bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron microscopy of spermatocytes previously studied in life: methods and some observations on micromanipulated chromosomes
Authors: Nicklas R. Bruce , Brinkley B. R. , Pepper Daniel A. , Kubai Donna F. , Rickards G. K. 
Published: April 2021

ABSTRACT
A new method is offered for combined living cell and electron-microscopic studies of spermatocytes (or other cells) which normally do not adhere to glass. The key step is microinjection of glutaraldehyde near the target cell whenever desired during observation in life. Fixation begins and simultaneously the cell is stuck very firmly to the underlying coverslip. The method is easy and reliable: cells are almost never lost and are well preserved, except for membranes. The application of the method is illustrated by studies of micromanipulated grasshopper spermatocytes. A chromosome was detached from the spindle and placed in the cytoplasm. Before or after the beginning of chromosome movement back toward the spindle, the cell was fixed, sectioned and the manipulated chromosome observed in the electron microscope. If the detached chromosome had not moved by the time of fixation, no or only one or two microtubules were seen at its kinetochore, but if movement had occurred, a few microtubules were always present. The arrangement of these microtubules corresponded to the direction of movement, but they commonly were at an unusual angle relative to the kinetochore. The origin and role in chromosome movement of the microtubules seen near moving chromosomes far from the spindle is not yet established, but a speculation is offered. A goal for future work is the detailed analysis of the microtubules associated with individual moving chromosomes. Such an analysis is feasible because the moving chromosome is far removed from the confusing mass of spindle microtubules, and its value is enhanced because the direction of movement at the time of fixation is known.
Dual capacity for nutrient uptake in Tetrahymena: V. utilization of amino acids and proteins
Authors: Orias Eduardo , Rasmussen Leif 
Published: April 2021

ABSTRACT
We investigated the relative contributions of phagocytosis and plasma membrane transport to the uptake of amino acids and a protein (egg albumin) in amounts which allow Tetrahymena thermophila to grow and multiply. We used a mutant capable of indefinite growth without food vacuole formation (phagocytosis) and its wild type (phagocytosis-competent) isogenic parental strain.
Our results suggest that phagocytosis is not required for free amino acid uptake, most or all of which can be attributed to carrier-mediated transport systems, apparently located on the plasma membrane. In contrast, phagocytosis is required for utilization of the protein. Proteins can supply required amino acids in amounts sufficient for growth only when food vacuoles are formed. We conclude that Tetrahymena thermophila either possesses no endocytic mechanisms at the cell surface other than food vacuole formation or, if it does, these putative mechanisms are not capable of nutritionally meaningful rates of protein uptake.
Studies on the subcellular localization of human neutrophil alkaline phosphatase
Authors: Rustin G. J. S. , Wilson P. D. , Peters T. J. 
Published: April 2021

ABSTRACT
The intracellular localization of alkaline phosphatase has been determined in human neutrophils with analytical subcellular fractionation by density gradient centrifugation and EM cytochemistry.
Centrifugation on sucrose gradients containing 1 mM EDTA and 5 units/ml of heparin showed that alkaline phosphatase was associated with a membranous component distinct from plasma membrane, mitochondria, specific granules and azurophil granules. There was no resolution from the endoplasmic reticulum. Density gradient centrifugation on a sucrose— imidazole-heparin gradient showed a clear resolution of the alkaline phosphatase-containing membranes from the Golgi and endoplasmic reticulum. Density gradient centrifugation of neutrophils that had been disrupted in the presence of 0·12 mmol/1. digitonin clearly separated alkaline phosphatase-containing membranes from the endoplasmic reticulum. Part of the γ-glutamyl transferase has a similar localization to that of alkaline phosphatase.
EM cytochemistry of neutrophils, neutrophil homogenates and of the density gradient fractions identified alkaline phosphatase-containing granules as irregular-shaped, often tubular, structures. It is suggested that alkaline phosphatase and part of the γ-glutamyl transferase activity are localized to a unique organelle in the human neutrophil.
On the differential divisions and preprophase microtubule bands involved in the development of stomata of Vigna Sinensis
Authors: Galatis B. , Mitrakos K. 
Published: April 2021

ABSTRACT
The manifestation of premitotic cell polarity and the resultant structural asymmetry of the differential divisions participating in the development of stomata of Vigna sinensis vary considerably. However, two morphologically distinct types of differential division were distinguished : (a) ‘asymmetrical differential divisions ‘, in which the premitotic polarization of the cell, the eccentric position of the nucleus during division and the differences in size and organization of the daughter cells are obvious; and (b) differential divisions in which the above features are inconspicuous or almost absent. The former occur in the ordinary protodermal cells, the latter in some meristemoids.
The organization of a sharply demarcated preprophase microtubule band (PMB) precedes, all differential and non-differential divisions. In the first type of differential division the PMB is formed eccentrically, while in the second it may display either an approximately symmetrical or a clearly asymmetrical disposition, always indicating with surprising accuracy the sites where the succeeding cell plate will join the parent walls. The PMB foreshadowing the highly curved cell plates in meristemoids I of the mesoperigenous process, as well as in meristemoids I and II of the mesogenous one, are apposed only on one anticlinal wall and therefore do not encircle the nucleus or traverse the cell.
In the symmetrical divisions of guard cell mother cells (GMC), as well as in those of proto-dermal cells, the PMB runs right round the internal plasmalemma surface in an equatorial position, coinciding with that of the future cell plate. In the former cells the wall abutting the cortical cytoplasm traversed by the band becomes locally thickened. The variability in the pattern of the microtubules of the band along the walls of the GMC is directly mirrored in the pattern of the thickening. It seems that in GMC the PMB mediates a directed exocytosis of dictyosome vesicles.
In contrast to what is now generally accepted in dicotyledonous plants, each meristemoid I of both the mesogenous and mesoperigenous stomata in Vigna sinensis leaves does not inhibit but induces the formation of other meristemoids close to it.
Cell-to-substratum contacts in living cells: A direct correlation between interference-reflexion and indirect-immunofluorescence microscopy using antibodies against actin and A-actinin
Authors: wehland Jürgen , Osborn Mary , weber Klaus 
Published: April 2021

ABSTRACT
Rat mammary cells growing on glass coverslips were photographed first using interferencereflexion microscopy and then after processing for indirect-immunofluorescence microscopy with antibodies to actin or to α-actinin. A comparison of the images of the same cell given by the 2 microscopical procedures indicates that the focal contacts between the cell and the substratum correspond to distal ends of microfilament bundles, and that these bundles are only in limited areas close to the substratum. The focal contacts are rich in α-actinin which has been proposed as a membrane-anchorage protein for microfilament bundles. Use of stereo immunofluorescence microscopy allows a direct comparison between the interference-reflexion image, and the underside of the cell after staining with antibodies to actin or α-actinin.
A morphological study of the interaction between Trypanosoma Cruzi and rat eosinophils, neutrophils and macrophages In Vitro
Authors: Sanderson Colin J. , Souza Wanderley de 
Published: April 2021

ABSTRACT
The interaction between trypomastigotes of T. cruzi and purified rat eosinophils, neutrophils and macrophages has been studied. Macrophages induced by dextran, became infected and the parasites multipliedasamastigotes, eventually beingreleased as trypomastigotes into the medium. Eosinophils show an antibody-dependent phagocytosis, while neutrophil phagocytosis is enhanced by antibody. Electron microscopy showed that once inside the granulocyte phagosome, the trypomastigotes transform to amastigotes as a prelude to degeneration. This occurs as material apparently of granule origin accumulates in the phagosome. Eosinophils have the capacity to eject incompletely degenerated amastigotes into the medium. This phenomenon is discussed in relation to previous time-lapse cinematography studies of the lysis of chick erythrocytes by eosinophils, and reports that eosinophils release granule contents by means of a secretory vesicle.
An ultrastructural study of the effects of wheat germ agglutinin (WGA) on cell cortex organization during the first cleavage of Xenopus Laevis eggs: I. inhibition of furrow formation
Authors: Geuskens M. , Tencer R. 
Published: April 2021

ABSTRACT
Xenopus laevis fertilized eggs have been treated with wheat germ agglutinin (WGA) before the onset of the first cleavage, at the stripe stage and during groove deepening. The ultrastructure of the animal cortex of the arrested embryos has been compared with that of the same region of control embryos at different stages of first furrow formation and of cytochalasin B-treated embryos. The outer side of the plasma membrane of WGA-treated embryos is covered with a coat which is different from the diffuse material observed in either control or cytochalasin B-treated embryos and which is distributed in patches in the groove region. Narrow indentations of the plasma membrane in the cortex of WGA-treated eggs have been observed, particularly in the blocked or regressed groove. In WGA-treated eggs, a few bundles of microfilaments are located under the plasma membrane at the animal pole, but they are never arrayed in a continuous layer as in the control eggs. In the latter, many microtubules are located in close proximity to the microfilament layer at the beginning of cleavage, but they are only occasionally observed in the same region of WGA-treated eggs.
It is concluded that the binding of WGA molecules to their receptors on the surface of the Xenopus zygote interferes with the alignment of microfilaments in the furrow region and provokes the disorganization of the aligned microfilaments once the cleavage has begun. Internalization of portions of the nascent membrane in the groove could play an important part in the arrest of cleavage.
Transfer of mouse nuclear envelope specific proteins to nuclei of chick erythrocytes during reactivation in heterokaryons with mouse a9 cells
Authors: Jost Erich , d’arcy Allan , Ely Susan 
Published: April 2021

ABSTRACT
When chick erythrocyte nuclei are introduced into the cytoplasm of mouse A9 cells by cell fusion, proteins present in a fraction of the mouse nuclear envelope begin to appear in the envelope of the chick erythrocyte. The protein uptake was examined using antisera raised in chickens against the 3 major polypeptides of the nuclear pore complex-fibrous lamina fraction from rat liver nuclei. In indirect immunofluorescence studies these antisera give a strong envelope-specific Staining with various mammalian but not chicken cells.
Eighteen hours after cell fusion the first murine antigens can be observed in the erythrocyte nucleus. Two days after cell fusion the vast majority of the erythrocyte nuclei in cell hybrids contain some antigen and by 3 days the fluorescence of the reactivated erythrocyte nuclei reaches a level comparable to that of the mouse A9 nuclei. The rate of appearance of fluorescence in the chick nuclei depends upon the ratio of A9 cytoplasm to chick nuclei. Antigen uptake by the erythrocyte envelope is inhibited when protein synthesis is blocked suggesting that synthesis of mouse antigen, rather than a redistribution, determines the velocity of erythrocyte envelope reactivation. The early uptake of nucleospecific protein into the reactivating chick erythrocyte may not require any alteration in the nuclear envelope.
Cytology, growth characteristics and cellular alterations following SV40-induced transformation of human foetal brain cells derived from a Gm2 gangliosidosis and control
Authors: Brooks Steven E. , Amsterdam Daniel , Hoffman Linda M. , Adachi Masazumi , Schneck Larry 
Published: April 2021

ABSTRACT
Cell cultures were derived from the cerebra of a control and a Gm2 gangliosidosis (Tay-Sachs disease (TSD)) foetus. Both cell lines were identified as astrocytic, based on the ultrastructural demonstration of glial fibres. The control culture exhibited morphological differentiation when exposed to dibutyryl cAMP, a finding which was not observed with the TSD cells. The TSD culture demonstrated the pathobiological features of the disease, which included the absence of hexosaminidase A, increased concentration of Gm2 ganglioside and the detection of membranous cytoplasmic bodies by electron microscopy.
Control and TSD cells were exposed to SV40 virus, resulting ultimately in the isolation of transformants which differed from the parental cell types in morphology, growth rate and greatly accelerated cell death. Both control and TSD cell lines have been in propagation for over 200 subcultures and the transformants were identified as astrocytic, based on the retention of characteristic glial fibres. The control culture demonstrated a chromosome range of 34-63, with a mean of 47. In contrast, the TSD transformants exhibited a range of 50-107 and a mean of 74. Transformed lines retained their parental hexosaminidase isoenzyme profiles; Hex A and B in control, and Hex B in TSD cells. Membraneous cytoplasmic bodies persisted in the TSD line. Neither line could be induced to differentiate after exposure to cAMP. Additionally, they had a population doubling time of under 85 h and failed to release infectious virus particles.
Significant alterations in the total quantity and distribution profile of gangliosides were noted following viral transformation. A large increase in the percentage of Gm3 and a more modest increase in Gm2 were detected. In contrast, transformed lines were characterized by substantial reduction in the percentage of glucosamine-containing Gm2 and polysialoganglioside. Additionally, cultures exhibited a characteristic reduction in gangliosidc content after trans formation.
The in vitro transformation of human brain cells has resulted in the derivation of permanent astrocytic lines which arc, by virtue of their rapid growth rate and long-term survival, uniquely suited and adapted to the large scale in vitro production of substantial quantities of cells required for extensive biochemical study. Significantly, those characteristics which are unique to the Gm2 gangliosidosis storage disease have been retained in a permanent model CNS cell line.
*All correspondence should be addressed to: Dr Daniel Amsterdam, Kingsbrook Jewish Medical Center, Rutland Road & East 49th Street, Brooklyn, New York, n203, U.S.A.
Detection of small amounts of human DNA in human−rodent hybrids
Authors: Rodgers A. 
Published: April 2021

ABSTRACT
A method of measuring semi-quantitatively small amounts of human DNA in irradiated human × mouse and irradiated human × Chinese-hamster somatic cell hybrids is described. One method uses molecular hybridization of cell DNA bound to nitrocellulose filters with a cRNA probe to Cot 0–1 human DNA. Alternatively hybrid cell DNA is reassociated in solution with a Cot 0-1 fraction of nick-translated human DNA. Formamide buffers give specificity to the reaction. The detection limit of the filter method is 0·2–0·5 % equivalents and reassociation kinetics 0·005−0·01 % equivalents of a human genome.
Experiments with cell hybrids suggest that a fragment of repetitive DNA may be retained along with the selected genes after a cell fusion. In one case however, of a hybrid cell in which malignancy is suppressed, highly repetitious sequences were not found.
Structural changes in the pollinated and unpollinated avocado stigma and style
Authors: Sedgley Margaret 
Published: April 2021

ABSTRACT
Structural changes in the pollinated and unpollinated avocado (Persea americana Mill) stigma and style up to 42 h after first opening of the flower were investigated using light and electron microscopy. The pollen tubes grew in the stigma secretion and intercellular substance and initial contact occurred between the plasma membrane of the male and the cuticle and stigma secretion of the female. The pollen tube wall started to develop 15 min after pollination and increased in thickness up to 24 h after pollination.
By 18 h after first opening of the flower, starch had disappeared and cell wall thickenings were present in both the pollinated and unpollinated stigma and style. The wall thickenings developed more slowly in the upollinated than in the pollinated tissue. They contained lipid and were bounded by callose. Degeneration of the cytoplasm of some of the papilla and transmitting tissue cells occurred only following the passage of the pollen tubes and may be of importance in tube nutrition. There was no degeneration in the unpollinated stigma and style and the cytoplasm did not start to lose clarity until 42 h after first opening of the flower.
Ultrastructural localization of calcium-binding sites in the electrocyte of electrophorus electrices (L.)
Authors: Jorge T. C. De Araujo , Souza W. De , Machado R. D. 
Published: April 2021

ABSTRACT
Calcium-binding sites were detected in the electrocyte of Electrophorus electricus (L.) using the Oschman & Wall technique, in which CaCl2 was added to the fixative and washing solutions. Deposits were seen scattered along the plasma membrane of the electrocyte, inside mito-chondria, associated with the post-synaptic membrane and the membrane of synaptic vesicles.
Epithelial-fibroblastic organization in cultures grown from human embryonic kidney: its significance for morphogenesis in vivo
Authors: Bard Jonathan B. L. 
Published: April 2021

ABSTRACT
The morphological behaviour of explants of human embryonic kidney has been studied in order to investigate the rules governing interactions between epithelial and fibroblastic cells from the same tissue. When the fragments are cultured, epithelia migrate out first and are followed, a few days later, by cables which grow out from the fragments and which are composed of multilayered fibroblasts. These cables extend through the epithelia to reach the substratum, to which they adhere. The epithelia maintain an upper surface free of spread fibroblasts and are unable to multilayer, although occasional rounded-up cells adhere to this surface. Fibroblasts, however, not only multilayer in the cables but can act as a substratum for epithelial cells which migrate on the cable surface. Fibroblasts and epithelia from kidney thus follow the same behavioural rules that govern the interactions between kidney epithelia and fibroblasts from different tissues. The suggestion that these rules derive from tissue differences and that cells from the same tissue are more tolerant of one another is not borne out. These observations and those reported by others are interpreted in terms of the functional properties of the cells in vivo. It is further pointed out that only those epithelia that maintain a free surface in vivo would be expected to show this property in vitro. Finally, the implications of cells with essentially the same properties generating more than one structure are considered.
Sodium and potassium in oocytes of Triturus cristatus
Authors: Riemann W. , Muir C. , Macgregor H. C. 
Published: April 2021

ABSTRACT
Newt oocytes were dissected under liquid paraffin and known volumes of clean nucleoplasm and cytoplasm were obtained from oocytes in different stages of oogenesis. The samples were digested in redistilled nitric acid, diluted with deionized water, and their Na and K contents were measured by flame spectrophotometry. The results were expressed as micro-equivalents of Na and K per millilitre of nucleoplasm or cytoplasm. In oocytes of 0·3—0·5 mm diameter nucleoplasm and cytoplasm have similar Na and K concentrations, and the molar K:Na ratio is about 3:1. As the oocyte grows to maturity the nucleoplasmic Na and K concentrations do not change, but the cytoplasmic K concentration falls steadily until, in nearly mature oocytes, the cytoplasmic K:Na ratio is near 1:1. Measurements of Na and K concentrations in yolky and clear cytoplasm show that both fractions have the same K content and the concentration of K decreases in both fractions as the oocyte grows. The significance of these results is discussed in terms of the possible effects of changes in the intracellular ion balance on the morphology and synthetic activity of the chromosomes.
The fine structure of photoreceptors in Mitopus morio (phalangida)
Authors: Curtis D. J. 
Published: April 2021

ABSTRACT
Fine structural studies on the eyes of the harvestman Mitopus morio revealed the presence of microvilli in the rhabdom. The microvilli vary in length between 1 μand 2 μ, are about 800 Å wide, and curved or straight. They derive from the plasma membranes of the four retinula cells which surround the rhabdom. Approximately cylindrical in shape, the rhabdoms are about 40 μ long by about 4–6 μ in cross-diameter. Each rhabdom is situated at the centre of a retinula, and these retinulae are packed in a hexagonal array to form the retina. Distally, rhabdom fusion occurs to form a rhabdom network. The retina lies beneath the dioptric apparatus which consists of a single lens, surmounting a glassy body composed of lentigen cells.
The cytoplasmic organelles of the retinula cells include mitochondria, lysosomes, sparse elements of endoplasmic reticulum, vesicular components, prominent Golgi complexes and pigment granules which possess a laminated structure. An important feature of the retinula cell is the presence of many small vesicles, about 0·1μin diameter, clustered beneath the rhabdom. Incubation of glutaraldehyde-fixed eyes in a Gomori medium with acetylthio-choline as substrate, coupled with inhibition of controls by 62C47, indicates the presence of a presumed acetylcholinesterase in these vesicles. Similar vesicles also occur in the proximal cytoplasm of the retinula cells. Other larger vesicles, often with a core of whorled membranes, as well as dense bodies, also show acetylthiocholine-splitting activity. This latter activity is not inhibited by 62C47 and is probably the effect of lysosomal non-specific esterase. These bodies also exhibit acid phosphatase activity when incubated in a Gomori medium with β-glycerophosphate as substrate.
The presence of acetylcholinesterase activity, as distinct from non-specific esterase, in vesicles closely associated with the rhabdom and in more proximally situated vesicles is significant. It would point to the presence of an acetylcholine/acetylcholinesterase system involved in the generation and/or propagation of the sensory impulse arising from photo-stimulation of the rhabdom.