bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effective site of the lesion resulting from a trichocyst non-discharge stable differentiation of somatic nuclei in Paramecium tetraurelia
Authors: Aufderheide Karl J. , Sonneborn T. M. 
Published: April 2021

ABSTRACT
Previous work has shown in Paramecium tetraurelia that recessive genic mutants with the phenotype N, non-discharge of trichocysts from intact cells in response to a standard test (exposure to tannic or picric acid), are in some mutants due to lesions in trichocyst development and in others due to lesions in the cytoplasm; and that in stock dII3 the same homozygous germinal genotype can yield by stable differentiation of somatic nuclei both N clones and D (discharge) clones. The site of the lesion in the N clones of dII3 was investigated by the same microinjection protocol used earlier for analysis of the genic mutants: cytoplasm containing trichocysts was removed from wild-type (D) and from dII3 (N) cells and injected into cells of both dII3 (N) and the genic mutant ftA (normal cytoplasm, but morphologically abnormal trichocysts incapable of insertion in the cell cortex or of discharge from intact cells). Trichocysts from each donor behaved the same in both recipients: trichocysts from D cells could discharge; those from dII3 N cells could not. Thus, the cytoplasm of dII3 (N) cells does not prevent the discharge of trichocysts from D cells and the trichocysts from dII3 (N) cells cannot discharge in ftA cells in which trichocysts from wild-type (D) cells can. It appears, therefore, that the lesion in dII3 (N) cells, due to a stable differentiation of somatic nuclei, is in the trichocysts themselves, as it is in certain genic mutants.
The loss of morphogenetic potential and induction of phenylalanine ammonia-lyase in suspension cultures of Phaseolus vulgaris
Authors: Bevan Michael , Northcote D. H. 
Published: April 2021

ABSTRACT
The loss of morphogenetic potential in bean suspension cultures has been investigated by measuring the amounts of phenylalanine ammonia-lyase activity induced in the cells when they are transferred from a medium in which they are grown and maintained to an induction medium.
The tissue has been grown in 2 types of medium: (1) supplemented with 2,4-dichlorophenoxy-acetic acid as the only growth hormone, and (2) supplemented with 2,4-dichlorophenoxyacetic acid and coconut milk. When cells were grown in medium with only 2,4-dichlorophenoxyacetic acid for a period of 5–10 subcultures and samples were transferred to the induction medium at intervals during the subcultures, the amounts of phenylalanine ammonia-lyase activity and the number of xylem elements induced progressively declined. Cells grown in the presence of coconut milk did not lose the ability to induce phenylalanine ammonia-lyase or xylem elements.
Cells grown in the presence of coconut milk were cloned and clones capable of producing different amounts of phenylalanine ammonia-lyase when transferred to induction medium were obtained. However, clones producing low amounts of activity did not grow faster in the medium lacking coconut milk and no evidence was obtained to show that selective growth of non-inducible cells was responsible for the loss of morphogenetic potential.
In addition to the induction brought about by the presence of naphthylacetic acid and kinetin in the induction medium the cells could also be stimulated to produce phenylalanine ammonialyase activity by dilution at subculture.
This increase in activity occurred within 10 h of the dilution, whereas that produced by the hormones in the induction medium occurred after 120 h. The induction produced by dilution also occurred in these cells which had lost their ability to respond to the hormonal induction. Thus the mechanism that produced the increase in phenylalanine ammonia-lyase activity was intact but had lost its ability to respond to the hormones of the induction medium. The loss of inducibility was therefore probably not due to a genetic change in the cells bought about by continuous growth in a medium lacking coconut milk, but to reversible changes in the hormonal requirements of the cells necessary for induction.
An unusual cell surface modification: A double plasma membrane
Authors: Lane Nancy J. , Harrison J. Barrie 
Published: April 2021

ABSTRACT
The occurrence of an unusual double plasma membrane structure is reported; it has been studied in conventional thin sections, after lanthanum-impregnation and with freeze-fracturing. This modification of the plasmalemma is found where the luminal cell membrane (I membrane) of gut microvilli in the haematophagous insect, Rhodnius prolixus, is surrounded by a second, outer membrane (O membrane), the 2 separated from one another by a highly regular I–O space of about 10 nm. Lanthanum impregnation reveals the presence of columns inclined at an angle, within this I–O space; as in the continuous junctions which link the lateral borders of these cells, these columns may maintain the very precise I–O distance. From the outer microvillar membranes radiate short spoke-like fibrils or sheets which encounter another more extensive system of myelin-like sheets. Freeze-fracturing reveals that the spoke-like sheets and the other ones which lie like a tube, around and parallel to the microvilli, contain linear ridges composed of particles, lying at random within layers of the myelin-like material which also extends into the lumen of the gut. The microvillar membranes, both O and I, fracture into faces containing rows of either PF particles or EF pits arranged as spiral ridges or grooves around the sides and across the tip of each microvillus. These could be the insertion sites of one or both of the I–O columns and spoke-like sheets while the sheets could represent a variant of peritrophic membrane. The double membrane may be a cellular device to increase the strength of the microvillar layer in these blood-sucking animals, since the cell layer must withstand great pressure owing to the sudden massive extension of the gut during a blood meal.
Synthesis and deposition of oocyte envelopes (vitelline membrane, chorion) and the uptake of yolk in the dragonfly (odonata: aeschnidae)
Authors: Beams H. W. , Kessel R. G. 
Published: April 2021

ABSTRACT
Light and electron-microscope studies on dragonfly ovarioles reveal evidence that the precursor vitelline membrane and chorion secretions are synthesized within the follicle cells. It is suggested that the sequence of synthesis and deposition of the vitelline membrane occurs as follows. The vitelline membrane presecretion appears to be synthesized by the rough-surfaced endoplasmic reticulum, giving rise to intracisternal granules. These appear to migrate in the cisternae to the region of the Golgi complex where the endoplasmic reticulum loses most of its ribosomes and the intracisternal granules move into the Golgi region where they appear within small vesicles. These seem to find their way into the Golgi cisternae where they may be incorporated with the secretions from the Golgi cisternae to produce the definitive previtelline secretion. The previtelline secretion bodies are eventually discharged into the space between the oocyte and follicle cells, forming rows of secretion bodies between the microvilli. These fuse into progressively larger bodies until a complete membrane is established. Follicle cells actively secreting precursor vitelline membrane substance show many disk-shaped, relatively clear vesicles in the cytoplasm.
After the vitelline membrane is laid down, the follicle cells take on an entirely different function; namely, the synthesis and deposition of the chorion. The first visible chorion secretion appears in profile as elongate dense bodies within the Golgi cisternae which tend to coil, and in so doing, expand the cisternae. As this occurs, the enlarged cisterna, loaded with concentric coiled secretion material, separates from the remainder of the Golgi cisternae and becomes free in the cytoplasm as a prechorion secretion body. These migrate to, and collect below, the surface of the cell where they are eventually ejected between the surface folds and become incorporated into the developing chorion.
Uptake of yolk in the dragonfly seems to be predominantly by micropinocytosis. The oocyte surface during active vitellogenesis bears many pits which contain an extracellular material closely applied to the outer surface of the plasma membrane. Thin, radially oriented bristles are continuous with the inner surface of the plasma membrane in this region. The pits continue to invaginate until they are cut off from the plasma membrane and come to lie in the oocyte cortex as coated vesicles. These appear to lose their coats gradually and fuse with one another to produce definitive yolk spheres.
Metabolic co-operation between biochemically marked mammalian cells in tissue culture
Authors: Subak-Sharpe H. , Bürk R. R. , Pitts J. D. 
Published: April 2021

ABSTRACT
Cells of a genetic variant of the hamster fibroblast line BHK 21 which lack inosinic pyrophosphorylase activity (IPP− cells) and therefore cannot normally incorporate [3]hypo-xanthine were grown in mixed culture with cells of BHK 21 sublines which have inosinic pyrophosphorylase activity (IPP+ cells). If not in contact with IPP+ cells, IPP− cells do not incorporate added [3H]hypoxanthine into nucleic acid. IPP+ cells always do incorporate [3H]hypoxanthine and IPP− cells when in direct or indirect contact with IPP+ cells also incorporate the isotope. Cell to cell contact appears to be essential for this gain of a metabolic function by IPP− cells.
The possible molecular basis and general implications of the phenomenon are discussed.
The cellular basis of movement of the migrating grex of the slime mould Dictyostelium Discoideum
Authors: Garrod D. R. 
Published: April 2021

ABSTRACT
Previous work has failed to suggest a mechanism for grex movement, which takes account of both the movement and contact interaction of grex cells, and properties of the whole grex. Here, some observations on the movement of grex cells under different conditions are reported. From these, it seems that the production of pseudopods by grex cells depends upon mechanical factors of their environment and that movement depends on pseudopods being able to form stable adhesion with the surfaces of other cells. Intercellular adhesions are stable to forces applied at right angles to the plane of adhesion, but a force parallel to the plane of adhesion causes the cell surfaces to slide past each other. It is suggested from observations on grex placed in aqueous media and paraffin oil that the slime sheath may play an important role in controlling the polarity of grex movement by restricting pseudopod formation in all directions except forwards. These suggestions are discussed briefly in relation to previous observations on grex movement.
A molecular basis for indiscriminate and selective cell adhesion
Authors: Jones B.M. , Morrison G. A. 
Published: April 2021

ABSTRACT
When cells of different type are intermixed they will adhere to one another indiscriminately. In mixed aggregates of o.th-incubation-day fibroblasts and 12th-day liver cells from chick embryos, the liver cells accumulated as groups which moved at random relative to the surrounding fibroblasts; groups of liver cells were liable to migrate from the interior to occupy the surface.
Quantitative estimations of the effect of temperature on the rate of reaggregation of dissociated fibroblast cells, using a turbidimetric method, indicated that the rate was controlled by a chemical reaction. The energy of activation calculated for this reaction was 21·1 kcal/mole. The significance of this value is discussed in relation to values associated with other kinds of reactions.
The indiscriminate adhesions formed between the unlike cells allowed them to move relative to one another, whereas the adhesions (selective) formed between like cells, when by chance they made contact, did not. Thus the aggregates of like cells increased in extent and the inherent ability of homogeneous aggregates to consolidate the intercellular bonding ensured that the process became effectively irreversible.
If, as is evident, there is a basic similarity in the adhesive mechanisms of the various types of cells that exist, the question that required answering was what kind of differences could occur in the bonds to account for differential adhesiveness upon which the sorting out process depends. It is suggested that the linkage sites at the surfaces of cells move (oscillate) between two positions, the one unfavourable and the other favourable to adhesion, and the theory put forward is that differential adhesiveness is the expression of differences in the frequency of the oscillations of the otherwise equivalent linkage sites. The theory provides an explanation for the temporary nature of indiscriminate adhesion allowing the movement of unlike cells in contact relative to one another and the more permanent nature of selective adhesions responsible for the consolidation of like cells in their appointed territories.
Injected histone antibodies interfere with transcription of lampbrush chromosome loops in oocytes of Pleurodeles
Authors: Scheer U. , Sommerville J. , Bustin M. 
Published: April 2021

ABSTRACT
Antibodies to calf thymus histone H2B were purified by chromatography on DEAE-cellulose and injected into oocyte nuclei of Pleurodeles waltlii. As shown by indirect immunofluorescence these antibodies cross-reacted strongly with corresponding histones associated with lampbrush chromosomes. Shortly after injection the lateral loops of the chromosomes retracted into the chromomeres and by 3 h postinjection the ‘lampbrush’ appearance was completely lost and the chromosomes appeared in light-microscopic preparations as rod-like structures consisting of longitudinally coalesced chromomeres. In control oocytes injected with non-immune immunoglobulins or antibodies against a ubiquitous transcript-associated protein no morphological alterations of the lampbrush chromosomes could be observed. Electron microscopic spreads of chromosomes prepared at various times after injection of anti-H2B revealed a progressive loss of transcriptional complexes from the loop axes. Finally, higher-order chromatin configurations, like supranucleosomal globules (‘superbeads’) or cable-like chromatin strands 50–60 nm thick predominated, indicating complete transcriptional inactivation of all chromosomal regions. The results indicate that H2B antibodies react specifically with histones associated with the transcribed DNA of lateral loops in their native state. The resulting antigenantibody complexes seem to inhibit progression of the RNA polymerases along the template, thus causing the premature release of transcripts, a process analogous to the stripping effect of actinomycin D. The demonstration of histones associated with heavily transcribed regions, which are not compacted into nucleosomes but largely extended, supports the current concept that unfolding of nucleosomes to allow transcription of the DNA does not involve dissociation of histones. In contrast, amplified ribosomal RNA genes are unaffected by injected H2B antibodies. This does not necessarily indicate absence of histones from nucleolar chromatin, since we do not know whether it is accessible in vivo to antibodies or whether the histone antigenic determinants are masked by the presence of other proteins. The technique of injecting specific antibodies should be widely applicable when analysing the in vivo distribution of chromosomal components at the electron-microscopic level and when studying complex metabolic processes, like the cleavage and modification of RNA, by selective inhibition of defined enzymic steps.
Location of fucosyl transferases in the membrane system of maize root cells
Authors: Green John R. , Northcote D. H. 
Published: April 2021

ABSTRACT
There are two fucosyl transferase activities present within, the endomembranes of the cells of maize root-tips. One transfers fucose to polyprenyl phosphate and occurs in the endoplasmic reticulum, the second transfers fucose probably to polysaccharide or glycoprotein. In order to show an association of this second fucoayl transferase activity with the endoplasmic reticulum as well as the Golgi apparatus, a method of fractionating the membranes in a discontinuous sucrose gradient was used. Membranes were prepared in the presence of Mg3+, which maintained the attachment of ribosomes to the endoplasmic reticulum, and also in the presence of EDTA, which removed most of the ribosome complex. This caused a shift in density of these membranes. Two types of experiments were carried out; either maize roots were incubated in L-[1-3H]fucose and then membranes prepared and the amount of polymer synthesized in vivo determined or isolated membranes were incubated with GDP-L-[U-14C]fucose in vitro and the amount of polymer synthesized was found. The results showed that the Golgi apparatus had the highest amount of this fucosyl transferase activity, but there was a significant amount of activity associated with the endoplasmic reticulum and the latter was shifted in the sucrose gradient depending on the conditions used.
Induction of G
1
− cells at high frequency
Authors: Naha P. M. 
Published: April 2021

ABSTRACT
Experimental conditions are reported on the induction of G1- cells at high frequency by ultraviolet irradiation of temperature-sensitive cells arrested in G1 phase at the restricted temperature. Neither the wild type cells of Balb/C-3T3 nor the temperature-sensitive derivative of t8 A83 grown at the permissive temperature could be ‘mutated’ under similar conditions. One such ‘mutant’ (R18) was ‘inducible’ from a G1+ phenotype at 33 °C to G1- state at 38 °C within one cell generation time. The ‘inducible’ property of R18 from G1+ to G1_ lends support to the theory that the duration of the G1+phenotype is determined by the level of precursors for DNA synthesis. Since the G1- variants were isolated from revertants, the frequency of ‘mutagenesis’ appeared to be artificially high.
Analysis of sister-chromatid exchanges and tumorigenicity in cell hybrids
Authors: Jonasson J. , Santesson B. , Ström A. 
Published: April 2021

ABSTRACT
The relationship between the ‘spontaneous’ frequency of sister-chromatid exchanges (SCE) and tumorigenicity was studied in a series of hybrids between a C57BL melanoma cell line and diploid cells, but no correlation was found between the 2 variables. Hybrids in which malignancy was suppressed and malignant segregants derived from them showed virtually identical SCE frequencies.
Variation of SCE frequencies was observed, however, between the different hybrid clones, and most hybrids showed consistently less SCE per chromosome than the corresponding parental cell types did under similar growth conditions. The lower SCE frequencies could neither be related to a higher number of chromosomes in the hybrid nor could they be related to the method of hybrid selection. These findings suggest that cell fusion might have induced epigenetic SCE frequency changes possibly in the same way as modulation of SCE frequencies is known to occur in the human leukocyte series.
The role of cell swelling and haemolysis in sendai virus-induced cell fusion and in the diffusion of incorporated viral antigens
Authors: Knutton S. , Bächi T. 
Published: April 2021

ABSTRACT
The role of the haemolytic activity of Sendai virus in cell–cell fusion has been examined in monolayers of human erythrocytes and erythrocyte ghosts fused with either haemolytic or non-haemolytic virus. Morphological observations indicate that cell swelling and haemolysis is a distinct event in cell-cell fusion irrespective of whether it is vitally induced or, in the case of non-haemolytic virus, experimentally induced. Osmotic swelling appears to be the driving force by which cells which have established sites of membrane fusion expand such sites to form poly-erythrocytes. Immunofluorescent labelling of viral antigens incorporated into the erythrocyte membrane as a result of viral envelope–cell fusion indicates that diffusion of antigens in the plane of the membrane is restricted in intact erythrocytes and resealed erythrocyte ghosts but not in haemolysed erythrocytes or unsealed ghosts. A perturbation of the erythrocyte membrane resulting from osmotic lysis appears to form a prerequisite for the lateral diffusion of viral elements.
Structures linking the tips of ciliary and flagellar microtubules to the membrane
Authors: Dentler William L. 
Published: April 2021

ABSTRACT
The distal tips of both central pair and outer doublet microtubules are linked to flagellar membranes of Chlamydomonas and to ciliary membranes of both Tetrahyniena and Aequipecten by the central microtubule cap and by distal filaments, respectively. The distal filaments are linked to ciliary membranes at their distal ends and, at their proximal ends, form a carrot-shaped plug which inserts into the lumen of the A-tubule of each outer doublet. Both types of tip structures are present in regenerating cilia and flagella. At least 2 different types of distal filaments are present in Tetrahyniena. Certain cilia in Tetrahymena oral apparatuses and in certain molluscan gills contain distal filaments which join with the central microtubule cap and with the ciliary membrane to form a cap-filament-membrane complex.
Organization of chromosomes in hela cells: Isolation of histone-depleted nuclei and nuclear scaffolds
Authors: Adolph Kenneth W. 
Published: April 2021

ABSTRACT
Histone-depleted nuclei were prepared from, isolated HeLa nuclei by extracting the histones and other proteins with polyanions (dextran sulphate and heparin) or with high salt concentrations as used previously. The particles were characterized by sucrose density gradient sedimentation, thin sectioning and electron microscopy, and by polyacrylamide gel electrophoresis. The general result of the experiments is that the DNA in the histone-depleted nuclei is highly organized, and that this residual, higher-order structure is maintained by a reproducible subset of nuclear proteins, and perhaps by RNA. Furthermore, the residual proteins remain associated, in some conditions, as rapidly sedimenting structures even when the DNA is digested with nucleases. These nuclear scaffolds can resemble extracted nuclei.
Histone-depleted HeLa nuclei sediment in sucrose density gradients as well defined peaks with sedimentation coefficients of around 12000 s, when 2 M NaCl is used to extract the histones, or 6000 s, when dextran sulphate is used. The rate of sedimentation is drastically decreased by treating the particles with trypsin, and reduced to a lesser extent with RNase A. Thin sectioning and electron microscopy show that histone-depleted nuclei possess the nuclear periphery and that internal material is also present. These general features are also seen in thin sections of nuclear scaffolds, which are prepared by treating the nuclei with micrococcal nuclease or DNase I in addition to extracting the histones. Two groups of major proteins are associated with histone-depleted HeLa nuclei and the nuclear scaffolds: One group has molecular weights of around 65000–70000 Daltons, while the second group has molecular weights of 50000–55000 Daltons. The major species of this latter group of proteins have mobilities that are similar to the proteins of the metaphase chromosomal scaffold.