bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined microspectrophotometry and automated quantitative autoradiography applied to the analysis of the plant cell cycle
Authors: Gould Alan R.
Published: April 2021

Two methods, which relate grain number to cell cycle phase in Feulgen-stained autoradiographic preparations, have been developed and compared. Both methods automate grain number estimations, one by taking integrated absorbance measurements at different wavelengths, the other by measuring absorption at a single wavelength before and after chemical removal of silver grains. With tritium-labelled tobacco mosaic virus as a probe, a quantitative analysis has been made of the binding of virus particles to plant protoplasts in different compartments of the DNA replication and partition cycle. The preliminary results indicate that the quantity of virus bound by protoplasts is related to their cell cycle phase. Whilst in this case, the methods have been used with plant cells, both techniques are equally applicable to animal cells.
Electron-microscopy of intact nuclear dna from human cells
Authors: McCready S. J. , Akrigg A. , Cook P. R.
Published: April 2021

Structures retaining many of the morphological features of nuclei may be released by lysing human cells in a non-ionic detergent and 2 M NaCl. Such nucleoids contain all the nuclear DNA packaged within a flexible cage of RNA and protein. HeLa nucleoids have been spread at an air-water interface and viewed in the electron microscope. A tangled network of superhelical fibres surrounds the collapsed cage. Irradiation with γ-rays abolishes supercoiling and treatment with the untwisting enzyme or a low concentration of ethidium reduces it. A high concentration of ethidium induces supertwisting. The nuclear DNA of higher cells can be isolated naked, supercoiled and intact.
Wall substructure of microtubules polymerized in vitro from tubulin of crayfish nerve cord and fixed with tannic acid
Authors: Pierson George B. , Burton Paul R. , Himes Richard H.
Published: April 2021

Microtubules of axons of crayfish nerve cord normally have 1 2 wall protofilaments and microtubules of surrounding glial cells have 13 protofilaments. Tubulin was isolated from such nerve cords and polymerized in vitro; tannic acid staining of sedimented microtubules showed that microtubules with 12 and 13 wall protofilaments were present, suggesting that the ability to form a microtubule with a given number of protofilaments is inherent in the tubulin or its associated proteins. The temperature of polymerization was found to influence the number of protofilaments in resultant microtubules. With assembly at 20 °C, for example, most of the complete microtubules had 13 protofilaments, while at 40 °C most showed 10 protofilaments. It is suggested that the temperature of in vitro polymerization, among other factors, can influence the angle of binding between adjacent protofilaments and thus alter the number of protofilaments required to complete the circumference of the tubule.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: II. effect of sucrose on cellular fine structure
Authors: Glauert Audrey M. , Fell Honor B. , Dingle J. T.
Published: April 2021

A study of the fine structure of embryonic chick limb-bone rudiments in organ culture has shown that exposure to 0·08 M sucrose causes intense cytoplasmic vacuolation of the peripheral cells, while the structure of the cytoplasmic organelles is apparently unaltered. The lamellae and vesicles of the Golgi apparatus are more abundant than in the controls and the vesicles are no longer confined to the Golgi zone. The first vacuoles appear in the articular chondrocytes after exposure to sucrose and are autophagic vacuoles or clear vacuoles, probably containing sucrose. After 24 h or more the vacuoles are more heterogeneous and contain a great variety of membranous, granular and fibrous material. These vacuoles appear to be formed by fusion between endocytotic coated vesicles, autophagic vacuoles, multivesicular bodies, clear vacuoles and vesicles derived from the Golgi zone. After 2 days some vacuoles contain fibrils identical in appearance to those in the surrounding cartilage matrix. The development of vacuoles in the chondrocytes in the inner regions of the epiphyses is much slower and autophagic vacuoles are only seen after 6 days’ exposure to sucrose.

Similar changes are observed in the fine structure of the perichondrial and periosteal fibroblasts, and after 2 days in the presence of sucrose many fibroblasts have cytoplasmic vacuoles containing banded fibres similar to the extracellular collagen fibres. In shafts of 11-day embryonic chicks exposed to sucrose for 8 days the cytoplasmic vacuoles in the osteoblasts contain banded fibres and dense crystallites resembling those of the bone matrix.

When rudiments are transferred to normal medium after 2 days’ exposure to sucrose the vacuoles are gradually lost; some of the vacuoles appear to move to the periphery of the cell and then fuse with the plasma membrane, thus releasing their contents. Throughout this process the fine structure of the cytoplasmic organelles is unaltered.

It is suggested that exposure to sucrose stimulates an increased production of lysosomal enzymes which are transported in small vesicles from the enlarged Golgi region to the clear vacuoles and to the autophagic vacuoles. It seems possible that during this process enzymes are released into the surrounding matrix and modify the ground substance sufficiently to enable some of the connective tissue cells to become actively phagocytic and to ingest collagen fibres and bone crystallites.
Development and dispersal of p-protein in the phloem of Coleus blumei benth
Authors: Steer M. W. , Newcomb E. H.
Published: April 2021

The development of P-protein (slime) in the phloem of Coleus stem apices has been studied electron microscopically using material fixed in glutaraldehyde followed by osmium tetroxide. In phloem parenchyma cells the earliest-appearing groups of tubular P-protein commonly are seen in close association with clusters of ‘spiny’ vesicles similar to those reported in Phaseolus phloem (Newcomb, 1967). The vesicles break down as the P-protein masses enlarge, and are assumed to contribute to P-protein formation. Subsequently the groups of tubules are consolidated into a single spindle-shaped body aligned longitudinally in each phloem parenchyma cell or sieve element. The microtubules observed frequently in the vicinity of the young P-protein body may play a role in its consolidation or in the longitudinal alignment of its constituent tubules. Some P-protein bodies acquire a highly organized structure in which the tubules are arranged hexagonally around lightly staining centres.

Disaggregation of the P-protein body occurs during disintegration of the cytoplasm and nucleus, and results initially in the presence of swirls of packed fibrils. During disaggregation, the tubules of the mature P-protein body, which are about 200 Å in diameter, are converted to fibrils about 70 Å in diameter in a process apparently with several intermediate stages. In longitudinal view the fibrils exhibit alternate electron transparent and dense bands that impart a striated appearance to the mass. During maturation of the sieve element the swirls of fibrillar masses separate into individual fibrils which become dispersed through the cell lumen.
Electrophoretic and chemical characterization of the charged groups at the surface of murine CL3 ascites leukaemia cells
Authors: Ward P. D. , Ambrose E. J.
Published: April 2021

The electrophoretic characteristics of the murine CL3 ascites tumour were investigated.

Treatment of the cells with formaldehyde raised the electrophoretic mobility (E.P.M.) from—1· 06 to—1 ·28 μ/sec/V/cm; subsequent treatment with diazomethane reduced their mobility to zero. The E.P.M. of the diazomethane-treated cells did not alter over the pH range 3·0–8·0. This proved that the only ionic groups at this cell surface were amino and carboxyl groups. The absence of phosphate groups, another possibility, was confirmed by the lack of calcium-ion binding from 10 mM Ca+ solutions.

Neuraminidase treatment reduced the E.P.M. from—1·06 to—0·55 μ/sec/V/cm and free sialic acid was identified in the enzyme supernatant. Subsequent treatment of the cells with formaldehyde raised the mobility to—1·22 μ/sec/V/cm indicating that the change in E.P.M. on neuraminidase treatment was not due solely to the removal of the carboxyl groups of sialic acid but also to a change in the ionic nature of the surface. This change is ascribed to a change in the conformation of the surface protein. The reason for this change and a suggestion for the possible role of sialic acid at the cell surface are mentioned.

Treatment of the cells with trypsin did not affect the viable cells in any way, suggesting that the surface proteins lack the basic amino acids lysine and arginine. Pronase treatment served only to show that much of the sialic acid was bound to protein; the total amount was not determined.
Particles present in the haemolymph and defensive secretions of insects
Authors: Kay D. , Rothschild Miriam , Aplin R.
Published: April 2021

Defensive fluids obtained from the Garden Tiger, Scarlet Tiger and Burnet Moths and from the Monarch Butterfly and the Seven-Spot Ladybird Beetle, haemolymphs taken from the wasp, the Burying Beetle and the Rat Flea, and fluids from the eggs of the Garden Tiger, Gypsy Moth and Oak Eggar Moth were examined in the electron microscope after negative staining.

Except for the ladybird all the defensive fluids, haemolymphs and egg fluids contained particles 100–150 Å across which frequently had rectangular or square outlines. In some species the particles were occasionally arranged in groups of 2 and 4 and in the egg fluid of the Garden Tiger they were arranged in rows which were aligned side by side to form strands of considerable length.

The particles are believed to be protein. They correspond in size to the 16 s component of the haemocyanins of Limulus and Homarus and the protein particles found in Calliphora by other workers.
Alteration of nuclear distribution in B-mutant strains of Schizophyllum Commune
Authors: Koltin Y. , Flexer A. S.
Published: April 2021

Sexual morphogenesis in Schizophyltum commune, a higher basidiomycete, is controlled by two incompatibility factors, A and B. A key event, the migration of nuclei from each mate throughout the mycelium of the other, is controlled by the B factor and occurs in A = B ‡ = matings. The distribution of nuclei in the resulting heterokaryon is irregular, and anucleate, uninucleate, binucleate and multinucleate cells are found. A similar distribution of nuclei is found in homokaryons carrying a mutation in the B factor. Because of their developmental history, strains that carry a mutated B factor offer a relatively simple system for the study of the events associated with nuclear migration. Growth of mutant-B germlings occurs in three stages: (I) most cells are binucleate; (II) most cells are uninucleate; (III) cells contain varied numbers of nuclei. The ratio of nuclei: cells remains constant during the transition from stage II to stage III. Changes in nuclear distribution result from movement of the nuclei from cell to cell, and the movement is associated with the disruption of the dolipore septum. The mutant-B system appears to offer an opportunity for the biochemical resolution of the events related to nuclear migration.
Karyotype analysis of the plant-parasitic nematode Heterodera glycines by electron microscopy I. the diploid
Authors: Goldstein Paul , Triantaphyllou A. C.
Published: April 2021

Heterodera glycines is a diploid amphimictic nematode with n = 9 chromosomes. Nine normal synaptonemal complexes (SC) were detected following 3-dimensional reconstruction of pachytene nuclei from electron microscopy of serial sections. Regions of unique ‘modified synaptonemal complexes’ (M.SC) were observed along 2 SCs. These consist of a heterochromatic knob within which the SC appears either disorganized or stacked in layers of lateral elements. Its function is not known. Recombination nodules and ‘cylindrical granular complexes’, were not observed in H. glycines.
Directional change of ciliary beat effected with Mg2+ in Paramecium
Authors: Nakaoka Yasuo , Toyotama Hideki
Published: April 2021

Two types of Triton X-100 extracted model of Paramecium caudatum were prepared and effects of the ionic compositions of the reactivating medium on the swimming behaviour of the extracted models were examined. Type I, prepared by the method of Naitoh and Kaneko, did not change swimming direction depending on the concentrations of Mg2+ and K+ in the reactivating medium. Type II, prepared by a different method, however, reversed the swimming direction depending on the concentrations of Mg2+ and K + in the reactivating medium, even when the concentration of Ca2+ was kept at an extremely low level (below 10−8 M). Decreasing the concentration of Mg2+ induced the type II model to swim backwards.

Intracellular injection of EDTA into a live paramecium cell induced reversal of the direction of ciliary beat. The concentration of Mg2+ at which the reversal of swimming direction occurred varied with the concentration of adenosine triphosphate (ATP) in a manner which suggested that the concentration of free ATP4- might be the critical determinant of swimming direction.
Infiltration and survival: the behaviour of normal, invasive cells implanted to the developing chick wing
Authors: Tickle C. , Crawley A.
Published: April 2021

The invasiveness of mouse lymphocytes and thymocytes, rabbit peritoneal neutrophil granulocytes (PMNs), mouse peritoneal macrophages (both activated and non-activated) and pig endothelial cells was assayed by implanting these cells to the chick wing bud. Ceils of each type moved into the wing mesenchyme, although activated macrophages invaded poorly. PMNs were the most invasive cells and had moved well into the limb after only a few hours. PMNs, lymphocytes and thymocytes were ingested by wing mesenchyme cells. Endothelial cells, however, ingested chick blood cells. The implanted cells showed differences in ability to survive in the limb: PMNs disappeared rapidly, lymphocytes and thymocytes sometimes persisted for 24 h, while grafts of macrophages and endothelial cells were present at 24 h. Mechanisms which might be involved in the invasiveness of these cells, and also in their different abilities to survive in the chick wing, are discussed with particular reference to the production of plasminogen activator.
Necessary amino acids and vitamins for the growth of human diploid fibroblasts
Authors: Litwin Jack
Published: April 2021

Only 2 amino acids and one vitamin were found to be essential for the growth of human embryonic diploid lung fibroblasts when 10% undialysed calf serum was used as a medium supplement. These amino acids were either glutamine + cysteine or serine + homocysteine. Replacing cysteine or homocysteine with cystine or homocystine, respectively, reduced growth. The growth rate in the glutamine+ cysteine medium was slightly less than that in Eagle’s medium, but the in vitro life time was similar.

Folic acid was the only vitamin needed to support cell growth in vitro. The addition of other vitamins had no stimulatory effect with the possible exception of nicotinamide.

When other amino acids were added to glutamine + cysteine none showed stimulatory effects but tryptophan was either toxic or inhibitory for the 3 human diploid strains examined. Serine was inhibitory for WI-38 but not for MRC5 cells.

Subtle nutritional differences appear to exist between fibroblasts of the same type obtained from different embryos.
Ultrastructural cytochemistry of the nucleus in zea mays embryos during germination
Authors: Deltour R. , Gautier A. , Fakan J.
Published: April 2021

The ultrastructure of embryonic root cells of Zea mays was studied from the quiescent stage (dry seeds) to 72 h of germination. Semithin and ultrathin sections of tissues fixed with only glutaraldehyde and embedded in Epon were observed after usual section staining and after cytochemical reactions specific for DNA or preferential for ribonucleoproteins.

In quiescent cells, dense chromatin forms a network which fills a great part of the nucleoplasm. Following germination, gradual dispersion of chromatin occurs: total dispersion is reached at 24 h. After 48 h the chromatin appears moderately condensed again.

The nucleolus is compact and predominantly fibrillar in dry cells. At 48 h a typical pars granulosa is differentiated. At 8 h a pronounced vacuolation of the nucleolus is observed; nucleolar vacuoles persist until 72 h but become less numerous. During the first 8 h of germination a nucleolus organizer region (NOR) in an eccentric position is associated with the nucleolus; by 24 h and later this NOR has disappeared.

No DNA can be visualized in the nucleolar matrix between o and 8 h of germination, whereas later, when the nucleolus is reactivated, DNA is always detected in the nucleolar matrix and vacuoles.

During the first 72 h of germination, heavily contrasted areas, rich in ribonucleoproteins and appearing to be of fibrillar texture, are found in the nucleoplasm, often in close contact with the dense chromatin.

In quiescent cells dense ribonucleoprotein granules, approximately 40 nm in diameter are found dispersed or clustered in the nucleoplasm; after 8h larger (50 nm), dense ribonucleoprotein granules are found frequently clustered in granular areas in the extranucleolar space.

At 8 h of germination, when the nucleolus is temporarily highly vacuolated, unusual 35-nm ribonucleoprotein granules are found both in the smallest vacuoles and on the periphery of the nucleolus.
Different cytoskeletal domains in murine fibroblasts
Authors: Temmink J. H. M. , Spiele H.
Published: April 2021

The morphology of the cytoskeleton of normal 3T3 fibroblasts was studied in the electron microscope on embedded and sectioned cells as well as on critical-point-dried whole mounts. Four ultrastructurally different cytoplasmic domains could be distinguished within every 3T3 cell, namely: Cytocortex, ruffle area, endoplasm, and stress fibre. However, many transitions between the different domains were also found. In addition, 2 other domains were occasionally encountered in the same cells. Based on the knowledge that actin is present in relatively high concentration throughout non-muscle cells and that it can, under different physiological conditions, assume different morphological appearances, an attempt has been made to formulate a hypothesis that links the ultrastructural domains to different cellular functions. Many experimental approaches are available to test the hypothesis and at the same time increase our knowledge of the cytoskeleton of 3T3 cells.
Evidence that spectrin binds to macromolecular complexes on the inner surface of the red cell membrane
Authors: Litman D. , Hsu C. J. , Marchesi V. T.
Published: April 2021

Spectrin binds to a population of high-affinity sites on the exposed surfaces of inverted vesicles prepared from human red blood cell ghost membranes. Optimal spectrin binding requires the presence of monovalent salts but does not require calcium or magnesium. The band 2 subunit of spectrin, prepared in SDS, can also bind to vesicles, but isolated band 1 is inactive.

Pre-incubation of inverted vesicles with antibodies directed against the cytoplasmic segment of band 3 or against bands 4.1–4.2 inhibits the binding of spectrin to the same vesicles. Antibodies against the cytoplasmic portion of glycophorin A have no effect.

These results suggest that spectrin binds to a protein acceptor on the cytoplasmic surface of the red cell membrane which is close to the cytoplasmic segments of bands 3 and 4.1 and/or 4.2.
Role of cell surface receptor mobility in concanavalin a-induced agglutination of novikoff hepatoma and normal rat liver cells
Authors: Mastromarino Paola , Neri Giovanni , Serra Angelo , Walborg Earl F.
Published: April 2021

The relationship between Con A-receptor mobility and Con A-induced agglutination of Novikoff hepatoma and normal rat liver cells was investigated. Novikoff cells, incubated with fluorescein-labelled Con A at 3 °C displayed uniform, ring-like surface fluorescence. Increasing the temperature of the cells to 37 °C caused capping of Con A receptors in approximately 65% of the cells, a phenomenon that could be prevented by prefixing the cells with glutaraldehyde. In spite of these variations in Con A-receptor distribution, Con A-induced agglutination was remarkably constant over a temperature range from 3 to 37 °C. In contrast to Novikoff cells, normal hepatocytes displayed a uniform, ringlike surface fluorescence at both 3 and 37 °C. No capping was observed. However, hepatocytes, similar to Novikoff cells, were agglutinable by low concentrations of Con A. These findings indicate that, in this model system, Con A-induced cytoagglutination is not dependent upon long-range lateral mobility of Con A receptors. The qualitative differences in the lateral mobility of cell-surface Con A receptors of normal and malignant rat liver cells may represent a marker for neoplastic transformation during hepatocarcinogenesis, adaptation to growth in ascitic form, or progression of a tumour to a more malignant state.
Origin and development of free kinetosomes in the flagellates Deltotrichonympha and Koruga
Authors: Tamm Signhild , Tamm Sidney L.
Published: April 2021

The formation of more than half a million free (non-flagellated) kinetosomes in post-mitotic Deltotrichonympha and Koruga from Mastotermes is described. Ladder-like configurations of prokinetosomes extend from the 2 fibrous walls of the centriolar apparatus in the rostrum. The prokinetosomes within the ladders are arranged side by side in 2 layers. Because the fibrous walls are oriented perpendicular to each other, the 2 groups of prokinetosomal ladders are also mutually perpendicular. The prokinetosomes arise continously next to the fibrous walls, and migrate outward along the ladders as they develop. Consequently, progressive stages in kineto-some formation occur sequentially along the ladders in a polarized fashion. A cartwheelstructure appears first. This is followed by the formation of A tubules, B tubules and C tubules in an orderly sequence around the cartwheel (counter-clockwise, viewed from the distal end). The cartwheel ring disappears after the triplets have formed. The new free kinetosomes accumulate in a disorganized mass at the ends of the ladders. Later, the kinetosomes become organized end to end into the polarized chains found in interphase cells. The fibrous wall of the centriolar apparatus is thus a new type of intermediate structure associated with the mass production of basal bodies. It appears to determine the spatial organization of the ‘assembly lines’ of developing kinetosomes.
The effects of applied electric fields on Micrasterias: I. morphogenesis and the pattern of cell wall deposition
Authors: Brower Danny L. , Mcintosh J. Richard
Published: April 2021

Applied electric fields of approximately 14 V/cm have profound effects on the morphogenesis of the unicellular green alga, Micrasterias denticulata. This field corresponds to a potential drop of 15–40 mV across lobes oriented perpendicular to the applied field. These lobes show a galvanotropism toward the cathode. Lobes growing parallel to the field are stunted to varying degrees, depending on their orientation.

As shown by other investigators, most cell wall material is normally deposited at the tips of growing lobes. If, however, cell expansion is osmotically inhibited in electric fields, wall material also accumulates along the cathode-facing (CF) sides of lobes oriented perpendicular to the field. Similarly, in cells growing under the influence of an applied field, radioactively abelled glucose and the methyl groups from methionine are incorporated along the CF sides of lobes as well as the lobe tips. This is also true when the label is added immediately after cells are removed from the fields, indicating that the wall-depositing machinery itself has been temporarily altered by the field.

These results demonstrate that applied electric fields can be a valuable tool in elucidating the mechanisms of growth localization in Micrasterias cells.
Eosinophil interaction with antibody-coated, non-phagocytosable surfaces: Changes in cell surface proteins
Authors: Thorne Kareen J. I. , Oliver Rhonda C. , Glauert Audrey M.
Published: April 2021

Plasma membrane changes during the interaction of human eosinophils with large, antibody-coated, non-phagocytosable surfaces have been investigated in a model system. Human peripheral blood eosinophils were incubated with layers of agar into which tetanus toxoid and human anti-tetanus immunoglobulin, together with an eosinophil chemotactic factor (EOF), were incorporated. Changes in organization of the eosinophil plasma membrane proteins during interaction with the agar layer were detected by lactoperoxidase-catalysed iodination with [125]iodide.

A protein of apparent mol. wt 55000 became newly accessible on the eosinophil surface as a specific consequence of interaction with antigen-antibody complexes in the agar layer. This protein appeared in the early attachment phase of the interaction which preceded extracellular degranulation. Cytochalasin D enhanced its appearance, while Mg2+-deficiency prevented it. A second newly accessible protein of apparent mol. wt 58000 was blocked when ECF was present and may therefore be a receptor for ECF. Other proteins of apparent mol. wt 68000 and 46000 newly appeared at the surface of eosinophils even after incubation in suspension, apparently as a consequence of the rapid cycling of membrane components which occurs in eosinophils.
Microtubule-organizing centres in mammalian cells in culture
Authors: Watt Fiona M. , Harris H.
Published: April 2021

When microtubules in animal cells are dissociated and then allowed to recover, they re-grow from discrete points in the cytoplasm known as microtubule-organizing centres (MTOC). The microtubules may be dissociated by antimitotic drugs such as colcemid, vinblastine and griseofulvin, or by chilling the cells. Immunofluorescence studies show that the number of MTOC seen does not depend on the concentration of antimitotic drug used or the duration of exposure to the drug; the same results are obtained with vinblastine, griseofulvin and colcemid. However, after cold treatment, the proportion of cells showing only a single MTOC is greater than that seen with the antimitotic drugs and may exceed 90 %. Evidence is presented for the view that procedures involving the use of antimitotic drugs give artificially high values for the number of MTOC per cell.
Microtubule-organizing centres in binucleate cells and homosynkaryons
Authors: Watt Fiona M. , Sidebottom E. , Harris H.
Published: April 2021

Immunofluorescence studies showed that most binucleate Vero cells formed by virus-induced fusion or by inhibition of cytokinesis had a single microtubule-organizing centre (MTOC) when examined during the reassembly of microtubules after chilling, but two or more organizing centres when examined after exposure to colcemid. These findings suggest that although binucleate cells initially contain more MTOC than mononucleate cells, the extra MTOC are normally aggregated, so that the number of MTOC in binucleate cells tends to be reduced very quickly to that in mononucleate cells.
Sliding velocity between outer doublet microtubules of sea-urchin sperm axonemes
Authors: Yano Y. , Miki-Noumura T.
Published: April 2021

Using a dark-field microscope equipped with a high-efficiency TV camera including a video tape-recorder, we recorded the sliding movement between outer doublet microtubules of the demembranated axonemes of sea-urchin (Pseudocentrotus depressus and Heniicentrotus puleherrimus) sperm flagella by adding ATP and trypsin at 25 °C. The time and length of the sliding doublet microtubules from axonemes were measured directly from the image on the picture monitor from the video tape.

The sliding velocity was almost constant in the range from o to 2 % polyethylene glycol concentration in the reactivation medium and decreased a little at more than 2 %. We prepared various lengths of axoneme fragments by homogenizing whole axonemes and found that the shorter fragments showed similar sliding velocity to that of longer ones at less than 200 μM ATP, but slightly decreased speed at more than 500 μM ATP. The sliding movement sometimes stopped and the percentage of sliding axonemes was lower below 2 μg/ml trypsin. Above 3 μg/ml the process appeared to be more like disintegration than sliding movement, which may be due to excess digestion by trypsin. Sliding speed was therefore measured in a reactivation medium containing 2 % polyethylene glycol with the addition of ATP and 2 μg/ml trypsin. The velocity increased in proportion to the increase in ATP concentration. was approximately 14 μm/s at 1 mM ATP.

In order to compare the Km for the sliding velocity with that of the ATPase activity of the axonemes, we measured ATPase activity of axonemes prepared and assayed under conditions in which sliding movement in the axonemes could be induced. Neither the curve of ATPase activity nor the curve of sliding velocity plotted against ATP concentration obeyed Michaelis-Menten kinetics. The close relationship between ATPase activity and sliding velocity suggested that ‘sliding-movement-coupled ATPase activity’ may well be reflected in the axoneme ATPase reported here.
Locomotion and cell-substratum contacts ofXenopusepidermal cellsin vitroandin situ
Authors: Radice Gary P.
Published: April 2021

Studies of tissue cell locomotion in culture have revealed much about cell motility, but whether behaviour in vitro resembles movement of the same cells in the animal is not clear. To investigate this, I compared the locomotion and cell-substratum contacts of epidermal cells from Xenopus tadpoles, migrating from explants on glass and plastic, with the same cells spreading in vivo during wound closure. Time-lapse cinemicrography showed that in both cases, cells spread by extending broad lamellipodia across the substratum, and did not form microspikes, filopodia, or blebs. The net rate of translocation was significantly slower in vitro, however, because cells both protruded lamellipodia slower and spent more time stationary or withdrawing, compared with cells in situ. The increased fluctuation seemed in part due to greater tension within the expanding sheet in vitro, since when tension was reduced, for example by wounding, the cells spread with less fluctuation and at a greater rate (6·5 μm/min compared with 0·77 μm/min). Micromanipulation showed that cells adhered to the substratum, both in situ and in vitro, by a broad contact where transmission electron microscopy (TEM) of sectioned material showed the cells to be less than 30 nm from the substratum. A similar separation was observed beneath cells in vitro when viewed in life with interference-reflexion optics (IRM). A few focal contacts (adhesion plaques) were also seen with IRM and TEM of cells in vitro, but were not seen with TEM of cells in situ. Submarginal as well as marginal basal cells of the advancing sheet adhere and spread on the substratum in both situations, whereas cells of the outer layer are passive. Hence, the overall pattern of migration of these cells is similar in vitro and in situ, the differences in rates of movement may be explained in part by the different degree of tension in the epithelium under the 2 conditions.
Adhesion and spreading ofLimulusblood cells on artificial surfaces
Authors: Armstrong Peter B.
Published: April 2021

The horseshoe crab Limulus has a single cell type in the blood, the granular amoebocyte. These cells, which are non-adhesive and non-motile in the blood, transform to an adhesive and motile state following extravasation. In the present study, the events of transformation were studied by time-lapse microcinematography of cells plated on to glass. Following attachment of cells to the glass, the cells protrude filopods and engage in active motility. Motile cells show 2 convertible forms; a contracted form and a reversibly flattened form. Eventually the motile cells undergo irreversible flattening which is accompanied by spontaneous degranulation. The shapes of irreversibly spread cells are influenced by the arrangement of cell-substrate contacts established prior to degranulation, and by the pattern of contact of domains of granule-derived membrane introduced into the cell surface during granule exocytosis and their subsequent endoctyosis by the cell. The clottable protein released by spontaneous degranulation of the amoebocytes undergoes gelation in the absence of bacterial endotoxin. The ability to undergo spontaneous gelation stands in marked contrast to the absolute requirement for endotoxin for gelation of the clottable protein present in ‘Limulus amoebocyte lysate’, a commercially valuable preparation obtained from amoebocytes used to detect endotoxin.
Regulation of macrophage lysosomal enzyme secretion: Role of arachidonate metabolites, divalent cations and cyclic amp
Authors: Mcmillan Rodger M. , Macintyre D. Euan , Beesley Julian E. , Gordon John L.
Published: April 2021

We have investigated the role in macrophage lysosomal enzyme release of arachidonate metabolites, extracellular divalent cations and cyclic AMP (cAMP) which modulate secretion in other cell types. Lysosomal enzyme secretion induced by zymosan was accompanied by release of malondialdehyde (MDA), which is derived from arachidonic acid via prostaglandin synthase. Blockade of MDA formation, by aspirin or indomethacin, was associated with only a small inhibitory effect on lysosomal enzyme release by zymosan: arachidonate metabolites thus play only a minor role in mediating macrophage lysosomal enzyme release.

Zymosan-induced secretion of lysosomal enzymes from macrophages did not require extracellular magnesium or calcium although release was enhanced by magnesium and inhibited by calcium. These effects may be related to an influence of the ions on phagocytosis. Elevation of intracellular divalent cation concentrations, by ionophore A23187, induced release of lysosomal enzymes but this was a result of cell lysis.

Adenylate cyclase stimulants and dibutyryl cAMP produced slight inhibition of zymosan-induced lysosomal enzyme release. Aminophylline and papaverine caused more marked inhibition but their effects may be due to actions independent of phosphodiesterase inhibition.

Our data indicate that arachidonate metabolites and cAMP do not play a major role in regulating zymosan-induced enzyme release from macrophages. Extracellular calcium and magnesium may modulate secretion but the role of intracellular divalent cations remains to be established. We conclude that macrophage lysosomal enzyme secretion is controlled by regulatory mechanisms different from those which control similar degranulation processes in other cell types.
Ultrastructure and histochemistry of the watermelon stigma
Authors: Sedgley Margaret
Published: April 2021

The ultrastructure and histochemistry of the watermelon stigma were followed from 6 days before flower opening to anthesis. Starch and lipid were present in the immature papilla cells but had largely disappeared from the cells by anthesis, when carbohydrate and lipid were present in the stigma secretion external to the cell wall. The mature papilla cells had simple wall thickenings and were transfer cells. The wall thickenings were associated with dictyosomes and secretory vesicles. Other characteristics indicating a secretory function for the papilla cells included plastid—ER complexes and close associations between ER and secretory vesicles at the plasmalemma. Granulocrine secretion involving dictyosomes and ER is suggested for the carbohydrate component of the secretion.
Studies on the surface properties of hybrid cells: III. A membrane glycoprotein found on the surface of a wide range of malignant cells
Authors: Atkinson M. A. L. , Bramwell M. E.
Published: April 2021

We report here the presence of a glycoprotein of apparent molecular mass 90000 daltons on the surface of membranes of malignant cells, which is absent or very much reduced on the surface of non-malignant cells. This glycoprotein is rich in sialic acid and appears to be sensitive to the concentration of cAMP under certain conditions.

Analysis of the labelled sugars present in the glycoproteins of cells metabolically labelled with [14C]glucosamine suggests that all the enzymes necessary for the conversion of the tracer precursor into the sugars normally found to be labelled are present in both the malignant and the non-malignant cells.
Analysis of skin fibroblast aggregation in duchenne muscular dystrophy
Authors: Jones G. E. , Witkowski J. A.
Published: April 2021

Skin fibroblasts from patients with Duchenne muscular dystrophy have a low intercellular adhesiveness compared with normal cells when aggregated in a Couette viscometer (collison efficiencies of 2-52 and 4-62, respectively). The pattern of aggregation was quantitated using a digitizer system to measure the areas of particles (single cells and aggregates) formed after 20 min aggregation. This size analysis showed that the majority of dystrophic cells remained unaggregated but that a small number of very large aggregates was always formed. Normal cell suspensions only rarely contained large aggregates but contained many intermediate-size aggregates. These differences in intercellular adhesiveness and aggregate pattern formation indicate that there may be an alteration in the surface of dystrophic cells.
Comparison of multiple injections with continuous infusion of tritiated thymidine, and estimation of the cell cycle time
Authors: Blenkinsopp W. K. , Gilbert C. W.
Published: April 2021

Labelled nuclei were counted in stratified squamous epithelium in mice killed after 24 h intraperitoneal administration of tritiated thymidine to label cells synthesizing deoxyribonucleic acid. Multiple injections produced the same result as an infusion of tritiated thymidine given after 24 h infusion of saline, but infusion of tritiated thymidine alone produced a different result. Thus, cell proliferation was depressed during the first 24 h of continuous infusion but was normal during the second 24 h.

Comparison of proliferation of the oesophageal epithelium at the level of the thyroid and at the level of the diaphragm showed no difference between the two.

Comparison of male with female mice given 72-h infusions of tritiated thymidine showed that cell proliferation occurred at the same rate in both.

The cell cycle time was estimated in the epithelium of the oesophagus and tongue by comparison of mice given a single injection with mice given multiple injections of tritiated thymidine.
Sodium butyrate blocks hela cells preferentially in early G
1 phase of the cell cycle
Authors: Xue Shaobai , Rao Potu N.
Published: April 2021

The effects of sodium butyrate on the cell-cycle traverse of HeLa cells was re-examined using the kinetic and the premature chromosome condensation methods of cell-cycle analysis. The results of this study indicate that the sodium butyrate effects are dose-dependent and cell-cycle phase-specific. Cells in the early G1 period are the most sensitive to the inhibitory effects of the drug. When HeLa cells in exponential growth were exposed to a 5 mM concentration of butyrate for 48 h, 67% of the cell population was preferentially arrested in the early G1 period as indicated by the condensed morphology of the prematurely condensed chromosomes (PCC). There was no accumulation of cells in the G1 period. The results of this study suggest that hyperacetylation of histones induced by sodium butyrate does not necessarily result in decondensation of chromatin and the butyrate-enhanced protein, which has been reported to be present in butryate-treated cells, may have a role in the regulation of the transition of cells from early G1 to the subsequent phases of the cell cycle.
High-resolution electron microscopy of glycoproteins: The crystalline cell wall of lobomonas
Authors: Roberts K. , Shaw P. J. , Hills G. J.
Published: April 2021

Lobomonas piriformis is a member of an order of green algae (Volvocales) that have crystalline glycoprotein cell walls. As part of a program of investigation of these glycoproteins and their architecture we have studied the cell wall of Lobomonas by a variety of chemical, electron- microscopical and image-analysis techniques. Lobomonas and Vitreochlamys incisa show a very similar structure in their cell walls and represent 1 of the 4 classes into which all the structures of the walls of these algae that we have so far examined fall. The 2 classes that we have previously studied in detail, represented by Chlamydomonas reinhardii and Chlorogonium elongatum, have a crystalline component of the wall that is a more or less smooth continuous surface overlying an amorphous inner wall layer. Although Lobomonas also has this 2-layer structure, the crystalline layer consists of distinct plates, each of which is built around a single, very coherent crystal lattice. The polar nature of the architecture of the cell wall is shown by sectioning and by examination of the cell-wall surface by metal-shadowing of carbon replicas, both of intact cells and of isolated cell-wall plates.

There are great similarities in chemical composition between the glycoproteins of the cell wall of C. reinhardii and those of Lobomonas. Both have a large content of hydroxyproline in their amino acid composition and a sugar/hydroxyproline ratio of about 6·0, and both contain sugar sulphates. Lobomonas however has a large glucose content, whereas Chlamydomonas has almost none. Electron micrographs of walls stained with methylamine tungstate and shadowed specimens show that the Lobomonas crystal structure is entirely different from that of C. reinhardii, and that there is a distinctly different structure in the centre of the plates from that at their edges, although the transition between the 2 areas occurs with no distortion of the crystal lattice. Computer image analysis has been used to calculate reconstructed images of the 2 areas, and by using minimal-dose techniques has yielded 2-dimensional maps of the negatively stained structure at a resolution of 1·8 nm. The 2-sided plane group of both areas of the crystal is P2, and the centre area contains 2 distinct structural units, both centred on dyad axes, together with other more complex features. In the edge structure, one of the structural units appears unchanged, but the other unit has a considerably different appearance. The most likely interpretation of this is as a conformational or positional change in one of the subunits. However, because the underlying lattice is so accurately maintained across this transition, it seems probable that the basic structural arrangement that defines the lattice is common to the 2 areas. Some of the computational and mathematical techniques used in the image analysis have not been previously published and are described in detail and compared with published techniques in an Appendix.
Cell-to-substrate contacts in an adhesion-defective mutant of balb/c3T3 cells
Authors: Yates James R. , Izzard Colin S.
Published: April 2021

The cell-to-substrate contacts of the adhesion-defective mutant, AD6, have been examined by interference reflexion microscopy and compared with those of the wild-type Balb/c3T3 cell. The 2 cell-types differed in their ability to produce focal contacts with the substrate (10–15 nm separation distance). Only 10% of AD6 versus 92% of Balb/c3T3 cells formed these contacts. When present in AD6 the focal contacts were smaller and fewer in number per cell than in Balb/c3T3. Close contact with the substrate (approx. 30 nm separation distance) was formed by both cell types. The absence of the stronger focal contacts accounts for the reduced substrate adhesion of the mutant cells and for other phenotypic characteristics such as reduced spreading, rounded shape, altered pattern of movement, and absence of stress fibres. The reduced adhesion of the mutant has been attributed to a change in the pattern of glycoproteins exposed at the cell surface, which results from a defect in glycosylation. This suggests that normal glycosylation and correct exposure of one or more cell surface components are required for the formation of a specific substrate adhesion, the focal contact, and offers the possibility of identifying individual surface components involved in formation of this adhesion.

Attention is drawn to zero-order minima originating from cell thickness and not cell-to-substrate separation distance in the interference reflexion image.
The amphibian epidermis: distribution of mitochondria-rich cells and the effect of oxytocin
Authors: Brown D. , Grosso A. , Sousa R. C. De
Published: April 2021

It is known that the ion-transporting capacity and the permeability to water of amphibian skins vary greatly both between and within species. Furthermore, the extent to which different skins respond to hormonal stimulation of these parameters also shows considerable inter- and intra-specific variation. As a first step towards defining a possible morphological basis for this physiological heterogeneity, we examined different regions of skins from 3 anurans, Bufo bufo, Rana ridibunda and Xenopus laevis, that are species with widely differing habitats. The mitochondria-rich cell population of the epidermis was counted and the epidermal thickness was measured. There were large differences in the mitochondria-rich cell content and in the epidermal thickness of the skins from different species and from different regions of skin from the same animal.

In a second set of studies, the same morphological features were examined and, in addition, routine functional parameters were measured to monitor some transport properties of the skins used. The skins also varied considerably with respect to short-circuit current, potential difference, water permeability and sensitivity to oxytocin. Although no apparent relationship was noted between either basal or hormone-stimulated physiological parameters and the morphological features of the individual skins, the striking variation in the density of mitochondria-rich cells in amphibian epidermis merits further studies, including the use of techniques or experimental designs that allow the movement of individual species of ion across the skin to be followed.
The structure and chemistry of plastid differentiation during male meiosis in Lilium Henryi
Authors: Dickinson H. G.
Published: April 2021

The unusual content of the plastids characteristic of male meiosis and microsporogenesis in Lilium henryi has been investigated using enzymic digestion of material prepared for electron microscopy. Apart from membranous tubules and osmiophilic droplets, commonly regarded as normal constituents of the stroma of undifferentiated plastids, these organelles contained a single conspicuous association between membrane and particulate material and wefts of filaments. Enzymic digestion revealed the membrane-particle association (MPA) to contain RNA and some protein, and the filaments to be entirely proteinaceous. The use of DNase on this material proved both unreliable and, on occasions, unspecific, so no new information has emerged as to the disposition of DNA within these organelles. Many of the plastids divide immediately after meiosis and the MPAs normally divide in step with the orgenelles. The activities of the MPA and those of the filaments are discussed in terms of changes in the organelle population as a whole, and also in consideration of the fundamental events occurring elsewhere in the cells during the alternation from the diploid sporophyte to the haploid gametophyte.