bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of nucleomorph division in species of cryptophyceae and its evolutionary implications
Authors: Morrall Susan , Greenwood A. D.
Published: April 2021

An ultrastructural study of nucleomorphs in species of Cryptophyceae revealed aspects of division not previously reported, including the formation of a structured fibrous system, which accompanies the ordered alignment, duplication and separation into two groups of the densely staining particles typically characteristic of each nucleomorph. Despite reports indicating the presence of nucleic acids in the nucleomorph, the division process appears to be unlike any known form of nuclear division. However, the possibility exists that the nucleomorph represents the nucleus of a primitive ancestral red algal endosymbiont displaying a form so antique that its nuclear division bears no resemblance to any other known form of mitotic division.
Sensory behaviour in Dictyostelium Discoideum slugs: Phototaxis and thermotaxis are not mediated by a change in slug speed
Authors: Smith Elizabeth , Fisher Paul R. , Grant Warwick N. , Williams Keith L.
Published: April 2021

The speed of sustained migration of Dictyostelium discoideum slugs was similar in a temperature gradient and at different light intensities, including a light intensity sufficient to cause significant disorientation of slugs. No change was observed in slug speed in the presence of high levels of Slug Turning Factor (STF), a low molecular weight compound through which phototaxis and thermotaxis are mediated. Thus orientation of D. discoideum slugs is not mediated by a sustained changed in slug speed and we propose that slug movement is not directly coupled to tactic responses. Slug speed depended on the size, age and genotype of slugs as well as the nature of the substratum (charcoal-containing water agar versus water agar).
Protein and glycoprotein synthesis by friend erythroleukaemic cells during erythroid differentiation
Authors: Marshall Linda M. , Hunt Richard C.
Published: April 2021

The proteins synthesized by Friend erythroleukemic cells (line 707B) have been studied by high-resolution polyacrylamide gel electrophoresis at various stages after the induction of erythroid differentiation by addition of dimethyl sulphoxide to the medium. After 24 h of differentiation, the rate of synthesis of most of the more abundant proteins is reduced, correlating with the reduction in the proliferation rate of the cells. However, the qualitative composition of the major proteins synthesized by control and differentiating cells remains very similar until at least 96 h after the induction of differentiation. Proteins characteristic of the mature erythrocyte membrane are an exception to the reduction in synthesis in line with the proliferation rate, for they continue to be synthesized at similar rates to those found in control cells. Only two major proteins (an as yet unidentified cytoplasmic protein and globin) are reproducibly induced, while the synthesis of a few proteins is almost completely abolished. In contrast to the similarity of the synthesis of the major proteins in the control and differentiating cells, the synthesis of glycoproteins that bind to Concanavalin A is markedly changed. The synthesis of many Concanavalin A-binding glycoproteins is abolished and they disappear from differentiating cells. The synthesis of a major glycoprotein is, however, induced early in differentiation. This protein, which has an apparent molecular weight of 100000, becomes the most abundant Concanavalin A-binding glycoprotein in the cell.
Electrophoretic movement of fertilized sea-urchin eggs
Authors: Oshima Noriko
Published: April 2021

The eccentric shift of the sea-urchin egg within the fertilization membrane under an electric field was analysed by measuring the electrophoretic mobility of the isolated fertilization membrane and that of the egg deprived of the fertilization membrane. In addition, the migration speed of the egg proper was measured within the fertilization membrane under the conditions that: either (1) the movement of the whole egg was arrested, or (2) protamine sulphate was adsorbed on the fertilization membrane to reduce its mobility.

The results led to conclusions that: (1) both the fertilization membrane and the egg cell with the hyaline layer are negatively charged; (2) movement of the normal fertilized eggs is due mainly to the surface charge of the fertilization membrane; and (3) the eccentric position of the egg within the fertilization membrane is due to migration of the egg proper, which is independent of the movement of the whole egg.
Electron microscopic observations on the development and cytochemistry of the large granule complexes in chicken erythrocyte nuclei
Authors: Pearson E.C. , Davies H.G.
Published: April 2021

Large granule complexes are structures found in a small percentage of chicken erythrocyte nuclei when observed in ultra-thin sections in the electron microscope. They consist of an amorphous region associated with a number of large (approximately 30 min) granules. We have shown, by a novel use of phenylhydrazine to synchronize populations of chicken erythrocytes in vivo, that large granule complexes do not occur in the nuclei until the cells have reached one-third to one-half of their normal intravascular lifespan. The mature large granule complexes are formed by aggregation of pre-existing fibrillar, granular and amorphous material, and their presence is correlated with the presence of another ultrastructural feature of the nucleus, the so-called “filled cavities' in the chromatin. Digestion of ultra-thin sections of erythrocytes embedded in the hydrophilic resin glycol methacrylate (GMA) has shown that the major component of the amorphous region is a rather acidic protein that is not haemoglobin, the most abundant protein in the erythrocyte. The large granules also contain protein and, almost certainly, RNA. The problems encountered in reaching this conclusion have emphasized the lack of unambiguous cytochemical tests for use on ultra-thin sections. We have shown that the large granule complex differs in many respects from the nucleolus in the erythrocyte series, even though the two organelles have certain superficial similarities such as their overall dimensions and the presence of granular and fibrillar regions. The most likely function of the large granule complex is as a repository for material, including RNA, the processing of which has ceased in the inactivated erythrocyte nucleus.
Purified tumour angiogenesis factor enhances proliferation of capillary, but not aortic, endothelial cells in vitro
Authors: Keegan A. , Hill C. , Kumar S. , Phillips P. , Schor A. , Weiss J.
Published: April 2021

Purified tumour angiogenesis factor (TAF) obtained from rat Walker 256 carcinoma and found to induce neovascularization in vivo was examined for its effect on endothelial cell cultures of capillary (CBEC), cow aorta (CAEC) and pig aorta (PAEC) in vitro. Treatment with TAF increased the growth of capillary but not aortic endothelial cells, and then only when the cells were growing on a native collagen substratum. These data show an important growth difference between endothelial cells in that the ability to proliferate in response to TAF depends not only on the substratum used but also on the vascular origin of the cells.
Concanavalin-a-mediated thymocyte agglutination: a model for a quantitative study of cell adhesion
Authors: Capo Christian , Garrouste FranÇoise , Benoliel Anne-Marie , Bongrand Pierre , Ryter Antoinette , Bell George I.
Published: April 2021

This report describes a quantitative study of the agglutination of rat thymocytes with concanavalin A (ConA).

The probability that two ConA-coated cells remain bound after centrifugation was determined over a wide range of lectin concentrations. The minimal force required to separate agglutinated cells and the number of ConA molecules bound per cell were measured in similar experimental conditions. Agglutinated cells were examined by electron microscopy to estimate the area of membrane involved in adhesion. The dependence of agglutination on cell metabolism was studied: cold (4 °C), sodium azide (15 mM) and cytochalasin B (10μg/ml) inhibited thymocyte adhesion. The importance of lateral movements of ConA molecules was assayed by measuring the adhesion of ConA-coated glutaraldehyde-fixed thymocytes to untreated cells: substantial binding occurred, but at a reduced level relative to untreated cells.

A mathematical analysis of experimental data allowed the following conclusions. At least 103 ConA bonds were involved in cross-linking two bound cells, which required the lectin molecules to be concentrated in the binding area, at least when low ConA concentrations (0·5 μg/ml or less) were used.The dependence of the binding probability on lectin concentration was fairly linear when the latter was small, which implied that the limiting step in cell-cell adhesion was the formation of a bond between a single ConA molecule and a ligand on the other cell.The mean intercellular-contact time for the formation of this first bond was about 10 s for high concentrations of ligand (8 μg/ml).

It was possible to fit the above data into a physically consistent quantitative model of cell adhesion.
Mechanism of entry and development of Trypanosoma dionisii in non-phagocytic cells
Authors: Glauert Audrey M. , Baker J. R. , Selden Linda F.
Published: April 2021

Cultures of ‘buffalo’ (bison) lung (BL) cells were infected with epimastigotes or trypo-mastigotes of Trypanosoma (Schizotrypanum) dionisii derived from cultures in vitro, fixed after various periods of incubation at 37 °C and examined by light or electron microscopy. Few if any epimastigotes entered the BL cells, but many trypomastigotes did so; they adhered to the cell surface within 2 h and then appeared to sink into furrows on the cell surface until engulfed in parasitophorous vacuoles. Cytochalasin D (5–10 μg ml−1) completely, but reversibly, inhibited entry of trypomastigotes without affecting parasite motility. It was concluded that entry depended on the interaction of stage-specific components on the trypomastigote’s surface with receptors on the BL cells, and that this interaction induced active uptake of the protozoa by a phagocytic process not involving pseudopod formation.

Soon after entry of the trypomastigotes into BL cells, the membranes of the parasitophorous vacuoles disintegrated and the parasites, which were now lying free in the cytoplasm of the host cell, transformed into amastigotes (micromastigotes) during the next 24–48 h. Replication then occurred, followed by transformation, beginning after 3 days, through a transitional promastigote phase to small intracellular trypomastigotes at 7 days. The promastigotes had a characteristic curved protrusion extending from the lip of the flagellar pocket (or reservoir) into the host cell’s cytoplasm. Trypomastigotes, released into the supernatant medium by rupture of the plasma membranes of the BL cells after 8 days, could re-invade other cells.
Mosaic structure in the plasma membrane: spiral arrays of subunits in the cytoplasmic tubules of lamprey chloride cells
Authors: Hatae Tanenori , Benedetti E. Lucio
Published: April 2021

The membrane architecture of the cytoplasmic tubules in lamprey chloride cells has been studied by electron microscopy using thin-section and freeze-fracture techniques.

The chloride cell of lampreys (Lampetra japónica, Petromyzon marinus) is largely occupied with a continuous network of cytoplasmic tubules, which are derived from the invagination of the basolateral plasma membrane The lumenal surface of this tubular network is covered with spirally wound parallel rows of electron-dense material, which consist of linear aggregates of particles. Freeze-fracture of the membrane of the tubules also shows spiral arrangements of particles (∽ 9 nm in diameter) on the P-face and complementary shallow grooves on the Eface. These arrangements of particles are about 17 nm apart and wound at a pitch of about 45°.

These complex organizations of the membrane of the tubules are probably the sites of transport of ion and water, which is essential for the maintenance of ionic homeostasis in both low- and high-salinity environments.
Fine structure of the longitudinal flagellum in Ceratium tripos, a marine dinoflagellate
Authors: Maruyama Tadashi
Published: April 2021

The fine structure of the longitudinal flagellum in Ceratium tripos, which performs not only undulations but also retractions, has been examined in both the retracted and relaxed states. Although conventional fixation always triggered retraction, the flagellum was found to remain relaxed when it was washed briefly with Ca2+-free medium prior to fixation. Previous light-microscopic investigation showed that it contained two fibres, the axoneme and the R-fibre. The present study by transmission electron microscopy has revealed that the axoneme that appeared to be a single fibre under the light microscope is a bundle of four fibres; the 9 + 2 microtubular axoneme, the packing material, the striated fibre, and the paraxial fibre. The first two are common in the longitudinal flagella of dinoflagellates, and the axoneme presumably generates the undulation. The last two are new and unique to the longitudinal flagellum of Ceratittm. The R-fibre, which probably contracts to fold the flagellum during retraction, consists of fine filaments, which pursue a loosely spiral course in the contracted state, but align longitudinally in the relaxed state. Periodic striations appear only on the extended R-fibre. The R-fibre shortens to approximately one third of its extended length and pursues a left-handed helix. The packing material, which sticks to the microtubular axoneme on one side, is connected with the R-fibre on the other side at intervals of approximately 5–8 μm. The retraction seems to be regulated by the Ca2+ concentration in the flagellum.
Observations on the molecular components stabilizing the microtubular system of the marginal band in the newt erythrocyte
Authors: Monaco Gianni , Salustrp Antonietta , Bertolini Bruno
Published: April 2021

Microtubules have been classified as either stable or labile, according to their resistance towards depolymerizing agents. The highest stability belongs to those organized in composite structures, in which many other proteins are associated with the tubulin. Among these micro-tubular systems, the marginal band of amphibian erythrocytes is unusually stable. This system can be readily isolated from Triturus red blood cells, and therefore lends itself very readily to ultrastructural and biochemical analyses.

Immunofluorescence and electrophoretic analyses of the isolated bands reveal 14 components, among which tubulin, actin, myosin and a 90K glycoprotein were identified.

Tannic acid-glutaraldehyde fixation reveals a conspicuous opaque material surrounding the microtubules. Cationized ferritin binding suggests the presence of anionic sites. Moreover, neuraminidase causes the disorganization of the microtubule-associated opaque material.

The 90K glycoprotein is presumed to be related to the unusual stability of the microtubular system forming the marginal band.
Gene expression in Acetabularia. II. Analysis of in vitro translation products
Authors: Shoeman Robert L. , Schweiger Hans-Georg
Published: April 2021

The translation products induced by poly(A)+ RNA from Acetabularia mediterránea, A. cliftonii and A. ryukyuensis in a modified, highly efficient wheat germ cell-free in vitro system were separated by two-dimensional gel electrophoresis. A comparison of the translation products on the basis of their molecular weight and their isoelectric point revealed only a limited similarity between the patterns of the three species. The pronounced species specificity will permit the study of the in vivo translation of heterologous poly(A)+ RNA in Acetabularia cytoplasm.
Infections of Paramecium bursaria with bacteria and yeasts
Authors: Görtz Hans-Dieter
Published: April 2021

Infections of Paramecium bursaria with bacteria and yeasts are reported. Bacteria and yeasts multiply in the algae-free ciliate and are transmitted at various conditions as are symbiotic chlorellae. Like chlorellae, the bacteria and the yeast cells are situated in perisymbiont vacuoles. Both bacteria and yeasts maintain their capability for independent existence and can be grown on standard nutrient agar.

Infection experiments show that aposymbiotic P. bursaria can be infected with Chlorella, bacteria and yeast. CAZore/Za-bearing P. bursaria cannot be infected with bacteria or yeast. Bacteria-bearing paramecia can be infected with Chlorella but not with yeast. Yeast-bearing paramecia can be infected with Chlorella but not with bacteria. Following infections with Chlorella the paramecia lose their bacteria or yeast symbionts. The bacteria found in P. bursaria probably belong to the genus Pseudomonas; the yeast has been identified as Rodutorula rubra.
Redistribution of material labelled with [3H]mannose in amoebae induced to undergo pinocytosis
Authors: Flickinger Charles J.
Published: April 2021

The synthesis, transport, and disposition of material labelled with [3H]mannose were studied by electron microscopic radioautography in normal amoebae and in cells that had internalized cell surface as a result of being induced to undergo pinocytosis. Control amoebae were injected with the precursor and placed in normal medium. The Golgi apparatus and rough endoplasmic reticulum were heavily labelled at the earliest intervals, while radioactivity of the cell surface peaked 12 h after injection of precursor. The experimental cells were injected, placed in bovine serum albumin solution from 15 to 60 min after injection, and then removed to normal medium until fixation. Incorporation of the precursor into the rough endoplasmic reticulum was near normal, but the proportions of grains associated with the Golgi apparatus and the cell surface were greatly reduced. The percentage of grains overlying vacuoles increased 12 h after injection, notably in the case of polymorphous vacuoles and dense vacuoles, both of which were identified as lysosomes with the acid phosphatase reaction. The results suggest that addition to the surface of components labelled with [*H]mannose was diminished following induction of pinocytosis. Incorporation of the precursor appeared to be shifted from cell surface material to lysosomal contents, possibly lysosomal enzymes. It is thought that this shift occurred in response to the need for the cell to digest unusually large amounts of endocytosed protein. Recycling of cell surface under these conditions is considered possible.
Migration of human neutrophils in hydrated collagen lattices
Authors: Grinnell Frederick
Published: April 2021

The migration of human neutrophilic granulocytes in hydrated collagen lattices was studied by a combination of cinemicroscopy, and scanning and transmission electron microscopy. The basic pattern of cell migration in collagen was similar to that observed previously for these cells on inert material surfaces; i.e., a cycle of cell extension and cytoplasmic flow into the leading extension. In general, however, neutrophils in collagen were less spread than on glass or plastic surfaces. Thin lamellipodia were absent and the leading extension of the cells was often an elaborately folded pseudopodium. In addition, neutrophils migrating in collagen were never observed to have retraction fibres at the tail end of the cells, although a uropod was usually seen. In the region of the uropod, extensive blebbing of the cells often occurred, and when this happened, forward movement of the cells ceased. At the ultrastructural level, both the leading pseudopodium and the blebs at the tail of the cell were found to contain a dense cytoskeletal network from which cell organelles were excluded. Finally, the cells were found to be coated with an extensive glycocalyx, and individual collagen fibres were sometimes observed within the glycocalyx.
Similarity of sister-cell trajectories in fibroblast clones
Authors: Levinstone D. , Eden M. , Bell E.
Published: April 2021

The observation that sister cells of a fibroblast division execute somewhat symmetric trajectories has led to the controversial hypothesis that cell pathways on a substrate are preprogrammed in detail. We have investigated symmetry and structure in the paths of 170 human AG1519 sister-fibroblast pairs recorded on film and analysed by interactive computer techniques.

In a set of plots of sister-cell trajectories recorded immediately after cell division, we found an average of 31 % mirror symmetry and 14 % rotation identity after rejecting tracks that crossed over each other, a result in substantial agreement with published data. Such ‘symmetries’ are quite inexact, however. A symmetry-controlled perceptual experiment using a stimulus set based on real tracks showed a bias towards mirror symmetry over identity. A large fraction of paired random trajectories of few independent steps and turning angles can be expected to exhibit true turn symmetry on the basis of chance alone. But as the number of turning angles increases the number of rigorously symmetrical pairs decreases sharply. Subjects classified nearly 50% of 10-step computer generated random persistent trajectory pairs as symmetrical while only a fraction of a per cent are rigorously so. In fact, they were classified as though they contained only three to four random independent steps. The bias of the human observer and chance may thus account for the perception of a high occurrence of sister trajectory symmetry in vitro.

Since branching patterns of sister trajectories do not possess rigorous symmetry, we feel they cannot be taken as evidence of preprogramming. However, the dissimilarity of the structure of sister-cell walks does not rule out the possibility that sister cells are alike in other respects. We found a significant correlation between the time-average velocities of newly born sister cells, and suggest that it and other similarities may be due to the equipartitive character of mitosis. The correlation decays over a 2 · 5-day period after mitosis. But phenotypic sister-cell similarities do not appear to determine the sequence of turning angles in cell walks. If they did a claim might be made for the preprogramming of locomotion.
Phagocytosis by macrophages: III. Effects of heat-labile opsonin and poly(L-lysine)
Authors: Matsui Hiroshi , Ito Tadanao , Ohnishi Shun-Ichi
Published: April 2021

To study the mechanism of action of fresh serum (heat-labile opsonin) and poly(L-lysine) (a non-physiological opsonin) on particle uptake by phagocytes, a kinetic analysis of attachment and ingestion of lipopolysaccharide-coated particles during phagocytosis by mouse peritoneal macrophages was undertaken. The relative attachment rate was obtained from the initial overall rate of phagocytosis. The ingestion rate constant was obtained from the time-course of ingestion of the particles attached to the cell surface into the cytoplasm, using spin-labelled paraffin particles and ascorbate, a membrane-impermeable reducing reagent.

Although the lipopolysaccharide-coated particles readily attached to the cell surface, they were ingested to only a small extent. Treatment of the particles with poly(L-lysine) and fresh serum influenced both attachment and ingestion. Poly(L-lysine) greatly increased the attachment rate, whereas fresh serum decreased it. The attachment rate was found to be closely correlated with the difference in surface charge density of the particles caused by such treatments, increasing with the decrease in negative charge density. Attachment of particles treated with fresh serum was strongly dependent on incubation temperature, and was inhibited by treatment of the cells with cytochalasin B or trypsin, whereas attachment of poly(L-lysine)-treated particles was only slightly, if at all, dependent on incubation temperature or treatment. Divalent cations in the incubation medium stimulated attachment of fresh-serum-treated particles. Treatment of the particles with both poly(L-lysine) and fresh serum made it possible for the particles to be ingested into the cytoplasm. The ingestion rate constants (k) for the two types of particles were almost identical (k = 1’2 × 10−1/min at 37°C), and they showed a similar temperature dependence. They were independent of the divalent cations in the incubation medium. Treatment of the cells with cytochalasin B inhibited ingestion. These results suggest that ingestion of the poly(L-lysine)-treated particles results from electrostatic non-specific interaction between the particles and the cell surface, whereas ingestion of the fresh-serum-treated particles results from specific interaction via ‘ligand-specific receptor)’ on the cell surface. Ingestion proceeded independently of such differences in the interaction, though attachment was strongly dependent on the electrostatic environment of the particle surface.
The quantitative utilization of amino acids and glucose and contact inhibition of growth in cultures of the human diploid cell, WI-38
Authors: Griffiths J. B.
Published: April 2021

There are many reports in the literature showing that contact inhibition of growth is affected by the culture medium. A quantitative study of amino acid and glucose uptake by the human diploid cell line, WI-38 was carried out to determine more precisely what effect nutritional factors have on contact inhibition of growth.

Eagle’s minimal essential medium (MEM) was found to support higher cell yields than Eagle’s basal medium (BME) and for growth to continue beyond 96 h a medium change was essential. However, analysis of the used growth media showed that neither amino acids nor glucose were fully depleted after 96 h. The rate of glucose utilization was in the range 65–100 μg/mg dry wt./h and this agreed very closely with the results of other authors. The pattern of amino acid uptake also closely resembled that for other cell lines except that the utilization of cystine was higher. The nutritional requirements were further studied as the results from the medium analyses failed to explain the growth-promoting activity of MEM. Daily medium changes greatly increased cell yields even though the medium nutrients were not exhausted. This effect was dependent upon fresh medium being used and the only medium component found to be of importance was the amino acid complement. These results are discussed in relation to the low saturation density of diploid cells in culture and a possible explanation is proposed in terms of differences in the cell membrane between normal and altered cells.
A micromass culture method for rat embryonic neural cells
Authors: Flint O. P.
Published: April 2021

A method of culturing early (13-day) rat embryo neural cells is described. Undifferentiated neural epithelium is disaggregated and cultured in small discrete islands. Cells that are destined to differentiate as neurons actively segregate from the other cells in the island and aggregate together into small clumps. Other cells flatten and attach to the substrate and resemble typical fibroblasts throughout the culture period. The clumps of preneuron cells spread out forming large irregular foci. Spreading is mediated by active cell movements. Cells in the foci differentiate as a pure population of neurons identifiable by specific inhibition of 3H-labelled y-amino butyric acid incorporation or by labelling with a monoclonal antibody to GQ-ganglioside. The ganglioside is not found on the cell surface at the start of culture after trypsinization, but emerges during the 5 days of culture. The antigen is similarly not present in the embryonic mesencephalon in vivo at 13 days post coitum, only emerging later in the differentiated midbrain. There is thus an apparent de novo synthesis, which is paralleled in vivo and in vitro.
Fibrinogen And Fibronectin As Substrates For Epidermal Cell Migration During Wound Closure
Authors: Donaldson Donald J. , Mahan James T.
Published: April 2021

Pieces of glass coverslip coated with human fibronectin or human fibrinogen were implanted under one margin of a skin wound on adult newt (Notophthalmus viridescens) hind limbs. In contrast to uncoated glass or glass coated with newt serum, bovine serum or bovine serum albumin, glass treated with either fibronectin or fibrinogen supported considerable epidermal cell migration. When optimal amounts of each protein were used, the amount of migration on fibrinogen-coated glass did not differ from the amount on fibronectin-coated glass or from the amount on the wound bed. Migration on a fibronectin substrate could be blocked by treating the substrate with an antiserum against fibronectin just prior to implantation. Similarly, migration on a fibrinogen substrate could be blocked by exposing it to an antiserum against fibrinogen. While we have yet to determine if fibrinogen and fibronectin are interacting directly with the cell surface, our observations suggest that these two proteins may play an important role in wound closure by providing a suitable substrate for epithelial cell migration.
Cell fractionation with affinity ligands conjugated to agarose-polyacrolein microsphere beads
Authors: Margel S. , Ofarim M. , Eshhar Z.
Published: April 2021

A new effective insoluble support useful for cell fractionation based on agarose-polyacrolein microsphere beads (APAMB) of diameters 150–250 μm has been developed. The synthesized polyacrolein (PA) microspheres, of average diameter 0·2 μm, are provided with reactive aldehyde groups through which various ligands containing primary amino groups are bound covalently in a single step at physiological pH. Antibodies coupled to the microspheres are very effective for labelling of cell surface receptors on human red blood cells and mouse lymphoid cells.

APAMB were obtained by encapsulating the PA microspheres with agarose. Antibodies and lectins bound to the APAMB served to construct affinity columns for the separation of red blood cells and murine lymphocyte subpopulations. Anti-human red blood cell antibodies coupled to antiimmunoglobulin APAMB are effective in separating human from turkey red blood cells, whereas either anti-Thy l·2 anti-immunoglobulin antibodies or soybean agglutinin coupled to APAMB have proved useful for the separation of T and B cells from heterogeneous population of spleen cells. The separation procedure is simple, rapid and effective. The viability of the fractionated cells is unaffected by the procedure and the recovery of the cells is high: between 80 % and 100 %.
Theoretical Analysis Of A Method For Determining The Pattern Of Macromolecular Synthesis During The Cell Cycle
Authors: Fraser R. S. S. , Barnes A.
Published: April 2021

The dual-labelling centrifugal-elutriation method has been extensively used to study patterns of macromolecular synthesis and accumulation in the yeast cell cycle. Cells are long-term labelled with a radioactive precursor for about 1· 5 cycles (a measure of macromolecular mass), then pulse-labelled with a precursor containing a different radioactive isotope for the final 0·1 cycle (a measure of rate of synthesis). Harvested cells are fractionated into cell cycle stages by centrifugal elutriation, and changes in pulse: long-term labelling during the cycle determined. This pattern of change is compared with theoretical changes in rate: mass calculated for various patterns of synthesis. Using this method, it has been suggested that rates of synthesis and accumulation of several types of RNA and protein all increase exponentially through the cycle.

In contrast, experiments using synchronous cultures or zonal centrifugation for cell cycle analysis have suggested other synthetic patterns, including periodic doubling in rate in each cycle. In this paper we analyse whether the dual-labelling, centrifugal-elutriation method is capable of discriminating between exponential and periodic rate-doubling patterns. Three possible sources of imprecision in the method and its application are examined.

(1) Theoretical rate: mass curves have been simulated for macromolecules with a wider range of properties than previously considered. It is shown that for some important classes, such as messenger RNAs, with turnover rates in the range measured experimentally, and proteins, differences between rate: mass curves for exponential and periodic rate-doubling models are considerably smaller than previously suggested.

(2) Long-term labelling is shown to be an accurate measure of macromolecular mass, but pulse-labelling can be inadequate as a measure of rate of synthesis. The error is greater with RNAs with faster turnover, and again reduces the ability of the method to discriminate exponential and periodic rate-doubling models of synthesis.

(3) Imperfections in cell cycle fractionation by centrifugal elutriation are examined, and by computer simulation it is shown that these also reduce the ability of the method to distinguish between the two models of synthesis.

The three sources of imprecision are cumulative. It is concluded from simulation analyses that the differences between exponential and periodic rate-doubling patterns analysed by the method would be so small as to be almost impossible to establish against the background of error in experimental measurement. We therefore suggest that in practice, the dual-labelling centrifugal-elutriation method is unable to discriminate between the exponentially increasing and periodic ratedoubling models.

The mathematical treatment developed in this paper should be applicable to analysis of other methods and cell cycle events.
Regulation Of Ciliary Pattern In Dileptus (CILIATA) : II. Formation Of A Cortical Domain Of Sensory Cilia From A Domain Of Locomotor Cilia
Authors: Golinska K.
Published: April 2021

The surface of the ciliate Dileptus contains locomotor and sensory domains. Each domain contains cilia of its own kind, arranged in a characteristic pattern. Transformation of a portion of the locomotor area into the sensory domain has been studied. Locomotor ciliary units in the transforming area undergo resorption of ciliary shafts, which are subsequently replaced by shafts of a sensory type. Anterior to each transforming ciliary unit a new one is formed, and both acquire sensory rootlets. As a result, a double-kinetosomal sensory unit emerges. A regulatory change in structure occurs over a definite area that is determined to become the sensory cortical domain.
Ca2 +-dependent regulation of beat frequency of cilia in Paramecium
Authors: Nakaoka Yasuo , Tanaka Haruhiko , Oosawa Fumio
Published: April 2021

Triton-extracted models of Paramecium cells prepared in the presence of Mg2+ and EGTA showed Ca2+ sensitivity not only in the direction of beat but also in the beat frequency of cilia. The beat frequency increased over a range of concentration of Ca2+ from 2 × 10−7to 4 × 10−7 M, in which the model swam forwards. The frequency increased also above 10−6M-Ca2+, in which the model swam backwards. The increase in frequency was inhibited by calmodulin antagonists. Intracellular injection of a Ca2+ buffer giving a free Ca2+ concentration of 2 × 10−7 to 5 × 10−7M in intact cells induced an increase in the beat frequency. Therefore, it is very likely that the beat frequency of cilia is regulated by the intracellular concentration of Ca2+.
Permissive effect of cytochalasin B on DNA synthesis in concanavalin-A-treated lymphocytes
Authors: Sundqvist K.G. , Wanger L. , Ensgstom W.
Published: April 2021

Unfractionated or T-cell-enriched human lymphocytes can be stimulated to undergo DNA synthesis and mitosis by the addition of polyclonal cell activators such as the plant lectins phytohaemagglutinin and concanavalin A (ConA). Under conventional culture conditions stimulated cells cease proliferating only a few days after the first cells have initiated DNA synthesis. Cytochalasin B (CB), which is non-mitogenic per se, causes a prolongation of the period during which ConA stimulates DNA synthesis from normally 3–5 days to more than 3 weeks. The CB-induced prolongation of cell proliferation is clearly stage-specific in the sense that the CB effects are exerted after an initial period of 24 h and do not come into effect until 48 h after onset of ConA stimulation. In contrast, CB exerts a slight suppressive action on DNA synthesis between 24 h (when activated cells initiate DNA synthesis) and 48 h after onset of stimulation. These two separate effects of CB, i.e. augmentation of lymphocyte stimulation 48 h after stimulation, and suppression of stimulation before this point of time, are relatively independent of the concentration of CB.
Desmosomes in hamster cheek pouch epithelium: Their quantitative characterization during epithelial differentiation
Authors: White F. H. , Gohari K.
Published: April 2021

Desmosomes in stratified squamous epithelia appear to exhibit quantitative alterations during differentiation. In this work we use stereological and other morphometric methods to quantify these structures in epithelial cells from defined basal, spinous and granular strata. Hamster cheek pouch mucosa from five animals was processed for electron microscopy using strictly standardized techniques and a stratified random sampling procedure was used to obtain micrographs of cells from basal, spinous and granular layers. Stereological intersection counting techniques were used to determine for each layer the relative surface area of plasma membrane occupied by desmosomes (Ss), the number of desmosomesper unit surface area of plasma membrane (NS), the mean individual desmosomal diameter and the mean individual desmosomal surface area . In addition, estimates of nuclear volume were obtained by direct measurement of nuclear profiles and volume-to-surface ratios were obtained by a combination of point and intersection counting, which enabled estimates for the volume (Vccell) and plasma membrane surface area (SPM) of the ‘average’ cell within each stratum to be acquired. Using this information, it was then possible to calculate both the total surface area (S) and the number (N) of desmosomes on the plasma membranes of average cells.

The parameters SS and NS showed progressive increases between basal and granular layers, whereas values for and were lower in granular cells when compared with basal and spinous cells. The parameters Vccell, SPM, S and N all increased progressively and significantly during differentiation. Between basal and granular layers, the mean cell volume and surface area had each increased approximately threefold, whereas the surface area and number of desmosomes on the average cell plasma membrane had increased approximately seven- and eleven-fold, respectively. Granular cells thus possess more numerous desmosomes, which occupy a greater proportion of the plasma membrane area but which are individually smaller, when compared with basal and spinous layers.
A neurofibrillar method stains solitary (primary) cilia in the mammalian retina: Their distribution and age-related changes
Authors: Boycott B. B. , Hopkins J. M.
Published: April 2021

Richardson’s reduced silver method, developed for the staining of autonomic nerve fibres in the mammalian intestine, is shown consistently to stain solitary (primary) cilia and diplosomes of the cells of the retinae of cats and rabbits. The cilia comprise a centriole, a basal body and an axoneme with a 9+0 complement of microtubules.

Probably all retinal cells possess a cilium during their development but, contrary to previous reports, not all retain the axoneme after birth. Axonemes are absent from horizontal, bipolar, microglia, Müllerian, and probably some other glial, cells; all of which showed paired centrioles (diplosomes) after staining. Photoreceptor, amacrine, Interplexiform, displaced amacrine and ganglion cells have each one cilium. These differences between cell types persist, without significant change, in the retina of adult rabbits up to the age of 2 years, and in the cat up to 5 years.

The alpha-type ganglion cells of the cat are an exception. In 4 to 8-week-old kittens they are all ciliated, like other types of ganglion cells. But by two years about 30% of central area α-cells lack an axoneme. Individual cells may have only diplosomes, unusual dispositions of the centrioles in the perikaryal cytoplasm, or even show complete loss of the whole ciliary apparatus. By 5 years of age the proportion of those α-cells showing unusual arrangements has increased to approximately 70%, while less than 5% of the other types of ganglion cells are so affected. Cilia of peripheral α-cells change at a different rate and by 5 years of age are approximately like the 2-year-old central area population.
Role Of Glycosaminoglycans And Collagen In The Development Of A Fibronectin-Rich Extracellular Matrix In Cultured Embryonic Corneal Epithelial Cells
Authors: Mattey D. L. , Garrod D. R.
Published: April 2021

Corneal epithelial cells from 15-day chick embryos produce a fibronectin-rich extracellular matrix when cultured on glass, plastic and fibronectin-coated substrata. Cell culture in the presence of Streptomyces hyaluronidase or chondroitinase ABC resulted in considerable reduction of the matrix; collagenase had a lesser effect but nevertheless also reduced the matrix. In all enzyme treatments the cells attached and spread to form characteristic epithelial cell islands, but the margi nal cells of these islands showed a marked reduction in the number of lamellipodia and focal contacts. Also, the immunoAuorescent staining pattern for fibronectin was considerably reduced. Control cells cultured on a fibronectin-coated surface were able to reorganize the fibronectin into fibrils, whereas cells cultured in enzymes showed little or no ability to do so. The cellular reorganiza tion of fibronectin could also be inhibited by the addition of L-azetidine-2-carboxylic acid (LACA), an inhibitor of collagen secretion. Cells plated out in the presence of LACA spread much better on collagen substrata than on plastic, glass or fibronectin. However, in all cases very little fibronectin matrix was detectable in the epithelial islands.

The results suggest that components of the extracellular matrix (ECM) such as collagen, hyaluronic acid and chondroitin sulphates are not essential for the initial attachment and spreading of corneal epithelial cells in culture, but are important in the development of the ECM, and in maintaining a flattened morphology and spreading behaviour. It is suggested that fibronectin plays an important role in these interactions and that the ability of cells to organize fibronectin into fibrils is dependent on the presence of other ECM components such as glycosaminoglycans and collagen.
The cytoskeleton of the apical border of the lateral cells of freshwater mussel gill: Structural integration of microtubule and actin filament-based organelles
Authors: Reed William , Avolio Jock , Satir Peter
Published: April 2021

The coexistence of densely packed microtubule- and microfilament-based elements in the apex of ciliated epithelial cells, such as the lateral (L) cells of freshwater mussel gill, suggests that with this system it may be possible to define structural connections and interactions that permit integrated cytoskeletal responses to known physiological stimuli. In this study we examine the structure of the L cell apex in detail. The central elements of the elaborate cytoskeleton of the cortex are the basal bodies whose specialized accessory processes are points of integration and the focus of cortical microtubule and microfilament networks. Each basal body supports a cilium and interacts with adjacent basal bodies and with the cell periphery via a dual set of fibre-containing flat trabeculae, both of which are attached to a special organizing centre, the basal foot cap. The distal trabecula is composed of microtubules and the proximal of microfilaments. Connecting the trabeculae, at vertices in the filamentous grids, are core bundles of microfilaments from apical microvilli. In this way, a zig-zag pattern that characterizes microvillar organization at the cell surface is generated. At the cell periphery, the microfilaments from basal foot caps join a peripheral band of microfilaments that underlies the cell border and is associated with four special sites, one in each corner of the cell. Mussel gill epithelial cells contain a polypeptide that resembles actin in its mobility in sodium dodecyl sulphate/10% (w/v) polyacrylamide gels and its affinity for DNase I. Decoration with heavy meromyosin demonstrates that many microfilaments of the L cell apex contain actin, including the microvillar core and peripheral band microfilaments. Actin-associated proteins are also present in these epithelial cells. The actin filaments of the peripheral band are organized to support contraction of the cell border, which would also affect each element of the cortex. This structural complexity, combined with the limited number of modes of interaction between various elements, suggests that the L cell apical cytoskeleton endows the cell with significant positional and morphogenetic information that could be used to compute organellar and cytoskeletal lengths, spacing and changes upon stimulation.
Non-random chromosome segregation in Neocurtilla hexadactyla is controlled by chromosomal spindle fibres: An ultraviolet microbeam analysis
Authors: Wise Dwayne , Sillers Peggy J. , Forer Arthur
Published: April 2021

Single spindle fibres in Neocurtilla spermatocytes were irradiated by means of an ultraviolet microbeam. Irradiations were with monochromatic ultraviolet light. The single sex chromosome (the X1 univalent) reoriented after irradiation of its spindle fibre or of any of the spindle fibres associated with the heteromorphic bivalent (the X2Y bivalent): the X1 moved toward the Y half-spindle, and sometimes rotated as it moved. Irradiations of autosomal spindle fibres did not induce X1 movements, and hence the induction of reorientation is specific to irradiation of the spindle fibres associated with X1 or X2Y. In no case did the X2Y bivalent reorient; hence, the X1 is the active chromosome in ensuring that there is non-random segregation in Neocurtilla spermatocytes. The irradiations sometimes caused the X2Y bivalent to contract, but the reorientation movements of the X1 were independent of the contraction of the X2Y bivalent. We suggest that the X1 and X2Y chromosomal spindle fibres form a network that is able to send signals to the X1 univalent to cause it to reorient.
Quick-freeze, deep-etch rotary replication ofTrypanosoma cruziandHerpetomonas megaseliae
Authors: Souto-Padrón Thais , Souza Wanderley De , Heuser John E.
Published: April 2021

The fine structure of epimastigotes of Trypanosoma cruzi and promastigotes of Herpetomonas megasehae was analysed in replicas of quick-frozen, freeze-fractured, deeply etched and rotary-replicated cells. Using control cells and cells treated with Triton X-100 before glutaraldehyde fixation, images were obtained that showed connections of the sub-pellicular microtubules with each other, with the plasma membrane, and with the endoplasmic reticulum. Images were also obtained that showed the DNA network in the kinetoplast. Filamentous structures were found to connect the kinetoplast to the basal body, and to connect the main basal body to the accessory one. In addition, deep-etch images of detergent-extracted flagella display dynein arm substructure and the filamentous architecture of the paraxial structures.