bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fusion of human erythrocytes induced by sendai virus: Freezefracture aspects
Authors: Silva Pedro Pinto Da , Shimizu Kazufumi , Parkison Clifford 
Published: April 2021

ABSTRACT
Analysis of the freeze-fracture morphology of human erythrocytes during Sendai virus-induced fusion indicates that it occurs in several spots, with the formation of membranebound cytoplasmic connexions. Radial expansion of these connexions causes the formation of a polymorphic network of membrane tubules with a lumen continuous with the external space. Our results are best explained assuming that the viral envelopes do not necessarily participate directly in inter-membrane fusion but, instead, indirectly through conditioning and modification of the erythrocyte membranes by viral membrane components.
Temperature-sensitive periods of mutations affecting cell division in Tetrahymena thermophila
Authors: Frankel Joseph , Mohler Jym , Frankel Anne Koopmans 
Published: April 2021

ABSTRACT
Temperature-sensitive periods were determined by application of temperature shifts and shocks to 3 temperature-sensitive cell division arrest (cda) mutants of Tetrahymena thermophila. A restrictive temperature, 36 °C, was found at which all 3 mutants are fully penetrant, yet other physiological effects are minimal. At this temperature, the temperature-sensitive period of cdaC2, is a unique 5-min period in mid-division, that of cdaAi is a similarly brief period situated about 0.5 h prior to cell division, while the temperature-sensitive period of cdaHI is 20 to 30 min long and immediately precedes cell division. These periods either coincide with (cdaC2, cdaHI) or immediately precede (cdaAt) the onset of phenotypic abnormality at the restrictive temperature. Brief exposure to 36 °C during the temperature-sensitive period in any of these mutants brings about irreversible arrest of division furrows in progress or preparation. Mutant cells suffering such arrest can, however, divide again at a permissive temperature by forming new furrows at different sites.
Vitellogenesis in the stick insect Carausius morosus I. Specific protein synthesis during ovarian development
Authors: Giorgi Franco , Macchi Fausto 
Published: April 2021

ABSTRACT
Vitellogenesis in the stick insect Carausius morosus (Br.) has been studied with the goal of identifying vitellogenin in various tissues. Following exposure in vivo to radioactive amino acids, oocytes in the medium size range are labelled with a minimum delay of 6 h after the time of injection. Incorporation of radioactivity under these conditions is shown to depend upon accumulation of proteins rather than on a differential rate of protein synthesis in succeeding stages of oogenesis.
By immunochemical analyses, it is shown that at least two antigens are common to both haemolymph and ovary and that one of these is also present in the fat body. Both antigens are labelled during exposure to radioactive amino acids. When analysed by SDS polyacrylamide gel electrophoresis, extracts from both haemolymph and ovary appear to share a number of protein fractions which range in molecular weight from 40000 to 200000 Daltons. The labelling pattern exhibited by these fractions is clearly indicative of a protein transfer from the fat body to the oocyte. Fat body cultured in vitro for up to 4 h releases a major macromolecular complex in the external medium. The latter has been identified as vitellogenin by both immunoprecipitation assay and SDS polyacrylamide gel electrophoresis. The protein which is synthesized and secreted under these conditions results from the processing of a protein complex of higher molecular weight.
Relationships between mitochondrial outer membranes and agranular reticulum in nervous tissue: ultrastructural observations and a new interpretation
Authors: Špaček J. , Lieberman A. R. 
Published: April 2021

ABSTRACT
This study is concerned with extensions of the outer membrane of mitochondria in cells of nenous tissue, and with possible relationships between the extensions and the agranular reticulum. A variety of preparative techniques was applied to a large number of different central nervous tissues (CNS) and peripheral nervous tissues (PNS), using conventional thin sections, thicker sections (100 nm or more) and 3-dimensional reconstructions of serial thin sections. Extensions were commonly observed, particularly from the ends of longitudinally oriented mitochondria in axons and dendrites. Often these had the appearance of, and could be traced into apparent continuity with, adjacent elements of the agranular reticulum. In addition to these apical tubular extensions, we also observed and reconstructed short lateral tubular or sac-like extensions and vesicular protrusions of the outer mitochondrial membrane. We discuss and discount the possibility that the extensions are artefacts, consider the structural and biochemical similarities between the outer mitochondrial membrane and the agranular reticulum and propose that the outer mitochondrial membrane is part of the agranular reticulum (or a specialized portion of the agranular reticulum). We suggest that the translocation of mitochondria in nerve cells, and probably in other cells as well, involves movement of the inner mitochondrial membrane and the enclosed matrix (mitoplast) within channels of agranular reticulum in continuity, or in transient continuity, with the outer mitochondrial membrane.
Flagellar roots, mating structure and gametic fusion in the green alga Ulva lactuca (Ulvales)
Authors: Melkonian M. 
Published: April 2021

ABSTRACT
The slightly anisogamous gametes of Ulva lactuca exhibit a cruciate flagellar root system consisting of 4 microtubular roots (4-2-4-2-system) and an elaborate system of fibrous roots associated with the 2-stranded microtubular roots. Two fibres (32-nm striation periodicity; system I fibres) closely underlie each of the 2-stranded roots, while different fibres (150-nm striation periodicity; system II fibres) run parallel to the root microtubules, and are 150-200 nm more internally located. Female gametes have 4 system II fibres, 3 of which are combined into a compound fibre associated with one microtubular root, while the fourth fibre is associated with the opposite root. In male gametes only 2 system II fibres are present, each underlying one of the two 2-stranded roots.
A special region of the plasmalemma of both gamete types about 0·5 µ m away from the basal bodies and located between 2 adjacent microtubular roots is structurally specialized and acts as a mating structure in gametic fusion. The region is oval-shaped and up to I·I µ m long with a maximum diameter of 0·7 µm. A continuous electron-d ense boundary layer underlies the plasmalemma at the edges of the mating structure. In both gamete types the mating structure consists of a fuzzy layer of material underlying the plasmalemma and special granules (60 nm diameter) are associated with this layer on its cytoplasmic side. In addition diffuse material overlies the mating structure, especially in male gametes. The mating structure is connected to 3 different kinds of flagellar roots: the boundary layer is linked to a 2-stranded microtubular root and its associated system I fibre; the fuzzy layer of the mating structure is connected with a system II fibre; and in female gametes this is the compound system II fibre.
The ultrastructural changes which occur after mixing the 2 gamete types have been followed. Mating structure activation involves contraction of system II fibres (change of striation periodicity to 100 nm), detachment of special granules from the fuzzy layer of the mating structure and their replacement by electron-transparent vesicles at the prospective cell fusion site. Furthermore, release of electron-dense contents from Golgi-derived vesicles in the anterior part of both gamete types precedes cell fusion. Cell fusion is exclusively initiated in a region delimited by the 2 mating structures. After partial dissolution the 2 plasma membranes unite within the mating structure regions.
The ultrastructure of gametic fusion in Ulva lactuca is compared to that of other green algae and the significance of flagellar roots in the mating process of green algae is discussed.
The effects of Con A on cell surface shedding in cell cultures
Authors: Doetschman Thomas C. 
Published: April 2021

ABSTRACT
A cell surface immobilizing concentration of Con A inhibits the shedding of [sH]fucose-containing glycoproteins from the surface of chick embryonic leg and breast muscle cell cultures and cultures of the rat skeletal muscle cell line L6. The Con A-induced inhibition of shedding is much less in the mouse fibroblast cell line 3T3. In all 4 cell types the lectin inhibits the shedding of some fucosyl-glycoproteins more than others, especially those of a lipid-containing fraction which is excluded in Biogel A-5m chromatography. This differential nature of the Con A effect is not changed by the cytoskeletal disruptors cytochalasin B or colchicine. Con A causes an increase in the amount of trypsin-sensitive surface fucosyl-glycoprotein in the cell surface and appears to decrease the overall amount of cell surface degradation suggesting that the inhibition of shedding caused by Con A is not due to an increase in internalization and degradation. The data suggest that some shedding may occur at specific cell surface sites to which surface materials must laterally migrate.
Observations on the mitochondrial reticulum in the yeast Candida utilis as revealed by freeze-fracture electron microscopy
Authors: Keyhani Ezzatollah 
Published: April 2021

ABSTRACT
Freeze-fracture of Candida utilis yeast cells grown to early logarithmic phase (5 h) and stationary phase (24 h) revealed a branched mitochondrial reticulum both in longitudinal and transverse cross-fracture studies. In contrast, longitudinal and transverse sections of permanganate-fixed cells showed that the small ovoid or spherical mitochondria were located at the periphery of the cell, without formation of a reticulum. Data indicate that the separate mitochondrial profiles seen in thin sections of permanganate-fixed yeast cells are not separate round or ovoid mitochondria, but rather are cross-sections of the mitochondrial reticulum.
The influence of the microtubule inhibitor, methyl benzimidazol-2-yl carbamate (MBC) on nuclear division and the cell cycle in Saccharomyces cerevisiae
Authors: Quinlan R. A. , Pogson C. I. , Gull K. 
Published: April 2021

ABSTRACT
Methyl benzimidazol-2-yl-carbamate (MBC), at a concentration of 100 μM, has a pronounced effect on the growth of Saccharomyces cerevisiae, resulting in the accumulation of cells as large doublets. We have determined a specific execution point for the effect of MBC on the yeast cell cycle, and have shown that this execution point is between the cell cycle events of spindle pole body duplication and spindle pole body separation. An ultrastructural examination of the MBC-treated cells revealed the absence of cytoplasmic and spindle microtubules. MBC treatment also produced an altered spindle pole body morphology, causing the disappearance of the outer component. Nuclear size was also markedly increased in the MBC-induced doublet cells, although septa were completely absent from these doublet cells.
It is proposed that MBC inhibits microtubule polymerization, rather than causing the depolymerization of stable microtubules.
Similar size of the replicons in Chironomus polytene chromosomes at two developmental stages
Authors: Lönn Ulf 
Published: April 2021

ABSTRACT
The size of the DNA replication units in salivary gland polytene chromosomes of Chironomus arvae at 2 developmental stages (red-head and late 4th instar) was investigated. The 2 developmental stages differ with respect to intensity of DNA replication with much lower values at the red-head stage. Also the level of polytenization is lower at the red-head stage. The size of the replication units was measured by determining the size of double-stranded DNA fragments released from active replication units during cell lysis. At both stages it is possible to release from the polytene chromosome a double-stranded DNA fragment of similar size. This indicates that there is no or very little difference in size of active replication units in the same tissue at the 2 development stages.
The distribution of cell-spreading activities in sera: a quantitative approach
Authors: Knox P. , Griffiths S. 
Published: April 2021

ABSTRACT
Sephacryl S-300 gel filtration of animal sera is used to demonstrate that there are at least 2 components that promote the ‘spreading’ of cells in culture. A morphometric technique is described to quantitate the spreading process. For a number of cell strains and established cell lines the more quantitatively significant spreading factor is not fibronectin. Rather it is a component with a molecular weight of approximately 70000. This factor does not cross-react immunologically with fibronectin and seems to cause spreading via a different mechanism from that stimulated by fibronectin. Thus fibronectin will cause spreading in the absence of protein synthesis, whereas the smaller component requires protein synthesis. The kinetics of spreading are also different at all concentrations of the factors that are effective.
By comparing the spreading promoted by whole sera with that promoted by separate serum fractions following chromatography we conclude that under normal culture conditions plasma fibronectin plays little part in initial cell spreading. This view is supported by the fact that fibronectin-depleted serum will stimulate cell spreading.
The intranuclear relationship between centromere volume and chromosome size in Festuca scariosa × drymeja
Authors: Jenkins G. , Bennett M. D. 
Published: April 2021

ABSTRACT
In the hybrid Festuca scariosa × drymeja where pairing is incomplete at pachytene, there is preferential pairing between the longer chromosomes of the complement. EM serial-section reconstruction of nuclei at zygotene and pachytene reveals that there is equally pronounced preferential pairing between larger centromeres. This evidence suggests that the longer chromosomes have large centromeres and that centromere volume is correlated with chromosome length. Confirmation of this comes from the comparison of the frequency distributions of observed centromere volumes and those predicted on the basis of chromosome length.
Although there is a positive correlation between centromere volume and chromosome length, it is not possible to identify the centromeres of each individual chromosome within the complement because (a) the differences between the lengths of each chromosome are small and (b) the estimates of relative centromere volumes vary significantly between cells.
Persistence, suppression and re-expression of pigment formation in somatic cell hybrids between mouse melanoma cells and non-melanoma cells
Authors: Junker Steffen 
Published: April 2021

ABSTRACT
Pigmented subtetraploid and subhexaploid mouse melanoma cells were fused with a range of different cell types. Expression of pigment formation appeared to be dependent on the phenotype of the non-melanoma parent cell, so that hybrids with lymphoid cells or chick embryo erythrocytes produced pigment, but hybrids between fibroblasts or epithelial rat hepatoma cells did not. The results were independent of gene dosage of either parent cell, γ-irradiation of suppressing partner cells prior to fusion caused progressive increase of pigmentation with increasing dose of radiation. Cybrids between cytoplasts of suppressing fibroblasts and melanoma cells were pigmented.
Nuclear lamina assembly, synthesis and disaggregation during the cell cycle in synchronized HeLa cells
Authors: Jost Erich , Johnson Robert T. 
Published: April 2021

ABSTRACT
The pattern of assembly, synthesis and disaggregation of the nuclear envelope-associated lamina in synchronized HeLa cells has been examined by means of immunofluorescence microscopy of cell preparations treated with antibody to lamina polypeptide LP67 or lamin B, using the nomenclature of Gerace and Blobel. During the cell cycle the distribution of lamina polypeptide varies dramatically. Three distinct stages can be detected with respect to its location and synthesis: Lamina polypeptide is cytoplasmically distributed during cell division particularly at the time of complete nuclear envelope breakdown. At telophase it is reassembled and becomes associated with regions of the chromosome surface. This process continues into early G1, lamina polypeptide associating progressively with the outer surface of the chromosomes; simultaneously its cytoplasmic concentration is reduced. The traffic of antigen from cytoplasm to the chromosomes is highest between telophase and G1 but continues at a reduced rate during G1. Inhibition of protein synthesis during division and G1 does not inhibit G1 lamina reformation, suggesting that the G1 lamina is constructed from depolymerized cytoplasmically-stored polypeptide derived from the previous cell cycle.Lamin B is synthesized in S-phase. The protein is rapidly accumulated at the nuclear periphery during the doubling of the nuclear surface. There is very little if any cytoplasmic location of lamina polypeptide in S-phase cells. The S-phase pattern of lamina distribution persists through early and mid G2Towards the end of G2, and particularly with the onset of prophase, the nuclear membrane-bound lamina is released into the cytoplasm over approximately 30 min. (Fusion between metaphase and either G1 or S-phase cells also results in the depolymerization of lamin B within 30 min.) Lamina polypeptides appear in the cytoplasm before the nuclear envelope has disappeared, and protein synthesis in G2, is required for complete lamina disaggregation.
Lamina reformation in late mitosis and the polarity of its appearance in the telophase cell can be perturbed by treatment with colcemid or low temperature so that lamina is induced to associate with metaphase and anaphase chromosomes. In the absence of spindle microtubules lamina reformation may proceed around the surface of whole chromosomes, leading to the formation of micronuclei in G1 cells. We propose that in the normal cell nuclear envelope formation at telophase is related to the terminal distribution of cytoskeleton structures such that lamina is laid down only on the outer surface of the telophase genome beginning at the telomeric chromosome ends adjacent to the remaining mitotic fibres of the cleavage furrow.
Studies on the rhizoplast from Naegleria gruberi
Authors: Gardiner Peter R. , Miller Robert H. , Marsh Mark C. P. 
Published: April 2021

ABSTRACT
A procedure, utilizing homogenization and centrifugation in a low ionic strength buffer containing Triton X-100, has been used to facilitate the isolation of the rhizoplast from flagellates of Naegleria gruberi. This has enabled a study to be made of the physical and biochemical properties of this organelle. The rhizoplast is shown to be a proteinaceous structure with chemical properties similar to those of the molluscan gill ciliary rootlet. Polyacrylamide gel electrophoresis gives a possible subunit molecular weight of approximately 240000 Daltons. Studies with antisera raised against the rhizoplast fraction demonstrated the absence of rhizoplast antigens in amoeboid forms of Naegleria gruberi and is taken as evidence that the organelle is synthesized de novo during transformation of the amoeba to the flagellate form. Results of optical diffraction studies on isolated rhizoplasts are also presented.
Chromosomal basis of dosage compensation in Drosophila. X. Assessment of hyperactivity of the male X in situ
Authors: Chatterjee R. N. , Mukherjee A. S. 
Published: April 2021

ABSTRACT
The results of examination of the template activity of the fixed polytene chromosomes of Drosophila hydei, monitored by 3H-UTP, under in situ assay conditions, upon the use of endogenous Drosophila polymerase, exogenous Escherichia coli RNA polymerase (holoenzyme) and exogenous Drosophila RNA polymerase II (or B) have been presented. Analysis of the data reveals that the transcription patterns with the 3 enzymes are not strictly comparable with the pattern obtained under in vivo conditions. Yet, with each of the 3 conditions of assay, there is a reasonable concordance between the template activity on the single X chromosome of the male and the paired Xs of the female, as observed under in vivo. There is also, in every case, a high positive correlation between the 3H-UMP incorporation into the X chromosome and that into a specific autosome. A site-wise analysis of 3H-UMP labelling under the 3 assay conditions also reveals that for most of the regions, the sites which are highly active in vivo also show high labelling in situ,’ the proportionality is maintained in both sexes. These results have been interpreted to have suggested that the hyperactivity of the male X vis-a-vis dosage compensation in Drosophila is primarily a property of the inherent organization of the X chromosome itself and is achieved through modulation in the organization, rather than exclusively through autosomal factor(s), although a secondary level of autosomal regulation has not yet been ruled out.
Membrane particle arrays in SV40-transformed 3T3 Cells
Authors: Montesano Roberto , Philippeaux Marie-Marthe 
Published: April 2021

ABSTRACT
The ultrastructural organization of the plasma membrane of untransformed and simian virus (SV)40-transformed 3T3 cells in culture was studied by an in situ freeze-fracturing technique. Both 3T3 and SV3T3 cells showed randomly distributed intramembrane particles as well as gap junctions. In addition, the plasma membrane (P-face) of confluent SV40-transformed 3T3 cells was found to display a unique membrane specialization which was not observed in normal 3T3 cells. This membrane specialization consisted of irregularly-shaped arrays of loosely dispersed large (11–12 nm) intramembrane particles, located in regions of close contact between adjacent SV3T3 cells. When a P-to E-fracture face transition occurred within the boundaries of a particle array, the intercellular space appeared uniformly reduced and arrays of pits coextensive with the P-face particles could be recognized on the E-face. Particle arrays appeared particularly prominent in SV3T3 cells grown in the presence of high serum concentrations (20 % foetal calf serum or calf serum). Particle arrays resembling those found in SV3T3 cells were observed only in very rare instances in the plasma membrane of other virus-transformed cell lines. Several possible interpretations of the meaning of the particle arrays, including the hypothesis that they represent an unusual or abortive form of intercellular junction, are discussed. The absence of similar membrane specializations in the plasma membrane of untransformed 3T3 cells points to a difference in membrane organization and cell contact ultrastructure between normal and SV40-transformed 3T3 cells.