bluuebunny/crossref_metadata_2025 huggingface dataset:
A gradual decrease in nucleolar size with the maturation of columnar epithelial cells in the adult rat intestine under normal and various experimental conditions
Authors: Altmann G. G.
Published: April 2021

The columnar cells, which form over 90% of the epithelium in the small intestine, undergo rapid and continuous renewal and maturation. Samples from duodenum, jejunum, upper, mid- and terminal ileum of young male rats were processed for histology. The average maximal nucleolar area was determined in 10-cell-wide bands of the basal, mid and upper levels of crypts and villi, respectively, by image analysis; in’the duodenum, it was 2·8, 2·1, 1·7, 1’5, 1·3 and 0·8 (in μm2) in the respective epithelial levels from crypt base to villus top. Although villus size jlecreased by 68% from duodenum to terminal ileum, nucleolar area was similar at each respective epithelial level along the intestine. This indicated that nucleolar size was related to cell maturity, rather than to the size of epithelium. In other groups of rats, the duodenum was examined after administering specific inhibitors. Methotrexate (within a day) and cycloheximide (within 3 h) did not significantly affect nucleolar size, indicating that the decrease in size was not under the influence of immediate synthesis of nucleic acid or protein. On the other hand, tunicamycin (within a day) delayed the decrease and actinomycin D (within 3 h) caused a maximal decrease in all nucleoli. This implied that a glycoprotein factor and some changes in DNA were involved in the decrease in nucleolar size. The rate of protein synthesis in duodenum was then measured by grain count per cell area in autoradiographs made after 1 h of injection of [3H]leucine. From crypt base to villus base, the grain count doubled while the nucleoli decreased to nearly half of their size in the crypt base. When actinomycin D injection preceded the [3H]leucine administration, all nucleoli decreased markedly and the grain counts increased by about 30% in all epithelial levels. It thus appears that the decrease in nucleolar size stimulates protein synthesis, possibly by the release of ribosomal material or some other factor. Protein synthesis in turn has been shown to be related to cell maturation. It is concluded that the nucleolus is involved in some manner in the regulation of the maturation and renewal of the epithelial cells.
Plasma membranes from adrenal cells: Purification and properties
Authors: Osawa Shoji , Hall Peter F.
Published: April 2021

A method is reported for preparing surface (plasma) membranes from adrenal tumour (Y-l) cells. The procedure is based upon homogenization in hypotonic ZnCl2 followed by sedimentation through two sucrose density gradients. The purified membranes consist of large sheets of membrane. The identity and purity of the membranes was demonstrated by: (1) microscopy (phase contrast and electron); (2) enzyme markers; and (3) functional activities associated with plasma membranes (binding of ACTH and LDL and adenylate cyclase). Phase-contrast microscopy revealed the release of membrane ghosts free from cytoplasm and nuclei. Electron microscopy showed membranes with small fragments of cytoplasm attached to the inside. Binding of ACTH was found to be specific with KD 0·12nM and the equivalent of 2500 sites per cell. Binding of LDL was also specific with KD 0·5 nM and the equivalent of 4800 sites per cell. Specific activities of binding for ACTH and LDL were increased by 21-fold and 15-fold, respectively, relative to whole homogenate. Membranes were also prepared from beef fasciculata cells by the same method.
Competition between Chlorellae in chimeric infections of Hydra viridis: The evolution of a stable symbiosis
Authors: Rahat M.
Published: April 2021

Aposymbiotic polyps of Hydra viridis were infected with one or two of the following strains of Chlorella : the native strain obtained from green H. viridis, and the originally non-symbiotic strains Fs and 211/8p cultured in vitro. Larvae of Artemia served as infecting vectors.

Chimeric infections were obtained with two different Chlorella strains cohabiting in the same cells and polyps. In time, the chimeric infections disappeared and mixed populations of Hydra were formed with different strains of Chlorella in different polyps.

We suggest that the Chlorella/Hydra symbiosis was initiated originally by an infection of preadapted hydra by preadapted chlorellae. Through intracellular interalgal competition and competition between dissimilar infected cells and polyps, the present-day stable symbiosis has evolved.
Enrichment of cfu-s proliferation inhibitor-producing cells based on their identification by the monoclonal antibody f4/80
Authors: Simmons P. J. , Lord B. I.
Published: April 2021

Cells capable of synthesizing a factor that can specifically inhibit the proliferation of haemopoietic spleen colony-forming units, CFU-S, carry many of the characteristics of macrophages. The monoclonal antibody, F4/80, which is specific for murine macrophages, has therefore been used to isolate macrophages from bone marrow. These macrophages were then assayed for their ability to produce the inhibitor. Low-density bone marrow cells were first separated by a density-cut procedure and then labelled with F4/80. Fluorescence-activated cell sorting was then used to select F4/80 positive and negative cell fractions. It was found that the F4/80 positive fraction contains inhibitor cells, enriched by at least 200-fold compared to unfractionated marrow. Subsequent culture of this fraction over a period of several weeks produced a further 15-to 20-fold increase in inhibitor-producing capacity. The cultured cells producing inhibitor were virtually 100% F4/80 positive, phagocytic and exhibited histochemical properties characteristic of macrophages. The macrophage-like character of the producer cells was thus confirmed and the removal of the majority of unwanted cells means that many of the impurities in the normal crude extracts have been excluded.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Coordinate expression of Mn-containing superoxide dismutase and Cu,Zn-containing superoxide dismutase in human fibroblasts with trisomy 21
Authors: Crosti N. , Bajer J. , Serra A. , Rigo A. , Scarpa M. , Viglino P.
Published: April 2021

The amount of Mn superoxide dismutase (MnSOD) and the activity of Cu.Zn-superoxide dismutase (CuZnSOD) have been studied in human fibroblasts of five subjects with trisomy 21 and five subjects with normal karyotype, using nuclear magnetic relaxation and polarographic methods. In the trisomic fibroblasts we have found a mean molar amount of MnSOD 25·4% lower than in the control, and an amount of CuZnSOD 54·7% higher. A positive significant correlation between the activities of both enzymes has been observed indicating that the two enzymes dismute the O2− cooperatively. However, the increase of MnSOD per unit of CuZnSOD appears significantly lower in the trisomic fibroblasts, an effect that is not due to a diminished inducibility of MnSOD. These findings suggest that the MnSOD and CuZnSOD genes interact to preserve the normal level of total SOD activity.
Observations on the membranous components of amphibian oocyte nucleoli
Authors: Kezer J. , Macgregor H. C. , Schabtach E.
Published: April 2021

Nucleoli in some large yolky oocytes of Plethodon cinerens and Ascaphus truei have attached to them a filament which may or may not have a beaded appearance. These filaments have been called ‘nucleolar tails’. One nucleus may contain several hundred of them. They may be up to 200 μm long and are usually about 1 μm wide. The beads which are sometimes attached to the filament are round, refractile and up to 3 μm in diameter. The tails are a feature of nuclei in which the nucleoli have left the nuclear envelope and migrated inward to cluster around the chromosomes in the centre of the nucleus. The tails project radially outwards from the central mass of nucleoli. Tails may be attached to round solid nucleoli, as is usually the case in A. truei, or they may be attached to ring nucleoli, as is often the case in P. cinereus, or they may lie free in the nuclear sap. Those nucleoli which remain attached to the nucleolar organizing site on the lampbrush chromosomes of P. cinereus never have tails. Nucleolar tails are Feulgen-negative and do not stain with gallocyanine when it is used under the proper conditions for staining nucleic acids. Tails are unaffected by deoxyribonuclease and ribonuclease but are destroyed by proteolytic enzymes.

Thin sections of oocytes whose nuclei contained nucleolar tails showed chains of membranous vesicles lying near to many of the nucleoli. These vesicles appeared empty, some of them were confluent with their neighbours, all were bounded by a unit membrane and all were coated on their outer surfaces by a fine fibrous material. The chains of vesicles commonly ended near a depression on the surface of the core of a nucleolus. Chains of vesicles sometimes extended into a long membranous tube. We have interpreted these chains of vesicles and tubes as sections through nucleolar tails.

It is suggested that nucleolar tails may be associated with the replication of nucleolar DNA, or with the division of nucleolar cores and nucleoli, or with the production of nuclear membrane at a time when the nucleus is enlarging rapidly. Each of these suggestions is discussed. A likeness between nucleolar tails and the mesosomes of bacteria is proposed and discussed.
Fine structure study of pollen development in Haemanthus katherinae baker: II. microtubules and elongation of the generative cells
Authors: Sanger Jean M. , Jackson W. T.
Published: April 2021

The newly formed generative cell of the pollen grain of the African blood lily is spheroidal after its detachment from the pollen wall. Plastids are almost always excluded from the generative cell, while dictyosomes, mitochondria, ribosomes, endoplasmic reticulum, and micro-tubules are present throughout development of the cell. During the time that the generative cell is spheroidal, microtubules are found scattered randomly throughout the cytoplasm. The cell subsequently elongates and concurrently an oriented system of microtubules appears along the wall of the cell. The microtubules are aligned with their long axes parallel to the long axis of the cell. This system of microtubules persists in the generative cell throughout its development. The microtubules can be destroyed by exposure to isopropyl N-phenylcarbamate or colchicine and as a result the generative cell reverts to a near spheroidal shape.
Isolation and characterization of secretory vesicles in germinated pollen of Lilium longiflorum
Authors: Vandbrwoude W. J. , Morré D. J. , Bracker C. E.
Published: April 2021

Secretory vesicles containing polysaccharide were isolated from germinated pollen of Lilium longiflorum and characterized by biochemical and ultrastructural investigation. Pollen tubes exhibit a secretory pathway in which the vesicles concentrated in the tube apex are produced by the Golgi apparatus and contributed to the cell wall at the apex upon fusion of the vesicle membrane with the plasma membrane.

Secretory vesicles were isolated by a method involving the size discrimination of cytoplasmic components using Millipore filters. Cells were disrupted under conditions which minimized membrane vesiculation. Identification was made by electron-microscopic comparison of the periodic acid-silver hexamine (PASH) reactivities of in situ and isolated secretory vesicles.

The secretory vesicles contained polysaccharides which were high in galacturonic acid and similar in sugar composition to those of the hot-water-soluble fraction of pollen tube cell wall. A hot-water-insoluble, non-cellulosic glucan was the major component of the cell wall. Less than 7 % of the wall was cellulosic. Chitin was absent. Similarities in the ultrastructure and PASH staining of apical secretory vesicles and an amorphous component of the cell wall support a precursor-product relationship between these 2 cell components. Ultrastructural investigations revealed complexes of the endoplasmic reticulum (ER) associated with electron-translucent regions of cytoplasm, suggesting a possible function of the ER in cell wall formation. Additionally, patterns of PASH staining show that changes in polysaccharides occur in secretory vesicles after vesicles have been formed by dictyosomes. Therefore, secretory vesicles may have a role in polysaccharide synthesis as well as in membrane and product transport.
The effects of sucrose and various salts on the growth and lysosomal enzyme activity of L5178Y cells
Authors: Bernacki R. J. , Bosmann H. B.
Published: April 2021

L5178 Y murine leukemic cells do not seem to be affected by sucrose in the same manner as other mammalian cells. Although there is active uptake of sucrose with no concomitant metabolism, there is no increase in vacuolation or cell size and there is only a slight increase in acid phosphatase, acid protease and β-glucuronidase activities. However, the glycosidases are significantly elevated in the presence of 0·08 M sucrose. This may be due to a specific induction of these enzymes by the sucrose not related to a general increase in lysosomes.

As the sucrose concentration is raised, a depression of the growth rate and an elevation of glycosidase activities occurs, reaching a maximum at 0·08 M sucrose. This depression of growth with a concomitant increase in generation time is primarily a result of the increased osmolarity of the medium; the same effect is observed with increased concentrations of NaCl. Although the growth effects are similar with either sucrose or NaCl, the elevation of glycosidase activity occurs only with increased concentrations of sucrose.

Sucrose-induced vacuolation with an increase in cell size is not evident in L5178Y cells; therefore this effect does not seem to be common to all mammalian cells, even though it has been reported for LS cells, Chinese hamster fibroblasts, and chick bone rudiments and in vivo for liver cells.
The form of haemoglobin in the erythrocytes of the cod, Gadus callarias
Authors: Thomas N. W.
Published: April 2021

The erythrocytes of the cod, Gadus callarias have a flattened discoid shape; each contains a peripheral marginal band of approximately 10 microtubules and a centrally placed nucleus. The cytoplasmic and nuclear haemoglobins have a paracrystalline organization; individual filaments, presumably polymers of haemoglobin, are grouped into bundles which course in all directions through the cell. This organization shows a remarkable similarity to that of deoxygenated haemoglobin in sickled human red cells. However, paracrystalline haemoglobin in the cod is characteristic of the normal red cells and is not associated with a crenated shape.
Incorporation of [me-3H] methionine into wool follicle proteins: a biochemical and ultrastructural study
Authors: Wilson Patricia A. , Henrikson R. C. , Downes A. M.
Published: April 2021

The formation of the ‘low-sulphur’ group of proteins which constitutes more than half the cortical cell content of wool was investigated. Of the amino acids present in the low- and high-sulphur proteins isolated from wool, methionine is the only one which is exclusive to the low-S group. The incorporation of [Me-3H]methionine, administered intradermally to a sheep, was examined using both biochemical and autoradiographic procedures.

During the first hour after injection, most of the [3H]methionine appeared in the blood, but some was incorporated into the wool follicle proteins at the injection sites. Most of the radio-activity incorporated by the fibre during this period was subsequently retained. Initially, more than 90 % of the activity was present in the prekeratin (8 M urea-soluble) portion of the fibre; 50 h elapsed before half of the radioactive material appeared in the keratinized (8 M urea-insoluble) part of the fibre. Methionine and its oxidation products accounted for more than 80 % of the radioactivity present in hydrolysates of wool removed from injection sites after 4 h or 22 days. Analysis of labelled wool showed that the specific radioactivities of those fractions low in sulphur (α- and β-keratose) were 7 and 14 times greater than that of the high-S (γ-keratose) fraction.

Autoradiographic studies showed that the main site of formation of the low-S proteins was in the bulb region of the follicle. Here there was no specific intracellular site of low-S protein synthesis, the [3H]methionine being incorporated into the nucleus, cytoplasm, the various cell organelles and intercellular membranes. The amount of radioactivity incorporated by the cortical cells diminished at progressively higher levels in the fibre. In the keratinization zone, the various cell components showed limited protein synthesis, but 1–8 h after injection there was a localization of tritium over the keratin fibrils. It is suggested that a large proportion of the low-S proteins formed within the developing cortical cell ultimately contribute to the keratin microfibrils. The results provide further evidence for the formation of the low-S and high-S proteins at different sites in the follicle.
The development of a simple pattern: Spaced hairs in Oncopeltus fasciatus
Authors: Lawrence P. A. , Hayward P.
Published: April 2021

Adults of Oncopeltus fasciatus, the milkweed bug, are covered with an evenly spaced mat of hairs. Each of these hairs develops from a single selected epidermal cell which divides and differentiates in situ. The process which picks out the particular epidermal cell is a simple example of pattern formation. Using a measure of uniformity of distribution an attempt was made to analyse the development of the hair pattern in time and space. Three methods were used: (i) Direct mapping of epidermis undergoing hair differentiation which allowed analysis of the spatial and temporal order in a single developing pattern: (ii) The injection of an agent which killed cells in DNA synthesis and which allowed the development of only those hairs that had completed DNA synthesis at the time of injection. Thus adults developed in which only the first-formed hairs differentiated, (iii) Treatment with the insect moulting hormone ecdysone which led to premature deposition of cuticle and curtailed hair development.

Results from these 3 approaches showed that the first hairs, far from being a random sample of the complete hair population in the normal adult, were a highly dispersed group. It is concluded that the hair pattern is built up in a precise order, with the centre of the largest available spaces being the sites where differentiation begins.
Microtubules and a contractile ring of microfilaments associated with a cleavage furrow
Authors: Tucker J. B.
Published: April 2021

A ring composed largely of microfilaments is situated underneath the pellicle and at the base of the cleavage furrow in the ciliate Nassula during binary fission. The microfilaments have diameters ranging from 4 to 10 run. There are substantial indications that the ring actively constricts in a sphincter-like fashion and is the main contractile agent causing furrowing. As cleavage proceeds the ring thickens and the dense layer of the pellicle becomes progressively more deeply folded. The longitudinal axes of the folds are at right angles to the longitudinal axes of the microfilaments and the plane of the ring. Folds form only where the pellicle overlies the ring. Two distinct phases of cleavage have been distinguished. The furrow constricts the organism at a progressively more rapid rate until the cleavage constriction has a diameter of about 5 μm and the microfilaments plug the constriction. After this furrowing proceeds much more slowly. A girdle of several thousand microtubules embedded in a densely staining material forms between the ring and the pellicular folds during the final stages of cleavage. Constriction and severance of the narrow cleavage constriction joining daughter oiganisms during the final phase of cleavage involve mechanisms different from those acting during the earlier phase of furrow development.
Dynamic rearrangements of erythrocyte membrane internal architecture induced by infection with Plasmodium falciparum
Authors: Allred David R. , Gruenberg Jean E. , Sherman Irwin W.
Published: April 2021

Cultured human erythrocytes infected with Plasmodium falciparum were studied by freezefracture electron microscopy. Special emphasis was placed upon the formation of the membrane surface excrescences (‘knobs’) found on red cells containing mature parasites. Knobs were visualized as conoid projections of the protoplasmic fracture face (PF) and depressions of the exoplasmic fracture face (EF). Knob formation was correlated with parasite growth and, on the basis of the organization of intramembranous particles (IMP) in the PF leaflet, a series of changes associated with parasite maturation was discerned:’ (1) a focal IMP cluster with minimal erythrocyte membrane elevation; (2) an elevated central IMP cluster surrounded by an IMP-free zone and concentric IMP ring; (3) maximal erythrocyte membrane deformation, concomitant with a loss of obvious IMP organization. Subtle changes in PF IMP organization were seen with knob formation and parasite maturation, including an apparent lateral partitioning of endogenous red cell membrane proteins between knobby or knob-free membrane areas in trophozoite-infected cells. IMP size distributions of the PF were shifted toward smaller particles in schizont-infected cells. Parasite development did not affect IMP densities in the PF; however, a decrease from 464 ± 106 µm−2 to 374 ± 94 µm−2 was seen in the EF of schizont-infected cells. IMP densities were similar over knobs and knob-free areas of either membrane leaflet, and there was no apparent EF IMP reorganization associated with the presence of knobs. These findings indicate that dynamic membrane changes are associated with knob formation and parasite maturation.
Characterization of a specific antiserum for mammalian collagenase from several species: immunolocalization of collagenase in rabbit chondrocytes and uterus
Authors: Hembry Rosalind M. , Murphy Gillian , Cawston Tim E. , Dingle John T. , Reynolds John J.
Published: April 2021

A specific antiserum to rabbit bone collagenase was raised in a sheep and shown to react with collagenase from several mammalian species. This antiserum was used to demonstrate that only active collagenase binds to and can be immunolocalized on collagen fibrils and, by indirect immunofluorescence, the secretion of latent collagenase by stimulated rabbit chondrocytes and cells’ of the post-partum involuting rabbit uterus. The ionophore monensin was used to demonstrate intracellular accumulation of collagenase in the Golgi apparatus of both stimulated chondrocytes and involuting uterine cells. Collagenase was not detectable in either normal cartilage or non-gravid uterus. These results are discussed in relation to other studies of collagenase immunolocalization reported in the literature.
Analysing collisions between fibroblasts and fibrosarcoma cells: fibrosarcoma cells show an active invasionary response
Authors: Paddock S. W. , Dunn G. A.
Published: April 2021

We describe a direct way of measuring contact inhibition of locomotion by analysing the changes in motion of pairs of colliding cells. This allows values to be assigned to each type of cell in mixed collisions and will enable certain hypotheses about the relationship between contact inhibition and invasion in culture to be tested critically. We find that fibrosarcoma (FS9) cells, on colliding with chick heart fibroblasts, show a reversed contact-inhibition response that we call contact promotion of locomotion. We also describe a measure of the lateral changes in motion that result from collisions between cells and show that this is dependent on the type of colliding cell but, unlike contact inhibition, it does not appear to be dependent on the type of cell with which it collides for the types studied here. Finally, we analyse how the total response is dependent on the dispositions and motions of the cells before collision and we find that FS9 cells, on colliding with fibroblasts, tend to turn towards the point of initial marginal contact. We conclude that the FS9 cells show a pronounced response on colliding with the fibroblasts, which is in contrast to the subjective impression that the FS9 cells do not respond much. These findings support the thesis of Abercrombie and colleagues, that the infiltration of a population of normal cells by a population of invasive cells in culture is dependent on the nature of the response of each cell type to collision with the other and that the invasive cells fail to show contact inhibition in these heterotypic collisions; but the findings further suggest that these invasive cells show an active invasionary response as opposed to merely failing to show contact inhibition.