bluuebunny/crossref_metadata_2025 huggingface dataset:
A new occludens-like junction linking endothelial cells of small capillaries (probably venules) of rat jejunum
Authors: Staehelin L. A.
Published: April 2021

Freeze-cleave replicas of small capillaries of rat jejunum have revealed the presence of a new type of junction linking endothelial cells. This new junction resembles tight junctions (zonulae occludentes) in that the adjacent plasma membranes are held closely together along lines of attachment organized in the form of a loose, but frequently discontinuous network. In contrast to tight junctions, the A-face ridges possess a very low profile, and only at low shadowing angles can a repeating, particulate substructure occasionally be resolved. The shallow B-face furrows lack any particulate components. Images of cross-fractured focal points of attachment suggest that the external leaflets of adjacent membranes are closely apposed but not actually fused, as is the case with zonulae occludentes. It appears that this new type of endothelial junction is characteristic of small venules. Thus we propose that it be termed small venule endothelial junction.
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

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

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

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

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

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

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

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

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

[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

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

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

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

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

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.
Movement of the cell surface and change in surface area during cleavage in the newt’s egg
Authors: Sawai Tsuyoshi
Published: April 2021

In cleaving eggs of the newt, Cynops pyrrhogaster, the behaviour of the egg surface was analysed by observing linear and area changes in a transplanted piece of cortex which differed in pigmentation from the background.

Results from the animal hemisphere showed that the surface in the cleavage plane shrank extensively in the region where the early cleavage furrow was being formed. On both sides of the cleavage plane, the surface began to shrink in a direction parallel to the cleavage furrow and to stretch perpendicularly to the furrow, simultaneously with the onset of cleavage. The nearer the grafted region was to the furrow, the greater the change. These changes continued until about the time of the appearance of unpigmented surface on both walls of the furrow, when a maximum was reached. Thereafter a slight reversal was observed. Similar changes of lesser magnitude were encountered in regions remote from the cleavage plane. The surface area decreased in the vicinity of the furrow during the early phase of cleavage and returned roughly to its original value during the late phase, while, in the distant region, only an increase occurred.

Results from the vegetal hemisphere showed that little linear change of surface occurred even in the region adjacent to the furrow, while the surface area changed in the furrow region similarly to the animal half. In the vegetal hemisphere remote from the furrow, the changes took place to a lesser extent.
Pinocytosis and intracellular digestion of 125I-labelled haemoglobin by trophoblastic cells in tissue culture in the presence and absence of serum
Authors: Contractor S. F. , Krakauer Kathryn
Published: April 2021

One aspect of human placental function which has not hitherto been studied is the ability of the placenta to digest proteins intracellularly and use the products of hydrolysis to supply its own and foetal needs for nutrition and protein synthesis. Placental lysosomes have a full complement of hydrolytic enzymes, including the acid proteases cathepsin C and D. We have used trophoblast cells in monolayer tissue culture as a model for the study of endocytosis and intracellular digestion of 125I-haemoglobin. The normal use of serum in tissue culture medium has shown up differences from the pattern observed with other phagocytic cells such as macrophages, in that serum allows endocytosis but prevents intracellular digestion 125I- haemoglobin. Replacement of serum by lactalbumin hydrolysate enables both endocytosis and intracellular digestion of 125I-haemoglobin to occur as in other phagocytic cells. Digestion is followed by release into the medium of acid-soluble, lower-molecular-weight compounds. The reasons for this major difference between trophoblast and other cells are discussed in the light of our results and their possible relevance to placental function.
Studies on the template activity of ‘isolated’ Xenopus erythrocyte nuclei: II. the effects of cytoplasmic extracts
Authors: Maclean Norman , Hilder Vaughan A.
Published: April 2021

The effects of exposing nuclei isolated from Xenopus erythrocytes to cytoplasmic extracts prepared from various sources on their template activity are described. The cytoplasm of rat liver cells and the immature blood cells of Xenopus contain factors which stimulate RNA synthesis in these essentially inactive nuclei, whereas the cytoplasm of many other cells does not yield such factors. The active factors in rat liver cytoplasmic extracts appear to be proteins of molecular weight about 40000 Daltons. The implications of these results for genetic control in eukaryotes are discussed.
Calcium-rich, refractile granules in Tetrahymena pyriformis and their possible role in the intracellular ion-regulation
Authors: Nilsson Jytte R. , Coleman James R.
Published: April 2021

Tetrahymena pyriformis GL is known to accumulate small, refractile granules during unfavourable growth conditions. Furthermore, electron microprobe analysis of granules in situ has shown them to be calcium-rich, with calcium bound in an apatite-like material.

The present study deals with the identification of these granules in the electron microscope. During granule formation Tetrahymena contains several structures with increased electron density, e.g. mitochondria, lipid droplets, and autophagic-like vacuoles; however, the most conspicuous feature is a membrane-bound structure with amorphous contents of varying electron density. These structures are believed to represent the calcium-rich granules. Their limiting membrane resembles the cell membrane in structure and polarization, i.e. one side of the membrane bilayer is thick and electron-dense. The electron-dense layer of the granule membrane faces the lumen of the granule (high content of calcium) and that of the cell membrane faces the external medium (high concentration of calcium); in both cases the less electron-dense layer of the membrane borders the cytoplasm (low concentration of calcium). This polarization is believed to be connected with the functions of the membrane. The cells also contain small tubular structures with a membrane similar in structure to that of the granules and with an amorphous content similar to that of the granules. These tubular structures are often found close to or in direct connexion with the granules and their possible involvement in granulogenesis is proposed.

The calcium-rich granules may play a role in the regulation of the intracellular concentration of calcium. Their formation correlates with a decrease in the general metabolism of the cells, i.e. conditions during which the intracellular concentration of calcium is likely to increase. A model is proposed for the possible pathways of calcium in Tetrahymena during normal and unfavourable growth conditions. In addition, the possible involvement of other cytoplasmic inclusions, e.g. mitochondria, in this regulation is discussed.
Linear increase in glycolytic activity through the cell cycle of Schizosaccharomyces pombe
Authors: Hamburger Kirsten , Kramhøft Birte , Nissen Susanne B. , Zeuthen Erik
Published: April 2021

The glycolytic activity of 3 different synchronous systems in S. pombe was studied. Synchronous cultures were produced by a selection procedure, by cyclic heat treatment, or by cloning cells from an exponentially multiplying culture. In all experiments a complex medium with 3 % glucose was used. The glycolytic activity was recorded with a gasometric method, the gradient diver. A single cell in exponential growth or a small number of synchronized cells were placed in ampulla divers in which the cells progressed undisturbed through a number of cycles. An ampulla diver is in principle a narrow pipette by which a single or a few cells are removed from the mother culture. It serves next as an axenic growth chamber and at the same time as a gasometer. The divers were placed in linear saline density gradients and the gaseous exchanges taking place in the divers resulted in migration of the divers. The migration rate is a measure of the glycolytic activity of the cells. Our results show that the glycolytic activity increases in a linear fashion between successive divisions. The rate of increase doubles at each division. This is true in all 3 synchronous systems, and we take this as an indication that the cell cycles of heat-synchronized cells do not deviate seriously from the normal.
High-density induction of a quiescent cell state in Physarum Polycephalum
Authors: Mcalister L. E. , Allison V. F. , Jeter J. R. , Nations C.
Published: April 2021

The non-histone protein complement of Physarum polycephalum changes rapidly when microplasmodia are subjected to conditions of high density. The changes in these proteins induced by high density are similar to the changes observed during starvation-induced encystment. A 50% decrease in DNA synthesis, observed after 7 h of starvation, is observed after only 1 h of high density. High density also results in a decrease in RNA synthesis comparable to decreases induced by prolonged starvation. Total heterochromatin increases in response to either high density or starvation. Increased heterochromatization is preceded by an increase in nuclear actin. Mitochondrial morphology and cytoplasmic organization are also similarly altered by starvation and high density. These observations suggest the possibility of a generalized mechanism for cellular transition from active growth to a non-proliferative cell state.
The ultrastructure of the somatic cortex of Pseudomicrothorax Dubius-: Structure and function of the epiplasm in ciliated protozoa
Authors: Peck Robert K.
Published: April 2021

The ultrastructure of the somatic cortex of the ciliate Pseudomicrothorax dubius is studied with emphasis on the epiplasm layer which lies immediately under the inner alveolar membrane and is continuous with the terminal plates of cortical basal bodies.

In addition to a clearly demonstrable cytoskeletal role, the epiplasm appears to function as a cementing substance which integrates numerous cortical fibres and membranes. The kinetodesmal, postciliary and transverse fibre systems which originate at the proximal ends of basal bodies extend toward the cell surface and end at or in the epiplasm. Inner alveolar membranes and trichocyst membranes are attached to the epiplasm. Basal bodies are anchored into the epiplasm via their terminal plates.

The epiplasm appears to be morphogenetically important as a matrix into which newly formed basal bodies insert. Electron-opaque arms occur at the terminal plate level of new basal bodies, and these arms fuse with the epiplasm when basal body insertion occurs. The position of trichocysts in the cortex is specified by the epiplasm.

Evidence from numerous other ciliates tends to confirm both structural and morphogenetic roles of the epiplasm.
Evidence from serial sections that some cells contain large numbers of mitochondria
Authors: Heywood Peter
Published: April 2021

Three-dimensional reconstructions based on serial sections through cells of the chloro-monadophycean alga Gonyostomum semen Diesing indicate that there are many small unbranched mitochondria in log-phase cells. These organelles are approximately ellipsoid in shape with their longest axis usually ranging from 0 7 to 2·0 μm in length. Occasionally mitochondria reaching up to 3·6 μm in length have been observed: these have the same general morphology as their smaller counterparts. Preliminary observations indicate that cells of a related alga, Vacuolaria virescens Cienkowsky, also possess many small unbranched mitochondria.

These observations are discussed in relation to recent reports that some cells contain a single branched mitochondrion or, at most, a small number of these organelles. It is suggested that mitochondrial number may be related to cell volume and that large cells may contain many mitochondria.
Outgrowth of human fibroblast aggregates on a substratum triggers a wide variety of morphogenetic properties in the cells
Authors: Schueren Bernadette Van Der , Cassiman Jean-Jacques , Berghe Herman Van Den
Published: April 2021

Twenty-four-hour-old aggregates of human diploid skin fibroblasts are allowed to attach to a glass or plastic substratum. As a result of this attachment the cells in the aggregate demonstrate rapid and generalized changes in cell shape, cell surface and cytoplasm ultrastructure and in their ability to incorporate [3H]thymidine. Within 24 h they grow out on the substratum to attain the regular monolayer configuration. During the process of leaving the aggregate for the substratum a great number of different morphogenetic properties are displayed by the cells, resembling the properties of embryonic or epithelial cells. The simultaneous occurrence of this great variety of cell shape and cell surface changes, many of them unusual for fibroblasts, as well as the concurrent formation of organized cytoplasmic structures — microfilaments, microtubules –at localized areas of the cells, makes this system a potentially useful tool in the study of cell behaviour.
Structural changes in the epidermal cells of Rhodnius during tracheole capture
Authors: Wigglesworth V. B.
Published: April 2021

Epidermal cells deprived of their oxygen supply by tracheal section give off cytoplasmic processes which become attached to air-filled tracheoles in neighbouring areas and draw these into the oxygen-deficient zone.

Many of these cytoplasmic strands exceed 100 μm in length but may be no more than 50 nm in diameter; they contain mitochondria, ribosomes, microtubules and microfilaments. In basic structure they resemble the tendon cells; and also the tapering conical epidermal cells along the intersegmental borders of the abdomen, the terminal strands of which are inserted into the basement membrane behind and in front of the segmental boundaries.

The cytoplasmic walls of those tracheoles most exposed to tension during the process of tracheole capture become thickened and packed with microtubules.

In all these structures the microtubules are believed to be concerned in resistance to tension. Contraction is presumably effected by microfilaments, but no new evidence is given. The possible role of the epidermal strands in the transport of energy-rich metabolites is discussed.
Intercellular junctions in the central nervous system of insects
Authors: Lane Nancy J. , Skaer Helen Le B. , Swales Esley S.
Published: April 2021

The intercellular junctional complexes in the central nervous system (CNS) from a variety of insect species have been examined by thin-sectioning and freeze-fracturing techniques. Of particular concern has been the fine-structural basis of the blood-brain barrier observed to be present in the outer perineurial layer around the avascular insect CNS. The basis of this has been found in the form of tight junctions (zonulae occludentes) present both in sections and in replicas of the perineurium. In the latter, they appear as one or two simple linear ridges, lying parallel to the outer surface, which occasionally display overlapping. The complex geometry of the interdigitating perineurial cells apparently permits such a relatively simple series of ridges to function as a barrier, since tracers are found not to penetrate beyond this level into the underlying nervous tissue. Such evidence is supported by microprobe X-ray analysis of lanthanum-incubated tissues, the perineurium compared with the glia-ensheathed axons showing the presence and absence of lanthanum, respectively. Possible physiological mechanisms that could operate ‘in vivo’ to maintain the blood-brain barrier are also considered. Other intercellular junctions such as desmosomes, septate junctions and gap junctions are found in the perineurial layer too, the last exhibiting EF particle plaques and PF pits. Glia-glia junctions also occur in some insect species; they include desmosomes, inverted gap junctions and occasional tight junctions. Septate, gap and tight junctions are also found on the membranes of trecheóles penetrating the CNS. Short, ridge-like elaborations and other particle arrays are found on the PF of the axon surfaces and the significance of these structures is discussed.
Combined histochemical and x-ray microanalytical studies on the copper-accumulating granules in the mid-gut of larval Drosophila
Authors: TAPP R. L. , Hockaday Austin
Published: April 2021

The copper-containing granules in the mid-gut epithelium of larval Drosophila melanogaster were examined for acid phosphatase by combined histochemistry and energy-dispersive, X-ray microanalysis. After incubation, many of the granules were shown to contain simultaneously copper and sulphur (which are normal constituents), and lead and phosphorus (which are the detectable elements of the reaction product). Earlier work has been consolidated and extended and the evidence that the granules are formed as cytolysosomes is reviewed.
Effects on cell adhesion and membrane fluidity of changes in plasmalemmal lipids in mouse l929 cells
Authors: Schaeffer Barry E. , Curtis A. S. G.
Published: April 2021

It has recently been shown that the lipid composition of the plasmalemma may be altered by taking advantage of the acyltransferase system to incorporate selected fatty acids into phosphatidyl lipids of the plasmalemma. Such lipid alterations have been shown to effect changes in cell adhesion in chick neural retina cells. Based on the fluid-mosaic model, it has been suggested that such changee in cell behaviour may be related to the degree of plasmalemmal fluidity. In the present study, when mouse L929 cells are incubated in the presence of stearic or arachidic acid (saturated), cell adhesion levels, as measured by an assay based on cellsubstrate interaction, increase. Similar incubation with linoleic or linolenic acid (unsaturated) decreases cell adhesion.

In addition, we have found significant changes in plasmalemmal fluidity, using an assay based on patching of fluorescent antibody. Unsaturated fatty acids have a fluidizing effect on the membrane, while saturated fatty acids exert a solidifying effect, when substituted into the membrane. Although alternative interpretations are possible, we suggest that membrane fluidity changes are induced by alterations in lipid thermal transition temperatures of plasmalemmal phosphatidyl compounds, in which fatty acid substitutions were made. We also suggest that changes in membrane fluidity might affect adhesion by altering the aggregability of any membrane sites that may be involved in adhesion. Although a very fluid membrane may allow rapid lateral migration of sites, it might also aid their rapid dispersal, thereby reducing adhesion.
Role of Ca2+ In preserving viability of friend erythroleukaemic cells after ultramicroinjection
Authors: Wasserman Moshe , Loyter Abraham , Kulka Richard G.
Published: April 2021

Ca2+ facilitated the fusion by Sendai virus of Friend erythroleukaemic cells and Ehrlich ascites tumour cells but not that of hepatoma tissue culture cells. In the absence of Ca2+ Sendai virus caused the complete depletion of ATP and abolished protein synthesis in Friend erythroleukaemic cells fused with each other. Addition of high concentrations of Ca2+ (10 – 20 mM) partially protected the cells from ATP depletion. After a further incubation of cells in complete medium plus 0 ·2 MM adenine, ATP levels and protein synthesis were restored to 60 – 85 % of those of the untreated control. The protective effect of Ca*÷ was used to improve the ultramicroinjection method which involves the fusion of human erythrocyte ghosts with cells. When human erythrocyte ghosts containing high K+ were fused with Friend erythroleukaemic cells in the presence of 10 mM Ca2+ ATP levels and protein synthesis after recovery were about 60 – 85 % of the control. Friend erythroleukaemic cells subjected to ultramicroinjection under these conditions had a cloning efficiency of 75 – 95 % of that of the untreated controls. In these experiments 70 · 100 % of the cells had fused with ghosts. Induction of haemoglobin synthesis by dimethylsulphoxide was unimpaired in cells subjected to ultramicroinjection under the same conditions.
Behaviour of kinetochore fibres in Haemanthus katherinae during anaphase movements of chromosomes
Authors: Hard Robert , Allen Robert D.
Published: April 2021

A laser light source along with a new method of preparing endosperm cells of Haemanthus katherinae for differential interference contrast (DIC) microscopy has led to increased visibility of kinetochore fibres. Little information is available concerning the behaviour of these fibres during anaphase in living cells. In metaphase, kinetochore fibres are seen as distinct bundles of microtubules, here referred to as ‘filaments ‘, extending from the kinetochore to the ‘diffuse ‘pole. They possess an apparent globular substructure which corresponds to the moving ‘particles or states’ described previously from ciné films. In early anaphase, the filaments of each kinetochore fibre lose their parallel orientation characteristic of metaphase and splay out so that the more peripheral filaments intermingle with those of other kinetochore fibres. This process begins at the poles and proceeds as a wave toward the kinetochores as chromosomal movement progresses. This behaviour has been examined in relation to a number of proposed models for the mechanism of chromosome movement and has been found to place some constraints on some models but to be consistent with any model that hypothesizes that chromosomes move as a consequence of cumulative cohesive lateral interactions of microtubules.
Localization of histone gene transcripts in newt lampbrush chromosomes by in situ hybridization
Authors: Old R. W. , Callan H. G. , Gross K. W.
Published: April 2021

Denatured 3H-labelled DNAs containing histone gene sequences originating from the echinoderms Psammechinus miliaris, Echinus esculentus and Strongylocentrotus purpuratus have been in situ hybridized to RNA transcripts on newt lampbrush chromosomes. Autoradiographs of the hybridized lampbrush preparations show labelling restricted to four or fewer lateral loop pairs all lying within the heteromorphic regions of chromosome I, also one or two loop pairs on chromosome VI, one loop pair on chromosome X and one loop pair on chromosome XI. For oocytes from a single newt, coincident label distribution is found with DNAs of diverse echinoderm origin; however different newts show some specific individual diversity in label distribution, including heterozygosity in the case of loops on bivalents VI and X. The more conspicuously labelled loops, particularly those on chromosome I, show a pattern of labelling which is explicable if the newt histone DNA sequences are confined to short intercepts of lateral loop axis. Transcription is initiated prior to the histone DNA sequences, proceeds through the histone DNA sequences, and beyond, and the histone RNA sequences are cut from the transcripts before the termination of transcription.
An inhibitor of cell cohesion from axenically grown cells of the slime mould, dictyostelium discoideum
Authors: Swan Alma P. , Garrod D. R. , MORRIS D.
Published: April 2021

Medium from a stationary phase culture of axenically grown D. discoideum cells contains an inhibitor of cohesion of log phase cells. The inhibitor is a heat-stable, low molecular weight substance. Its biological effects include inhibition of cohesion of aggregation-competent cells, of cells of other slime mould species, the blocking of development on Millipore filters and a reduction in adhesiveness of slime mould cells to glass. Present evidence suggests that the inhibitor may bind to the cell surface.
Immunofluorescent anti-tubulin staining of spindles during meiotic maturation of mouse oocytes in vitro
Authors: Wassarman Paul M. , Fujiwara Keigi
Published: April 2021

Immunofluorescent anti-tubulin staining has been used to follow nuclear progression from dictyate to metaphase II during meiotic maturation of mouse oocytes in vitro. Antibody directed against tubulin isolated from sea-urchin eggs decorates the metaphase I and metaphase II spindles, as well as the cytoplasmic bridge, midbody, and polar body of the maturing mouse oocyte. Changes in the tubulin-specific staining pattern during meiotic maturation in vitro take place in a highly reproducible manner. Oocytes exposed continuously to cytochalasin B arrest at metaphase I and display a spindle which by immunofluorescent staining is virtually indistinguishable from the spindle of untreated oocytes.