bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructure of the endoplasmic factor responsible for cytoplasmic streaming in Chara internodal cells
Authors: Nagai Reiko , Hayama Tomio 
Published: April 2021

ABSTRACT
Previous investigators have proposed that cytoplasmic streaming in Chara intemodal cells results from the interaction between an endoplasmic factor and fibrils composed of microfilaments in the stationary cortex. Using the internal perfusion technique, we confirmed the observation that organelles which had been attached to the fibrils by decreasing the internal concentration of ATP moved along the fibrils after ATP was introduced. Thin-sectioned specimens revealed that endoplasmic organelles of various shapes were linked to microfilament bundles in the absence of ATP. Linkage was effected by regularly arranged electron-dense materials with a spacing of 100 – 130 nm at definite regions on each organelle. The organelles in question were studied in negatively stained preparations of endoplasm. The organelles had some common features. (1) They were all membrane-limited. (2) Their sizes and configurations varied largely. (3) One or more protuberances were present on them. (4) The protuberances were usually rod- or hom-like. (5) Small globular bodies 20 – 30 nm in diameter were found in ordered array with the same spacing as those in thin sections at the surface of the protuberances. (6) Many fine filaments were always attached to the surface of the protuberances. These fine filaments differed from F-actin in diameter (less than 4 nm) and inability to react with heavy meromyosin from rabbit skeletal muscle. The role of such components of the organelles in cytoplasmic streaming is discussed.
A paracrystalline array of microfilaments with a transverse periodicity of about 38 nm is presented, together with its optical diffraction pattern.
A control acting over the initiation of dna replication in the yeast Schizosaccharomyces pombe
Authors: Nasmyth Kim A. 
Published: April 2021

ABSTRACT
The control of cell division in the yeast Schizosaccharomyces pombe appears to be quite different to that of any other eukaryotic organisms for it is usually exerted not at the initiation of S-phase but at that of mitosis. However, it has been suggested that a control over the initiation of S-phase does also exist but that its action is redundant whilst the mitotic control is operating. This study has chosen conditions in which the latter appears to be largely absent in order to study the cryptic S-phase control. The timing of S-phase has been studied in cells grown at varying rates under nitrogen limitation in a chemostat. It is found that under these conditions the control of cell division resembles that of other eukaryotes. As the dilution rate of the chemostat is reduced, all increase in the generation time can be accounted for by a lengthened G1 period. In contrast, the length of S + G2 remains invariant Thus, there must indeed be a control acting in G1 in S. pombe. An analysis of the size of cells at different growth rates shows that the initiation of S-phase is correlated with a particular cell size.
Replication in Drosophila chromosomes: I. replication of intranucleolar dna in polytene cells of D. nasuta
Authors: Lakhotia S. C. , Roy Sabita 
Published: April 2021

ABSTRACT
The organization and replication of intranucleolar DNA in polytene cells of Drosophila nasuta have been examined. Normal Giemsa and fluorescent (Hoechst 33258 and quinacrine mustard) staining reveal that in D. nasuta polytene cells, the intranucleolar DNA is organized into condensed and disperse forms and very often shows connexion to the alpha heterochromatin of the chromocentre. Results of [3H]thymidine autoradiography indicate that the known underreplication of rDNA sequences in polytene cells is due to the slower replication of the intranucleolar DNA. Some aspects of the organization of condensed and disperse intranucleolar DNA are discussed.
Fertilization in brown algae: II. evidence for lectin-sensitive complementary receptors involved in gamete recognition in Fucus serratus
Authors: Bolwell G. P. , Callow J. A. , Callow Maureen E. , Evans L. V. 
Published: April 2021

ABSTRACT
Fertilization in Fucus serratus is directly proportional to the number of sperm added, saturating at approximately 250 sperm per egg with an apparent Km of 120 sperm per egg. The effect of a range of lectins on fertilization has been tested. Preincubation of gametes with Con A and fucose-binding protein (FBP) inhibited fertilization. At low concentrations this was by specifically binding to eggs; at high concentrations pretreatment of either gametes inhibited fertilization probably due to cytotoxicity. Fertilization was not inhibited by simple sugar haptens, but polysaccharides containing fucosyl or mannosyl residues (yeast mannan, fucoidan, ascophyllan) inhibited fertilization by binding to sperm. Pretreatment of eggs with α-fucosidase or α-mannosidase was effective in inhibiting fertilization. All the results indirectly demonstrate that fertilization in Fucus serratus is based on an association between fucosyl- and mannosyl-containing ligands on the egg surface and specific carbohydrate-binding receptors on the sperm surface.
Transport of glial cell acid phosphatase by endoplasmic reticulum into damaged axons
Authors: Griffiths Gareth W. 
Published: April 2021

ABSTRACT
Earlier observations indicated that cutting the photoreceptor (R) cell perikarya in the retina of the flies Musca domestica and Calliphora erythrocephala resulted in an extremely rapid degeneration of the R-cell axons. The process manifested itself within minutes and secondary lysosomes appeared early on in the degenerating axons. In this study, biochemical assays of the classical lysosomal marker enzyme acid phosphatase (AcPase) showed a rapid increase in activity upon cutting the retina, reaching a peak around 5 min, followed by a drop and a subsequent slow steady rise in activity between about 4 and 24 h after the cut. Inhibitor studies indicated that atleast 2 different acid phosphatases were involved, which showed identical activity changes. EM cytochemical studies with either β-glycerophosphate or cytidine monophosphate as substrates indicated that the degeneration-dependent AcPase activity originated exclusively in one specific glial cell type in the distal lamina, the satellite glia. These cells are contiguous with R-cell axons in the pseudocartridges, directly proximal to the basement membrane of the retina. In normal uncut flies, reaction product indicative of AcPase activity was found in satellite glial cells in both rough ER (and perinuclear cistemae) and in smooth ER, the 2 types of cistemae being clearly in continuity. The electron-dense reaction product resulting from AcPase activity often showed continuity between the smooth ER of satellite glial cells and extracellular sites between the satellite glia and R-axons. This may result from the low levels of AcPase being synthesized in rough ER, and then exported to extra-cellular sites. Within minutes of cutting the retina the frequency of satellite glia smooth ER staining for AcPase increases significantly. Increases in AcPase activity were subsequently found sequentially in extracellular sites, in axons in the distal lamina, and finally in the axon terminals. The time course for these increases in AcPase activity correlated well with the time course of the fine-structural pathological changes in the axons.
A significant feature of the satellite glia cells is the massive packing of unidirectional microtubules (MTs), running perpendicular to the projections of the R-axons -in the same direction as AcPase transport. The MTs terminate at the glial membrane directly adjacent to the axon. The smooth ER cistemae interdigitate among the MTs and may be structurally connected to them by thin fibrils.
Thick-section cytochemistry and stereology were used to reveal the 3-dimensional extent of the AcPase-reactive smooth ER system. Evidence is presented which suggests that this system represents GERL, a specialized region of smooth ER involved in lysosome formation, that in this glial cell appears to function also to export hydrolytic enzymes.
Mechanical tension produced by nerve cells in tissue culture
Authors: Bray D 
Published: April 2021

ABSTRACT
Evidence is presented that (a) the growth cone of cultured neurons can exert mechanical tension, and (b) that the direction of advance of the growth cone is determined by the tension existing between it and the rest of the cell.
(a) The evidence that growth cones can pull comes from a vectorial analysis of the outlines of individually isolated sensory neurons. The angles formed in these outgrowths are very close to those of tension-generated networks anchored at their free ends and these values are restored shortly after an experimental displacement. The relative mechanical tension on each segment of an outgrowth can be calculated by standard methods and is found to decrease at each branch point. It appears to be correlated with the diameter of the fibre so that thicker fibres maintain more tension than thinner ones.
(b) The influence of tension on the direction of advance of the growth cone is shown by 2 kinds of experiment. If a growing neurite is pulled to one side with a microelectrode then the direction of its advance is changed immediately according to the new stress. If the mechanical tension on the growth cone of a neurite is released by amputation or displacement the growth cone is found to have a high probability of branching shortly afterwards.
The ability of the growth cone to exert tension is discussed in relation to evidence that microspikes have contractile properties and in terms of the distribution of microfilaments within the neurite. It is suggested that the exertion of tension by a growth cone could serve to guide the neurite along paths of high adhesivity both in vitro and in vivo.
Interpolation of microtubules into cortical arrays during cell elongation and differentiation in roots of Azolla Finn Ata
Authors: Hardham A. R. , Gunning B. E. S. 
Published: April 2021

ABSTRACT
Longitudinal sections of roots of Azolla pirmata R. Br. were prepared for electron microscopy so that cortical microtubules could be counted along the longitudinal walls in cell files in the endodermis, pericycle, and inner and outer cortex, and in sieve and xylem elements. With the exception of the xylem, where there are no transverse cell divisions, each file of cells commences with its initial cell and then possesses a zone of concomitant cell expansion and transverse cell division, followed, after completion of the divisions, by a zone of terminal cell differentiation.
The cells augment their population of cortical microtubules as they elongate and divide, showing a net increase of up to 0.6 μm of polymerized microtubule length per min. Two main sub-processes were found: (i) When a longitudinal wall is first formed it is supplied with a higher number of microtubules per unit length of wall than it will have later, when it is being expanded. This initial quota becomes diluted as the second sub-process commences, (ii) The cells interpolate new microtubules at a rate which is characteristic of the cell, and, in the endodermis, of the face of the cell, while the cell elongates. Most cell types thus maintain a set density of cortical microtubules while they elongate and divide. Comparisons of endodermal cells in untreated controls, and roots that had been treated with colchicine, low temperature, or high pressure indicate that the initial quota of microtubules, and the later interpolations, and differentially sensitive to microtubule perturbations.
Three types of behaviour, all related to changes in the cell walls, were noted as cortex, xylem and sieve element cells entered their respective phases of cell differentiation. The cortical cells expanded in all dimensions, and the interpolation of microtubules diminished or ceased. The sieve elements continued to elongate, and interpolated at a high rate, reaching unusually high densities of microtubules when the cell walls were being thickened. During this period a net increase of 2.0 μm of polymerized microtubule length per min was calculated. Thereafter interpolation ceased and the density of microtubules declined. The same applied to developing xylem except that, because wall-thickening is localized rather than widespread, the rise and subsequent fall in the density of microtubules was less marked.
The data are discussed in relation to the participation of microtubules in wall deposition and to the hypothesis that cortical microtubules arise in discrete zones along the edges of cells.
Different mechanisms in the attachment of cells to native and denatured collagen
Authors: Schor Seth L. , Court Janet 
Published: April 2021

ABSTRACT
The attachment of cells to collagen has been reported previously to require the presence of serum and the particular serum protein involved in this process, variously known as CIG, CAP or fibronectin, has been isolated. This conclusion that cell attachment to collagen requires serum (or more precisely, fibronectin) is based on experiments measuring the kinetics of cell attachment to films of collagen. We have measured the kinetics of attachment of HeLa and PyBHK cells to different collagen-containing substrata under a variety of experimental conditions and present evidence that the serum-dependent mechanism of cell attachment described by others is actually only the case for films of denatured collagen, while cell attachment to native collagen fibres occurs by a different, serum-independent, mechanism. The possible relevance of these findings to cell-matrix interactions in vivo is discussed.
Phenylglyoxal is not a selective inhibitor of phagocytosis
Authors: Schaik Margriet L. J. Van , Weening Rons. , Roos Dirk 
Published: April 2021

ABSTRACT
In 1976, it has been reported that phenylglyoxal (C0H5COCHO) selectively inhibits endo eytosis in phagocytes of rabbit and mouse. We have tested the specificity of this compound by measuring its effect on human neutrophil chemotaxis, respiration and release of lysosomal enzymes. Pretreatment of human neutrophils with 100 µg phenylglyoxal/ml for 30 min at 37 °C resulted in almost complete inhibition of phagocytosis of opsonized zymosan. However, after treatment with phenylglyoxal, spontaneous mobility as well as chemotaxis of these cells towards casein, rosette formation with opsonized zymosan, stimulation of the oxidative metabolism and release of lysosomal enzymes were also severely decreased. Most of these functions were only partially restored by resuspension of the cells in a medium without phenylglyoxal. The intracellular level of ATP was not affected by phenylglyoxal, but the level of reduced glutathione was decreased. We conclude from the inhibitory action of phenylglyoxal on the stimulated oxygen consumption and its reaction with intracellular glutathione that phenylglyoxal does not necessarily act exclusively on the outside of the plasma membrane.
From our studies, it follows that phenylglyoxal is not a specific inhibitor of endo- or exocytosis in human neutrophils. Phenylglyoxal can be used effectively in the bacterial-killing test of phagocytes to inhibit intracellular killing after an initial period of ingestion.
Specific contact-dependent cell-to-cell communication during preconjugant interaction of the ciliate Euplotes crassus
Authors: Luporini Pierangelo , Bracchi Paolo , Esposito Fulvio 
Published: April 2021

ABSTRACT
A system has been developed to study cellular interactions between cells of complementary mating types prior to mating in the ciliate, Euplotes crassus. The presumptive mates were distinguished by using singlet and doublet cells of appropriate mating types in the mixtures. Cells of a given mating type were prelabelled with [3H] leucine and mixed with unlabelled complementary cells. Exchange of [3H]leucine-labelled material from donor to recipient cells was monitored through the various stages of the preconjugant interaction. A label transfer between the mating type complementary cells was detected from the beginning of the visible mating reaction, which occurs after a waiting period from the time of cell mixing and involves ciliary agglutination prior to cell body fusion. Complementary cells which were prevented from physically contacting each other and cells which were not competent to mate appeared unable to take up the labelled material. It is suggested that this material consists of some sub-stance(s) playing an important role in the preconjugant cell-to-cell interactions of E. crassus.
Expression of the transformed phenotype and tumorigenicity in somatic cell hybrids
Authors: Marshall C. J. 
Published: April 2021

ABSTRACT
We have previously shown by examining the anchorage dependence, density-dependent inhibition of growth, LETS protein and microfilament bundles that the transformed phenotype of the parental tumours are suppressed in hybrids between rat embryo fibroblasts (REF) and mouse tumour cells (TA3B). Hybrids between TA3B and Syrian hamster sarcoma cells (BHK-Bi) also show suppression. We now demonstrate that tumorigenicity in nude mice is also suppressed in TA3B × REF and B1 × TA3B hybrids. Tumours arise from the suppressed hybrids by the selective outgrowth of variants with properties different from the majority of cells inoculated. These tumour variants always had an altered cytoskeleton but 1 out of 14 cases retained anchorage-dependent growth. Selection in culture for anchorage-independent growth selected for tumorigenicity. The coordinate suppression of the transformed phenotype and tumorigenicity could be explained by postulating a pleiotropic control mechanism affecting both. However the occasional dissociation of tumorigenicity from anchorage dependence in the variants suggests that the targets for the control mechanism must be different.
Ultraviolet-induced DNA excision repair in human B and T lymphocytes: III. Repair in lymphocytes from chronic lymphocytic leukaemia
Authors: Yew F.-H. , Johnson R. T. 
Published: April 2021

ABSTRACT
There have been conflicting reports about the capacity of lymphocytes from individuals with chronic lymphocytic leukaemia (CLL) to undertake u.v.-induced DNA repair. We have examined repair in CLL cells and in control and age-matched purified B and T lymphocytes by a technique independent of incorporation of radioactive precursor, i.e. by the recovery of normal sedimentation behaviour of nucleoid bodies obtained from these cells by lysis in high salt and non-ionic detergent. Recovery of normal sedimentation is associated with restoration of DNA supercoiling. CLL cells were found to be as sensitive to u.v. and to repair at similar rates as age-matched B controls. They are considerably more sensitive than young B cells and repair less efficiently. Reasons for the reported discrepancies in CLL repair are discussed.
Insulin-induced receptor loss in the cultured human lymphocyte: quantitative morphological perturbations in the cell and plasma membrane
Authors: Gorden Phillip , Carpentier Jean-Louis , Van Obberghen Emmanuel , Barazzone Philippe , Roth Jesse , Orci Lelio 
Published: April 2021

ABSTRACT
When cultured human lymphocytes (IM-9) are exposed to 10−6 M porcine insulin for 6 h, washed, and incubated with 125I-insulin, the ability of the cell to bind the labelled hormone is reduced by a mean of 78 %. Under these experimental conditions that induce insulin-receptor loss in this cell there is a mean 95 % increase in microinvaginations in the plasma membrane revealed by electron microscopy on freeze-fractured replicas of the cell. At the same time, horseradish peroxidase uptake, a marker of endocytosis, is increased in the cells incubated with insulin.
Coupled with our recent EM autoradiographic evidence that labelled insulin is acutely internalized by this cell, these studies are consistent with the possibility that endocytosis represents a mechanism by which receptor is removed from the cell surface.
Freeze-drying methods for the scanning electron-microscopical study of the protozoon Spirostomum ambiguum and the statocyst of the cephalopod mollusc loligo vulgaris
Authors: Boyde A. , Barber V. C. 
Published: April 2021

ABSTRACT
The present study concerns methods of preparing ciliated surfaces for direct examination in the scanning electron microscope.
Air-drying methods provide good results with some ciliated structures but do not always preserve the cilia of ciliated protozoons, although the pellicle is well preserved. Air-drying is not suitable for certain epithelia because considerable shrinkage and tearing occur.
Freeze-drying methods, with or without pre-fixing, are described. These preserve the cilia in the protozoon Spirostomum in a fairly life-like position. There are some differences in the appearance of unfixed and fixed freeze-dried material—for example, the peristomial membranelles are not seen in the unfixed material. Freeze-drying again proved to be a better method of preparing the sensory epithelium lining the statocyst of the cephalopod mollusc Loligo, because it was successful in preventing the distortion due to shrinkage. The number of hair cells, their orientation, and the area covered by the cells was determined for the macula. The crista was found to be asymmetrical.
Extra-chromosomal dna in early stages of oogenesis in Acheta Domesticus
Authors: Cave M. D. , Allen E. R. 
Published: April 2021

ABSTRACT
A large extra-chromosomal DNA body is found in gonial and oocyte nuclei of Acheta domesticus. Somatic cells within the ovary do not contain the DNA body which is limited to the nuclei of gametogenic cells. During early prophase of meiosis this bodyisspherically shaped and intensely Feulgen positive. Electron microscopy shows it to be composed of tightly packed fibrogranular material. The body is formed in the nuclei of premeiotic interphase cells where it first appears as a mass of dense chromatin material located within the nucleolus. In nuclei of early prophase cells the body is closely associated with the nuclear membrane. It increases in size, reaching a maximum in mid-pachytene nuclei. During late pachytene-early diplotene stage of meiosis the tight fibrillar material within the body loosens and takes on a less compact appearance. At the same time large fascicles of RNA-containing material accumulate within and around the DNA body. The amount of RNA material surrounding the body increases as the oocytes proceed into an arrested diplotene stage of development.
Effects of chloramphenicol on growth, size distribution, chlorophyll synthesis and ultrastructure of Euglena Gracilis
Authors: Ben-Shaul Y. , Markus Y. 
Published: April 2021

ABSTRACT
Multiplication of Euglena cells treated by 0-5-1-0 mg/ml chloramphenicol was not disturbed for the first 36 h and inhibition appeared only at later stages.
The mean cell volume of treated dividing cells was decreased, although the initial rise in cell volume, which normally occurred during the first 12 h of incubation, was not prevented. The antibiotic also lowered the chlorophyll content of green dividing cells. In dark-grown cells transferred to light, inhibition of chlorophyll synthesis was immediate but not complete, and was followed by a decreased rate of plastid elongation and thylakoid formation. Our findings suggest that chloramphenicol does not cause the loss of existing pigment and that impaired chlorophyll synthesis is a secondary effect of inhibition of protein synthesis. The results also indicate that the greening process is more sensitive than cell division to the antibiotic.