bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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

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

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

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

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

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

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

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

The 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.
The purification and immunocytochemical localization of the major iodinatable cell surface glycoproteins of chinese hamster ovary cells
Authors: Fitzgerald L. A. , Horst G. A. Baumbach, M. N. , Noonan K. D. , Roberts R. M.
Published: April 2021

A group of high molecular weight, acidic glycoproteins (HMWAG) are enriched in a plasma membrane subfraction of low density that can be isolated from Chinese hamster ovary (CHO) cells. The HMWAG represent the major components labelled by either lactoperoxidase-catalysed iodination of whole cells or by 125I-labelled wheat germ agglutinin (WGA) overlays of the membrane fraction after it had been analysed by 2-dimensional electrophoresis. The HMWAG were solubilized from membrane in Triton X100/borate buffer and purified by affinity chromatography on WGA-Sepharose. Antisera prepared against these glycoproteins in mice bound to several CHO cell lines including the WGA-resistant line Pro-5 WGAB1. Indirect immunofluorescence experiments performed at 4 °C showed that the glycoproteins had a fairly uniform but punctate distribution over the cell edge and dorsal surface of substratum-attached cells. Filopodia projecting along the substratum were also intensely labelled. After permeabilizing the cells the HMWAG were also shown to be located in cytoplasmic vesicles and in a perinuclear zone, which is assumed to be Golgi-associated. Electron microscopic observations using indirect immunoferritin procedures confirmed that the cell surface HMWAG were heavily concentrated on microvilli. The distribution of label seen with fluorescein-conjugated WGA was similar to that noted with fluorescent antibody, except that WGA was more uniformly distributed on the cell surface and also bound to the nuclear envelope in permeabilized cells. However, if cells labelled at 4 °C were warmed to 37 °C for 30 min the patterns of internalization of WGA and antibody were distinct. With the lectin, label rapidly became concentrated in the perinuclear zone, whereas with antibody the microvilli became denuded of label, which was then internalized into cytoplasmic vacuoles just beneath the plasma membrane. These results confirm that the HMWAG are concentrated on regions of the cell surface that are likely to produce vesicles readily upon cell breakage. They also suggest that pattern of internalization of a cell surface glycoprotein may be influenced by the nature of the ligand that binds to it.
Regulation of interstitial cell differentiation in Hydra attenuata: VI. Positional pattern of nerve cell commitment is independent of local nerve cell density
Authors: Heimfeld Shelly , BODE Hans R.
Published: April 2021

The interstitial cell of hydra is a multipotent stem cell, which produces nerve cells as one of its differentiated cell types. The amount of interstitial cell commitment to nerve differentiation varies in an axially dependent pattern along the body column. The distribution of nerve cell density has the same equivalent axial pattern. These facts have led to speculation that the regulation of nerve cell commitment is dictated by the nerve cell density.

We examined this question by assaying interstitial cell commitment behaviour in 2 cases where the normal nerve cell density of the tissue had been perturbed: (1) in epithelial hydra in which no nerve cells were present; and (2) in hydra derived from regenerating-tip isolates in which the nerve density was increased nearly 4-fold. We found no evidence of regulation of nerve cell commitment in response to the abnormal nerve cell densities. However, the typical axial pattern of nerve commitment was still obtained in both sets of experiments, which suggests that interstitial cell commitment to nerve differentiation is dependent on some parameter of axial location that is not associated directly with the local nerve cell density.
Functional differentiation of enterocytes in the follicle-associated epithelium of rat peyer’s patch
Authors: Smith Michael W. , Syme Gabrielle
Published: April 2021

The ability of the follicle-associated epithelium (FAE) of rat Peyer’s patch to accumulate valine has been measured using a new technique of autoradiographic analysis. Maximum uptake of valine was achieved by enterocytes present in the dome region of the FAE. Valine uptake was not seen in enterocytes present on the lower slopes of the FAE or in follicle-associated crypts. The ability of the FAE to absorb valine was generally much less than that seen in enterocytes present on adjacent villi. The main reason for this discrepancy lay in the apparent inability of the FAE to develop a second phase of amino acid transport similar to that seen in villus enterocytes. It is suggested that this failure results from some unexplained interaction taking place between the FAE and its underlying lymphoid tissue.
Cell versus nuclear morphometry of serum-stimulated fibroblasts: Nuclear changes precede cell changes
Authors: Belmont Andrew S. , Nicolini Claudio A.
Published: April 2021

Changes in the cell and nuclear morphology of sparsely plated WI38 fibroblasts were followed as a function of time after increasing the serum concentration from 0 ·3 % to 10 %. Quantitative measurements were carried out in parallel on Feulgen-stained nuclei and Wright-stained cells using the Quantimet 720-D image analysis system. We report a rapid, significant change in nuclear morphology indicative of nuclear rounding taking place within 30 min after increasing the serum concentration. In contrast, cell morphology showed only a slight change within the first 30 min but showed a significant change, also indicative of cell rounding, between 30 min and 3 h after increasing the concentration. Thus our results indicate a coupling between cell and nuclear morphology, but one in which nuclear changes precede cellular changes. As variations in both cell and nuclear morphology have been linked to the control of cell growth and transformation we also discuss briefly the implications of our results in relation to the regulation of cell growth and transformation.
Effects of temperature on the replication of chromosomal DNA of Xenopus laevis cells
Authors: Al-Saleh A. A.
Published: April 2021

DNA fibre autoradiography has been used to study the effects of temperature on the replication of chromomosomal DNA of Xenopus laevis cells in tissue culture at 18, 23 and 28°C. Pulse/stepdown labelling shows that the DNA replicates bidirectionally. Origin-to-origin distances (initiation intervals) vary, but the range of and the mean initiation intervals at all three temperatures are much the same. The mean interval between initiation points is of the order of 60 to 66 μm. Staggering of initiation is evident at all three temperatures. Evidence against the existence of replication termini is provided. The rates of progress of DNA replication forks are 6μm/h at 18°C, 10μm/h at 23 °C and 16μm/h at 28°C.
Polysomal organization in growing and resting cultures and its relation to protein synthesis in Tetrahymena
Authors: Isberner Petra , Cleffmann Günter
Published: April 2021

Cytosol from Tetrahymena cells growing at different rates was isolated and separated by centrifugation into polysomal and non-polysomal fractions. The RNAs of either fraction were separated chromatographically into poly(A)+ RNA and poly(A)− RNA. It was found that in resting cultures the total RNA per cell is only about half of that of rapidly growing cultures. All fractions of RNA were reduced proportionally. Thus, the percentage of polysomally bound total RNA (70 % of cytosol RNA) and polysomally bound poly(A)+ RNA (72% of cytosol poly(A)+ RNA) is the same in growing and resting cultures. Differences, however, were found in the polysomal structure. Polysomes from resting cultures contained significantly fewer ribosomes.

The amounts of RNA bound to polysomes were related to the rate of protein synthesis under different growth conditions. The decrease in cellular RNA corresponded well with the reduction in amino acid incorporation in resting cells. The rate of protein accumulation in resting cells, on the other hand, was considerably less, suggesting that polypeptides in resting cultures are less stable.
Neutrophil behaviour in the presence of protease inhibitors
Authors: Forrester J. V. , Lackie J. M. , Brown A. F.
Published: April 2021

Neutrophil leucocytes circulate in plasma, which contains broad-spectrum antiproteases such as alpha-2-macroglobulin and alpha-1-antitrypsin, and move into environments in which antiproteases are present. Plasma antiproteases significantly reduce the adhesiveness of leucocytes in both static and dynamic adhesion assays, although their action does not seem to depend upon their anti-protease capacity. Contrary to expectation, leucocyte movement over surfaces and through both rigid and deformable three-dimensional matrices (micropore filters and collagen gels) is unaffected by antiproteases. This renders the idea that forward movement depends upon the proteolytic cleavage of redundant adhesion sites less probable. Various non-physiological antiproteases (chloromethyl ketones, soya bean trypsin inhibitor, and ε-aminocaproic acid are also ineffective in reducing locomotion, although they do cause minor changes in adhesiveness.
Formation of centriole and centriole-like structures during meiosis and mitosis in Labyrinthula sp. (rhizopodea, labyrinthulida): an electron-microscope study *
Authors: Perkins F. O.
Published: April 2021

The fine structure of mitosis in vegetative cells of the marine protist Labyrinthida was found to involve formation of two approximately spherical, electron-dense aggregates (termed protocentrioles) 200–300 nm in diameter. Spindle microtubules were directly attached to the structures. The aggregates contained centrally located cartwheel structures but no microtubular elements in the form of a centriole-like cylinder. In non-sporulating cells the aggregates occurred only during mitosis or possibly in late interphase cells. During meiotic zoosporulation de novo centriole formation was observed. Vegetative spindle cells, which contained no centrioles, procentrioles, or centriolar plaques, aggregated then changed into approximately round or oval presporangia within sori. Two protocentrioles were formed in the cytoplasm a few hundred nanometres from each nucleus. Microtubules, oriented in astral ray patterns, were attached directly to each of the protocentrioles. Following migration to opposite sides of the nucleus, each of the protocentrioles differentiated into two centrioles attached at the cartwheel or proximal ends in a longitudinally continuous orientation. Binary fission of the paired centrioles (termed bicentrioles) and reorientation yielded a diplosome or an approximate orthogonal orientation of the organelles. Each mature centriole consisted of the usual cylinder of 9 triplet microtubular blades with a cartwheel complex at the proximal end consisting of 5 or 6 tiers of cartwheels. Further centriole replication appeared to occur by orthogonal budding from mature centrioles.
Chromocentres and the synaptinemal complex
Authors: Cour L. F. La , Wells B.
Published: April 2021

The 1–4 chromocentres seen in nuclei of Fritillaria lanceolata, which derive from fusion of heterochromatic segments situated proximal to the centromere in all but two of the 24 chromosomes, were studied with the electron microscope in thin sections of pollen mother cells at zygotene and pachytene, in respect of the synaptinemal complex. Prophase stages of meiosis in two plants were also surveyed briefly with the light microscope.

The latter observations revealed that the timing of the separation of heterochromatic segments from chromocentres is genetically controlled. In one plant the segments were still contained in chromocentres at pachytene, whereas in the other they were free at zygotene. At this time they could be identified by a near-surface position in the nucleus and an even condensation concomitant with an absence of chromomeres.

In thin section, the fine structure of the chromocentres in zygotene nuclei was distinctive in that the chromatin fibrils were less condensed and more widely dispersed than those in euchromatic regions. The fibrillar network was also interspersed with ‘clear areas’ or channels. After further chromosome condensation, the condensation of fibrils in the chromocentres became equivalent at pachytene to those in euchromatic regions.

Synaptinemal complexes were seen at zygotene and pachytene both in euchromatic regions and chromocentres. Their presence in the chromocentres signifies that homologous chromo-somes must have been closely paired in regions extending from the centromeres to the distal ends of the heterochromatic segments already at telophase of the last pre-meiotic mitosis.

Configurations involving entangled pairs of axial cores, peculiar to zygotene and chromo-centres and parts of euchromatic regions proximal to them, are interpreted as resulting from restricted movement.
Structural analysis of basal bodies of the isolated oral apparatus of Tetrahymena Pyriformis
Authors: Wolfe J.
Published: April 2021

The oral apparatus of Tetraliymena pyriformis was isolated using a non-ionic detergent to disrupt the cell membrane. The mouth consists largely of basal bodies and microfilaments. Each basal body is attached to the mouth by a basal plate which is integrated into the mesh work of microfilaments that confers upon the oral apparatus its structural integrity.

Each basal body is composed of 9 triplet microtubules. Two of the 3 tubules, subfibres ‘A’ and ‘B’ are composed of filamentous rows of globules with a spacing of 4·5 nm. The third tubule, subfibre ‘C’, is only one-third the length of the basal body.
The intracellular origin of flagellar hairs in the chrysophyceae and xanthophyceae
Authors: Leedale G. F. , Leadbeater B. S. C. , Massalski A.
Published: April 2021

Cells of the chrysophycean flagellate Olisthodiscus luteus contain bundles of aligned tubes and fibres within membrane-limited vesicles. Each element in a vesicle consists of a tapering portion 0 · 25 μm long, a shaft 1 · 5 μm long and a terminal fibre 0·25μm long; the shaft is approximately 15 nm in diameter and has a helical cross-banding with a periodicity of 8 nm. The flagellar hairs of Olisthodiscus have identical morphology and dimensions to these internal elements. Zoospores of the filamentous xanthophycean algae Bumilleria sicula, Heterococcus spp. and Tribonema spp. have similar internal vesicles containing aligned tubes and fibres with precisely the same morphology and dimensions as the flagellar hairs: base plus shaft, 1· 2 μm long, two terminal fibres per hair, 0 · 5—0 · 8 μm long, shaft diameter of approximately 15 nm and a helical periodicity of the shaft of 8 nm. The aligned tubes are absent from the vegetative xanthophycean cell, appear during zoosporogenesis and disappear during early stages of zoospore settlement. It is suggested that the aligned tubes and fibres are potential flagellar hairs which are formed in the perinuclear space (and possibly other regions of the endoplasmic reticulum) and are then transported to the cell surface in vesicles of the ER for deposition on the flagella. A review of information available on the Chrysophyceae, Xanthophyceae, Phaeophyceae and Bacillario phyceae indicates that internal formation of flagellar hairs is probably the rule in the heterokont algal groups, and a similar process apparently occurs in at least the dinoflagellates, the crypto-monads and some aquatic fungi among other groups of organisms with hairy flagella.
Fine structure of degenerating and regenerating flight muscles in a bark beetle, Ips confusus: I. degeneration
Authors: Bhakthan N. M. G. , Borden J. H. , Nair K. K.
Published: April 2021

The flight muscles of the bark beetle Ips confusus undergo a pronounced degeneration within 4 days of introducing beetles into the bark of pine logs. Numerous lysosomes develop between the myofibrils, and the fibrils become greatly reduced in size. In female beetles many of the mitochondria and most of the myofilaments disappear from the muscle, and apart from lysosomes, tracheoles and a few fine granules, little structural organization remains in the fibres. The muscles of males degenerate to a lesser extent and, unlike those of females, contain numerous lipid globules in the degenerating condition. The significance of flight muscle degeneration as a possible prerequisite for reproduction in females is discussed. In males, flight muscle degeneration may have behavioural significance in confining the flightless insect to the host tree for repetitive mating and gallery maintenance.
Seasonal changes in secretory granules and crystalloid inclusions of bat thyroid parafollicular cells
Authors: Nunez E.A. , Gould R. P. , Holt S. J.
Published: April 2021

Parafollicular cells of active Autumn bats sometimes contain many large dense secretory granules (diameter 1–2 μm) enclosed within ribosome-studded membranes. At the same time, parafollicular cells containing small granules were often characterized by the presence of slender crystalloid rods, up to several microns in length.

Parafollicular cells with large granules become depleted of them following exposure of non-hibernating bats to cold (4 °C) for 12–48 h. This treatment causes no change in the cells containing small granules, although partial degranulation in such cells was seen in early hibernating (November) bats.

On the basis of these and previous studies it is suggested that the two types of granules in bat parafollicular cells have different fates during the animal’s annual cycle of physiological activity.
The disposition of proteinpoly-saccharide in the epiphysial plate cartilage of the young rabbit
Authors: Smith J. W.
Published: April 2021

Although acidic bismuth nitrate stains the polysaccharide in the unfixed bovine epiphysial plate, it fails to do so in that of the rabbit. After fixation in glutaraldehyde, however, Araldite sections stained with bismuth nitrate exhibit 3-nm spots which are interpreted as polysaccharide chains in coiled conformation.

In the matrix of the proliferative zone, and in the large Golgi vesicles of the associated chondrocytes, the polysaccharide spots are arranged in closely packed groups. Lead citrate and uranyl acetate staining shows the non-fibrillar material in these situations as a continuous network of particles. The centre of each particle is translucent, and double staining with phos photungstic acid and bismuth indicates that these central regions contain the groups of polysaccharide spots.

It is suggested that in the unfixed tissue bismuth binding is prevented by screening of the polysaccharide sulphates by positively charged non-collagenous protein, and that fixation, by precipitating this protein as a network around groups of proteinpolysaccharide molecules, frees the sulphate groups to react with bismuth.

Proteinpolysaccharide molecules appear to be tangentially attached to each period of the small collagen fibrils of the matrix. Fixation precipitation of the associated protein tends to aggregate these molecules into groups which are often somewhat eccentric to their original attachment sites, and consequently the fibrillar attachment of proteinpolysaccharide usually appears to be rather irregular.

In the zone of early calcification single mineral crystals are associated with dense bodies of unknown nature and function. Many are also associated with short linear rows of polysaccharide spots. This and the similarity in the lengths of the two structures suggest that initial mineral crystals may grow along a proteinpolysaccharide molecule from one end to the other. Absence of polysaccharide spots in relation to crystal clusters suggest that these clusters are formed as a result of the seeding effect of the initial single crystals.
The midpiece of the mouse sperma tozoon: Its form and development as seen by surface replication
Authors: Woolley D. M.
Published: April 2021

A method is described for making carbon replicas of the surface of fixed spermatozoa and spermatids. In a study of the undulations of the surface of the midpiece, it has been shown that in the mouse spermatozoon the mitochondria are arranged predominantly in two parallel helices—without exception sinistral—totalling about 87 windings around the flagellum. The variability of this number has been calculated. The origin of this arrangement in spermateleosis has been examined in replicas of spermatids, revealing a rather complicated morphogenesis. It seems that, following the migration of the terminal annulus, elongated mitochondria form a single dextral helix around the flagellum; they then divide, making an orderly arrangement of spherical units; finally, each unit elongates, pushes between the contiguous units, and, by end-to end apposition, contributes to the formation of the regular system of two sinistral helices. A detailed account of this transformation is presented. It is suggested that, for tissues of sufficient hardness, the replica technique can usefully complement the cutting of thin sections.
Kinetic analysis of cell spreading: I. Theory and modelling of curves
Authors: Bardsley William G. , Aplin John D.
Published: April 2021

The spreading of cells on suitably treated surfaces is briefly discussed and the need to analyse this phenomenon numerically is emphasized. Possible mathematical models for fitting experimental data are classified as statistical, kinetic or empirical and examples of each of these types are given. A possible protocol for analysing cell spreading kinetics and determining goodness of fit and parameter redundancy is presented.
The Nature Of Conditioning Nutrients For Human Malignant Melanoma Cultures
Authors: Ellem K. A. O. , Kay G. F.
Published: April 2021

From a human melanoma line (MM96), showing some dependence of its rate of growth and cell attachment on serum concentration, sublines were selected for even greater dependence on serum factors. These sublines were used to identify the production of substances by other melanoma cells in culture that would supplement or replace the requirement for serum. Most of the sublines showed higher colony-forming efficiency in medium conditioned by one of several cell types in the presence of a low concentration of serum (2·5 %) compared with fresh medium containing a high concentration of serum (10%). The conditioning factor(s) were found to be moderately heat-stable, non-lipophilic, and to be of low molecular weight (≤400).

Screening of a variety of non-essential low molecular weight nutrients, which have been reported to potentiate the growth of a variety of cell types in low-density culture, was positive for the MM96 sublines only for pyruvate. In particular, L-alanine, L-serine, putrescine and αMSH (melanocytestimulating hormone) were ineffective. Despite the problems of comparing conditioned media with fresh medium, a reasonable correlation between the stimulatory effect and the cell content of added 2-oxocarboxylates was apparent. As would be anticipated, MM96 cultures showed a population density-dependent enhancement of growth up to a cell density of 2 to 4 × 104 cells cm-2. Further increase in the initial cell density of these cultures led to a decline in growth rate.

An important additional observation was that simple dilution of the ingredients of RPMI1640 with phosphate-buffered saline or Hanks’ balanced salt solution led to a reversal of the growth inhibition accompanying a serum shift-down.
X-Ray Microanalysis Of HeLa S3 Cells II. Analysis of elemental levels during the cell cycle
Authors: Warley Alice , Stephen J. , Hockaday A. , Appleton T. C.
Published: April 2021

HeLa S3 cells were synchronized using hydroxyurea. Cryoultramicrotomy and X-ray microanalysis were used to study changes occurring in concentrations of elements during the cell cycle of the synchronized cells. Three subcellular compartments were studied: cytoplasm, nucleus and nucleolus. Potassium concentrations showed little fluctuation in all of the cell compartments during the cell cycle. Sodium concentrations increased during S and M phases, returning to lower levels in the G1 phase. Chlorine concentrations were highest during the S and G2 phases. At all stages of the cell cycle respective concentrations of potassium, sodium, sulphur and chlorine were similar in the cytoplasm and nucleus. Concentrations of phosphorus increased in the nucleus during S, G2 and M, and also showed fluctuations in the nucleolus during the cycle; these were not seen in the cytoplasm. In S, M and M/G1 sodium concentrations were highest in the nucleolus compared with the other compartments. In the cytoplasm these changes resulted in an increase in total monovalent cation concentration (i.e. sodium-t-potassium) during S, G2 and M, which returned to base levels after mitosis. This increase in monovalent cation concentration is due almost entirely to the increase in sodium, with little change occurring in the concentration of potassium.
Kinetic Parameters Of Hexose Transport In Hybrids Between Malignant And Non-Malignant Cells
Authors: White M. K. , Bramwell M. E. , Harris H.
Published: April 2021

Matched pairs of isogeneic hybrid cells, in which one member of the pair was malignant and the other not, were used to examine the linkage between malignancy and functional alterations in hexose transport. The kinetic parameters of uptake of 2-deoxy-D-glucose were measured in a range of such hybrids, both human and murine. Some other malignant cell lines were also examined and were compared with non-tumorigenic derivatives of tumour cells selected by exposure to the lectin, wheat-germ agglutinin. In every case, malignancy, as defined by the ability of cells to grow progressively in vivo, was found to be linked to a decrease in the Michaelis constant of hexose uptake. Independent measurement of the transport and phosphorylation reactions involved in hexose uptake revealed that this decrease was determined by the membrane transport system. The difference in Michaelis constant between malignant and non-malignant cells was observed with 3–0-methylglucose, a hexose that is transported into the cell but not further metabolized. The activity of hexokinase in cell homogenates was higher than the level that would be required to cope with transport and showed no correlation with tumorigenicity. Measurement of the uptake of D-glucose itself, by a rapid filtration centrifugation method, gave results similar to those obtained with 2-deoxy-D-glucose.