bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spheroplasts of Lactobacillus casei and the cellular distribution of bactoprenol
Authors: Barker D. C. , Thorne Kareen J. I. 
Published: April 2021

ABSTRACT
Spheroplasts of L. casei were prepared by the simultaneous action of trypsin and lysozymc in the presence of EDTA and 20 % sucrose. Electron microscopy of thin sections of cells during the formation of spheroplasts showed that the spheroplasts emerged from the cell wall through a weak point at one end of the cell. Electron microscopy of negatively stained preparations showed that the structure of spheroplast membranes obtained by disruption in hypotonic medium varied according to the nature of the hypotonic medium used. Disruption in water gave small, delicate membrane fragments; disruption in 0·1 M tris-Cl gave large pieces with tubulo-vesicular attachments. The effects of Mg2+ and EDTA were also investigated. Bacto-prenol, the C55 isoprenoid alcohol concerned in cell wall biosynthesis, was located by growing L. casei in [14C] mevalonic acid. Over 90% of the cellular bactoprenol was found in the sphero-plast membrane when this was obtained with 0·1 M tris-Cl, but only 42% when the sphero-plasts were burst in water. It is suggested that the missing bactoprenol may be solubilized with the membranes of mesosomal orgin, and that bactoprenol is therefore a component of both plasma and mesosomal membranes.
Germination of stress-tolerant Eucalyptus pollen
Authors: Heslop-Harrison J. , Heslop-Harrison Y. 
Published: April 2021

ABSTRACT
Earlier reports have indicated that the pollen of Eucalyptus is mechanically robust and unusually resistant to the osmotic stress imposed by immersion in water. We have investigated some of the features of the germination mechanism in the pollen of E. rhodantha with a view to clarifying the role of pollen-wall specializations in determining this resistance. Cultured in vitro, the pollen showed erratic germination, with a scatter of germination times up to 24 h. This was associated with variation between individual grains in the rate of hydration and dispersal of the pectins of the oncus, the thickened outer component of the intine present at each aperture. The oncus is itself differentiated, with a refractive outer layer lying within a sporopollenin operculum and itself overlying the protein-bearing layer of the intine. The outer layer, interpreted as a compacted pectin, undergoes only slow dissolution in aqueous media after the lifting of the operculum, and it is this that apparently protects the grain from the effects of short-term osmotic stress. The rate of dissolution varies between grains, possibly as a consequence of minor differences in developmental rate in the final stages of differentiation in the anther, and this contributes to the wider scatter of germination times. The dehydrated pollen gave one-third of the potential germination after 24 h exposure to 60°C, and a small proportion survived 24 h at 70°C. This degree of heat tolerance must primarily reflect properties of the protoplast of the vegetative cell, not examined in the present study; but the wall specializations may well provide a guard against extreme desiccation, and it is noteworthy that the function of the germination mechanism is not prejudiced by exposure to high temperatures.
Manipulating chromosome structure and metaphase status with ultraviolet light and repair synthesis inhibitors
Authors: Mullinger Ann M. , Johnson Robert T. 
Published: April 2021

ABSTRACT
DNA repair occurs in metaphase-arrested cells in response to ultraviolet irradiation. In the presence of the repair synthesis inhibitors hydroxyurea and 1-β-D-arabinofuranosylcytosine the chromosomes of such cells, as seen in Carnoy-fixed preparations, are decondensed. The extent of decondensation is related to both the u.v. dose and the duration of incubation in the presence of inhibitors. For any particular cell type there is a reasonable correlation between the amount of decondensation and the number of single-strand DNA breaks generated by the repair process under the same inhibitory conditions, though the chromosome changes continue after the number of single-strand breaks has reached a plateau.
The dose response of chromosome decondensation varies between different cell types but is in general correlated with differences in levels of single-strand breaks accumulated under comparable inhibitory conditions. Decondensation can be detected after 0·5 Jm−2 in repair-competent human cells. In human cells defective in excision repair there is much less chromosome decondensation in response to the same u.v. dose and time of repair inhibition. However, a simian virus 40-transformed muntjac cell displays pronounced chromosome decondensation but has limited incision ability.
Both chromosome decondensation and single-strand break accumulation in the presence of inhibitors are reversed when DNA precursors are provided, but reversal after higher u.v. doses and longer periods of incubation leads to recondensed chromosomes that are fragmented. Elution of the DNA from such cells through polycarbonate filters under non-denaturing conditions reveals that double-strand DNA breaks are generated during the period of incubation with inhibitors.
Although the chromosomes of repair-inhibited metaphase cells are decondensed in fixed preparations, their morphology appears normal in intact cells. The cells also retain a capacity to induce prematurely condensed chromosomes (PCC) when fused with interphase cells: compared with control mitotic cells, the speed of induction is sometimes reduced but the final amount of PCC produced is similar.
Three-dimensional behaviour of mitochondria during cell division and germ tube formation in the dimorphic yeast Candida albicans
Authors: Tanaka Kenji , Kanbe Toshio , Kuroiwa Tsuneyoshi 
Published: April 2021

ABSTRACT
This study was done to correlate mitochondrial behaviour with nuclear behaviour and cell division as well as with the germ tube formation in the dimorphic yeast Candida albicans. Threedimensional reconstruction of electron micrographs of serially sectioned cells of the three strains was used to determine the morphological and quantitative relationships between the structures. The results suggested that at the time of entry into the bud a few mitochondria fused into a single giant one, which fragmented during mitosis and resumed a single giant form before cytokinesis, and was then partitioned into two parts. This tendency was also shown during germ tube formation. Quantitative analysis has established that growth of organelles such as the nucleus and mitochondria closely followed total cell growth, the ratio of organelle volume to total cell volume being held relatively constant.
Antigenic heterogeneity of breast cell lines detected by monoclonal antibodies and its relationship with the cell cycle
Authors: Edwards Paul A. W. , Skilton Robert A. , Payne Andrew W. R. , Ormerod Michael G. 
Published: April 2021

ABSTRACT
Established cell lines were stained by immunofluorescence with four monoclonal antibodies to study the phenomenon of antigenic heterogeneity and its possible relation to the cell cycle. Five cell lines thought to be of breast origin, MCF-7, ZR-75–1, T47D, MDA-MB-231 and HBL-100, were stained with three monoclonal antibodies (LICR-LON-M8, LICR-LON-M18, LICR-LON-M24) that each stain a distinct subset of normal breast epithelial cells, i.e. demonstrate antigenic heterogeneity in normal breast epithelial cells. Contrasting monoclonal antibodies LICR-LON-FIB75 and LICR-LON-FIB86 to homogeneously expressed antigens were also used.
For the antibodies demonstrating heterogeneity distinct positive and negative fractions were not seen by flow cytometry; the intensity of fluorescence varied continuously from background to a hundred times stronger than background. Fluorescent DNA staining showed no obvious relation between antigen expression and the cell cycle. The essentially constant proportion of cells of a given antigenic phenotype in the various phases suggests that these antibodies do not distinguish a phenotype associated with a distinct proliferating population of cells.
Cell-cycle-specific induction of quiescence achieved by limited inhibition of protein synthesis: Counteractive effect of addition of purified growth factors
Authors: Larsson Olle , Zetterberg Anders , Engstrom Wilhelm 
Published: April 2021

ABSTRACT
We have previously shown that Swiss 3T3 cells located in the first part of G| (post-mitotic G1 cells younger than 4·0 h or Giprn cells) were arrested after 9–10 h in the cell cycle by a short (1 -8 h) exposure to serum-free medium or by a short (2–4 h) exposure to low doses of the protein synthesis inhibitor cycloheximide (CH). Kinetic data indicate that such Giprn cells rapidly return to G1 during this brief treatment and thereafter require a preparatory period of 8h before continuing to G1
Cells older than 4h, i.e. cells in mid or late G1 are already committed to DNA synthesis (presynthesis or G1 ps cells). These cells as well as S and G2 cells were consequently unaffected by the brief serum starvation or the brief treatment with cycloheximide.
In the present paper we show that the 10-h intermitotic delay that follows a 1–2 h exposure to serum-free medium can be completely counteracted by the presence of any one of the purified growth factors, epidermal growth factor (EGF), insulin or platelet-derived growth factor (PDGF). In contrast, the intermitotic delay following a longer exposure (8 h) to serum-free medium could no longer be counteracted by EGF or insulin. However, PDGF was still active in this respect.
Most interestingly, the 12h gross intermitotic delay induced by a 4h exposure to CH could be efficiently counteracted by EGF, PDGF or insulin. However, this effect on CH-treated cells could be counteracted by the growth factor only in the presence of 10% serum. This indicates the existence of a cooperative effect between PDGF, EGF or insulin and an unidentified serum factor.
The effects on the cell cycle time of brief serum starvation and exposure to CH were compared with the effects on rate of protein synthesis and degradation. Although the effects of serum starvation on protein synthesis and degradation were found to be partially normalized by growth factors, we suggest that growth factors prevent cells from leaving the cell cycle by another mechanism and not merely by affecting the level of overall protein accumulation.
Glycogen metabolism and the nuclear envelope-annulate lamella system in the early chick embryo
Authors: Eyal-Giladi Hefzibah , Feinstein Naomi , Friedlander Michael , Raveh Dina 
Published: April 2021

ABSTRACT
The intracellular sites of glycogen degradation in the mid to late uterine chick embryo were determined by cytochemical localization of glucose-6-phosphatase at the ultrastructural level. Enzyme activity was found between the two membranes of the nuclear envelope, in the annulate lamellae and in specialized glycogen-containing membrane scrolls. Annulate lamellae and glycogen scrolls were most frequent during the stages of intensive glycogen degradation. Annulate lamellae appear to be formed from the nuclear envelope. During the early post-laying stages annulate lamellae disappeared and were replaced by endoplasmic reticulum that appeared initially in scroll-like formations.
Behaviour of neutrophil leucocytes in uniform concentrations of chemotactic factors: Contraction waves, cell polarity and persistence
Authors: Shields James M. , Haston Wendy S. 
Published: April 2021

ABSTRACT
The essential component of any hypothesis of random or directed cell movement is the mechanism of cell polarity. In this paper we describe the polar behaviour of human neutrophil leucocytes in uniform concentrations of chemotactic factors both in suspension and while moving across surfaces. Neutrophils exposed to uniform concentrations of chemotactic factors in suspension around the dissociation constant (Kd) for the receptor rapidly become distinctly bipolar; neutrophils exposed to supraoptimal uniform concentrations (100-foldKd) of chemotactic factors in suspension, although morphologically active, never reached the same degree of polarity as cells in optimal concentrations. These differences in polarity were shown to be the direct result of equatorial contraction waves stimulated on the cell surface by interaction with chemotactic factors. In optimal concentrations of chemotactic factors, contraction waves were initiated from one region of the cell, whereas in supraoptimal concentrations of chemotactic factors contraction waves emanated from all areas of the cell surface. Asymmetry in the distribution of surface receptors for Fc and C3b were observed in neutrophils polarized in uniform concentrations of chemotactic factor. In neutrophils, motile but not well polarized (in 10-6 M-jV-formylmethionyl-leucyl-phenylalanine (fMLP), receptors were uniformly distributed. In neutrophils polarized in concentrations of fMLP near the for the receptor (10-8 M) receptors for C3b and Fc were localized in the anterior region of the moving cell.
The link between contraction waves, cell polarity and receptor redistribution and their initiation by chemotactic peptides is discussed in the context of neutrophil locomotion and response to chemical signals.
Immunofluorescence microscopy of microtubules in intact cell lineages of the moss, Physcomitrella patens: I. normal and cipc-treated tip cells
Authors: Doonan John H. , Cove David J. , Lloyd Clive W. 
Published: April 2021

ABSTRACT
Monoclonal antibodies to yeast tubulin have been used to visualize the distribution of microtubules in the intact filamentous protonemata of the moss Physcomitrella patens. Protonemata were prepared for immunofluorescence by fixation in formaldehyde and cells were made permeable with Driselase. Extensive cell files were preserved by ‘blotting’ the moss onto glutaraldehydederi vatized coverslips. Problems due to fluorescence from chloroplasts were obviated by extraction with dimethyl sulphoxide and the non-ionic detergent, Nonidet NP4O. These improvements allowed us to determine that microtubules were present throughout the cell cycle in the apical dome of caulonemal tip cells, that there was a pronounced association of microtubules with the nucleus, that ‘astral’ microtubules were associated with the mitotic spindle and during anaphase may be involved in reorientation of the spindle before an oblique cytokinesis in caulonemata and that the cytokinetic phragmoplast appeared identical to the structure described for higher plants.
Microtubules appeared to converge at the very tip of apical caulonemal cells and this was studied further by treating cells with CIPC - a drug that is known to produce multiple microtubuleorganizing centres — and which here produces multiple foci for microtubules at the tip.
These observations emphasize the involvement of microtubules in tip growth, alignment of the cell plate and nuclear migration - processes that are fundamental to the morphogenesis of filamentous organisms.
X chromosome inactivation during induced differentiation of a female mouse embryonal carcinoma cell line
Authors: Paterno Gary D. , McBurney Michael W. 
Published: April 2021

ABSTRACT
P10 is a line of embryonal carcinoma cells with a euploid female karyotype. By making use of variant alleles of X-linked genes and of cytogenetic procedures, we have previously shown that the P10 cells have two genetically active X chromosomes. We show here that P10 cells rapidly differentiate into a cell type resembling extraembryonic endoderm when cultured in the presence of retinoic acid. This differentiation is accompanied by X chromosome inactivation as determined by the appearance of a late-replicating X chromosome. Analysis of the X-linked variant alleles indicated that the P10-derived endoderm did not preferentially inactivate paternally derived X chromosomes. This result is in contrast to the situation in normal extraembryonic endoderm, and suggests that the X inactivation process in differentiating P10 cultures resembles that which occurs in normal embryonic rather than extraembryonic tissues.
Thylakoid formation from coiled lamellar bodies during carposporogenesis in Faucheocolax attenuata setch. (rhodophyta, rhodymeniales)
Authors: Delivopoulos Stylianos G. , Kugrens Paul 
Published: April 2021

ABSTRACT
Chloroplast development during carposporogenesis in the parasitic red alga Faucheocolax attenuata Setch. was studied by electron microscopy. Proplastids are usually found in the peripheral cytoplasm of young carpospores and are characterized by the presence of portions of a peripheral thylakoid and coiled lamellar bodies that range in size up to 0·5μm. One type of coiled lamellar body occurs in the peripheral region of the proplastid and is continuous with the peripheral thylakoid, while the other type is found in the central portion of the stroma. These coiled lamellae separate and expand, adding membranes to both thylakoid systems, thereby functioning as thylakoid-forming bodies. As each coiled lamella unravels, it forms an undulated double-membraned structure having the same width as a thylakoid. After substantial expansion, the developing thylakoids begin to straighten and assume a parallel orientation to each other, thus becoming mature thylakoids. Small coiled lamellae often persist in mature carpospore chloroplasts, and are utilized in additional thylakoid formation during carpospore germination.
Microtubules are at the tips of root hairs and form helical patterns corresponding to inner wall fibrils
Authors: Lloyd Clive W. , Wells Brian 
Published: April 2021

ABSTRACT
Root hairs have sometimes provided contradictory evidence for microtubule/microfibril parallelism. This tissue was re-examined using optimized conditions for the fixation, before immunofluorescence, of root hairs. In phosphate buffer, microtubules did not enter the apical tip of radish root hairs and were clearly fragmented. However, in an osmotically adjusted microtubule-stabilizing buffer, microtubules were observed within the apical dome and appeared unfragmented. Microtubules are not, therefore, absent from the region where new cell wall is presumed to be generated during tip growth. A spiralling of microtubules was seen at the apices of onion root hairs.
Using shadow-cast preparations of macerated radish root hairs, it was confirmed that steeply helical microtubules matched the texture of the inner wall. In onion, the 45° microtubular helices are accompanied by similarly wound inner wall fibrils.
Results do not support the view that microtubules are not involved in the oriented deposition of fibrils in root hairs. Instead, they are interpreted in terms of a flexible helical cytoskeleton, which is capable of changing its pitch but is sensitive to fixation conditions.
Use of aqueous two-phase partition to detect cell surface changes during growth of Dictyostelium discoideum
Authors: Sharpe Paul T. , Watts D. J. 
Published: April 2021

ABSTRACT
Changes in the cell surface properties of amoebae of Dictyostelium discoideum during growth in different culture conditions have been studied by aqueous two-phase partitioning on a thin-layer countercurrent distribution apparatus. Changes in cell surface properties were not dependent on the source of nutrients but only on cell density. There was a progressive increase in cell surface hydrophobicity with cell density in both axenic cultures and cultures grown with a bacterial substrate. It is proposed that it is these cell-density-related surface changes that account for the ability of amoebae grown in different conditions to sort out during subsequent development in a manner related to cell fate.
Flow cytometer study of anterior-like cells in Dictyostelium discoideum
Authors: Voet Ludwig , Krefft Marianne , BrÜderlein Martina , Williams Keith L. 
Published: April 2021

ABSTRACT
The Dictyostelium discoideum asexual fruiting body consists of spores, stalk and basal disk cells. Recently, a fourth cell class has been proposed. It has been suggested that these cells originate from anterior-like cells that remain undifferentiated. Anterior-like cells are randomly distributed among prespore cells in the posterior part of the slug. Here monoclonal antibodies that recognize the surface of prespore cells (MUD1), and spores (MUD3) are used in a quantitative flow cytometer assay to demonstrate that this fourth cell class does not exist in the mature fruiting body. However, the tip cells are slow to differentiate, and hence immature fruiting bodies contain a small population of undifferentiated tip cells. We confirm that anterior-like cells represent a large percentage of the nonprespore cell population in the slug. In this report we were unable to distinguish these anterior-like cells from prestalk cells on the basis of size or monoclonal antibody staining.
Tetrazolium salt and electron-microscopic studies of cellular degeneration and necrosis in the interdigital areas of the developing chick limb
Authors: Hammar S. P. , Mottet N. K. 
Published: April 2021

ABSTRACT
Cellular degeneration and necrosis were studied in the interdigital areas of developing hind limb buds of normal chick embryos by means of enzyme-specific tetrazolium salts and electron microscopy.
Using succinic acid as a substrate and the tetrazolium salt, nitro blue tetrazolium, succinate dehydrogenase was specifically demonstrated via a colour reaction in which degenerating and necrotic cells—those with no enzyme activity—did not stain, while those with enzyme activity stained deeply blue-black.The interdigital cells exhibited near absent levels of succinate dehy-drogenase as early as stage 26–27, one to two days prior to when morphological evidence of degeneration and necrosis was present. It was postulated that the mechanism of cell death resulted from decreased activity and/or loss of strategic cellular enzymes such as succinate dehydrogenase, with a subsequent fall in the cellular adenosine triphosphate (ATP) level and a resultant compromise in vital cellular processes, eventually leading to cell death. The evidence indicated that ‘biochemical degeneration’ occurred prior to morphological changes in cells.
The ultrastructural events of degenerating and necrotic cells were also studied. Most ‘dying’ cells observed had already been phagocytosed and were observedin various stages of degenera-tion. The degenerating cells exhibited both nuclear and cytoplasmic changes. There was evidence of active intracellular digestion within the phagocytes. Numerous lysosomes were observed within these cells and some appeared fused with the digestive vacuole’s membranes.The origin of the phagocytes was not determined.
No definite information was obtained concerning the utility of cellular degeneration and necrosis in the interdigital areas of the hind limb buds. It appeared to be at least partially causal in separation of the digits.