bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cholesterol in the plasma membrane of uterine epithelial cells: A freeze-fracture cytochemical study with digitonin
Authors: Murphy C. R. , Martin B. 
Published: April 2021

ABSTRACT
Freeze-fracture cytochemistry with digitonin has been used to examine the cholesterol content of the plasma membrane of uterine epithelial cells during the early stages of pregnancy in the rat. Lesions caused by digitonin complexing with cholesterol were seen on both lateral and apical portions of the membrane but tight junctions and desmosomes were lesion-free. Compared with day 1 of pregnancy, lesions on the apical plasma membrane were much more extensive and some were of different morphology on day 6 - the day of blastocyst implantation. We consider mechanisms of lesion formation and interpret the results to indicate a higher content and perhaps a different organization of cholesterol in the apical plasma membrane on day 6 of pregnancy. We also suggest how this increase may occur.
Assembly of 2·5 nm filaments from giardin, a protein associated with cytoskeletal microtubules in Giardia
Authors: Crossley Richard , Holberton David 
Published: April 2021

ABSTRACT
The giardins are a family of ∼30 000 M, structural proteins found in microribbons attached to microtubules in the disc cytoskeleton of Giardia. After examining the solubility of giardins in various agents, a method has been developed to extract these polypeptides and subsequently precipitate them selectively. The giardin chains are soluble in 10 mM-HEPES/EDTA buffer at high pH and low ionic strength, but become insoluble in 10 mM-MES/EDTA buffer at pH 6·7 when the ionic strength is raised above 50 mM salt. By dialysing giardin extracts in turn against dissociating and reassembly buffers, the purification is obtained of a subset of giardin chains identified by sodium dodecyl sulphate/polyacrylamide gel electrophoresis as the cytoskeleton bands 14a, 14b and 15.
The structures forming under assembly conditions are all composed of fine filaments, 2-3 nm in diameter. Filaments after the first cycle of assembly are found in bundles, narrow ribbons of two or three filaments, and large ordered tactoids. Assembly after a second cycle of solubilization yields a more uniform population of long ribbons. Both the tactoids and the second cycle ribbons are transversely banded at the 15 nm interval characteristic of microribbons in the cytoskeleton. Fila-ments in the tactoids are precisely placed at a centre-to-centre separation of 2·5 nm. Other structural features of the tactoids are discussed in relation to the association behaviour and possible dimensions of the giardin molecular subunit.
Cell hybridization and cell agglutination II. enhancement of cell hybridization by polycations
Authors: Matsuya Yutaka , Yamane Isao 
Published: April 2021

ABSTRACT
An efficient technique for hybridization of mammalian cells was developed by combining agglutination by pretreatment with polycations, such as polyarginine, and conventional polyethylene glycol(PEG)-mediated cell fusion. Polyarginine and subsequent PEG treatment resulted in markedly decreased viability in the treated cells, but addition of polyvinyl pyrrolidone or glycerol to the polyarginine prevented this cytotoxicity.
Polyarginine was much more effective than polylysine or polyornithine in inducing hybridization. Other polycations, including polybrene and protamine but not DEAE-dextran, were also active in inducing hybridization.
The condition of the cells at the time of polycation treatment was an important factor in the enhancement of hybridization.
The enhancement of hybridization of cells in monolayer incubated for 2 h was much higher than that of cells incubated for 24 h. These findings suggest that polycations do not necessarily operate by agglutinating cells. The mechanism of polycation-enhanced cell hybridization is discussed.
Genesis of cilia and microvilli of rat nasal epithelia during pre-natal development I. Olfactory epithelium, qualitative studies *
Authors: Menco Bert Ph. M. , Farbman Albert I. 
Published: April 2021

ABSTRACT
Rat foetuses from intra-uterine days E13 through E22 (day before parturition) and adults were used for a qualitative electron-microscopic investigation of the development of ciliated/microvilldus surfaces of the olfactory epithelium. In the E13 and most of the E14 embryos the epithelial surface is not yet characteristically olfactory. Apical cell profiles show primary cilia. These can arise at the epithelial surface or below. From E14 onwards the epithelial surface acquires olfactory characteristics. Dendritic endings of the olfactory receptor cells can be found amidst microvillous profiles of supporting cells. Either cell type may bear primary cilia. F rom E16 onwards the receptor cells sprout multiple olfactory cilia, but cells with primary cilia are found throughout pre-natal development. These primary cilia are, at least for a while, retained during the formation of the secondary cilia. Primary cilia always have distinct necklaces at their base. Otherwise, especially with respect to their tips, their morphology can vary. Originally they have expanded tips (up to E14) ; later on such wide tips are no longer encountered (E16 and E17). Primary cilia of receptor cells never have wide tips. Appreciable numbers of endings with tapering olfactory cilia are discerned around E18 and especially E19.
Throughout pre-natal development posterior/superior parts of the septal olfactory epithelium are more precocious than anterior/inferior parts, in particular in the region of transition with the respiratory epithelium. This advance in development includes total densities of dendritic endings of olfactory receptor cells, densities of multiciliated endings alone and lengths of supporting cell microvilli. This difference is discussed with respect to the topography of the olfactory epithelial surface in adult animals.
In addition to the systematic topographic variation, a number of more local, apparently not-systematically distributed, topographic variations present during development are described. Most of these also occur in adult animals and they include heterogeneity in length of supporting cell microvilli and the presence of patches of supporting cells with rounded apical protuberances, of patches displaying dendrites with polyaxonemes rather than individual cilia and of scattered atypical cells (neither typical olfactory receptor nor olfactory supporting cells). At their surfaces such atypical cells can resemble inner-ear hair cells. Relative to olfactory receptor and supporting cells there are only very few atypical cells.
Finally, we describe some differences in the appearance of membrane surfaces of olfactory cilia and supporting cell microvilli as a function of development.
Acinar structure and membrane regionalization as a prerequisite for exocrine secretion in the rat submandibular gland
Authors: Segawa Akihisa , Sahara Noriyuki , Suzuki Kazuo , Yamashina Shohei 
Published: April 2021

ABSTRACT
The significance of glandular organization in exocrine secretion was examined by analysing the functional and morphological features of the dissociated rat submandibular gland with special reference to the acinar structure and luminal specialization. The digestion of the gland with collagenase (C preparation) produced relatively large cellular masses having well-preserved acinar structures. When EGTA and the proteolytic enzyme Dispase were added to the C preparation (CED preparation), the gland was dissociated into small cellular aggregates in which the acinar structure disintegrated. Upon stimulation with either isoproterenol or dibutyryl cyclic AMP, a large amount of peroxidase, one of the secretory products of the rat submandibular gland, was released from C-treated cells, while discharged peroxidase was greatly reduced after the CED preparation was used. Measurements of dye exclusion, oxygen consumption, protein synthetic activity and receptor binding, as well as ultrastructural features and the absence of inhibitory effects of EGTA and Dispase, suggested that the reduced secretory response of CED-treated cells was not attributable to cellular death, denaturation of receptors or the inhibitory effects of EGTA and Dispase. When the localization of dipeptidyl aminopeptidase IV was surveyed by both enzyme histochemistry and immunohistochemistry, the luminal plasma membrane was the exclusive site for the reaction in C-treated cells as well as intact acini, whereas the entire cell surface was reaction-positive in CED-treated cells. In addition, the luminal microfilament system and tight junctions, as revealed by nitrobenz-oxadiazole-phallacidin staining and freeze-replica studies, respectively, were well-preserved in the C-treated cells, but considerably disorganized in the CED-treated cells. All these results strongly suggest that : (1) luminal specialization plays an important role in exocrine secretion ; and (2) normal acinar arrangement provides the luminal specialization.
The oncogene of bav-3 as a mutagen
Authors: Lukash L. L. , Varshaver N. B. , Buzhiyevskaya T. I. , Shapiro N. I. 
Published: April 2021

ABSTRACT
We studied the mutagenic and carcinogenic effects on mammalian cells of two EcoRl DNA fragments of bovine adenovirus type3 (BAV-3) integrated into the pBR325 plasmid. Fragment D located between 3·6 and 19·7 map units, contains the viral oncogene, fragment C, located between 44·3 and 63-7 map units, has no oncogenic activity. The BAV-3 oncogene was shown to increase significantly the frequency of 6-mercaptopurine (6MP)-resistant mutants in Chinese hamster calls. Fragment C, pBR325 without viral sequences and DNA from normal Syrian hamster cells did not have any mutagenic effect.
We also looked at the combined action of the viral DNA fragments and the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA), which enhances the transforming effect of carcinogens. TPA was shown to increase the mutant yield on exposure to the viral oncogene but not to induce mutagenic activity in those types of DNA that are unable to transform cells. Probably TPA does not affect the initiation of the mutation process, but acts on later stages just as it affects carcinogenic activity. Thus the results obtained confirm the existence of parallelism between the mutagenic and transforming effects of viral DNA and show that both activities are mapped in the same region of viral DNA - its oncogene.
Studies on the endogenous galactose-binding lectin during early development of the embryo of Xenopus laevis
Authors: Harris Harriet , Zalik Sara E. 
Published: April 2021

ABSTRACT
Embryos of the frog Xenopus laevis at cleavage, blastula, gastrula and neurula stages contain a galactose-specific lectin. Extracts of gastrula embryos show the highest specific activity for this lectin compared to the other stages. Haemagglutinating activity of crude extracts is inhibited by lactose, α-galactose, β-galactose, αGal(l→4)βGal, βGal(l→3) αGalNAc, βGal(l→3) βGlcNAc, βGal (1 → 4)/5GlcNAc, and most effectively by the disaccharide αGal(l→3) βGal. Lectin from all stages was purified by absorption to galactose-linked immunoadsorbent or by affinity chromatography on a column of p-aminophenyl-β-D-lactoside coupled to Sepharose 4B. In order to identify a single lectin band under reducing conditions in sodium dodecyl sulphate/polyacrylamide electrophoresis SDS/PAGE, it was necessary to treat aqueous suspensions of the purified lectin with chloroform/methanol (2:1, v/v). The lectin remained in the aqueous layer and gave rise on SDS/PAGE to a distinct band of 65 500 ± 2780 molecular weight. Aqueous suspensions of the purified lectin that were not subjected to extraction with chloroform/methanol gave rise to several bands. Isoelectric focussing of the purified lectin resulted in two bands that separated at pl 4·3 and 4·5. In aqueous solution in the presence of lactose the chloroform/methanol-treated lectin appears to be an aggregate of apparent molecular weight of 375 000; the non-treated lectin under the same conditions has an apparent molecular weight of 490000.
Tmb-8 inhibits respiration and cyclic gmp formation in Dictyostelium discoideum
Authors: Finner G. N. Europe , Tillinghast H. S. , McROBBIE S. J. , Newell P. C. 
Published: April 2021

ABSTRACT
The putative inhibitor of intracellular calcium mobilization, TMB-8, was found to be a powerful inhibitor of respiration in amoebae of Dictyostelium discoideum. Consequently, the previously reported effects of this drug on cyclic GMP formation induced by chemoattractants were reassessed. It was found that TMB-8 abolished both folate and cyclic AMP-mediated accumulation of cyclic GMP in D. discoideum amoebae and that addition of Ca2+ completely restored this response. Tire Ca2+ chelating agent EGTA did not mimic the effect of TMB-8. The effect on cyclic GMP formation, however, occurred only at a concentration of TMB-8 that was ten times that causing maximal inhibition of respiration, and inhibition of cyclic GMP formation was completely restored by addition of excess Ca2+, whereas inhibition of respiration was only partially restored. The data suggest that TMB-8 has more than one inhibitory action, and because of the differential sensitivity of respiration and cyclic GMP formation to this drug, and the differential antagonism of excess Ca2+, we conclude that the effect of TMB-8 on the cyclic GMP response is probably due to its effect on Ca2+ mobilization, rather than indirectly via its effects on respiration. However, we advise caution in interpretation of data using this inhibitor where the responses measured are prolonged, are energy-requiring or are not freely reversible by excess Ca2+.
Visualization of changes in ciliary tip configuration caused by sliding displacement of microtubules in macrocilia of the ctenophore Beroë
Authors: Tamm Sidney L. , Tamm Signhild 
Published: April 2021

ABSTRACT
Macrocilia from the lips of the ctenophore Benë consist of multiple rows of ciliary axonemes surrounded by a common membrane, with a giant capping structure at the tip. The cap is formed by extensions of the A and central-pair microtubules, which are bound together by electron-dense material into a pointed projection about l·5 μm long. The tip undergoes visible changes in configuration during the beat cycle of macrocilia. In the rest position at the end of the effective stroke (+30° total bend angle), there is no displacement between the tips of the axonemes, and the capping structure points straight into the stomach cavity. In the sigmoid arrest position at the end of the recovery stroke (–60° total bend angle), the tip of the macrocilium is hook-shaped and points toward the stomach in the direction of the subsequent effective stroke. This change in tip configuration is caused by sliding displacement of microtubules that are bound together at their distal ends. Electron microscopy and two-dimensional models show that the singlet microtubule cap acts as if it were hinged to the ends of the axonemes and tilted to absorb the microtubule displacement that occurs during the recovery stroke. The straight and hooked shapes of the tip are thought to help the ctenophore ingest prey.
Cholesterol distribution in cells of the stria vascularis of the mammalian cochlea and some effects of ototoxic diuretics
Authors: Forge Andrew 
Published: April 2021

ABSTRACT
The distribution of cholesterol in cells of the stria vascularis of guinea pigs and gerbils has been investigated at the ultrastructural level by incubation of tissue in filipin, followed by freeze-fracture. Verification of results has been sought by using tomatin. It is shown that in the cell body region of the marginal cells, the apical and lateral membranes reacted intensely with both agents, but the membranes of the basal processes of the marginal cells did not respond significantly to either filipin or tomatin. On basal cell membranes, filipin—cholesterol complexes were present at a high density, even within the strands of the tight-junctional network of these cells and occasionally within the gap-junctional areas also. Complexes were present on intermediate cell membranes at a lower density than on other plasma membranes that showed a positive response. Tissue from animals that had received an ototoxic diuretic, either ethacrynic acid or furosemide, was characterized by the appearance of membrane regions with closely clustered filipin complexes, suggesting some change in cell membrane structure. At an early stage following diuretic administration, such clusters were particularly noticeable on the membranes of intermediate cells. As intercellular spaces enlarged in response to the effects of diuretics, vesicles released into the extracellular spaces appeared to be cholesterol-enriched. The results are discussed in relation to known features of the structure and function of cells in the normal stria vascularis and of the changes that follow from acute diuretic ototoxicity.
Xenopus marginal band disassembly by calcium-activated cytoplasmic factors
Authors: Gambino John , Ross Margery J. , Weatherbee James A. , Gavin R. H. , Eckhardt Ronald A. 
Published: April 2021

ABSTRACT
The marginal band microtubules of isolated Xenopus erythrocyte cytoskeletons possess the stability properties of non-steady-state microtubules. They are unperturbed by low temperatures, a variety of microtubule inhibitors, hypotonic treatment and the direct action of calcium. These microtubules can be rapidly depolymerized by erythrocyte lysis in the presence of calcium or by exposure of cytoskeletons obtained and washed in calcium-free media to calcium-containing supernatants of other cell lysates. Thus, marginal band microtubules are calcium-sensitive only in the presence of cytoplasm. The calcium-activated disassembly of the marginal band does not appear to be the result of general or tubulin-specific proteolysis and is prevented by the calmodulin inhibitor, trifluoperazine. On sodium dodecyl sulphate/polyacrylamide gels, samples of calcium-induced, marginal band disassembled cytoskeletons are always tubulin-depleted and also possess a new high molecular weight polypeptide doublet that is believed to constitute stable partial degradation products of spectrin. In the presence of calcium, addition of calmodulin and ATP to cytoskeletons washed free of cytoplasm does not initiate marginal band disassembly. Therefore, if calmodulin mediates marginal band disassembly, it requires cytoplasmic binding proteins or cytoplasmic cofactors.
Intracellular positional control of survival or degeneration of nuclei during conjugation in Paramecium caudatum
Authors: Yanagi Akira , Hiwatashi Koichi 
Published: April 2021

ABSTRACT
The survival or degeneration of nuclei produced after meiosis in Paramecium caudatum depends upon their position in the cytoplasm. The surviving nucleus lies in the paroral region, which is the region around the cytostome. In this study, this was confirmed by quantitative measurements of the location of surviving nuclei in both stained and living conjugating cells. Observation of nuclear behaviour in living cells shows that there is an active mechanism for localizing one of the four meiotic products into the paroral region after the second meiotic division. When this mechanism is inhibited by vinblastine, none of the four nuclei gets into the paroral region and all of them become pycnotic, before degenerating. The results show that migration into the paroral region is essential for survival of the nucleus and that microtubules are involved in this nuclear migration.
Ultrastructural localization of nucleolar material by a simple silver staining technique devised for plant cells
Authors: Sato Seiichi 
Published: April 2021

ABSTRACT
A simple silver staining technique for use at the electron microscopic level, consisting only of treatment with aqueous silver nitrate at high temperature for a prolonged time, was applied to thin sections of root tip meristems of Vicia faba. This technique contrasted the fibrillar component and the granular component in interphase nucleoli as a reflection of the degree of packing. In contrast, silver impregnation was scarcely discerned in chromosomes. A comparison of silver staining and conventional double staining showed that the fibrillar centres did not always respond positively to silver. During the course from metaphase to late anaphase the nucleolus organizing secondary constriction was always seen as a heavily impregnated region and the electron density of the cytoplasm increased, probably due to dispersed nucleolar material. An argyrophilic substance began to accumulate on chromosomes in late anaphase. In the beginning of telophase a uniformly impregnated nucleolus was formed at the secondary constriction. It is concluded from these results that argyrophilic substance is associated with RNA-containing structures rather than DNA-containing structures. The silver staining technique presented here is very convenient and favourable, especially for plant cells, to detect specifically the nucleolus organizing region and to survey the nucleolar material during mitosis at the electron microscopic level.
Differences in the uptake of modified low density lipoproteins by tissue cultured endothelial cells
Authors: Gaffney J. , West D. , Arnold F. , Sattar A. , Kumar S. 
Published: April 2021

ABSTRACT
Acetylated low density lipoprotein (Ac-LDL) is taken up by bovine aortic and adrenal capillary cells but not by brain capillary cells. This indicates that the uptake of Ac-LDL is not a feature of all types of endothelial cell. A quantitative examination of lipoprotein uptake by flow cytometry showed cells in G2M took up 45% more Ac-LDL than those in G1S. Compared with confluent cultures, sub-confluent bovine aortic cells took up three times as much LDL but Ac-LDL uptake was increased by only 34%. This indicates that the Ac-LDL receptor is not down-regulated to the same extent as that for LDL.
The kinetic polarities of spindle microtubules in vivo, in crane-fly spermatocytes. ii. kinetochore microtubules in non-treated spindles
Authors: Czaban B. Barbara , Forer Arthur 
Published: April 2021

ABSTRACT
We determined the kinetic polarities of chromosomal spindle fibre microtubules in vivo: either the kinetochore or pole ends of chromosomal spindle fibres were irradiated with near-ultraviolet light to prevent depolymerization by colcemid. Irradiations began either just before or just after colcemid addition; cells were continually irradiated and continuously immersed in colcemid. Irradiations of kinetochore ends of chromosomal spindle fibres prevented depolymerization; irradiations of pole ends did not. Therefore, since colcemid acts by binding to the ‘on’ (assembly) ends of microtubules, the on ends of chromosomal spindle fibre microtubules are at the kinetochores. That is, in untreated chromosomal spindle fibres in vivo tubulin monomers add to kinetochore microtubules at the kinetochore ends.
Tubulin diffused from the irradiation sites: irradiations of the cytoplasm sometimes prevented depolymerization of chromosomal spindle fibres. Prevention of chromosomal spindle fibre depolymerization was dependent on the distance of the irradiated region from the nearest chromosome; the longer the distance the less likely was it that the irradiation prevented depolymerization. On the other hand, prevention of chromosomal spindle fibre depolymerization was not dependent on the distance from the irradiated spot to the nearer pole. This analysis, too, we argue, strongly suggests that the kinetochore ends of the chromosomal spindle fibres are the on ends.