bluuebunny/crossref_metadata_2025 huggingface dataset:
Association between tension and orientation of periodontal ligament fibroblasts and exogenous collagen fibres in collagen gels in vitro
Authors: Bellows C. G. , Melcher A. H. , Aubin J. E.
Published: April 2021

The relationship between the development of tension in sheets of fibroblasts and the orientation of these cells and collagen fibres in collagen gels was examined. Cell-containing, three-dimensional collagen gels were established in agarose-coated Epon dies measuring 10 mm × 4 mm × 4 mm, to which pieces of demineralized tooth and bone had been attached at opposite ends. Contraction of the gel into an opaque structure suspended between the two particles occurred over 24 h and resulted in concave upper and lateral surfaces and a flat to slightly concave lower surface. Initial orientation of the fibres along the tooth-bone axis was followed by similar orientation of the cells. Gels cast without cells exhibited no change in dimensions. Release of the tooth particle after 12 or 24 h of incubation led to shortening of the contracted gels 5 min following release. This shortening was significantly greater (P < 0·001) than that of uncontracted or slightly contracted gels (1 h and 3 h incubation). Gels attached at one end only compacted around the site of attachment but did not show orientation of cells or fibres. Gels containing colcemid or cytochalasin D were only slightly compacted and did not develop tension. Collagen fibres, but not cell in colcemid-containing gels, showed some alignment; neither were aligned in the presence of cytochalasin D. These data suggest that both microtubules and microfilaments are necessary for alignment of cells and the establishment of tension between two points of attachment in collagen gels. Furthermore, they lend support to our previously advanced hypothesis that the development of tension between two points can result in the orientation of the cells along an axis connecting the points of attachment. This could provide a mechanism for the development of oriented fibre systems in vivo.
The mononuclear cell population in rat leg muscle: its contribution to the lysosomal enzyme activities of whole muscle extracts
Authors: Etherington David J. , Wardale R. John
Published: April 2021

The mononuclear cell fraction of rat hind-limb muscle was obtained by digestion with clostridial collagenase in the presence of calcium ions, filtration through nylon screens and washing to remove the enzyme. Final traces of contaminant myofibrillar debris were separated by isopycnic centrifugation in a Percoll density gradient. Whole muscle, Washed cells and Percoll-fractionated cells were extracted in the presence of non-ionic detergent and the supernatants assayed for the lysosomal enzymes cathepsins B + L, 2V-acetyl-β-glucosaminidase, β-glucuronidase and protein. The enzyme levels were highest in the muscle from young rats, but the percentage of recovered activity in the mononuclear cell fraction was little altered by the age of the animal. The values obtained were: cathepsin B + L, 2·4–4·o%; N-acetylβ-glucuronidase, 4·3-7·6%; and β-glucuronidase, 6·3-10·3%. Because of unavoidable losses in preparation these are minimal values and the actual levels of activity from the mononuclear cell fraction in muscle would be higher. The specific activity values of the cell lysates were raised after isopycnic centrifugation and were nearly constant over the age range 65–180 days. Substantially higher specific activity values were obtained for the cells from rats of 38 days. When grown in culture the mononuclear cell fractions were seen to contain mainly fibroblasts and myoblasts with only few leucocytes. The cultures reached confluence by the second week, at which time numerous myotubes had formed. In addition there were groups of large, circular cells with a prominent centrosphere. The origin of these latter cells is uncertain.

It was concluded that although total lysosomal enzyme activity was higher in young rats there was little effect of age on the distribution of activity between muscle fibres and mononuclear cells in the muscle.
The effect of surface microvilli on the water permeability of single toad oocytes
Authors: Dick Elizabeth G. , Dick D. A. T. , Bradbury S.
Published: April 2021

The water permeability of isolated toad ovarian oocytes was found from their rate of shrinkage in hypertonic Ringer’s solution. Apparent membrane permeability coefficients, (k), calculated on the assumption that the cell surface was smooth, rose from about 20 μm s−1 in small cells 200 μm in diameter, to 35 μm s−1 in cells 800 μm in diameter and then fell to 5 μm s−1 in large cells of 2000 μm diameter.

The factor (f) by which microvilh extend the oocyte surface area beyond that of a smooth sphere was estimated from an analysis of electron micrographs of the cell surface. The value of f rose from 2 × at 200 μm diameter, to 11 × at 800 μm diameter and then fell to 5 × at 2000 μm diameter. The correlation coefficient between k and f was 0 474 (0 005 > P > 0·001). Corrected permeability coefficients, (k’), calculated so as to take account of the effects of the microvilh, (k’ = k/f), declined with increasing oocyte size, from 5 μm s−1 in small cells (200 μm) to 1 μm s−1 in large cells (2000 μm).

The correlation between k and f indicates resistance to water flow by the cell membrane, while the decrease in k’ as the cell grows suggests that diffusion in the cytoplasm may also be sufficiently slow to affect water flow out of the cell. It may be calculated that a surface membrane permeability coefficient in the range from 2 to 30 μm s−1 combined with an internal diffusion coefficient in the range from 6 × 10−8 to 10−6 cm2 s−1 could account for the effects found.
Ultrastructural features of defective In Vitro keratinization of chick embryonic skin
Authors: Jensen H.M. , Mottet N. K.
Published: April 2021

Thirty-four explants of epithelium and subjacent mesenchyme from the hind limb buds of 5-day chick embryos were cultured for 1 to 14 days. Controls consisted of a series of in ovo limb bud specimens from 5 day’s incubation to hatching. Both experimental and control specimens were examined by similar electron-microscopic methods.

Differentiation of epidermis was precocious and that of dermis extremely retarded in vitro, contrasting with the events in ovo where epidermal differentiation occurred later and differentiation of dermis was early and vigorous. The two types of epidermal cells developed to a different degree in vitro. Pencytes and their derivatives at times developed precociously and reached full maturity, although their pattern of differentiation was asynchronous compared with that in ovo. Basal cells and their derivatives produced filaments precociously but mature keratrnized cells were not found. Absence of keratohyaline granules in the epithelial cells appeared to be the initial defect in the keratinization process. Hyperplasia of mitochondria in basal and parabasal cells was also noted. The underlying mesenchyme, which in ovo begins to produce large amounts of collagen at an exponentially accelerating rate at 5 days, synthesized only scant collagen under the in vitro conditions employed. The hypothesis is presented that the mesenchyme alters epithelial differentiation by affecting keratohyaline synthesis which in turn controls keratinization.
The effect of neuraminidase (3:2:1:18) on the aggregation of cells dissociated from embryonic chick muscle tissue
Authors: Kemp R.B.
Published: April 2021

Embryonic chick muscle cells were used to investigate the effect of removing cell-surface sialic acids on cell aggregation in vitro. Single cell suspensions were prepared by dissociating skeletal muscle tissue of 9-day-old chick embryos with either crystalline or crude trypsin. Cell aggregation was quantitatively estimated by turbidimetric and gyratory shaker methods.

Cells dissociated with crude trypsin and suspended in Hanks’s balanced salts solution (BSS) containing 25 u./ml neuraminidase (NANase) only aggregated for 2 h when rotated in an absorptiometer. The inhibitory effect of the enzyme was more pronounced with increasing concentration up to 25 u./ml. Cells dissociated with crystalline trypsin and treated with 100 u./ml NANase immediately exhibited a reduced aggregative competence when gyrated in Eagle’s minimum essential medium (MEM) containing 25 u./ml NANase, compared with the controls which were not exposed to NANase. The aggregation rate of muscle cells pretreated with 100 u./ml NANase and suspended in Eagle’s MEM was similar to that of the untreated controls. Cell counts showed that under all three experimental conditions cells were not added to aggregates after the 12-h stage. Aggregates formed in Eagle’s MEM (the controls) joined together to form larger aggregates after 12 h, but those rotating in the presence of NANase did not display this property.

Lissamine green viability tests showed that cells remained alive throughout the 24-h period in the presence of NANase. Determinations of oxygen uptake, protein synthesis and mitotic index confirmed that general cellular viability was not affected by NANase. Fluorescent-labelled NANase was not taken up by the cells.

Treatment of crystalline trypsin-dissociated muscle cells with 100 u./ml NANase for 30 min at 37 °C significantly reduced their negative electrophoretic mobility. This diminution closely corresponded to the removal of cell-surface sialic acids, as measured by colorimetric tests.

Interpretation of the results in the light of current theories of cell adhesion failed to give support to the concept of adhesion by physical forces. The mechanism by which cellular deformability could influence cellular adhesiveness is modified in the knowledge of the present results.
The magnitude of the extracellular space in electron micrographs of superficial and deep regions of the cerebral cortex
Authors: Harreveld A. Van , Steiner Jana
Published: April 2021

Electron micrographs (EMs) of central nervous tissue perfused with glutaraldehyde and post-fixed with osmium tetroxide exhibit more extracellular space in superficial than in deep regions of the brain. It was postulated that this is due to the availability to the surface tissue of the cerebrospinal fluid in the subarachnoidal space. It was assumed that in addition to the extracellular material this fluid is taken up by dendritic elements in the surface layer of the cortex during the glutaraldehyde perfusion. Indeed, dendritic structures in EMs of the surface layer of glutaraldehyde-perfused and OsO4-post-fixed cortex exhibited a more pronounced swelling than similar structures in deeper cortical regions, where only extracellular material was available to the dendrites. The extracellular space in such preparations consisted of narrow slits surrounding the tissue elements. These slits were formed during the post-fixation since they were not present in freeze-substituted, glutaraldehyde-perfused tissue, which showed a paucity of extracellular material. The slits were in general wider in the superficial than in the deep cortical tissue. That this difference is related to the amount of material taken up by the dendrites during the glutaraldehyde perfusion was supported by experiments in which the exposed cortical surface was flooded with Ringer’s solution during the glutaraldehyde perfusion. This resulted in a ballooning of dendritic elements in the cortical surface due to the availability of an unlimited amount of fluid on the cortex. Post-fixed material of these flooded cortices yielded EMs with unusually wide extracellular slits around the tissue elements.
Mapping of highly ordered membrane domains in the plasma membrane of the ciliate Cyclidium glaucoma
Authors: Bardele Christian F.
Published: April 2021

The entire cortex of Cyclidium glaucoma has been analysed in a correlated freeze-fracturing and ultrathin-scctioning study. Three types of highly ordered domains of intramembranous particles were found in the plasma membrane; owing to the many landmarks in the cortex of C. glaucoma it was possible to map their location in relation to the precisely known position of every single cilium. Eight particle plates made of parallel tripartite particle ridges have been found in precisely determined locations at the anterior pole of the cell and in the buccal cavity. It is suggested that these membrane specializations represent mechanosensitive sites. An array of three parallel rows of particles, termed a ‘simple pellicular rug’, forms a second type of membrane domain, which is closely associated with somatic dikinetids found exclusively in the anterior half of the cell. A third extremely complex array, termed a ‘complex pellicular rug’, is associated with the monokinetids in the posterior half of the cell. There is no gradient in the distribution of these domains but a sharp boundary at the level of the future fission zone. The function of the pellicular rugs is unknown, but their specific distribution will be helpful in further studies on their assembly prior to or during cell division.

The intracellular diversification of the cell surface is further augmented by the disclosure of three different aspects of the proximal part of the ciliary membrane. Beyond the double-stranded ciliary necklace, which is a common feature of all cilia, only the motile somatic cilia of C. glaucoma have typical ciliary plaques made of three rows of particles, while all oral cilia have modified plaques, which consist of four rows of particles. The single stiff caudal cilium has no plaques at all. The functional significance of the topographic differences in the plaque areas is discussed. Obviously, the plasma membrane and at least parts of the ciliary membrane form a non-fluid mosaic membrane.
Adaptation of human diploid fibroblasts in vitro to serum from different sources
Authors: Zamansky Glen B. , Arundel Carla , Nagasawa Hatsumi , Little John B.
Published: April 2021

The growth of two human diploid skin fibroblast cell lines, originally grown in medium supplemented with foetal bovine serum and later adapted to medium supplemented with newborn bovine, bovine calf or horse serum, has been studied. Prolonged generation times, increased cell volumes and decreased plating efficiencies were observed in cultures grown in newborn bovine, bovine calf or horse serum. In general, the deleterious effects were most severe as a result of growth in bovine calf or horse serum. In the light of the present findings, we believe investigators should exert great caution in switching human fibroblast cultures from foetal bovine serum to alternative sera, even at times of scarcity and high prices.
Degeneration and regeneration of chloroplasts in Euglena gracilis grown in the presence of acetate: Ultrastructural evidence
Authors: Vannini Gian Luigi
Published: April 2021

When green cells of Euglena gracilis, strain Z, were light-grown for several months on a solid medium containing an excess of sodium acetate (1·0% instead of the normal 0·1 %), some 30% of the cells were colourless. The ‘acetate-bleached’ organisms, isolated by plating methods and subsequently incubated in the light in a liquid medium, regained the capacity to form chlorophyll in a few days in the absence of any organic carbon source, and within 1-2 weeks in the presence of 0·1 % acetate. A number of bleached colonies, however, gave rise to populations in which the delay in pigment synthesis initiation was at least 2 months.

Besides numerous paramylum granules and lipid inclusions, the acetate-bleached cells exhibited variably shaped and sized plastids, apparently lacking in ribosomes and showing a deeply disorganized membrane system. In the alga greened in the presence of 0·1% acetate, the pattern of plastidome reorganization was altered; the thylakoids were often unpaired and vesiculated in different degrees, owing primarily to the swelling of the lumen. A complete recovery of normal chloroplast structure occurred only after several weeks of exponential growth. The entire population greened in the absence of acetate constantly showed normal chloroplasts with perfectly reassociated thylakoids and clear partitions.
Polyacrylamide Gel Electrophoretic Screening of Mammalian Cells Cultured In Vitro For The Presence Of The Intermediate Filament Protein Vimentin
Authors: Traub Ulrike E. , Nelson W. James , Traub Peter
Published: April 2021

A total of 63 different cell lines originating from a variety of mammalian species were cultured in vitro and analysed for the presence of vimentin, employing polyacrylamide gradient slab gel electrophoresis in urea/acetic acid as buffer system. Irrespective of the cell culture conditions, and the growth potential and morphology of the cells, vimentin was expressed in all cell lines examined, with two exceptions: MPC-11 mouse myeloma and M0PC-31C mouse plasmacytoma cells. Immunoblotting with the monoclonal antibody α-IFA, which is directed against an antigenic determinant shared by all classes of intermediate filaments, did not detect any other of the known intermediate filament proteins in MPC-11 and M0PC-31C cells.

Vimentin synthesized by various cell lines was characterized by four different criteria: (1) its extractability with Triton X-100 under various ionic conditions; (2) its behaviour in (NH4)2SO4 fractionation of cellular extracts; (3) its electrophoretic mobility in polyacrylamide gel electrophoresis in urea/acetic acid ; and (4) the co-isolation of polypeptides of higher electrophoretic mobility, which, by comparison with degradation products of vimentin obtained with the Ca2+-activated proteinase specific for intermediate filament proteins in vitro, were identified as products of Ca2+-dependent proteolysis of vimentin. Although the degradation products occurred in different ratios in extracts of different cell lines, they constituted the same characteristic set of proteins whenever degradation of vimentin was observed. The formation of proteolytic breakdown products could be partially to totally suppressed when the cells were harvested, washed and processed in the presence of EGTA and proteinase inhibitors.

The experimental data show that: (1) vimentin, as well as the Ca2+-activated proteinase specific for intermediate filament proteins, is highly conserved during the evolution of mammalian species; (2) the proteolytic breakdown products of vimentin, which give rise to a characteristic ‘staircase’ in two-dimensional gel electrophoresis, are probably artefacts of isolation ; (3) the expression of vimen-tin is neither a prerequisite for nor necessarily indicative of rapid cell proliferation in vitro; and (4) the techniques described can be used for the routine identification of vimentin in cells and tissues in case vimentin-specific antibodies are not available.
Development Of Cell Junctions In Seaurchin Embryos
Authors: Spiegel E. , Howard L.
Published: April 2021

The development of cell junctions in sea-urchin embryos has been investigated using thin sections, lanthanum-tracer and freeze-fracture techniques. Three types of desmosomes are present: belt desmosomes and spot desmosomes, which attach cells to each other, and hemi-desmosomes, which attach cells to the basement membrane. Two types of septate junctions are present: the straight, unbranched, double-septum septate, which is present in epithelial cells throughout embryogenesis, and the pleated, anastomosing, single-septum septate. The latter is formed only on cells that have invaginated to the interior of the embryo to form the digestive tract. The pleated junctions are shown to replace the straight junctions that were originally present before the cells migrated to the interior. It is suggested that these pleated septates may be specialized for digestive processes, since they are developed just prior to feeding and are retained in the adult intestine. Tricellular junctions, which join the bicellular junctions of three adjoining cells, have been identified in the embryo and in the adult intestine. Evidence for the presence of gap junctions was not obtained, but there are indications of their presence.
Conformational response of the glycocalyx to ionic strength and interaction with modified glass surfaces: Study of live red cells by interferometry
Authors: Wolf H. , Gingell D.
Published: April 2021

We have measured separation distances between live human red blood cells and simple or modified glass surfaces, using the finite aperture technique of microscope interferometry. In general, separation increases as the ionic strength falls, in isotonic solutions. Restriction on movement parallel to the glass in all except the most dilute salt solutions, coupled with the absence of Brownian motion, indicates direct molecular contact with the substratum. Thus increased separation must be due to swelling of the glycocalyx under electrostatic forces. However, at ⪯2 mM adherent cells show a separation > 100 nm, execute Brownian motion and the restriction on lateral motion is less evident. This suggests that secondary minimum adhesion by long-range forces with little or no direct molecular connection occurs at extreme dilution only.

Treatment of cells with trypsin reduces separation by up to 40 nm, but the extent to which this reflects reduced double-layer repulsion due to loss of surface charge, as opposed to the reduced opportunity for swelling in a trimmed-down glycocalyx, is unclear. Adhesion at a separation ∼ 100nm in 1 min buffer after trypsinization supports the view that adhesion can occur without very long glycoprotein connections, but does not prove it.

Adhesion to unwettable methylated glass and completely wettable unmethylated glass, with an identical ionic strength dependence of the separation, shows that hydrophilicity is not an absolute requirement. Red cells interact closely at all ionic strengths with glass made polycationic with poly-L-lysine, owing to electrostatic attraction.

The interference technique also shows that adherent cells can be spaced from the glass by an intervening layer of previously absorbed serum albumin.
Ultrastructural aspects of sporogenesis in the apogamous fern Dryopteris borreri
Authors: Sheffield E. , Laird S. , Bell P. R.
Published: April 2021

The events that accompany sporogenesis in the apogamous fem Dryopteris borreri parallel those seen in sexually reproducing ferns. Organelles dedifferentiate and redifferentiate, and form a discrete band across the equator of dyads; nuclear vacuoles and lipid spherosomes appear during prophase, and the major part of the ribosome population is removed and subsequently replaced during meiosis. Similar events have been found to occur during sporogenesis in mosses, gymnosperms and angiosperms, and are therefore characteristic of the meiotic transition from sporophyte to gametophyte, even in the absence of a transition from diplophase to haplophase.

The novel aspects of meiosis in D. borreri are largely those connected with the restitution event that precedes meiosis I and serves to maintain the sporophytic chromosome number throughout the life cycle of this fem. Pre-meiotic cells are regularly found to be cleaved by annular wall ingrowths, which traverse the cytoplasm but not the nuclei. The significance of these ingrowths in relation to theories concerning apogamy and plant cell division are discussed.
Effect of substratum wettability and charge on adhesion in vitro and encapsulation in vivo by insect haemocytes
Authors: Lackie Ann M.
Published: April 2021

The circulating leucocytes of insects, the haemocytes, adhere to and encapsulate foreign material that enters the insect’s body cavity. The thickness of the capsule depends not only on the insect species but also on the nature of the object concerned, a fact that is of great importance to invading parasites and pathogens. In this paper, some of the factors that may stimulate haemocyte adhesion and subsequent encapsulation of the object have been investigated using abiotic materials with surfaces of different charge and wettability. The negativity and wettability of surfaces of polystyrene beads and plates can be increased by pretreatment with acid, and adhesion of haemocytes to these modified surfaces has been examined in vivo and in vitro. A similar proportion of haemocytes of the locust Schistocerca gregaria adhere to the plates in vitro, irrespective of the changes in charge and wettability, but the adhesion of haemocytes of the cockroach Periplaneta americana is proportional to the increases in both parameters. These differences in cell behaviour are reflected in vivo: cockroach haemocytes form thicker capsules around more hydrophilic and more negatively charged polystyrene beads, while locust cells encapsulate both types of surface to the same, minimal, degree. Positively and negatively charged Sepharose beads are encapsulated more thickly than are neutral beads in cockroaches; negatively charged Sepharose beads are not encapsulated at all in locusts.

There are thus obvious differences between the two species in the ways in which their haemocytes respond to these modified abiotic surfaces. It is suggested that capsule thickness in vivo depends on the initial cell-substratum contact; different surfaces stimulate the cell to different extents, which in turn causes variations in the recruitment of other cells to the capsule.
Antibody-induced membrane fusion in Paramecium
Authors: Barnett Audrey
Published: April 2021

Immobilization of cells by specific immune serum involves crosslinking between immunoglobulin G (IgG) and the i-antigen in the cell membrane. Globular material is seen to accumulate at the ciliary tips by phase-contrast and fluorescence microscopy in a manner analogous to ‘capping’ in more typical eukaryotes. When immobilized cells of Paramecium are examined by scanning electron microscopy, the fused ciliary tips are seen to be distended, discoidal membranes. Transmission electron microscopy often reveals several ciliary axonemes enclosed within a single, enlarged membrane that is oriented with the ferritin-labelled second antibody directed against the i-antigen antibody on the outer surface only. Fixed cells or living cells treated with immune Fab do not show membrane changes, but do bind antibody. Membrane fusion occurs only if cells are alive and the i-antigen is directly or indirectly cross-linked by intact immune IgG.
The mitotic spindle of chinese hamster ovary cells isolated in taxol-containing medium
Authors: Kuriyama Ryoko , Keryer Guy , Borisy Gary G.
Published: April 2021

Mitotic spindles from Chinese hamster ovary (CHO) cells were isolated and purified by a one-step procedure in an isolation medium containing the microtubule-stabilizing drug, taxol. Released mitotic spindles were examined by phase-contrast, polarizing and differential-interference microscopy. They were also stained with monoclonal antibody raised against yeast tubulin and examined by epifluorescence microscopy. The spindles were free from visible cytoplasmic contaminants and the chromosomes were generally lost from the preparations. Electron microscopy showed that microtubules were the dominant structural component and sodium dodecyl sulphate/gel electrophoresis showed that tubulin was the major molecular species present, although a number of minor components, possibly representing microtubule-associated proteins (MAPs), were present. The taxol procedure was also useful in obtaining other microtubule-containing structures such as the midbody or the cytoplasmic microtubule complex in interphase cells. The taxol procedure was also used to isolate mitotic spindles from HeLa cells. The HeLa spindles stained positively with an antibody specific for the 210 × 103 Mr microtubule-associated protein, indicating that the MAP was retained by the taxol procedure. The taxol procedure appears to be of great advantage in large-scale preparations of spindles for biochemical analysis.
Intermediate filaments in the cytoskeletons of fish chromatophores
Authors: Murphy Douglas B. , Grasser William A.
Published: April 2021

When fish pigment cells (melanophores, erythrophores) are lysed by a modified Kleinschmidt method on a buffer–air interface and examined by electron microscopy, large numbers of intermediate filaments are observed. The intermediate filament networks are distinct from actin and tubulin, and entrap the pigment as determined by stereo viewing of freeze-dried rotary-shadowed specimens. During lysis, under conditions that do not preserve actin filaments or microtubules, the area covered by dispersed pigment granules reaches a maximum size and remains stable for many minutes, suggesting that intermediate filaments are responsible for holding the pigment in position and preventing further cytoplasmic dispersion. These observations demonstrate that fish pigment cells contain large numbers of intermediate filaments and suggest that they may be important for coordinating pigment granule movement.
Resorption of bone by isolated rabbit osteoclasts
Authors: Chambers T.J. , Revell P.A. , Fuller K. , Athanasou N.A.
Published: April 2021

A carborundum wheel was used to prepare slices of cortical bone that demonstrate a predictable surface appearance in the scanning electron microscope. Osteoclasts were mechanically disaggregated from neonatal rabbit long bones and settled onto these slices. After 24h in culture osteoclasts were associated with areas of excavation in the bone surface. These excavated areas typically showed a well-defined outline and a distinctive fibrillar base, which resembled the pattern of collagen fibrils in bone. The majority of such concavities were of approximately circular outline and of smaller diameter than the associated osteoclast, but other excavations were elongated or of complex morphology, and may have been produced by osteoclasts that were resorbing bone while they migrated. Irregular concavities tended to be more shallow but to occupy a greater area of the bone surface than circular concavities. Roughening of the bone surface without detectable excavation was also seen adjacent to osteoclasts. Calcitonin and cytochalasin B, which inhibit osteoclastic motility, also inhibited bone resorptive activity by these cells. The techniques described in this paper represent a model system with which to assess the direct and indirect effects of hormones, cells and substrate composition on the induction, stimulation and inhibition of osteoclastic bone resorption and to investigate the mechanisms by which cells degrade extracellular matrices.
Reorganization of hydrated collagen lattices by human skin fibroblasts
Authors: Grinnell Frederick , Lamke Cheryl R.
Published: April 2021

Fibroblasts were cultured on top of or at the bottom of hydrated collagen lattices. Shortly after initially interacting with the collagen lattices, fibroblasts appeared to attach to individual collagen fibrils and in many cases cell processes were found wrapped around clusters of collagen fibrils. Tension generated by cells during spreading resulted in proximal collagen fibrils becoming aligned in the plane of spreading and more densely packed. During subsequent culture, the collagen fibrils distal to the cells underwent a similar reorganization and the lattice thinned to one-tenth of its original thickness. The rate of thinning was similar regardless of whether the cells were originally above or at the bottom of the lattices. The presence of cells distributed throughout the lattice was unnecessary for lattice reorganization to occur. When the lattices were allowed to come off the underlying substratum, compaction of the collagen gels was observed, and the resulting matrix had the typical appearance of dermis as observed by both light and electron microscopy. Collagen fibrils associated with the cell surface often appeared to be under tension and, in regions of close fibril binding, there was a prominent reorganization of submembranous microfilaments. It is suggested that reorganization of the collagen lattice by fibroblasts may depend upon secreted cell factors as well as physical forces generated by the cells.
Isolation And Phenotypic Characterization Of Tetrahymena Thermophila Size Mutants: The Relationship Between Cell Size And Regulation Of Dna Content
Authors: Seyfert H. M. , Hipke H. , Schmidt W.
Published: April 2021

Temperature-sensitive size mutants of the ciliate Telrahymena thermophila were selected following chemical mutagenesis. Phenotypical characteristics are given for seven cell lines, which have a range of average cell volumes from 8000μm3 to more than 100 000μm3. Wild-type Tetrahymena cells have an average cell volume of 15 000 μm3. Two of the mutagenized cell lines have comparatively small cells at 29°C but normal cells at 37°C; whereas the other five lines are normal at 29°C but large at 37°C. While the small cells are poor growers, the large cells grow excellently at 37°C. Measurements of DNA, RNA and protein contents indicate a significant correlation between all parameters and cell size. However, since the cells tolerate considerably different concentrations of each class of macromolecules, the amount of any of these macromolecules cannot be tightly controlled by cell size.
The Cellular Program For The Formation And Dissolution Of The Synaptonemal Complex In Coprinus
Authors: Lu B. C.
Published: April 2021

Inhibition of protein synthesis by cycloheximide on processes in meiosis was used to probe the cellular program for the formation and dissolution of the synaptonemal complex (SC) in the synchronous meiotic system of Coprinus cinereus.

The pathway for the synthesis and assembly of the synaptonemal complex is proposed to be as follows: (1) synthesis and assembly of lateral components on the chromosomes; (2) synthesis and assembly of the central components in the nucleolus; (3) the lateral components of the homologous chromosomes are brought together to pair when the homologous pairing occurs at zygotene; (4) the transport of the central components from the nucleolus to join the paired lateral components and thus complete the synaptonemal complex.

Continued protein synthesis is required for all steps. Step (1) is nearly complete 2 h after the onset of karyogamy, because continued assembly is possible in the presence of cycloheximide. The transition point for step (2) is 4 h after the onset of karyogamy, as inhibition at this point results in accumulation of central components in the nucleolar dense body. The paired lateral components of step (3) are deprived of the central component. The transition point for step (4) is 5 h after the onset of karyogamy, for inhibition at this point no longer prevents transport.

Two steps are proposed for dissociation and dissolution of the SC at the end of pachytene. Protein synthesis is required for the dissolution of SC. Inhibition at this point causes accumulation of polycomplexes.

Mutations in various organisms from the literature relating to the SC support the validity of the proposed pathway.
The concentrations of water, sodium and potassium in the nucleus and cytoplasm of amphibian oocytes
Authors: Century T. J. , Fenichel I. R. , Horowitz S. B.
Published: April 2021

Techniques are described for the isolation of nuclei and cytoplasm from frozen amphibian oocytes at − 40 °C and their analysis for water, sodium, and potassium contents. Nuclei of the 4 species studied contain 74–85% water while cytoplasm is only 35–50% water. Nuclei contain 7–17 μequiv. Na/ml H2O and 123-129 μequiv. K/ml H,O; cytoplasm contains 50–84 μequiv. Na/ml H2O and 81–94 μequiv. K/ml H2O. Mechanisms suggested to explain the observed nucleo-cytoplasmic asymmetries are the selective sequestering of sodium in the cytoplasm and a fraction of cytoplasmic water which does not act as solvent. Asymmetric cation transport by the nuclear membrane is not indicated.
An ultrastructural study of pyrenoids from Chlorella pyrenoidosa
Authors: Bertagnolli B. L. , Nadakavukaren M. J.
Published: April 2021

The fine structure of pyrenoids from Chlorella pyrenoidosa shows a crystalline matrix with an8-o-nm periodicity. In certain areas of the pyrenoid 2 sets of parallel lines intersect at approximately 80° to give a criss-crossed appearance to the matrix. The recognition of the crystalline structure depends on the portion of the pyrenoid that is sectioned, as well as the plane of sectioning.

A distinct crystal-like body which is closely associated with the thylakoid lamellae that traverse the pyrenoid matrix is observed in one cell.

Although 2 pairs of thylakoid lamellae run separately through the pyrenoid matrix of a cell, they appear to be continuous with each other outside the pyrenoid.

The fine structure of the pyrenoid, at any given time, seems to be a reflection of its metabolic state. A lack of understanding of the exact function or functions of pyrenoids makes a more rational interpretation of pyrenoid ultrastructure difficult.
The mitral and short axon cells of the olfactory bulb
Authors: Price J. L. , Powell T. P. S.
Published: April 2021

A description is given of the mitral and short axon cells of the olfactory bulb of the rat from Golgi material examined with the light microscope and from material examined with the electron microscope. The mitral cells are large neurons with primary and secondary dendrites which both extend into the overlying external plexiform layer, although only the primary dendrite enters the glomerular formations. No predominant antero-posterior orientation of the secondary dendrites has been found. Within the glomeruli the mitral cell dendrites are in synaptic contact with the olfactory nerves and also with the periglomeiular cells, but elsewhere the only synapses on the mitral cells are the ‘reciprocal synapses’ with the granule cells. Synaptic-type vesicles are found in all parts of the mitral cells, including the axon initial segments; they appear to be especially concentrated in the distal portions of the dendrites.

Several types of short axon cells have been found in the granule cell layer in Golgi-impregnated material. Their cell bodies can also be distinguished with the electron microscope, and from previous work it is probable that the axons of at least some of these cells form flattened vesicle symmetrical synapses upon the granule cells.
Destruction of immaturin activity in early mature mutants of Paramecium caudatum
Authors: Miwa Isoji
Published: April 2021

Cells of Paramecium in the sexually immature period of the clonal life cycle contain a protein called immaturin, which represses mating activity when injected into sexually mature cells. The amount of immaturin at various stages of the immaturity period was examined by injecting cytoplasm from immature cells of one wild-type and two early mature mutant clones into mature cells of wild-type. The proportion of immature cells brought about by the injection increased until about 10-15 fissions after conjugation of the donor cells in all three clones. But the percentage of immature cells induced by the injection decreased rapidly from the 25th to the 30th fission of both early mature donors, while the percentage was still high with a wild-type donor of the same fission age. When cytoplasm of the Emt A (early mature mutant) homozygote taken immediately before maturation (about 27 fissions) was injected into the wild-type immature cells of 45 fissions after conjugation, 13% of the recipient cells expressed mating reactivity. But when cytoplasm of Emt A cells 20 and 50 fissions after conjugation was injected into the same cells, no reactive cell appeared. The results suggest that cytoplasm of the early mature mutant immediately before maturation contains some material that accelerates maturation when injected into wild-type cells in the late stage of immaturity. On the other hand, the immature cytoplasm of wild-type cells about 25 fissions after conjugation showed no effect when injected into early mature cells immediately before maturation. The function of the early mature gene product was suggested to be the destruction of immaturin activity.
Unique calcium-dependent hydrophobic binding proteins: Possible independent mediators of intracellular calcium distinct from calmodulin
Authors: Moore Pamela B. , Kraus-Friedmann Naomi , Dedman John R.
Published: April 2021

Calcium-dependent regulation of cellular processes is mediated by specific intracellular proteins. A newly described set of proteins isolated from chicken gizzard with Mr of 67 × 103, 35 × 103, 33 × 103 and 30 × 103 also express a hydrophobic site in the presence of calcium. These proteins are isolated from several other cellular tissues and are termed calcimedins. These proteins differ from calmodulin in isoelectric point, DEAE-cellulose binding characteristics and heat stability. The calcimedins do not activate calmodulin-dependent cyclic nucleotide phosphodiesterase but do activate a hepatic microsomal Ca2+-ATPase system. Hence, the possibility is opened that calcium regulation of cellular processes is mediated by calcium-binding proteins in addition to calmodulin.
Ultrastructural analysis of the initiation and development of cytasters in sea-urchin eggs
Authors: Kallenbach Rein J.
Published: April 2021

Two approaches were used to study the origin and overall development of cytasters in relation to the emergence and maturation of new centrioles in sea-urchin eggs. A continuous hypertonic treatment was used to gather information on cytoplasmic areas of potential cytaster formation and the subsequent development of these cytastral areas. A two-step parthenogenetic stimulation procedure was used to analyse various cytastral changes during and after mitosis. Potential cytastral areas are associated with extensive Golgi complexes and astral formation occurs only about newly induced centrioles. The construction of a single aster involves a large redistribution of local cytoplasmic structures, concentrating some components, excluding others and orienting more and more microtubules in an increasingly focussed arrangement. These events are correlated with an extensive accumulation of astral endoplasmic reticulum, an increase in the size of the astral area, and a gradual acquisition of a more typical radial configuration. The astral shape becomes more pronounced during mitosis, after which the cytasters regress, but retain the mature centrioles. The data reveal that cytaster formation is initiated after the activation and appearance of centriolar precursor bodies, and that both centrioles and associated cytasters are complementary structures, which develop in unison. The results suggest that developing centrioles, from the moment of their emergence, control and direct the events of cytastral formation.
Proliferation of a human embryonal carcinoma-derived cell line in serum-free medium: Inter-relationship between growth factor requirements and membrane receptor expression
Authors: Engström Wilhelm , Rees Anthony R. , Heath John K.
Published: April 2021

Substantial multiplication in vitro of cloned cells from a human embryonal carcinoma cell line, Tera 2, has been obtained in a basal medium (DMEM/Ham’s F12,50:50, v/v) supplemented with 10μg low density lipoprotein/ml, 100μeg high density lipoprotein/ml, 100ng multiplication stimulating activity/ml, 100 ng insulin/ml and 1 μg transferrin/ml. The growth rate appears to be similar to that obtained in 10% serum. Furthermore, studies on the expression of cell surface receptors revealed that cloned Tera 2 cells express high-affinity receptors for IGF-II but not for insulin. The cells also express receptors for Epidermal Growth Factor (EGF) even though the addition of EGF does not stimulate their proliferation in serum-free medium. These results suggest that the expression of specific growth factor receptors is not an absolute determinant of hormone responsiveness.
Consequences of parental exposure to serum-free medium for progeny cell division
Authors: Larsson Olle , Zetterberg Anders , Engströmi Wilhelm
Published: April 2021

Proliferating serum-dependent 3T3 cells prolong their intermitotic time by 9-10 h after exposure to serum-free medium for only 1 h. This delay was only observed in cells younger than 4h, i.e. cells in the postmitotic G1 phase (G 1 pm), as defined by time elapsed since previous mitosis. These data confirm earlier findings that cells are very sensitive to growth factor or serum depletion during the first part of G1 and that only a short exposure to serum-free medium is sufficient for the cells to leave the cell cycle. However, such cells that have delayed their first cell cycle in response to a short exposure to serum-free medium in early G1 exhibit a reduced capacity to delay the subsequent cycle in response to a repeated exposure to serum-free medium. In contrast cells older than 4 h that are exposed for short periods to serum-free medium undergo cell division on schedule, but delay the subsequent cell cycle by several hours. This delay of the progeny cycle is mainly ascribable to the postmitotic part of G1 (G1pm). These data suggest that short exposures to serum-free medium exert an indirect effect on the progeny cell cycle and demonstrate that cycle times are not necessarily determined de novo in the lifetime of every cell, but may be influenced by events in the preceding cycle.
Caveolae intracellulares and sarcoplasmic reticulum in smooth muscle
Authors: Gabella G.
Published: April 2021

In the smooth-muscle cells from guinea-pig ileum a highly developed sarcoplasmic reticulum has been observed immediately underneath the plasma membrane in close relationship to the caveolae intracellulares. It is suggested that sarcoplasmic reticulum in smooth muscle may play a similar role as in skeletal muscle, constituting the main intracellular store for calcium.
Bound lipid in the tissues of mammal and insect: A new histochemical method
Authors: Wigglesworth V. B.
Published: April 2021

‘Bound’ lipids persist in ester wax sections of tissues fixed in glutaraldehyde. They do not take up Sudan black B. They are unmasked by dilute sodium hypochlorite and then stain readily with the Sudan dye and are extractable in warm chloroform and methanol.

Bound lipids have been studied in tissues from the mouse and from the insects Rhodnius, Periplaneta and Calliphora. They are so widely distributed that Sudan staining alone gives an informative histological picture.

They occur in nucleoli and the nuclear envelope, in the nuclear matrix and in the cytoplasm (especially when rich in endoplasmic reticulum), in plasma membranes and their invaginations and évaginations (microvilli), in septate desmosomes, and particularly in mitochondria, dictyosomes and myelin.

In erythrocytes they are not only concentrated in the surface membrane but are distributed throughout the interior of the cell. In muscle fibrils (papillary muscle of the ventricle and fibrillar flight muscle of Calliphora) bound lipid occurs in small amounts in the dark regions of the unstained muscle (‘A’-bands) but is normally absent from the ‘Z’-line and from the ‘I’-bands. In highly contracted muscle this relation is reversed: lipid is concentrated around the ‘Z’-line. The elastic layers and fibrils in arteries are rich in bound lipid.

Bound lipids are presumably lipoproteins. Purified lipoprotein from egg yolk examined histochemically has the same properties.
Immunolocalization of keratan sulphate in the human embryonic cornea and other human foetal organs
Authors: Hyldahl Louise , Aspinall Richard , Watt Fiona M.
Published: April 2021

An antibody raised against keratan sulphate was used to localize keratan sulphate in the human embryonic cornea and other human foetal organs. It was found that keratan sulphate was present in the corneal endothelium, as well as in the corneal stroma. In contrast, no keratan sulphate could be demonstrated in the corneal epithelium or in any posterior parts of the human foetal eye. Human corneal stromal cells grown in monolayers in tissue culture lost their capacity to bind this antibody. This suggests that explantation in vitro decreases or alters the expression of keratan sulphate in this cell type. Keratan sulphate was found to be present in abundant quantities in human embryonic cartilage and to a lesser extent in placenta. In contrast, keratan sulphate could not be detected in the foetal intestine, liver, suprarenal glands, the umbilical cord or in the foetal yolk sack.