bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrastructure of mitotic arrest induced by isoprenaline in rat parotid acinar cells
Authors: Radley J.M.
Published: April 2021

The mitotic arrest of acinar cells in the rat parotid gland in response to isoprenaline has been investigated at the ultrastructural level. The arrested cells were characterized by the presence of both centriole pairs at the cell centre, around which chromosomes formed an approximately spherical array. Microtubules radiated out from both centriole pairs, indicating that they were part of a bipolar system. The microtubule population included both non-kinetochore and kinetochore microtubules. Metaphase arrest appeared to be due to failure of the poles to separate, or to remain separated in the case of cells already in metaphase at the time of drug administration. This could be explained by the drug interfering with the ability of interpolar microtubules from opposite poles to interact with one another.

The distribution of the chromosomes around the centrioles appears to depend on the presence of kinetochore microtubules, which are thought to act as tethers, either by themselves or in conjunction with non-kinetochore microtubules. It is suggested that tension is necessary between the kinetochores and poles to attain the arrest configuration. Chromosomes were observed in which both kinetochores had attached microtubules but whether or not they were linked to opposite poles remains to be investigated.

Two types of arrested cell were distinguished by their content of secretory granules. Cells already in mitosis at the time of isoprenaline administration were not depleted by drug action, and during the period of arrest numerous large secretory granules were intermingled with the chromosomes. Those cells which entered mitosis after the drug was given were initially blocked in the G2 phase, during which time they were depleted of secretory granules. On entering mitosis, these cells possessed only small secretory granules, which were newly synthesized. In the metaphase-arrested state the small secretory granules were clustered around the centriolar complexes, demonstrating the presence of a poleward force operating on them. It is possible that the same force acts on the secretory granules in the first type of arrested cell, but because of the relatively large size of the granules, the clustering around the poles is not pronounced. The nature of the forces acting on the chromosomes and on the secretory granules is discussed. The functioning of these forces during the arrest state has to be considered in any general model for mitosis.
Nucleolar development in the interphase of the cell cycle
Authors: Sacristán-Gárate A. , Navarrete M. H. , Torre C. De La
Published: April 2021

Stereology of nucleoli at 3 different points of the cell cycle, in the middle of the G1 S and G2 of interphase, was accomplished in a naturally synchronous cell population rendered binucleate and thus ‘labelled’ and made identifiable by 1 h caffeine treatment in root meri-stems of Allium cepa L.

Consistent structural changes were found so that nucleolar parameters by themselves can locate a cell at any interphase period.

The growth of the nucleolus in the course of interphase takes place exclusively in its granular portion. The growth rate of this last component was found to be greater in the first half of interphase (5·4μm3h−1) than in the second (2·9 μm3 h”−1), as calculated for a nucleus with only one fused nucleolus. The changes in volume of the nucleolar components during interphase do not parallel the gene dosage.

Nucleolar surface at each point seems to be the factor which determines the growth rate in the preceding interval, since these rates are inverted for fused and unfused nucleoli.

The nucleolar volume occupied by lacunae is minimal in the S-period and shows an enormous increase by the middle of G2.

We think our data may be the structural basis on which a model for nucleolar functioning in proliferating cells could be built.
The antagonistic effects of antimitotic agents on contraction and re-extension in the ciliate Spirostomum ambiguum
Authors: Ettienne E. M. , Selitsky M.
Published: April 2021

Contraction in Spirostomum is apparently directed by 2 antagonistic systems which respond to changes in free calcium concentration. The system responsible for imparting contractile tension consists of bundles of 4–5 nm microfilaments which can be calcium-activated. The second system consists of pellicular microtubules which may have the capacity to impart tensile force and react with each other through cross-bridging. Cells subjected to electrical stimulation to induce contraction in the presence of 0·1 mM 2,4-dinitrophenol and KCN failed to recover their original resting lengths. Similar treatment with colchicine produced the same effect, implying an interruption in the activity or structural integrity of the microtubular system. Treatment with 0·5 μg/ml cytochalasin B inhibited all contractile responses, presumably by blocking the activity of microfilaments.
Descriptive and quantitative study of ultrastructural changes in the apical meristem of mustard in transition to flowering: II. the cytoplasm, mitochondria and proplastids
Authors: Havelange A. , Bernier G. , Jacqmard A.
Published: April 2021

Transition to flowering was induced in the shoot apical meristem of Sinapis alba (mustard), a long-day species, by subjecting vegetative plants to a single 22-h long day. The ultrastructural changes occurring in the meristematic cells during the complete morphogenetic switch were investigated by quantitative methods.

The earliest detectable changes are seen 18 h after the start of the inductive long day. One of these changes is the replacement of the large vacuoles of the cells of vegetative meristems by an increased number of smaller vacuoles in the cells of meristems of plants induced to flower (evoked meristems). The other earliest change is an increase in size of the chondriome. Remarkably enough both changes have in common that they lead to an increase in membrane area and are thus concerned with increased membrane synthesis. In this respect this very early effect of the leaf-generated floral stimulus is very similar to that produced by various animal and plant hormones in their respective target tissues.

The large rise in chondriome size is paralleled by an increase in succinic dehydrogenase activity. Both changes certainly reflect a rise in cellular respiratory activity which produces the necessary energy supply for the morphogenetic switch.

As the size of the plastidome does not change during the transition to flowering, the plasti dome: chondriome ratio decreases markedly.

The size of the cytoplasmic matrix is greater in cells of evoked meristems than in cells of vegetative meristems. A first size maximum is reached at 26 h after the start of the long day and a second at 54 h. These 2 maxima occur just prior to 2 mitotic waves culminating respectively at 26–30 and 62 h. The increases in amount of endoplasmic reticulum (ER) and dictyosome number that are found in evoked meristems collected just prior to or at the time of the second mitotic wave are also probably related to the mitotic activation of the tissue.

As the size of the vacuolar apparatus considered as a whole does not change at all and the size of the cytoplasmic matrix increases, the vacuoles:cytoplasm ratio decreases in evoked meristems collected following 26 h after the start of the long day. Also, there is an unexpected decrease in the nucleus:cytoplasm ratio in the cells of evoked meristems after 46 h.
Protoplast regeneration from normal and bromodeoxyuridine-resistant sycamore callus
Authors: Bright S. W. J. , Northcote D. H.
Published: April 2021

Protoplasts have been prepared from normal and mutant lines of sycamore callus, maize root and tobacco leaf. Fusion was rare in sodium nitrate solutions. A mutant tissue culture was selected for by its resistance to 10 μg/ml bromodeoxyuridine. The mutant is sensitive to the Hypoxanthine-Aminopterin-Thymidine (HAT) selective medium but has normal thymidine transport and thymidine kinase activity.
Sodium exchange in the cytoplasm and nucleus of amphibian oocytes
Authors: Century T. J. , Horowitz S. B.
Published: April 2021

Oocytes of Rana pipiens were incubated in 22Na-Ringer’s solution and 22Na - 23Na exchange in the nucleus and cytoplasm followed by low-temperature microdissection. Cytoplasmic sodium consists of 2 kinetic fractions: the larger (88 %) slowly exchanging (t1/ 2 ∼ 2 days), and the smaller (12%) rapidly exchanging (t1/2 ∼53 min). Nuclear sodium consists of a single fraction whose concentration is similar and whose rate constant is identical with that of the rapidly exchanging cytoplasmic fraction. Our findings are consistent with a model of compartmentalization in which rapidly exchanging sodium is nearly uniformly distributed in the water of the nucleus and cytoplasm and its exchange limited by movement through the cell surface. On the other hand, slowly exchanging sodium is restricted to the cytoplasm, sorbed to or sequestered in some as yet unidentified cytoplasmic constituent.
The reaction of mitochondria in the coleoptiles of rice (Oryza sativa L.) with diaminobenzidine
Authors: Öpik Helgi
Published: April 2021

Diaminobenzidine, DAB, was applied to segments of aerobically and anaerobically grown coleoptiles of rice, Oryza sativa L., with the object of studying the location of cytochrome oxidase at the electron-microscope level. A specific staining of mitochondrial cristae and inner membrane was obtained, with no reaction in other organelles; with extended periods of incubation, the reaction product filled the mitochondria completely. In anaerobically grown coleoptiles, the reaction was much slower and the difference was particularly marked in vascular bundle companion cells and parenchyma, which gave the strongest reaction in aerobic tissue, but in the anaerobic stained even less than the cortical parenchyma. The reaction was inhibited by boiling and slowed very much by lowering of the incubation temperature from 27 to 4 °C. This indicated the involvement of an enzymic reaction and cyanide inhibition indicated that a haem enzyme was involved. The catalase inhibitor aminotriazole did not inhibit DAB oxidation. Nevertheless the specificity of the reaction for cytochrome oxidase must be questioned, because preheating of the tissue to 60 °C before incubation, which would be expected to destroy cytochrome oxidase activity, failed to decrease the oxidation, at least in aerobically grown coleoptiles. It is concluded that DAB is oxidized in the rice coleoptile tissue by a cytochrome system, and the development of this system is inhibited by anaerobiosis, but the oxidation cannot be claimed to represent cytochrome oxidase activity exclusively. Perhaps other autoxidizable, more heat-stable cytochromes participate in the reaction.
Role of zinc in cell division of Euglena gracilis
Authors: Falchuk K. H. , Fawcett D. W. , Vallee B. L.
Published: April 2021

Euglena gracilis is a suitable model system to investigate the role of zinc in the process of cell division. In zinc-deficient organisms there is a characteristic arrest of cellular proliferation, the DNA content of the cells doubles, whereas RNA and protein contents decrease. The present investigations include the growth characteristics, changes in cellular morphology at various stages in the growth cycle, quantitation of zinc uptake and incorporation of tritium-labelled precursors into RNA by organisms grown in zinc sufficient (Zn+), (Zn,+ content 1 ×10−5 M) or zinc-deficient (Zn−), (Zn+ content 1 × 10−7 M) medium. Cell division ceases on depletion of zinc from the medium. There are 20-fold less cells in (Zn−) medium than in control cultures. The size of (Zn+) cells decreases during log phase due to a reduction in the paramylon content of the cytoplasm. The size of (Zn−) cells, however, increases, due to an accumulation of paramylon. This results in a 13-fold increment in dry weight compared to control. Other cytoplasmic organelles, including Golgi bodies, mitochondria, etc. are normal. Nuclear morphology also is unchanged. There is a reduction in the rate of incorporation of labelled precursors into RNA by (Zn−) cells.

The DNA content of (Zn−) E. gracilis, the absence of morphologic evidence to indicate that cell division has followed the doubling of the DNA, and the arrest in proliferation suggests that a critical zinc-dependent step in the cell cycle, localized to G2, is blocked in zinc deficiency.
Ultrastructural localization of cationic proteins in cytoplasmic granules of chicken and rabbit polymorphonuclear leukocytes
Authors: Macrae Edith K. , Spitznagel J. K.
Published: April 2021

Cytoplasmic granules known to contain cationic arginine-rich proteins can be identified by the ammoniacal silver reaction (ASR) which provides a cytochemical marker detectable under the electron microscope. Only the large rod-shaped granules of the chicken polymorphonuclear leukocytes (heterophils) and the large spherical azurophilic granules of the rabbit neutrophilic polymorphonuclear leukocytes show the ASR product as a discrete particulate electron-dense deposit. The other smaller granules are devoid of reaction product, as are membranes and mitochondria. The intracellular localization of the ASR product on the large granules coincides with the ASR product localization on the same isolated granule populations, when the ammoniacal silver reaction is applied to these granules after their separation by sucrose-density gradients. The cationic proteins may have intraleukocytic bacteriolytic properties, since ASR product, presumably indicating cationic protein from discharged granules, appears to surround ingested bacteria within cytoplasmic phagosomes.
Phase-contrast and electron-microscopic observations on a membranous complex in primary spermatocytes of the mouse
Authors: Pleshkewych A. , Levine L.
Published: April 2021

A prominent cytoplasmic inclusion present in living mouse primary spermatocytes has been observed by both light and electron microscopy. It began to form at prometaphase and continued to increase in thickness and length as the cells developed. By metaphase it was a distinct sausage-shaped boundary that enclosed a portion of the cytoplasm between the spindle and the cell membrane. At the end of metaphase, the inclusion reached its maximum length. At telophase, it was divided between the daughter secondaries. The inclusion persisted as a circular contour in the interphase secondary spermatocyte.

Electron microscopy of the same cultured cells that were previously observed with light microscopy revealed that the inclusion was a distinctive formation of membranes. It consisted of agranular cisternae and vesicles, and was therefore a membranous complex. Many of the smaller vesicles in the membranous complex resembled those found in the spindle. The cisternae in the membranous complex were identical to the cisternal endoplasmic reticulum of interphase primary spermatocytes. Neverthless, the organization of vesicles and cisternae into the membranous complex was unique for the primaries in division stages, since such an organization was not present in their interphase stages.
The pattern of microtubules in the axonemes of Gymnosphaera albida sassaki: evidence for 13 protofilaments
Authors: Jones W.C.
Published: April 2021

The axonemes of Gymnosphaera albida radiate from a central axoplast. Their proximal ends form a shell around the axoplast. Within the shell each axoneme is enveloped by a fibrillar sheath and the microtubules are interconnected by electron-dense linkages, which sometimes appear to be double. In nearly transverse sections the microtubules and their linkages form hexagons of 2 irregular types arranged in alternating rows. The shapes of the hexagons vary from one axoneme to the next. The variation is caused largely by the inclination of the axonemes to the line of sight, but also by distortion occurring during the preparation, observation and photography of the sections. Calculations show that, of a number of likely basic patterns (as would be seen in strictly transverse section), only one is compatible with measurements made on 9 of the axonemes. This involves only one type of hexagon oriented in 2 directions to form a ‘parquet-floor’ pattern. The hexagon is bilaterally symmetrical and its 6 microtubules all have the same set of angles between their linkages, namely an unpaired angle of 138 degrees 28′ and paired angles of 110 degrees 46′. Because these angles are in the ratio of 5:4:4, it is deduced that the microtubules have 13 protofilaments forming their walls. Morphogenetically the lateral growth of the pattern is governed by 2 rules: (1) there must be one, and only one, direction of 2-step zig-zagging of the linkages, and (2) linkages forming opposite sides of a hexagon must be in parallel.
Extraocular muscle degeneration and regeneration after exposure of rats to incandescent radiant energy
Authors: O’steen W. K. , Shear C. R. , Anderson K. V.
Published: April 2021

Exposure of albino rats to incandescent radiant energy for a short period of time in an elevated environmental temperature (39 °C) causes degenerative changes in the extraocular muscles. The muscle fibres regenerate and the muscles reorganize if the animals are returned to room lighting and temperature. Extraocular muscles (EOMs) were damaged first near their insertion on the eyeball. All EOMs of both eyes were affected, but the degeneration did not extend the entire length of the muscle. The peripheral fibres of each muscle-were damaged before the more central fibres. Mitochondria were swollen and often contained dense bodies. Numerous vesicular profiles, possibly from the sarcotubular system, were present. Myofibrils of the more severely damaged fibres lacked typical Z-disk structures, and I-bands had disappeared by 24 h after the exposure period, a degenerative pattern which seems to be unique for this method of EOM damage.

EOM degeneration appeared to be dependent on the interaction between thermal and radiant energy on the orbital contents. However, EOMs were only rarely and very slightly affected when rats were exposed to elevated temperature in the absence of incandescent radiant energy. When an opaque, black, ocular occluder was placed over one eye and the contralateral eye was left unoccluded, EOMs and retinas of occluded eyes were undamaged, while those tissues were severely damaged in unoccluded eyes. Therefore, the most critical single variable in inducing EOM degeneration appears to be exposure to radiant energy.
Some evidence for replication transcription coupling in Physarum polycephalum
Authors: Fouquet H. , Böhme R. , Wick R. , Sauer H. W. , Scheller K.
Published: April 2021

Hydroxyurea, at concentrations of 40–60 mM, selectively and effectively blocked incorporation of thymidine into DNA. Inhibition occurred within 5–10 min of application of the agent when DNA synthesis was in progress, while the onset of replication at the beginning of S-phase and DNA synthesis in G2 phase were not affected.

Uridine incorporation into TCA-precipitable material, in the presence of hydroxyurea, was significantly (up to 70%) inhibited in early S-phase of the cell cycle. Selective inhibition of RNA synthesis was confirmed for RNA separated into rRNA-rich and poly-(A)-rich RNA fractions and analysed by the 2 kinds of DNA-RNA hybridization reactions. Uridine incorporation into poly (A) RNA was also inhibited under conditions where cycloheximide prevented maturation of nascent DNA molecules in early S-phase.

We assume that chromatin which is replicating early DNA sequences may be a more competent template for transcription.
Localization of atpase activity in striated muscle and probable sources of artifact
Authors: Gillis J. M. , Page Sally G.
Published: April 2021

An attempt has been made to localize sites of ATPase activity in stretched fibrils from glycerinated rabbit muscle by precipitating the liberated phosphate with lead ions. As a control, the distribution of lead phosphate grains precipitated by adding phosphate solutions to fibrils incubated with lead (without ATP) has been studied. In these conditions, the grains are not uniformly distributed along the fibrils, but show many of the features of the pattern of distribution that is found after the fibres have been incubated in ATP and lead. It is suggested that differential lead binding by the protein filaments, or movement of the grains, may be responsible for this non-uniform distribution, and that consequently no conclusions concerning sites of ATPase activity within the sarcomere can be drawn from the results of methods using lead precipitation.
The ultrastructure of the perineurium in two insect species, carausius morosus and periplaneta americana
Authors: Maddrell S. H. P. , Treherne J. E.
Published: April 2021

The organization of the perineurium in two insect species (Carausius morosus and Periplaneta americana) has been examined with the electron microscope. In both species this cellular layer has been found to possess an extensive system of tortuous channels between the lateral cell walls. These channels are open at the outer margin adjacent to the fibrous connective-tissue sheath, but appear to be closed at the inner margin by regions of septate desmosomes and/or ‘ tight’ junctions. There is an increased surface area at the inner margin of the perineurial cells produced by the presence of long inwardly directed flanges. An electron-dense coat has also been identified on the cytoplasmic side of the type II perineurial cell membranes at points of contact with the underlying extracellular system and at the outer surface adjacent to the connective-tissue sheath. This organization of the perineurium is strikingly similar to that observed in a variety of fluid-secreting epithelia and its possible function in fluid transport is discussed in relation to the available evidence on the physiology of the insect central nervous system. It is suggested, contrary to some earlier suppositions, that the perineurium may not be primarily involved in the control of the extracellular sodium level and that this regulation may be effected at a deeper level in the central nervous tissues.
The activation and reactivation of peripheral lymphocytes in culture
Authors: Ling N. R. , Holt P. J. L.
Published: April 2021

Human lymphocytes stimulated for 16 h and then cultured without stimulant showed maximal activity on days 2–3 following a stimulus of phytohaemagglutinin (PHA) and on days 3–4 following a stimulus of staphylococcal filtrate (SF). At low dosage of stimulant the response of the cells was less marked but persisted for a longer period than at high dosage. The pattern of response is discussed in relation to the mechanism of activation.

After the effect of the initial stimulus had died away cell populations which had been stimulated with SF or PHA could be restimulated with either stimulant. Their response, when stimulated this second time, was quicker than that of incubated cells from the same donor which had not been previously stimulated. Prestimulated cells were also tested in two immunospecific reactions : the reaction to tuberculin-purified protein derivative (PPD), and the mixed lymphocyte reaction. Cells which had been previously exposed to SF responded more quickly to PPD than cells not previously stimulated. Cell populations which had been previously stimulated also reacted more quickly in a mixed lymphocyte reaction. It is concluded that lymphocyte populations which have been recently stimulated not only retain their capacity to react to immunospecific mitotic stimuli but also react more quickly.
Fine-structural changes in relation to ion and water transport in the rectal papillae of the blowfly, calliphora
Authors: Berridge M. J. , Gupta B. L.
Published: April 2021

The fine structure of the epithelial cells of the rectal papillae in the blowfly, Calliphora erythrocephala Meig., has been investigated to elucidate the possible mechanism of reabsorption of water and ions from the rectal lumen. To observe the variations in the structure of the epithelium in response to the absorptive processes the material was taken (a) from flies at the various stages of their first oviposition cycle, and (b) from freshly emerged imagoes starved for 2 days and injected into the rectum with solutions of various tonicities. It has been found that the complex system of intercellular spaces, formed by a prolific infolding of the lateral plasma membrane of the cells, shows a direct response to the conditions of supposedly maximal and minimal transport of fluid. These spaces are (a) grossly distended in the flies injected with hypotonic media, (b) highly dilated under normal conditions, and (c) completely collapsed in fasting and starved flies. These observations have been discussed in the light of the available theories to explain the mechanism of water transport in biological tissues. It is proposed that the structural design of the rectal papillae favours the application of double-membrane theory to explain the reabsorption of water against osmotic gradients as a consequence of an active transport of solutes into enclosed spaces.
Studies on plasma membranes: IV. the ultrastructural localization and content of sialic acid in plasma membranes isolated from rat liver and hepatoma
Authors: Benedetti E. L. , Emmelot P.
Published: April 2021

Plasma membranes were isolated from rat liver and a transplanted rat hepatoma of the hepato-cellular type. After glutaraldehyde fixation the membranes were treated with colloidal iron hydroxide (CIH) at pH 1·7, which was found to react specifically with the neuraminidase-sensitive sialic acid of the liver membranes. The CIH-reactive, neuraminidase-sensitive sialic acid, comprising 70 % of the membrane-bound sialic acid, was exclusively located in the outer leaflet of the liver membranes as shown by the rather regular distribution of electron-dense CIH granules. This granular, asymmetric type of staining was also observed in the hepatoma membranes, which contained some 50% more sialic acid than did the liver membranes. In addition, the hepatoma membranes showed an intense and uniform staining by CIH of short segments of both membrane leaflets; the latter type of staining was but little impaired by neuraminidase pre-treatment. None of the junctional complexes of the liver membranes was stained by CIH. Tight junctions were very rarely observed in the hepatoma membrane preparations, and the desmosomes and intermediate junctions of these membranes not infrequently exhibited a loosened appearance exposing CIH-reactive neuraminidase-sensitive sialic acid at their opposite plates. This aspect could be induced in the desmosomes and intermediate junctions, but not in the tight junctions, by pre-treatment of the liver membranes with the chelating agent ethylenediaminetetra-acetate.
The structure of the macromolecular units on the cell walls of Bacillus polymyxa
Authors: Finch J. T. , Klug A. , Nermut M.V.
Published: April 2021

Electron micrographs of negatively stained preparations of cell walls of Bacillus polymyxa have been investigated by optical diffraction and optical filtering techniques. Images of single layers of the cell wall, from which the ‘ noise’ has been filtered optically, show hollow, square-shaped morphological units arranged on a square lattice of side 100 A. Single-layer images showing the same pattern have been filtered from moir6 patterns arising from two overlapping single layers. The morphological units are composed of four smaller subunits. The optical diffraction patterns from regions of two overlapping layers show extra reflexions which are attributed to multiple electron scattering.
Polyploidy and nuclear fusion in the fat body of Rhodnius (hemiptera)
Authors: Wigglesworth V. B.
Published: April 2021

The diploid number in Rhodnius is 22 in both sexes. At hatching the fat-body cells are tetraploid, with a few octoploid. This polyploidy is presumed to arise by endomitosis in the egg. In the fully nourished insect this state persists throughout life; and occasional 16n and 32n nuclei occur. Whether these arise by endomitosis or by nuclear fusion has not been established.

In extreme starvation (e.g. 8 months from the time of moulting in the 4th-stage larva at 26 °C) polyploidy increases greatly. This results from nuclear fusion in interphase. The evidence is as follows: All intermediate stages in fusion can be observed.Polyploidy develops many months after growth and mitosis have been arrested. (iii) It occurs mainly in those regions where the food reserves first become exhausted. (iv) When these starved insects are fed the polyploid cells divide and chromosome counts include 12n, 20n, 24n, etc., as well as the regular series 4n, 8n, 16n, 32n, etc. Contiguous nuclei which have not fused in interphase often amalgamate their chromosomes to form a single plate and spindle at metaphase and likewise produce more highly polyploid daughter cells. The high incidence of nuclear fusion in Rhodnius is ascribed to the low rate of metabolism which permits prolonged survival in the starving insect.
Light- and electron microscope studies on the spleen of the newtTriturus cristatus:The fine structure of erythropoietic cells
Authors: Tooze J. , Davies H. G.
Published: April 2021

The stages of erythrocyte maturation were identified in spleen smears stained with May-Grünwald-Giemsa. The fine structure of sectioned cells from about the basophilic erythroblast stage onwards was investigated in the electron microscope and serial 1-μ sections were examined by microspectrophotometry to ascertain haemoglobin content. The nuclei of basophilic erythro-blasts contain large and small blocks of chromatin as well as light-staining zones of unknown composition and ill-defined structure: the nuclear sap contains numerous interchromatin granules, about 400 Å in diameter. During maturation the small blocks of chromatin aggregate and the nuclear light-staining zones tend to disappear, as do the interchromatin granules. Storage lysosomes occur in the basophilic and early polychromatic erythroblasts and during subsequent maturation these lysosomes are probably involved in the degradation of mito-chondria. The changes in distribution of ribosomes in cells at the later stages of maturation have been investigated by counting the numbers of single ribosomes and polysomes seen in electron micrographs. During erythropoiesis the ratio of the amount of fibrillar material to the amount of granular material in the nucleolus increases; in the mature erythrocyte the nucleolus consists almost exclusively of fine fibrillar material.
A localized region of basal body proliferation in growing cells of Dileptus visscheri (ciliata, gymnostomata)
Authors: Kink J.
Published: April 2021

In the ciliate Dileptus organisms are completely organized at the time of excystation. They grow intensively, increasing in volume several times, before they reach the trophic cell size. The growth includes both the somatic part of the body as well as the oral parts, consisting of the cytostomal field and the ventral band of the proboscis. From the time of excystation, during the growth of the cell, the oral apparatus is able to capture and ingest food. Growth of an oral apparatus while functioning has not previously been reported in ciliates.

The proliferation of new oral kinetosomes in the growing oral apparatus occurs only in the cytostomal field. There is no proliferation of ciliature in the oral kineties of the growing proboscis. In those regions of the somatic kineties bordering the cytostomal field an extensive proliferation of somatic ciliature takes place. The zone of proliferation common to the oral and somatic ciliature supplies new kinetosomes for the elongating proboscis, the growing oral apparatus and the growth of the rest of the body.

The mode of proliferation of the oral kinetosomes differs from that of the somatic kinetosomes. The oral kinetosomes form randomly in large numbers, appearing similar to an anarchic field such as is found in other ciliates. The somatic kinetosomes always arise singly and in a defined position in relation to the mature kinetosome.

The proliferation of basal bodies in a defined area in Dileptus suggests the existence of a growth zone localized around the cytostomal field.
Salivary epithelial cells in primary culture: Characterization of their growth and functional properties
Authors: Wigley Caroline B. , Franks L. M.
Published: April 2021

Mouse submandibular salivary gland cells were grown in primary explant culture. After an initial period of degeneration within the explant, surviving epithelial cells proliferated rapidly and duct-like structures recolonized the explant. Autoradiographic studies showed that a peak of DNA synthesis occurred after 4 days in vitro and that proliferation was enhanced by insulin and hydrocortisone. These cells retained specialized secretory function (protease activity) for at least 2 weeks in vitro. This enzyme is a differentiated product of granular tubule cells in vivo. Between 6 and 10 days, explants attached to the substrate. An outgrowth developed, consisting largely of ultrastructurally identifiable epithelial cells which formed pseudoglandular structures in the monolayer. Epithelium survived for over 6 months in primary culture but could not be serially transferred. Secondary cultures were rapidly overgrown by mesenchymal cells.
Macronuclear division with and without microtubules in Tetrahymena
Authors: Williams N. E. , Williams R. Jaeckel
Published: April 2021

The effects of cold shocks (0 °C) and colchicine (4 mg/ml) on macronuclear microtubules and macronuclear division have been investigated in Tetrahymena. Macronuclear division was affected by both treatments, but loss of microtubules occurred only in the presence of colchicine.

When colchicine was applied immediately prior to macronuclear elongation, the nuclei underwent a partial elongation without microtubules, but were unable to constrict and separate into daughter nuclei. Such nuclei were cut in two by the advancing cytoplasmic fission furrow. When colchicine was applied to macronuclei in the fully elongated state, they maintained their elongation in the absence of microtubules, and were subsequently separated into daughter nuclei by the cytoplasmic furrow. It is suggested that macronuclear microtubules, most probably the membrane-associated microtubules, are required for the terminal stages of nuclear elongation and separation. However, the considerable macronuclear elongation which takes place in the absence of microtubules serves to focus attention on molecular mechanisms of force production which must reside elsewhere in the macronucleus.
Early events during substrate adhesion of normal and virus-transformed mouse fibroblasts
Authors: Mapstone T. B. , Culp L. A.
Published: April 2021

The relationship between attachment of Balb/c 3T3 cells and their SV40 transformants to glass or plastic substrates and deposition of substrate-attached material (SAM – proteoglycans implicated in substrate adhesion) has been examined very early after inoculation of cells subcultured with ethylenebis (oxyethylenenitrilo) tetra-acetic acid (EGTA). The metabolic inhibitors cycloheximide and colchicine minimally affected the kinetics or short-term stability of attachment of cells or deposition of SAM. SAM deposition on to the substrate began immediately after inoculation of cells and was maximal prior to the highest cell attachment level (30–40 min after inoculation). At 4 °C, there was no attachment of cells to the substrate and no deposition of leucine- or glucosamine-radiolabelled SAM on to the substrate. 3T3 cells deposited SAM to a maximal level earlier during the attachment process than SV4O-transformed cells. SVT2 cells deposited much smaller amounts of SAM (measured on a per-cell basis) to 3T3 SAM-coated substrates during attachment processes, whereas 3T3 cells and concanavalin A (con A) revertant variants of SVT2 cells, which have regained density-dependent inhibition of growth, deposited identical amounts of SAM (per-cell) on untreated or SAM-coated substrates. Serial attachment experiments with SVT2 cells indicated that all SVT2 cells reduced their deposition amounts on SAM-coated substrates, rather than there being an ability of a small proportion of cells to attach preferentially to SAM-coated substrates while being unable to deposit SAM themselves. The data are consistent with the presence of a sizeable pool of SAM-like proteoglycans being present on the surface of EGTA-removed cells whose deposition may be a requirement for, but may not necessarily be sufficient for, stable adhesion of cells to the substrate.
Stationary phase and the cell cycle of Dictyostelium discoideum in liquid nutrient medium
Authors: Soll D. R. , Yarger J. , Mirick M.
Published: April 2021

Cells of the axenic strain of the cellular slime mould Dictyostelium discoideum, Ax-3, multiply in the liquid nutrient medium HL-5 with a doubling time of 12 h. When the cell concentration reaches approximately 1 ×107 per ml the rate of cell multiplication begins decreasing and after 20—30 h reaches zero, at a stationary phase cell concentration of 2 to 2 5 ×107 cells per ml. The intercept of the extrapolated log phase and stationary phase plots has arbitrarily been considered the onset of the stationary phase. We have found that after cells have been in stationary phase for 24– 32 h, mean cell volume increases by 25 %, average dry weight by 37 %, and average protein content by 24 %. These values are close to the expected values for a cell population which is blocked at a point late in the cell cycle. Stationary phase cells also contain 25 % more nuclear DNA than log phase cells, indicating that the population of cells at stationary phase is blocked after the DNA replication phase. Finally, when stationary phase cells are washed free of stationary phase medium and reinoculated into fresh medium, they reinitiate cell division synchronously. In the light of the demonstrated relationship between stationary phase and the cell cycle, a possible role for the growth inhibitor produced at stationary phase is considered.
Inhibition of cell division in amoebae: the incorporation of tritiated precursors into Amoeba proteus after the injection of non-homologous cytoplasm
Authors: Cameron J. M. , Hawkins Shirley E.
Published: April 2021

The injection of non-homologous cytoplasm into any strain of large free-living amoebae leads to a 60 % inhibition of division amongst recipient cells. When the post-microsomal supernatant fraction of Amoeba discoides was injected into A. proteus, this inhibition of division was as high as 95 %. The incorporation of tritiated precursors, either [3H]uridine or 3H-amino acids, into these inhibited amoebae was studied at various times after the injection of the inhibitory material using autoradiography.

When cells were grown in [3H]uridine, autoradiographs indicated that RNA synthesis had ceased 2 days after the injection of non-homologous material. However, if [3H]uridine was injected into the inhibited cells, some synthesis of RNA could be detected up to 4 days after the injection of inhibitor. These results suggested that uptake of [3H]uridine was impaired and that one site of action of the inhibitory molecules was RNA synthesis for membrane components.

Experiments with a variety of 3H-amino acids suggested that protein synthesis continued for at least 9 days after the injection of non-homologous cytoplasm, and that in these cells some informational RNA molecules were long-lived. There seemed to be accumulation of material containing [3H]lysine in the nuclei of control cells taken at random from cultures, and this was seen in the nuclei of inhibited cells 1 day after injection. However, 2 days after the injection of inhibitor, no accumulation of [3H]lysine-containing material was found in the nuclei.
Similarities between platelet contraction and cellular motility during mitosis: role of platelet microtubules in clot retraction
Authors: Chao F. C. , Shepro D. , Tullis J. L. , Belamarich F. A. , Curby W. A.
Published: April 2021

The effects of inhibitors of mitosis, energy metabolism and protein synthesis on clot retraction were investigated. The results show that (1) Incubation of colchicine (0·01–0·1 mM) with platelet-rich plasma (PRP) inhibits the subsequent retraction of clots derived from diluted PRP. (2) Inhibition of clot retraction by high concentrations of colchicine (up to 40 mM) can be overcome by increasing the platelet concentration in the system. (3) Incubation of clots in colchicine or 80 % D2O solutions inhibits their retraction. Exposure of partially retracted clots to these agents is without effect. (4) Hydrostatic pressure retards clot retraction. (5) Incubation of PRP with either 2-deoxy-D-glucose or antimycin alone does not affect clot retraction, but a combination of these agents is inhibitory. (6) Clot retraction is not inhibited by puromycin or cycloheximide. (7) Platelets in retracting clots have constricted regions containing microfilaments and pseudopods containing microtubules. Fibrin strands are progressively condensed around the constricted regions as retraction advances. (8) The development of platelet constriction, platelet pseudopods and the intracellular microfilaments are delayed in colchicinized clots, corresponding to the retardation of retraction. Following the initial delay of retraction colchicinized clots, like controls, show condensation of fibrin strands adjacent to these constricted areas of platelets containing microfilaments. The formation of pseudopods is impaired and no microtubules are found in platelets in the presence of colchicine. The above results suggest that the thrombin-induced platelet contraction during clot retraction is a coordinated movement, which, under optimal conditions involves both microtubules and microfilaments. The contraction of microfilaments produces the constriction of platelets and brings about clot retraction by reducing the angle between fibrin strands. Platelet microtubules are related to the development of pseudopods and play a supplementary role in facilitating microfilament-mediated cellular constriction. The similarities between platelet contraction and cellular motility in mitosis is discussed.
The morphology of green Hydra endosymbionts as influenced by host strain and host environment
Authors: Pardy R. L.
Published: April 2021

The ultrastructure of Chlorella-like algal endosymbionts from the Florida and English strains of green hydra was compared under different host feeding and photoperiodic regimes. Under standard conditions (host fed daily, 12-h photoperiod) the algae from the 2 strains exhibited considerable differences. The English symbionts had a pyrenoid, compact chloroplast membranes and vesiculated polyphosphate bodies. By comparison, Florida symbionts lacked a pyrenoid, had chloroplasts with less compact membranes and exhibited spherical polyphosphate bodies.

When maintained in the dark, algae from English hydra lost their pyrenoids, showed great compaction of the chloroplast and developed large, shield-shaped, electron-dense bodies. In contrast, algae from Florida hosts did not exhibit gross ultrastructural modification.

Reciprocal cross-transfers of symbionts were made by placing Florida algae in English aposymbiotic (algal-free) hosts and vice versa. After residence in Florida hosts, English symbionts appeared to undergo ultrastructural modifications resulting in a morphology indistinguishable from the native Florida symbionts. Florida algae showed no modifications resulting from residence in English hosts. It thus appears that the English symbiont has great morphological plasticity, as its structure is greatly modified depending upon the host in which it resides and the conditions under which the host is maintained.

The results of these studies are discussed and compared with published accounts of free-living Chlorella and with reports dealing with other Chlorella symbionts.
Brittle fracture of epidermal cells by liquid shear
Authors: Gray G. M. , Yardley H. J.
Published: April 2021

A suspension of epidermal cells obtained from pig tail skin by trypsinization was subjected to high liquid-shear forces in a French press. The material issuing from the press was examined by phase-contrast microscopy, transmission electron microscopy and scanning electron microscopy. The cytoskeleton of tonofibrils retained the shape of cell fragments, and subcellular organelles remained enmeshed in the network of tonofibrils. Examination of some cell fragments by scanning electron microscopy revealed the internal organization of the tonofibrils. The relevance of these findings to the problem of isolating subcellular fractions from epidermis is discussed.
Patterns of calcium localization in pancreatic endocrine cells
Authors: Ravazzola Mariella , Malaisse-Lagae Francine , Amherdt Myléne , Perrelet A. , Malaisse W. J. , Orci L.
Published: April 2021

Subcellular calcium localization in the endocrine cells of rat pancreas was studied by the pyroantimonate precipitation technique. Calcium-containing electron-dense deposits in the endocrine cells were mostly found within secretory granules and along the plasma membrane, but their pattern of distribution in A-, B- and D-cells displayed qualitative and quantitative differences. In B-cells, numerous secretory granules contained deposits located in the halo surrounding the granule core. In A-cells, only few granules contained precipitates in their halo, whereas in D-cells, deposits were situated in the dense core of the secretory granules. Deposits along the plasma membrane occurred generally on the outer leaflet of the plasma membrane of B- and D-cells and on the inner leaflet of that of A-cells. In islets incubated at a high glucose concentration or in the presence of the calcium ionophore A23187, the number of beta granules containing precipitates was significantly increased. By contrast, only few deposits were observed in B-cells incubated in calcium-deprived medium enriched with EGTA. These findings indicate that: the pattern of calcium localization varies in different islet cell types; in B-cells the secretory granules represent one of the major stores of intracellular calcium; and that this store undergoes changes in conditions which alter insulin release.
Subcellular localization of diffusible ions in the yeast Saccharomyces Cerevisiae: quantitative microprobe analysis of thin freeze-dried sections
Authors: Roomans G. M. , Sevéus L. A.
Published: April 2021

In yeast cells, of which the intracellular potassium had been partly replaced by rubidium or caesium, the intracellular ion distribution was studied by means of energy-dispersive X-ray microanalysis. The cells were rapidly frozen and thin sections were cut at low temperature on a cryo-ultramicrotome without the use of a trough liquid. By this dry cryosectioning procedure, complete retention of the diffusible ions in the cells was obtained. Unless the sections had been exposed to moisture, no signs of redistribution were apparent. For quantitative determinations a gelatin standard, containing known amounts of the elements of interest, was prepared in the same way as the cells. The concentrations of potassium, rubidium, caesium and chloride in the nucleus, the cytoplasm and the vacuole could be measured. The intracellular distributions of potassium, rubidium and caesium were very similar. The concentrations of these ions in the cytoplasm were about equal to those in the nucleus and twice those in the vacuole. The total concentration in the cytoplasm was 180–190 mmol/kg fresh weight, in the nucleus 190—200 mmol/kg fresh weight and in the vacuole 75–0 mmol/kg fresh weight. The permeability of the yeast cell for chloride is markedly lower than for the cations.