bluuebunny/crossref_metadata_2025_split huggingface dataset:
New aspects of intranuclear structures following partial decondensation of chromatin: A cytochemical and high-resolution autoradiographical study
Authors: Puvion-Dutilleul Francine , Puvion Edmond 
Published: April 2021

ABSTRACT
Exposure of cultured CV1 monkey kidney cells to a hypotonic medium containing a nonionic detergent induces a partial decondensation of nuclear components which can be studied advantageously in ultrathin sections. In addition to previously described 20–25 nm, DNA-containing chromatin fibres arrayed perpendicularly to the nuclear lamina, a new nuclear configuration was found which consists of abundant clusters of 6–7 nm fibrils. These ‘filamentous masses’ are the most heavily labelled component of the nucleus in autoradiographs after brief (2 min) exposure to [5-3H]uridine, and they are greatly diminished in number after treatment of the cells with a low dose of actinomycin D. Therefore, we interpret the filamentous masses to be nascent RNP and to represent the fibrillar regions of the nucleolus which have become decondensed into partially spread ‘Christmas-tree’-like figures detectable in situ in ultrathin sections. Similar structures occur in all cell types examined to date. This paper outlines the preparative procedure.
Double-replica topography of disk membrane structures in the carp (Cyprinus carpio)
Authors: Tonosaki A. , Washioka H. , Yamasaki M. , Mizoguchi J. 
Published: April 2021

ABSTRACT
By an improved freeze-fracture device, a number of double replicas were obtained from the rod disk membranes of the carp retina for investigation of complementary, continuing, and transitional relationships between fracture faces. Some separate particles found along the smooth edge bordering on the adjacent interdisk cytoplasm can be occasionally matched with gaps found between particles forming the complementary rough face edge. Consequently the particles on both faces can be derived from a single continuous layer, corresponding to the ad-cytoplasmic component of the disk membrane. This observation seems to agree with a prevailing disk-membrane model in which the visual pigment molecules are localized in the ad-cytoplasmic lipid lamella, but not to conform with a recent hypothesis, based upon single replicas, that the fracture plane might pass along either the inner or outer true surface of the membrane and the visual pigment molecules be attached to the latter.
Effect of antitubulins on spontaneous and chemotactic migration of neutrophils under agarose
Authors: Wski M. A. Dziezano , Destefano M. J. , Rabinovitch M. 
Published: April 2021

ABSTRACT
The effect of colchicine, Nocodazole or vinblastine on the movement of mouse bone marrow neutrophils was examined by the method of migration under agarose. Migration was estimated by counts of the numbers of cells that left the wells and moved under the gel. Micromolar concentrations of the agents increased spontaneous migration 2-to 4-fold, while lumicolchicine was ineffective. The increase may be due to the disassembly of the microtubular skeleton, making the cells more fluid, or to some other effect of the drugs. Since other agents, such as serum, low osmolality and low pH also enhance migration, these were tried in combination with a pretreatment of the cells with colchicine. Serum and colchicine acted synergistically, low osmolality and colchicine were additive. Possibly, the enhancement of neutrophil migration by serum or lowered osmolality does not require intact microtubules. At low pH, colchicine had very little stimulatory effect, perhaps indicating that the microtubules are more colchicine-resistant at low pH.
Although antibular drugs showed such marked effects on spontaneous migration, the chemotactic attraction of the neutrophils towards activated serum was unaffected. This indicates that the sensory and control mechanisms of the cells are resistant to antibulins.
Characterization of a strain-specific inhibitor of cell division from Amoeba cytoplasm
Authors: Ireland Christina M. , Hawkins Shirley E. 
Published: April 2021

ABSTRACT
The microinjection of cytoplasm taken from one strain of large free-living amoeba into another strain is followed by an incompatibility phenomenon, the inhibition of division amongst the recipient cells. The post-microsomal supernatant fraction from Amoeba discoides (T1D13) injected into A. proteus (T1P) inhibited division in 90% of the injected cells. Further centrifugation of this fraction yielded a pellet which when resuspended and injected, inhibited division in over 95% (and sometimes 100%) of the cells. No inhibitory activity remained in the supernatant after the removal of this pellet. Treatment with 10 μg/ml trypsin destroyed the activity of this pellet, while 25 μg/m.1 ribonuclease reduced the inhibitory activity by approximately 40 %. Passage of the resuspended post-microsomal pellet through Sephadex G-200 gave one main peak of material which eluted in the void volume. Concentration of this material by either dialysis or lyophilization followed by microinjection into A. proteus showed that this void volume peak contained the inhibitory material, although the most active preparations did not give more than 66 % inhibition of division. After elution from Sephadex, the void volume material was analysed by electrophoresis under non-denaturing and denaturing conditions, and by isoelectric focusing. One problem was the loss of inhibitory activity after keeping the pellet at 4 °C for 4–5 days, which made further analysis by microinjection difficult.
Preliminary experiments using a post-microsomal pellet prepared from Dawson’s A. proteus (DP) which inhibited division in A. proteus (T1P) gave a similar profile after Sephadex chromatography and gel electrophoresis.
Calcium accumulation in vacuoles of Physarum polycephalum following starvation
Authors: Kuroda Ritsu , Kuroda Hideyo 
Published: April 2021

ABSTRACT
The plasmodium of Physarum polycephalum contained 15·3 mmol Ca/kg fresh weight of sample, 11·8 mmol Mg/kg, 24·5 mmol K/kg and 1·4 mmol Na/kg. When the plasmodium was starved of food, the Ca content increased gradually up to 71·9 mmol/kg during 5 days of starvation. The concentration of other elements changed only slightly. The endoplasm contained 23·0 mmol Ca/kg, 12-6 mmol Mg/kg, 26·6 mmol K/kg and 1·7 mmol Na/kg, but these contents changed only slightly during starvation. The Ca, Mg, K and Na contents of the slime and the soluble fraction were also determined. In order to clarify where the accumulated Ca was localized, Ca in the plasmodium was precipitated with potassium pyroantimonate and examined by electron microscopy. In the starved plasmodium, the vacuoles which contained the electron-opaque precipitates and were located in the ectoplasm increased in number, compared with the unstarved plasmodium. At the same time the large electron-opaque granules in the extracellular slime increased in number. The electron-opaque precipitates were identified as Ca pyroantimonate by its susceptibility to removal by chelation with ethyleneglycol bis (β-aminoethyl ether) N, N, N′, N′-tetraacetic acid (EGTA) and X-ray microprobe analysis.
Ultrastructural studies on chromatin digestion by micrococcal nuclease in the presence of polyamines
Authors: Rowlatt Charles , Smith Garry John 
Published: April 2021

ABSTRACT
Nuclei purified from C57BL mouse submandibular salivary gland were treated with a range of micrococcal nuclease concentrations and times of treatment (from 0 · 5 unit for 2 · 5 min to 50 units for 30 min) in the presence of polyamines. About 50 % of the chromatin was solubilized initially but with jarolonged digestion this chromatin became insoluble again. Electron microscopy showed destruction of the finely dispersed chromatin with mild digestion, followed by aggregation of chromatin with more vigorous digestion. The early disappearance of finely dispersed chromatin filaments was not accompanied by preferential solubilization of chromatin associated with RNA polymerase II (euchromatin). These data suggest that the polyamines markedly reduce the susceptibility of euchromatin to micrococcal nuclease digestion.
A probe for flagellar dynein in the mammalian mitotic apparatus
Authors: Zieve Gary W. , Mcintosh J. Richard 
Published: April 2021

ABSTRACT
An anti-serum has been prepared in rabbits that precipitates high-molecular-weight bovine sperm proteins, including the dyneins. The activity of the serum against the dyneins is demonstrated by the recognition of dynein polypeptides in stained electrophoretic profiles of sperm proteins and in immunoprecipitates of radiolabelled sperm proteins. In addition, the serum stains the sperm flagella when used in indirect immunofluorescence and quantitatively inhibits the motility of demembranated sperm reactivated with ATP. However, the serum has additional anti-sperm activities besides those directed against the dyneins as demonstrated by the staining of the acrosome in indirect immunofluorescence. When used to immune precipitate proteins from extracts of cultured cells, the serum precipitates 2 polypeptides ; one has a molecular weight higher than the flagellar dyneins, one lower. No specific staining of cultured cells is observed when an affinity-purified anti-dynein fraction IgG is used to stain a variety of cultured cells including bovine fibroblasts. We interpret these data to suggest that flagellar dynein is not a component of the mammalian mitotic spindle and discuss how this conclusion is consistent with recent genetic and structural studies on the mitotic spindle.
Cell surface marker proteins during mouse spermatogenesis: Two-dimensional electrophoretic analysis
Authors: Millette Clarke F. , Moulding Christopher T. 
Published: April 2021

ABSTRACT
Purified plasma membranes isolated from separated highly homogeneous populations of mouse pachytene spermatocytes, round spermatids (steps 1—8), and residual bodies have been compared using 2-dimensional polyacrylamide gel electrophoresis. Two polypeptides apparently specific to pachytene spermatocytes have been identified. Component Pa has a molecular weight of 90 k daltons (K) and a pl of 5·6. Component Pb has a molecular weight of 56·5 K and a pl of 6·0. Four polypeptides detected only in plasma membranes of round spermatids have been identified as follows: RSa, 90–95 K and pl 5·9; RSb, also 90–95 K and pl 5·9; RSc, approximately 88 K and pl 5·5; RSd, 58 K and pl 6·0–6·3. No polypeptides unique to residual body membranes were identified.
Short-term culture experiments have established that separated adult mouse spermatogenic cells survive short-term culture in vitro. These cells actively synthesize numerous cellular proteins as determined by the incorporation of [3H]leucine. Investigations concerning the effect of the cell separation procedure on mouse spermatogenic cell membranes indicate that only 7 of 110–120 total plasma membrane constituents are degraded enzymically during cell purification. Only one of these constituents may correspond to the presumptive cell differentiation markers described for pachytene spermatocytes and round spermatids. These results indicate, therefore, that plasma membranes obtained immediately after cell separation are suitable for the detailed biochemical analysis of most integral surface proteins during spermatogenesis in the mouse.
Properties of dna associated with raffinose-isolated pellicles of Paramecium aurelia
Authors: Hufnagel Linda A. 
Published: April 2021

ABSTRACT
Pellicular fractions, rich in basal bodies, have been obtained from Paramecium aurelia after the animals were homogenized in the presence of buffered raffinose. DNA was extracted from these fractions. This DNA was examined with respect to density and to its susceptibility to digestion by DNase while still associated with pellicles, and was found to be of two kinds: (a) Most resembles nuclear DNA in density, is completely removed from pellicles by pancreatic DNase and forms a broad band when centrifuged to equilibrium in cesium chloride. This DNA may be of nuclear origin, although a pellicular source cannot be ruled out. (b) Several minor species of DNA with densities of 1·698, 1·703 –1·704 and 1·717 –1·718 g/cm3 (1·698 ×103, 1·703 –1·704 × 103 and 1·717 –1·718 × 103 kg m−3 respectively) are also present. These species were not digested when pellicles were treated with DNase. None of these DNA species occurs consistently in all preparations of pellicular DNA and the results indicate that they are probably attributable to bacteria present during culture of the animals in non-axenic medium.
To test the ability of pellicles to become associated with exogenous DNA during isolation, DNA of Escherichia coli, labelled with [3H]thymidine, was added to whole cell homogenate before isolation of pellicles. Comparison of the specific activities of DNA extracted from the homogenate with that from isolated pellicles provided evidence that exogenous E. coli DNA can bind to pellicles.
These observations suggest that pellicles or basal bodies may become contaminated with nuclear DNA during isolation. This would create a serious problem, which must be rigorously dealt with in experiments designed to demonstrate the existence of basal-body DNA in isolated pellicles by cytochemical, biochemical or autoradiographic methods. The results indicate that it has not been established beyond reasonable doubt that basal bodies or centrioles contain DNA. In addition, the results suggest that further verification of existing evidence for basal body DNA may require further sophistication of existing analyses or a novel approach, involving different biological material or new techniques.
Ciliary specializations in mating cells of the ciliate Euplotes crassus
Authors: Luporini Pierangelo , Dallai Romano 
Published: April 2021

ABSTRACT
In the ciliate Euplotes crassus, mixed cells of different compatible mating types pass through an induction period before agglutinating with each other by means of cilia in the mating reaction. We examined the ciliary membranes of cells involved in the mating reaction by the freeze-fracture technique and detected at least 5 distinct types of specialization, each indicated by a special congregation of intramembrane particles. Near to the necklace, at the ciliary base, we observed a set of several parallel transverse rows of 10–15 nm particles; a longitudinal row of 12 nm particles appeared more distally from the necklace, preferentially in replicas of intermediate regions of the ciliary shaft. These 3 specializations were common to both mating and vegetative cells. The other 2 appeared as more dynamic specializations found exclusively, at least in their most patterned organization, in the ciliary membranes of mating cells. Taking on the aspects of rosette-like arrays and patches, respectively, the former were positioned regularly on ciliary membrane bulges (containing an electron-opaque granule) and consisted of 8—9 nm particles; the latter had an elliptic shape and contained up to 50 closely packed 9–10 nm particles.
Phagocytosis by macrophages: II. The dissociation of the attachment and ingestion steps
Authors: Ito Tadanao , Okada Masamichi J. , Ueda T. S. , Ohnishi Shun-Ichi 
Published: April 2021

ABSTRACT
The phagocytic process of mouse peritoneal macrophages was dissociated, using bovine serum albumin (BSA)-coated particles containing spin-labelled cholestanone, into 2 steps: attachment of particles to the cell surface and ingestion of the particles into the cytoplasm. The number of particles was estimated from electron spin resonance (e.s.r.) measurements. The particles ingested into the cytoplasm were distinguished from those attached to the cell surface by treatment with a membrane-impermeable reducing agent, ascorbate. The validity of the assay method was tested under various conditions. The measurements piovided accurate and reproducible data. The phagocytic reaction was followed as a function of time and the rate constants for the attachment and ingestion steps were obtained from the initial phase. Both steps were highly dependent on temperature. Divalent cations in the incubation medium were essential for the attachment step but apparently had no effect on the ingestion step. The metabolic inhibitors, KCN and 2-deoxyglucose, inhibited both steps. Cytochalasin B inhibited both steps, while colchicine inhibited only the attachment step but apparently had no effect on the ingestion step.
The effect of neuraminidase- and ribonuclease-susceptible surface anionic groups on the aggregation of embryonic chick neural retina cells
Authors: Maslow D. E. , Harlos J. P. 
Published: April 2021

ABSTRACT
The role of cell surface charge in cellular interactions has been the subject of conflicting reports. The major contribution to the net cell surface negativity of all mammalian cells studied is made by the sialic acid moieties of the surface glycoproteins, while ribonuclease-susceptible sites have been shown to contribute to a lesser extent on some cell types. Experiments were done to determine whether these anionic groups at the cell periphery affect the aggregation and sorting behaviour of embryonic chick neural retina cells when cultured alone or in combination with embryonic heart cells. The net negative surface charge density, as determined by cell electrophoretic mobility, of neuraminidase- or ribonuclease-treated cells was significantly decreased immediately after incubation with the enzymes, and the treatment with neuraminidase resulted in a reduction in the binding of colloidal iron hydroxide particles at the cell surface. Both enzymes caused reduced aggregate size in gyratory shaker cultures of neural retina and mixed cell suspensions, and fewer neural retina cells adherent to microtest plate surfaces, but no differences were seen in their histological appearance or sorting pattern in mixed shaker culture. The results indicate that the neuraminidase- and ribonuclease-susceptible groups at the periphery of embryonic neural retina cells play a role in some aspects of cell contact behaviour in ways other than reduction in net negative surface charge.
Effects of vanadate, Mg2+ and electric current injection on the stiffness of impaled bull spermatozoa
Authors: Rikmenspoel Robert , Orris Sandra E. , Isles Cheryl A. 
Published: April 2021

ABSTRACT
Measurements were made of the rigor stiffness of impaled bull sperm flagella. Vanadate-free ATP was found to have a stronger plasticizing action than vanadate-contaminated ATP. Trace amounts of Mg2+ were found to be necessary to relieve the rigor condition by ATP. During the injection of negative electric current into the sperm head, the flagella stiffened, presumably by depletion of Mg2+ from the flagellar interior.
Mechanisms of nutritive endocytosis : II.* The effect of charged agents on phagocytic recognition by digestive cells
Authors: Mcneil L.Paul , Hohman Thomas C. , Muscatine Leonard 
Published: April 2021

ABSTRACT
Phagocytosis by digestive cells of green hydra was affected by polycations and polyanions. Polycations probably act by reversing negative charges on surfaces of particles or digestive cells; polyanions by inducing dynamic changes in the morphology of digestive cell surfaces.
The polycation, poly-L-lysine, at concentrations as low as 0.1 μg/ml, inhibited phagocytosis when presented concurrently with 5.7 μm latex spheres. Phagocytosis was also inhibited when latex spheres were pretreated with poly-L-lysine, washed and then presented to untreated digestive cells. In contrast, pretreatment of digestive cells with poly-L-lysine (1.0μg/ml) enhanced subsequent uptake of untreated latex spheres. Treatment with other agents, such as FeCl, and carbodiimide, that are presumed to reduce negative surface charge on the particle (the latter by covalent neutralization of surface carboxyl groups), also inhibited phagocytosis. The phagocytically active digestive cell surface bears a net positive surface charge since it showed an affinity for negatively but not positively charged ferritin. Unmodified latex spheres possessed a net negative surface-charge, as measured by electrophoresis of whole cells. In contrast, particles treated with polycations and other presumptive modifiers of surface charge were shown by electrophoresis to have reduced negative or, in some cases, net positive surfacecharge. Electrostatic attraction of particles for the digestive cell surface may play a major role in determining the extent of phagocytic uptake by digestive cells, and polycation inhibition of uptake may result from neutralization of negative charges on the particle surface.
The polyanion, poly-L-glutamic acid, enhanced phagocytosis when presented concurrently with latex spheres at concentrations greater than 1.0 μg/ml. Pretreatment of digestive cells with poly-L-glutamic acid also enhanced uptake of latex spheres. Scanning electron microscopy showed that latex spheres presented concurrently with poly-L-glutamic acid rapidly (within 10 min) induced the formation of a dense array of microvilli on digestive cell surfaces, and that these microvilli participated in phagocytic enclosure of latex spheres. Polyanions, therefore, enhanced uptake by a mechanism unrelated to electrostatic forces; rather, by activating digestive cells to produce dynamic morphological alterations, they may reduce the resistance encountered by the enveloping plasma membrane to its movement over particles and increase the surface area available for interiorization.
The influence of polyanions and polycations on phagocytosis of several other particles: freshly isolated symbionts, Chlorella spp.; heat-treated symbionts; and free-living algae, Chlorella vulgaris, were also examined, with results that were, in general, consistent with those described for latex spheres. Thus, the influence of charged agents on phagocytosis by digestive cells may be a general phenomenon.
The quantitative relationship of the fibrillar centres and other nucleolar components to changes in growth conditions, serum deprivation and low doses of actinomycin D in cultured diploid human fibroblasts (strain mrc-5)
Authors: Jordan E. G. , Mcgovern J. H. 
Published: April 2021

ABSTRACTThe proportions of the 4 components of nucleoli: namely, granular component, fibrillar component, vacuolar space and the fibrillar centre material, were calculated by electron microscopical stereological procedures for human diploid fibroblasts (strain MRC-5) under 6 different culture conditions. Using nucleolar volumes obtained by light microscopy of unsectioned cells, estimates of the volume of each constituent per nucleolus were obtained.From the size and number of fibrillar centres encountered it was possible to estimate approximately their numbers per nucleolus. This ranged from an average of 42 ±4 to 234 ±25, depending on the level of cell activity, the number rising with increasing cell activity. Their volumes were inversely proportional to their number per nucleolus, indicating a possible fusion with cell inactivation. The number of fibrillar centres exceeds the number of nucleolus organizers in man (which is ten) and is nearer the number of ribosomal genes, which has been quoted at between 100 and 400 for diploid cells.The volumes of granular and fibrillar components also reflect changes in cell activity. A different response follows drug-induced inactivity when compared with the less artificial inactivation resulting from confluence or serum starvation. There was less fibrillar component in the actinomycin D-inactivated nucleoli. It is suggested that the nature of the fibrillar component may not be the same in cells in different states and that the simple interpretation that this is the transcriptional component may need to be revised.The change to fewer larger fibrillar centres upon nucleolar inactivation may be a consequence of 3 simultaneous processes. First, that the organizers increase in size by the condensation of previously active organizer chromatin, which is withdrawing from its transcriptional configuration. Secondly, this process may be accompanied by the fusion of the resultant larger nucleolar organizer regions. And finally, the increase in sizes of fibrillar centres may be further affected by an accretion of some non-chromatin material, possibly matrix or skeletal protein material, onto the organizers.