bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ciliary granule plaques: Membrane-intercalated particle aggregates associated with Ca2+-binding sites in Paramecium
Authors: Plattner H. 
Published: April 2021

ABSTRACT
In Paramecium nine rectangular aggregates of membrane-intercalated particles surround the freeze-cleaved membrane of the ciliary base. These ‘ciliary granule plaques’ occur independently of the ‘ciliary necklace’ which is observed in a more basal position on some cilia. In each individual plaque the ∼ 10 nm large granules are arranged in a square grid pattern: the granules of one plaque invariably form 3 vertical rows (number of horizontally arranged particles per row: Nh = 3) and 3–6 horizontal rows (mean value for Nv = 4 ·8); the centre-to-centre spacing of granules is dh = 22 nm in the horizontal and dv = 24 in the vertical direction. The ciliary granule plaques coincide with electron-dense deposits which can be produced in a position adjacent to the inner side of the basal ciliary shaft membrane by 3 procedures: (a) when cells are fixed in glutaraldehyde after incubation with Ca2+ concentrations (up to 25 mM) which are higher than normally present in the medium (about 0·5 HIM) but which do not immobilize the animals prior to fixation in glutaraldehyde; (b) when Ca2+ (up to 75 mM) was added to glutaraldehyde; (c) when cells were incubated with Ca2+’ as in (a) and then fixed in OsO4 solutions to which oxalate ions were added in concentrations equivalent to Ca2+. Comparable deposits were observed also with Ca2+ concentrations normally present in the medium, but they occurred much more rarely. The occurrence of electron-dense deposits was not enhanced by addition of Na+, Mg2+ or La3+ instead of Ca2+. In cross-sectioned ciliary bases the electron-dense Ca2+-dependent deposits face the 9 doublet microtubules. Occasionally the substructure of Ca2+-dependent deposits is resolved in median sections; their periodicity in the vertical direction (dv = 25nm; Nv = 5 ·2) corresponds to the periodicity of membrane-intercalated particles of freeze-cleaved plaques. Other parameters determined for Ca2+-dependent electron-dense deposits coincide also with those determined for freeze-cleaved ciliary granule plaques (values in parentheses are for cells with Ca2+ added before fixation with glutaraldehyde and ultrathin sectioning): The height of plaques (or deposits) is 84(115) nm; the distance from their lower end to the ciliary base is 138 (121) nm. Plaques (or deposits) are 45 (44) nm broad and the distance separating adjacent plaques (deposits) is 48 (50) nm. Plaques (deposits) are arranged with a horizontal periodicity of mean 93–102 (92) nm. It is concluded that the ciliary granule plaques are identical to or associated with Ca2+-binding sites involved in ciliary activity or other functions.
The effects of ionic lanthanum and hypertonic physiological salines on the nervous systems of larval and adult stick insects
Authors: Leslie R. A. 
Published: April 2021

ABSTRACT
The effects of the electron-opaque tracer ionic lanthanum in various concentrations and of hyperosmotic physiological salines on the nervous system of the stick insect, Carausius morosus, have been studied.
Examination of the experimentally treated tissues revealed that the diffusion barrier to the exogenous tracer was maintained in all cases in the adult central and peripheral nervous systems, but not in the hatchling. When hatchling nervous tissues were incubated in 50 mM ionic lanthanum in hyperosmotic physiological saline, the tracer readily infiltrated all the extracellular spaces between axons and glia of all components of the nervous system examined. No difference was noted in this regard between fed and unfed hatchlings. Further, in all cases examined of adults and hatchlings, lanthanum readily surrounded those neurosecretory axons which are found in the neural lamella, or extracellular nerve sheath, of the insect.
The possible meanings of these variations in hatchling and adult nervous systems and in the accessibility of different elements of the nervous system to exogenous ionic lanthanum are discussed.
Fine structure of an organelle associated with the nucleus and cytoplasmic microtubules in the cellular slime mould Polysphondylium violaceum
Authors: Roos U. P. 
Published: April 2021

ABSTRACT
Polysphondylium violaceum was grown in association with Escherichia coli. Vegetative amoebae and pseudoplasmodia were fixed under different conditions and processed for electron microscopy.
An electron-opaque body (nucleus-associated body, NAB) lies in the cytoplasm near the tapered end of interphase nuclei. The NAB consists of a disk-shaped, multilayered core, approximately 200 nm in diameter and 150 nm thick, embedded in a granular matrix from which electron-opaque nodules protrude. The nodules are termination points of microtubules radiating from the NAB into the cytoplasm or running along the nucleus. On the average there are 16 nodules per NAB. One or two microtubules terminate in each nodule. Spindle pole bodies, arising by duplication of the NAB at the beginning of mitosis, are unstructured foci for spindle microtubules in mitotic cells.
It is suggested that cytoplasmic microtubules do not determine cell shape, but they probably cause the tapering deformation of the nucleus. They may, furthermore, represent a storage form of subunits for utilization during the formation of the mitotic spindle. The nodules of the NAB are potential nucleation sites of cytoplasmic microtubules during interphase. Spindle pole bodies presumably acquire a microtubule-organizing capability by integration of the decondensed nodules.
Observations with cytochemistry and ultracryotomy on the fine structure of the expanding walls in actively elongating plant cells
Authors: Roland J. C. , Vian Brigitte , Reis Daniéle 
Published: April 2021

ABSTRACT
Ultracryotomy with negative staining and cytochemistry (periodic acid – thiocarbohydrazide - silver proteinate test for polysaccharides, in conjunction with mild extractions) were used to study the architecture of the cell wall and its modifications during expansion. Those techniques were applied to the study in situ of the walls of actively elongating parenchyma of mung bean (Phaseolus aureus), and pea (Pisum sativum) root and of collenchyma of celery (Apium graveolens) petioles.
These complementary techniques provide information on the 3-dimensional disposition and fine structure of the subunits of the wall. In all the examples examined, the bulk of growing primary wall appears well-ordered and no progressive evolution from a transverse texture near the plasmalemma to a scattered texture near the middle lamella was observed.
It seems unlikely that the development of the wall structure in relation to growth could be explained mechanically by a passive shift of the fibrillar elements in response to cellular stress. There is no evidence for an inert change in fibrillar orientation in the major part of the wall. If such occurs, the process is limited to the outermost and senescent part of the wall. Thus, the texture observed does not agree with the classical multinet growth hypothesis but rather with the idea of an ordered structure of the primary wall. With the latter, the components should be able to respond in different ways to specific growth regulators and other environmental signals and thus exert a more positive control over the processes of oriented cell growth.
The formation of annulated lamellae induced by the disintegration of microtubules
Authors: De Brabander M. , Borgers M. 
Published: April 2021

ABSTRACT
Investigations with different ‘antitubulins’ have shown that different cell types in culture respond to prolonged treatment with the formation of annulated lamellae. These annulated lamellae are possibly derived from previously accumulated smooth endoplasmic profiles. A hypothetical explanation would be that annulated lamellae (and the nuclear membrane) are sites of tubulin synthesis or microtubular polymerization. Their appearance after induced microtubule disintegration could then be viewed upon as a reactive hyperproduction of such sites.
Calcium distribution in islets of langerhans: A study of calcium concentrations and of calcium accumulation in b cell organelles
Authors: Howell S. L. , Montague W. , Tyhurst Margaret 
Published: April 2021

ABSTRACT
Calcium concentrations of various pancreatic B cell organelles have been determined by X-ray microanalysis of areas of frozen sections of unfixed rat islets of Langerhans. Highest concentrations were detected in storage granules and in mitochondria, although calcium was also present in nuclei, in areas of endoplasmic reticulum and of cytoplasm.
Accumulation of 45Ca by isolated organelles has been studied in homogenates and isolated subcellular fractions of rat islets of Langerhans. In the presence of a permeant anion (oxalate or phosphate), accumulation of 45Ca into mitochondria and microsomes was strongly stimulated by ATP. This net uptake was diminished during incubation of homogenates or of a mito-chondria-plus storage granule-rich fraction in the presence of cyclic AMP, dibutyryl cyclic GMP, z:4-dinitrophenol or of ruthenium red. Investigations of the characteristics of 45Ca accumulation by homogenates prepared from storage granule-depleted islets showed no differences from those of normal islets, suggesting that the granules do not represent an important labile pool of calcium. With the exception of cyclic AMP and cyclic GMP none of the insulin secretagogues tested (glucose, leucine, arginine, adrenalin, noradrenalin, theophylline, glibenclamide) altered calcium accumulation by islet homogenates.
On the basis of absolute calcium levels and of 46Ca uptake studies it is concluded that islet B cells contain a readily exchangeable mitochondrial calcium pool, and an endoplasmic reticulum pool containing a lower concentration of calcium which is also readily exchangeable. The storage granules, despite their high calcium content, do not appear to constitute a labile pool. It seems likely that the labile mitochondria and endoplasmic reticulum pools play a predominant role in the regulation of cytoplasmic free calcium levels, which may in turn be important in the regulation of rates of insulin secretion.
Distribution of lipid in the lamellate endocuticle of Rhodnius prolixus (hemiptera)
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
The lamellate appearance of the cuticle in the abdomen of the Rhodnius larva conforms to the conception of Bouligand in being an optical artifact which results from the spiral arrangement of successive layers of oriented fibrils. But superimposed on this structure is an actual lamination of bound lipid with the same spacing. The relation of the lipid layers to the optical lamination changes with the aspect from which the system is viewed.
There must therefore be a cyclical secretion of lipid by the epidermal cells. Since the period of this cycle agrees with the cycle of rotation of the fibrous layers, which is supposedly inherent in the chemistry of the system, it is possible that it is the lipid which controls or initiates this helicoidal ‘cholesteric crystallization’.
There is evidence of a cyclical change in the secretion of lipid by the microvilli; it is suggested that there may be alternating cycles of eccrine and apocrine secretion, and that the lipid laminae represent the apocrine phases.
The pore canals in Rhodnius are roughly cylindrical in cross-section, with lipid-impregnated walls. The contents of the lumen become slightly more electron opaque before the cuticle is stretched by feeding. There is probably some enzymic dissolution of the cuticle which precedes stretching; and this may concern particularly the lipid fraction. After the great distension and expansion of the cuticle which occur at feeding, lipid laminae can no longer be demonstrated in the old cuticle.
The erythroid cells of anaemic Xenopus laevis. I. studies on cellular morphology and protein and nucleic acid synthesis during differentiation
Authors: Thomas Nesta , Maclean N. 
Published: April 2021

ABSTRACT
Phenylhydrazine has been used to induce anaemia in Xenopus laevis. The dosage used causes the complete destruction of all mature erythrocytes within twelve days. The anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. The morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. The origin of the circulating erythroid cells is also discussed.
Effect of tritiated thymidine on cell proliferation
Authors: Blenkinsopp W. K. 
Published: April 2021

Abstract
The effect of tritiated thymidine on the rate of entry of cells into mitosis was studied in mice; 1·5 μc of tritiated thymidine (specific activity 5 c/mM) per g body weight did not alter the rate of entry. Other workers have reported an increased number of mitoses following administration of larger amounts of thymidine than those used in the present work ; the suggestion is therefore made that when tritiated thymidine is given to animals for studies on cell proliferation the dose of thymidine in a single injection should be not greater than 0·1μg/g body weight.
An electron-microscope study of the in vitro transformation of human leucocytes: I transformation of lymphocytes to blastoid cells in the presence of phytohaemagglutinin
Authors: Chapman J. A. , Elves M. W. , Gough J. 
Published: April 2021

Abstract
Electron-microscope studies of cultured small lymphocytes from human peripheral blood transforming into larger blastoid cells in the presence of phytohaemagglutinin (PHA) show that the transformed cell possesses the preliminary stages of development of a protein-synthesizing system. The transformed blastoid cell has abundant ribosomes, although, in contrast with in vivo protein-secreting cells, many of these occur as single particles with only a small proportion linked in polysomal clusters. Endoplasmic reticulum membranes occur to a very limited extent and with a marked paucity of attached ribosomal particles; the few attached particles are usually located in groups. Some endoplasmic reticulum membranes revealed degenerative changes in otherwise normal cells. A moderately well-developed Golgi apparatus was a characteristic feature of the cells. Apart from the relatively low proportion of polysomes, in vitro PHA-transformed blastoid cells are identical in fine structure to in vivo blast cells (otherwise known as immunoblasts, haemocytoblasts, etc.) occurring in the immune response. It is suggested that messenger-RNA production in PHA-stimulated transformed cells may be reduced and that this could explain the limited number of polysomes and the restricted development of the endoplasmic reticulum.
Seasonal changes in the fine structure of the basal granular cells of the bat thyroid
Authors: Nunez E. A. , Gould R. P. , Hamilton D. W. , Hayward J. S. , Holt S. J. 
Published: April 2021

Abstract
The fine structure of the thyroid gland of non-hibernating, hibernating, and intermittently aroused hibernating bats was examined. It was found that in addition to the ordinary, follicular cell, another widespread thyroid cell type is present in all bats examined. This cell is situated in the basal region of the thyroid follicle and is characterized by a cytoplasm full of secretory-like granules. In the basal cells of bats captured in April and June the granules consist of an extremely dense core and are of a uniform size averaging from 0·1–0·5 μ diameter. In bats caught in August the solid dense granules vary greatly in size and large granules of diameters from 2 to 5 μ are common. These large granules are often found concentrated in groups in the most basal region of the follicular epithelium. Hibernating bats are characterized by partly or totally degranulated basal thyroid cells. The cytoplasmic granules in the partly degranulated cell vary greatly in appearance, ranging from solid dense granules to empty vesicles. In totally degranulated basal cells, empty vesicles fill the cytoplasmic matrix. The granular endoplasmic reticulum of the basal thyroid cell also shows seasonal changes, while the Golgi complex remains a well-developed organelle throughout the year. These observations suggest that the thyroid basal granular cell is involved in secretory activities; its possible functional role is discussed.
Plasmodesmata in Nitella translucens: Structure and electrical resistance
Authors: Spanswick R. M. , Costerton J. W. F. 
Published: April 2021

Abstract
Electrical resistance measurements, made with intracellular microelectrodes on a system consisting of two giant intemodal cells of Nitella translucens joined by a node, show that the specific resistance of the node is 50 times smaller than the specific resistance of the intemodal cell plasmalemma. The node is a complex structure of small cells which separate the intemodal cells by a single layer at the nearest point of approach. Information on the size and distribution of the plasmodesmata in the node, obtained from electron micrographs, suggests that the specific resistance of the node should be smaller than the observed value by a factor of 330. It must therefore be assumed that there is some restriction on the diffusion of ions in the plasmodesmata.
The electrical coupling between some internodal cells is sufficient for an action potential in one cell to initiate an action potential in the neighbouring cell.
Proliferation and agglutinability of primary and transformed human epithelial cells in culture
Authors: Ricard Mary Ann , Hay R. J. 
Published: April 2021

ABSTRACT
Primary epithelial populations (HAM) were obtained by dissociation of the amniotic membrane stripped from human placentae. Agglutinability of cells from such normal populations and of cells from the transformed epithelial line WISH was then compared using concanavalin A as mediator. Extensive similar studies have previously been reported with cell strains isolated from other species. Freshly dissociated HAM cells from primary cultures agglutinated much less readily than did cells from WISH populations. Furthermore, the former exhibited a drastic decline in agglutinability as a function of time in suspension culture after trypsinization. Short-term exposure (60 h) of HAM cells in monolayer culture to 5-bromodeoxyuridine (BrdU) elicited heightened agglutinability detectable through 22 days in vitro.
Addition of the protease inhibitors n-tosyl-L-lysyl-chloromethyl ketone (TLCK) or p-tosyl-L-arginine-methyl ester (TAME) to the culture medium inhibited proliferation of the WISH line by 40–50% while effecting only a 10–15% inhibition of HAM cells. These results also confirm data with other cell species indicating that high proteolytic activity at the surface of transformed cells may be related to the rapid proliferation rate.
Effect of glutaraldehyde fixation on lectin-mediated agglutination of mouse leukaemia cells
Authors: Blitterswijk W. J. Van , Walborg E. F. , Feltkamp Constance A. , Hilkmann H. A. M. , Emmelot P. 
Published: April 2021

ABSTRACT
The effect of glutaraldehyde fixation on lectin-mediated agglutination of murine leukaemia (GRSL) cells was investigated using 2 assay methods which differed in the shear forces to which the agglutinated cells were subjected. First, lectin and cells were allowed to interact under conditions in which shear forces were minimized and the degree of agglutination was evaluated microscopically by the appearance and size of the cell aggregates. This assay demonstrated that concanavalin A (con A)-, wheat germ agglutinin (WGA)- or Ricinus communis agglutinin I (RCAI)-mediated cytoagglutination was unaffected (WGA and RCA1) or somewhat enhanced (con A) by prior fixation of the cells with glutaraldehyde. Secondly, an electronic particle counter was used to measure the disappearance of single cells and concomitant appearance of cell aggregates as a function of the lectin concentration. In this assay, in which the aggregated cells are subjected to significant shear forces during dilution and cell counting, agglutination of GRSL cells by each of the 3 lectins was drastically inhibited by prior fixation of the cells with glutaraldehyde. This assay also demonstrated enhanced nonlectin-induced cell aggregation after fixation. In both cytoagglutination assays about the same lectin concentration was required for threshold agglutination of unfixed cells. Comparatively, the results of the 2 cytoagglutination assays indicate that a fraction of the lectin-mediated bonds between unfixed cells is shear resistant and that fixation of the cells either weakens these bonds or inhibits their formation.
Morphologically, cells prefixed with glutaraldehyde were spherical at all lectin concentrations, with a continuous dense distribution of cell surface-bound con A, labelled directly with haemocyanin or indirectly using the peroxidase-diaminobenzidine reaction. Unfixed cells showed angular and toadstool-shaped deformations, especially at the highest lectin con- centrations, the agglutinating surfaces being flattened against each other over extended areas. The distribution of con A label was continuous and dense between the apposed surfaces and discontinuous on free surfaces. In the presence of con A the free surfaces of prefixed cells exhibited more microvilli than the surfaces of non-prefixed cells. These results favour the view that fixation prevents the formation of shear-resistant, lectin-mediated bonds between cells, not by restricting the lateral mobility of lectin receptors, but by impairing the apposition of rigid cell surfaces.
Timing of nucleolar DNA replication in Amoeba proteus
Authors: Minassian I. , Bell L. G. E. 
Published: April 2021

ABSTRACT
Light- and electron-microscope autoradiography have been used to follow the incorporation of [3H]thymidine at different stages during the interphase of synchronously growing populations of Amoeta proteus. Two main patterns were found for tritiated thymidine incorporation, i.e, DNA synthesis. The major incorporation was in the central region of the nucleus, but a lesser degree of incorporation occurred in the nucleolar region. The bulk of this nucleolar DNA was found to be late replicating, i.e. it replicated during the G2 phase.
A decay of gap junctions in association with cell differentiation of neural retina in chick embryonic development
Authors: Fujisawa H. , Morioka H. , Watanabe K. , Nakamura H. 
Published: April 2021

ABSTRACT
Ultrastructural studies of thin-sectioned and freeze-cleaved materials were performed on developing retinal tissues of 3- to 9-day-0ld chick embryos to clarify the junctional structures between neural retinal cells and between neural retinal cells and cells of the pigmented epithelium.
Frequency, size and position of gap junctions in developing neural retina are different at each stage of development. In 3-day-0ld embryos, some cells adhere to each other by gap junctions immediately below the outer limiting membrane of neural retinae. The size and number of gap junctions increase remarkably during 5–6 days of incubation. In this period of development, well developed gap junctions consisting of subcompartments of intramembrane particles are found between cell surfaces at both the outer limiting membrane region and the deeper portion of the neural retina. Gap junctions disappear thereafter, and at 7·5 days of incubation, small gap junctions are predominant between cell surfaces at the outer limiting membrane region, while the frequency of gap junctions in the deeper portion is very low. At 9 days of incubation, gap junctions are rarely found.
Typical gap junctions are always found between neural retinal cells andthoseof the pigmented epithelium in embryos up to 7·5 days of incubation.
Tight junctions are not found in the neural retina or between neural retina and pigmented epithelium throughout the stages examined.