bluuebunny/crossref_metadata_2025_split huggingface dataset:
Complementary plasma membrane fracture faces in freeze-etch replicas
Authors: Flower N. E. 
Published: April 2021

ABSTRACT
Recent studies have all shown that membranes fracture internally during freeze-etching or freeze-cleaving, confirming that 2 internal membrane faces are produced. That these faces are not complementary is one of the main features of freeze-etch replicas still requiring explanation. In the present investigation certain plasma membranes in light organs of the New Zealand glow worm are found to be an exception to this general rule of non-complementarity, as there is a sufficient number of holes present in one membrane face to match the number of particles on the other. This finding suggests that most of the theories put forward to explain non-complementarity do not apply and that holes are probably lost in most membrane faces by distortion during fracturing.
Erythropoiesis in the newt, Triturus Cristatus laur. : II. characteristics of the erythropoietic process
Authors: Grasso J. A. 
Published: April 2021

ABSTRACT
In splenectomized newts (Triturus cristatus Laur.) rendered anaemic by acetylphenylhydrazine (APH), an erythropoietic response is delayed so that the animals are completely devoid of the erythron, including erythrocytes. At 11–14 days after APH, ‘erythroid precursor cells’ (EPC) in the blood signal the occurrence of an erythropoietic response. Ultrastructural studies have shown few or no ribosomes in EPCs, but well developed nucleoli and intense RNA synthesis are seen in these cells. Correlated morphological and cytochemical data indicate the production of ribosomes in EPCs, a process culminating in the formation of basophilic erythroblasts (BE). Microphotometric studies show the accumulation of haem during this interval. Thus, in EPCs and BEs, both ribosomal (rRNA) and messenger (m) RNA are synthesized, making possible the early synthesis of haemoglobin. In subsequent stages, nucleoli exhibit a size decrease, most evident in the particulate component, while all RNA synthesis ceases during the mid-poly chromatophilic erythroblast (MPE) stage. Coupled with the gradual loss of ribosomes characteristic of this developmental period, the results suggest that rRNA synthesis occurs in EPCs, BEs, and in early polychromatophilic erythroblasts, where it is completed. Haemoglobin mRNA is also formed in these stages since ultrastructural and microphotometric data show the accumulation of haemoglobin. Beyond the MPE, haemoglobin production is dependent upon stable messenger RNA since no RNA synthesis is detected in this period. Ultrastructural studies demonstrate that autophagy may play an important role in the loss of cytoplasmic organelles characteristic of the erythropoietic process. The occurrence of swollen cristae and outer compartment in mitochondria coupled with the presence of myelin-like membrane whorls in association with mitochondria is seen in all erythroid cells except EPCs. Membrane profiles derived from endoplasmic reticulum are frequently encountered in the vicinity of mitochondria and appear to encircle these organelles and adjacent cytoplasm to form autophagic vacuoles. In the process, the limiting membranes assume a dense laminar appearance. Elements of the Golgi complex also display morphological alterations suggestive of degeneration. Cytoplasmic bodies of varying appearance and content, some of which are similar to lysosomes in other cell types, are seen in all erythroid cells. Ferritin is seen in some bodies, in vacuoles, or in aggre gates, but does not appear in micropinocytotic vesicles.
The effect of vincristine sulphate on the axoplasmic flow of proteins in cultured sympathetic neurons
Authors: England J. M. , Kadin M. E. , Goldstein M. N. 
Published: April 2021

ABSTRACT
The effect of vincristine sulphate on the axoplasmic flow of labelled proteins in neurites of chick embryo sympathetic neurons growing in tissue culture was studied by autoradiography. In control neurons most of the 3H-proteins synthesized during a 90-min pulse with a 3H-amino acid were localized in cell bodies. There was a diminishing gradient of labelled proteins in the neurites which was highest in portions adjacent to the cell bodies and lowest at the periphery. During a physiological chase there was a gradual increase in the amount of label in the neurites, so that after a 15-h chase even the most peripheral portions were well labelled. This indicates that a portion of the labelled proteins synthesized in the cell bodies are transported peripherally into the neurites.
The centrifugal movement of labelled proteins in neurites was markedly decreased when cells were grown in medium containing 10 μg/ml vincristine sulphate. After a 15-h chase in the presence of drug only a small amount of label was in the peripheral portion of the neurites. Treatment with vincristine did not decrease the rate of amino acid incorporation or alter the rate of protein turnover during the course of the experiment. Thus an explanation of the results based on an altered rate of total cell protein synthesis or degradation is unlikely. The capacity of sympathetic neurons to take up and concentrate exogenous [3H]norepinephrine in their neurites was only slightly reduced by vincristine. This indicates that at least some cellular activities requiring metabolic energy are relatively unaffected by the interruption in axoplasmic flow caused by vincristine and that the mechanism by which vincristine interferes with axoplasmic flow does not involve general cellular toxicity.
The major morphological differences between control and vincristine-treated neurons were the absence of microtubules and the presence of crystal-like structures within the cells. The relationship between the effect of vincristine on the axoplasmic flow of proteins and the arrangement of the microtubule system is discussed.
Intestinal goblet cell mucus: Isolation and identification by immuno-fluorescence of a goblet cell glycoprotein
Authors: Forstner J. , Taichman N. , Kalnins V. , Forstner G. 
Published: April 2021

ABSTRACTA high-molecular-weight glycoprotein (HMG), representing the majority of the soluble glycoprotein hexosamine and hexose in the intestine, was isolated by Sepharose 4B chromatography from high-speed supernatants of rat small intestinal homogenate. Fluorescein-labelled globulin, from rabbit antiserum produced against HMG, specifically stained supra-nuclear mucus vesicles of goblet cells in small intestine and colon as well as gastric pit cells in the body of the stomach and mucus-producing cells in the sublingual salivary gland. A single precipitin line was found when HMG was tested against its antibody by agar immunodiffusion and immunoelectrophoresis. No cross-reactivity was observed between antibody and rat serum or extracts from microvillus membrane, human colon and pig intestine. Precipitin lines which fused with the HMG precipitin arc in apparent identity were observed with antigens in intestinal lumen washings, and in small-molecular-weight fractions from intestinal cell sap. When studied by cellulose acetate electrophoresis, cetyl trimethylammonium bromide precipitation and precursor labelling with [1-14C]glucosamine, HMG behaved as a single homogeneous glycoprotein free of detectable protein contamination. These results imply that HMG is a major component of goblet-cell mucus in the small intestine, and suggest that it is similar to mucin produced throughout the gastrointestinal tract. HMG is the first glycoprotein, isolated without the aid of proteolytic agents, which has been specifically identified as a product of the goblet cell.
Association of the two glycosyl transferase activities of glycoprotein synthesis with low equilibrium density smooth microsomes
Authors: Wagner R. R. , Pettersson Elisabeth , Dallner G. 
Published: April 2021

ABSTRACTSmooth microsomes of rat liver were subfractionated on a continuous sucrose gradient to isopyenic equilibrium density. All the microsomal electron-transport enzymes and phosphatases exhibit a broad distribution in the various microsomal subtractions. On the other hand, the N-acetylglucosaminyl and galactosyl transferase activities, which are known to participate in the synthesis of the oligosaccharide chain of the plasma glycoproteins, exhibit a markedly different distribution pattern. They are concentrated to a small fraction having an isopyenic equilibrium density of 1·10. These membranes represent a separate entity of the smooth microsomal fraction, the exact cellular origin of which remains to be clarified.
Some effects of actinomycin D, cycloheximide and puromycin on cell adhesion
Authors: Weiss L. , Chang M. K. 
Published: April 2021

ABSTRACT
The metabolic inhibitors cycloheximide, puromycin and actinomycin D, increased the rate of adhesion of Ehrlich ascites tumour cells to coverslips and plastic surfaces, over periods of up to 2 h in vitro. Among a number of possible explanations of this effect is a decreased production of hypothetical anti-adhesion factor(s). It is suggested that the difference between the increased rate of adhesion observed by us, and the decrease or lack of effect of the drugs observed by others, is related to prior trypsin-treatment of cells by the other observers.
A possible alteration in the permeability of ascites cell membranes after exposure to acoustic microstreaming
Authors: Williams A. R. 
Published: April 2021

ABSTRACT
Single-cell suspensions of mouse Ehrlich ascites cells in isotonic saline were subjected to a small-scale acoustic microstreaming field generated around a transversely oscillating wire. Cells sheared at wire displacement amplitudes below the threshold for membrane rupture contained more fluid than their controls. Evidence is presented which suggests that a slight change has occurred in the permeability of the plasma membranes of the intact sheared cells.
Acetylcholinesterase in human erythroid cells
Authors: Skaer R. J. 
Published: April 2021

ABSTRACT
Acetylcholinesterase is present in human red cells but cannot be demonstrated by the copper thiocholine test. The enzyme is revealed, however, in the perinuclear cisterna, endoplasmic reticulum and Golgi apparatus of red cell precursors. It is suggested that 2 forms of the enzyme are present, one of which can be demonstrated by the copper thiocholine test, the other cannot; one form may be the precursor of the other. These observations may cast light on the kinetics of red cell replacement and on the interpretation of the results from the copper thiocholine test on other tissues such as the nervous system.
An electron-microscope study of the reaction of collagen with some monoaldehydes and bifunctional aldehydes
Authors: Cox R. W. , Grant R. A. , Kent C. M. 
Published: April 2021

ABSTRACT
Rat tail tendon collagen has been treated with the monoaldehydes, formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde, and with the dialdehydes, glyoxal and glutaraldehyde. The treated collagen was then examined in the electron microscope using a negative stain. Alterations to the native collagen pattern were seen with formaldehyde, acetaldehyde, propionaldehyde, glyoxal and glutaraldehyde. A correlation was noted between the changes in the band pattern and the degree of cross-linking estimated from chemical and physical changes in the treated collagen and from measurements of cross-linking made by other workers. The results indicate that the use of electron microscopy and negative staining may be a valuable method of assessing the degree of cross-linking in collagen treated with aldehydes and other reagents.
Chemical and structural differences between cilia and flagella from the lamellibranch mollusc, Aequipecten irradians
Authors: Linck R. W. 
Published: April 2021

ABSTRACT
Gill cilia and sperm flagella from the lamellibranch mollusc Aequipecten irradians were isolated by several methods and chemically fractionated by low-ionic-strength dialysis. These organelles differ in their forms of dynein and in the stabilities of their homologous microtubules and subsidiary structures (i.e. nexin fibres and spoke material). In flagella more than 80% of the axoneme ATPase is solubilized, appearing as a 14s peak in the ultracentrifuge, and the whole axoneme is broken down to unlinked, doublet outer fibres. In cilia only half of the ATPase is solubilized from axonemes as a 14S component. The ciliary B-tubules and one member of the central pair also dissolve, leaving the A-tubules and the other central tubule held together by nexin fibres and matrix material as a 9 + 1 singlet axoneme, to which is bound the remaining half of the ATPase. This tightly bound form of the ciliary ATPase can be removed in an enzymically active form by brief trypsin treatment which causes the breakdown of the singlet axoneme. The trypsin-solubilized ATPase behaves like native 14s dynein in the ultracentrifuge but breaks down to polypeptides when electrophoresed in the presence of sodium dodecyl sulphate (SDS).
The native 14 s material containing the dynein was partially purified by column chromatography and was shown on SDS-polyacrylamide gels to be composed of 2 components. The molecular weights of these as determined by 3% acrylamide SDS-gels are 450000 and 500000, and they are not reduced by prior treatment with 8 M urea. Parallel SDS-gels loaded with identical amounts of ciliary and flagellar axonemes show very nearly identical components; the ratio of the amounts of the 500000 and 450000 mol. wt. components is about 2:1 respectively. The fractionation of ciliary and flagellar axonemes was analysed quantitatively on SDS-gels. Essentially all of the 450000 and 500000 mol. wt. components are found in the soluble fraction from dialysed flagella. The soluble fraction from cilia contains the 2 components in a 1:1 ratio, along with half the axoneme ATPase, while the singlet axoneme fraction contains the remainder of the 500000 material and the remaining half of the ATPase. On this basis it is believed that the 500000 component is the dynein ATPase, while the 450000 material represents a non-ATPase protein.
The chemical and structural differences between cilia and flagella may offer an explanation for their different modes of beat.
A simple light-microscope technique for the examination of cell surfaces
Authors: Ross A. , Gormley I. P. 
Published: April 2021

ABSTRACT
A simple technique for the examination of cell surfaces by shadowing them with a heavy metal and examining by light microscopy has been described. Stained preparations can be examined and photographed initially prior to investigation by this technique. It is suggested that this technique could be used instead of the scanning electron microscope or replica techniques where the limited resolution of the light microscope is sufficient.
Kinetics of the regeneration of sea-urchin cilia
Authors: Burns R.G. 
Published: April 2021

ABSTRACT
The kinetics of the regeneration of cilia of the sea urchin Tripneutes gratilla have been examined. The maximum cilia length is attained asymptotically which may reflect the transport of precursors to the distal tip. However, a detailed analysis indicates that the maximum length is regulated by a mechanism other than the availability of precursors at the distal end. It is argued that this control is independent of the size of the precursor pool, the rate of protein synthesis or the rate of precursor transport to the distal tip.
The secretion and development of nematocysts in a siphonophore
Authors: Skaer R. J. 
Published: April 2021

ABSTRACT
Nematocyst development was watched in living cells of a siphonophore, Rosacea cymbiformis. The secretion differentiates in the formative cell into an ovoid capsule, continuous with a long apical tube. The entry of this ‘external’ tube into the capsule creates the coiled internal’ thread’ of the mature nematocyst. Electron microscopy shows that the tip of the external tube inverts and moves down the tube towards the capsule. Complex pleats form during inversion. Thus formation of the internal thread is the geometrical converse of discharge. Extensive repacking of the triply pleated, internal thread occurs, and subsequently the barbs form.
Further experiments on the role of the nucleolus in the transfer of rna from nucleus to cytoplasm
Authors: Deák I. I. 
Published: April 2021

ABSTRACT
The role of the nucleolus in the transfer of RNA from nucleus to cytoplasm was examined by means of experiments in which the nucleolus or other parts of the nucleus were inactivated by a microbeam of ultraviolet light. These experiments confirmed previous work in showing that such inactivation of the nucleolus inhibited the appearance in the cytoplasm, not only of ribosomal RNA, but also of other types of RNA made in the nucleus, in particular transfer RNA.
Clonal variability of adenovirus transformed cells
Authors: Weber Joseph 
Published: April 2021

ABSTRACT
Cells transformed by DNA oncogenic viruses acquire characteristic properties which have been considered criteria for transformation. SV40- and polyoma virus-transformed cells are capable of selective reversion for several of these properties. Until now, reversion of trans-formed cell properties has not been reported in the adenovirus system. The stability of several transformed cell properties was examined in a line (HTC) of Ad. 12-transformed (in vivo) cells after several hundred generations of in vitro passage. From a large number of clones isolated by the soft-agar suspension technique, 7 were selected for detailed examination. The clones, as the parental cells, were free of infectious virus and type-specific antigen, but contained intranuclear Ad. 12 T antigen. Cell growth profiles with o, 1 and 10% serum in the culture medium revealed that while 4 clones retained the parental characteristic of growth in the absence of serum, 3 lost this ability and grew only in serum concentrations greater than 1 %. Agglutination profiles with 4-fold dilutions of concanavalin A (Con. A) and wheat germ agglutinin (WGA) directly or after trypsin treatment revealed 2 clones which failedto agglu-tinate with Con. A; trypsin treatment reversed this effect. Each clone agglutinated with WGA directly, though one clone showed reduced agglutination. On the basis of superinfection with Ad. 2 the clones could be grouped into low, intermediate and high yielders with 10-fold intervals. All clones were transplantable into random-bred adult Syrian hamsters. There was no marked correlation between the reversion or modification of individual transformed cell properties among the clones. The phenotypic stability of these transformed cell properties was confirmed by re-cloning the tumours induced by one of the revertant clones. It was concluded that some of these properties are not essential for the maintenance of oncogenic potential.
On the In Vitro behaviour of mouse submaxillary gland cells
Authors: Marcante Maria Luisa 
Published: April 2021

ABSTRACT
Investigations on the morphological features and some biochemical properties of cells isolated from mouse C3H/He (IRE/Ar) submaxillary glands cultivated in vitro are reported. Two types of cells have been recognized: the dark cells differ from the light in the shape of their mitochondria, and number of vacuoles, while endoplasmic reticulum is absent. The enzymic activities, which have been tested, are phosphofructokinase, pyruvate kinase, amylase and lactate dehydrogenase. The values for enzyme activities in vitro are in good agreement with those obtained for submaxillary gland in vivo.
Therefore, it can be concluded that during their growth in vitro cells from submaxillary glands retain their enzymic properties.
A rapidly sedimenting fraction of rat liver endoplasmic reticulum
Authors: Lewis J. A. , Tata J. R. 
Published: April 2021

ABSTRACT
Balance-sheet experiments carried out to account for the distribution of endoplasmic reticulum fragments during subcellular fractionation of rat liver showed that a large proportion of these fragments are present in the pellets of low-speed centrifugation. Using glucose-6-phosphatase and RNA as markers we found that approximately 50 % of the fragments of endo-plasmic reticulum sedimented in the pellet of a 640-g centrifugation, 10 % in that of a 6000-g centrifugation and 35 % in the pellet of a 105000-g centrifugation. Starvation of the animals before use did not alter this distribution, nor did the use of more vigorous homogenization conditions. We have developed a procedure for removing nuclei and erythrocytes from the material sedimenting at 640 g to give a fraction (rapidly sedimenting ER fraction or RS-ER) similar to the standard microsomal preparation. Centrifugation of this RS-ER fraction over 1·3 M sucrose yields sub fractions of high and low RNA content analogous to the rough and smooth microsomal fractions. Electron-microscopic studies showed that, whereas the rough microsomal fraction consisted of ribosome-studded vesicles of varying size and content density, the rough RS-ER fraction contained a mixture of mitochondria and double lamellar membranes with ribosomes attached. These double lamellar membranes closely resemble the endoplasmic reticulum of intact rat liver. The double lamellar membranes are frequently observed grouped in stacks and in close association with the mitochondria. The significance of the association between endoplasmic reticulum and mitochondria of the RS-ER fraction and the relation between it and the standard microsomal preparation are discuased.
Peroxidases in tobacco abscission zone tissue i. fine-structural localization in cell walls during ethylene-induced abscission
Authors: Henry E. W. , Jensen T. E. 
Published: April 2021

ABSTRACT
The fine-structural localization of peroxidases during ethylene-induced abscission of flower pedicels of Nicotiana tabacum L. cv. ‘Little Turkish’ has been investigated. Peroxidase activity has been localized in both the cell walls and intercellular spaces of ethylene-treated flower pedicels which were fixed in glutaraldehyde, incubated in diaminobenzidine (DAB) medium with postfixation in 2 % osmium tetroxide. Peroxidase staining is present in the cell walls and intercellular spaces of control tissue but is not as intense as in ethylene-treated tissue. Increased peroxidase staining is evident in the intercellular spaces and cell walls after 2 h of exposure to ethylene and increases in intensity between 2 and 5 h. At 5 h, ethylene-induced abscission occurs. Fine-structural investigations revealed prominent staining in the middle-lamellar and peripheral areas of the cell walls in ethylene-treated tissue. The peroxidase staining appears to be due to peroxidase as prior incubation with potassium cyanide gives a marked reduction in the staining reaction. Incubation of the ethylene-exposed tissue in aminotriazole, a specific inhibitor of catalase, does not reduce peroxidase staining, except in the microbodies, which reportedly contain catalase.
Fracture planes of the plasmalemma of some higher plants revealed by freeze-etch
Authors: Hereward F. V. , Northcote D. H. 
Published: April 2021

ABSTRACT
Freeze-substitution studies have been carried out on plant material which had been fractured while frozen in order to locate the planes of fracture. It was clearly shown that in some cases the plasmalemma was split along the hydrophobic interface while in others the fracture passed on either side of the membrane. The freeze-etch process exposed different surfaces at the cell periphery and these were related to both types of fracture seen in the freeze-substituted material.