bluuebunny/crossref_metadata_2025 huggingface dataset:
Behaviour of thymocyte nuclei in non activated and activated mouse oocytes
Authors: Czołowska Renata , Modliński Jacek A. , Tarkowski Andrzej K.
Published: April 2021

Cells originating from the thymus of newborn mice were fused with mouse oocytes using polyethylene glycol. The behaviour of thymocyte nuclei was studied in non-activated metaphase II oocytes, and in oocytes activated in vitro with ethanol.

In non-activated oocytes all thymocyte nuclei undergo premature chromosome condensation with individualization of chromosomes; the chromosomes form separate groups in the cytoplasm, or are assembled around the metaphase II spindle, or located on the extra-spindle.

In activated oocytes thymocyte nuclei start to develop along a pronucleus-like pathway (decon-densation, visualization of nucleoli, swelling) and increase up to 200 times in volume during 24h culture in vitro, eventually reaching the size of a fully grown pronucleus. Activation/fusion timing seems to be critical for the full remodelling of thymocyte nuclei. Nuclei introduced before (10–30 min) or shortly after (up to 60 min) activation often grow larger than the female pronucleus. Those introduced into oocytes long before activation (>30min) undergo premature condensation with subsequent reformation of nuclei that are sometimes deficient (as indicated by the presence of micronuclei), or of hybrid character. Nuclei introduced late after activation (>60min) are mostly doomed to retarded development.

The implications of the present observations for nuclear transfer experiments in mammals are discussed.
The synaptology of the granule cells of the olfactory bulb
Authors: Price J. L. , Powell T. P. S
Published: April 2021

The synapses related to the granule cells of the olfactory bulb of rat brain have been studied in aldehyde-fixed material. The synapses can be divided into three classes: (1) those which have asymmetrical synaptic membrane thickenings and spheroidal synaptic vesicles; (2) those with symmetrical synaptic thickenings and flattened vesicles; and (3) the reciprocal synapses, one half of which (from mitral to granule cell) has an asymmetrical synaptic thickening associated with spheroidal vesicles, while the other half (from granule to mitral cell) has a symmetrical synaptic thickening and flattened vesicles. Qualitative observations, supported by preliminary quantitative measurements, suggest that it may be possible to divide both the spheroidal and flattened-vesicle types into two further varieties, on the basis of size, The smaller variety of spheroidal vesicles is found in most axon terminals, while the larger spheroidal vesicles are present in mitral cell dendrites and in some of the axon terminals. The flattened vesicles associated with symmetrical synapses which are oriented on to the granule cells are smaller than the spheroidal vesicles, but the flattened vesicles in the spines and gemmules of the granule cells are the same size or larger than the spheroidal vesicles. The division of flattened vesicles into two sizes is supported by statistical analysis of measurements of these vesicles, but because of difficulty in identifying the axon terminals with asymmetrical synapses there is no quantitative evidence for such a division of spheroidal vesicles.

The asymmetrical synapses are found predominantly on spines, gemmules, and dendritic varicosities, although they are occasionally present on shafts of dendrites and on the cell somata. The symmetrical synapses are almost completely restricted to the shafts of the peripheral processes and the deep dendrites, and to the cell somata; only very rarely are synapses of this type found on spines, and then always in conjunction with an asymmetrical synapse.
The haemoglobin in the condensed chromatin of mature amphibian erythrocytes: a further study
Authors: Small J. V. , Davies H. G.
Published: April 2021

The condensed chromatin in mature nucleated erythrocytes is surrounded by nuclear haemo-globin at a concentration about equal to that in the cytoplasm. New measurements employing improved fixation, glutaraldehyde instead of OsO4, and microspectrophotometnc analyses instead of photographic photometry at one wavelength, show that previously reported values for the content of haemoglobin in the mass of the chromatin in Triturus crutatus, 45–50%, were far too high. In the condensed chromatin of 3 species of amphibia the concentrations of intrachromatin haemoglobin relative to the cytoplasm are 10% (Triturus crutatus), 10% (Necturus maculosa) and 8 % (Amphtuma trtdactylum). It is concluded that haemoglobin is only a minor component of chromatin, and this result is discussed in relation to the condensation of erythrocyte chromatin and observations on its ultrastructure.
The spindle as a basal body distributor: a study in the meiosis of the male silkworm moth, Bombyx mori
Authors: Friedländer M. , Wahrman J.
Published: April 2021

The spindle of metazoan cells functions as a dual distributor that guarantees the accurate segregation of both chromosomes and centnoles (basal bodies). This combined mechanism may have evolved from the separate distribution devices for chromosomes and basal bodies found in Protozoa.

Typical eupyrene spermatocytes of the silk moth were compared with atypical apyrene spermatocytes. (a) Long microtubules, persisting during centnolar movements, develop in the meiotic prophases in continuity with the centrtoles (b) There is no longer a centriole-microtubule continuity at metaphase-anaphase (c) Spindles comprise microtubules and endoplasmic reticulum (ER). The microtubules form a barrel-shaped structure terminating far in front of the centrioles. The two types of spermatocytes differ in the structure of the ER, which is vesicular in the eupyrene and lamellar in the apyrene line. It is suggested that the ER influences the anaphase movement of chromosomes, (d) The chromosomes lack localized centromeres. Microtubules penetrate all along the polar faces of the eupyrene metaphase chromosomes. The apyrene chromosomes form irregular blocks that are penetrated by microtubules all around their periphery, (e) The centriole comprises 3 concentric zones. Typical changes in the centnole are correlated with changes in the cell cycle. Replication, de novo formation and disappearance of centrioles are manifestations of the state of flux of the microtubules.
Low-angle x-ray diffraction and electron-microscope studies of isolated erythrocyte membranes
Authors: Knutton S. , Finean J. B. , Coleman R. , Limbrick A. R.
Published: April 2021

Two alternative sequences of low angle X-ray diffraction patterns (Type I and Type II) have been observed during the controlled dehydration of rat (and human) erythrocyte ghost preparations in which the residual haemoglobin content has varied.

The Type I sequence has been obtained when haemoglobin has comprised more than 30 % of the total protein of the membrane preparation. It features an initial lamellar pattern that has been interpreted in terms of a predominantly continuous lipoprotein sandwich structure. Subsequent changes in diffraction pattern have been suggested to represent a partial breakdown of the lipoprotein structure to give a multiphase system.

The Type II sequence was most readily obtained from haemoglobin-free ghosts. At no stage during the dehydration of these ghosts did the diffraction feature a stable lamellar pattern. At all levels of hydration the X-ray reflections appeared to represent independent lipid and lipoprotein phases. Osmium tetroxide fixation of haemoglobin-free membranes prevented the separation of lipid and lipoprotein phases during dehydration.

Comparisons of electron micrographs of condensed membrane preparations have revealed some structural differences between membranes which give rise to the Type I and Type II diffraction sequences.
Growth and macromolecular synthesis in the 3T6 mouse fibroblast: I. general description and the role of ascorbic acid
Authors: Levene C. I. , Bates C. J.
Published: April 2021

The growth of the 3T6 mouse fibroblast and synthesis of macromolecules has been studied over the last 6 days of the cultures’ 14-day life span. The effect of ascorbic acid was also tested.

During this period, the cells synthesized collagen, as judged by the appearance of non dialysable hydroxyproline, which was identified by chemical assay and by radioactive incorporation studies. A high proportion of the collagen in the cell layer was insoluble in 0·1 N acetic acid. Of the hydroxyproline synthesized in the presence of ascorbic acid, about 75 % was eventually liberated into the growth medium, and about 25–30% of the liberated material behaved as free hydroxyproline. In the absence of ascorbic acid, the cell layer hydroxyproline was reduced to one-third, but the growth medium hydroxyproline was unaffected.

The cells also synthesized glycosaminoglycans, as judged by the appearance of cetyl pyri dinium-precipitable uronic acid, and the incorporation of labelled glucosamine into macro molecules. A large proportion of this material has the properties of hyaluronic acid. Ascorbic acid had no detectable effect on overall glycosaminoglycan synthesis, in contrast to healing tendonectomy wounds in guinea-pigs.

Cell proliferation and general protein synthesis were virtually unaffected by ascorbic acid. Whereas general protein synthesis, like cell proliferation, declined in the ageing culture, glycosaminoglycan synthesis and collagen synthesis continued at a steady or increasing rate.
Maturation of the reticulocyte in vitro
Authors: Gronowicz Gloria , Swift Hewson , Steck Theodore L.
Published: April 2021

The maturation of reticulocytes into erythrocytes was demonstrated in vitro. Reticulocytosis was induced in rats by repeated bleeding or by phenylhydrazine injections. Whole blood samples were then incubated for 2 days at 37 °C. Reticulocytes in culture changed from poly tabulated, monoconcave or triconcave forms to biconcave disks. During the first 12h in vitro, the average reticulocyte count decreased from 39% to 12%, and the membrane-bound organelles, ribosomes and exocytic figures in the remaining reticulocytes were markedly diminished. In contrast, the number of red cells containing inclusions of denatured haemoglobin (Heinz bodies) in phenylhydrazine-treated blood did not decline. The reduction in reticulocyte count was not the result of differential cell destruction, since little haemolysis occurred in vitro.

During red cell maturation three modes of organelle removal were observed particularly well when mitochondria were followed by cytochrome oxidase cytochemistry. First, some mitochondria degenerated, presumably through autolysis, by swelling, losing cristae and forming small single membrane-bound vesicles. Second, individual mitochondria became enclosed in vacuoles that fused with the plasma membrane and expelled their mitochondria by exocytosis. Third, autophagic vacuoles containing mitochondria, cytosol and membrane fragments fused with existing lysosomes. We conclude that all aspects of normal reticulocyte maturation occur in vitro, independent of the spleen, including the removal of organelles and the assumption of the mature biconcave disk shape.
Regulation of a ribonucleoside reductase during the early generative phase in Acetabularia
Authors: Groot Egon J. De , Schweiger Hans-Georg
Published: April 2021

The activity of a ribonucleoside reductase was estimated during the life cycle of Acetabularia. During the early generative phase the enzyme activity was dramatically increased. Regulation of the ribonucleoside reductase was observed even in the absence of the nucleus. The increase in activity was inhibited by chloramphenicol but not by cycloheximide. These results indicate that the enzyme is translated on 70S ribosomes.
Chemotactic factor binding by metastatic tumour cells: Evidence for a formyl-peptide receptor on a non-myelogenous cell
Authors: Marasco Wayne A. , Ward Peter A. , Feltner Douglas E. , Varani James
Published: April 2021

Analysis of fMet-Leu-[3H]Phe binding to Walker 256 carcinosarcoma cells demonstrated both saturable and reversible binding, and indicated the presence of a single population of binding sites having an equilibrium dissociation constant: KD = 15·7 ± 3·3× 10−9M, and with 2425 +204 binding sites per cell. The specificity of the binding site was investigated by competitive inhibition of fMet-Leu-[3H]Phe binding studies using 10 oligoformyl peptides. These results demonstrated an order of peptide reactivity with marked similarity in specificity to the leucocyte binding sites for the formyl-peptides. The most active peptides also had potent agonist activity as determined by their ability to increase the cells’ adherence response to nylon-wool fibres. In addition, a competitive antagonist of the formyl-peptide receptor, tert-butoxy-Phe-Leu-Phe-Leu-Phe, completely abolished the adherence response induced by fMet-Leu-Phe, but had no inhibitory effect on the adherence response caused by the tumour-promoting agent, phorbol myristate acetate.

These data demonstrate that formyl-peptide receptors may be more common than we have anticipated and may be found on cells not derived from the myeloid series. Furthermore, these studies advance our understanding of stimulus-coupled responses in tumour cells.
Biochemical evidence for the presence of an actin protein in Tetrahymena pyriformis
Authors: Mitchell E. Jane , Zimmerman Arthur M.
Published: April 2021

A protein from an ATP extract prepared from an acetone powder of Tetrahymena pyrifonnis GL was identified as actin. The protein migrated slightly behind muscle actin on sodium dodecyl sulphate (SDS)/10% polyacrylamide gels (SDS/PAGE) with an apparent molecular weight of 47500 (47·5 ×103Mr). Partial proteolysis of this band with Staphylococcus aureus V-8 protease followed by electrophoresis revealed a pattern of peptides in which at least four peptides were similar to those observed after digestion of rabbit skeletal muscle actin. The 47·5 × 103 Mr protein appeared particularly susceptible to endogenous proteolvtic cleavage, which was inhibited by leupeptin. An ATP extract prepared with leupeptin was applied to a DNase I-affinity column and a distinct peak was eluted with 3 xi-guanidincHCl; the DNase I-binding protein appeared as a distinct band on SDS/PAGE with an apparent molecular weight of 47·5× 103. Mr. In the absence of leupeptin, the DNase I-binding protein appeared as a broad 34×103Mr band on gels. Both the ATP extract and the DNase I-binding protein showed reactivity with commercially available antiserum raised against native chicken skeletal muscle actin as determined bv an enzvme-linked immunosorbance assay (ELISA). Immuno-blotting-studies and affinity purification of this antiserum showed that the recognition was not specific to the 47·5×103 Mr protein. However, using affinity-purified anti-actin antibodies raised against denatured actin from chick smooth muscle, recognition of the 47’5×103Mr protein and a 34×103Mr protein was shown. In negatively stained preparations from an ATP extract after two cycles of polymerization and depolymerization there were filaments, 8–12nm diameter, which did not decorate with subfragment S-l of myosin, but which resembled intermediate filaments. Analysis of these filaments on SDS/PAGE indicated an intensely stained 54×103Mr band. It is suggested that, in vitro, Tetrahymena intermediate filaments assemble under conditions expected to assemble actin filaments. Thus, in Tetrahymena there is a protein that resembles actin in its extractability, molecular weight, peptide pattern after partial proteolysis, DNase I-binding capacity and reactivity with anti-actin antibodies. However, this protein did not assemble into actin filaments in crude extracts.
Binding of Tetrahymena dynein to axonemes of Marsilea vestita lacking the outer dynein arm
Authors: Hyams Jeremy S.
Published: April 2021

Axonemes from the heterosporous water fern Marsilea vestita were fixed in the presence of tannic acid and examined by thin-section electron microscopy. Transverse sections revealed the normal 9+2 configuration except for the absence of the outer of the two dynein arms. Both arms were normally preserved in parallel preparations of Chlamydomonas axonemes. Isolated dynein from the ciliated protozoon Tetrahymena bound to Marsilea axonemes at the site normally occupied by the outer arm. Dynein binding was partially reversed by ATP as judged by both electron microscopy and polyacrylamide gel electrophoresis. This system should provide a valuable insight into the biochemistry and function of the inner dynein arm and the relationship of the two arms to motility in more conventionally equipped axonemes.
Differentiation in Trypanosoma brucei: Host-parasite cell junctions and their persistence during acquisition of the variable antigen coat
Authors: Tetley L. , Vickerman K.
Published: April 2021

Acquisition of the variable antigen-containing surface coat of Trypanosoma brucei occurs at the metacyclic stage in the salivary glands of the tsetse fly vector. The differentiation of the metacyclic trypanosome in the gland has been studied by scanning electron microscopy and by transmission electron microscopy of thin sections and freeze-fracture replicas. The uncoated epimastigote trypanosomes (with a prenuclear kinetoplast) divide while attached to the salivary gland epithelium brush border by elaborate branched flagellar outgrowths, which ramify between the host cell microvilli and form punctate hemidesmosome-like attachment plaques where they are indented by the microvilli. These outgrowths become reduced as the epimastigotes transform to uncoated trypomastigotes (with postnuclear kinetoplast), which remain attached and capable of binary fission. The flagellar outgrowths disappear but the attachment plaques persist as the uncoated trypomastigotes (premetacyclics) stop dividing and acquire the surface coat to become ‘nascent metacyclics’. Coat acquisition therefore occurs in the attached trypanosome and not, as previously believed, after detachment. Coating is accompanied by morphological changes in the glycosomes and mitochondrion of the parasite. Freeze-fracture replicas of the host-parasite junctional complexes show membrane particle aggregates on the host membrane but not on the parasite membrane. It is suggested that disruption of the complex occurs when maximum packing of the glycoprotein molecules has been achieved in the trypanosome surface coat, releasing the metacyclic trypanosome into the lumen of the gland.
Regulation of cell shape in Euglena gracilis. iii. involvement of stable microtubules
Authors: Lachney Carole L. , Lonergan Thomas A.
Published: April 2021

The role of cytoplasmic microtubules in a recently reported biological clock-controlled rhythm in cell shape of the alga Euglena gracilis (strain Z) was examined using indirect immunofluorescence microscopy. The resulting fluorescent patterns indicated that, unlike many other cell systems, Euglena cells apparently change from round to long to round cell shape without associated cytoplasmic microtubule assembly and disassembly. Instead, the different cell shapes were correlated with microtubule patterns, which suggested the movement of stable microtubules to accomplish cell shape changes. In live intact cells, these microtubules were demonstrated by immunofluorescence to be stable to lowered temperature and elevated intracellular Ca2+ levels, treatments that are commonly used to depolymerize microtubules. In cells extracted in detergent at low temperature or in the presence of elevated Ca2+ levels, the fluorescent image of the microtubules was disrupted. Transmission electron microscopy confirmed the loss of one subset of pellicle microtubules. The difference in microtubule stability to these agents between live intact cells and cells extracted in detergent suggested the presence of a microtubule-stabilizing factor in live cells, which is released from the cell by extraction with detergent, thereby permitting microtubule depolymerization by Ca2+ or lowered temperature. The calmodulin antagonist trifluoperazine prevented the Ca2+-induced disruption of the fluorescent microtubule pattern in cells extracted in detergent. These results implied the involvement of calmodulin in the sensitivity to Ca2+ of the microtubules of cells extracted in detergent.
The ultrastructural organization of proteoglycans and collagen in human and rabbit scleral matrix
Authors: Young Robert D.
Published: April 2021

The distribution of proteoglycans and their association with collagen fibrils were studied in human and rabbit sclera following fixation of tissue in glutaraldehyde containing Cuprolinic Blue, a specific stain for proteoglycans when used in the presence of critical concentrations of electrolytes. Proteoglycans were visualized by electron microscopy as fine filaments, approximately 54 nm in length and 5 nm in diameter, associated with the d band in the gap zone of the periodic collagen banding pattern. Filaments were present in three orientations: (1) radiating from the d band to associate with corresponding sites on adjacent collagen fibrils; (2) encircling the collagen fibril at the d band position; and (3) lying along the fibril axis, often linking consecutive d bands.

No difference was apparent between the proteoglycan-collagen organization in human and rabbit sclera. A similar arrangement of proteoglycan filaments in association with the collagen d band was also evident throughout all levels of the sclera in spite of considerable variations in fibril diameter from inner to outer stroma.

Furthermore, the specific relationship of proteoglycans with the collagen fibrils in sclera closely resembled that previously described in tendon and in articular cartilage, lending support to the view that the association of proteoglycans with collagen may be consistent in a majority of connective tissues, irrespective of their diverse functional specializations.
Changes occurring in chloroplasts of Phaseolus following infection by Sclerotinia: A cytochemical study
Authors: Tariq V. N. , Jeffries P.
Published: April 2021

Dramatic changes occur in the ultrastructure of chloroplasts within host tissues during the infection of Phaseolus by the plant pathogenic fungus Sclerotinia. Electron-opaque deposits develop initially in the peripheral region of the chloroplast stroma, in cells in advance of the hyphal front. As infection continues, the amount and intensity of deposition increases and spreads throughout the chloroplast. The deposits possess a high degree of structural integrity in the form of a crystalline square lattice with 10 nm periodicity. Enzyme digestion studies have been used to show that the deposits are proteinaceous. Similar deposits are also induced by treatment with oxalic and citric acids, but not by the potassium salts of these acids buffered at pH7·2. It is suggested that a pH change within the chloroplasts, resulting from oxalic acid secretion by the fungus, is responsible for induction of protein deposition. The likelihood that the deposits are ribulose, 1,5-bisphosphate carboxylase-oxygenase is discussed.
The alteration of mitotic events by ionophore a23187 and carbonyl cyanide N-chlorophenylhydrazone
Authors: Ziegler Michael L. , Sisken Jesse E. , Vedbrat Sharanjit
Published: April 2021

A large quantity of published work indicates that calcium ions may be involved in the regulation of mitotic events and recent reports suggest that the onset of chromosome movement is dependent upon a transient increase in free cytosolic calcium ions. In this paper we examine the effects of two agents known to perturb intracellular calcium pools on mitosis in HeLa cells. These were the calcium-selective ionophore A23187 and carbonyl cyanide n-chlorophenylhydrazone (CCCP), which is a protonophoric inhibitor of oxidative phosphorylation. Owing to a stimulation of glycolysis, the latter agent does not decrease intracellular ATP in HeLa but does cause mitochondria to release calcium ions. Our data show that, at low concentrations, both agents prolong metaphase but differ in their effects on anaphase and cytokinesis. Studies with chlorotetracycline, a commonly used probe for membrane-associated calcium, verify that these agents do affect calcium pools under the conditions of our experiments. The data presented are consistent with the idea that increased cytosolic calcium levels can directly or indirectly affect mitotic events but, contrary to other suggestions, cause a prolongation of metaphase, i.e. they delaythe onset of chromosome movement.
X-ray microanalysis of synchronized hela s3 cells infected with vaccinia virus
Authors: Warley Alice , Stephen J.
Published: April 2021

X-ray microanalysis has been used to study changes in concentration of P, S, Cl Na and K in synchronized HeLa S3 cells in G1phase infected with Vaccinia virus. No dramatic redistribution of elements between nucleus and cytoplasm was demonstrated during the first 6h post-infection, during which time viral shut-off of host protein synthesis occurred. [Cl] increased relative to [Na] and [K] during the first 3 h post-infection. The magnitude and direction of change in [K] and [Na] (from approximately 10 cells/analysis) was compared with data previously obtained by flame photometry (from approximately 106 cells/analysis) and found to be remarkably parallel.
Fine structure and radiation resistance in Acinetobacter: A comparison of a range of strains
Authors: Glauert Audrey M. , Thornley Margaret J.
Published: April 2021

Nine strains of the Gram-negative bacterium, Acinetobacter, showed a wide variation in resistance to ionizing radiation; all gave sigmoid survival curves, with D10 values for the ex- ponential portion ranging from 70 to 460 J kg;−1 (7–46 krd). The fine structure of these strains was studied by electron microscopy. Results for a resistant strain were described earlier and the present paper gives comparative results for the other 8 strains.

The mode of division varied, 5 strains dividing predominantly by constriction of all the layers of the cell wall, while the other 4strains showed ingrowth of thick septa. These 4 included the 3 most resistant strains and 1 strain of intermediate resistance.

The arrangement of surface layers was the same as that usually found in Gram-negative bacteria. In 1 strain an extra layer was visible outside the outer membrane; this layer does not appear to influence radiation resistance since it is lacking in another strain of similar resistance.

The layer of wrinkled material, previously observed in the resistant strain between the outer membrane and the intermediate dense layer of the cell wall, in negatively stained preparations of isolated cell walls, was seen in 5 other strains of intermediate and high resistance, while in 3 sensitive strains finely granular material appeared to occupy a corresponding position in the cell wall.

These observations suggest that morphological features, such as the wrinkled layer of the cell wall, and possibly the mode of cell division, may influence the radiation resistance of Acinetobacter strains, but their function is not yet known.
Systemic viral material in the cells of the freshwater red alga Sirodotia tenuissima (holden) skuja
Authors: Lee R. E.
Published: April 2021

A cytoplasmic inclusion consisting of polygonal viral particles surrounding a spherical viroplasm is described in the cells of Sirodotia tenuissima but not in other species of Sirodotia and Batracliospermum investigated. Some polygonal viral particles are also found associated with nucleolar material in the nucleus of S. tenuissima. The viral material is present in the apical cell and appears to be distributed to the daughter cells during division of the apical cell.
The uptake of vitamins by mouse fibroblast cells (strain LS) during growth in a chemically defined medium
Authors: Blaker G. J. , Pirt S. J.
Published: April 2021

The uptake of biotin, choline, folic acid, hypoxanthine, inositol, nicotinamide, pantothenic acid, pyridoxine, riboflavin, thiamine and vitamin B12 by mouse LS cells in suspension culture was determined by microbiological assay methods. Based on the extent of uptake during cell growth, vitamin growth yields (cells produced/unit mass of vitamin utilized) were estimated for all of the vitamins, except folic acid, thiamine and B12. The growth yields were lower during the early phases of culture. No uptakes of folic acid or B12 could be demonstrated. During the period of incubation about half of the thiamine was irretrievably lost through spontaneous decomposition.
Effect of temperature on the mutual adhesion of preaggregation cells of the slime mould, Dictyostelium discoideum
Authors: Garrod D. R. , Born G. V. R.
Published: April 2021

The mutual adhesion of slime-mould cells was investigated at 24 and 1 °C in stirred and unstirred medium. Adhesion was induced by adding sodium chloride and followed by recording the diminution in optical density of the cell suspension associated with the formation of cell aggregates. It was found that: (1) when cells, previously stored at 1 °C, were stirred in distilled water at 24 °C the optical density of the suspension increased; (2) when sodium chloride was added after this increase, the optical density fell as cells adhered to each other; (3) both the increase in optical density and subsequent adhesion were reversibly inhibited at 1 °C; and (4) the rise in optical density was a prerequisite for adhesion.

Comparison of cell shape and volume at the 2 temperatures suggested that the rise in optical density was due to (a) extension of pseudopodia and a consequent change from a spherical to an irregular shape, and (b) an increase in mean cell volume of about 17%.

Observations on the formation of adhesions in still medium at 24 °C showed that initial contacts were formed either by microspikes or by rounded parts of the cell surface. The cell surfaces then flattened against each other, thereby increasing the area of contact. No flattening occurred at 1 °C. Microspikes were present on the surfaces of both cold and warm cells and contained longitudinal fibrils.

It is suggested that adhesion of these cells is inhibited in the cold in stirred medium because the cells are unable to expand areas of mutual contact. Cold adhesions are, therefore, weak and easily disrupted by shearing forces. The inability to expand adhesive contacts may be due to the inhibition of cell motility at low temperature.
The role of microfilaments in cytoplasmic streaming in Drosophila follicles
Authors: Gutzeit Herwig O.
Published: April 2021

During the last phase of oogenesis in Drosophila, nurse cell cytoplasm can be seen to be streaming into the growing oocyte when visualized in time-lapse films. This process can be reversibly inhibited by cytochalasins. The distribution of F-actin filaments in the nurse cells has been studied by staining with rhodamine-conjugated phalloidin. At the beginning of cytoplasmic streaming (stage 10B) increasingly thick bundles of microfilaments formed, many of *which spanned the nurse cell cytoplasm from the cell membrane to the nuclear membrane. The association of F-actin with the nuclear membrane persisted when nurse cell nuclei were isolated mechanically. The experimental evidence suggests that microfilament contraction in the nurse cells leads to cytoplasmic streaming by pressure flow.
Biosynthesis of nuclear proteins after stimulation of quiescent swiss mouse 3t3 cells
Authors: O’Farrell Minnie K. , Dixon Cynthia
Published: April 2021

Stimulation of quiescent Swiss mouse 3T3 fibroblasts either by serum or by the low molecular weight hormones, prostaglandin and insulin, induces DNA synthesis after a lag period of about 15 h. Following restimulation by serum or these pure hormones there is an overall increase of two-to fourfold in the rate of biosynthesis of nuclear proteins. In addition, there is a relative decrease in some proteins (Mr = 200×103, pI 6·0—6’5), while others increase (e.g. actin). Two polypeptides show specific correlations with the exit from Go-The synthesis of p30 (Mr = 30×103, pI 5·2) is at a maximum within 5 h of restimulation, while the synthesis of p36 (Mr = 36×103, pI = 4#x00B7;25) is first seen at 10— 20 h after restimulation. Synthesis of p36 correlates well with the initiation of DNA synthesis. The synthesis of both proteins is stimulated by serum and by the hormones. Thus there are common biosynthetic responses to different stimuli indicating convergent pathways leading to DNA biosynthesis. Addition of hydrocortisone with the growth-stimulatory hormones inhibits both entry into the S phase and biosynthesis of p36. In contrast, hydrocortisone does not alter the biosynthesis of p30. This ‘early’ protein, p30, is different from the products of both c-fos and c-myc. Therefore, we have identified two specific components that might participate in the regulation of cell proliferation.
Either exogenous or endogenous fibronectin can promote adherence of human endothelial cells
Authors: Clark Richard A. F. , Folkvord Joy M. , Nielsen Larry D.
Published: April 2021

Recently, we have presented evidence that proliferating blood vessels produce and deposit fibronectin in situ during the angiogenesis of wound repair. This report extends these observations by demonstrating that human endothelial cells from both large and small vessels depend on fibronectin for their adherence in vitro. Endothelial cells were grown from human umbilical veins (HUVEC) by the method of Gimbrone and from the microvasculature of human omentum by the method of Kern, Knedler and Eckel. Second-passage cells were plated into microtitre wells that had been coated with 100/tgml−1 of fibronectin, types I and III collagen, type IV collagen or laminin. After a 3-h incubation, adherent cells were solubilized with Zap-Isoton and quantified on a Coulter Counter. Under normal culture conditions HUVEC showed no preference for fibronectin substrates while microvascular cells always demonstrated a striking preference for fibronectin substrates. However, when HUVEC were exposed to 2·5 or 25μgml−1 of cycloheximide for 4h before and during the adherence assays, the adherence to fibronectin was 50—200% greater than to types I and III collagen. Immunofluorescence studies showed that while HUVEC expressed a large quantity of surface fibronectin, microvascular cells expressed very little. Metabolic labelling studies confirmed that HUVEC cultures had substantial quantities of fibronectin in their cell layer while microvascular cells did not. In antibody blocking experiments, preincubation of fibronectin-coated surfaces with anti-fibronectin antibodies totally blocked microvascular cell adhesion but only abrogated HUVEC adherence by 50%, presumably since these latter cells were able to deposit additional fibronectin onto the surface during the 3 h assay period. In the presence of cycloheximide anti-fibronectin antibodies totally blocked HUVEC adherence. These results demonstrate that both endothelial cell types rely, at least in part, on fibronectin for adherence in vitro. HUVEC can synthesize, secrete and deposit enough fibronectin for their adherence in vitro, while microvascular cells rely on an exogenous source of fibronectin under these culture conditions. Thus, the increased blood vessel fibronectin observed during angiogenesis in vivo may mediate adherence of the proliferating and migrating endothelial cells.
Tight and gap junctions in the intestinal tract of tunicates (urochordata): A freeze-fracture study
Authors: Lane Nancy J. , Dallai R. , Burighel P. , Martinucci G. B.
Published: April 2021

The intestinal tracts from seven different species of tunicates, some solitary, some colonial, were studied fine-structurally by freeze-fracture. These urochordates occupy an intermediate position phylogenetically between the vertebrates and the invertebrates. The various regions of their gut were isolated for examination and the junctional characteristics of each part investigated. All the species examined exhibited unequivocal vertebrate-like belts of tight-junctional networks at the luminal border of their intestinal cells. No septate junctions were observed. The tight junctions varied in the number of their component strands and the depth to which they extended basally, some becoming loose and fragmented towards that border. The junctions consisted of ridges or rows of intramembranous particles (IMPs) on the P face, with complementary, but offset, E face grooves into which IMPs sometimes fractured. Tracer studies show that punctate appositions, the thin-section correlate of these ridge/groove systems, are sites beyond which exogenous molecules do not penetrate. These junctions are therefore likely to represent permeability barriers as in the gut tract of higher chordates. Associated with these occluding zonular junctions are intermediate junctions, which exhibit no identifiable freeze-fracture profile, and macular gap junctions, characterized by a reduced intercellular cleft in thin section and by clustered arrays of P face particles in freeze-fractured replicas; these display complementary aggregates of E face pits. The diameters of these maculae are rarely very large, but in certain species (for example, Ciona), they are unusually small. In some tissues, notably those of Diplosoma and Botryllus, they are all of rather similar size, but very numerous. In yet others, such as Molgula, they are polygonal with angular outlines, as might be indicative of the uncoupled state. In many attributes, these various junctions are more similar to those found in the tissues of vertebrates, than to those in the invertebrates, which the adult zooid forms of these lowly chordates resemble anatomically.
The presence of epidermal growth factor binding sites in the intracellular organelles of term human placenta
Authors: Ramani N. , Chegini N. , Rao Ch. V. , Woost P. G. , Schultz G. S.
Published: April 2021

Highly purified lysosomes, rough and smooth endoplasmic reticulum, and Golgi apparatus, as well as microvillus plasma membranes, bound 125I-labelled epidermal growth factor ([125I]EGF) with similar affinity. Scatchard plots for all the organelles were curvilinear. The apparent number of available binding sites per mg protein of intracellular organelles was 27–71% of that found in microvillus plasma membranes. The bound and free [125I]EGF were not degraded by any of the organelles.

Binding and dissociation of [125I]EGF in all organelles were dependent on the time and temperature of incubation. The specificity of [125I]EGF binding was similar in all organelles. The optimal pH for binding to lysosomes was 6·0, in contrast to 7·0 for all the other organelles. Exposure of different organelles to enzymes and protein-modifying reagents resulted in numerous binding differences between the intracellular organelles and microvillus plasma membranes. Covalent affinity labelling with [125I]EGF revealed two major proteins of 155 and 140(×103)Mr in all the organelles. The 155×103Mr protein was labelled predominantly in all organelles except rough endoplasmic reticulum, where both proteins were equally labelled. Addition of proteolytic inhibitors during isolation of organelles did not alter the pattern of [125I]EGF-labelled binding proteins found in the organelles.

EGF also stimulated phosphorylation of the 155 and 140(× 103)Mr proteins in all the organelles. The 155×103Mr protein was phosphorylated more than the 140×103Mr protein in microvillus plasma membranes and smooth endoplasmic reticulum, whereas the 140×103Mr protein was phosphorylated more than the 155×103Mr protein in lysosomes and both proteins were equally phosphorylated in rough endoplasmic reticulum. Several organelles also contained minor [125I]EGF-binding proteins that did not show phosphorylation response and proteins that showed phosphorylation response but did not bind [125I]EGF.

Thus, the present study demonstrates by a number of different criteria, that several intracellular organelles of term human placenta also contain EGF-binding and kinase activities.
Three-dimensional reconstruction of the chondriome of the unicellular red alga Rhodella reticulata
Authors: Broadwater Sharon , Scott Joe
Published: April 2021

Three cells of the unicellular red alga Rhodella reticulata were serially sectioned and photographed in a transmission electron microscope in order to analyse the organization of the mitochondrial system, or chondriome, which, on the basis of cursory examination, appeared to consist of an interconnected network of one to a few organelles. The chondriome of all three cells was traced and superimposed on acetate paper and a three-dimensional model using balsa wood was constructed of one cell. The chondriome was found to consist primarily of one large, anastomosing mitochondrion located principally at the cell periphery. In addition, it appears that some cells can contain a few small mitochondria that are not connected to the main body of the chondriome. This is the first study to reveal the three-dimensional nature of the chondriome in a red alga.
Large-scale selection synchrony of Tetrahymena thermophila
Authors: Hill Robin J. , Kroft T. , Zuker M. , Smith Ian C. P.
Published: April 2021

A method is described, based on the phagocytosis of colloidal ferrite particles, which gives highly synchronous populations of Tetrahymena thermophila. To ensure a successful synchrony, the cell culture doubling time, the limits of the phagocytic period and the distribution of cell stages must first be determined. Once these parameters are known, synchrony can be achieved under a variety of growth conditions and with cultures ranging in volume from a few millilitres to 12 litres or more.

The main advantages of the method are that the apparatus required is simple, large volumes of cells can tie handled easily, and the synchronous populations can be prepared within a few hours. In principle, the method should be applicable to any cell population in which phagocytosis occurs discontinuously over the cell cycle.
Quantitative electron microscopic autoradiographic studies on internalization of 125I-labelled epidermal growth factor in term human placenta
Authors: Chegini N. , Rao Ch. V.
Published: April 2021

The electron microscopic autoradiographic studies described here revealed the presence of specific silver grains over nuclei, lysosomal vesicles, rough endoplasmic reticulum and Golgi apparatus after incubation of placental tissue for 2h at 38°C with 1 nM-[125I]EGF. Three-step mask analysis, which corrects for radiation spread, showed that the relative grain density was the highest in nuclei, followed by lysosomal vesicles, then Golgi and rough endoplasmic reticulum, equally. The nuclear grain density, however, was lower than that in microvillus plasma membranes. There were very few grains in basolateral plasma membranes, none in the basement membrane area and a considerable number in capillary endothelial cells. The present results demonstrating the association of internalized [125I]EGF with a variety of intracellular organelles raise the possibility of EGF acting on the intracellular sites in addition to cell surface sites.
Direct cell-to-cell transmission of vesicular stomatitis virus
Authors: Vassalli J.-D. , Lombardi T. , Wohlwend A. , Montesano R. , Orci L.
Published: April 2021

Vesicular stomatitis virus (VSV) infection of kidney-derived, LLC-PK1 epithelial cells resulted in the budding of new viral particles into the basolateral space of the cultures. In lateral regions where cells were in close apposition, the majority of assembling viral particles in the process of budding from the producing cell had their apex already engaged in clathrin-coated pits of the neighbouring cell surface. These observations suggest that the viral envelope-plasma membrane interaction triggers the focal formation of clathrin-coated pits; they also show how VSV infection could spread throughout a tissue with only minimal exposure to a host’s extracellular environment.
Photosensitization to ultraviolet irradiation and selective killing of cells following uptake of pyrene-containing fatty acid
Authors: Fibach Eitan , Morand Olivier , Gatt Shimon
Published: April 2021

Cells were incubated with 12-(l-pyrene)-dodecanoic acid (P12), a long-chain fatty acid to which a pyrene ring has been attached covalently. This acid was transported across the plasma membranes of cells and subsequently incorporated into their neutral lipids and phospholipids. Irradiation of these pyrene-containing cells for short periods (0·5–4 min) with ultraviolet light at 366 nm resulted in eventual cell death. Similar irradiation had no effect on cells that had not been exposed to Pl2. The time of the period of irradiation necessary for inducing the toxic process was related to the quantity of Pl2 incorporated, the latter being a function of the respective metabolic activity of the individual cell type. The degree of incorporation of P12 into a cell, and consequently its acquired sensitivity to killing by ultraviolet irradiation at 366 nm, was affected by the incubation temperature and addition of non-fluorescent fatty acid, albumin or other serum proteins. Different degrees of incorporation of P12 into various cell types were used for selective killing and elimination of cell populations by irradiation at 366 nm. The combined procedure of preincubation with P12 followed by ultraviolet irradiation thus permitted selection of cell types with a greater resistance to this procedure.
The cell cycle of symbiotic chlorella: iii. numbers of algae in green hydra digestive cells are regulated at digestive cell division
Authors: Mcauley P. J.
Published: April 2021

Regression analysis of the relationship between the size of interphase and mitotic digestive cells of green hydra, and the numbers and total volume of the symbiotic Chlorella algae they contain showed a partial correlation only, suggesting that numbers of algae per cell are not regulated by limiting them to a specific proportion of the host cell, and that the variation observed in numbers of algae per cell is not due to variation in host cell size. After hydra were fed, which stimulates algae and digestive cells to divide at the same time, numbers of algae per cell were higher in prophase than in interphase cells, and numbers increased as mitosis proceeded. In excised regenerating peduncles algae divide before digestive cells, and at the onset of digestive cell division mitotic cells were found to contain almost twice the number of algae as before excision. Thus, almost all of the algal cell division necessary to maintain a constant population size was associated with digestive cell division. Analysis of variance in numbers of algae in telophase mother and daughter cells suggested that the proportion of algae dividing as a result of host cell mitosis was greater in digestive cells with few algae than in those with many algae. The fact that the mechanism controlling the proportion of algae dividing in host cells is expressed at host cell division and is manifested in the daughter cells may contribute to wide variation in numbers of algae per cell.
The cell cycle of symbiotic chlorella: IV. DNA content of algae slowly increases during host starvation of green hydra
Authors: Mcauley P. J. , Muscatine L.
Published: April 2021

The distribution of DNA content of symbiotic Chlorella algae freshly isolated from green hydra was compared with that of cultured Chlorella of the NC64A strain, using flow cytometry. In non-logarithmic cultures of NC64A most cells had accumulated in G\ phase, while in logarithmic cultures a peak containing cells in S phase and mitosis could be distinguished from the larger peak. However, symbiotic algae showed a single broad peak in which there was no clear distinction between G1 and S phase/mitosis. When hydra were starved for a prolonged period, inhibiting host cell and algal division, the DNA content of the symbiotic algae slowly increased, and the number of daughter cells produced after a single feeding increased with the length of the preceding period of starvation. This suggests that symbiotic algae are able to cycle slowly through S phase, but unless the host is fed they cannot traverse into mitosis and complete the cell division cycle. No significant difference in cell size was found between algae producing either four or eight daughter cells after 1-day- or 22-day-starved hydra were fed, suggesting that algal cell size did not determine the number of daughter cells produced. Instead, this may be dependent upon the length of time the cell had spent in S phase prior to receiving the, as yet unknown, stimulus to enter into mitosis.