bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological heterogeneity of hela cell mitochondria visualized by a modified diaminobenzidine staining technique
Authors: Posakony J. W. , England J. M. , Attardi G. 
Published: April 2021

ABSTRACT
The diaminobenzidine (DAB) technique for the ultrastructural localization of sites of cytochrome c oxidase activity in animal tissues has been adapted to the visualization of mitochondria in animal cells growing in culture.
The modified technique allows the staining of mitochondria in all cells in coverslip preparations for light microscopy. Electron microscopy of thin sections of material treated by this method has revealed that all mitochondrial profiles within a cell (and only these) are stained, and they exhibit a well preserved size and internal structure.
Coverslip cultures of synchronized and unsynchronized HeLa (F-315) cells stained with the DAB reaction were examined under oil immersion. In the majority of the cells, mitochondria were recognized as discrete bodies in the thinner peripheral portion of the cytoplasm. This observation indicates that in a large proportion of HeLa F-315 cells, at least under the growth conditions used here, the mitochondrial complement is divided into distinct organelles. This examination also revealed a considerable morphological heterogeneity of mitochondria, which exhibited an ovoid or short rod-like or, less frequently, long filamentous shape, with some evidence of branching. The variability in mitochondrial morphology appeared to be far more pronounced between different cells than within individual cells; this cellular heterogeneity was not related in any obvious way to cell-cycle-dependent changes.
The perturbation of the human erythrocyte membrane by phospholipase c
Authors: Limbrick A. R. , Knutton S. 
Published: April 2021

ABSTRACT
A study has been made of freeze-fractured preparations of erythrocyte ghosts modified by phospholipase C (Clostridium welchii). Such membranes show a decrease in surface area of up to about 47 % and lipid droplets appear on their external surface but there is no loss of protein. Freeze-fracture of maximally hydrolysed membranes exposes only very small areas of A faces and these appear particle-free. Most of the membranes are simply cross-fractured. At lower levels of hydrolysis there is more extensive exposure of A fracture faces but the particle density is less than in control preparations. If such exposed faces were representative of the whole membrane then the particle density would have been expected to increase. It is suggested either that areas of membrane with increased particle density do not fracture or that the particles revealed by freeze-fracture involve phospholipid as well as protein and are not revealed in the absence of phospholipid.
Incorporation of lipid into the epicuticle of Rhodnius (Hemiptera)
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
The incorporation of lipid into both the outer and inner epicuticle during deposition is described. Waterproofing of the epicuticle by secretion of the wax layer, and sclerotization with or without melanization, are controlled from a distance by the epidermal cells by way of the pore canals.
The pore canals gradually narrow as they approach the epicuticle. On reaching the inner epicuticle the canal ends in a conical projection from the apex of which a permeable lipophilic channel about 20–25 nm in diameter runs vertically to the surface.
Shortly before ecdysis, silver-binding material (perhaps protein rich in tyrosine, or other precursors concerned in sclerotization) spreads radially from a point in the cuticular channels just below the outer epicuticle, and gradually impregnates the outer two thirds or more of the inner epicuticle. The precise pattern varies in different cuticular structures. Argentaffin materials (polyphenols) first appear in these same sites at the time of ecdysis and increase rapidly during the next 24 h.
Lipid appears in the lumen of the distal parts of the pore canals (with a patchy distribution) shortly before ecdysis. When digestion and absorption of the old endocuticle are almost complete, minute lipid droplets appear on the surface of the epicuticle, apparently exuded from the epicuticular channels, and spread to make a uniform layer. When first formed this layer stains readily with Sudan B, but the lipid becomes incorporated in a delicate non-lipid silver-binding membrane (also exuded from the epicuticular channels) and hardens just before ecdysis, to form the so-called ‘wax layer’ which then no longer stains with Sudan B. Within half an hour after ecdysis the alcian blue-staining cement layer is poured out by the dermal glands, and forms a continuous but somewhat irregular covering over the ‘wax layer’.
Changes in the epicuticle that accompany the repair of abrasions are described.
An ultrastructural study of acid phosphatase localization in Phaseolus vulgaris xylem by the use of an azo-dye method
Authors: Charvat Iris , Esau Katherine 
Published: April 2021

ABSTRACT
The localization of acid phosphatase during xylem development has been examined in the bean, Phaseolus vulgaris. The azo dye, the final reaction product, is initially prominent in the dictyosomes, vesicles apparently participating in secondary wall formation, and in the middle lamella of the young vessel element. Final reaction particles are also present in mitochondria, chloroplasts, and certain vacuoles and are sparsely scattered in the cytoplasm. At a later stage of vessel differentiation, the azo dye is concentrated in the disintegrating cytoplasm and along the fibrils of the partially hydrolysed primary wall and middle lamella. In the mature vessel element, the azo dye is still present along the disintegrated primary wall at the side of the vessel and covers the secondary wall. In the parenchyma cell adjacent to the vessel element, acid phosphatase localization is found in the dictyosomes, endoplasmic reticulum, mitochondria, small vacuoles, and the middle lamella. The controls from all stages of vessel element development were free of azo dye particles. The concentration of acid phosphatase along the secondary walls of the mature vessels and in the middle lamella between other cells indicates that this enzyme has other functions besides autolysis of the cytoplasm and primary cell wall. Acid phosphatase may participate in the formation of the secondary wall and may also have a role in the secretion and transport of sugars.
Cell surface saccharides of Trypanosoma lewisi: I. polycation-induced cell agglutination and fine-structure cytochemistry
Authors: Dwyer D. M. 
Published: April 2021

ABSTRACT
Trypanosoma lewisi bloodstream and culture forms were agglutinated differentially with low concentrations of the cationic compounds: ruthenium red, ruthenium violet, Alcian blue chloride, 1-hexadecylpyridinium chloride, lanthanum chloride, and cationized ferritin. The bloodstream form trypanosomes gave the highest agglutination levels with each of the compounds tested. Ruthenium red was the most effective inducer of cell agglutination among the several cations used. Trypsin-treated bloodstream forms were agglutinated less in the presence of ruthenium red than untreated controls. Ruthenium red-induced cell agglutination also was lowered with chondroitin sulphate and dextran sulphate, but not with α-D-glucose, α-D-mannose or with several methyl glycosides. Treatment of the bloodstream trypanosomes with α-amylase, dextranase, or neuraminidase had little effect on agglutination levels obtained with ruthenium red.
Fine-structure cytochemical staining with ruthenium red, ruthenium violet, and Alcian blue-lanthanum nitrate was used to ascertain the presence and distribution of presumptive carbohydrates in the trypanosome cell surface. The extracellular surface coat of the bloodstream forms stained densely with each of the polycationic dyes. Trypsin treatment removed the surface coat from bloodstream trypanosomes; however, the surface membranes of the organisms were stained densely with the several dyes. Similar surface-membrane staining was obtained with the cationic compounds and the culture forms, which lack a cell surface coat. Cationized ferritin was used at the fine-structure level to visualize the negative surface charge present in the cell surface coat and external membrane of the several trypanosome stages.
Results obtained from the agglutination and cytochemistry experiments indicate that complex polysaccharides are present in the surface membranes and cell surface coat of T. lewisi bloodstream forms. Similar conclusions also pertain to the surface membranes of the T. lewisi culture form trypanosomes. The carbohydrates probably represent glycopeptide and glycoprotein structural components of the surface membrane of this organism.
Evidence for four classes of microtubules in individual cells
Authors: Behnke O. , Forer A. 
Published: April 2021

ABSTRACT
Experiments were performed on crane-fly spermatids (Nephrotoma suturalis Loew), ratsperm, and rat tracheal cilia to test whether all microtubules respond in the same way to different treatments. Crane-fly spermatids contain cytoplasmic microtubules, accessory tubules, and the 9 + 2 complex of tubules ; rat sperm and rat tracheal cilia contain only the 9 + 2 tubules.
Crane-fly spermatid tubules responded to the experimental treatments as follows. After colchicine treatment, or storage at 0°C, the cytoplasmic microtubules disappeared, while the 9 + 2 tubules were normal. After storage at 50 °C the cytoplasmic microtubules disappeared, and then the 9 + 2 tubules were affected : first the central tubules and B-tubules were affected, and later the A-tubules. After brief pepsin treatment, the 9 doublet tubules disappeared, while the other tubules appeared normal ; after prolonged pepsin treatment the accessory, central, and cytoplasmic tubules disappeared. After negative staining at pH 7, the cytoplasmic microtubules were never seen, the central tubules were only sometimes seen, the B-tubules were sometimes fragmented, and the A-tubules were intact. On the basis of these responses, it was concluded that there are 4 classes of tubules in crane-fly spermatids, namely cytoplasmic microtubules; accessory tubules and central tubules (of the 9 + 2 complex) ; B-tubules (of the 9 + 2 complex) ; and A-tubules (of the 9 + 2 complex). At least some of the different responses appeared to be due to intrinsic physical and/or chemical differences between the tubules themselves.
Pepsin digestion and negative staining of rat sperm tails gave results similar to those with crane-fly spermatids. In addition, the 9 + 2 tubules responded differently to pepsin digestion at different points along their length. This gradient of sensitivity was attributed to synthesis of new tubules occurring at one end of the sperm tail. Pepsin digestion and negative staining of rat tracheal cilia gave results similar to those with crane-fly spermatids and rat sperm tails.
All the tubules had a similar substructure, as revealed by negative-staining techniques. It was concluded that microtubules are proteinaceous, at least in part, and that microtubules are different in composition from membranes.
It is suggested that the walls of the B-tubules are composed of two materials—(1) the portions adjacent to the A-tubules, and (2) the remaining portion.
Studies on the surface antigens of interspecific mammalian cell heterokaryons
Authors: Watkins J. F. , Grace D. M. 
Published: April 2021

ABSTRACT
The surface antigens of HeLa-Ehrlich ascites cell heterokaryons were studied by mixed immune haemadsorption and by a development of this technique which permitted two surface antigens to be simultaneously marked, one with killed bacteria and the other with erythrocytes. Antigens of both species were present on the surfaces of heterokaryons and appeared to be randomly mixed. Small clones of hybrid cells containing both HeLa and Ehrlich surface antigens were detected.
The fine structure and histochemistry of the fat body in the locust, Schistocerca gregaria
Authors: Odhiambo T. R. 
Published: April 2021

ABSTRACT
A histochemical study of the fat body attached to the male accessory reproductive glands of the mature desert locust shows that most of the fat body is occupied by neutral fat and probably a little acidic lipid. The cytoplasmic strands between the enormous fat globules contain large deposits of glycogen and some protein.
An electron-microscopic study of the mature fat body demonstrates that the synthetic machinery within the cytoplasm is sparse : the endoplasmic reticulum is scarce and in the form of isolated and flattened cistemae; there are few ribosomes; the Golgi units are rather rare and small; and the cytoplasmic bodies, which are thought to be derived from pinocytotic vesicles and probably contain precursors for carbohydrate and lipid synthesis, are few in number. Microtubules, of about 200 Å diameter, and each formed as a compact helical structure with a repeating period of about 150 Å, are found occasionally in the cytoplasm. Their function is unknown, but they are found closely associated with mitochondria and lipid globules.
It is suggested that little synthesis takes place in the mature fat body since there is little nutrient circulating in the haemolymph, and that at this stage it acts mainly as a storage organ for glycogen and neutral fat.
Transfer of growth inhibition between normal and virus-transformed cells: autoradiographic studies using marked cells
Authors: Stoker M. G. P. 
Published: April 2021

Abstract
[3H]Thymidine and [3H]hypoxanthine incorporation were investigated by autoradiography in mixed cultures of polyoma-transformed BHK21 cells and freshly isolated mouse fibroblasts, with ingested carbon or carmine granules as markers to distinguish the cells. An assessment of the marking technique showed that there was some exchange of granules in the mixed cultures which prevented certain identification of individual cells, but suitable criteria were chosen for distinguishing the cells on a statistical basis.
Thymidine incorporation was inhibited in one third to two thirds of the transformed cells when they were in contact with stationary layers of normal cells, which themselves showed a low proportion with thymidine incorporation. Transformed cells in the same dish which were not touching the normal cells showed no inhibition of thymidine incorporation. This is in agreement with the earlier observation that growth of transformed BHK21 cells is inhibited by contact with stationary normal fibroblasts.
Experiments were also carried out on hypoxanthine incorporation with the TG1 variant of polyoma-transformed cells. TG1 cells are deficient in inosinic pyrophosphorylase and autoradiography shows a failure to incorporate hypoxanthine. When TG1 cells were cultured in contact with normal mouse embryo cells, however, it was found that hypoxanthine was present in the TG1 cells as well as in the normal cells. Increased incorporation did not occur in TG1 cells in the same dish which were not in contact with normal cells. This confirms earlier observations and shows that certain substances can pass directly from normal to transformed cells. It suggests the possibility that molecules concerned in growth regulation might also be transferred directly between contiguous cells.
Further observations on scale formation in Chrysochromulina chiton
Authors: Manton Irene 
Published: April 2021

Abstract
The normal form of the species has been compared with a deviant form and the processes of scale production in both more fully studied. The deviation is shown to be genetically based, possibly a mutation, of which the main structural expression is loss of capacity to develop the normal outer layer of material on each scale. The large scales also lack rims, a flange on the back giving a spurious resemblance to an inverted rim. A significant factor in determining orientation of the large scales appears to be a deposit of amorphous material on the morphologically outer side, which though much reduced in the deviant strain is still present. Orientation of scales in both strains of the species is therefore basically identical and independent of overall shape, though it is structurally determined before liberation from the parent Golgi cistemae. Changes in the latter have been traced up to and including the act of liberation of the contents to the exterior. This takes place near to the flagellar bases and there are some indications that participation by endoplasmic reticulum may be involved.
Electron-microscopic studies on a double-stranded beaded filament of embryonic collagen
Authors: Hayes R. L. , Allen E. R. 
Published: April 2021

Abstract
Beaded filaments consisting of paired 40-Å strands in parallel coupled by 150-Å beads at periodic spacings of 640 Å have been isolated from embryonic pig dermis. These filaments are found in association with embryonic collagenous fibrils and exclusively at sites of active fibrillogenesis of collagen. They have been identified within sectioned native fibrils as well as in interfibrillar regions. Furthermore, they have been recovered from fibrils denatured by exposure to alkalinity or to heat. In those instances, the filaments are packed in parallel array and the component beads are registered to produce a banding pattern with a major 640 Å repeat.
The strands of the complex are composed of non-rigid fibrous protein as deduced from their fixation with aldehyde fixatives and from their degradation by urea. The beads are also proteinaceous, as indicated by their susceptibility to tryptic digestion. Moreover, these beads contain lipid, since they stain with lipid stains and dissolve in lipid solvents. Additional evidence suggests the inclusion of polysaccharide in the beads : periodic acid destroys these structures, and in native fibrils silver staining for carbohydrate occurs at loci of registered beads. The structural integrity of the conjugated protein bead does not depend upon the lipid or polysaccharide components, since lipases or β-amylase do not digest the structures.
The filament proper is collagenase-resistant, but trypsin-sensitive. The latter enzyme bisects the beaded filament, forming single-stranded filaments with alternating 640-Å and 200-Å segments between beads. The double-stranded filaments are soluble in acid solutions below pH 4 but are stable at higher pH’s through 9–10.
The beaded filament fits into the scheme of extracellular collagen fibrillogenesis as the primary stable fibril or protofibril of collagen. It is presented as a doublet of procollagen fibrils which serves as a template for the polymerization of tropocollagen into additional beaded filaments. Aligned in parallel array and in register as they are assembled, the aggregate of beaded filaments is built into an immature fibril. By the establishment of interfilamentous cross-links, the individuality of the beaded filament is lost within the progressively maturing fibril.
Studies on Changes in the Nuclear Helices of Amoeba Proteus During the Cell Cycle
Authors: Minassian I. , Bell L. G. E. 
Published: April 2021

ABSTRACT
The fine structure of the nuclei of synchronously growing cell populations of Amoeba proteus was studied at 1-h intervals during the interphase. This study showed that the nuclear helices undergo increases in their number at certain stages during interphase. These changes were found to correlate with ultrastructural changes occurring in the nucleoli.
Fine structure of the heterochromatin of the kangaroo rat Dipidomys ordii, and examination of the possible role of actin and myosin in heterochromatin condensation
Authors: Comings D. E. , Okada T. A. 
Published: April 2021

ABSTRACT
Biochemical studies have suggested that some actin, and myosin may be present in the nucleus. This raises the possibility that heterochromatin condensation might be the result of an actin-myosin rigour type complex. Since ATP dissociates actin and myosin, this possibility could be examined by determining the effect of ATP on heterochromatin condensation. Thin-section electron microscopy showed large amounts of condensed constitutive heterochromatin in the kidney nuclei and somewhat less in the liver nuclei of the kangaroo rat, Dipidomys ordii. Surprisingly, there were some nuclei in the brain which contained no condensed heterochromatin despite the fact that this genome is composed of 50% satellite DNA. Although washing kidney nuclei with solutions of 10 mM Tris-ATP caused marked decondensation of the heterochromatin, when they were washed with Mg-ATP the heterochromatin was more condensed than in the controls. This suggests the decondensation by Tris-ATP is due to its ability to chelate divalent cations and provides no support for condensation of heterochromatin being the result of myosin-actin interaction. Despite being decondensed, the chromatin fibres of heterochromatin were distinct from those of euchromatin. The heterochromatin formed rod-like 19·5-nm fibres, the euchromatin formed random coils of 11·0-nm fibres.
Rates of synthesis of polyadenylated messenger rna and ribosomal rna during the cell cycle of Schizosaccharomyces pombe : Calculation of the pattern of protein accumulation from observed changes in the rate of messenger rna synthesis
Authors: Fraser R. S. S. , Moreno F. 
Published: April 2021

ABSTRACT
The rates of polyadenylated messenger RNA and ribosomal RNA synthesis were measured in synchronously dividing cultures of fission yeast (Schizosaccharomyces pombe). Control asynchronous cultures, which had been exposed to the conditions used for preparing syn- chronous cultures, were investigated to check for effects of the synchronization procedure itself on RNA synthesis. After each period of DNA synthesis in synchronous culture, the rates of messenger and ribosomal RNA synthesis doubled, suggesting that gene number controls the rate of messenger and ribosomal RNA synthesis. This was confirmed by experiments with asynchronous, exponential-phase cultures in which DNA synthesis was inhibited by hydroxy- urea. Both synchronous culture and hydroxyurea experiments suggested that there is a delay of 15 min (0 ·1 of the cell generation time) between replication of the DNA and transcription of both gene copies.
A pattern of protein accumulation was calculated from changes in the rate of polyadenylated messenger RNA synthesis during synchronous culture. This simulated pattern indicates that protein is accumulated linearly, with a doubling in the rate of accumulation once per cell cycle. The simulated pattern of protein accumulation is very similar to measurements previously reported by other workers of changes in activities of 3 enzymes in synchronous cultures.
It is suggested that the doubling of the rate of messenger RNA synthesis, as a consequence of the replication of the DNA once per cycle, provides the basis of a mechanism for control of the doubling of other cellular constituents during the cell cycle.