bluuebunny/crossref_metadata_2025 huggingface dataset:
A sharp cell surface conformational transition at low ionic strength changes the nature of the adhesion of enzyme-treated red blood cells to a hydrocarbon interface
Authors: Donath E. , Gingell D.
Published: April 2021

Aldehyde-fixed human red cells have previously been used to assess the roles of electrostatic and electrodynamic forces in adhesion. We have attempted to test the prediction that enzymic removal of cell surface negative charges should increase adhesion in dilute salt solutions by reducing electrostatic repulsion. While this is indeed the case for neuraminidase-treated cells and also for Pronase- and trypsin-treated cells over much of the low ionic strength range, the latter two treatments cause very strong adhesion over a remarkably narrow range of ionic strength centred on 1 mM-NaCl. At 0·5 and 1·5 mM adhesion is negligible. After Pronase treatment a further adhesive peak occurs at 2·5 mM. Electrophoresis of protease-treated cells shows small but clear reductions in mobility at precisely these peak adhesion values. These electrophoretic potential changes are almost certainly not large enough to cause increased adhesion directly, and it is thought that they are second-order changes, symptomatic of a structural rearrangement of the cell surface. How this causes such vastly augmented adhesion is an intriguing problem.
Coated pits and pinocytosis in Tetrahymena
Authors: Nilsson Jytte R. , Deurs Bo Van
Published: April 2021

The possible role in pinocytosis of coated pits at the parasomal sacs of Tetrahymena has been studied using cationized ferritin (CF; pl = 8·5) as a marker of membrane and content. It is shown that CF binds evenly to the surface, including the coated pits, of Tetrahymena in an inorganic salt medium (to avoid formation of food vacuoles) at the normal growth temperature. Moreover, CF is internalized by coated vesicles (shown to be truly free by thin serial-section analysis) and delivered initially (1–5 min of incubation) to cisterns near the cell surface. Later (5–10 min) CF occurs also in autophagic vacuoles, formed as a result of starvation, and eventually (15–90 min) it is present in preformed (old) food vacuoles. These observations indicate that the coated pits at the parasomal sacs of Tetrahymena function in adsorptive pinocytosis in much the same manner as coated pits at the surface of mammalian cells.
The complexity of poly(a)+ RNA in the alga Chlorella fusca
Authors: McBride N. K. , Thurston C. F.
Published: April 2021

RNA excess hybridization with radioactively labelled complementary DNA (cDNA) was used to reveal the complexity of poly(A)+ RNA from Chlorellafusca var. vacuolata. RNA was tested from cells during photosynthetic exponential growth and during adaptation to heterotrophic growth in the dark on acetate. Both RNA populations were resolved into abundant, intermediate and rare sequence classes. Abundant sequences (200—400 copies per cell) constituted a significantly larger proportion of total poly(A)+ RNA in acetate-adapting cells than in exponentially growing autotrophic cells. Both types of RNA contained a rare sequence class of complexity consistent with a composition of about 20 000 different sequences. This indicated a substantially greater complexity of genes expressed in this alga and Euglena than in fungi and slime moulds. Heterologous hybridization, and hybridization with fractionated cDNA, showed that the majority of differences between RNA populations from exponentially growing and adapting cells were changes in relative abundance of groups of sequences, rather than presence of different sets of sequences in the two populations.
Junction formation between cultured normal rat hepatocytes an ultrastructural study on the presence of cholesterol and the structure of developing tight-junction strands
Authors: Feltkamp Constance A. , Waerden Alexandra W. M. Van Der
Published: April 2021

In cultures of normal rat hepatocytes, isolated by collagenase perfusion, formation of junctions started 4—7 h after seeding. The junctional complexes were localized at two preferential sites of the contiguous membrane : apically and on both sides of open spaces with microvilli at some distance from the free upper surface.

The domains of early contact formation are characierized by a flattening of the membranes, a decrease in intercellular space, a depletion of intramembrane particles (IMPs) and a concentration of electron-dense and of fine fibrillar material in the cytoplasm immediately adjacent to the membrane. We were able to demonstrate the presence of cholesterol in these domains by formation of cholesterol-filipin complexes that deformed the membrane. However, membrane-deformation in these domains was often inhibited. This inhibition appeared to be due to the presence of pepsinsensitive material, since full deformation was induced after mild proteolysis. The arrangement of IMPs into small gap junctions and short tight-junction strands is synchronous in the membranes of the neighbouring cells. The tight junctions are composed of two strands arranged in a slightly offset configuration. The possibility that the strands are lipidie in nature is not excluded.
Fibronectin-independent adhesion of fibroblasts to extracellular matrix material: Partial characterization of the matrix components
Authors: Harper P. A. , Brown Patricia , Juliano R. L.
Published: April 2021

Fibroblasts can adhere to extracellular matrix (ECM) material by fibronectin-dependent (type I) and fibronectin-independent (type II) mechanisms. In this report we investigate the biochemical characteristics of ECM that contribute to type II adhesion. ECM capable of mediating type II adhesion is produced primarily by normal diploid fibroblasts, but not by transformed cells or epithelial cells. Treatment of fibroblast ECM under conditions that result in the removal of most of the ECM lipid or most of the ECM glycosaminoglycan does not impair type II adhesion. Likewise, treatment of the ECM with large amounts of purified collagenase does not block type II adhesion. However, treatment of ECM with low doses of trypsin or with an agent that reacts with tyrosine residues, results in complete ablation of the ability of the ECM to support type II adhesion. On the basis of these observations we suggest that the matrix component(s) mediating type II adhesion are non-collagenous proteins or glycoproteins.
Calcium regulation of flagellation in Naegleria gruberi
Authors: Schuster F.L. , Twomey R.
Published: April 2021

The amoeba-to-flagellate transformation of Naegleria gruberi was studied, exploring the role of calcium in control of this pattern of morphogenesis. A direct and an indirect role for calcium are postulated based on experimental results. Direct inhibition in the presence of calcium is caused by ionophore A23187, substances with ionophore-like activity (amphotericin) and the hormone calcitonin, which facilitate calcium uptake into the cytosol. The indirect role is difficult to assess, but is believed to be related to calcium regulatory protein and its control of cyclic nucleotide levels in the cell, based on inhibition by trifluoperazine. Calcium flux was studied by addition of 45Ca2+ to cell cultures, and tracing its movement during the transformation period. Ultrastructural localization of calcium was attempted in amoeboid and flagellate stages, as well as in reverting flagellates. Deposits that might represent calcium were observed under the plasma membrane and, in calcium-induced reversion, in electron-dense spheres seen in the cytoplasm and at sub-membrane locations, suggesting expulsion of excess calcium.
Differential effect of arginine modification with 1,2-cyclohexanedione on the capacity of vimentin and desmin to assemble into intermediate filaments and to bind to nucleic acids
Authors: Traub Peter , Vorgias Constantin E.
Published: April 2021

When the intermediate filament proteins vimentin and desmin were reacted for a short period of time with the arginine-specific reagent 1,2-cyclohexanedione, the modification had a severe, inhibitory effect on the assembly of intermediate filaments and on the susceptibility of the basic, aminoterminal polypeptide of both proteins to degradation by the intermediate filament-specific, Ca2+-acti vated proteinase. However, it had only a slightly inhibitory effect on the binding of vimentin and desmin to ribosomal RNA from Ehrlich ascites tumour cells. Since the Ca2+-activated proteinase is very likely to be a trypsin-like enzyme, with a preference for arginyl and lysyl peptide bonds, the results indicate that the arginine residues of the amino-terminal polypeptide of vimentin and desmin are highly essential for filament assembly but largely dispensable for the binding of both proteins to nucleic acids. This was supported by the observation that two breakdown products of vimentin lacking a 5 × 103Mr and an 8 × 103Mr polypeptide from the amino terminus, respectively, did not assemble into intermediate filaments but were still capable of binding to rRNA. Both polypeptides also bound to single-stranded DNA-cellulose under non-denaturing conditions, but passed the affinity column in the presence of 6m-urea. Thus, the binding of vimentin to nucleic acids appears to be based on two components: a non-specific electrostatic interaction mediated by the positively charged arginine residues of the amino-terminal polypeptide that is insensitive to denaturation by urea, and a specific interaction that is sensitive to denaturation by urea.
Identification of a laminin-like substance on the surface of high-malignant murine fibrosarcoma cells
Authors: McCoy J.P. , Lloyd R. V. , Wicha M. S. , Varani J.
Published: April 2021

High- and low-malignant murine fibrosarcoma cells were stained with anti-laminin antibodies using immunoperoxidase techniques and examined by electron microscopy. With the high malignant cells, specific staining was observed along the cell surface. Use of normal rabbit serum in place of the rabbit anti-laminin or pretreatment of the anti-laminin with soluble laminin complete ly eliminated this staining. No immunoperoxidase staining was observed with the low-malignant cells. In additional studies, membrane fractions were prepared from the high- and low-malignant cells and used to immunize rabbits. The animals immunized with the membrane fractions from the high-malignant cells produced antibodies that reacted by enzyme-linked immunosorbent assay (ELISA) with murine laminin obtained from the EHS sarcoma. The animals immunized with membrane fractions from the low-malignant cells did not. These studies provide strong evidence that the high-malignant cells (but not the low) express on their cell surface a substance that is immunologically cross-reactive with laminin. In addition, the high-malignant cells (but not the low) secreted a material into the cell culture fluid that could be specifically immunoprecipitated with anti laminin antibodies. The immunoprecipitated material co-migrated with purified laminin when examined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis under reducing con ditions. The existence of this substance associated with the surface of the high-malignant cells and its absence from that of the low-malignant cells may explain the previously noted difference between these cells in their ability to attach to type IV collagen. This difference may also contribute to the dissimilarity between these cells in their metastatic potential.
Control of cell mobility by cyclic AMP
Authors: Katzin William E. , Gershman Howard
Published: April 2021

Cyclic AMP concentrations have been measured in a number of different cell types under a variety of culture conditions in an attempt to define the relationship between the endogenous concentration of cyclic AMP and cell mobility. In previous work it was shown that agents that increase the intracellular concentration of cyclic AMP can effectively suppress cell movement. In Balb/c 3T3 cells, which have a very low mobility in cellular aggregates, the intracellular concentration of cyclic AMP was elevated only transiently soon after the formation of the three-dimensional cell masses. In contrast, in the highly mobile virally transformed counterpart of Balb/c 3T3 cells, called SVT- 2, the concentration of cyclic AMP was relatively low soon after the cell masses were formed, but later rose to a level that was higher than that in Balb/c 3T3 cells. Using NIL B cells, SV40- transformed NIL B cells, and several lines of tumour cells derived from NIL B cells, it was found that the average intracellular concentration of cyclic AMP did not vary significantly from one population of cells to another. Finally, the intracellular concentration of cyclic AMP was measured in chick embryo ventricle cells. The mobility of these cells had previously been found to decrease as embryonic development progressed; furthermore, it had been shown that dibutyryl cyclic AMP plus theophylline produced nearly complete inhibition of their movement in cell masses. In the series of experiments reported here we found that the endogenous concentration of cyclic AMP in aggregates and fragments of chick embryo ventricle cells decreases as development proceeds; these data are consistent with preliminary experiments reported by other investigators. In a separate set of experiments, the intracellular concentration of cyclic AMP was measured in cells that had been cultured in a medium containing 1 · 2 mM-dibutyryl cyclic AMP plus 1 · 0 mM-theophylline. This drug treatment has previously been shown to inhibit the movement of cells both in aggregates and in monolayers; it also produces striking effects on cell shape and ultrastructure. In aggregates of chick embryo ventricle cells, treatment with these drugs resulted in increases in the intracellular concentrations of cyclic AMP from approximately 10 picomol/mg protein to approximately 500 picomol/mg protein. In Balb/c 3T3 and SVT-2 cells this treatment increased cyclic AMP con centrations from 3 · 7 to 160 and from 6 · 4 to 470 picomol/mg protein, respectively.
The polar ring of coccidian sporozoites: A unique microtubule-organizing centre
Authors: Russell D. G. , Burns R. G.
Published: April 2021

The infective stages, or’zoites, of coccidian parasites possess an organized network of spirally arranged microtubules that closely follow the helical body shape of these vermiform cells. These subpellicular microtubules are anchored anteriorly by insertion into a highly structured circular microtubule-organizing centre (MTOC) known as the polar ring.

This MTOC has been examined both in situ and in isolated, critical-point-dried whole cytoskeletons. The 24 microtubules attach laterally to the MTOC through shallow depressions on the inner face of the ring: the ends do not appear to be physically capped. The polar ring has no obvious or regular substructure, although it has a faintly fibrous appearance. The polarity of the microtubules, determined by ‘hook decoration’, is such that the plus or fast-growing end is distal to the MTOC.

The coccidian’zoite MTOC is unique both in its highly defined structure and in the degree of organization it confers upon the developing cell in terms of the number, spacing, orientation and polarity of the subpellicular microtubules.
Identification of spermatogenic cell plasma membrane glycoproteins by twodimensional electrophoresis and lectin blotting
Authors: Millette Clarke F. , Scott B. Keyes
Published: April 2021

Plasma membrane glycoproteins present in purified mouse spermatogenic cells have been identified by two-dimensional polyacrylamide gel electrophoresis and lectin blotting techniques. Four membrane glycoproteins labelled with Bandeiraea simplicifolia lectin (I) have been detected, ranging in Mr from 55 000 to 76000 and in pl from 6·0 to 6·3. Only one of these proteins, p76/6·3, is synthesized by short-term in vitro cultures of spermatogenic cells, as determined by the incorporation of [35S]methionine. Approximately 20 surface glycoproteins labelled with concanavalin A have been identified, ranging in Mr from 50000 to 151000 and in pl from 5·7 to 7·0. None of the components detected with B. simplicifolia lectin (I) are labelled significantly with concanavalin A. A major concanavalin A-binding protein in the membranes of both pachytene spermatocytes and round spermatids is pl51/6·0. This glycoprotein has been previously shown to be exposed on the outer surface of spermatogenic cell membranes and may represent a mediator of germ cell-Sertoli cell interactions. Furthermore, two constituents identified in the present study represent stagespecific markers. Component p73/5·7 is detected with concanavalin A only in the membranes of pachytene spermatocytes. Conversely, p84/6·3 is found only in round spermatid membranes. These results, then have: (a) provided a map of membrane glycoproteins in developing mouse male germ cells; (b) identified p151/6·0 as a membrane constituent of possible functional significance; and (c) identified the first reported glycoprotein surface differentiation markers for mouse spermatogenesis.
Intracellular infection of aposymbiotic Hydra viridis by a foreign free-living Chlorella sp.: Initiation of a stable symbiosis
Authors: Rahat M. , Reich V.
Published: April 2021

An aposymbiotic strain of Hydra vin’dis became infected with free-living Chlorella sp. A stable symbiosis formed that differed in its characteristics from other known Chlorella/Hydra symbioses. The algae reproduced and formed clusters in host endodermal cells, inside large vacuoles filled with an electron-dense substance. A few algae were found to be digested by the hydra, but the apparently uncontrolled reproduct10n rate of the algae more than compensated for this loss. Surplus algae were expelled into the coelenteron and eventually into the surrounding medium. The expelled algae were repeatedly re-engulfed by the hydra during its feeding, forming a process of continuous reinfection.

We suggest that such repeated reinfection of the hydra by the expelled algae provides the host with an endless number of Ch/ore/la from which it might in time select a suitable adapted, controllable symbiont. The present newly formed symbiosis might serve as a model for the study of evolution of algal endosymbioses.
Ultrastructural localization of nucleolar organizers during oogenesis in xenopus laevis using a silver technique
Authors: Boloukhère M.
Published: April 2021

Silver staining at the electron microscopic level of the nucleolar organizers was carried out on Xenopus laevis oocytes at various stages of oogenesis.

The results indicate that a positive reaction takes place exclusively in the dense fibrillar component of the extrachromosomal nucleoli. This constituent undergoes morphological changes of distribution and architecture, which have been correlated with modifications of the transcriptional activity of the nucleoli. When nucleolar activity is reduced, during previtellogenesis, this constituent appears as dense homogeneous spherules well-segregated from the granular component. In contrast, when nucleolar activity is high, during vitellogenesis, it forms an heterogeneous area with an ill-delimited outline: it is organized into a fibrillar core with emerging skein-like strings. It thus seems that this constituent remains silver-stained throughout oogenesis.

These findings suggest that the method used would allow one to follow the evolution of the nucleolar organizer region (NOR) topography during oogenesis. Moreover, they point out facts that have relevance to the problem of the correlation between Ag stainability of NORs and nucleolar transcriptional activity.
Attachment of the cap to the central microtubules of Tetrahymena cilia
Authors: Dentler W.L.
Published: April 2021

The central microtubule cap is bound to the ends of the two central microtubules in Tetrahymena thermophila cilia by plug-shaped structures similar in appearance to the distal filament plugs attached to the ends of the A-microtubules. The caps have been separated from the microtubules and are composed of a bead, two plates, and two peg-like plugs to which the microtubules are attached. The structure of the cap is discussed in relation to the directionality of microtubule assembly in vivo.
The mononuclear phagocyte system of the mouse defined by immunohistochemical localization of antigen f4/80: Macrophages of bone and associated connective tissue
Authors: Hume David A. , Loutit John F. , Gordon Siamon
Published: April 2021

The macrophage-specific antigen F4/80 has been localized in adult mouse bone and connective tissue. F4/80 positive cells form the centre of haemopoietic islands, line the periosteal and subendosteal bone surfaces and are a major component of connective tissue and the synovial membrane (presumptive type A cells). F4/80 is absent from fibroblasts, chondrocytes, osteoblasts, osteocytes, osteoclasts and a subpopulation of synovial lining cells (presumptive type B cells).
The cell cycle and sorting behaviour in Dictyostelium discoideum
Authors: Mcdonald S. A. , Durston A. J.
Published: April 2021

Synchronized cells of the cellular slime mould Dictyostelium discoideum were prepared by mitotic wash-off. Cell counts and DNA synthesis measurements indicated a high degree of synchrony. Cells from each phase of the cell cycle were fluorescently labelled and mixed with unlabelled asynchronous cells. Cells that were in S-phase and very early G2 at the onset of starvation demonstrated a strong tendency to sort to the tip of the subsequent slugs. With reference to these results and published evidence, we discuss the possible role of cell-cycle-related adhesion differences in cell sorting.
Fluorescence microscopic studies of mitochondrial nucleoids during meiosis and sporulation in the yeast, Saccharomyces cerevisiae
Authors: Miyakawa Isamu , Aoi Hiroyuki , Sando Nobundo , Kuroiwa Tsuneyoshi
Published: April 2021

Configurational changes of mitochondria and mitochondrial nucleoids (mt-nucleoids) during meiosis and sporulation in the yeast, Saccharomyces cerevisiae, were examined using the mitochondrial membrane-binding fluorescent dye, dimethyl aminostyrylmethylpyridiniumiodine (DASPMI) and the DNA-binding fluorescent dye, 4’,6-diamidino-2-phenylindole (DAPI).

In zygotes just after mating, mt-nucleoids were observed as many small discrete light spots in the cytoplasm. During meiosis in zygotes, mt-nucleoids at first coalesced with each other into a long string and then separated into spherical nucleoids in four spores. These changes paralleled those in mitochondria observed using DASPMI.

The use of spheroplasts allowed us to examine the behaviour of mt-nucleoids at higher resolution and to identify several distinct meiotic prophase stages of the cell nucleus during early sporulation. In diploid spheroplasts at the stationary phase, 50–7 0 of the mt-nucleoids were observed to be separated from each other and each spherical mitochondrion contained only one mt-nucleoid. At the later stage of premeiotic DNA synthesis, a single branched giant mitochondrion was formed as a result of complete mitochondrial fusion. All of the mt-nucleoids were arranged in an array on a giant mitochondrion and coalesced into a string-like network. Through meiosis I and II, strings of mt-nucleoids were observed close to the dividing nuclei. At late meiosis II, a ring of mt-nucleoids enclosing each daughter nucleus was formed. In ascospores, discrete small nucleoids were visible close to each spore nucleus with a ‘string-of-beads’ appearance. Many mt-nucleoids were excluded from the ascospores and remained in the residual cytoplasm of the ascus.
Pollen-stigma interactions inBrassica oleracea:II. the fate of stigma surface proteins following pollination and their role in the selfincompatibility response
Authors: Roberts Ian N. , Harrod Gillian , Dickinson Hugh G.
Published: April 2021

Mature, self-incompatible stigmas exposed to cycloheximide for 2 h prior to pollination supported identical germination and growth of both cross and self pollen. Treatment of self-pollinated pistils with cycloheximide resulted in the germination of hitherto inactive pollen after some 2–4 h. Pollen germination and initial tube growth in an in vitro germination medium were not significantly affected by cycloheximide. A continuous synthesis of stigmatic proteins is therefore essential for the operation of the self-incompatibility (S.I.) system. However, light-microscope autoradiography of stigmas fed with L-[3H]leucine prior to pollination revealed no movement of stigmatic proteins into the pollen, independent of the compatibility of the pollen with respect to the stigma. Further, tunicamycin, when applied in the same way as cycloheximide, had no effect on the S.I. system. These results are discussed in terms of the proposed cycling of proteins in the papillar cell wall and the involvement of a stigmatic glycoprotein in the S.I. response.
The reproductive potential of normal mouse embryo fibroblasts during culture in vitro
Authors: Karatza Calliopi , Shall Sydney
Published: April 2021

A direct estimate of the reproductive potential of mouse embryo fibroblasts through their entire lifespan has been made using the mini-clone technique, which permits the direct observation of the growth fraction in a bulk population by inspection of the growth behaviour of individual cells. We have measured the colony size on each island that contained one or two cells at the beginning and the fraction of islands which, starting from one or two cells failed to divide even once.

We observed that even in a young culture there are individual cells that can only reproduce two or three times. With each succeeding passage the distribution of colony sizes shifts to a greater proportion of small colonies. The median colony size decreases with each passage. Furthermore, the fraction of non-dividers directly observed increases smoothly with time; the fraction of non-dividers is quite small at the first passage but increases steadily to reach 0·6 at the last passage, after about 30 generations.

These smooth changes in the growth behaviour of this cell strain are accurately described by the mortalization theory of Shall and Stein, in which the single parameter γ, describes the change in reproductive potential over the entire lifespan. The parameter γ describes the rate at which the doubling time of the culture increases; it is the number of generations at which half of the newborn cells are themselves reproductively sterile. Our present data provide an estimate of y.for this cell strain equal to 21 ·2 generations, which compares well with a previous estimate of 20·3 generations.
An Ultrastructural Study Of Ovarian Development In The OTU
7 Mutant OF Drosophila Melanogaster
Authors: Bishop Donna L. , King Robert C.
Published: April 2021

Females homozygous for the otu7 allele produce ovarian tumours, as well as egg chambers that reach a relatively late stage of development. Mutant ovarian nurse cells contain giant polytene chromosomes. These are transcriptionally active, and RNA is transported to the oocyte through ring canals, although at a reduced rate. Vitellogenic oocytes are endocytotically active. Protein (a yolk) spheres are formed, but glycogen (ft yolk) spheres were never seen in the ooplasm. Follicle cells migrate normally and secrete more vitelline membrane and chorion than is required to cover the slowly growing oocyte. Specialized follicle cells also secrete relatively normal dorsal appendages. The micropylar cone is secreted by another cluster of specialized follicle cells called border cells. These are out of phase with the oocyte, and the forming micropylar cone prevents the nurse cells from passing the remainder of their cytoplasm to the oocyte. The result is a morphologically abnormal chamber blocked at the p-12 stage. Sections through the micropylar cone of a p-12 chamber demonstrated that one of the border cells formed a projection containing a bundle of microtubules. Secretions of the border cells and oocyte were deposited against this tube, which later degenerates or is withdrawn. Normally this results in a canal, the micropyle, through which the sperm enters the egg. The slowed growth of the mutant oocyte presumably results from a defect in the transport of fluids or charged molecules to it, and the otu+ gene is therefore believed to play a vital role in this process.
In situ arrangement of nor-bearing chromosomes in the interphase nucleus of Aotus trivirgatus
Authors: Bourgeois C. A. , Costagliola D. , Laquerriere F. , Bard F. , Hemon D. , Bouteille M.
Published: April 2021

The spatial organization of the two nucleolus-organizing region(NOR)-bearing chromosomes during interphase was studied in Aotus trivirgatus fibroblasts, using nucleoli as ultrastructural markers. Their distribution was examined by measuring the distances between them in 30 reconstructed nuclei, and comparing these experimental values with the theoretical ones obtained by simulation.

Results were as follows: (1) the nucleoli are arranged in a polarized manner inside the nucleus; (2) the nucleoli are tightly bound to the nuclear envelope at two opposites sites; (3) the distance between the two nucleoli is variable, and is shorter than it would be if the two nucleoli were distributed at random.

These findings indicate that the NOR-bearing chromosomes are fixed at the nuclear envelope in two opposite areas. They are also consistent with the hypothesis that each chromosome occupies a separate domain inside the nucleus. They can be interpreted according to the model in which chromosome arrangement within the interphase nucleus is based on the separation of the diploid complement into two independent haploid sets.
Microfilament organization and total actin content are decreased in hybrids derived from the fusion of HeLa cells with human fibroblasts
Authors: Gowing Linda R. , Tellam Ross L. , Banyard M. R. C.
Published: April 2021

The organization of the microfilaments and the actin content of matched pairs of tumorigenic and non-tumorigenic HeLa/fibroblast hybrid cells was compared. Each pair consisted of a hybrid cell line with suppressed tumorigenicity and a segregant tumorigenic cell line derived from it. The tumorigenic HeLa parent cell line and a non-tumorigenic human fibroblast line were also included in the comparison. Microfilament organization of the cell lines was assessed by fluorescence microscopy using NBD-phallacidin, a probe that specifically binds to actin filaments. The re-expression of tumorigenicity is associated with a loss of microfilament organization. The actin content, as measured by the DNase I inhibition assay, was significantly lower in the tumorigenic hybrids and the HeLa parent than in the non-tumorigenic cells. The comparison was significant when the actin concentration was expressed either per cell or per protein. Despite this reduced level of total actin in tumorigenic cells, the ratio of monomeric to total actin remained constant in all cell lines tested.
Septum pattern in ts mutants of Schizosaccharomyces pombe defective in genes CDC3, CDC4, CDC8 and CDC12
Authors: Streiblová Eva , Hašek Jiří , Jelke Eckart
Published: April 2021

Septum-defective mutants of Schizosaccharomyces pombe impaired in cdc genes 3, 4, 8 and 12 were compared by fluorescence microscopy, freeze-etching and ultrathin sectioning. This approach made it possible to recognize the internal organization of defective phenotypes under restrictive conditions. Of special interest in this study was the pattern of unusual septum malformations found to be regular features of the terminal phenotypes of the mutants. Their overall topology was visualized at the cellular level by primulin fluorescence. The subcellular location of septum defects was found to be identical in origin to the compartment where normal septum was assembled in the wild type. Delocalized septation involved both microfibrillar and matrix components, which participated in the final assembly of malformations. Unique contour views of delocalized septa were exposed by freeze-fracturing. Cytoplasmic microtubules and microfilaments were detected in ultrathin sections of the cytoplasm of mutant cells. The internal organization of malformationaccumulating phenotypes suggested a disruption of the directional mechanism that steers septum material to the periplasm at the cell equator.
An electron-microscopic study of the termination of the afferent fibres to the olfactory bulb from the cerebral hemisphere
Authors: Price J. L. , Powell T. P. S.
Published: April 2021

An experimental investigation has been made of the site and mode of termination of the 3 groups of afferent fibres to the olfactory bulb which come from more caudal parts of the cerebral hemisphere. Lesions have been placed in the relevant parts of the brain of the rat and the resulting degeneration of axon terminals in the olfactory bulb studied with the electron microscope. All 3 groups of these extrinsic afferent fibres end in asymmetrical synapses upon the granule cells, and they have a differential termination upon its various processes. The possibility that these fibres also end upon other cells in the bulb (particularly the short-axon and penglomerular cells) cannot be excluded.

The centrifugal fibres end upon gemmules in the deep half of the external plexiform layer only; no degenerating terminals were found in relation to the glomeruh although degenerating centrifugal axons are present here. The fibres of the anterior commissure terminate upon spines and vancosities of the deep dendrites and upon somatic spines of the granule cells. After lesions of the anterior olfactory nucleus, degenerating terminals were found in the ipsilateral olfactory bulb, which could not be ascribed to the centrifugal fibres or to the fibres of the anterior commissure, as they ended upon the spines of peripheral processes in the granule cell layer, and upon gemmules in the superficial as well as in the deep half of the external plexiform layer. It is proposed that these terminals are those of the axon collaterals from the ipsilateral anterior olfactory nucleus. The axons which form symmetrical synapses, and many which form asymmetrical synapses, do not degenerate even after a lesion immediately behind the olfactory bulb, and are therefore intrinsic to the bulb. It is suggested that the axons which are associated with symmetrical synapses are those of the short-axon cells, and the asymmetrical synapses are formed by the axon collaterals of the mitral and tufted cells.
Electron-microscope observations on the structure of condensed chromatin: evidence for orderly arrays of unit threads on the surface of chicken erythrocyte nuclei
Authors: Everid A. C. , Small J. V. , Davies H. G.
Published: April 2021

A unit thread has been identified by electron microscopy as the common structural element in the condensed chromatin of a variety of cell nuclei. From the previous studies of thin sections normal to the nuclear envelope it was concluded that the unit thread, of diameter about 17 nm but varying somewhat depending on fixation, packed with spacings of about 28 nm on the surface of the nucleus to form one or more layers. Thin sections tangential to the nuclear envelope, described in this paper, reveal directly the degree of order within the surface layer; there are small areas or patches in which the units are regularly arranged. Units are also orderly arranged around the pores in the nuclear envelope. Unit threads are less easily visible in electron micro graphs of mature erythrocytes than at earlier stages of development but the clarity with which they can be seen is increased by a brief treatment prior to fixation with sodium citrate.
The fine structure of meiotic chromosome pairing in natural and artificial Lilium polyploids
Authors: Moens P. B.
Published: April 2021

In the autotetraploid Lilmm longiflonim (4n = 48), there are 12 sets of 4 homologous chromo somes. Within each set of 4 homologues, switches of pairing partners and crossovers occur at meiotic prophase. At the fine-structural level, the behaviour of the chromosomes is reflected in the switches between the axial cores of the homologous chromosomes. The normal synapto nemal complexes of the autotetraploid are compared with the complexes of the allotriploid L. tigrtnuvi, which have synaptonemal complexes with abnormal lateral elements. The possibility that the deformed lateral elements are the products of heteromorphisms between’ homologues’ is explored in the discussion. The observations on the chromosome cores are interpreted as support for the notion that the cores may be associated with the recombinationally active hereditary material during meiotic prophase.
The effect of insulin on the growth and metabolism of the human diploid cell, WI-38
Authors: Griffiths J.B.
Published: April 2021

In a confluent culture of WI-38 cells the membrane area available for nutrient uptake is greatly reduced and the possibility exists that this reduction in uptake capacity of the cell is a contributory factor in contact inhibition. Insulin has been reported by many authors to facilitate glucose uptak and also to stimulate protein, DNA and RNA synthesis, glycolysis, pinocytosis and growth in cultured cells. The effect of insulin on WI-38 cells was determined, therefore, to find out whether it enabled the cell to escape from contact inhibition of growth.

The action of insulin was found to be dependent upon medium composition. Growth and protein synthesis were stimulated in Eagle’s minimal essential medium, but not when this medium was supplemented with glucose and glutamine. Apparently insulin is only effective when high-energy compounds become limiting. Whilst insulin did not induce any post-confluent division, the protein content of cells was increased by 30%, and this was correlated with an increased rate of protein synthesis. Despite this increased activity in protein metabolism, the utilization of amino acids was less in the presence of insulin indicating that a control mechanism for more economical utilization of amino acids for protein synthesis was activated by insulin. Insulin had no effect on RNA synthesis, and only a slight inhibitory effect on DNA synthesis. Evidence was produced suggesting that insulin blocked cell division and encouraged differentiation. Glucose uptake and incorporation into the cell was stimulated by insulin, and this was especially noticeable after the cell sheet became confluent. The turnover of labelled glucose and derivatives was also enhanced by insulin and this was accompanied by a much higher rate of lactic acid production.

It is concluded that insulin does not overcome contact inhibition and permit post-confluent division, but that it does enable the cell to take up and utilize nutrients more efficiently in confluent cultures with a resultant increase in metabolic activity and cell size.
Growth and macromolecular synthesis in the 3T6 mouse fibroblast: II. the role of serum
Authors: Bates C. J. , Levene C. I.
Published: April 2021

Serum is necessary for growth of 3T6 mouse fibroblasts in log phase and for their maintenance in crowded cultures, at or near the stationary phase. Removal of the dialysable components of serum has only a small effect on growth and maintenance of these cells, and has no significant effect on macromolecular synthetic processes.

Fractionation of serum by ammonium sulphate precipitation did not reveal a specific association of growth-promoting activity with either of the major protein components: albumin or fetuin. The purest albumin-containing fraction, which was practically devoid of growth promoting activity, served as a control for the physical effects of protein in the absence of serum.

Omission of serum, or its replacement by albumin, caused the cells to die (i.e. disappear from the attached cell layer) at an approximately linear rate; the remainder increased in volume. Protein synthesis, including collagen synthesis, continued at a normal or enhanced rate in the remaining cells, but glucosamine incorporation was reduced.
Initiation and differentiation of microtubule patterns in the ciliate Nassula
Authors: Tucker J. B.
Published: April 2021

The mechanisms specifying microtubule arrangement and controlling the dimensions and shaping of microtubular components during cytopharyngeal development have been investigated. Heat shocks interfere with, or prevent, the operation of some of the processes involved, while others continue in a fairly normal fashion. For certain microtubular components the patterns of microtubule packing and the shapes of the components are very largely specified by the arrangement of the sites where tubule growth is initiated. Here the development of cross connexions between tubules serves only to stablize pre-existing tubule arrangements. However, there are indications that other intertubular materials are involved in the rearrangement of certain tubules. At several points in development the shapes and positions of extant microtubular components influence the patterns of tubules and other components subsequently developing in contact with them.

Heat shocks inhibit initiation of the development of certain tubules but longitudinal growth of existing tubules continues. When the number of developing tubules is reduced they attain greater than normal lengths, indicating that the extent of longitudinal tubule growth is largely determined by the size of the tubule precursor pool.
Comparative freeze-fracture study of perialgal and digestive vacuoles in Paramecium bursaria
Authors: Meier Renate , Lefort-Tran Marcelle , Pouphile Monique , Reisser Werner , Wiessner Wolfgang
Published: April 2021

In the endosymbiotic unit of Paramecium bursaria (Ciliata) and Chlorella sp. (Chlorophyceae) algae are enclosed individually in perialgal vacuoles, which do not show acid phosphatase activity and thus differ from digestive vacuoles. Both types of vacuoles have been studied by freeze-fracture.

Perialgal vacuoles are nearly spherical; their membrane always fits tightly to the algal surface. The vacuole size and shape do not vary much. During division of the algal cell into four autospores the vacuole diameter only doubles. After autospore formation the vacuole invaginates around the algal daughter cells and divides. Newly formed perialgal vacuoles remain in intimate contact and exhibit characteristic attachment zones before final separation. The two fracture faces of perialgal vacuole membranes are homogeneously covered with intramembranous particles (IMPs) but rarely show signs of vesicles pinching off or fusing with the membrane, except during vacuole division. The P-faces bear more IMPs (3164 ± 625 IMP/μ m2) than the E-faces (654 ± 208 IMP/μ m2). The range of IMP density on both faces is enormous, suggesting that the membrane is not static. Membrane changes are supposed to occur simultaneously with the enlargement of the vacuole and to be caused by fusion with cytoplasmic vesicles, as the fractured necks on vacuole membranes may indicate.

Digestive vacuoles in P. bursaria show significant variations in size, shape, membrane topography and IMP density, as well as signs of endocytic activity. Different vacuole populations are present in P. bursaria according to different feeding conditions: ciliates fed for a long time have small vacuoles with few IMPs (322 ±198 IMP/μ m2 on the E-faces, 1438 ± 458 IMP/μ m2on the P-faces), which are probably condensed digestive vacuoles, whereas organisms fed for a short time have larger vacuoles with highly particulate faces (680 ± 282 IMP/μ m2 on the E-faces, 2701 ± 503 IMP/μ m2 on the P-faces) and thus are supposed to be older vacuoles. The digestive vacuole membrane changes continuously.

Compared to digestive vacuoles perialgal vacuoles are characterized by small size combined with high IMP density on the two fracture faces. Their IMP densities resemble those of old digestive vacuole membranes. However, it would be premature to conclude that membranes of perialgal and old digestive vacuoles are identical. Membranes of old digestive vacuoles are mainly derived from lysosomal material, which presumably does not contribute to the formation of perialgal vacuole membranes as is indicated by the small vacuole diameter; fusion with lysosomes would considerably enlarge it. The conclusions from these results are discussed in relation to the formation of perialgal vacuoles during the establishment of a stable symbiotic unit after infection of alga-free P. bursaria with the Chlorella species exsymbiotic from green paramecia.
Structural and biochemical aspects of liver cell nuclear organization in normal and scalded rats
Authors: Śevaljević Ljiljana , Petrović Miodrag , Poznanović Goran , Śkaro Andjelija , Pantelić Dragoljub
Published: April 2021

The response of rat liver nuclei to thermal injury was studied at the ultrastructural and biochemical levels using nuclei isolated in the presence of either Mg2+ or polyamines and metal chelators.

The extent of chromatin condensation, as revealed by electron microscopy, increased in the order: nuclei in situ, Mg-stabilized nuclei, polyamine-stabilized nuclei. In addition, we observed that thermal injury caused an increase in the number of nuclear pores, an enlargement of nucleoli and an accumulation of ribonucleoprotein material. Along with this, greater amounts of protein, DNA and RNA were retained in nuclei from scalded rats.

The salt-resistant residue from Mg-stabilized nuclei was a spherical proteinaceous structure of the nuclear matrix, whereas that of the polyamine-stabilized nuclei was amorphous and deprived of three major constituents of the spherical matrix, the 60 –70 × 103Mr lamina proteins. However, exposure of the polyamine-stabilized nuclei to Ca2+ and Mg24- rendered the 60 –70 × 103Mr proteins salt-insoluble and thus enabled the extraction of a spherical residual nuclear structure. This structure was highly enriched in DNA, RNA and non-histone proteins and, hence, more like dehis-tonized nuclei than the minimal residual nuclear structure. It retained 70% of DNA in the controls but virtually all the DNA in scalded rats. This difference was interpreted to reflect activation-related changes in chromatin organization.
Activatable esterase activity of murine natural killer cell-yac tumour cell conjugates
Authors: Petty Howard R. , Hermann William , Dereski William , Frey Tom , Mcconnell Harden M.
Published: April 2021

Natural killer (NK) cells have been obtained from mouse spleens and grown in vitro. These cells: (1) retained cytotoxicity against YAC targets; and (2) were homogeneous as judged by morphology and surface markers. The a-naphthol acetate esterases (ANAE) and diisopropyl-fluorophosphate (DFP)-binding proteins of NK cells, YAC cells and NK-YAC conjugates have been examined. Ultrastructural cytochemistry indicates that NK cells have two types of ANAE: an enzyme primarily associated with the granule externum and an activatable ANAE associated with the granule internum. Both of these activities are inhibited by DFP. The activatable ANAE appears during incubation of NK cells with YAC cells.

DFP-binding proteins were examined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and autofluorography. NK cells and YAC cells have major DFP-binding proteins of 35 × 103 and 20 × 103Mr, respectively. NK-YAC conjugates had a new band at 55 × 103MrThis new protein may be identical to the activatable ANAE described above. Our studies provide evidence for an NK cell esterase that becomes activated when incubated in the presence of tumour cells. This esterase may be related to the cytolytic mechanism.
Cell type specific electrophoretic polypeptide profiles of cultured bovine cells
Authors: Lincoln David W. , Braunschweiger II, Karen I. , Braunschweiger Walter R. , Smith James R.
Published: April 2021

The polypeptide profiles of bovine vascular endothelial cells (from pulmonary artery and descending aorta), smooth muscle cells (from pulmonary artery) and fibroblast cells (from skin and lung) were examined by high-resolution two-dimensional polyacrylamide gel electrophoretic techniques. A set of polypeptides (molecular weights between 43 × 103 and 47 × 103 and pl values from 6·0—4·8, respectively) exhibited patterns that were unique to the three cell types. In the case of smooth muscle cells, these polypeptides exhibited cell-density-dependent expression. These results allow for identification of the three cell types on the basis of their highly specific polypeptide signatures.