bluuebunny/crossref_metadata_2025 huggingface dataset:
The formation of annulated lamellae induced by the disintegration of microtubules
Authors: De Brabander M. , Borgers M.
Published: April 2021

Investigations with different ‘antitubulins’ have shown that different cell types in culture respond to prolonged treatment with the formation of annulated lamellae. These annulated lamellae are possibly derived from previously accumulated smooth endoplasmic profiles. A hypothetical explanation would be that annulated lamellae (and the nuclear membrane) are sites of tubulin synthesis or microtubular polymerization. Their appearance after induced microtubule disintegration could then be viewed upon as a reactive hyperproduction of such sites.
Calcium distribution in islets of langerhans: A study of calcium concentrations and of calcium accumulation in b cell organelles
Authors: Howell S. L. , Montague W. , Tyhurst Margaret
Published: April 2021

Calcium concentrations of various pancreatic B cell organelles have been determined by X-ray microanalysis of areas of frozen sections of unfixed rat islets of Langerhans. Highest concentrations were detected in storage granules and in mitochondria, although calcium was also present in nuclei, in areas of endoplasmic reticulum and of cytoplasm.

Accumulation of 45Ca by isolated organelles has been studied in homogenates and isolated subcellular fractions of rat islets of Langerhans. In the presence of a permeant anion (oxalate or phosphate), accumulation of 45Ca into mitochondria and microsomes was strongly stimulated by ATP. This net uptake was diminished during incubation of homogenates or of a mito-chondria-plus storage granule-rich fraction in the presence of cyclic AMP, dibutyryl cyclic GMP, z:4-dinitrophenol or of ruthenium red. Investigations of the characteristics of 45Ca accumulation by homogenates prepared from storage granule-depleted islets showed no differences from those of normal islets, suggesting that the granules do not represent an important labile pool of calcium. With the exception of cyclic AMP and cyclic GMP none of the insulin secretagogues tested (glucose, leucine, arginine, adrenalin, noradrenalin, theophylline, glibenclamide) altered calcium accumulation by islet homogenates.

On the basis of absolute calcium levels and of 46Ca uptake studies it is concluded that islet B cells contain a readily exchangeable mitochondrial calcium pool, and an endoplasmic reticulum pool containing a lower concentration of calcium which is also readily exchangeable. The storage granules, despite their high calcium content, do not appear to constitute a labile pool. It seems likely that the labile mitochondria and endoplasmic reticulum pools play a predominant role in the regulation of cytoplasmic free calcium levels, which may in turn be important in the regulation of rates of insulin secretion.
Distribution of lipid in the lamellate endocuticle of Rhodnius prolixus (hemiptera)
Authors: Wigglesworth V. B.
Published: April 2021

The lamellate appearance of the cuticle in the abdomen of the Rhodnius larva conforms to the conception of Bouligand in being an optical artifact which results from the spiral arrangement of successive layers of oriented fibrils. But superimposed on this structure is an actual lamination of bound lipid with the same spacing. The relation of the lipid layers to the optical lamination changes with the aspect from which the system is viewed.

There must therefore be a cyclical secretion of lipid by the epidermal cells. Since the period of this cycle agrees with the cycle of rotation of the fibrous layers, which is supposedly inherent in the chemistry of the system, it is possible that it is the lipid which controls or initiates this helicoidal ‘cholesteric crystallization’.

There is evidence of a cyclical change in the secretion of lipid by the microvilli; it is suggested that there may be alternating cycles of eccrine and apocrine secretion, and that the lipid laminae represent the apocrine phases.

The pore canals in Rhodnius are roughly cylindrical in cross-section, with lipid-impregnated walls. The contents of the lumen become slightly more electron opaque before the cuticle is stretched by feeding. There is probably some enzymic dissolution of the cuticle which precedes stretching; and this may concern particularly the lipid fraction. After the great distension and expansion of the cuticle which occur at feeding, lipid laminae can no longer be demonstrated in the old cuticle.
The erythroid cells of anaemic Xenopus laevis. I. studies on cellular morphology and protein and nucleic acid synthesis during differentiation
Authors: Thomas Nesta , Maclean N.
Published: April 2021

Phenylhydrazine has been used to induce anaemia in Xenopus laevis. The dosage used causes the complete destruction of all mature erythrocytes within twelve days. The anaemia results in the initiation of a wave of erythropoiesis and large numbers of immature erythroid cells are released into the circulation. The morphological and biosynthetic changes which these cells undergo as they differentiate in circulation are described. The origin of the circulating erythroid cells is also discussed.
Effect of tritiated thymidine on cell proliferation
Authors: Blenkinsopp W. K.
Published: April 2021

The effect of tritiated thymidine on the rate of entry of cells into mitosis was studied in mice; 1·5 μc of tritiated thymidine (specific activity 5 c/mM) per g body weight did not alter the rate of entry. Other workers have reported an increased number of mitoses following administration of larger amounts of thymidine than those used in the present work ; the suggestion is therefore made that when tritiated thymidine is given to animals for studies on cell proliferation the dose of thymidine in a single injection should be not greater than 0·1μg/g body weight.
An electron-microscope study of the in vitro transformation of human leucocytes: I transformation of lymphocytes to blastoid cells in the presence of phytohaemagglutinin
Authors: Chapman J. A. , Elves M. W. , Gough J.
Published: April 2021

Electron-microscope studies of cultured small lymphocytes from human peripheral blood transforming into larger blastoid cells in the presence of phytohaemagglutinin (PHA) show that the transformed cell possesses the preliminary stages of development of a protein-synthesizing system. The transformed blastoid cell has abundant ribosomes, although, in contrast with in vivo protein-secreting cells, many of these occur as single particles with only a small proportion linked in polysomal clusters. Endoplasmic reticulum membranes occur to a very limited extent and with a marked paucity of attached ribosomal particles; the few attached particles are usually located in groups. Some endoplasmic reticulum membranes revealed degenerative changes in otherwise normal cells. A moderately well-developed Golgi apparatus was a characteristic feature of the cells. Apart from the relatively low proportion of polysomes, in vitro PHA-transformed blastoid cells are identical in fine structure to in vivo blast cells (otherwise known as immunoblasts, haemocytoblasts, etc.) occurring in the immune response. It is suggested that messenger-RNA production in PHA-stimulated transformed cells may be reduced and that this could explain the limited number of polysomes and the restricted development of the endoplasmic reticulum.
Seasonal changes in the fine structure of the basal granular cells of the bat thyroid
Authors: Nunez E. A. , Gould R. P. , Hamilton D. W. , Hayward J. S. , Holt S. J.
Published: April 2021

The fine structure of the thyroid gland of non-hibernating, hibernating, and intermittently aroused hibernating bats was examined. It was found that in addition to the ordinary, follicular cell, another widespread thyroid cell type is present in all bats examined. This cell is situated in the basal region of the thyroid follicle and is characterized by a cytoplasm full of secretory-like granules. In the basal cells of bats captured in April and June the granules consist of an extremely dense core and are of a uniform size averaging from 0·1–0·5 μ diameter. In bats caught in August the solid dense granules vary greatly in size and large granules of diameters from 2 to 5 μ are common. These large granules are often found concentrated in groups in the most basal region of the follicular epithelium. Hibernating bats are characterized by partly or totally degranulated basal thyroid cells. The cytoplasmic granules in the partly degranulated cell vary greatly in appearance, ranging from solid dense granules to empty vesicles. In totally degranulated basal cells, empty vesicles fill the cytoplasmic matrix. The granular endoplasmic reticulum of the basal thyroid cell also shows seasonal changes, while the Golgi complex remains a well-developed organelle throughout the year. These observations suggest that the thyroid basal granular cell is involved in secretory activities; its possible functional role is discussed.
Plasmodesmata in Nitella translucens: Structure and electrical resistance
Authors: Spanswick R. M. , Costerton J. W. F.
Published: April 2021

Electrical resistance measurements, made with intracellular microelectrodes on a system consisting of two giant intemodal cells of Nitella translucens joined by a node, show that the specific resistance of the node is 50 times smaller than the specific resistance of the intemodal cell plasmalemma. The node is a complex structure of small cells which separate the intemodal cells by a single layer at the nearest point of approach. Information on the size and distribution of the plasmodesmata in the node, obtained from electron micrographs, suggests that the specific resistance of the node should be smaller than the observed value by a factor of 330. It must therefore be assumed that there is some restriction on the diffusion of ions in the plasmodesmata.

The electrical coupling between some internodal cells is sufficient for an action potential in one cell to initiate an action potential in the neighbouring cell.
Proliferation and agglutinability of primary and transformed human epithelial cells in culture
Authors: Ricard Mary Ann , Hay R. J.
Published: April 2021

Primary epithelial populations (HAM) were obtained by dissociation of the amniotic membrane stripped from human placentae. Agglutinability of cells from such normal populations and of cells from the transformed epithelial line WISH was then compared using concanavalin A as mediator. Extensive similar studies have previously been reported with cell strains isolated from other species. Freshly dissociated HAM cells from primary cultures agglutinated much less readily than did cells from WISH populations. Furthermore, the former exhibited a drastic decline in agglutinability as a function of time in suspension culture after trypsinization. Short-term exposure (60 h) of HAM cells in monolayer culture to 5-bromodeoxyuridine (BrdU) elicited heightened agglutinability detectable through 22 days in vitro.

Addition of the protease inhibitors n-tosyl-L-lysyl-chloromethyl ketone (TLCK) or p-tosyl-L-arginine-methyl ester (TAME) to the culture medium inhibited proliferation of the WISH line by 40–50% while effecting only a 10–15% inhibition of HAM cells. These results also confirm data with other cell species indicating that high proteolytic activity at the surface of transformed cells may be related to the rapid proliferation rate.
Effect of glutaraldehyde fixation on lectin-mediated agglutination of mouse leukaemia cells
Authors: Blitterswijk W. J. Van , Walborg E. F. , Feltkamp Constance A. , Hilkmann H. A. M. , Emmelot P.
Published: April 2021

The effect of glutaraldehyde fixation on lectin-mediated agglutination of murine leukaemia (GRSL) cells was investigated using 2 assay methods which differed in the shear forces to which the agglutinated cells were subjected. First, lectin and cells were allowed to interact under conditions in which shear forces were minimized and the degree of agglutination was evaluated microscopically by the appearance and size of the cell aggregates. This assay demonstrated that concanavalin A (con A)-, wheat germ agglutinin (WGA)- or Ricinus communis agglutinin I (RCAI)-mediated cytoagglutination was unaffected (WGA and RCA1) or somewhat enhanced (con A) by prior fixation of the cells with glutaraldehyde. Secondly, an electronic particle counter was used to measure the disappearance of single cells and concomitant appearance of cell aggregates as a function of the lectin concentration. In this assay, in which the aggregated cells are subjected to significant shear forces during dilution and cell counting, agglutination of GRSL cells by each of the 3 lectins was drastically inhibited by prior fixation of the cells with glutaraldehyde. This assay also demonstrated enhanced nonlectin-induced cell aggregation after fixation. In both cytoagglutination assays about the same lectin concentration was required for threshold agglutination of unfixed cells. Comparatively, the results of the 2 cytoagglutination assays indicate that a fraction of the lectin-mediated bonds between unfixed cells is shear resistant and that fixation of the cells either weakens these bonds or inhibits their formation.

Morphologically, cells prefixed with glutaraldehyde were spherical at all lectin concentrations, with a continuous dense distribution of cell surface-bound con A, labelled directly with haemocyanin or indirectly using the peroxidase-diaminobenzidine reaction. Unfixed cells showed angular and toadstool-shaped deformations, especially at the highest lectin con- centrations, the agglutinating surfaces being flattened against each other over extended areas. The distribution of con A label was continuous and dense between the apposed surfaces and discontinuous on free surfaces. In the presence of con A the free surfaces of prefixed cells exhibited more microvilli than the surfaces of non-prefixed cells. These results favour the view that fixation prevents the formation of shear-resistant, lectin-mediated bonds between cells, not by restricting the lateral mobility of lectin receptors, but by impairing the apposition of rigid cell surfaces.
Timing of nucleolar DNA replication in Amoeba proteus
Authors: Minassian I. , Bell L. G. E.
Published: April 2021

Light- and electron-microscope autoradiography have been used to follow the incorporation of [3H]thymidine at different stages during the interphase of synchronously growing populations of Amoeta proteus. Two main patterns were found for tritiated thymidine incorporation, i.e, DNA synthesis. The major incorporation was in the central region of the nucleus, but a lesser degree of incorporation occurred in the nucleolar region. The bulk of this nucleolar DNA was found to be late replicating, i.e. it replicated during the G2 phase.
A decay of gap junctions in association with cell differentiation of neural retina in chick embryonic development
Authors: Fujisawa H. , Morioka H. , Watanabe K. , Nakamura H.
Published: April 2021

Ultrastructural studies of thin-sectioned and freeze-cleaved materials were performed on developing retinal tissues of 3- to 9-day-0ld chick embryos to clarify the junctional structures between neural retinal cells and between neural retinal cells and cells of the pigmented epithelium.

Frequency, size and position of gap junctions in developing neural retina are different at each stage of development. In 3-day-0ld embryos, some cells adhere to each other by gap junctions immediately below the outer limiting membrane of neural retinae. The size and number of gap junctions increase remarkably during 5–6 days of incubation. In this period of development, well developed gap junctions consisting of subcompartments of intramembrane particles are found between cell surfaces at both the outer limiting membrane region and the deeper portion of the neural retina. Gap junctions disappear thereafter, and at 7·5 days of incubation, small gap junctions are predominant between cell surfaces at the outer limiting membrane region, while the frequency of gap junctions in the deeper portion is very low. At 9 days of incubation, gap junctions are rarely found.

Typical gap junctions are always found between neural retinal cells andthoseof the pigmented epithelium in embryos up to 7·5 days of incubation.

Tight junctions are not found in the neural retina or between neural retina and pigmented epithelium throughout the stages examined.
A special pattern of the smooth endoplasmic reticulum in the kidney of the snail Cryptomphalus Aspersa
Authors: Paniagua R. , Vázquez J. J.
Published: April 2021

A special structural pattern of the smooth endoplasmic reticulum (SER) has been observed in the kidney of the snail Cryptomphalus aspersa. Two types of cells (clear and dark) cover the foldings of the renal sac; the dark cells are by far the most numerous. A cisterna of SER enveloping the nucleus appears invariably in both types of cells, with no disruptions, or small ones (from 50 to 90 nm) along its profile. The layer of cytoplasm lodged between the external nuclear membrane and this cisterna is found invariably to be from 0.20 to 0.25 μm in width. Glycogen is abundant in the cytoplasm as alpha particles, and also in the nucleus, but as beta particles. It is noteworthy that absolutely no glycogen is present in the layer of cytoplasm lodged between the nuclear membrane and the surrounding SER envelope. Long profiles of SER are also observed closely approaching and parallel to the plasma membrane of the dark cells. Considering the role of SER in glycogen metabolism in the kidney of the snail, the possible function of these cisternae as a support system for enzymes involved in the metabolism of glucides is discussed.
Inversion heterozygosity in females of the newt No tophthalmus viridescens and its influence on chiasma distribution
Authors: Hartley Sheila E. , Callan H. G.
Published: April 2021

In a wild population of the American newt Notophthalmus viridescens 15 females out of a total of 94 were found to be heterozygous for a paracentric inversion which includes almost the whole of the longer arm of the smallest chromosome (XI). The inversion was recognized in preparations of lampbrush chromosomes because it transfers the sequential loops, which normally lie close to the telomere, to a position neighbouring the centromere. Because of inversion the transcriptional polarity of the sequential loops is reversed vis-à-vis the chromosome as a whole.

In normal bivalents XI (both in male and female meiosis) each arm pair generally forms a single chiasma close to the telomeres (proterminal localization). In bivalents XI heterozygous for the inversion no chiasmata are formed between the mutually inverted longer arm pairs, presumably because they fail to synapse, but chiasma frequency in the non-inverted shorter arm pairs is increased, and the normal restraint on chiasma distribution in this arm pair is lifted. An explanation is offered in terms of the availability of recombination nodules, and the time of their association with the synaptonemal complex.
Fine-structural studies of the gametes and embryo of Fucus vesiculosus L. (Phaeophyta): III. cytokinesis and the multicellular embryo
Authors: Brawley Susan H. , Quatrano Ralph S. , Wetherbee Richard
Published: April 2021

Condensation of the chromosomes during the first cell division following fertilization of the brown alga Fucus vesiculosas L. is accompanied by the almost complete disappearance of the nuclear envelope. Golgi vesicles and other small vesicles appear within the spindle, which has paired centrioles at each end. A large amount of rough endoplasmic reticulum is in the sur- rounding cytoplasm during mitosis, and many vesicles at the spindle margin are encircled by stacks of endoplasmic reticulum. Annulate lamellae are observed during mitosis. The envelope which initially reforms around the chromatin in telophase has unevenly spaced nuclear pores. Cytokinesis results primarily by vesicle addition to a centripetal furrow. Mitochondria and chloroplasts concentrate around the partition site, possibly in association with microfilaments. Fibrillar material is added rapidly to the space between the daughter cells from vesicle discharge of both cells and seems to spread into the older cell wall surrounding the embryo. The rhizoid daughter cell contains numerous mitochondria and hypertrophied Golgi bodies whose vesicles increasingly pack the cell. The thallus daughter cell is packed with a variety of vesicles, and the nucleus is surrounded by many dilated cistemae of rough endoplasmic reticulum. By the four-cell stage, chloroplasts of the rhizoid cells have weakly staining lamellae, while chloro- plasts of the thallus cells are actively dividing with deeply staining lamellae.
A study of the arrangement of osteoblasts of rat calvarium cultured in medium with, or without, added parathyroid extract
Authors: Jones Sheila J. , Ness Alan R.
Published: April 2021

The osteoblast layers on the inner surfaces of the half-calvaria of neonatal rats of 2 litters were studied by scanning electron microscopy. Some halves were fixed immediately on dissection. Others were carried through incubation in an Eagle’s medium, with or without the addition of parathyroid extract (PTE): for 2, 4, 8 or, most importantly, 24 b. In their initial state, presumed as like the 0-h material, the osteoblasts presented as a dense tesselation. After 24 h of culture in the medium, osteoblasts were more sparse in the fields examined and although, in a set of 4 preparations, they retained significant alignment, their orientation had become more random. In addition, they were broader and larger in area. By contrast, with PTE added to the medium, osteoblasts almost maintained their number per field, did maintain their cell area, but became longer and narrower and strikingly parallel in their array. The aligning effect of the PTE preceded, and thus was independent of, its elongating effect.
Visualization of interphase chromosomes
Authors: Stack Stephen M. , Brown David B. , Dewey William C.
Published: April 2021

Using a modified Giemsa-banding technique we have observed what appear to be chromosomes during interphase in nuclei from Allium cepa root tips and Chinese hamster cells (CHO line). During telophase through G1 chromosomes progressively uncoil and decondense. During 5 chromosomes are comparatively decondensed, but some segments have structure similar to chromosomes in G1 and G2. During G2 the chromosomes progressively recondense and coil in apparent preparation for prophase. Although specific structural modifications of chromosomes occur in G1,S, and G2 nuclei, chromosomes appear never to decondense to the point that they lose their 3-dimensional integrity, but remain in distinct domains throughout interphase.
The mechanism of concanavalin a cap formation in leukocytes
Authors: Albertini D. F. , Berlin R. D. , Oliver J. M.
Published: April 2021

The process of Concanavalin A (Con A) cap formation on human blood polymorphonuclear leukocytes, monocytes and lymphocytes and rabbit alveolar macrophages has been studied by correlative use of light, fluorescence and electron microscopy. The most important precondition for Con A capping on these cells is the disassembly of cytoplasmic microtubules by colchicine or the glutathione-oxidizing agent, ‘diamide’. Incubation of microtubule-depleted leukocytes with fluorescein-conjugated Con A (F-Con A) leads to the aggregation of lectin into a cap which usually occupies a protuberance at one pole of the cell. F-Con A can also be concentrated at a constriction in the cell body. The protuberance is shown to consist of highly plicated membrane subtended by a network of densely packed microfilaments. Additional microfilaments originate from this network and course into individual plications of the protuberance. However, the formation of the protuberance with its organized structure follows the disassembly of microtubules alone and does not require Con A. Thus when cells are treated with colchicine or diamide, then fixed and labelled with F-Con A the typical changes in cell shape that are associated with capping are observed but lectin is distributed homogeneously over the cell surface. Similarly if cells are first capped with low concentrations of unlabelled lectin, then fixed and incubated with F-Con A, fluorescence is again uniformly distributed over the whole membrane. This indicates that membrane Con A receptors have not been concentrated over the protuberance despite the prior aggregation of microfilaments. By contrast, when precapped cells are labelled with F-Con A before fixation, fluorescence is concentrated through the previously established cap. Thus extensive organization of microfilaments and unlabelled lectin does not inhibit the movement of F-Con A-receptor complexes on unfixed cells. Further, the Con A cap is sufficiently fluid to permit mixing of sequentially formed Con A-receptor complexes. Although the aggregation of microfilaments into a protuberance and the concentration of Con A into the membrane of the protuberance are clearly separable events, microfilaments and Con A-receptor complexes are ultimately found in close association in the cap. This association appears to stabilize the localization of both the surface-bound lectin and the submembranous network of microfilaments. Such stabilization could result from physical interactions between microfilaments and Con A within the protuberance. However, we favour an alternative mechanism in which a region of low membrane fluidity that limits further diffusion is established following microtubule disassembly and is preserved by microfilament-membrane interactions.
Development and regulation of the phosphorylase-glycogen complex in myogenic cells of the L7 line
Authors: Wahrmann J. P. , Recouvreur M. , Favard-Séréno C.
Published: April 2021

The development of the phosphorylase-glycogen complex was studied in cells of the myogenic line L6 at different stages of differentiation. Our results indicate that the complex is already present in mononucleated myoblasts. However, several features of the complex observed in the myoblasts, such as the total amount of phosphorylase bound to the polysaccharide, and the type of glycogen agglomerates present in the cells, differ from those of the myotubes. It is postulated that at the moment when the myoblasts differentiate, definitive metabolic events take place. At this time the protein-glycogen complex is completed, phosphorylase being bound to small glycogen particles, and the multinucleated myotubes begin to accumulate a reserve of free glycogen. This latter constituent is mobilized first upon glucose starvation.
Lectin-mediated agglutination of amphibian embryonic cells
Authors: Fraser Brock R. , Zalik Sara E.
Published: April 2021

Dissociated blastula cells of Xenopus laevis are agglutinated with wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA), Concanavalin A (Con A) and, to a lesser extent with soya bean agglutinin (SBA). They are not agglutinated with fucose-binding protein. Neuraminidase treatment of cells enhances their agglutinability with RCA and SBA, but has no effect on Con A- and WGA-mediated agglutinability. Treatment of cells with procaine, or xylocaine, has no effect on the cells’ agglutinability or on the extrusion of lobopodia. Treatment with colchicine or cytochalasin B either separately or simultaneously has no effect on lectin-mediated agglutinability. Cells treated with cytochalasin B or colchicine and cytochalasin B simultaneously lack lobopodial extensions, while colchicine alone has no effect on these structures. Phenothiazine tranquillizers inhibit agglutination mediated by all of the above mentioned lectins. Lobopodial extensions are absent in cells treated with these compounds. Glutaraldehyde fixation inhibits RCA and WGA mediated agglutinability and reduces the Con A-mediated agglutinability. Results suggest that in this system microtubules and micrcfilaments are not involved in lectin-mediated agglutination.
Effects of experimental alterations in phospholipid composition on the size and number of mitochondria in the flight muscles of the housefly, Musca domestica
Authors: Sohal R. S. , Bridges R. G.
Published: April 2021

The objective of this study was to investigate the effects of experimentally altered phospholipid composition on the size and number of mitochondria in the flight muscles of houseflies of different ages. The phospholipid composition was altered by a decrease in choline content, substitution of choline by an analogue, and by the addition of 2-aminobutan-I-0l to the casein-based larval diet. Analysis of the phospholipids extracted from the thoraces and ‘giant’ mitochondria of adult flies confirmed the presence of altered phospholipids. The number, size, and total volume of the mitochondria were measured in electron micrographs of crosssections of the dorsal longitudinal flight muscle in 1-day, 8-day and 17-day-old flies. In the control flies, the mean mitochondrial size increased while the number decreased during 1 to 8 days of age due to mitochondrial fusion. During 8–17 days of age there was a modest increase in mitochondrial number and a decrease in their average size due to mitochondrial fission. In flies with low choline concentration, the mitochondrial fusion was speeded up and fission was delayed; in the flies with a choline analogue, fusion was speeded up, but fission was normal and in those fed on 2-aminobutan-I-0l, both fusion and fission were delayed. In the 8-day and 17-day-old flies the total volume of mitochondria in the sarcoplasm was approximately the same in all groups. Mitochondria in all experimental groups reached the maximal size achieved in the control flies although at different ages. It is concluded that alterations in phospholipid composition of the thorax affect the rate of mitochondrial fusion and fission; however, the maximal size achieved by the mitochondria is independent of the phospholipid content.
Cytoplasmic inclusions in Xenopus spermatogenic cells. ultrastructural and cytochemical analysis of the action of antimitotic agents on subcellular elements
Authors: Kalt Marvin R.
Published: April 2021

The effects of vinblastine sulphate, alone and in combination with other antimitotic agents, were tested in vitro on testicular tissue from the anuran, Xenopus laevis. Treatment with vinblastine alone resulted in dissolution of spindle and intercellular bridge microtubules, but centrioles and sperm tail axonemes remained intact. In addition, no paracrystalloid inclusions typical of those reported in other cell types treated with vinblastine alone were observed in Xenopus spermatogenic cells. Such inclusions were formed, however, when vinblastine was administered in combination with colchicine, colcemid, or puromycin. Under optimal conditions, paracrystalloids were formed in all cells from primary spermatogonia to late spermatids. The maximum size paracrystalloid formed differed in different spermatogenic cell stages, with late primary spermatocytes containing the largest such inclusions, often averaging over 34 μ m3 each. Autoradiographic analysis of spermatogenic cells labelled with [3H]leucine prior to drug treatment indicated that some radioactive material was incorporated into paracrystalloids in all cell stages. Treatment of Xenopus spermatogenic cells with vinblastine and puromycin was also employed to investigate the possible relationship between paracrystalloid material and a naturally occurring spermatogenic cell inclusion, the chromatoid body, since previous experiments indicated that microtubule protein might contribute to the mass of this structure. It was found that under certain conditions, both paracrystalloids and giant chromatoid bodies can occur together in the same cell, each inclusion reaching a characteristic size independent of the other. This suggests that the two inclusions are aggregates of materials drawn from different subcellular precursor pools.

In addition, autoradiographic analysis of isotope incorporation indicated that giant chromatoid bodies could be clearly labelled with tritiated amino acids, but not with [3H]uridine. The pattern of isotope incorporation observed in giant chromatoid bodies, coupled with their histochemical staining characteristics, rules out the possibility that these structures function as cytoplasmic nucleoli.
Studies of membrane fusion II. fusion of human erythrocytes by sendai virus
Authors: Knutton S.
Published: April 2021

Thin section, negative stain and freeze-fracture electron microscopy have been used to study the fusion of human erythrocytes by Sendai virus. Sendai virus particles are shown to consist of an envelope covered with ∼ 12 nm-long projections or spikes which encloses a helical nucleocapsid. The spike complexes are dumbell-shaped and consist of 2 knobs, one ∼ 8 nm, the other ∼14 nm, in diameter connected by a narrow ∼ 3 nm-thick stalk, with the larger knob embedded in the lipid bilayer of the viral envelope. Virus particles bind to and agglutinate cells at 4 °C; fusion of viral envelopes with the erythrocyte membrane and extensive cell-cell fusion takes place following a brief incubation at 37 °C. At 4 °C most virus particles are roughly spherical and fractures through the viral envelope reveal concave E fracture faces with ∼ 14-nm-diameter intramembrane particles and convex P faces with a complementary arrangement of pits. Incubation at 37 °C results in a dramatic change in the structure of the viral envelope of many virus particles. Invaginations of the viral envelope give the virus a convoluted profile and such virus particles are characterized in freeze-fracture replicas by the presence of smooth linear ridges 30 nm wide and up to 0. ·5 μm long on E faces and by a complementary arrangement of linear grooves on P faces. Instead of ∼ 14 nm-diameter intramembrane particles on E faces, ∼ 8 nm particles are present on both P and E faces. These changes, which only take place when virus particles are bound to erythrocytes, are also accompanied by the disappearance of clearly defined surface spikes. Only virus particles having this altered morphology actually fuse with the erythrocyte membrane. The characteristic ‘ridged’ morphology of the viral envelope allows specific sites of viral envelope-cell fusion to be identified in freezefracture replicas and successive stages during the incorporation of the viral envelope to be reconstructed. These observations show that viral envelope-cell fusion is initiated by a cell- mediated temperature-sensitive change in the molecular organization of the viral envelope which allows the particle—denuded linear invaginations, possibly lipid bilayer, to interact and fuse with the erythrocyte membrane. Further observations suggest that cell-cell fusion does not occur directly between cells but is achieved by the simultaneous fusion of a virus particle with 2 adjacent erythrocytes.
Immunocytochemical visualization of microtubules and tubulin at the light- and electron-microscopic level
Authors: Brabander M. De , Mey J. De , Joniau M. , Geuens S.
Published: April 2021

An antibody against rat brain tubulin was purified by affinity chromatography and used for the immunocytochemical staining of tubulin-containing structures in tissue-cultured cells at the light- and electron-microscopic level. For this purpose the unlabelled antibody enzyme method (PAP method) was used. Tissue-cultured cells were fixed with glutaraldehyde or formaldehyde, postfixed with acetone and stained with the PAP procedure. With the light microscope, a dense network of darkly stained fibres was visible in non-dividing cells. The fibres converged towards a point in the nuclear vicinity and radiated throughout the cytoplasm towards the cell periphery. Mitotic spindles were also heavily stained in all stages. The cytoplasm of non-dividing and dividing cells contained a variable amount of diffuse staining. The nucleus was unstained. The network could be destroyed by treating the cells with microtubule inhibitors. An intense diffuse staining was visible in cells treated with colchicine or nocodazole.

The paracrystalline tubulin precipitates that appeared in cells treated with vinblastine were heavily stained.

Preliminary ultrastructural observations were made on sections through cells that were fixed with glutaraldehyde, stained with the PAP procedure and embedded in Epon. The microtubules were seen to be covered with stained PAP complexes. The cortical microfilaments, the 10–nm filaments and the plasma membrane were unstained, as were the contents of nuclei, mitochondria, endoplasmic reticulum, Golgi elements, lysosomes and vacuoles. A variable amount of diffuse staining was visible in the cytoplasm and the membranes of several organelles often showed PAP deposits. This staining was presumed to localize tubulin in non-microtubular form. It is probable that at least part of this staining was immunologically specific, since no PAP complexes were seen in the cells when the antitubulin antibody was omitted from the procedure or when it was replaced by an unrelated antibody solution.
Changes induced by ultraviolet light in the superhelical dna of lymphocytes from subjects with xeroderma pigmentosum and normal controls
Authors: Cook P. R. , Brazell I. A. , Pawsey S. A. , Giannelli F.
Published: April 2021

Patients with the light-sensitive disease xeroderma pigmentosum (XP) are genetically heterogeneous. Most patients are defective in the excision repair of u.v.-induced DNA damage while some, the XP-variants, seem proficient in excision repair but replicate u.v.-damaged DNA with difficulty. The former have so far been assigned to 5 complementation groups (A-E) of which B and E are extremely rare.

Information on the nature of the defect in XP is contradictory. Studies based on the sedimentation of DNA in alkaline gradients suggest that patients of complementation group A can perform the first step of excision repair (‘incision’) while others, based on the elution by alkali of the DNA of cells lysed on filters, suggest that they cannot. We have therefore investigated the repair of DNA damaged by u.v. irradiation using a method based on a precisely defined theoretical approach. A single break in one of the strands of a double-stranded and supercoiled circle of DNA releases supercoiling and reduces its rate of sedimentation in sucrose gradients. Structures resembling nuclei (‘nucleoids’) containing superhelical DNA may be obtained from human lymphocytes and their rate of sedimentation is influenced by the integrity of their DNA.

Analysis of the sedimentation of nucleoids from normal and XP lymphocytes in sucrose gradients containing different concentrations of ethidium indicates that their DNA is similarly supercoiled. The lymphocytes of patients of complementation groups A, C and D repair damage induced by γ-rays just like controls. However, they cannot repair normally DNA damaged by u.v. irradiation; the cells are defective in the first step of excision repair.

The XP-variant and XP-heterozygous cells repaired u.v.- and γ-ray-induced damage like controls.

Some problems regarding the nature of the defect in XP are discussed.
Cell cycle-dependent changes in non-membranous nuclear ghosts from HeLa cells
Authors: Riley D. E. , Keller J. M.
Published: April 2021

Non-membranous nuclear ghosts are isolated from the nuclei of cultured HeLa cells after successive treatments with detergents and high ionic strength (0·5 M MgCl2) buffers. These ghosts have been shown by Keller & Riley to consist of a network consisting of annuli (90 nm in diameter), rod-like structures and dense bodies interconnected by DNase-sensitive strands. In nuclear ghosts purified from HeLa cells synchronized by a double thymidine block technique, the arrangement of these components exhibits dramatic cell cycle-dependent organizational differences. During G1 the small dense bodies (or aggregates) are widely dispersed and appear to be associated with the surface of the ghost. In S-phase, only a single (large) dense body is present and it is located in the centre of the ghost. The appearance of nuclear ghosts from cells in G2 is intermediate between those observed in G1 and S. These cell cycle-dependent organizational differences in the ultrastructure of nuclear ghosts are paralleled by differences in their susceptibility in suspension to DNase I. The G1 -phase ghost is markedly sensitive, whereas the S-phase ghost has both a sensitive component, the network consisting of annuli and rod-like structures connected by thin strands, and a resistant component, the single (large) dense aggregate. The unique morphology of ghosts at a particular phase of the cell cycle and the similarity of the polypeptide species present in ghosts isolated at these 3 phases of the cell cycle lead us to conclude that the various organizational patterns described are alternative cell cycle-dependent configurations of what is fundamentally the same macromolecular complex. A model is presented in which internal nuclear skeletal components and the non-membranous nuclear envelope are considered to be dynamic interacting components of interphase nuclei. This model provides a physiological rationale for nuclear envelope expansion capability which has been observed under experimental conditions by many investigators.
Characterization of columnar absorptive epithelial cells isolated from rat jejunum
Authors: Towler Christopher M. , Pugh-Humphreys Geoffrey P. , Porteous John W.
Published: April 2021

The origin and yield of cells isolated from rat jejunum have been assessed; 80—90% of the mature columnar absorptive cells but none of the Paneth, endocrine or regenerating crypt cells were recovered by the methods described. The structural integrity of the isolated cells was tested by phase contrast-, Nomarski interference- and fluorescence light-microscopy; and also by transmission electron microscopy; the isolated cells appeared structurally intact by all microscopic criteria applied. The isolated cells were judged to be functionally intact because they satisfied a number of tests designed to answer three logically related questions, namely: was the cell-surface membrane intact; were the cells able to accumulate selected solutes against a concentration gradient from the exterior medium; and were the cells able to perform biochemical functions which depended upon the integrated activities of several subcellular structures? The isolated cells did retain and accumulate selected solutes, respired at a steady rate on endogenous substrates, showed enhanced respiration on exogenous glucose and glutamine, maintained favourable intracellular proportions of adenine nucleotides (ATP: ADP: AMP), and synthesized cell protein from extracellular amino acids in proportion to the time of incubation. The isolated cells accounted for 80% of the lactic acid produced by intact rat jejunum under similar conditions of incubation.
The viability of the anucleate cytoplasm of Amoeba Proteus
Authors: Ord M. J.
Published: April 2021

The viability of Amoeba proteus cytoplasm was tested at 1-to 2-day intervals throughout the 14 days following enucleation. Viability was demonstrated by renucleating the anucleate cytoplasms and observing whether the resultant amoebae could resume normal activities such as moving, feeding and dividing. Four lines of A. proteus were studied, approximately 200 transfers being made on amoebae of each line. The introduction of a nucleus into anucleate cytoplasm initiated a temporary reactivation followed by a period of relative inactivity before either death by cytolysis or permanent reactivation with feeding, growth and division. Though approximately 70 % of anucleate cytoplasms were still viable 6 days after enucleation, temporary reactivation disappeared about this time and the period of relative inactivity which generally followed it increased in duration from a few days to several weeks. Few amoebae which were able to divide failed to form clones. Anucleate cytoplasms of wheat-cultured amoebae remained viable for longer periods than anucleate cytoplasms of tetrahymena-fed amoebae.
Labelling of the cell surface of the collective amoeba Dictyostelium Discoideum with fluorescent antiserum
Authors: Shaffer B. M.
Published: April 2021

The surface of a separate Dictyostelium discoideum cell exposed to fluorescent antiserum is initially uniformly stained. When the cell moves, labelled material is left on the glass over the area occupied by the cell while in the antiserum. The surface of new pseudopods is fluorescent. The bulk of the label soon accumulates on the rear of the cell and is towed along behind it. The rest of the surface may remain faintly fluorescent for long periods, but this residual label is immediately left behind if the cell advances while strongly compressed between agar and glass. This evidence does not clearly decide between the hypotheses of a permanent, advancing, lateral cell surface and a temporary, stationary one. The fact that the lateral surface of an advancing cell does not drag forward viscous medium in contact with it does not favour the former hypothesis.
Problems of electron stereoscopy of biological tissue
Authors: Gray E. G. , Willis R. A.
Published: April 2021

A detailed study of stereoscopy of tissue sections with the transmission electron microscope has been carried out using different tilt angles and staining techniques, aided with models. Pictures with tilt angle difference of 20° or more can be fused to give pairs of micrographs showing stereodepth. Cytoplasmic filaments, glycogen and ribosomal granules give good stereodepth. Oblique membranes, especially when stained with lead or phosphotungstic acid, give good depth in stereo-pairs but membranes running more vertically in the section do not. A theory, based on the ‘transparency factor ‘that is a feature of transmission electron microscopy, is given to account for this discrepancy. A learning process is involved in achieving depth perception when viewing stereo-pairs of electron micrographs of tissue sections. Complex structures often cannot be perceived in depth even after prolonged scrutiny through the stereoscope. Where structures overlap in the thickness of the section, they can be ‘separated out’ with stereoscopy and in this way clarified, for depending on which micrograph of a stereo-pair is presented to which eye, a structure can be made to appear either in the front or the back of a section. In general, problems of depth perception in stereo-pairs of micrographs obtained with transmission electron microscopy arise because with our normal everyday vision using reflected light, we look at things, whereas with the electron microscope using a transmission electron beam we look through things.
Electron microscopic observations on the basal lamina of chick limb buds after trypsin and edta treatment
Authors: Goel S. C. , Jurand A.
Published: April 2021

Chick hind-limb buds were treated first with calcium- and magnesium-free balanced salt solution and then with either trypsin or EDTA. Treatment with these chemicals, and the subsequent separation of the ectodermal covering from the mesoderm, produces two different results as regards the basal lamina. In the case of trypsin, the lamina stays with the ectoderm but shows signs of probable tryptic digestion. After EDTA treatment the lamina stays with the mesoderm and becomes very loose and swollen. This loosening allows the structure of the otherwise compact lamina to be resolved so that banded collagen fibrils are seen participating in its substance. The above observations are discussed in relation to the mode of action of the two chemicals. The physiological role and the origin of the basal lamina, as well as the possible implications of the present findings to the question of limb development and morphogenesis, are also discussed. A note has also been made regarding the various terms used to describe the epitheliomesenchymal junction layers.