bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uptake of [3H]uridine into precursor pools and RNA in osteogenic cells
Authors: Owen Maureen 
Published: April 2021

ABSTRACT
Young rabbits were given a single intraperitoneal injection of [3H]uridine. Using the technique of water-soluble autoradiography a study was made of the uptake of the radioactive label into soluble precursors and RNA in cells on an actively growing bone surface. Labelling of the soluble intracellular pools was immediate, but incorporation of label from these pools into RNA was not completed until 24 h after injection. At this time all the label in the sections was in RNA but this represented only 30 % of the total label initially in the soluble pools. This means that 70 % of the label is lost from the cell in the first 24 h either as degradation products of RNA synthesis or by other as yet unknown mechanisms.
The pattern of labelling of the RNA was similar to that previously found for other mammalian cells in vivo or in vitro. There was a rapid uptake of label into nuclear RNA which reached a maximum by 2 h after injection and a slower uptake into cytoplasmic RNA which reached a maximum by 24 h after injection. There was a slow loss of label from the cells after 24 h indicating a half-life of about 8 days for this relatively stable RNA. A comparison was made of RNA synthesis in the proliferating preosteoblasts and the highly differentiated nondividing osteoblasts. Labelling of the nuclear RNA for the two cell types was identical. The rate of labelling of the cytoplasmic RNA was similar for the two cell types but the maximum level of labelling in the cytoplasm of the osteoblasts was 2 to 3 times that in the preosteoblasts. This could be correlated with the more active protein synthesis by the osteoblasts.
There was a slow loss of labelled RNA by the osteoblasts and preosteoblasts and a rapid loss by the osteocytes after the cells had been incorporated within the bone. It was suggested that this loss paralleled the decline in the rate of protein synthesis by the cells as their environment changed.
Electron microscopic study of penetration of newcastle disease virus into cells leading to formation of polykaryocytes
Authors: Meiselman N. , Kohn A. , Danon D. 
Published: April 2021

ABSTRACT
Treatment of FL or Lu 106 epithelial cells with Newcastle disease virus (NDV) at an input multiplicity of 500 EIDM per cell induces in these cells the formation of polykaryocytes at the end of 2–3 h of contact. Electron micrographs of such NDV-treated monolayers after 2-10 min of incubation show the presence of virions adsorbed to the cell membranes, in vacuoles and with the viral envelope partly fused with the cell membrane. In polykaryocytes induced by NDV, remnants of cell membranes showing numerous breaks may still be present after 3 h.
A cycloid model for the chromosome
Authors: Whitehouse H. L. K. 
Published: April 2021

ABSTRACT
Investigations of lampbrush chromosomes and the nucleolar organizer have suggested that each gene may be duplicated many times in consecutive linear series within one DNA molecule. This conclusion is in direct conflict with recombination data which indicate, not only that each gene is represented only once per chromatid, but that different genes are contiguous.
This paradox is resolved by postulating that the chromosome has the form of a cycloid. Each loop of the cycloid would correspond to a set of copies of a gene forming a chromomere. It is suggested that at meiosis the copies of the gene are detached as a result of intrachromatid crossing-over between the first and last members of the series. The master copy remaining in the chromatid would then be in a position to undergo crossing-over with a homologous chromatid, while the duplicate copies in the detached chromomere would all be included in a single circular DNA molecule. They could subsequently be restored to the chromatid by crossing-over between one of their number and the master copy. This intrachromatid crossing-over would imply that the chromosome can alternate between two states with each set of duplicate genes either detached as a circle or integrated with the DNA axis.
Callan’s model for matching slave genes against a master copy so that all acquire identical nucleotide sequences is modified to facilitate coiling and uncoiling of nucleotide chains, by postulating breakage of the matching chains at one end of the gene. Matching of only one chain of the slaves against the master is proposed or, if necessary, subsequent matching of the second slave chain to the first. It is suggested that matching may regularly precede the synthesis of messenger RNA.
Investigations of dipteran salivary gland chromosomes and amphibian oocyte nucleoli have established that the chromomere is the unit of replication of the chromosome. On the cycloid model the replicons would be adjacent to one another, and each would comprise a master gene and all the copies. It is suggested that the replicator may correspond to the operator of the master copy of the gene. This hypothesis provides an explanation for several previously unexplained features of crossing-over, including its occurrence at the four-strand stage.
Changes in nuclear structure during binary fission in the ciliate Nassula
Authors: Tucker J. B. 
Published: April 2021

ABSTRACT
During binary fission intranuclear spindles are formed in the three micronuclei and in the macronucleus. The nuclear envelopes remain intact throughout nuclear division. At one stage all the nuclei are linked together by the formation of membrane bridges in continuity with the outer membranes of their envelopes. Three types of filamentous structure have been distinguished in the spindles: microtubules of diameter 210–240 Å, fine branching filaments, and filaments which have a C-shaped transverse profile and a diameter of about 240 Å, for which the term C-filament is suggested. At metaphase a polar vesicle is situated at each pole of the micronuclei but centrioles are absent. During late anaphase a long central spindle, called here a separation spindle, is situated inside eachmicronucleus and elongates between the separating chromosomes. The nuclear pores of both types of nuclei are partly filled with dense material. In long, late anaphase micronuclei, pores are abundant in the parts of the envelope surrounding the ends of the nuclei but are rarely found elsewhere. Large numbers of ribosome-like granules are attached to the outer surfaces of the micronuclear envelopes where they sheathe the separation spindles.
Meiosis in Coprinus lagopus: A comparative study with light and electron microscopy
Authors: Lu B. C. 
Published: April 2021

ABSTRACT
Meiosis within fruiting bodies of Coprinus lagopus Fr. is closely synchronized. This conveniently facilitates joint light- and electron-microscope observations. Before nuclear fusion the chromatin appears diffuse in the light microscope; after nuclear fusion individual chromosomes can be recognized. In the electron micrographs the chromatin of pre-fusion and early fusion nuclei cannot be recognized as denned structures with the fixation and staining procedures employed. At the time of synapsis the lateral components of the synaptinemal complexes can be seen in the micrographs. The pairing process of the two chromosomes of the homologous pairs is believed to involve two steps: (1) two homologous chromosomes become aligned in parallel, and (2) pairing occurs by formation of the synaptinemal complex including the central synaptic component. The term synaptic centre is coined for the central component, which is believed to be the zone where crossing-over occurs. The formation of this structure in relation to homologous pairing, and the structural organization of the synaptinemal complexes are discussed. At meiotic metaphase, the chromosomes congregate around the central spindle microtubules. They are contracted and contain densely packed chromatin fibrils. Two types of spindle microtubules are demonstrated: (1) the chromosomal microtubules directly connecting the chromosomes to the centrosomes, and (2) the central spindle microtubules connecting the two centrosomes. The centrosomes are round, fibril-containing bodies approximately 0-3 fi in diameter. They have been observed outside the nuclear envelope at pachytene, but do not show the characteristic structure normally found in animal cells.
Studies on the mechanism of substrate induction and l-cyst(e)ine repression of alkaline phosphatase in mammalian cell cultures
Authors: Griffin M. J. , Cox R. P. 
Published: April 2021

ABSTRACT
The mechanisms of substrate induction and L-cyst(e)ine repression of alkaline phosphatase were studied in tissue culture using an established African green monkey kidney cell line (BS-C-1). L-Cyst(e)ine repression and substrate induction are mutually antagonistic. Evidence is presented which suggests that the increase in alkaline phosphatase levels induced by mono phosphate esters may in part be due to protection of the enzyme from cellular degradation, while L-cyst(e)ine is believed to act either by repressing the synthesis of the enzyme or by selectively increasing its catabolism.
Coated vesicles in absorptive cells of Hydra
Authors: Slautterback D. B. 
Published: April 2021

ABSTRACT
The apical cytoplasm of absorptive cells in hydra gastroderm contains numerous vesicles having a discoidal shape, an asymmetrical membrane and a peculiar coat firmly attached to the luminal surface of the membrane. The coat of these ‘ discoidal coated vesicles’ consists of a highly ordered array of subunits made up of ‘pegs’ and globules. That these vesicles are involved in selective absorption and transport of materials from the gastrovascular cavity can be seen readily using ferritin as tracer. They are also involved in the uptake of paniculate glycogen and the phagocytosis and possibly the subsequent digestion of complex food droplets. It may reasonably be supposed that the array of the coat subunits indicates a similar array of the molecular constituents of the membrane to which it is attached. In tangential sections of the membrane a compressed hexagonal lattice is seen which could fit the coat array.
Ciliary inter-microtubule bridges
Authors: Warner F. D. 
Published: April 2021

ABSTRACT
Electron micrographs of both negatively contrasted and thin-sectioned lamellibranch gill cilia reveal several new features of ciliary fine structure, particularly in regard to those structures forming intermittent or permanent crossbridges between microtubules. Negativecontrasting reveals the presence of a 14 5-nm repeating bridge between the central microtubules. Frontal views of negatively contrasted dynein arm rows along subfibre A show that the arms (23-nm repeat) in the outer row are displaced in a left-handed manner by 3–4 nm with respect to those in the inner row. This displacement is probably a direct reflexion of the helical tubulin subunit lattice of the subfibre. Interdoublet (nexin) links are seen connecting adjacent A and B subfibres at intervals of 86 nm along the doublet. Negative-contrasting shows thin, highly elastic connexions holding the doublets together. When seen in longitudinal thin sections, the interdoublet links are often tilted to considerable angles, indicating they may have an elastic response to interdoublet sliding.
Immunohistochemical localization of α-Amylase in barley aleurone cells
Authors: Jones R. L. , Chen Ru-Fang 
Published: April 2021

ABSTRACT
α-Amylase was localized in aleurone cells of barley using immunohistochemical methods. Anti-a-amylase antibody was produced by rabbits immunized with enzyme purified from malt diastase and Himalaya variety barley seeds. Immunoelectrophoresis showed that the antibodies to both antigens were immunologically similar, therefore, they were used interchangeably in the localization of α-amylase. Fluorescence of 8–10-μm sections of freeze-substituted and paraffin embedded, gibberellic acid (GA)-treated aleurone tissue incubated with rabbit anti-α-amylase IgG and rhodamine-conjugated goat-anti-rabbit IgG is localized in the cytoplasm, the nuclear region and the innermost portion of the cell wall. Cytoplasmic immunofluorescence is not associated with a specific organelle but rather is diffusely distributed. The fluorescence of the nuclear region, however, is intense and in thinner (4–5-μm) sections is associated not with the nucleoplasm but with the nuclear envelope and perinuclear region of the cytoplasm. Fluorescence of the cell wall is confined to the inner boundary of the wall corresponding to the resistant wall layer. The immunofluorescent properties of non-GA-treated cells are quantitatively different; fluorescence of these sections is low and diffuse and is particularly reduced in the nuclear region. Electron microscopy shows that GA-treatment results in the proliferation of endoplasmic reticulum (ER) in the perinuclear region of the cell. We suggest that the a-amylase localized by immunofluorescence in the perinuclear region of the cell is localized in this ER produced in response to GA treatment. Immunohistochemical localization of a-amylase in cells zonated by centrifugation also suggests that the enzyme is intimately associated with the perinuclear area.
Effects of prostaglandins E1, E2, and F2α on the growth of leukaemia cells in culture
Authors: Yang T. J. , Dale J. B. , Machanoff R. 
Published: April 2021

ABSTRACT
Prostaglandins E1 E2, and F2α (PGE1; PGE2, and PGF2α) were shown to inhibit the growth of mouse leukaemia lymphoblasts L5178Y in culture. The effects of PGE! and PGE2 were greater than that of PGF2α. PGE1 and PGE2, at the concentration of 100 μg per ml showed significant inhibitory effects on the rates of incorporation of tritiated thymidine, uridine and leucine. At concentrations of 50 and 25 μg per ml, there was significant inhibition of thymidine and uridine incorporation, but not of leucine. PGF2a showed significant inhibition of thymidine and uridine incorporation but not leucine incorporation, in all 3 concentrations studied (100, 50, and 25 μg/ml). The ability of the cells to form colonies in soft agar was significantly inhibited by PGE1 and PGE2 at concentrations as low as 1·8 μg/ml. For F2α, however, a concentration as high as 56 μg/ml was required to show inhibitory effect, but at t1·8 μg ml it was found to be stimulatory.
DNA repair synthesis in human heterokaryons: III. the rapid and slow complementing varieties of xeroderma pigmentosum
Authors: Giannelli F. , Pawsey S. A. 
Published: April 2021

ABSTRACT
Patients with Xeroderma pigmentosum and defective DNA excision repair can be distinguished as a rapid (r-XP) and slow (s-XP) complementing variety. When fused with normal cells, fibroblasts from the r-XP are complemented rapidly and in the absence of protein synthesis while those from the s-XP are complemented slowly by a process partly, but not entirely, dependent on protein synthesis. Heterokaryons with different ratios of r-XP to s-XP nuclei (i.e. 1:1–5 and 1–5:1) and control heterokaryons containing one normal and 1–5 r- or s-XP nuclei show that if cell fusion and incubation is conducted in medium preventing protein synthesis, the r-XP cells do not complement the 8-XP partner at all and, conversely, that the latter is not as effective as normal cells at complementing the r-XP partner. On the contrary, if protein synthesis is permitted, the 2 types of XP cells complement each other in a gene dose-dependent manner and to an extent similar to that observed in the control heterokaryons. These findings indicate that the r- and 8-XP varieties are caused by mutations at different loci and suggest that the products of these loci interact to produce a functional unit which is present in normal control cells but absent in the XP strains. The relationship between the complementation groups described here and those already reported in the literature is being investigated.
The Development of the Relaying Competence in Dictyostelium Discoideum
Authors: Gingle A. R. , Robertson A. 
Published: April 2021

ABSTRACT
The fraction, X2 of a population of D. discoideum cells competent to relay an aggregative signal has been measured as a function of time, t, spent in interphase. X2(t) is less than 0·1 up to 5 h, increases slowly to 0·4 by 8 h 20 min, and saturates at 1 by 10 h.
The hypothesis that cellular interactions might enhance X2(t) was tested by mixing populations of cells set into interphase at different times. No interactions were found. External stimulation did not affect X2(t).
The fixation of nuclei and chromosomes
Authors: Skaer R. J. , Whytock Susan 
Published: April 2021

ABSTRACT
Chromosomes in the nuclei of living salivary glands of Simulium have been observed with Nomarski optics and polarized light before and during irrigation with various fixatives. All cause loss of chromosomal organization to some degree. The best fixative is redistilled glutaraldehyde; even so, although it leaves the nucleus visually unaltered, a network forms in the nuclear sap and birefringence is lost. Calcium ions in the fixative cause chromosomal movements. The fixatives may alter nucleoli and may dissolve them completely. New fixatives are needed for reliable fine-structural studies of chromosomal organization.
Mitotic activity in rice seedlings germinating under oxygen deficiency
Authors: Kordan H. A. 
Published: April 2021

ABSTRACT
Rice seedlings germinating in oxygen-deficient environments do not manifest visual evidence of seminal or adventitious root growth or normal leaf growth, the coleoptile being the only seedling structure to emerge under these environmental conditions. Microscopic evidence, however, shows that mitotic activity occurs in the different tissues comprising the shoots of the seedlings germinating under oxygen deficiency. Thus evidence is presented here which shows that mitotic activity in rice seedlings germinating in oxygen-deficient environments is not confined solely to the emerging coleoptiles of the germinating seedlings.
Microtubules and associated microfilaments in the tentacles of the suctorian Heliophrya erhardi matthes
Authors: Hauser M. , Van Eys Helga 
Published: April 2021

ABSTRACT
At the ultrastructural level length changes accompanying linear movements of resting (nonfeeding) tentacles of the suctorian Heliophrya involve not only altered microtubule numbers, but also marked changes in the specific microtubule pattern of cross-sectioned tentacles. These changes in number and pattern indicate a sliding between axonemal microtubules. The visualization of microfilaments in the cytoplasm at the tentacle base and in the knob region could shed new light on the problem of whether microtubular sliding is an active or passive process. At the tentacle base, microfilaments are either arranged in a ring-shaped configuration around the axoneme, or they run parallel to the axonemal microtubules, whereas at the tentacle tip during the resting state, microfilaments are closely associated with the plasma membrane of the knob. They form a filamentous reticular layer, which is continuous at the anchorage site of axonemal microtubules with the dense epiplasmic layer of the tentacle shaft. Obviously, this filamentous layer is engaged in positioning the haptocysts at the plasma membrane and in holding the membrane itself under tension. The putative contractile nature of microfilaments and the epiplasmic layer is argued from ATP-sensitive glycerol models of tentacles and from the results of halothane treatment of native tentacles. Halothane treatment of resting tentacles also gave indications of the presence of differentially stable intermicrotubule-bridges. The role of microfilaments and halothane-resistant dynein-like inter-row bridges in tentacle movement is discussed.
As soon as the plasma membrane of the knob is ‘sealed’ with the prey pellicle during feeding, the microtubules of the sleeve region slide into the knob where they bend back and outwards. The microtubules now appear decorated and sometimes cross-connected by microfilaments which adhere closely to the plasma membrane — now acting as a peritrophic membrane — lining the prey cytoplasm against the microtubules of the inner tube. These microfilaments which show a close association with the microtubules of the active knob area, are thought to be engaged in microtubular bending and stretching during feeding. They may also be involved in the transport of the peritrophic membrane in distal tentacle regions. Microcinematographically recorded oscillations in tentacle diameter in these regions are in agreement with the electron-microscopic findings of various states of collapsed tentacle axonemes. These observations, as well as the occurrence of helically twisted tentacles during feeding, suggest microfilament-mediated sequential back and forth movements of sleeve microtubules in the knob region which generate a proximally migrating helical wave.
Rotary movements and fluid membranes in termite flagellates
Authors: Tamm S. L. , Tamm Signhild 
Published: April 2021

ABSTRACT
We previously described a remarkable type of cell motility that provided direct, visual evidence for the fluid nature of cell membranes. The movement involved continual, unidirectional rotation of one part of a protozoan, including the plasma membrane and cytoplasmic organelles, in relation to a neighbouring part. The cell membrane in the ‘shear zone’ appeared continuous with that of the rest of the cell. The rotary motor consisted, at least in part, of a non-contractile, microtubular axostyle which extended centrally through the cell. The protozoan was a devescovinid flagellate found in the hindgut of a Florida termite.
In this paper, we have confirmed earlier reports of this type of motility in other kinds of devescovinids from Australian termites. By demonstrating continuity of the plasma membrane in the shear zone of the Australian devescovinids as well, we have obtained additional examples that provide direct, visual evidence for fluid membranes. A comparative analysis of rotational motility in various devescovinids revealed 2 different kinds of rotary mechanisms. Hyperdevescovina probably have an internal motor, in which one part of the cell exerts forces against another part, as in the Florida termite devescovinid. Devescovina species, on the other hand, have an external motor, in which flagellar and/or papillar movements exert forces against the surrounding medium. The structure of the axostyle in different devescovinids was compared, and its role in rotational motility discussed with respect to the behavioural data.
Flagellar regeneration in Chlamydomonas reinhardtii: evidence that cycloheximide pulses induce a delay in morphogenesis
Authors: Farrell K. W. 
Published: April 2021

ABSTRACT
The behaviour of a pool of flagellar precursors, assayed by the ability of cells to regenerate flagella in the absence of de novo protein synthesis, has been examined during organelle morphogenesis in the biflagellate alga Chlamydomonas. The results demonstrate that flagellar elongation can continue even when this pool is apparently empty and suggest that 2 sources of precursors are available to the regenerating flagella: those pre-existing in the cellular pool and those synthesized de novo. Further evidence for this was obtained by subjecting regenerating cells to pulses of cycloheximide. Cells exposed to this drug during the first 60 min post deflagellation formed only half-length (5-μm) flagella, whereas a pulse administered after this point allowed the formation of longer flagella and suggested that some de novo protein synthesis was required for the formation of full-length flagella, although it was not a prerequisite for the initiation of regeneration. In addition, it was found that, subsequent to the removal of the cycloheximide, flagellar regeneration did not recommence immediately, but was delayed for a period of approximately 45 min, irrespective of length of flagella formed prior to drug inhibition.
The nature of this cycloheximide-induced delay is unclear and certain alternatives, based on the exhaustion of structural/regulatory components are considered. Although it is not possible to distinguish between these alternatives, tubulin is not the limiting component, since a pool of this protein is present when flagellar elongation is prevented by cycloheximide.