bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonhistone proteins of the oocyte nucleus of the newt
Authors: Hill R. J. , Maundrell K. , Callan H. G.
Published: April 2021

Evidence has been obtained which indicates that disulphide bond crosslinks contribute to the morphological integrity of isolated lampbrush chromosomes (both chromomeres and lateral loops) and nucleoli. It is suggested that the progressive formation of these bonds in vitro by aerial oxidation may provide the basis for the previously recognized time-dependent hardening or ‘denaturing’ of these structures.

Manually isolated germinal vesicle nuclei have been massed and fractionated by low-speed centrifugation into nucleoplasm and chromatin. Phase-contrast microscopy demonstrates the chromatin to consist of nucleoli, lampbrush chromosomes and nuclear membranes.

Urea gel electrophoresis has been employed to resolve the reduced and S-carboxymethylated proteins of whole nuclei into some 12 components, negatively charged at pH 8. The nucleoplasm alone gives an essentially similar pattern, but with the distinct depletion of one component and slight depletion of another. Both of these components are much enriched in the chromatin pellet where they predominate over all other proteins.

The total chromatin has been subfractionated by microdissection, taking advantage of the differential attachment of nucleoli to the nuclear membrane at different stages of oogenesis. It is concluded that the nuclear membrane per se does not contribute to the major chromatin proteins. The two major polypeptides are components of the nucleoli. Preparations of isolated lampbrush chromosomes have not, to date, provided sufficient material to give a distinctive electropherogram; only one faint band, a major component of whole nuclei, was apparent.

Sodium dodecyl sulphate gel electrophoresis has resolved some 25 components in whole nuclei, and again demonstrates the enrichment of the two major species in the total chromatin fraction. The apparent molecular weights of these two species are 43 kilodaltons and no kilodaltons. Approximately 20 minor species are also present in the chromatin and are obviously good candidates as components of the nucleolar and chromosomal structures. Histones, at most, make only a minor contribution to the overall chromatin protein population.
Fusion of mouse fibroblasts with oleylamine
Authors: Bruckdorfer K. R. , Cramp F. C. , Goodall A. H. , Verrinder M. , Lucy J. A.
Published: April 2021

As part of a search for chemical agents able to promote the fusion of mouse A 9 fibroblasts, oleylamine, a positively charged compound, has been investigated for its fusogenic properties. In the pH range 5·5–7·5 and in the presence of dextran, fibroblast polykaryons were produced on treatment of monolayers of cultured cells with oleylamine dispersed directly in a modified Eagle’s medium at concentrations of not less than 0·111 mg/ml. Electron microscopy demonstrated the absence of a dividing plasma membrane between the constituent nuclei of the polykaryons, and showed clustering of other subcellular organelles around their original parent nuclei.

Fusion, which was preceded by rounding and swelling of the cells, occurred between cells in contact after 10-15 min. Oleylamine in lipid droplets containing glyceryl mono- and dioleate also caused swelling and fusion but to a lesser extent. Phosphatidylcholine appeared to have an inhibitory effect on oleylamine-induced fusion : lecithin liposomes containing oleylamine were only weakly fusogenic. The fusion process, but not the preceding swelling, was calcium-dependent; fusion was inhibited by low concentrations of lanthanum ions.

While oleylamine inhibited cell division in monolayer cultures and prevented adhesion of fibroblasts in suspension to glass coverslips, oleylamine in lipid droplets was less toxic and is thus potentially more useful in this form for interspecific hybridization experiments.
Relationship between freezing rate, ultrastructure and recovery in a human diploid cell line
Authors: Beadle D. J. , Harris L. W.
Published: April 2021

The relationship between freezing rate, ultrastructure and recovery in a human diploid cell line has been studied by freezing cells at rates that are known to give high and low recoveries and examining them immediately after thawing. Some correlation was found between structural damage and recovery. The main types of damage observed were loss of cytoplasm and nucleoplasm, indicating disruption of cellular membranes, and swelling of subcellular organelles due to osmotic changes during the freeze—thaw cycle. No simple correlation was found between freezing rate and structural damage. In the absence of a cryoprotectant both rapid and slow freezing produced similar types and amounts of damage resulting in low recovery. In the presence of 10 % dimethylsulphoxide, however, slowly frozen cells showed few signs of damage and recovery was high. DMSO had no such protective effect on rapidly frozen cells.
Studies on the template activity of ‘isolated’ Xenopus erythrocyte nuclei: I. the effects of ions
Authors: H1Lder V. A. , Maclean N.
Published: April 2021

The isolation and characterization of nuclei from Xenopus erythrocytes is described. Such nuclei are freely permeable to ions and large molecules. They have an extremely low basal rate of RNA synthesis which can be increased by the addition of Escherichia coli RNA polymerase and by alteration in the ionic strength of the incubation medium within physiological limits. The results are discussed in terms of the mechanisms which control gene activity in these cells.
Binding of radiolabelled collagen to blood platelets
Authors: Gordon J. L. , Dingle J. T.
Published: April 2021

Purified, soluble collagen was prepared from rat skin, and the tyrosine residues were labelled with 125I by the chloramine T method. The collagen was added to platelet-rich plasma from rats or rabbits, and then layered on 23 % w/v Ficoll. After centrifugation at 3900 g for 20 min, the platelets were recovered from beneath the Ficoll, and the radioactivity associated with them was measured. This represented the platelet-bound collagen, since very little collagen penetrated the Ficoll if platelets were absent.

The amount of platelet-bound collagen paralleled the extent of collagen microfibril formation, which in turn increased with the time the collagen was preincubated at 36 °C before being added to the plasma.

The amount of binding in each sample was reproducible within groups of rats or rabbits, but the amount of collagen bound per platelet was about 3 times greater in samples from rabbits than from rats.
The aggregation of rabbit polymorphonuclear leucocytes: Effects of antimitotic agents, cyclic nucleotides and methyl xanthines
Authors: Lackie J. M.
Published: April 2021

The aggregation of rabbit peritoneal exudate polymorphonuclear leucocytes (PMNs) was investigated by following total particle number with time, in a shaken suspension. Aggregation was rapid and essentially complete by 30 min, but could be inhibited by microtubule-blocking agents, adenosine and methyl xanthines. The addition of cyclic adenosine 3’:s’-mono-phosphate (cAMP), or its dibutyryl derivative, also inhibited aggregation slightly, but guanosine nucleotides had no significant effect. By consideration of the maximum inhibition brought about by colchicine or theophylline alone, or the two in combination, it appears that they act at different sites to inhibit aggregation, though the effects of either were partially reversed by the addition of adenine. Adenine, lumicolchicine and high concentrations of vinblastine sulphate (10−4 M), enhanced aggregation.
Release from density-dependent inhibition of growth in the absence of cell locomotion
Authors: Yarnell Margaret M. , Schnebli H. P.
Published: April 2021

3T3 mouse fibroblasts are released from density-dependent inhibition of growth by treatment with insulin. The same insulin treatment stimulates cell locomotion several hours before any new mitoses become visible. Inhibition of cell locomotion by colcemid does not affect the overgrowth stimulation due to insulin. From this it is concluded that cellular locomotion is not a prerequisite for the release from density-dependent inhibition of growth.
Effects of dmso on vacuole formation, contractile vacuole function, and nuclear division in Tetrahymena Pyriformis GL
Authors: Nilsson J. R.
Published: April 2021

Increasing concentrations of dimethyl sulphoxide (DMSO) affect vacuole formation in Tetrahymena, as measured quantitatively by the uptake of carmine particles. The rate of vacuole formation decreased to about 50% of the control value in 5·0% DMSO (v/v) and to zero in 7·5%. At the latter concentration, the inhibition was expressed immediately; however, the effect of t-h exposure was reversible after removal of DMSO by washing. In vivo observations revealed abnormal function of the contractile vacuole in 7·5% DMSO, while cell motility and cell division appeared to be unaffected. Although cell division occurred there was little or no increase in cell number, as studied over a cell generation time. Feulgen preparations showed that nuclear division was inhibited and that cell division resulted in one anucleate and one nucleate daughter cell. This effect was also observed in some dividing cells at lower concentrations of DMSO. The effect of DMSO on Tetrahymena was dependent not only on the concentration of the compound but also on the physiological state of the cells.
Transcription and translation of the sex message in the smut fungus Ustilago Violacea: II. the effects of inhibitors
Authors: Cummins J. E. , Day A. W.
Published: April 2021

In Ustilago violacea conjugation involves a period of courtship followed by the cooperative assembly of a conjugation tube between paired sporidia of opposite mating type. During courtship information is exchanged between the paired sporidia directing transcription and translation of a ‘sex message’. This information exchange is completed even though the plasma membranes and walls of the mating sporidia remain intact until after the sex message has been translated. Once translation is completed the copulatory organelle is assembled.

Inhibitor studies show that translation of specific mRNA species (sex message) is essential during the 3–4 h period of courtship prio1 to assembly and that transcription of this sex message is completed 15–30 min prior to the completion of translation. Amino acid incorporation studies show that even though the cellular protein levels remain constant during courtship there is extensive amino acid turnover as the sporidia adjust to mating conditions. However, an enhancement of amino acid turnover by mating, in contrast to unmixed sporidia, is not detectable. Prototrophic strains continue to synthesize stable RNA during courtship while amino acid auxotrophs discontinue stable RNA synthesis immediately on transfer to mating conditions. Both prototrophs and auxotrophs show extensive RNA turnover during courtship but a specific enhancement of turnover due to mating activity is not detectable from the labelling pattern alone. A round of DNA replication may be completed during courtship but mating activity does not influence the gross pattern of DNA replication in either of the mating types.
Evidence for the association of rna with the ciliary basal bodies ofTetrahymena
Authors: Hartman H. , Puma J. P. , Gurney T.
Published: April 2021

A new procedure for isolating pellicles from TetraJiymena yields stable whole pellicles in good yield. Electron microscopy of fixed pellicles showed inner membranes and basal bodies but no mitochondria. Sucrose gradient sedimentation of pellicle extracts labelled with [sH]uridine showed an increase in the ratio 17 s RNA to 25 s RNA and little 4 s RNA. The method of long term labelling presumably excluded messenger RNA. The technique of RNA/DNA hybridization in the presence of competing RNA showed that 35 % of the pellicle RNA which could hybridize (Cot 2–3) to DNA did not contain sequences in common with ribosomal RNA. It is proposed that a stable RNA which is not mitochondrial RNA, transfer RNA or ribosomal RNA is associated with the pellicle. Fixed pellicles stained with acridine orange showed brilliant yellow-green fluorescence at the basal bodies. RNase reduced or abolished fluorescence; DNase, histone, and lysozyme had no effect. Mercaptoethanol changed the colour of the fluorescence of basal bodies from yellow-green to orange, while not changing yellow nuclear fluorescence. Fluorescence of basal bodies was seen in pellicles isolated from log-phase cells and also in synchronized cells. It is proposed that basal bodies contain, or are associated with, single-stranded RNA held in a rigid configuration by protein. The implications of this proposal are discussed.
Cell cycle kinetics and development of Hydra attenuata: II. interstitial cells
Authors: Campbell R. D. , David C. N.
Published: April 2021

The cell cycle parameters of interstitial cells in Hydra attenuata have been determined. Interstitial cells were classified according to cluster size in which they occur (1,2,4, 8 or 16 cells) and morphology using maceration preparations and histological sections. The lengths of G1, S, G2 and M were determined by standard methods of cell cycle analysis using pulse-chase and continuous labelling with [3H]- and [14C]thymidine. Nuclear DNA contents were measured microfluorimetrically. All classes of interstitial cells proliferate but the cell cycle of large interstitial cells occurring singly 01 in pairs is longer than that of interstitial cells occurring in clusters of 4, 8 and 16 cells. The S-phase is 11-12 h long and G1 is less than 1 h for all classes of interstitial cells. G2, is 3-4 h long for interstitial cells in clusters of 4, 8 and 16 cells giving these cells a total cell cycle duration of 16—17 h. In contrast, large interstitial cells occurring as singles and in clusters of 2 have G2, durations ranging from 4 to 22 h. Two subpopulations can be discerned among these cells, one having a G1 of about 6 h and a total cell cycle of about 19 h, the other having an average G2 of 14 h and a total cell cycle of about 27 h. The differences in cell cycle duration appear to be associated with interstitial cell function. Cells having a short cell cycle are probably committed to nematocyte differentiation, while large interstitial cells having long and variable cell cycles appear to be undetermined stem cells responsible for pro-liferating further interstitial cells. The variable length of G2 in these cells suggest it as a possible control point.
Acetylcholine receptors of cultured muscle cells demonstrated with ferritin-α-bungarotoxin conjugates
Authors: Hourani B. T. , Torain B. F. , Henkart M. P. , Carter R. L. , Marchesi V. T. , Fischbach G. D.
Published: April 2021

α-Bungarotoxin-ferritin conjugates were used to visualize by freeze-fracture and thin-section electron microscopy toxin-binding sites, presumably acetylcholine (ACh) receptors, in membranes of muscle cells grown in tissue culture. Toxin conjugated to ferritin by a glutaraldehyde reaction and purified by column chromatography in a buffer of high ionic strength remains active in blocking the effect of iontophoretically applied ACh. The potency of the conjugates was decreased 5–10 times compared to native α-bungarotoxin. Toxin-ferritin conjugates were identified in small clusters which were not uniformly distributed over the surface membrane. Binding was inhibited by preincubation in D-tubocurare or unconjugated toxin. The relation of the clusters to the non-uniform distribution of ACh sensitivity and α-bungarotoxin binding on cultured muscle fibres is discussed.
Cytoplasmic cleavage during zoosporogenesis in Thraustochytrium sp.: Ultrastructure and the effects of colchicine and D2O
Authors: Kazama F. Y.
Published: April 2021

Subplasmalemma microtubules were present in the cleavage furrows during zoosporogenesis in Thraustochytrium sp. The microtubules transversed the furrows but were not at right angles to nor circumferentially arranged in the plane of cleavage. Evidence of microtubuleplasmalemma bridges was found. Colchicine and deuterium oxide inhibited cleavage. The data suggested that microtubules had a motive rather than a structural function.
Junctional structures in the midgut cells of lepidopteran caterpillars
Authors: Flower N. E. , Filshie B. K.
Published: April 2021

The junctional structures present between the midgut cells of 2 lepidopteran caterpillars have been examined using freeze-etching, conventional staining and lanthanum tracer techniques. The bonding junction present in this type of tissue is the so-called continuous junction. Septa have only occasionally been reported in conventionally stained cross-sections of these junctions. During the present study septa have been observed in such sections but were more readily located in tissue treated with lanthanum tracer. Tangential sections of lanthanum-impregnated tissue show that these septa are parallel-sided, in contrast to the honeycomb appearance of the septa in septate junctions. The septa in freeze-etch replicas of glutaraldehyde-fixed tissue often show continuous rods on one membrane face, suggesting that the continuous junction may be more akin to the tight junction than to the normal septate junction. However, freeze-etch replicas of unfixed tissue appear much more like replicas of normal septate junctions. The main differences between septate and continuous junctions appear to be that the intermembrane septa of the continuous junction are parallel-sided in tangential section, as against the honeycomb appearance of the septate junction, and that the particles which delineate the septa in freeze-etched preparations appear to be both somewhat differently bonded and closer together in the continuous junction. A diagram is presented showing the internal and intermembrane structures of the 2 types of junction based on the present study, and suggesting a possible explanation of the fact that septa are more readily seen in cross-sections of septate junctions than in continuous junctions. As septa are present in both types of junction, and because their freeze-etch appearances are not very different, it is suggested that the two types of septate junction be called ‘smooth septate’ and ‘pleated septate’ junctions, to indicate their characteristic appearances in tangential section.
Changes in dna synthesis during cell growth and chloroplast replication in greening spinach leaf disks
Authors: Rose R. J. , Cran D. G. , Csiro J. V. Possingham
Published: April 2021

Spinach leaf disks grown initially in the dark, show increased cell expansion and chloroplast replication when transferred to the light. These changes are accompanied by increases in the total amount of DNA and the incorporation of [3H]thymidine (3H-TdR). Autoradiography of EDTA-separated cells dried on to glass slides was used to follow changes in 3H-TdR incorporation in both chloroplasts and nuclei. Specificity of incorporation was confirmed by nuclease studies. DNA synthesis occurs in both the chloroplasts and nuclei, and is highest just prior to, and during the period of most rapid cell growth and chloroplast replication which occurs shortly after the transfer to the light. Light, however, appears to have a greater and more immediate effect on nuclear DNA synthesis. Though nuclear and chloroplast DNA syntheses follow similar patterns during disk growth, in a given cell, chloroplast DNA synthesis can be separate in time from nuclear DNA synthesis. The increased nuclear DNA synthesis is possibly required to support the increased population of chloroplasts, while chloroplast DNA synthesis is associated with chloroplast division. If the disks are not transferred to the light but kept in darkness, chloroplast 3H-TdR incorporation remains high, though chloroplast division is reduced. Epidermal cells in light-grown tissue also show 3H-TdR incorporation but low rates of chloroplast division. It would appear that chloroplast DNA synthesis in mesophyll cells from light-grown tissue shows a general relation to chloroplast division, but there does not appear to be an obligatory close coupling between the 2 processes.
Adhesion of Phytophthora palmivora zoospores: Electron microscopy of cell attachment and cyst wall fibril formation
Authors: Sing V. O. , Bartnicki-Garcia S.
Published: April 2021

Zoospores of Phytophthora palmivora adhered to a plastic film surface were examined by electron microscopy. Three stages of adhesion were compared: (1) non-adhesive, unencysted zoospores, (2) adhered incipient cysts, and (3) adhered mature cysts. Thin sections of incipient cysts revealed cells attached to the film surface through the partially discharged contents of the so-called peripheral vesicles; this seems to be the first step in cell adhesion. In mature cysts, the adhesive appeared to have been compacted into an electron-dense deposit binding the cyst wall to the plastic surface. The adhesion zone was also examined in face view after lysing attached incipient cysts with sodium dodecyl sulphate. Cyst wall microfibrils were seen together with an amorphous substance (presumably the adhesive material). The microfibrils were in various stages of formation. Seemingly, adhesion and microfibril formation take place concurrently. The possibility was considered that the material contained in the peripheral vesicles serves in both cell adhesion and microfibril elaboration.
The giemsa-staining centromeres of Nigella damascena
Authors: Marks G. E.
Published: April 2021

The centromere regions of each chromosome in the complement of Nigella damascena (2n = 2x = 12) stain differentially with Giemsa at interphase and throughout all the principal stages of mitosis and meiosis. Each centromere is seen to consist of a pair of sister half-centromeres which appear as 2 differentially stained dots. The appearance and behaviour of these dots indicates that they are kinetochores. The technique used does not stain centromeres in other plant species investigated, a fact which shows that the centromeres of Nigella are in some way different. The implications of this observation in relation to centromere polymorphism are discussed.
Affinity chromatography of dna-binding proteins from human, murine and man-mouse hybrid cell lines
Authors: Jost E. , Lennox R. , Harris H.
Published: April 2021

About 60 proteins from human and murine cell lines were isolated by their ability to bind to different preparations of DNA. In the intact cell, the majority of these proteins are to be found in the cell nucleus. The electrophoretic mobilities of the DNA-binding proteins from human, murine and man-mouse hybrid cell lines were compared in two-dimensional acrylamide gels. Few, if any, species-specific differences were found. These observations suggest that the structures of the vast majority of the proteins that interact with DNA are conserved through evolution. A molecular basis is thus provided for the intracellular compatibility of hybrid cells derived from different animal species.
Cell surface lipids and adhesion: I. the effects of lysophosphatidyl compounds, phospholipase a2 and aggregation-inhibiting protein
Authors: Curtis A. S. G. , Campbell J. , Shaw Felicity M.
Published: April 2021

Aggregation-inhibiting protein (AIP: Curtis & Greaves, 1965), which diminishes the adhesiveness of cells, particularly at low temperatures, is identified in the present paper as phospholipase A2 (EC. 3.1.1.4). Our reasons for this identification are because phospholipase activity parallels AIP activity during purification of AIP, because pure phospholipase A2 acts in the same manner as AIP on cell adhesion, and because various inhibitors and sera act in a parallel manner on adhesion in the presence of AIP or phospholipase. We suggest that the enzyme acts on adhesion by producing lysolecithin and other lysolipids in the plasmalemma. Addition of lysolipids diminishes cell adhesion in a manner similar to phospholipase A. Incubation of cells in Hanks’ medium at 37 °C has a parallel effect.

Conditions which would be expected to stimulate reacylation of lysolipids in the plasma-lemma, i.e. incubation of cells in the external presence of CoA, ATP and a fatty acid, lead to a recovery or maintenance of adhesion after or during Hanks’ incubation at 37 °C. All these results suggest that lipid components of the cell, probably in the plasmalemma, are of importance in adhesion. The results are discussed in relation to the long-standing controversy about the effects of low temperatures and trypsinization on cell adhesion, for phospholipase treatment of cells affects adhesion in a manner similar to trypsinization.
The organization of genetic units in chromosomes
Authors: Callan H. G.
Published: April 2021

In the genomes of chromosomal organisms, cytological evidence from disparate sources suggests that each unit of information encoded as a DNA base sequence is serially repeated. Further cytological and genetical evidence suggests that among such serially repeated sequences a terminal unit serves as the ‘master’ sequence, within which recombinational events can occur, followed by ‘slave’ sequences which are not directly involved in recombination but which are made congruent to the master sequence once per life-cycle. The formation of lateral ‘lampbrush’ loops in meiotic prophase, after synapsis, is claimed to represent the outcome of the master/slave matching process.
Observations on the distribution of the proteinpolysaccharide complex and collagen in bovine articular cartilage
Authors: Smith J. W. , Peters T. J. , Serafini-Fracassini A.
Published: April 2021

The contents of collagen and chondroitin sulphate in bovine articular and nasal cartilage were determined by chemical analysis, and the distributions of collagen and proteinpolysac-charide in articular cartilage were studied by electron microscopy. Collagen was visualized, after osmium fixation, in Araldite sections stained with uranyl acetate or phosphotungstic acid (PTA), while the proteinpolysaccharide distribution was observed in Araldite sections of tissue which had been bulk stained with bismuth nitrate at low pH.

The intercellular tissue is divisible into a pericellular zone and a main matrix. The pericellular zone exhibits fine fibres which are less than 250 Å in diameter : although they do not stain typically with PTA, they are probably collagenous in nature. The main matrix contains native collagen fibres which vary in diameter from 250–900 Å. Proteinpolysaccharide exists in the intercellular tissue in two states, namely, as free and randomly oriented macromolecules, and as macromolecules which are attached transversely over the a and b1 bands of each 640-Å period of the collagen fibres. The concentration of free proteinpolysaccharide is high throughout the pericellular zone, but diminishes practically to zero from the margin of the pericellular zone to the central part of the main matrix. No attached proteinpolysaccharide is present in the pericellular zone whereas a large amount is evident throughout the whole of the main matrix.

It is suggested that this distribution conforms to the concept that the pericellular zone is a pool from which the proteinpolysaccharide, which has been synthesized by the neighbouring chondrocyte, migrates into the main matrix to effect the metabolic turnover of this tissue component.
Uptake of [3H]uridine into precursor pools and RNA in osteogenic cells
Authors: Owen Maureen
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.