bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the motility of the heliozoa I. the locomotion of Actinosphaerium Eichhorni and Actinophrys Sp
Authors: Watters C.
Published: April 2021

Analysis of ciné records indicates that the locomotion of Actinosphaerium eichhorni and Actinophrys sp. includes a definite rolling motion, in addition to evident horizontal and vertical displacements. Such movements could be correlated with significant changes in the lengths of supportive axopods, but not with axopodial rowing or sliding movements. The data also do not support a model of locomotion based simply on those systematic shifts in the cell’s centre of gravity that would be caused by sequential collapse of supportive axopods. Although active bending of attached axopods cannot be discounted, locomotion would seem to result from forces generated between the cytosome and substratum by attached axopods undergoing changes in length. The observations suggest, moreover, that axopodial retraction is more important than elongation in the generation of motive force.

It is proposed that the relative magnitude of each locomotory component is determined by the dimensional parameters of the particular species. As a consequence, changes in axopodial length can account for both the ‘rolling’ and ‘gliding’ behaviour reported in the literature.
Incorporation of [3H]Thymidine in mouse spleen
Authors: Pelc S. R.
Published: April 2021

Mice were given 4 injections of [3H]thymidine at 2-hourly intervals and killed at times varying from 1 h to 12 days after the last injection. Autoradiographs of spleen, oesophagus and heart were prepared by the stripping-film technique and exposed for 21, 189 and 367 days.

Groups of lymphoid cells surrounding trabeculae were heavily labelled, the decline in grain count suggesting division of these cells within 24 h. The appearance of large numbers of labelled nucleated cells in venules suggests that cells leave the spleen through the lining of the venules. The cells in germinal centres were preponderantly weakly labelled and spread into the white pulp after 2 days. It is suggested that the weak labelling indicates turnover of DNA rather than pre-mitotic synthesis. Megacaryocytes were unlabelled 1 h after a single injection of [3H]thymidine, nearly all being labelled from 1 to 8 days after the last of 4 injections. The grain count declined steadily with increasing interval between injection and fixation.
Occurrence, molecular structure, and induced formation of the ‘stromacentre’ in plastids
Authors: Gunning B. E. S. , Steer M. W. , Cochrane M. P.
Published: April 2021

The ‘stromacentre’ is a fibrillar spherulite found in plastids of aldehyde osmium-tetroxide fixed leaves of species in the genus Avena. Fibrils, each up to 0·2 μ. × 80–90 A, are associated in bundles, sometimes in hexagonal close packing, and the bundles in turn are aggregated in the spherulite. Individual bundles, or structures resembling them, occur in the plastid stroma in some other plants. In Avena, the stromacentre develops along with the internal membrane system of the plastids. Its staining reactions suggest absence of nucleic acid, and that it is proteinaceous. It is probably present in all mature Avena plastids.

Stromacentre fibrils have been negatively stained. They consist of linearly aggregated particles. In side view these measure about 85–90 Å square, though the outline of the particles varies according to the orientation of the fibril. Particle outlines and staining patterns within particles are illustrated in photographically reinforced images. Micrographs interpreted as illustrating disaggregation into free particles are presented. These free particles are indistinguishable from numerous others in the preparations, and these in turn are thought to be Fraction I protein molecules.

A process somewhat similar to stromacentre formation occurs in etioplasts and chloroplasts in Phaseolus leaves that have been dehydrated by plasmolysis, by wilting, or by high-speed centrifugation. These aggregates are not quite the same as the Avena stromacentre, but negative staining shows that they too are composed of units that are about the same size as Fraction I protein molecules.

The hypothesis that the stromacentre fibrils consist of linearly aggregated Fraction I protein molecules is discussed.
Synchronous pollen mitosis and the formation of the generative cell in massulate orchids
Authors: Heslop-Harrison J.
Published: April 2021

In orchd species forming microspores in aggregates, the pollen mitotic division occurs synchronously in all cells of each massula, as do the earlier meiotic divisions. The synchroneity can be traced to the persistence of cytoplasmic connexions between the cells, from the meiotic prophiase until pollen maturation. The mitosis giving the generative nucleus is asymmetrical, and the spindle is truncated at one side, where the microtubules converge towards an amorphuos polar structure lying against the spore wall. The cell plate formed after pollen mitosis is hemispherical, and its curved growth is related to a radial spread of the microtubules of the phragmoplast after the telophase of the division. The plate itself, and the wall derived from it, is identifiable as callose by its fluorescence properties. In the later development of the gametophyte, growth of the callose wall continues until the originally hemispherical generative cell becomes separated from the spore wall. The cell then assumes a spherical shape and moves to the vicinity of the vegetative nucleus, where it remains freely suspended, bathed in the cytoplasm of the vegetative cell but insulated from it by the completely ensheathing callose wall.
Genetic analysis of developmental mechanisms in Hydra: IV. characterization of a nematocystdeficient strain
Authors: Fujisawa Toshitaka , Sugiyama Tsutomu
Published: April 2021

The authors have previously found that mutant hydra strains showing various types of developmental defects can be isolated through sexual inbreeding of wild hydra. One such defective strain, called nem-4, contains virtually no stenoteles, one of the four types of nematocysts present in hydra, in its tentacles. However, stenoteles are present at a normal level in the body column of this strain, and they are turned over also at a normal rate.

Grafting experiments between the head region of nem-4 hydra and the body column of wild type hydra (and vice versa) showed that wild type stenotele nematocytes can move into nem-4 tentacles but that nem-4 stenotele nematocytes can not move into the wild type tentacles. These observations suggest that the stenotele nematocytes are produced normally by differentiation from the interstitial cells in the body column of nem-4 hydra, but that they are somehow prevented from migrating into the tentacles in this strain.
A technique for the freeze-fracture of tissue culture
Authors: Prescott Lise , Brightman Milton W.
Published: April 2021

Cultures of rat cerebellum grown on glass coverslips coated first with collodion and then collagen are fixed in glutaraldehyde to which ruthenium red has been added. After fixation, the collodion comes off the glass coverslips and the 3 layers: collodion-collagen-culture are handled as one piece. Following immersion in glycerol, selected areas are cut from the piece; the excised areas are a little smaller than those of the specimen carriers used in a Balzers apparatus. The ruthenium red, which stains all cells and processes, is a good indicator of specimen thickness. The explant which consists of several cell layers is redder than the peripheral monolayer of outgrowth. The square areas cut from either the explant or the outgrowth can be matched in thickness according to their shade of red. In frozen specimens, the red colour distinguishes the culture layer from the collodion-collagen support under it and from the white frost on top. During fracturing, the appearance of pink flakes on the edge of the knife indicates that the culture layer has been cleaved. The growth of cells on collodion-collagen and the fracture of the cultures with a knife, eliminate the restrictions inherent in the use of frozen ‘metallic sandwiches’.
Effects of pronase and concanavalin a upon the freeze-etch morphology of cell membranes of intact human erythrocytes
Authors: Wise Gary E. , Shienvold Frances L. , Rubin Robert W.
Published: April 2021

Freeze-etch studies reveal that mild pronase treatment with subsequent incubation in con-canavalin A induces aggregation of intramembranous particles (IMP) in intact human erythrocytes. This alteration in particle distribution is accompanied by a change in the distribution of the Con A molecules such that they also become clustered on the extracellular etch face. If divalent succinyl Con A is used after pronase instead of tetravalent Con A the IMPs still become clustered. Pronase only, Con A only, or succinyl Con A only does not cause the IMPs to become aggregated. Most surprising is the finding that pronase followed by Con A causes partial haemolysis of the cells whereas pronase only, Con A only, or pronase + succinyl Con A do not cause this haemoglobin loss. These perturbations of the erythrocyte plasma membrane appear to be a result of the pronase +Con A exerting a transmembrane effect on the spectrin. This conclusion is supported by sodium dodecylsulphate polyacrylamide gel electrophoresis of material crosslinked with dimethyl adipimidate dihydrochloride, which indicates that spectrin is more susceptible to being cross-linked after pronase + Con A; i.e. the spectrin is probably aggregated by the enzyme and lectin incubation.
Analysis of the penetrable space within the nucleus
Authors: Burgoyne Leigh A. , Skinner Jennifer D. , Marshall Alistair
Published: April 2021

Radioactive glycogen molecules have been used as passive probes to compare cavity systems within nuclei and isolated chromatin. Isolated chromatin was found to possess a narrow range of microspaces with mean effective diameters between 4·0 and 4·5 nm (40 and 45 A) depending on shape assumptions. Intact nuclei contained a far larger class of free spaces with average diameters in the order of 11·0–15·0 nm. This clearly shows that DNase-I (diam. 4-1 nm) can penetrate and occupy a large proportion of nuclear space even though this enzyme does not readily attack the undisturbed nuclear structure. A structure which simulated the pattern of penetrability and incorporated other known properties of chromatin was used to explain this DNase-I resistance of intact nuclei in terms of an ordered, compact, local structure interspersed by much larger spaces. A system for this local packing is suggested and the functional implications of this type of organization considered.
Sulphate metabolism in the exocrine pancreas. ii. the production of sulphated macromolecules by the mouse exocrine pancreas
Authors: Berg N. B.
Published: April 2021

The types of sulphated macromolecules produced by the exocrine pancreas were investigated. To determine whether this tissue utilized inorganic sulphate for protein production, the in-vitro behaviour of material labelled with 35S-sulphate was compared with material labelled with [3H]leucine (secretory proteins). While incubating tissue slices in the presence of cycloheximide resulted in an immediate and nearly complete inhibition of protein synthesis, a similar decrease in production of sulphated material was not observed until after 2 h of incubation in the presence of the drug. Likewise, the kinetics of pilocarpine-induced discharge of radioactive material from pancreatic slices pulse-labelled with either 3H-Leu. Or 35S-sulphate were compared. During the first 90 min of stimulation sulphated macromolecules were detected in chase medium 10–15 min prior to the appearance of [3H] labelled secretory proteins. That in-vitro behaviour of sulphated material differed from radioleucine-labelled material is indicative of the fact that the pancreas utilizes inorganic sulphate for the production of macromolecules other than secretory proteins.

Lipid and proteoglycan fractions were prepared from pancreatic tissue 4 h after intraperitoneal injection of radiosulphate. The recovery of a significant amount of radioactivity in both fractions demonstrated the ability of the pancreas to use inorganic sulphate for the production of both sulphated lipids and sulphated proteoglycans.

The possible function of sulphated macromolecules in pancreatic secretion is discussed.
Effect of ultraviolet or laser light irradiation on the growth of Micrasterias thomasiana
Authors: Nishimura M. , Ueda K.
Published: April 2021

The effect of ultraviolet or laser light on the growth of lobes in a green alga, Micrasterias thomasiana was investigated. During plasmolysis, the cell wall and the outermost region of the cytoplasm were separately irradiated with an ultraviolet or laser microbeam. Growth of the lobes was more effectively inhibited by irradiation of the cytoplasm than of the cell wall when the dose of irradiation was weak. Growth inhibition was observed in the irradiated cytoplasm where no apparent decrease in velocity of plasma streaming was seen, which suggested that irradiation caused more damage to the mechanism of exocytosis than to the migration of secretion vesicles. Strong irradiation resulted in gelatinization of the cytoplasm. With strong doses of irradiation on both the cytoplasm and cell wall, growth was completely inhibited.
Genetic aspects of intracellular motility: cortical localization and insertion of trichocysts inParamecium tetraurelia
Authors: Aufderheide Karl J.
Published: April 2021

Wild-type and selected mutants of Paramecium tetraurelia were subjected to detailed analysis of the trichocyst phenotype. The characteristics of morphology, saltatory motility, and cortical insertion of trichocysts were found to be genetically distinguishable. In mutants with defective trichocyst saltatory motility, other intracellular motility systems (i.e. mitochondrial saltatory motility, and cyclosis) appeared to be unaffected.

Saltatory motility appears to be an essential intermediate step in the functional development of the trichocyst, since it serves to transport the trichocyst from its site of assembly, deep in the cytoplasm, to the cortex, where it is inserted and becomes discharge-competent. If trichocyst saltatory motility is lost, as in the mutants ndA and tam8, then trichocysts are not transported to the cortex and are therefore not inserted. However, the successful transport of a trichocyst to the cortex does not guarantee the proper insertion of that trichocyst, as in the case of the mutant am. Apparently there are independent steps involved specifically with trichocyst insertion. The gross morphology of the trichocyst appears to be independent of its saltatory motility, and to a degree, independent of cortical insertion.
Cell movement and the mechanism of invasiveness: a survey of the behaviour of some normal and malignant cells implanted into the developing chick wing bud
Authors: Tickle C. , Crawley A. , Goodman M.
Published: April 2021

A survey of the behaviour of a variety of normal and malignant tumours and cells has been carried out to gain insights into the mechanisms of tumour invasiveness. The tumours and cells were implanted into the developing chick wing bud, which is a loose mesenchyme bounded by ectoderm. The distribution of the grafted cells was examined histologically after one or two days. The special feature of this assay is that the behaviour of cells is tested in a 3-dimensi0nal tissue. Cells from 3 different carcinomas, mouse lung tumour, rat bladder tumour and human breast tumour did not invade the mesenchyme, whereas trophoblast, sarcoma 180, cultured hamster fibroblasts (BHK, PyBHK, Nil 8, HSV Nil 8) and neuroblastoma cells did. Cells from embryonic pigmented retina and heart ventricle were non-invasive. These results suggest that cell movement may not be a common feature of all invasive tumours.

The cells that did move into the mesenchyme appeared to do so by various mechanisms. Lack of contact inhibition of movement, although probably involved in the invasiveness of sarcoma 18o cells, does not appear to be necessary for invasion: cells that have been shown to exhibit contact inhibition of movement (BHK and PyBHK) also invade. Both normal and transformed cells (BHK and PyBHK; Nil 8 and HSV Nil 8) moved into the mesenchyme. Other invading cells, such as trophoblast, neuroblastoma and to a small extent, HSV Nil 8 cells, destroy the adjacent host tissue and this may be important in the invasiveness of these cells.

The patterns of invasion and interactions with the host tissue were varied. Trophoblast and the fibroblasts were often elongated along the basement membrane at the ectoderm/mesen-chyme border and also closely apposed to the endothelial linings of blood vessels. Sarcoma 180 and neuroblastoma cells clustered around nerves. The embryonic tissues and neuroblastoma cells were often associated with blood vessels. These results are discussed in relation to tumour invasion.

A striking finding was that the carcinoma cells were frequently found positioned within the wing ectoderm on the basement membrane. This affinity of carcinoma cells for the epithelium rather than the mesenchyme leads to a reappraisal of the mechanisms involved in the invasiveness of carcinomas.
Ruthenium red-positive surface layer, extracellular filamentous material and intercellular junctions in hybrids between tumour and normal cells: abundant gap junctions correlate with density-dependent inhibition of growth
Authors: Stamatoglou S. C. , Marshall C. J.
Published: April 2021

The cell surface and intercellular junctions of transformed and non-transformed hybrid cells, obtained from fusion of murine mammary adenocarcinoma cells (TA3B) and normal rat embryo fibroblasts (REF), were compared with those of the parental cells, using ruthenium red (RR) staining of cells fixed in situ. An RR-positive layer of variable thickness was found on the surface of all cell types. Measurements of the thickness of this layer on the free surface of the cell cultures demonstrated a significant difference between transformed and non-transformed cells. The thickness distribution of the RR layer was similar on the surface of REF and nontransformed hybrid cells, but there was significant variation among all the transformed cell lines.

Extracellular filamentous RR-positive material, usually in direct contact with the cell surface, was present in confluent cultures of REF and non-transformed hybrid cells, but was absent in the transformed cell lines.

Gap junctions were few in both parental cell lines and rare or absent in transformed hybrids; a large increase in number and size of gap junctions was found in non-transformed hybrids. Abundance of long gap junctions was correlated with density-dependent inhibition of growth, since non-transformed hybrids grew in single layers whereas both normal and tumour parental cell types, and transformed hybrids grew in multilayers. Tight junctions were frequently encountered in TA3B and transformed hybrid cells but were not seen in REF cells and only occasionally seen in non-transformed hybrids. Intermediate-type junctions occurred in all cells, but desmosomes were found only rarely in TA3B cells and never in the other cell types.
Modulation of the effect of colchicine and cytochalasin b on fibroblast aggregates by the substratum
Authors: Van Der Schueren B. , Cassiman J. J. , Van Den Berghe H.
Published: April 2021

In previous investigations, we have shown that aggregates of normal human fibroblasts displayed a remarkable number of morphogenetic properties in suspension and on a substratum. The present investigation has attempted to illustrate more clearly the role of colchicine- and cytochalasin-sensitive structures in the observed ultrastructural properties of the fibroblasts in this system.

Cytochalasin B and colchicine alter the surface ultrastructure of the cells as well as the behaviour of the cells during aggregate outgrowth. In addition, the effects of both drugs on the cells in the aggregates are modulated by the attachment of the aggregates to a substratum.
Bhk21 myosin: isolation, biochemical characterization and intracellular localization
Authors: Yerna Marie-Jeanne , Aksoy Mark O. , Hartshorne David J. , Goldman Robert D.
Published: April 2021

Myosin has been isolated from baby hamster kidney cells (BHK21/C13) in high yield and characterized biochemically and immunologically. The subunit composition consists of 2 heavy chains, approximately 2ooo∞ Daltons each, and 2 classes of light chains of approximately 16 000 and 20000 Daltons. The myosin exhibits ATPase activity in the presence of K+-EDTA or Ca2+ but very little activity with Mg2+-ATP. The Mg2+-ATPase activity is stimulated only about 2-f0ld by skeletal actin, but a much larger activation is obtained in the presence of a protein kinase isolated from chicken gizzard. The increase in actin activation is accompanied by the phosphorylation of the 20000-Dalt0n light chain. BHK21 myosin is insoluble at low ionic strength and forms typical bipolar thick filaments. A specific antiserum generated against this protein forms a single precipitin line with the antigen but does not crossreact with either skeletal or smooth muscle myosin. The antiserum also specifically stains stress fibres in BHK21 cells as shown by indirect immunofluorescence.
Effects of temperature and nutritional conditions on the mitotic cell cycle of Saccharomyces cerevisiae
Authors: Jagadish M. N. , Carter B. L. A.
Published: April 2021

Yeast cells were cultivated at different growth rates in a chemostat by alterations in the flow of the limiting nutrient glucose and in batch cultures where variations in growth rate were achieved by alterations in the composition of nutrients. It was observed that the stage in the cycle at which S-phase was completed varied with growth rate. The faster the growth rate, the earlier the stage in the cycle in which completion of S-phase occurred. When stage in the cycle is converted into time before division it was observed that the time from completion of S-phase to cell division varied only slightly with growth rate except at extremely slow growth rates. Expansion of cell cycle transit time as the growth rate was slowed was achieved primarily by an expansion in time of the period from division to the completion of S-phase.

In contrast, when cells were grown at different rates by alterations in the temperature of cultivation, completion of S-phase occurred at approximately the same stage in the cell cycle at all growth rates.
The activation of proteolysis in the acrosome reaction of guinea-pig sperm
Authors: Green D. P. L.
Published: April 2021

The divalent metal cation ionophore A23187 rapidly induces a normal acrosome reaction in a population of guinea-pig sperm suspended in calcium medium. In the course of the acrosome reaction, proacrosin, the zymogen precursor of the protease acrosin, is activated. Although the acrosome reaction causes exocytosis of the acrosomal contents, ‘soluble’ acrosin is not released in significant amounts until well after the sperm population as a whole has undergone an acrosome reaction. This suggests that proacrosin is stored within the acrosome in an insoluble form and that exocytosis of the acrosomal contents in the acrosome reaction is insufficient, by itself, to cause its immediate dissolution.

Electron micrographs of sperm undergoing an Az3187-induced acrosome reaction in the presence of the acrosin inhibitors benzamidine, p-amino-benzamidine and phenylmethyl-sulphonyl fluoride show that the acrosome reaction proceeds normally but that dispersal of the acrosomal contents is inhibited. These morphological changes are, for the most part, below the limit of resolution of the light microscope and using light microscopy to assess whether an acrosome reaction has taken place, it can be mistakenly inferred that the reaction itself is inhibited by the acrosin inhibitors. The inhibition of the dispersal of the acrosomal contents by acrosin inhibitors suggests that acrosin activity is important in solubilizing acrosin.

These experimental observations, taken with the evidence that the acrosome reaction is a response to an increase in intracellular free calcium, have been taken as the basis of a proposal for the mechanism of proacrosin activation in the acrosome reaction.
The osmotic properties of the acrosome of guinea-pig sperm
Authors: Green D. P. L.
Published: April 2021

The osmotic behaviour of the acrosome in intact guinea-pig sperm has been examined by light and electron microscopy. Because the acrosome is retained within the cell, it can only experience the changes in tonicity of the cytoplasm and these have first to be related to the changes in tonicity in the external medium. Nevertheless, a qualitative description of the osmotic properties of the acrosome can be obtained. The evidence suggests that the acrosomal contents are normally close to their limit of compression. It has been proposed that a hydrostatic pressure is exerted inwards on the acrosomal membrane and that this is responsible for the maintenance of acrosomal shape. Swelling of the acrosome when sperm are suspended in hypotonic medium suggests that the acrosomal membrane does not have an abnormally low water permeability.

Two-thirds of the acrosomal volume are occupied by a single matrix which undergoes cavitation in the course of the acrosome reaction. It also undergoes cavitation when guinea-pig sperm are suspended in calcium-free medium containing the non-ionic detergent Triton X-100. This suggests that cavitation is caused by the loss of integrity of the plasma and acrosomal membranes. A mechanism for cavitation is proposed in which a colloid osmotic pressure within the acrosomal matrix is allowed expression when the crystalloids of the external medium pass into it, this internal colloid osmotic pressure forcing the matrix apart to produce a cavity.
The ultrastructure of non-membranous nuclear ghosts
Authors: Riley D. E. , Keller J. M.
Published: April 2021

Non-membranous HeLa cell nuclear ghosts, representing non-membranous nuclear envelope or ‘skeletal’ components, have been examined in whole-mount fashion by transmission electron microscopy. Major components of the ghosts include annuli with inner and outer diameters of 43 and 90 nm, respectively, which are consistent in dimensions with nuclear pore complexes. Also present are rod-like images (260 nm in length and 50 nm in width or diameter) representing either previously unobserved nuclear structures, or condensations of repeating functional units not otherwise observable. The annular and rod-like images were also observed when various steps in the ghost isolation procedure, such as the use of detergents, 0-5 M MgCl, and polylysine attachment of the ghosts to electron-microscope grids, were circumvented. The annular and rod-like images are connected into linear and polygonal arrays by strands (15-30 nm in width) that are sensitive to DNase I and DNase II but resistant to nuclease Sj. Thus, although the non-membranous ghosts from HeLa cells are composed primarily of protein, enzymic dissection indicates that their gross integrity is markedly dependent on double-stranded DNA. Nuclear ghosts prepared from a wide range of species including mammals, birds and plants, exhibited essentially the same components and organization.
Selective adhesion and impaired adhesive properties of transformed cells
Authors: Brugmans Mia , Cassiman Jean-Jacques , Van Den Berghe Herman
Published: April 2021

Quantitative studies on the adhesive properties of transformed cells have yielded inconclusive and sometimes contradictory results. The present investigation has examined adhesive interactions between normal human fibroblasts, established as well as virus-transformed animal cell lines, and human tumour-derived cell lines by the cell–cell layer binding assay.

The results of these investigations indicate that adhesive selectivity can be observed between normal human fibroblasts and 2 human tumour-derived cell lines, providing an in vitro system to study cell surface components involved in cellular interactions between normal and malignant cells.

In addition it is demonstrated that cell layers of transformed cells form a poorly adhesive substratum for both trypsinized normal and transformed cells. Furthermore, it is confirmed that the adhesive properties of transformed cells, including adhesive selectivity, are affected by the dissociation procedure (trypsin or EDTA). In view of the observations made by other investigators, the present results suggest that transformed cells display adhesive properties which can be quantitatively and reproducibly measured but which are modulated by the dissociation procedure as well as by the configuration in which the cells are at the time of the assay.
Suppression of the transformed phenotype in somatic cell hybrids
Authors: Marshall C. J. , Dave Harsha
Published: April 2021

Somatic cell hybrids between mouse mammary tumour cells (TA3B) and diploid rat embryo fibroblasts (REF) or between TA3B and Syrian hamster sarcoma cells (BI) were examined for the in vitro characteristics of transformed cells as soon as possible after cell fusion. Unlike the parental tumour cells three of four TA3B × REF and five BI × TA3B independent hybrid lines had low colony-forming efficiencies in agar, exhibited density-dependent inhibition of growth and did not form colonies on confluent monolayers of 3T3 cells, demonstrating that the transformed phenotype was suppressed in these hybrids. In addition tests of some of the hybrid lines for tumour production in nude mice showed that this was also suppressed. Suppression was more stable in the TA3B × REF than in the BI × TA3B hybrids, variants of the BI × TA3B hybrids with the properties of transformed cells could be readily isolated by subculturing cells that had grown in agar. Tumour growth selected for hybrids with the characteristics of transformed cells, and derivatives of the hybrids selected to show the transformed phenotype readily produced tumours. These correlations suggest that the transformed phenotype and malignancy may be under the same control in these cells. The phenomenon of suppression may be explained by the hypothesis that neoplastic transformation results from recessive mutations in genes which control the normal phenotype. On this model the finding of suppression in hybrids between two different tumour lines is interpreted as complementation and indicates that the mutations are not the same in all cell lines.
Microfilament bundles, lets protein and growth control in somatic cell hybrids
Authors: Marshall C. J. , Humphryes K. C. , Pollack R. E.
Published: April 2021

Hybrid cell lines between normal rat embryo fibroblasts and TA3B mouse tumour cells, or between TA3B and BI hamster sarcoma cells, have been examined for the expression of the cell surface large external-transformation-sensitive (LETS) protein and the organization of microfilament bundles. LETS protein was detected by lactoperoxidase-catalysed radioiodination and microfilament bundles were visualized by indirect immunofluorescence with antibodies directed against actin or myosin. Hybrids which exhibited normal growth control characteristics had high levels of LETS protein and extensive microfilament bundles. Neoplastic transformation appears to be suppressed in these hybrids. Hybrids which had the growth control characteristics typical of transformed cells had reduced or zero levels of LETS protein and few microfilament bundles. These results confirm previous studies on the expression of the transformed phenotype in these hybrids and demonstrate that there is a good correlation between normal growth control and the presence of LETS protein and microfilament bundles. However, the changes in cell surface LETS protein and in the organization of microfilament bundles often appeared to be quantitative reductions rather than all-or-none effects. The magnitude of the alterations in levels of LETS protein and in the organization of microfilaments appeared to correlate with the range of transformed characteristics exhibited by the cells. One transformed hybrid in particular, selected for growth in agar, had some surface LETS protein, some microfilament bundles and retained density-dependent inhibition of growth.
Comparison of cell attachment and caseinolytic activities of five tumour cell types
Authors: Varani J. , Orr W. , Ward P. A.
Published: April 2021

We have examined the ability of 5 tumour cell types to attach to plastic flasks in medium containing either 10% foetal calf serum or 10% normal human serum and compared this ability with cell-associated caseinolytic activity. The cell types used included fibrosarcoma cells which were obtained from a methylcholanthrene-induced tumour in a C57 BL/6 mouse, the SV40-transformed 3T3 (BALB/c) cells, the Walker carcinosarcoma cells and 2 lines of HeLa cells. All 5 cell types attached to the flasks and spread out efficiently in medium containing 10% foetal calf serum. The Walker carcinosarcoma cells and the 2 lines of HeLa cells also attached efficiently in medium containing 10% normal human serum and grew into monolayers in this medium. These 3 cell types had no detectable caseinolytic activity. The fibrosarcoma cells and the SV40-transformed 3T3 (BALB/c) cells did not attach in normal human serum-containing medium. These 2 cell types had readily detected caseinolytic activity. Normal human serum and foetal calf serum were compared for levels of protease-inhibitor activity. Human serum was found to have less activity than foetal calf serum against both trypsin and plasmin as well as the cell-associated caseinolytic activity. The low level of protease inhibitor activity in normal human serum may contribute to the inability of this serum to support the attachment of cells with detectable protease activity because the addition of protease inhibitors such as soybean trypsin inhibitor, lima bean trypsin inhibitor and bovine pancreas trypsin inhibitor to normal human serum dramatically enhanced cell attachment. In contrast to this, the addition of E-amino-π-caproic acid to normal human serum and the removal of plasminogen from normal human serum did not enhance its capacity to support cell attachment.
Fine-structural changes in the nucleus of primordial oocytes in immature hamsters
Authors: Habibi B. , Franchi L. L.
Published: April 2021

This study reports observations on fine-structural changes in the nucleus of the oocyte in hamsters during the establishment of the primordial (unilaminar) follicle at 7 to 12 days after birth. Following pachytene, the nuclei at early diplotene contain simple chromosomal cores surrounded by a sheath of fibrillo-granular material symmetrically disposed in the form of lateral projections and loops. From 9 days onwards increasing numbers of the oocytes show nuclei lacking such chromosomal threads: instead, they contain randomly disposed, condensed fibrillar clumps with associated dense knots of material, and prominent aggregations of 25 – 30-nm granules. This second nuclear form is assumed by all oocytes examined at 11 and 12 days and appears to be the definitive diplotene phase. These changes in the appearance of the nuclear chromatin are discussed in the light of those found in oocytes of other species, and it is concluded that the hamster diplotene phase consists of a transitory ‘compact’ or uniform lampbrush stage, followed by a definitive dictyate condition like that in the rat, but with markedly differential condensation or extreme diffusion of lateral loops.

This conclusion is examined in relation to findings which report a marked increase in the sensitivity of hamster oocytes to X-radiation at the time that the observed changes in nuclear configuration are taking place. The combined observations support the hypothesis that the dictyate stage in rodent oocytes represents a modified diplotene phase in which the high degree of spatial diffusion of components of chromosomes of the lampbrush type results in a reduced capacity for repair following exposure to ionizing radiations.
DNA-binding properties of nuclear matrix proteins
Authors: Comings David E. , Wallack Alice S.
Published: April 2021

Mouse nuclear matrix proteins, examined by a filter assay, were found to bind to DNA. There was no preference for homologous mouse compared to heterologous E. coli DNA. Competition assays showed a preference for AT-rich DNA and of the 4 single-stranded homopolymers there was a preference for poly(dT). These observations are consistent with the possibility that the matrix may play a role in the formation of AT-rich chromomeres (G-bands).
Regulation of interstitial cell differentiation in Hydra attenuata: IV. Nerve cell commitment in head regeneration is position-dependent
Authors: Yaross Marcia S. , Bode Hans R.
Published: April 2021

In hydra, nerve cells are a differentiation product of the interstitial cell, a multipotent stem cell. Nerve cell commitment was examined during head regeneration in Hydra attenuata. Within 3 h of head removal there is a 10- to 20-fold increase in nerve cell commitment in the tissue which subsequently forms the new head. Nerve cell commitment is unaltered in the remainder of the gastric region. This local increase in nerve cell commitment is responsible for about one half the new nerve cells formed during head regeneration, while one half differentiate from interstitial cells that migrate into the regenerating tip.
The preparation and ultrastructure of avian erythrocyte nuclear envelope enclosed by the plasma membrane
Authors: Harris James R.
Published: April 2021

A procedure is described for the preparation of avian erythrocyte nuclear envelope ghosts which remain enclosed by the ellipsoid plasma membrane. Haemoglobin-free nucleated chicken erythrocyte ghosts are treated in a low ionic strength buffer plus heparin which brings about decondensation of the chromatin. This is followed by solubilization of the chromatin by digestion with pancreatic deoxyribonuclease-1. When studied by light microscopy using either phase-contrast or Nomarski interference optics, the ellipsoid plasma membrane is clearly seen to remain with the collapsed nuclear envelope trapped inside. This interpretation is supported by negative-staining electron microscopy using ammonium molybdate, which in addition reveals the presence of the nuclear pore complexes. The suggestion is advanced that structural protection is provided for the fragile nuclear envelope system by the surrounding plasma membrane, which might account for the final nuclear envelope being in the form of relatively intact ghosts with well defined nuclear pore complexes. The nuclear envelope is highly fragmented when the plasma membrane is absent, the nuclear pore complexes showing appreciable breakdown. Thin sectioning supports the results of negative staining and in addition shows the nuclear envelope retained within the plasma membrane to be composed of both inner and outer nuclear membranes, but the nuclear pore complexes are not clearly defined.
Regulation of rna synthesis in Tetrahymena Pyriformis: secretion of regulatory factors
Authors: Andersen H. A. , Nielsen S. J.
Published: April 2021

The rate of ribosomal RNA synthesis varies greatly with the population density in both exponentially and synchronously growing populations of Tetrahymena pyriforntis. Shortly after inoculation of the population —at relatively low cell densities —a gene-dose effect dominates the picture, and a doubling in the gene number is immediately followed by a doubling in the rate of RNA synthesis. However, also other mechanisms are controlling the rate of RNA synthesis. Generally one finds high rates of RNA synthesis in the lag phase of newly inoculated cells, decreasing rate of RNA synthesis during most of the exponential growth phase and very low rate of synthesis in stationary phase cells. We now have results which show that the repression of RNA synthesis in densely populated cultures is caused by a dialysable factor, which is secreted by the cells. If cells are inoculated on a medium which contains this factor the high initial rate of RNA synthesis normally observed is prevented, but the cells multiply and grow with normal generation time until normal stationary-phase population densities are reached.
Induction of autogamy by treatment with trypsin in Paramecium Caudatum
Authors: Mikami Kazuyuki , Koizumi Sadaaki
Published: April 2021

Firmly united conjugant pairs of P. caudatum were easily separated by treatment with trypsin, 0 · 025–1 · 0 mg/ml in 2 mM phosphate buffer at pH 7 · 2. Cytological observations showed that pairs separated by this means undergo normal meiosis and subsequent prezygotic divisions. Microspectrophotometric comparisons of G1 micronuclei in the parent with those in clones derived from prematurely separated conjugants indicate usually the same DNA content in both. The stock dm-13, heterozygous for mating type gene loci, showed the definite ratio of segregation to 2 mating types in clones derived from prematurely separated conjugants. Those results suggest that the prematurely separated cells usually undergo autogamy.
Degradation of tight junctions in HT29, a human colon adenocarcinoma cell line
Authors: Polak-Charcon Sylvie , Ben-Shaul Yehuda
Published: April 2021

The process of right junction degradation was followed in a cell line of human colon adenocarcinoma.

Tight junctions are degraded by 2 mechanisms: (1) breakdown of junctional elements to intramembrane particles; (2) bleb formation by which tight-junctional elements are internalized into the cytoplasm or excluded into the medium. It is suggested that the first mechanism allows preservation of membrane particles for re-use, whereas the second is a mechanism by which the cells eliminate unneeded junctional elements.
Electron microscopy of spermatocytes previously studied in life: methods and some observations on micromanipulated chromosomes
Authors: Nicklas R. Bruce , Brinkley B. R. , Pepper Daniel A. , Kubai Donna F. , Rickards G. K.
Published: April 2021

A new method is offered for combined living cell and electron-microscopic studies of spermatocytes (or other cells) which normally do not adhere to glass. The key step is microinjection of glutaraldehyde near the target cell whenever desired during observation in life. Fixation begins and simultaneously the cell is stuck very firmly to the underlying coverslip. The method is easy and reliable: cells are almost never lost and are well preserved, except for membranes. The application of the method is illustrated by studies of micromanipulated grasshopper spermatocytes. A chromosome was detached from the spindle and placed in the cytoplasm. Before or after the beginning of chromosome movement back toward the spindle, the cell was fixed, sectioned and the manipulated chromosome observed in the electron microscope. If the detached chromosome had not moved by the time of fixation, no or only one or two microtubules were seen at its kinetochore, but if movement had occurred, a few microtubules were always present. The arrangement of these microtubules corresponded to the direction of movement, but they commonly were at an unusual angle relative to the kinetochore. The origin and role in chromosome movement of the microtubules seen near moving chromosomes far from the spindle is not yet established, but a speculation is offered. A goal for future work is the detailed analysis of the microtubules associated with individual moving chromosomes. Such an analysis is feasible because the moving chromosome is far removed from the confusing mass of spindle microtubules, and its value is enhanced because the direction of movement at the time of fixation is known.
Dual capacity for nutrient uptake in Tetrahymena: V. utilization of amino acids and proteins
Authors: Orias Eduardo , Rasmussen Leif
Published: April 2021

We investigated the relative contributions of phagocytosis and plasma membrane transport to the uptake of amino acids and a protein (egg albumin) in amounts which allow Tetrahymena thermophila to grow and multiply. We used a mutant capable of indefinite growth without food vacuole formation (phagocytosis) and its wild type (phagocytosis-competent) isogenic parental strain.

Our results suggest that phagocytosis is not required for free amino acid uptake, most or all of which can be attributed to carrier-mediated transport systems, apparently located on the plasma membrane. In contrast, phagocytosis is required for utilization of the protein. Proteins can supply required amino acids in amounts sufficient for growth only when food vacuoles are formed. We conclude that Tetrahymena thermophila either possesses no endocytic mechanisms at the cell surface other than food vacuole formation or, if it does, these putative mechanisms are not capable of nutritionally meaningful rates of protein uptake.
Studies on the subcellular localization of human neutrophil alkaline phosphatase
Authors: Rustin G. J. S. , Wilson P. D. , Peters T. J.
Published: April 2021

The intracellular localization of alkaline phosphatase has been determined in human neutrophils with analytical subcellular fractionation by density gradient centrifugation and EM cytochemistry.

Centrifugation on sucrose gradients containing 1 mM EDTA and 5 units/ml of heparin showed that alkaline phosphatase was associated with a membranous component distinct from plasma membrane, mitochondria, specific granules and azurophil granules. There was no resolution from the endoplasmic reticulum. Density gradient centrifugation on a sucrose— imidazole-heparin gradient showed a clear resolution of the alkaline phosphatase-containing membranes from the Golgi and endoplasmic reticulum. Density gradient centrifugation of neutrophils that had been disrupted in the presence of 0·12 mmol/1. digitonin clearly separated alkaline phosphatase-containing membranes from the endoplasmic reticulum. Part of the γ-glutamyl transferase has a similar localization to that of alkaline phosphatase.

EM cytochemistry of neutrophils, neutrophil homogenates and of the density gradient fractions identified alkaline phosphatase-containing granules as irregular-shaped, often tubular, structures. It is suggested that alkaline phosphatase and part of the γ-glutamyl transferase activity are localized to a unique organelle in the human neutrophil.