus
Authors: Ashley Terry , Moses M. J. , Solari A. J. 
Published: April 2021

ABSTRACT
In pachytene spermatocytes of the sand rat, Psammomys obesus, a long autosomal bivalent was observed, which was asynaptic for a large interstitial segment of its length in early pachytene. This bivalent also exhibited unaligned kinetochores. In late pachytene spermatocytes all autosomal bivalents were fully synapsed, but one of the shortest bivalents now possessed unaligned kinetochores. Evidence is presented in support of the proposition that the asynaptic interstitial region observed in early pachytene is due to the bivalent being heterozygous for a pericentric inversion. Using the maximum extent of homologous pairing, the break points were mapped at 26% from one end and 20% from the other. The unaligned kinetochores support the proposal that the aberration is an inversion and measurements of their positions confirm the estimated break points. In one cell a bivalent with interstitial (but no terminal) synapsis also confirms the inversion hypothesis. It is proposed that the bivalent is so small that topological considerations prevent the formation of the expected inversion loop. Evidence is also presented that complete synapsis of the bivalent during late pachytene can be attributed to ‘synaptic adjustment’, characterized by non-homologous synapsis (heterosynapsis). The position of the aberrant bivalent in relation to the sex chromosomes also changes during pachytene. When the bivalent is incompletely synapsed it generally associates by its ends with the ends of the sex chromosomes, but when it is non-homologously synapsed it is not associated with them.
Intracellular transport and secretion of fibroin in the posterior silk gland of the silkworm Bombyx mori
Authors: Sasaki Sadao , Nakajima Etsuko , Fujii-Kuriyama Yoshiaki , Tashiro Yutaka 
Published: April 2021

ABSTRACT
Intracellular transport and secretion of fibroin in the posterior silk gland cells of the silkworm, Bombyx mori, were investigated in relation to the radial microtubule and circular microtubule-microfilament systems of the cells.
The silk glands were pulse-labelled for 3 min with [3H]glycine in vitro and then chased in media containing excess cold glycine and in some cases antimitotic reagents (colchicine or vinblastine) or cytochalasin (B or D), and the flow of the label in the glands was investigated by radioautography. It was revealed that the label initially located over the rough endoplasmic reticulum subsequently moves to the Golgi bodies to be condensed there. The secretory granules of fibroin or fibroin globules thus formed are transported via the radial microtubule system to the apical cytoplasm to be secreted there under some regulation by the circular microtubule-microfilament system. In the presence of colchicine or vinblastine, the secretion of fibroin was suppressed and marked accumulation of fibroin globules in the Golgi regions was observed, while in the presence of cytochalasin B or D the secretion was accelerated and extensive invagination of the luminal surface, which was probably due to the serial exocytosis of fibroin globules, was observed. These results suggest that the radial microtubule system and the circular microtubule-microfilament system are responsible for intracellular transport of fibroin globules from Golgi bodies to the apical cytoplasm and secretion by exocytosis at the luminal surface, respectively.
Fibonectin is a component of the surface coat of human neutrophils
Authors: Hoffstein S. T. , Weissmann G. , Pearlstein E. 
Published: April 2021

ABSTRACT
Although adherence to surfaces is central to neutrophil function many of the determinants of neutrophil adherence are still unknown. The possible involvement of cell surface material, fibronectin in particular, was therefore studied. Surface coat material was visualized ultra-structurally by the ferrocyanide-reduced osmium technique of Kamovsky (1971). Loosely attached surface coat material was seen distributed uniformly on cells in suspension. Indirect immunofluorescence indicated the presence of fibronectin on the neutrophil surface. Distribution of fibronectin as determined by indirect immunoferritin localization corresponded with the distribution of cell coat material. Some, if not all, of this fibronectin was synthesized by neutrophils themselves since metabolically labelled fibronectin could be obtained by immunoprecipitation after short-term culture with [35S]methionine. Neutrophils also adhere to Sepharose beads to which gelatin is covalently linked (GS) but not to plain Sepharose beads (PS). In the process they transfer surface coat material to GS but not PS. Similar transfer was seen when cells were permitted to adhere to glass or plastic coverslips. Indirect immunofluorescence showed that fibronectin-containing material was transferred from neutrophils to GS but not PS. Parallel studies with antisera to 2 other plasma proteins, factor VIIIR and alpha1-antitrypsin showed that neutrophils did not transfer these to either GS or PS beads. The data suggest that material antigenically and functionally related to fibronectin is associated with the extracellular coat of neutrophils and is transferred with cell surface material to surfaces to which neutrophils adhere.
Differentiation between mitochondrial and cytoplasmic protein subunits of blowfly flight muscle mitochondria synthesized in vivo
Authors: Ashour M. Badr , Tribe Michael 
Published: April 2021

ABSTRACT
Total adult blowfly flight-muscle mitochondrial protein was labelled in vivo with [14C]leucine. The labelled proteins were enumerated and characterized by their electrophoretic mobility using sodium dodecyl sulphate/polyacrylamide gel electrophoresis and autoradiography.
When different gel concentrations were used to resolve the maximum number of bands and their molecular weights, it was possible to observe at least 35 electrophoretic bands after staining and scanning; their molecular weights ranged between 11000 and 130000.
When mitochondria were labelled in the presence of cycloheximide, only 6–8 bands could be identified on gradient gels after electrophoresis and autoradiography. By comparison, controls (where cycloheximide was absent), which were run alongside the drug-treated mitochondria, revealed 17–20 radioactively labelled bands from densitométrie tracings. Whilst the molecular weights of these bands could be estimated, it was difficult to identify the precise nature and function of the proteins made in these mitochondria.
Motility of basal fragments of sea urchin sperm flagella
Authors: Goldstein Stuart F. 
Published: April 2021

ABSTRACT
Both live and reactivated sea urchin sperm flagella were broken by passage through a pipette. Distal fragments stopped, but basal fragments continued to beat. Intact flagella were about 48 /4m long; basal fragments were about 4–20 μm long.
Beat periods of tritonated fragments were 1 1% shorter than those of unbroken controls, possibly reflecting decreased viscous loading; beat periods of live fragments were 18% shorter than those of unbroken controls, possibly reflecting reduced rates of ATP consumption as well as decreased viscous loading.
The undulations of basal fragments were compared with those of the basal regions of unbroken flagella, using the patterns of development of the radii and angles of basal bends. Fragments closely resembled basal regions of unbroken flagella, except that bends tended to open as they approached the distal end of a fragment, so that their radii increased more rapidly than those of unbroken flagella.
Fragments about 4 μm long contained only one bend during part of the cycle, and appeared to be straight during part of the cycle. They flipped back and forth with fairly constant angular speeds and abrupt changes in direction, so that plots of angle between their distal end and base often resembled triangular waves, although the peaks of the waveforms were often rounded. This behaviour suggests a mechanism in which sliding switches between 2 modes. Both the speed of sliding and the maximum angles attained in one direction of bending were greater than those attained in the other direction, suggesting differences between the doublets on the 2 sides of the axoneme. Sliding of the doublets continued at fast speeds as the fragments straightened, in contrast to the characteristics of some curvature-sensitive models.
These flagellar fragments provide a simplified system for the study of flagellar oscillations.
Cell adhesion on model substrata: Threshold effects and receptor modulation
Authors: Aplin J. D. , Hughes R. C. 
Published: April 2021

ABSTRACT
Trypsinized BHK cells become attached to glass that has been derivatized with a variety of lectins with well-defined specificity for cell-surface carbohydrates. Provided a threshold concentration of glass-immobilized protein is present the cells undergo a transformation to a wellspread morphology. The matrix density of lectins (ricin and concanavalin A) required to trigger this morphological transformation is higher by 10 to 40-fold than the value determined earlier (Hughes, Pena, Clark & Dourmashkin, 1979) for fibronectin.
Cells resistant to the toxic lectin, ricin, and expressing 10% or less of ricin-binding carbohydrate groups at their cell surfaces require correspondingly greater matrix densities of ricin to promote active cell spreading. All cell lines spread equally well on concanavalin A-based matrices consistent with their similar binding properties.
The quantitative interaction of complementary molecules on the cell surface and matrix, promoting cell adhesion, is demonstrated by these results and a model is proposed for the events leading to a well-spread cell morphology on a protein-coated substratum.
Oxygen gradients cause pattern orientation in Dictyostelium cell clumps
Authors: Sternfeld John , David Charles N. 
Published: April 2021

ABSTRACT
We have investigated the formation of the prestalk-prespore pattern in Dictyostelium discoideum. Pattern formation occurs in clumps of Dictyostelium cells embedded in agar under a 100% oxygen atmosphere. Agar embedding allows us to control spatially the environment surrounding the cell clumps. Our results suggest that the ambient oxygen concentration plays a role in controlling the size of the multicellular mass. Further, oxygen gradients established across clumps embedded in agar or held in holes in a plastic barrier cause orientation of the prestalk-prespore pattern such that the anterior prestalk region forms at the highest end of the gradient. The results also indicate that developing cells have the ability to migrate up a gradient of oxygen.
Freeze-fracture analysis of membrane events during early neogenesis of cilia in Tetrahymena: changes in fairy-ring morphology and membrane topography
Authors: Hufnagel Linda A. 
Published: April 2021

ABSTRACT
A freeze-fracture analysis of early neogenesis of somatic and oral cilia of Tetrahymena was conducted using exponentially grown cultures and also cells induced to undergo oral reorganization. In this report, presumptive ciliary domains (PCDs), sites of future outgrowth of somatic cilia, are identified and their membrane structure is described in detail. The fairy ring, an array of membrane particles that occurs within the PCD and appears to be a precursor of the ciliary necklace, is described. A sequence of early stages in the formation of the ciliary necklace of somatic cilia is deduced from topographical information and membrane particle arrangements and numbers. Evidence is presented that basal bodies are seated at the cell surface prior to initiation of necklace assembly and a possible role for the basal body in necklace assembly is suggested. In dividing cells, new oral cilia grow out prior to orientation of cilia-parasomal sac complexes relative to cell axes. In dividing cells and during oral reorganization, new cilia also develop prior to their alignment into membranelles. Thus, growth of cilia is independent of their spatial orientation. Fairy’ rings were not observed during oral reorganization. During cell division, proliferation of new cilia is accompanied by the formation of a network of junctions between a cortical system of membranous cisternae, the cortical ‘alveoli’. These interalveolar junctions may serve as tracks for early positioning and orientation of new oral basal bodies.
Evidence for the lack of actin involvement in mitosis and in the contractile process in Spirostomum teres
Authors: Hobbs Valerie S. , Jenkins Robert A. , Bamburg James R. 
Published: April 2021

ABSTRACT
Studies using actin decoration techniques and electron microscopy have failed to show the presence of actin in the ciliate Spirostomum teres. The internal and external membranes of dividing cells were made permeable by treatment with Triton. The myosin subfragment S-l was introduced into the cells for incubation under conditions suitable for actin decoration. Arrowhead decoration of microfilaments was not observed within dividing micronuclei or in cytoplasmic filament bundles. However, using similar procedures, the brush border of mouse small intestine yielded clearly decorated microfilaments. A spectrophotometric DNase I inhibition assay specific for G-actin demonstrated that the level of actin in S. teres extracts was less than 0·06% of the total soluble protein and confirms the observations made using the decoration procedures. On the basis of this work, it appears that actin does not play a significant part in either mitotic chromosome movement or contractility in S. teres.
Repair of a calcium-dependent adhesive mechanism of embryonic neural retina cells: kinetic and molecular analysis
Authors: Geller Robin L. , Lilien Jack 
Published: April 2021

ABSTRACT
In this paper, we examine the restitution of a Ca2+-dependent adhesive system of embryonic chick neural retina cells following trypsinization in the absence of divalent cations. The processes involved in the restitution of this system are dissected by monitoring the effects of various drugs, alone and in specific combinations, on the kinetics of adhesion and the morphology of 24-h aggregates. In agreement with prior observations, aggregate formation can be separated into two distinct phases: the formation of adhesions and their ultimate stabilization. The formation of adhesions appears to involve two processes, de novo synthesis of protein and mobilization of an endogenous pool, while stabilization requires de novo synthesis of RNA and protein glycosylation.
We also examine the appearance of two cell surface molecules previously implicated in the function of the Ca2+-dependent adhesive system. The cells are repaired in the presence or absence of the inhibitors and surface-iodinated at 3 and 5 h. The labelled molecules are then separated by two-dimensional polyacrylamide gel electrophoresis. The appearance of the two molecules, gp130/4·8 and gp70/4·8, is affected by the various drugs in a manner consistent with the effects of these agents on the kinetics of adhesion. These molecules appear to exist in endogenous pools and they are also synthesized de novo during the repair period.
Lectin binding to guinea-pig sperm zipper particles
Authors: Enders George C. , Werb Zena , Friend Daniel S. 
Published: April 2021

ABSTRACT
Zipper particles are morphologically distinct transmembrane specializations of sperm tails. In freeze-fracture replicas of the guinea-pig sperm, they appear as an interdigitating double row of intramembranous particles running longitudinally within the plasma membrane of the principal piece. In thin section, zipper particles appear as an increase in electron density both above and below the bilayer. Zipper particles have been observed on a variety of both mammalian and nonmammalian species, suggesting that they have been conserved to serve an essential sperm function. As a first step towards biochemically characterizing guinea-pig zipper particles and towards developing a zipper isolation procedure, we performed an in situ lectin-binding study. Examination of nine gold- or ferritin-conjugated lectins revealed that three lectins, concanavalin A, Ricinus communis agglutinin I and wheatgerm agglutinin, bound to zipper particles. These lectin binding results suggest the presence of N-linked oligosaccharides within zipper particles. The results of the lectin binding study were then used in conjunction with a detergent solubilization procedure to identify potential zipper components. Detergent solubilization involved two non-ionic detergents: digitonin, which solubilized most of the plasma membrane, but left approximately two thirds of the zipper particles attached to the cytoskeleton, and Triton X-100, which solubilized the remaining zipper particles while leaving most other sperm structures intact. Within sodium dodecyl sulphate /polyacrylamide gels of the Triton-X-100-soluble fraction potential zipper particle components with the same lectin-binding characteristics as in situ zipper particles were identified.
Transport of phagosomes in mouse peritoneal macrophages
Authors: Toyohara A. , Inaba K. 
Published: April 2021

ABSTRACT
Mouse macrophages were elicited by the peritoneal injection of chondroitin sulfate solution, harvested and purified, and used as experimental materials. Small and large (diameter: 0·9 μm and 3·0μm respectively) polystyrene beads (PB) were used as ingested particles.
When the macrophages were incubated with Hank’s solution containing small or large PB for 30 min, the phagosomes containing small or large PB were usually randomly distributed. When the macrophages were further incubated for 45 min in PB-free medium, both small and large phagosomes containing PB accumulated at the perinuclear region. The transport of large phagosomes containing 3·0 μm PB was inhibited by cytochalasin B, but not by vinblastine or podophyllotoxin. Conversely, the transport of small phagosomes containing 0·9μm PB was not inhibited by cytochalasin B but was inhibited by vinblastine or podophyllotoxin. Immunofluorescence microscopy showed that the small phagosomes appeared to accumulate at the central region of the microtubule network. The large phagosomes, on the other hand, appeared to be surrounded by actin-rich cytoplasm, and in some cells actin filament-like structures could be seen around large phagosomes.
These results suggest that there are two different transport systems of phagosomes in macrophages. Phagosomes smaller than 0·9 μm in diameter are, probably, mainly transported to the perinuclear region by a microtubule-based motility system and those larger than 3·0 μm in diameter by an actin-based mechanism.
It was observed electron-microscopically that accumulated phagosomes containing PB could fuse with each other and form larger phagosomes.
Localization of intracellular proteins at acetylcholine receptor clusters induced by electric fields in Xenopus muscle cells
Authors: Rochlin M. William , Peng H. Benjamin 
Published: April 2021

ABSTRACT
Electric fields cause acetylcholine receptor (AChR) patches to form on the cathodal sides of cultured muscle cells. These patches are stable for several hours following cessation of an electric field treatment, indicating that the receptors are anchored to the cluster sites. Furthermore, at the ultrastructural level, AChR patches induced by electric fields are marked by an accumulation of extracellular matrix material and a sarcolemmal density. Thus, these AChR patches are similar to those induced by other stimuli, including nerve, polycation-coated beads, and the tissue culture substratum. Proteins that may be involved in anchoring AChRs have been colocalized with AChR patches induced by the latter three stimuli, but not at AChR patches induced by electric fields. In this study, we demonstrate that three putative anchoring proteins, 43K (K=103Mr) protein, 58K protein and talin, are associated with field-induced AChR patches. We also show that these proteins persist at field-induced AChR patches following removal of the field, indicating that they are stabilized at the AChR patch. Our data are consistent with the possibility that these proteins contribute to the stabilization of AChRs at patches induced by the electric field. Since 43K, 58K and talin are intracellular proteins, and therefore could not undergo field-induced lateral electrophoresis, our observations support the notion that the electric field triggers the formation of an AChR-stabilizing specialization.