bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lanthanum penetration in crayfish nervous system: Observations on intact and ‘desheathed’ preparations
Authors: Lane Nancy J. , Swales Lesley S. , Abbott N. Joan 
Published: April 2021

ABSTRACT
Central neural connectives and peripheral nerves from the crayfish Procambarus clarkii were incubated in 5 mM lanthanum solutions in physiological saline, for periods from 15 min to 2 h. The tracer only rarely reaches the axon surfaces in the perineurium-ensheathed connectives, penetrating the elaborate perineurial layer slowly. In peripheral nerves, on the other hand, where the perineurium is extremely attenuated and interrupted by open extracellular clefts, inward movement of lanthanum to the axon surfaces occurs readily. When the perineurial layer of the neural connectives is removed by ‘desheathing’, penetration of the tracer to the level of the axolemma occurs rapidly, implicating the perineurium as the major site of restriction of entry of large ions and exogenous molecules. This conclusion is discussed in relation to recent electrophysiological studies on K+ movements.
In both peripheral nerves and desheathed connectives, the transcellular tubular lattice system present in crustacean glial cells appears to serve as a route for the entry of tracer to the axon surfaces, and is more direct than the long and complex extracellular pathway formed by the interdigitations of the extensive glial cell processes.
Precise levels of the Drosophila adaptor protein Dreadlocks maintain the size and stability of germline ring canals
Authors: Stark Kara , Crowe Olivia , Lewellyn Lindsay 
Published: April 2021

ABSTRACT
Intercellular bridges are essential for fertility in many organisms. The developing fruit fly egg has become the premier model system to study intercellular bridges. During oogenesis, the oocyte is connected to supporting nurse cells by relatively large intercellular bridges, or ring canals. Once formed, the ring canals undergo a 20-fold increase in diameter to support the movement of materials from the nurse cells to the oocyte. Here, we demonstrate a novel role for the conserved SH2/SH3 adaptor protein Dreadlocks (Dock) in regulating ring canal size and structural stability in the germline. Dock localizes at germline ring canals throughout oogenesis. Loss of Dock leads to a significant reduction in ring canal diameter, and overexpression of Dock causes dramatic defects in ring canal structure and nurse cell multinucleation. The SH2 domain of Dock is required for ring canal localization downstream of Src64 (also known as Src64B), and the function of one or more of the SH3 domains is necessary for the strong overexpression phenotype. Genetic interaction and localization studies suggest that Dock promotes WASp-mediated Arp2/3 activation in order to determine ring canal size and regulate growth.
This article has an associated First Person interview with the first author of the paper.
Cytological studies on physodes in the vegetative cells of Cystoseira stricta sauvageau (Phaeophyta, Fucales)
Authors: Pellegrini Liliane 
Published: April 2021

ABSTRACT
Physodes have been recognized in meristodermic and promeristematic cells by correlated light- and electron-microscope investigations using different fixation procedures. They are vesicles which contain an osmiophilic material of phenolic nature. Their content changes in appearance according to the fixative used. Osmiophilic deposits are often associated with coiled and disturbed lamellar formations.
It has been possible to distinguish Feveral ultrastructural stages which occur during the secretion of the content of the physodes, namely: a chloroplast accumulation and exudation, and a reticular transport to accumulation vacuoles where materials undergo evolution or hydrolysis. Inside plastids, osmiophilic granules are found in close association with thylakoid stacks. They may contain the polyphenolic precursors of physodes, though this has not yet been proved by electron-microscope procedures. They are expelled from plastids to the chloroplast endoplasmic reticulum. The mechanism of transfer through the chloroplast envelope remains to be elucidated. Lytic activities have been reported inside physodes which might thus act in the same way as the secondary lysosomes of animals and higher plants. Occasionally, the physode content seems to be excreted from the cytoplasm to the cell walls by exocytosis after the probable fusion of plasmalemma and tonoplast.
These cytological changes, observed in the vegetative apex of a brown alga, recall some ultrastructural characteristics of the secretory processes described in various glandular tissues of higher plants and which consist of the synthesis, the transport and the elimination of an exudate of flavonic, terpenic or lipophenolic nature.
Development of the mitochondrial mass and accumulation of mtdna in previtellogenic stages of Xenopus laevis oocytes
Authors: Callen J. C. , Dennebouy N. , Mounolou J. C. 
Published: April 2021

ABSTRACT
The development of the mitochondrial mass of the previtellogenic oocytes of Xenopus laevis has been analysed by a morphometric method and it has been correlated with the growth of the oocyte itself. The study which was performed with oocytes from females of very different ages shows that the relative size of the mitochondrial mass in the smallest oocytes decreases gradually with the age of the females. Cytophotometric analysis of the Feulgen-stained mitochondrial mass enabled the mtDNA content of that structure to be quantified during its development. This development involves about 12 rounds of replication out of the total 16 –17 rounds of replication during complete differentiation of large oocytes. It is possible to estimate the mean replication rate of the mtDNA during the course of the previtellogenic period. The calculated rate of replication is very high in the mitochondrial mass of all the growing oocytes of very young females (about 1 –2 months old), then it decreases rapidly when the oocytes reach 120 μm in diameter.
These results suggest that the mitochondrial masses found in small oocytes of old females do not correspond to sites of active mitochondrial biogenesis but rather they represent a physiologically arrested collection of organelles. Thus the aggregation of mitochondria is the cytological expression of rapid and strictly localized mitochondriogenesis only in very young females.
Relationships between anionic sites and lectin receptors in the plasma membrane of Dictyostelium discoideum and their role in phagocytosis
Authors: Hellio Raymond , Ryter Antoinette 
Published: April 2021

ABSTRACT
The disappearance of Wheat Germ Agglutinin (WGA) receptors from the membrane of yeast-engulfing-phagocytic cups in Dictyostelium suggested that these receptors could play a role in yeast adsorption or ingestion. This problem was approached by comparing the fate of WGA, Concanavalin A (Con A) and cationized ferritin (CF) and their effects on the phagocytosis of yeast, bacteria and latex beads. It can be concluded that CF capped in about 30 min and inhibited phagocytosis of any kind of particles for about 15 min. Con A capped in 20– 60 min and inhibited phagocytosis of all particles for 1 h 30 min. The time at which phagocytosis started to occur corresponded approximately to the moment at which large areas of plasma membrane were totally devoid of marker. WGA did not cap but induced the formation of large and tight aggregates. The surface of the peripheral cells progressively released WGA in 1 h 30 min. Afterwards, the cells were able to ingest latex beads and bacteria but did not phago-cytoze yeast. The latter started to be adsorbed onto the cells and to be ingested only 1 h later.
Double labelling experiments showed that CF and Con A receptors were still absent in the plasma membrane, when phagocytosis of any kind of particles started to occur. WGA-labelled cells ingested latex beads and bacteria when their plasma membrane was still devoid of WGA receptors but were able to ingest yeast only after their regeneration. These observations strongly suggest that WGA receptors may correspond to specific receptors for yeast phagocytosis.
Surface properties of normal and adenovirus-transformed rat embryo cells
Authors: Goldstein Neil I. , Sher Paul B. Fisher 
Published: April 2021

ABSTRACT
Previous studies have indicated that an early-passage type 5 adenovirus temperaturesensitive mutant (Hsts125) transformed secondary rat embryo clone exhibited in vitro growth properties which resembled the normal secondary rat embryo (2°RE) parental cells (Fisher, Goldstein & Weinstein, 1979 a). In contrast, clones of early-passage chemical carcinogen, benzo(a)pyrene (BP) or 7,12-dimethylbenz(a)anthracene (DMBA), pretreated viral transformants displayed a greater phenotypic expression of certain in vitro markers of transformation. In the present study, we have analysed the glycoproteins, glycopeptides and cell-surface proteins of normal and cloned populations of early passage solvent and chemical carcinogen-pretreated H5ts125 transformed 2°RE cells to determine if any systematic changes in surface composition had occurred in the different cell types.
When compared with normal 2°RE cells, all of the viral transformants exhibited a reduction in cell surface fibronectin (LETS protein) ranging from 25 % (solvent-pretreated culture) to 84 % (a DMBA-pretreated clone). This surface marker, however, did not accurately reflect the state of transformation of the individual clones, as indicated by cloning efficiency in agar, production of plasminogen activator, etc. Similarly, whereas the carcinogen-pretreated Hgtsizs-transformed clones showed a slight molecular weight shift in glucosamine-labelled glycopeptides, when run on Sephadex G-50 columns in parallel with 2°RE glycopeptides, this surface change also was not a good indicator of adenovirus transformation of 2°RE cells. On the other hand, a distinctive change which was observed in all of the carcinogen-pretreated H5ts125-transformed clones, but not in the normal 2°RE or solvent-pretreated transformed cells, was an increase in a glycoprotein of approximately 100 K molecular weight. A protein of similar molecular weight has been described by Bramwell & Harris (1978) to correlate with in vivo malignancy and may also be a good indicator for carcinogen-pretreated adenovirus-transformed 2°RE cells or Hsts125 transformants exhibiting anchorage-independent growth.
The secretion of the eggshell of schistocerca gregaria. analysis of the kinetics of secretion in vitro by light and electron microscope autoradiography
Authors: Kimber S. J. 
Published: April 2021

ABSTRACT
The secretion of the 2 main layers (endochorion and exochorion) of the eggshell of the desert locust Schistocerca gregaria was investigated using light and electron microscope autoradiography. Follicles undergoing endochorion secretion were labelled using a 3 min ‘pulse’ of [3H]leucine in vitro followed by a 0—115 min non-radioactive ‘chase’. Immediately after the pulse the silver grains were distributed over the cytoplasm and organelles including rough endoplasmic reticulum, while by 2 and 5 min Golgi bodies contained radioactivity. By 12 min from the beginning of the chase the cell apex containing small secretory vesicles was labelled. By 20 min most of the silver grains were over the endochorion. The half-transport time (t50) was 14-15 min (from mid pulse), the lag time was 9–10 min and the percentage transport rate was 14·15% per min. When a 3 min pulse of pHJgalactose was used to label exochorion precursors, the shorter t50 (11 min) and the clumped grain distribution in light microscope autoradiographs after o-min chase suggested that galactose was incorporated in Golgi bodies. The secretion of exochorion precursors appears to occur at a similar rate to that of endochorion precursors (approximately 15% per min). The results indicate that the follicle cells are among the fastest secreting cells.
Microtubule-organizing centres and assembly of the double-spiral microtubule pattern in certain heliozoan axonemes
Authors: Jones J. C. R. , Tucker J. B. 
Published: April 2021

ABSTRACT
The double-spiral microtubule pattern is established by a self-linkage procedure when axopodial axonemes reassemble after cold treatment in multinucleate Echinosphaerium nucleofilum and mononucleate Actinophrys sol. Nuclei are related spatially to axoneme morphogenesis in both organisms but in rather different ways.
Microtubules grow out in all directions from discrete clumps of dense material situated close to nuclei in E. nucleofilum as axonemal assembly begins. Each clump acts as a microtubuleorganizing centre (MTOC) in so far as it is associated spatially with the assembly of microtubules for a single axoneme. The dense material spreads along the sides of a developing axoneme for several μm, where it probably promotes further microtubule assembly as the double-spiral pattern is established. Pattern is generated as microtubules that are randomly oriented to begin with become more closely juxtaposed and aligned with each other. There are indications that juxtaposition is brought about by the contractile action of a filamentous meshwork that interconnects the microtubules. Final positioning and alignment appears to be accomplished by a ‘zippering’ together of adjacent portions of microtubules that proceeds in both directions along the lengths of developing axonemes as self-linkage is effected.
Considerable numbers of more or less radially oriented microtubules remain and project from the surface membrane of the single central nucleus during cold treatment of A. sol. Additional tubules assemble and become associated similarly with the nuclear envelope immediately after cold treatment. Initially these microtubules are not arranged in a doublespiral pattern, which is subsequently generated by procedures similar to those outlined above for E. nucleofilum. It is suggested that the surface of the nuclear envelope may act as an MTOC.
Stimulation of murine tumour cell motility by laminin
Authors: Situ Rui , Lee Euisung C. , Mccoy J. Philip , Varani James 
Published: April 2021

ABSTRACT
Several variant cell lines that are deficient in surface laminin have been isolated from heterogeneous murine tumour populations. The parent populations from which these variant lines were isolated contain cells that express high levels of surface laminin as indicated by immunofluorescence, immunoperoxidase/electron microscopy and immunoprecipitation. The laminin-deficient lines were compared with their respective parent populations for motility by both the Boyden Chamber assay and the agarose assay. In both assays, the laminin-positive populations were much more motile than the laminin-deficient lines. The addition of exogenous laminin to the laminin-deficient lines significantly increased their motility. These observations are of interest since cell motility is thought to contribute to tumour cell metastasis, and the laminin-positive cell populations are highly tumorigenic and metastatic, while the laminin-deficient cells are of low tumorigenicity and are virtually non-metastatic.
Permeability properties of mammalian cell nuclei in living cells and in vitro
Authors: Reynolds Christopher R. , Tedeschi Henry 
Published: April 2021

ABSTRACT
The present study evaluates the role of the nuclear envelope in mammalian cells by applying two different approaches using either intact cells of mouse liver or isolated nuclei. In one approach the nuclei were studied with microelectrodes. The transmembrane voltage drop produced by passing current through an impaling microelectrode was measured with a second impaling microelectrode. In the second approach, the permeability of the nuclear envelope was studied by injection of a series of fluorescent probes. Lucifer Yellow CH and a variety of exogenous proteins labelled by conjugation with Lucifer Yellow VS were delivered into either the cytoplasm or the nucleus in situ. The fluorescence of the probe was followed either with a video camera or photographically. The results agree with the idea that the mammalian nuclear envelope is permeable to rather large molecules. Molecules with estimated radii below 2·4 nm seem to exchange rapidly, whereas molecules with estimated radii of 2·8 nm or above are excluded. The low electrical resistance of the envelope yields an estimate of pore radius, in the range of 3·4–6·5 nm.
Diminution of microtubular organelles after experimental reduction in cell size in the ciliate, Dileptus
Authors: Golinska Krystyna 
Published: April 2021

ABSTRACT
Organelles of two kinds were studied: nemadesmata and transverse fibres, which are kinetosomal rootlets in oral parts of Dileptus. A diminution of microtubule number and length was found in organelles of size-reduced and regenerating cells, as compared to normal ones. It appeared, however, that organelles reduced in size were always larger and longer than could be expected on a basis of perfectly proportional regulation. The results give some insight into the modes of formation and regulation of the size of these organelles.
Cloned cdna sequence for the human mesothelial protein ‘mesosecrin’ discloses its identity as a plasminogen activator inhibitor (PAI-1) and a recent evolutionary change in transcript processing
Authors: Cicila George T. , O’Connell Therese M. , Hahn William C. , Rheinwald James G. 
Published: April 2021

ABSTRACT
Mesosecrin, a Mr ≈ 46 ×103 glycoprotein secreted in abundance by human mesothelial cells in culture, was recently described by this laboratory. We isolated partial cDNA clones for mesosecrin from a human mesothelial cell cDNA library in lambda gtll using a specific antiserum. Comparison of mesosecrin cDNA sequences with the recently published sequence for plasminogen activator inhibitor-1 (PAI-1) cloned from cDNA libraries of endothelial and other cell types revealed that mesosecrin and PAI-1 are the same protein. Reverse fibrin autography of electrophoretically fractionated medium from mesothelial cell cultures confirmed that mesosecrin is functional as a plasminogen activator inhibitor. The mesosecrin/PAI-1 cDNA clones hybridized to abundant 3’6 and 2 ·6 kb (kb = 103 bases) mRNAs on Northern blots of cultured human mesothelial cell and endothelial cell RNA. These mRNA sizes correspond to those recently published for human endothelial and fibrosarcoma PAI-1 mRNA, which most likely result from alternate polyadenylation sites. Messages 3 ·6 and 2 ·6 kb long were also detected in cells cultured from orangutans and African green monkeys, but only a ≈3 ·6 kb mRNA was detected in cells of lower primates and several other mammalian species. Thus the extra polyadenylation site in the PAI-1 gene, responsible for the shorter form of the RNA, apparently has been acquired recently during primate evolution. Because they are more easily propagated in culture than endothelial cells, human mesothelial cells offer a new and advantageous system for PAI-1 production and study of its regulation and function.
Fibrinogen-mediated epidermal cell migration: Structural correlates for fibrinogen function
Authors: Donaldson Donald J. , Mahan James T. , Amrani David , Hawiger Jacek 
Published: April 2021

ABSTRACT
Previously we showed that epidermal cells are able to use fibrinogen (FGN) as a migration substratum during wound closure. The goal of the present study was to determine the structural features of FGN that allow this migration. Pieces of glass coated with native, fragmented, or other modified forms of FGN were implanted into full-thickness skin wounds of adult newts such that migrating epidermal cells would encounter the implant. In this system, a coating of FGN allowed considerably more migration than a coating of BSA. At high concentrations, heat-denatured FGN supported as much migration as the same amount of intact FGN. Fraction 1-9, a circulating form of FGN missing a 20-30K (K = 103Mr) carboxy-terminal segment of the Aα chain, was no less effective than intact FGN. Comparison of the isolated D1 and E fragments of FGN showed migration only on D1 but never to the extent seen on intact FGN containing the same amount of D1. Plasmin digestion of Di in the presence of EDTA, a process which produces D3, a fragment differing from D1 by the loss of the carboxy-terminal 109 amino acids of the γ chain, caused a significant loss of activity in the D fragment. Migration was good on implants coated with relatively high concentrations of purified Aα chains but y chains were inactive. Migration over intact FGN was almost totally blocked by 230 μM-Arg-Gly-Asp-Ser (RGDS), a peptide known to interact with integrin-type receptors. This same concentration of μ400-411, a peptide modeled after the carboxyterminal 12 amino acids comprising the platelet receptor recognition domain in the γ chain, had no effect. These results are consistent with the idea that newt epidermal cell migration over FGN-coated glass involves integrin-type receptors capable of interacting with the Aα and perhaps the y chains of FGN. The ability of fraction 1-9 to support as much migration as intact FGN shows that the RGDS sequence in the carboxy-terminal segment of the Aα chain (α572-575) is not required for full activity. The contribution of the Arg-Gly-Asp-Phe (RGDF) sequence in the amino-terminal segment of the Aα chain (095.9g) to 1-9 activity remains to be determined. Absence of an effect on migration by the γ400-411 peptide suggests that epidermal receptors do not recognize this domain of the γ chain. Thus, the ability of FGN to support epidermal cell migration appears to reside primarily in its Aα chain, which may function in concert with a site in the y chain that does not coincide with the site recognized by platelets.
Identification of a filamin isoform enriched at the ends of stress fibers in chicken embryo fibroblasts
Authors: Pavalko Fredrick M. , Otey Carol A. , Burridge Keith 
Published: April 2021

ABSTRACT
Filamin (actin-binding protein) is a cytoskeletal protein that crosslinks actin filaments in vitro. Filamin is thought to be involved in a variety of cell types in stabilizing actin networks, and in platelets it may play a role in linking actin to the membrane. In this report, we describe a monoclonal antibody (Mab 6E) that was used to immunoprecipitate an isoform of filamin from extracts of chicken fibroblasts. Immunofluorescence staining of chicken fibroblasts revealed an unusual pattern: while other filamin antibodies stained the entire length of stress fibers, the Mab 6E staining was predominantly at the ends of stress fibers. In double-labeling experiments, the distribution of the Mab 6E antigen was found to be strikingly similar to that of a-actinin. Mab 6E staining was associated, in part, with focal adhesions, which are sites of actin-membrane attachment. Unlike other focal adhesion proteins, such as vinculin and talin, this filamin isoform is apparently not localized evenly throughout the entire area of adhesion, being absent from or greatly reduced in the distal portion of the area.
The Mab 6E antigen was identified as filamin by immunological crossreactivity with a panel of anti-filamin monoclonals as well as with a polyclonal anti-filamin. The Mab 6E isoform, however, was found to differ from the major form of filamin both by one-dimensional peptide analysis and slightly slower migration on SDS-containing gels. The Mab 6E antigen was also detected by immunofluorescence in the Z-lines of isolated adult myofibrils. These results suggest that chicken fibroblasts may express different isoforms of filamin that could have specialized roles within the cell.