bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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

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

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.
An experimental approach to nucleolar organization in plant cells: A morphological, cytochemical and quantitative study
Authors: Moreno Francisco Javier , Rodrigo Rosa Maria , Garcia-Herdugo Gregorio
Published: April 2021

We have used morphological, cytochemical and immunocytochemical techniques, along with transcription inhibitors, to try to understand the nucleolar organization in Allium cepa root meristem cells.

Our results reveal that the fibrillar component shows intense staining after using the NOR-silver technique, and gold particle labelling after incubation with DNase-gold and RNase-gold complexes. These different techniques reveal a reticular structure of the fibrillar component, supported by a central axis that is circular in transverse section. These structures are usually considered to be fibrillar centres, but we have called them clear areas, since we find in their interior neither Ag-NOR proteins nor labelling after incubation with nuclease-gold or anti-DNA.

Taking into account the specific localization of the Ag-NOR proteins, our cytochemical and quantitative results, after applying NOR-silver staining in nucleoli of control cells and cells treated with transcription inhibitors, help us to a better understanding of the mechanisms of action of these drugs. Our results support a structural and functional role for the Ag-NOR proteins throughout the course of transcription.
Replication of purified DNA in Xenopus egg extract is dependent on nuclear assembly
Authors: Blow J. Julian , Sleeman Andrea M.
Published: April 2021

Purified DNA undergoes a single round of semiconservative replication when incubated in extracts of Xenopus eggs. These extracts also assemble purified DNA into pseudo-nuclei, structures closely resembling normal interphase nuclei. In this paper we show that although <60% of purified DNA is assembled into pseudo-nuclei, DNA replication takes place only within these pseudo-nuclei. Further, when nuclear assembly is prevented, the initiation of replication on purified DNA molecules does not occur. In contrast to previous reports, we show that the initiation of DNA replication occurs only during interphase and not during mitosis, even when very high concentrations of purified DNA are used. These experiments show that nuclear formation is a general requirement for the initiation of DNA replication in this system.
Characterization of the cation-independent mannose 6-phosphate receptor-enriched prelysosomal compartment in NRK cells
Authors: Griffiths Gareth , Matteoni Raffaele , Back Ruth , Hoflack Bernard
Published: April 2021

The structure of a late endosomal compartment, which contains the bulk of the cation-independent mannose 6-phosphate receptor (MPR) in NRK cells, is documented using immunocytochemistry and cryo-sections, as well as conventional Epon sections. This compartment, which we refer to as the prelysosomal compartment (PLC), has a complex three-dimensional structure consisting of tubulo-reticular domains in continuity with vesicular parts. The latter are characterized by a high density of internal membranes, which may be either tubular or sheet-like, that label extensively for the MPR. This structural organization was also maintained after fractionation in sucrose gradients. The amount of MPR immunolabelling was then quantitated with respect to the membrane surface areas of the four compartments where it is found: namely, the plasma membrane, early endosomes, the trans Golgi network and the PLC. The results showed that in NRK cells 90% of the labelling for the receptor was found in the PLC, with the rest distributed over the other three compartments. Cytochemical studies indicated that the PLC is the first structure along the endocytic pathway that gives a significant reaction for acid phosphatase. However, the PLC is clearly distinct from the MPR-negative lysosomes, which are also acid phosphatase-positive, since the two organelles could be physically separated from each other after fractionation on Percoll gradients.
Isolation and characterization of membranes from oleic acid-induced peroxisomes of Candida tropicalis
Authors: Nuttley William M. , Bodnar Andrea G. , Mangroo Dev , Rachubinski Richard A.
Published: April 2021

We report a methodology for the isolation of peroxisome membranes from the yeast Candida tropicalis pK233 grown on oleic acid, and the characterization of the polypeptide and lipid compositions of these membranes. Peroxisomes purified in either sucrose or Nycodenz gradients are treated with Tris-HCl (pH 8·5) and then with sodium carbonate (pH 11·5) to yield a final peroxisome membrane preparation (hereafter called ‘peroxisome membranes’). Electron microscopy revealed peroxisome membranes that are approximately 8.1 nm thick, have a typical trilaminar appearance, and form either flattened sheets or whorled structures. Peroxisome membranes contain 3·1 % and 2·2 % of the total protein of sucrose- and Nycodenz-gradient-purified peroxisomes, respectively. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis showed three predominant polypeptide bands of 34 (PMP 34), 29 (PMP 29), and 24 (PMP 24) –103Mr in peroxisome membranes. Immunoblotting with an antiserum to PMP 24 showed that PMP 24 segregates with the peroxisome membrane fractions and is induced by growth of Candida tropicalis on oleic acid. Peroxisome membranes contain neutral lipids and phospholipids. The principal phospholipids are phosphatidyl choline and phosphatidyl ethanolamine. The phospholipid/protein ratio of peroxisome membranes is approximately 430 nmol mg − 1.
When is a centromere not a kinetochore?
Authors: Earnshaw William C.
Published: April 2021

The terms ‘centromere’ and ‘kinetochore’ were originally coined to describe the region(s) of each chromosome with which the spindle microtubules become associated (Rieger et al. 1976). In recent years, the term ‘centromere’ has largely come to be used by morphologists to describe the primary constriction of mitotic chromosomes. The term ‘kinetochore’ has been used to refer to the circular plaque structure that rests on the surface of the centromeric chromatin and into which microtubules are inserted (Jokelainen, 1967; Brinkley and Stubblefield, 1966). This commentary is concerned with development of a rationale for assignment of newly identified antigens to specific centromere domains and, in particular, to the kinetochore domain.
Dynamics of nuclear pore density and distribution patterns within developing pollen: implications for a functional relationship between the vegetative nucleus and the generative cell
Authors: Shi Liang , Mogensen H. Lloyd , Zhu Tong , Smith Steven E.
Published: April 2021

Quantitative transmission electron microscopy was used to study pore density (mean pore number ± standard deviation/nuclear envelope area) on developing pollen nuclei of alfalfa. We found that pore density is essentially uniform around the vegetative nucleus (VN) at an early developmental stage (29 ±6 pores /an-2), but later, when the VN forms a close physical association with the generative cell (GC), nuclear pore density is 69 % higher on the surface of the VN facing the GC (27 ±12 pores /on-2) compared to the surface away from the GC (16±9 pores pm 2). The surface area of the VN does not change significantly during the stages of this study. Pore density is nearly equal on vegetative and generative nuclei in young pollen, but at pollen maturity the VN has a mean pore density 3.5 times greater than that of the generative nucleus. Our results are consistent with those of other studies comparing pore densities on developing and mature pollen nuclei. However, this is the first study, to our knowledge, that has followed vegetative nuclear pore density and distribution as it relates to the formation of a close physical association between the VN and the GC. Taken together with biochemical studies on RNA and protein synthesis during pollen development, and studies on nuclear pore function, these results support the notion that even though mean pollen nuclear activity may decrease during pollen maturation, the potential for nucleocytoplasmic exchange is not diminished appreciably in the area of the VN-GC association. This suggests that there is a direct functional relationship between the VN and the GC, and that gene expression may be not only temporally but also spatially separated within the VN during pollen development.
Retroviral vector infection and transplantation in rats of primary fetal rat hepatocytes
Authors: Koch K. S. , Brownlee G. G. , Goss S. J. , Martinez-Conde A. , Leffert H. L.
Published: April 2021

Retroviral vectors were used to transduce recombinant DNA encoding firefly luciferase, Escherichia coli β-galactosidase or human factor IX into fetal rat hepatocytes in primary culture. Hepatocytes were transduced optimally during a restricted time interval, 2–4 days post-plating. Although efficient and stable expression of reporter gene products was observed in vitro, it was affected differentially by culture conditions (plating density, media constituents) and chemical modulators of hepatocyte growth and differentiation (gelatin, hydrocortisone, isobutylmethylxanthine). Cultured cells, mock-infected or infected with a luciferase-expressing vector, were harvested non-enzymatically and injected subcutaneously into the dorsal neck fascia of neonatal syngeneic rats. Tissue isolated from injection sites one week later contained hepatocyte foci. In animals transplanted with infected cells, the preliminary results suggest that luciferase activity was present at these sites in proportion to the numbers of injected cells.

These findings and previous observations made with hepatocytes from neonatal and adult primary cultures, indicate that from day 19 in utero through maturity the transient temporal ‘period of susceptibility’ to infection in vitro is independent of the developmental state of starting tissue. Transplantability of cultured fetal hepatocytes infected with retroviral vectors and stably expressing reporter gene products suggests that such cells might provide promising models for liver gene therapy.
Expression of a divalent cation-dependent erythroblast adhesion receptor by stromal macrophages from murine bone marrow
Authors: Morris Lynn , Crocker Paul R. , Fraser Iain , Hill Maxine , Gordon Siamon
Published: April 2021

Stromal macrophages in haemopoietic organs express novel surface receptors that are implicated in trophic interactions with developing blood cells. Macrophages isolated from foetal liver bind erythroblasts (Eb) by a divalent cation-dependent receptor (EbR), whereas stromal macrophages in adult bone marrow and lymphoid organs express a lectin-like receptor, sialoadhesin, which interacts with sialylated structures on sheep erythrocytes and murine haemopoietic cells. In order to learn more about the regulation of these haemagglutinins, we examined binding of Eb by stromal macrophages that had been isolated from adult murine tissues or generated in Dexter-type cultures of bone marrow. Macrophages were purified from bone marrow by collagenase digestion, adherence to a substratum and detachment of clustered haemopoietic cells, and tested for their ability to bind Eb from foetal liver or anaemic adult spleen. Freshly isolated bone marrow macrophages bound Eb mainly by a divalent cationdependent activity that was not inhibited by neuraminidase treatment of Eb or by specific anti-sialoadhesin monoclonal antibodies, although these macrophages express sialoadhesin and Eb bear a potential ligand for this receptor. Macrophages obtained by digestion from other adult lymphoid tissues also bound Eb by a divalent cation-dependent activity, whereas blood monocytes and lavaged peritoneal macrophages failed to do so. Peritoneal macrophages could be induced to express high levels of sialoadhesin by cultivation in homologous mouse serum, but such macrophages did not acquire sialoadhesin-independent EbR activity. By contrast, high levels of EbR (∼75% rosettes) were detected on bone marrow macrophages derived by cultivation for 3–10 days in medium containing foetal bovine or horse serum and supplemented with 10−6 M dexamethasone, similar to that required to obtain a functionally active stroma in long-term bone marrow culture. EbR activity remained low (<20%) on peritoneal macrophages cultivated under the same conditions. Our studies establish that the EbR is a major cell adhesion receptor on macrophages in adult as well as foetal tissues, that macrophages express distinct, independently regulated haemopoietic cell interaction receptors and that the EbR is a consistent marker of stromal macrophages in situ and in vitro.

Abbreviations: BMDMФ, bone-marrow culture derived macrophage(s); CSF-1, colony stimulating factor, type 1; Eb, erythroblast; EbR, erythroblast receptor: FBS, foetal bovine serum; FL, foetal liver; GM-CSF, granulocyte-macrophage colony stimulating factor; HS, horse serum; LCM, L-cell conditioned medium; mAb, monoclonal antibody; MФ, macrophage(s); RBMФ, resident bone marrow MФ; RPMФ, resident peritoneal MФ; SE, sheep erythrocytes; TPMФ, thioglycollate elicited peritoneal MФ.
Mutant analysis suggests that cyclic GMP mediates the cyclic AMP-induced Ca2+ uptake in Dictyostelium
Authors: Menz Susanne , Bumann Johann , Jaworski Elke , Malchow Dieter
Published: April 2021

Previous work has shown that streamer F (stmF) mutants of Dictyostelium discoideum exhibit prolonged chemotactic elongation in aggregation fields. The mutants carry an altered structural gene for cyclic GMP phosphodiesterase resulting in low activities of this enzyme. Chemotactic stimulation by cyclic AMP causes a rapid transient increase in the cyclic GMP concentration followed by association of myosin heavy chains with the cytoskeleton. Both events persist several times longer in stmF mutants than in the parental strain, indicating that the change in association of myosin with the cytoskeleton is transmitted directly or indirectly by cyclic GMP. We measured the cyclic AMP-induced Ca2+ uptake with a Ca2+-sensitive electrode and found that Ca2+ uptake was prolonged in stmF mutants but not in the parental strain. The Gα2 mutant strain HC33 (fgdA), devoid of InsP3 release and receptor/guanylate cyclase coupling, lacked Ca2+ uptake. However, the latter response and cyclic GMP formation were normal in the signal-relay mutant strain agip 53 where cyclic AMP-stimulated cyclic AMP synthesis is absent LiCl, which inhibits InsP3 formation in Dictyostelium, blocked Ca2+ uptake in a dosedependent manner. The data indicate that the receptor-mediated Ca2+ uptake depends on the InsP3 pathway and is regulated by cyclic GMP. The rate of Ca2+ uptake was correlated in time with the association of myosin with the cytoskeleton, suggesting that Ca2+ uptake is involved in the motility response of the cells.
Cell guidance by ultrafine topography in vitro
Authors: Clark P. , Connolly P. , Curtis A. S. G. , Dow J. A. T. , Wilkinson C. D. W.
Published: April 2021

Laser holography and microelectronic fabrication techniques have been employed to make grating surfaces in fused quartz with ultrafine period (260 nm) in an attempt to mimic the topography of aligned fibrillar extracellular matrix (ECM), which, in the past, has been shown to affect the behaviour of cells in vitro and in vivo. The alignment of BHK cells, MDCK cells and chick embryo cerebral neurones on 260 nm period grating surfaces (130 nm grooves separated by 130 nm) of various depths (100, 210 and 400 nm) was examined. While all gratings aligned BHK cell populations, the degree of alignment was dependent on depth. The response of single MDCK cells to the grating patterns was both to align precisely to the direction of the gratings, and to elongate; only their elongation was depth-dependent. MDCK cells that were part of epithelial cell islands, and the outgrowth of neurites from chick embryo neurones, were mainly unaffected by the grating surfaces. It is clear that topography on this scale can control cell behaviour, but guidance of this type is strongly dependent on cell type and cell-cell interactions.
On the Impregnation and Germination of algæ
Authors: Pringsheim M.
Published: April 2021

The existence of sexuality in the vegetable kingdom, though at first surmised simply upon a presumed analogy in this respect between animals and plants, and long a disputed point in science, has for some time been admitted as an indisputable fact. In the Phanerogamia especially, the necessity of the conjunction of the pollen tube and the ovule for the production of the embryo can no longer be denied by any one. Observations and experiments whose results admit of no dispute, have established this fact, although opinions may vary as to the essential nature of the act of impregnation.
On some British Fresh-water Algæ
Authors: Currey Frederick
Published: April 2021

The observations to which this paper relates were made in the year 1856, and have since been laid by under a doubt as to their being of sufficient importance to be made public ; but some recent observations in Germany have induced me to think that they may not be without value, especially if they should have the effect of directing the attention of some of the numerous microscopists of the present day to the abundance of material for interesting and important microscopical inquiries afforded by the fresh-water Algæ.
On a Submersion Microscope
Authors: Dudgeon R. E.
Published: April 2021

For the examination of minute aquatic vegetable and animal organisms in a considerable quantity of their native element, it is desirable to have a microscope which can be plunged into water without affecting its optical qualities. The ordinary microscopes are only intended for use in an aerial medium, and were we to insert the end of the objectpiece into water we should at once destroy the magnifying power of the object-glass to a considerable extent, and run the risk of injuring the brass work and screws constituting the mechanism of the object-piece.
On the Nature of the Cuticula Dentis (Nasmyth’s Membrane).
Authors: Tomes Charles S.
Published: April 2021

Since it was discovered by Nasmyth that by the use of acids a membrane could be raised from the surface of the enamel in a perfected but as yet unworn tooth, numerous and irreconcilable views have been propounded as to its nature and homologies. Nevertheless, if the preparations which serve to illustrate this paper are to be trusted, the theories of its origin which are set forth in the most recent histological text-books cannot be accepted.
The Freshwater Algæ of Gotland and Oland (with an Enumeration of the Species and Remarks)
Authors: Wittrock Veit Brecher , Archer William
Published: April 2021

A VALUABLE memoir (‘Om Gotlands och Ölands Sötvat-tensalger’), ‘On the Freshwater Algæ of Gotland and Öland’ (islands in the Baltic Sea), from the pen of Dr. Veit Brecher Wittrock, of the University of Upsala, communicated to the Royal Academy of Sciences, Stockholm, so far back as January, 1872, but which appears to have been only recently circulated, has just come to hand. As it possesses (notwithstanding that the algal-flora of those islands is not a rich one) considerable, not only local but general interest, and as the valuable remarks interspersed (with the exception of the descriptions of new species, which are in Latin) are in the author’s native tongue, it has been thought that a rèsumè thereof could not but be welcome to those algologists of this country to whom the Swedish language might be more or less a barrier to the full employment of the original memoir.
Note on the Foregoing
Authors: Lankester E. Ray
Published: April 2021

MY friend, Dr. Klein, kindly suggests that I should add to his paper a note calling the reader’s attention to the series of varieties of Bacterium rubescens which were described and figured by me in vol. xiii, p. 408 (1873), and in vol. xvi, p. 27 (1876) of this Journal, since they offer an interesting parallel to the important fact discovered by Dr. Klein.
Note on a Pink Torula
Authors: Klein E.
Published: April 2021

Some time ago I examined for my colleague at St. Bartholomew’s Hospital, Dr. W. J. Russell, F.R.S., a sample of distilled water contained in a water bottle, through which 25 cubic feet of London fog air had been passing every hour for twenty-four hours. In this water were present, besides numbers of soot and dirt particles, large numbers of mycelia, or what appeared to be the mycelium of penicillium and mucor.
Some recent Researches on the Continuity of the Protoplasm through the Walls of Vegetable Cells
Authors: Gardiner Walter
Published: April 2021

Having been for some time engaged in investigating the subject of the continuity of protoplasm through the walls of vegetable cells, it was with no small degree of interest that I read Dr. Elsberg’s paper1 in the hope of finding something that would be of value for my research. In this, however, I was disappointed, and having carefully gone over his paper, and worked through his methods, I resolved to publish my results, believing it to be of extreme importance in a subject such as he treats of, that his statements should, if correct, receive every confirmation and support, or if any mistake had arisen, that such mistakes should as quickly as. possible be rectified.
Review of Recent Researches on Spermatogenesis.
Authors: Blomfield J. E
Published: April 2021

Since the publication of my two former papers on the subject of Spermatogenesis (vide this Journal January, 1880, and July, 1881) some accounts of the researches of other observers have been published in foreign periodicals, which go far to support the attempt made in the papers referred to, to establish a general plan of Spermatogenesis which should be applicable to the animal kingdom, or, at any rate, to a large part of it. While our knowledge of the formation of the ovum was fairly perfect, observations on the development of the corresponding sexual element, though by no means deficient in number, yet were wanting in completeness and wideness of scope. For instance, in such an animal as the frog, many had observed the process for a short time and drawn conclusions as to how this was conducted from data which were neeessarily incomplete; since the observations to be of any value in such animals which procreate once in the year, must be continued during the whole period from the time of procreation till the next crop of spermatozoa is ready.
A Cytological Study of the Metabolism of Iron in the Leech, Glossiphonia complanata
Authors: Bradbury S.
Published: April 2021

Glossiphonia complanata is found to contain iron in the form of haemosiderin in the gut-content, in the cells of the intestinal epithelium, the coelomic epithelium, the connective tissue, and the epidermis. The haemosiderin is largely in granular deposits.

The amount of iron in the body is reduced on starvation; granular deposits do not now occur, but a positive reaction is still given by the ground cytoplasm of connective tissue and epidermal cells.

Iron is absorbed in limited amounts when the animal is kept in water artificially enriched with this element. It appears to be concentrated in the coelomic epithelial cells and in the connective tissue.

Feeding with Planorbis corneus causes significant increase in the iron content of the body of the leech; no such increase is apparent after feeding with Limnaea stagnalis.
Further Studies of the Third Instar Larval Cuticle of Calliphora erythrocephala
Authors: Wolfe L. S.
Published: April 2021

The penetration and reduction of ammoniacal silver nitrate solution in the epicuticle of the larva of Calliphora was studied. The epicuticle of the third instar larva is more permeable over the muscle insertions and cuticular sense organs. This finding is related to their development at the previous moult.

A surface layer of orientated wax is not present. Proteinaceous and fatty materials from the feeding medium modify the properties of the cuticle surface. Chloroformmethanol extracts a soft light brown acidic lipide from the protein of the epicuticle after contaminants from the medium are removed.

The water loss from larvae and puparia of different ages and after various treatments was studied. Young puparia recover from abrasion but larvae do not. An hypothesis that waxy substances are liberated on to the surface of the puparium during hardening and darkening of the cuticle is presented and discussed.

The pore canals penetrate the endocuticle until they are cut off from the epidermis by the development of the prepupal cuticle just after the puparial contraction. An inner endocuticle in which pore canals were absent was not found. The structure of the pore canals as shown by phase contrast examination is discussed. The pore canals are three times more concentrated in the lateral regions than in the dorsal or ventral regions.

The oenocytes go through a secretory cycle during puparium formation similar to that occurring before moulting of the larva.
Staining Differences in Cell Nuclei
Authors: Lison Lucien
Published: April 2021

If the parenchymal cells of the liver of the rat, or certain other cells, are stained with a modified Mallory stain or with iron haematoxylin, the nuclei are stained in two different ways. This effect may be observed after various fixatives.

Direct microscopical observation shows that when part of a nucleus is cut away hy the microtome-knife, the part of it remaining in the section stains differently from an intact nucleus. The probability of a nucleus being wholly or only partly contained in a section of a particular thickness can be calculated.

Counts made in sections of various thicknesses show that the proportion of nuclei stained in the different ways is consistent with the calculated probability.

It is suggested that the nuclear membrane in the fixed state presents a relatively low permeability.
The Structure and Connexions of the Corpora Pedunculata in Bees and Ants
Authors: Vowles D. M.
Published: April 2021

A method is described of using high frequency radio waves to produce localized and precisely controlled burns. The technique is employed to damage the cells of the corpora pedunculata in bees and ants, and to follow the subsequent degeneration in these lobes. The corpora pedunculata on each side of the brain are composed of four lobes: two calyces, an α lobe and a β lobe. Each fibre originates from a cell in the calyx, and has three branches, one to the calyx itself, one to the β lobe, and one to the β lobe. The arrangement of the tracts in these lobes is described. The calyces and the α lobe both receive tracts from all the sensory centres of the brain, while the β lobe sends tracts to the motor regions. The detailed connexions of these tracts are described. It is suggested that in the functioning of the corpora pedunculata the excitations from the calyx and the α lobe will interact, and that the excitation passing away down the β lobe is the result of this interaction.
Estimating Platform Market Power in Two-Sided Markets with an Application to Magazine Advertising
Authors: Song Minjae
Published: April 2021

In two-sided markets, two groups of agents interact through platforms. Because agents’ decision to join a platform is affected by the presence of agents on the other side, their interactions create indirect network externalities and make platforms’ strategies different from those of firms in one-sided markets. In this paper, I use a structural model to show that platforms may take a loss on one side of the market to make a profit on the other side and that platform mergers may benefit some agents by lowering prices or attracting more agents on the other side of the market. (JEL D62, G34, L82, M37)
Competition and Price Transparency in the Market for Lemons: Experimental Evidence
Authors: Bochet Olivier , Siegenthaler Simon
Published: April 2021

In markets with asymmetric information, where equilibria are often inefficient, bargaining can help promote welfare. We design an experiment to examine the impact of competition and price transparency in such settings. Consistent with the theoretical predictions, we find that competition promotes efficiency if bargainers cannot observe each other’s price offers. Contrary to the predictions, however, the efficiency-enhancing effect of competition persists even when offers are observable. We explore different behavioral explanations for the absence of a detrimental effect of price transparency. Remarkably, implementing the strategy method improves subjects’ conditional reasoning, delivering the predicted loss in efficiency when offers are observable. (JEL C78, D82, L15)
Exit, Tweets, and Loyalty
Authors: Gans Joshua S. , Goldfarb Avi , Lederman Mara
Published: April 2021

Hirschman’s Exit, Voice, and Loyalty highlights the role of “voice” when individuals confront an unexpected deterioration in quality. Yet, voice has received little attention. To motivate our empirical analysis, we develop a simple model of voice as the equilibrium of a relational contract between customers and firms. We use data on 4 million tweets to or about US airlines to study the relationship between quality, voice, and market structure. Voice increases when quality deteriorates. This relationship is greater for airlines that operate a large share of flights in a market. Supplemental analyses support a relational contracting role for voice. (JEL D83, L15, L82, L93)
Coordinating Public Good Provision by Mediated Communication
Authors: Halonen-Akatwijuka Maija , Park In-Uck
Published: April 2021

We examine a setup where two agents allocate a fixed budget between public goods in two areas. The agents may be biased to one area, which is their private information. Without communication, the funds are allocated inefficiently, resulting in gaps and duplication in public good provision. Direct communication between the agents is ineffective and cannot resolve the coordination failure even when the potential biases are negligible. Coordination can be improved by a mediator who filters the information communicated by the agents. Our results can throw light on how to improve coordination of humanitarian aid by an appropriately designed information management system. (JEL D82, D83, H41, H84)
Data management challenges for artificial intelligence in plant and agricultural research
Authors: Williamson Hugh F. , Brettschneider Julia , Caccamo Mario , Davey Robert P. , Goble Carole , Kersey Paul J. , May Sean , Morris Richard J. , Ostler Richard , Pridmore Tony , Rawlings Chris , Studholme David , Tsaftaris Sotirios A. , Leonelli Sabina
Published: April 2021

Artificial Intelligence (AI) is increasingly used within plant science, yet it is far from being routinely and effectively implemented in this domain. Particularly relevant to the development of novel food and agricultural technologies is the development of validated, meaningful and usable ways to integrate, compare and visualise large, multi-dimensional datasets from different sources and scientific approaches. After a brief summary of the reasons for the interest in data science and AI within plant science, the paper identifies and discusses eight key challenges in data management that must be addressed to further unlock the potential of AI in crop and agronomic research, and particularly the application of Machine Learning (AI) which holds much promise for this domain.