bluuebunny/crossref_metadata_2025_split huggingface dataset:
A special pattern of the smooth endoplasmic reticulum in the kidney of the snail Cryptomphalus Aspersa
Authors: Paniagua R. , Vázquez J. J. 
Published: April 2021

ABSTRACT
A special structural pattern of the smooth endoplasmic reticulum (SER) has been observed in the kidney of the snail Cryptomphalus aspersa. Two types of cells (clear and dark) cover the foldings of the renal sac; the dark cells are by far the most numerous. A cisterna of SER enveloping the nucleus appears invariably in both types of cells, with no disruptions, or small ones (from 50 to 90 nm) along its profile. The layer of cytoplasm lodged between the external nuclear membrane and this cisterna is found invariably to be from 0.20 to 0.25 μm in width. Glycogen is abundant in the cytoplasm as alpha particles, and also in the nucleus, but as beta particles. It is noteworthy that absolutely no glycogen is present in the layer of cytoplasm lodged between the nuclear membrane and the surrounding SER envelope. Long profiles of SER are also observed closely approaching and parallel to the plasma membrane of the dark cells. Considering the role of SER in glycogen metabolism in the kidney of the snail, the possible function of these cisternae as a support system for enzymes involved in the metabolism of glucides is discussed.
Inversion heterozygosity in females of the newt No tophthalmus viridescens and its influence on chiasma distribution
Authors: Hartley Sheila E. , Callan H. G. 
Published: April 2021

ABSTRACT
In a wild population of the American newt Notophthalmus viridescens 15 females out of a total of 94 were found to be heterozygous for a paracentric inversion which includes almost the whole of the longer arm of the smallest chromosome (XI). The inversion was recognized in preparations of lampbrush chromosomes because it transfers the sequential loops, which normally lie close to the telomere, to a position neighbouring the centromere. Because of inversion the transcriptional polarity of the sequential loops is reversed vis-à-vis the chromosome as a whole.
In normal bivalents XI (both in male and female meiosis) each arm pair generally forms a single chiasma close to the telomeres (proterminal localization). In bivalents XI heterozygous for the inversion no chiasmata are formed between the mutually inverted longer arm pairs, presumably because they fail to synapse, but chiasma frequency in the non-inverted shorter arm pairs is increased, and the normal restraint on chiasma distribution in this arm pair is lifted. An explanation is offered in terms of the availability of recombination nodules, and the time of their association with the synaptonemal complex.
Fine-structural studies of the gametes and embryo of Fucus vesiculosus L. (Phaeophyta): III. cytokinesis and the multicellular embryo
Authors: Brawley Susan H. , Quatrano Ralph S. , Wetherbee Richard 
Published: April 2021

ABSTRACT
Condensation of the chromosomes during the first cell division following fertilization of the brown alga Fucus vesiculosas L. is accompanied by the almost complete disappearance of the nuclear envelope. Golgi vesicles and other small vesicles appear within the spindle, which has paired centrioles at each end. A large amount of rough endoplasmic reticulum is in the sur- rounding cytoplasm during mitosis, and many vesicles at the spindle margin are encircled by stacks of endoplasmic reticulum. Annulate lamellae are observed during mitosis. The envelope which initially reforms around the chromatin in telophase has unevenly spaced nuclear pores. Cytokinesis results primarily by vesicle addition to a centripetal furrow. Mitochondria and chloroplasts concentrate around the partition site, possibly in association with microfilaments. Fibrillar material is added rapidly to the space between the daughter cells from vesicle discharge of both cells and seems to spread into the older cell wall surrounding the embryo. The rhizoid daughter cell contains numerous mitochondria and hypertrophied Golgi bodies whose vesicles increasingly pack the cell. The thallus daughter cell is packed with a variety of vesicles, and the nucleus is surrounded by many dilated cistemae of rough endoplasmic reticulum. By the four-cell stage, chloroplasts of the rhizoid cells have weakly staining lamellae, while chloro- plasts of the thallus cells are actively dividing with deeply staining lamellae.
A study of the arrangement of osteoblasts of rat calvarium cultured in medium with, or without, added parathyroid extract
Authors: Jones Sheila J. , Ness Alan R. 
Published: April 2021

ABSTRACT
The osteoblast layers on the inner surfaces of the half-calvaria of neonatal rats of 2 litters were studied by scanning electron microscopy. Some halves were fixed immediately on dissection. Others were carried through incubation in an Eagle’s medium, with or without the addition of parathyroid extract (PTE): for 2, 4, 8 or, most importantly, 24 b. In their initial state, presumed as like the 0-h material, the osteoblasts presented as a dense tesselation. After 24 h of culture in the medium, osteoblasts were more sparse in the fields examined and although, in a set of 4 preparations, they retained significant alignment, their orientation had become more random. In addition, they were broader and larger in area. By contrast, with PTE added to the medium, osteoblasts almost maintained their number per field, did maintain their cell area, but became longer and narrower and strikingly parallel in their array. The aligning effect of the PTE preceded, and thus was independent of, its elongating effect.
Visualization of interphase chromosomes
Authors: Stack Stephen M. , Brown David B. , Dewey William C. 
Published: April 2021

ABSTRACT
Using a modified Giemsa-banding technique we have observed what appear to be chromosomes during interphase in nuclei from Allium cepa root tips and Chinese hamster cells (CHO line). During telophase through G1 chromosomes progressively uncoil and decondense. During 5 chromosomes are comparatively decondensed, but some segments have structure similar to chromosomes in G1 and G2. During G2 the chromosomes progressively recondense and coil in apparent preparation for prophase. Although specific structural modifications of chromosomes occur in G1,S, and G2 nuclei, chromosomes appear never to decondense to the point that they lose their 3-dimensional integrity, but remain in distinct domains throughout interphase.
The mechanism of concanavalin a cap formation in leukocytes
Authors: Albertini D. F. , Berlin R. D. , Oliver J. M. 
Published: April 2021

ABSTRACT
The process of Concanavalin A (Con A) cap formation on human blood polymorphonuclear leukocytes, monocytes and lymphocytes and rabbit alveolar macrophages has been studied by correlative use of light, fluorescence and electron microscopy. The most important precondition for Con A capping on these cells is the disassembly of cytoplasmic microtubules by colchicine or the glutathione-oxidizing agent, ‘diamide’. Incubation of microtubule-depleted leukocytes with fluorescein-conjugated Con A (F-Con A) leads to the aggregation of lectin into a cap which usually occupies a protuberance at one pole of the cell. F-Con A can also be concentrated at a constriction in the cell body. The protuberance is shown to consist of highly plicated membrane subtended by a network of densely packed microfilaments. Additional microfilaments originate from this network and course into individual plications of the protuberance. However, the formation of the protuberance with its organized structure follows the disassembly of microtubules alone and does not require Con A. Thus when cells are treated with colchicine or diamide, then fixed and labelled with F-Con A the typical changes in cell shape that are associated with capping are observed but lectin is distributed homogeneously over the cell surface. Similarly if cells are first capped with low concentrations of unlabelled lectin, then fixed and incubated with F-Con A, fluorescence is again uniformly distributed over the whole membrane. This indicates that membrane Con A receptors have not been concentrated over the protuberance despite the prior aggregation of microfilaments. By contrast, when precapped cells are labelled with F-Con A before fixation, fluorescence is concentrated through the previously established cap. Thus extensive organization of microfilaments and unlabelled lectin does not inhibit the movement of F-Con A-receptor complexes on unfixed cells. Further, the Con A cap is sufficiently fluid to permit mixing of sequentially formed Con A-receptor complexes. Although the aggregation of microfilaments into a protuberance and the concentration of Con A into the membrane of the protuberance are clearly separable events, microfilaments and Con A-receptor complexes are ultimately found in close association in the cap. This association appears to stabilize the localization of both the surface-bound lectin and the submembranous network of microfilaments. Such stabilization could result from physical interactions between microfilaments and Con A within the protuberance. However, we favour an alternative mechanism in which a region of low membrane fluidity that limits further diffusion is established following microtubule disassembly and is preserved by microfilament-membrane interactions.
Development and regulation of the phosphorylase-glycogen complex in myogenic cells of the L7 line
Authors: Wahrmann J. P. , Recouvreur M. , Favard-Séréno C. 
Published: April 2021

ABSTRACT
The development of the phosphorylase-glycogen complex was studied in cells of the myogenic line L6 at different stages of differentiation. Our results indicate that the complex is already present in mononucleated myoblasts. However, several features of the complex observed in the myoblasts, such as the total amount of phosphorylase bound to the polysaccharide, and the type of glycogen agglomerates present in the cells, differ from those of the myotubes. It is postulated that at the moment when the myoblasts differentiate, definitive metabolic events take place. At this time the protein-glycogen complex is completed, phosphorylase being bound to small glycogen particles, and the multinucleated myotubes begin to accumulate a reserve of free glycogen. This latter constituent is mobilized first upon glucose starvation.
Lectin-mediated agglutination of amphibian embryonic cells
Authors: Fraser Brock R. , Zalik Sara E. 
Published: April 2021

ABSTRACT
Dissociated blastula cells of Xenopus laevis are agglutinated with wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA), Concanavalin A (Con A) and, to a lesser extent with soya bean agglutinin (SBA). They are not agglutinated with fucose-binding protein. Neuraminidase treatment of cells enhances their agglutinability with RCA and SBA, but has no effect on Con A- and WGA-mediated agglutinability. Treatment of cells with procaine, or xylocaine, has no effect on the cells’ agglutinability or on the extrusion of lobopodia. Treatment with colchicine or cytochalasin B either separately or simultaneously has no effect on lectin-mediated agglutinability. Cells treated with cytochalasin B or colchicine and cytochalasin B simultaneously lack lobopodial extensions, while colchicine alone has no effect on these structures. Phenothiazine tranquillizers inhibit agglutination mediated by all of the above mentioned lectins. Lobopodial extensions are absent in cells treated with these compounds. Glutaraldehyde fixation inhibits RCA and WGA mediated agglutinability and reduces the Con A-mediated agglutinability. Results suggest that in this system microtubules and micrcfilaments are not involved in lectin-mediated agglutination.
Effects of experimental alterations in phospholipid composition on the size and number of mitochondria in the flight muscles of the housefly, Musca domestica
Authors: Sohal R. S. , Bridges R. G. 
Published: April 2021

ABSTRACT
The objective of this study was to investigate the effects of experimentally altered phospholipid composition on the size and number of mitochondria in the flight muscles of houseflies of different ages. The phospholipid composition was altered by a decrease in choline content, substitution of choline by an analogue, and by the addition of 2-aminobutan-I-0l to the casein-based larval diet. Analysis of the phospholipids extracted from the thoraces and ‘giant’ mitochondria of adult flies confirmed the presence of altered phospholipids. The number, size, and total volume of the mitochondria were measured in electron micrographs of crosssections of the dorsal longitudinal flight muscle in 1-day, 8-day and 17-day-old flies. In the control flies, the mean mitochondrial size increased while the number decreased during 1 to 8 days of age due to mitochondrial fusion. During 8–17 days of age there was a modest increase in mitochondrial number and a decrease in their average size due to mitochondrial fission. In flies with low choline concentration, the mitochondrial fusion was speeded up and fission was delayed; in the flies with a choline analogue, fusion was speeded up, but fission was normal and in those fed on 2-aminobutan-I-0l, both fusion and fission were delayed. In the 8-day and 17-day-old flies the total volume of mitochondria in the sarcoplasm was approximately the same in all groups. Mitochondria in all experimental groups reached the maximal size achieved in the control flies although at different ages. It is concluded that alterations in phospholipid composition of the thorax affect the rate of mitochondrial fusion and fission; however, the maximal size achieved by the mitochondria is independent of the phospholipid content.
Cytoplasmic inclusions in Xenopus spermatogenic cells. ultrastructural and cytochemical analysis of the action of antimitotic agents on subcellular elements
Authors: Kalt Marvin R. 
Published: April 2021

ABSTRACT
The effects of vinblastine sulphate, alone and in combination with other antimitotic agents, were tested in vitro on testicular tissue from the anuran, Xenopus laevis. Treatment with vinblastine alone resulted in dissolution of spindle and intercellular bridge microtubules, but centrioles and sperm tail axonemes remained intact. In addition, no paracrystalloid inclusions typical of those reported in other cell types treated with vinblastine alone were observed in Xenopus spermatogenic cells. Such inclusions were formed, however, when vinblastine was administered in combination with colchicine, colcemid, or puromycin. Under optimal conditions, paracrystalloids were formed in all cells from primary spermatogonia to late spermatids. The maximum size paracrystalloid formed differed in different spermatogenic cell stages, with late primary spermatocytes containing the largest such inclusions, often averaging over 34 μ m3 each. Autoradiographic analysis of spermatogenic cells labelled with [3H]leucine prior to drug treatment indicated that some radioactive material was incorporated into paracrystalloids in all cell stages. Treatment of Xenopus spermatogenic cells with vinblastine and puromycin was also employed to investigate the possible relationship between paracrystalloid material and a naturally occurring spermatogenic cell inclusion, the chromatoid body, since previous experiments indicated that microtubule protein might contribute to the mass of this structure. It was found that under certain conditions, both paracrystalloids and giant chromatoid bodies can occur together in the same cell, each inclusion reaching a characteristic size independent of the other. This suggests that the two inclusions are aggregates of materials drawn from different subcellular precursor pools.
In addition, autoradiographic analysis of isotope incorporation indicated that giant chromatoid bodies could be clearly labelled with tritiated amino acids, but not with [3H]uridine. The pattern of isotope incorporation observed in giant chromatoid bodies, coupled with their histochemical staining characteristics, rules out the possibility that these structures function as cytoplasmic nucleoli.
Studies of membrane fusion II. fusion of human erythrocytes by sendai virus
Authors: Knutton S. 
Published: April 2021

ABSTRACT
Thin section, negative stain and freeze-fracture electron microscopy have been used to study the fusion of human erythrocytes by Sendai virus. Sendai virus particles are shown to consist of an envelope covered with ∼ 12 nm-long projections or spikes which encloses a helical nucleocapsid. The spike complexes are dumbell-shaped and consist of 2 knobs, one ∼ 8 nm, the other ∼14 nm, in diameter connected by a narrow ∼ 3 nm-thick stalk, with the larger knob embedded in the lipid bilayer of the viral envelope. Virus particles bind to and agglutinate cells at 4 °C; fusion of viral envelopes with the erythrocyte membrane and extensive cell-cell fusion takes place following a brief incubation at 37 °C. At 4 °C most virus particles are roughly spherical and fractures through the viral envelope reveal concave E fracture faces with ∼ 14-nm-diameter intramembrane particles and convex P faces with a complementary arrangement of pits. Incubation at 37 °C results in a dramatic change in the structure of the viral envelope of many virus particles. Invaginations of the viral envelope give the virus a convoluted profile and such virus particles are characterized in freeze-fracture replicas by the presence of smooth linear ridges 30 nm wide and up to 0. ·5 μm long on E faces and by a complementary arrangement of linear grooves on P faces. Instead of ∼ 14 nm-diameter intramembrane particles on E faces, ∼ 8 nm particles are present on both P and E faces. These changes, which only take place when virus particles are bound to erythrocytes, are also accompanied by the disappearance of clearly defined surface spikes. Only virus particles having this altered morphology actually fuse with the erythrocyte membrane. The characteristic ‘ridged’ morphology of the viral envelope allows specific sites of viral envelope-cell fusion to be identified in freezefracture replicas and successive stages during the incorporation of the viral envelope to be reconstructed. These observations show that viral envelope-cell fusion is initiated by a cell- mediated temperature-sensitive change in the molecular organization of the viral envelope which allows the particle—denuded linear invaginations, possibly lipid bilayer, to interact and fuse with the erythrocyte membrane. Further observations suggest that cell-cell fusion does not occur directly between cells but is achieved by the simultaneous fusion of a virus particle with 2 adjacent erythrocytes.
Immunocytochemical visualization of microtubules and tubulin at the light- and electron-microscopic level
Authors: Brabander M. De , Mey J. De , Joniau M. , Geuens S. 
Published: April 2021

ABSTRACT
An antibody against rat brain tubulin was purified by affinity chromatography and used for the immunocytochemical staining of tubulin-containing structures in tissue-cultured cells at the light- and electron-microscopic level. For this purpose the unlabelled antibody enzyme method (PAP method) was used. Tissue-cultured cells were fixed with glutaraldehyde or formaldehyde, postfixed with acetone and stained with the PAP procedure. With the light microscope, a dense network of darkly stained fibres was visible in non-dividing cells. The fibres converged towards a point in the nuclear vicinity and radiated throughout the cytoplasm towards the cell periphery. Mitotic spindles were also heavily stained in all stages. The cytoplasm of non-dividing and dividing cells contained a variable amount of diffuse staining. The nucleus was unstained. The network could be destroyed by treating the cells with microtubule inhibitors. An intense diffuse staining was visible in cells treated with colchicine or nocodazole.
The paracrystalline tubulin precipitates that appeared in cells treated with vinblastine were heavily stained.
Preliminary ultrastructural observations were made on sections through cells that were fixed with glutaraldehyde, stained with the PAP procedure and embedded in Epon. The microtubules were seen to be covered with stained PAP complexes. The cortical microfilaments, the 10–nm filaments and the plasma membrane were unstained, as were the contents of nuclei, mitochondria, endoplasmic reticulum, Golgi elements, lysosomes and vacuoles. A variable amount of diffuse staining was visible in the cytoplasm and the membranes of several organelles often showed PAP deposits. This staining was presumed to localize tubulin in non-microtubular form. It is probable that at least part of this staining was immunologically specific, since no PAP complexes were seen in the cells when the antitubulin antibody was omitted from the procedure or when it was replaced by an unrelated antibody solution.
Changes induced by ultraviolet light in the superhelical dna of lymphocytes from subjects with xeroderma pigmentosum and normal controls
Authors: Cook P. R. , Brazell I. A. , Pawsey S. A. , Giannelli F. 
Published: April 2021

ABSTRACT
Patients with the light-sensitive disease xeroderma pigmentosum (XP) are genetically heterogeneous. Most patients are defective in the excision repair of u.v.-induced DNA damage while some, the XP-variants, seem proficient in excision repair but replicate u.v.-damaged DNA with difficulty. The former have so far been assigned to 5 complementation groups (A-E) of which B and E are extremely rare.
Information on the nature of the defect in XP is contradictory. Studies based on the sedimentation of DNA in alkaline gradients suggest that patients of complementation group A can perform the first step of excision repair (‘incision’) while others, based on the elution by alkali of the DNA of cells lysed on filters, suggest that they cannot. We have therefore investigated the repair of DNA damaged by u.v. irradiation using a method based on a precisely defined theoretical approach. A single break in one of the strands of a double-stranded and supercoiled circle of DNA releases supercoiling and reduces its rate of sedimentation in sucrose gradients. Structures resembling nuclei (‘nucleoids’) containing superhelical DNA may be obtained from human lymphocytes and their rate of sedimentation is influenced by the integrity of their DNA.
Analysis of the sedimentation of nucleoids from normal and XP lymphocytes in sucrose gradients containing different concentrations of ethidium indicates that their DNA is similarly supercoiled. The lymphocytes of patients of complementation groups A, C and D repair damage induced by γ-rays just like controls. However, they cannot repair normally DNA damaged by u.v. irradiation; the cells are defective in the first step of excision repair.
The XP-variant and XP-heterozygous cells repaired u.v.- and γ-ray-induced damage like controls.
Some problems regarding the nature of the defect in XP are discussed.