bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACT
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

ABSTRACT
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 &lt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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 (&lt;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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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

ABSTRACT
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.