bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell volume and the control of the Chlamydomonas cell cycle
Authors: Craigie R. A. , Cavalier-smith T. 
Published: April 2021

ABSTRACT
Chlamydomonas reinhardii divides by multiple fission to produce 2n daughter cells per division burst, where n is an integer. By separating predivision cells from synchronous cultures into fractions of differing mean cell volumes, and electronically measuring the numbers and volume distributions of the daughter cells produced by the subsequent division burst, we have shown that n is determined by the volume of the parent cell. Control of n can occur simply, if after every cell division the daughter cells monitor their volume and divide again if, and only if, their volume is greater than a fixed minimum value.
In cultures synchronized by 12-h light/12-h dark cycles, the larger parent cells divide earlier in the dark period than do smaller cells. This has been shown by two independent methods: (1) by separating cells into different size fractions by Percoll density-gradient centrifugation and using the light microscope to see when they divide; and (2) by studying changes in the cell volume distribution of unfractioned cultures. Since daughter cells remain within the mother-cell wall for some hours after cell division, and cell division causes an overall swelling of the mother-cell wall, the timing of division can be determined electronically by measuring this increase in cell volume that occurs in the dark period in the absence of growth; we find that cells at the large end of the size distribution range undergo this swelling first, and are then followed by successively smaller size fractions.
A simple model embodying a sizer followed by a timer gives a good quantitative fit to these data for 12-h light/12-h dark cycles if cell division occurs 12-h after attaining a critical volume of approximately 140 μm3. However, this simple model is called into question by our finding that alterations in the length of the light period alter the rate of progress towards division even of cells that have attained their critical volume. We discuss the relative roles of light and cell volume in the control of division timing in the Chlamydomonas cell cycle.
Surface contraction waves in amphibian eggs
Authors: Yoneda Mitsuki , Kobayakawa Yoshitaka , Kubota Hiroshi Y. , Sakai Masao 
Published: April 2021

ABSTRACT
Circular waves of change in brightness, known as ‘surface contraction waves’ (SCW-1 and SCW-2), propagate over the animal surface of amphibian eggs at each cycle of cleavage. Movement of carbon particles attached to the egg surface indicated that SCW-1 involves expansion of the egg surface, whereas SCW-2 accompanies surface contraction. Stiffness of the cortex as measured by applying negative pressure through a micropipette increased concomitantly with the passage of SCW-2. Measurement of stiffness at two loci on the egg surface with two sets of pipettes confirmed the spatio-temporal coincidence of the wave of stiffness and SCW-2. The stiffness showed either no change or even a slight decrease on passage of SCW-1. Thus SCW-2 is a genuine wave of ‘contraction’, but SCW-1 can more properly be called a ‘surface relaxation wave ‘.
Use of immobilized lactoperoxidase to label murine fibroblast proteins involved in adhesion to polystyrene
Authors: Lanks Karl W. , Chin Nena W. 
Published: April 2021

ABSTRACT
Proteins involved in the attachment of murine embryo fibroblasts to polystyrene have been identified by a technique designed to iodinate only those macromolecules coming into closest apposition to the substratum. Lactoperoxidase (LPase) covalently bound to the surface of the culture flask labelled a subset of substratum-bound polypeptides with a 42000 Mr species being most heavily labelled. Fibronectin was not labelled by this method. Soluble LPase, on the other hand, iodinated a wide range of polypeptides in cells attached to ordinary tissue culture polystyrene. Many of these polypeptides, including fibronectin, were cell-associated after scraping; however, bands of 50000–55000 and 42000 M, remained bound to the substratum. The effect of serum was investigated and the results suggested that serum components blocked labelling of the 42000–55000 Mr species by soluble LPase, but did not abolish labelling of similar polypeptides by the immobilized enzyme. The identity of the prominently labelled bands is discussed in the light of a functional interaction between two polypeptides, probably 10 run filament protein subunits and actin, at sites of cell-substratum attachment.
Comparative studies of rat liver and sea urchin embryo nuclear matrices: partial fractionation and protein kinase activity distribution
Authors: Sevaljevlć Ljiljana , Petrović Miodrag , Konstantinović Miroslav , Krtolica Koviljka 
Published: April 2021

ABSTRACT
Rat liver and sea urchin embryo nuclear matrices were found to differ in composition and in the strength of the association of their structural elements. Apart from the qualitative differences in composition, the embryonic matrices retained greater amounts of nuclear proteins and DNA, and were less susceptible to ultrasonic treatment than those of rat liver. They were essentially resistant to mild sonication, by which the rat liver matrix structure was resolved into two distinct fractions, referred to by Berezney (1980) as matricin and ribonucleoprotein (RNP). Both sub-fractions exhibited a protein kinase activity; the phosphorylating capacity of the RNP-associated protein kinases was found to be higher than that of the matricin-bound enzyme. The preferred substrate was among the secondary matrix proteins. In sea urchin embryos, sonication introduced no change in the type and location of the matrix proteins phosphorylated by the associated enzyme.
Microtubule nucleation by the isolated microtubule-organizing centre of Physarum polycephalum myxamoebae
Authors: Roobol Anne , Havercroft Jane C. , Gull Keith 
Published: April 2021

ABSTRACT
The nucleus-centrosome complex from Physarum polycephalum myxamoebae has been purified. The complex contained the centriole pair and pericentriolar material in association with the nucleus. Apart from some unusually stable microtubules, which appeared to be involved in maintaining the nucleus-centrosome association, endogenous microtubule arrays had been stripped from the complex during isolation. When the nucleus-centrosome complex was incubated with purified brain or myxamoebal tubulins the growth of 45–70 microtubules was initiated onto the pericentriolar material. The number and length of the nucleated microtubules was proportional to the tubulin concentration. Pretreatment of the nucleus-centrosome complex with DNase 1, RNase A, antitubulin antibody and anticentriolar antibody did not affect pericentriolar nucleation capacity, although pretreatment with DNase 1 did expose perinuclear nucleation sites that had a much lower minimal tubulin concentration for assembly than the pericentriolar site. After pretreatment with trypsin pericentriolar material and nucleation were destroyed, and microtubule elongation occurred directly onto the centriole microtubules.
The relationship between endocytosis of concanavalin a and phytohaemagglutinin receptors and blast transformation, and direct identification of individual rabbit lymphocytes reactive to both mitogens
Authors: Raffel Corey , Sell Stewart 
Published: April 2021

ABSTRACT
Distribution and modulation of rabbit lymphocyte phytohaemagglutinin acceptors and concanavalin A acceptors during activation of rabbit lymphocytes have been examined by electron microscopy. Two types of cell surface acceptors have been tentatively identified, lectin binding acceptors that do not modulate, and receptors that are endocytosed when blast transformation is stimulated. All of the cells have binding acceptors for both lectins. Endocytosis correlates with early blast transformation and serves as an early marker for lymphocyte activation. When examined after 24 h of culture, those cells that undergo blast transformation contain endocytosed lectin receptors, whereas small untransformed cells do not. Capping prior to endocytosis is rarely observed. The mechanism whereby the signal for transformation is maintained after the reaction of lectin with cell surface receptors and transposed to the nucleus is not known. Although we conclude that endocytosis is an early event required for cell activation, it is possible that endocytosis is secondary to other activation events. By evaluation of sequential endocytosis, individual rabbit lymphocytes that endocytose only concanavalin A, only phytohaemagglutinin, both concanavalin A and phytohaemagglutinin, or neither lectin, have been identified.
Effects of cyclic AMP on contact formation and differentiation in Dictyostelium discoideum
Authors: Oyama Masakazu , Okamoto Koji , Takeuchi Ikuo 
Published: April 2021

ABSTRACT
It has been shown previously that Dictyostelium discoideum NC4 cells dissociated at the early aggregation stage form cell clumps and differentiate into prespore cells in a shaking culture containing glucose, albumin, EDTA and cyclic AMP.
In this culture system, we found that the cells neither differentiate nor form cell clumps in the absence of cyclic AMP. Wheat-germ agglutinin (WGA) completely inhibited the cyclic AMP-induced formation of cell contact and the inhibition was nullified by the addition of N-acetyl-D-glucosamine.
When the cells were prevented from forming contact by either rapid shaking or the addition of WGA, they were unable to differentiate even in the presence of cyclic AMP, indicating that contact formation is a prerequisite for prespore differentiation.
Cells dissociated from migrating slugs formed cell clumps in shaking culture, with or without cyclic AMP, and the cell contact was sensitive to WGA. In the absence of cyclic AMP, preβpore cells lost their differentiated state, even though the cells were in contact. This indicates that cyclic AMP has a second effect, that of pomoting differentiation, in addition to the effect of inducing contact formation. Both effects were required for prespore differentiation of strain NC4 cells.
Changes in the size and structure of the nucleolus of columnar cells during their migration from crypt base to villus top in rat jejunum
Authors: Altmann G. G. , Leblond C. P. 
Published: April 2021

ABSTRACT
An image analyser was used to measure the area of the nucleolus and its component parts in columnar cells at six levels of the jejunal epithelium, corresponding to stages in cell migration from crypt base to villus top.
In columnar cells of crypt base, which function as stem cells for the epithelium, the nucleolus is large (3·1μ m2), irregular and reticulated. As cells migrate up the crypt, divide and differentiate, the nucleolus decreases in size (1·7 μm2) and becomes spherical, but remains reticulated. In the fully differentiated cells of the midvillus, however, the nucleolus becomes small (0·9 μm2) and compact. At the villus top, as the cells display early signs of degeneration, the nucleolus is further compacted (0·5 μm2).
Most nucleolar components also decrease in size. Pars fibrosa (about 19% of the nucleolar area in crypt base) and pars granulosa (about 70 %) decrease in proportion to the rest of the nucleolus, except in mid-villus and villus top where loss of pars granulosa predominates. In contrast, the total area of fibrillar centres remains constant (about 0·1 μm2), even though individual centres are small and numerous in crypt base, larger and fewer at higher levels, and they coalesce into a single structure in villus top. The other nucleolar components are also segregated into distinct, but adjacent, areas at this level.
The changes in size and structure of the nucleolus taking place during the migration of columnar cells can be correlated with the maturation of the cells and the loss of their ability to synthesize ribosomal RNA.
Mean macronuclear dna contents are variable in the ciliate Tetrahymena
Authors: Seyfert H.-M. , Cleffmann G. 
Published: April 2021

ABSTRACT
Using cytophotometry the mean macronuclear DNA content of the ciliate Tetrahymena was found to be variable in two cell lines examined. While environmental changes (different culture fluids, temperature shifts) influence the mean DNA content of at least one of the two cell lines, spontaneous changes of the means are observed in both lines. The mean DNA contents of cultures maintained permanently in defined medium at various temperatures suggest the existence of a lower (7·5 pg) and an upper (13· 6 pg) limit of the mean macronuclear DNA contents. Greatly differing means, either below or above those limits, were only occasionally found in cultures shifted to different temperatures for periods of less than 3 days. Eventually, the Gt mean macronuclear DNA contents of these cultures differed greatly from the doubled G2 mean value (maximum: mean G, value equalling four times the G1 mean). Analysis of the maximum and minimum G1 DNA contents found in any culture indicates no absolute macronuclear DNA content triggering the regulation of macronuclear DNA content. There is no stringent correlation between the average cell volume and the average macronuclear DNA content. The data are discussed with reference to reported mechanisms of regulation of macronuclear DNA content.
Isolation and properties of vitellogenic ferritin from snails
Authors: Bottke W. 
Published: April 2021

ABSTRACT
The iron storage protein ferritin is the principal yolk protein in oocytes of the snails Planor- barius comeus L. and Lymnaea stagnalis L. This report gives an account of the isolation procedure and of some properties of snail ferritins. The isolation procedure includes a heat-denaturation step, gel filtration on Sepharose 6B and two ultracentrifugation steps followed by electrophoresis. Ferritins from both snails are highly reminiscent of vertebrate and plant ferritins in terms of heat stability, absorption spectrum and ultrastructure, and both share common antigen determinants with horse spleen ferritin. In different electrophoresis systems snail ferritins display considerable heterogeneity and microheterogeneity. Electrophoresis in the presence of sodium dodecyl sulphate (SDS) yields two major polypeptides with molecular weights of 19000 and 24000, which are interpreted to be authentic subunits of the ferritin molecule.
Different organs and tissues of the snails differ in subunit composition. Midgut gland ferritin consists predominantly of the 19000 Mr polypeptide, while in embryos only the 24000 Mr band was found. No carbohydrates or lipids could be detected by staining acrylamide gels. Results from SDS/acrylamide electrophoresis, electrophoresis under non-denaturing conditions on gradient gels and from isoelectric focusing indicate that the ferritins of both snails are composed of at least two different types of ferritin that are tissue-specific. One ferritin is typical of somatic tissue (midgut gland) and is most probably a homopolymer of the 19000 Mr subunit. The other ferritin is typical of oocytes, but since it is an exogenous protein it is also encountered in the midgut gland (the presumed site of yolk synthesis) and the haemolymph. Vitellogenic ferritin is either a homopolymer of the 24000 Mr subunit or is predominantly composed of it. So far, there is no evidence for a precursor-product relationship between the two subunits.
Structure of three-dimensionally rod-shaped mitochondrial nucleoids isolated from the slime mould Physarum polycephalum
Authors: Suzuki T. , Kawano S. , Kuroiwa T. 
Published: April 2021

ABSTRACT
Mitochondrial nucleoids were isolated from microplasmodia of the true slime mould Physarum polycephalum using a discontinuous sucrose gradient following treatment of the mitochondria with Nonidet P-40. Studies of the isolated mitochondrial nucleoids by fluorescence and electron microscopy showed that the isolated structure was morphologically intact when compared with the structure in the mitochondria.
Scanning and negative staining electron micrographs of the isolated mitochondrial nucleoids indicated the presence of ‘elemental fibres’, 10 nm in diameter, which were organized three- dimensionally into the rod-shaped structure of the nucleoid.
Increases in ionic strength brought about loss of shape of the nuceloids and the elementary fibres became bare in places, from which thin filaments, believed to be DNA, protruded.
After treatment of the isolated nucleoid with Pronase E, the three-dimensional shape was lost and a large number of DNA filaments appeared to radiate from the undigested region of the remaining nucleoid.
Biochemical analyses of the isolated nucleoids revealed that the ratio of A225 to A 260 was 0·7 while RNA: DNA and protein: DNA were 0·4 and 1 4, respectively. Sodium dodecyl sulphate/polyacrylamide gel electrophoresis of the isolated nucleoids indicated that polypeptides of molecular weight 20 K, 32 K, 34 K, 39 K, 41 K, 65 K, 66 K, 96 K and 125 K were associated specifically with the nucleoids.
Cell-cycle-dependent effects of sodium-n-butyrate in Physarum polycephalum
Authors: Loidl Peter , Gröbner Peter , Csordas Adam , Puschendorf Bernd 
Published: April 2021

ABSTRACT
Sodium-n-butyrate affects the length of the mitotic cycle of Physarum polycephalum. Application during S- or early G,-period results in a delay of the subsequent mitosis, whereas application later in the cycle has no delaying effect. Interestingly, the second mitotic cycle after application is considerably shortened when butyrate has been administered during Sor early G,-period of the preceding cycle. In comparison, other homologous short-chain fatty acids were tested; the retarding effect on mitosis increases with the number of carbon atoms, although only butyrate can shorten the second mitotic cycle. It is shown that butyrate causes an immediate depression of synthesis of DNA, RNA and protein. After a certain time-interval the plasmodium overcomes the butyrate block. DNA synthesis is fully recovered and the inhibition of RNA and protein synthesis is even overcompensated until the next mitosis, as reflected by elevated levels of RNA and protein.
Clonal analysis of the change in growth phenotype during embryonal carcinoma cell differentiation
Authors: Rayner M. J. , Graham C. F. 
Published: April 2021

ABSTRACT
Retinoic acid has been shown to induce the differentiation of mouse embryonal carcinoma cells. Previous workers have reported that bulk cultures of the differentiated derivatives have a slower growth rate and a reduced capacity to form tumours. We have analysed this change in growth rate for a sub-tetraploid EC cell line, PC 13 clone 5 MAz, at a clonal level and have shown that the production of cells with a slower growth rate is not a result of cell selection. We have also demonstrated that the action of retinoic acid on growth rate is delayed for approximately 48 h and that the new growth phenotype, once attained, is stable. Finally we have confirmed at a clonal level that the differentiated derivatives of EC cells exposed to retinoic acid have a reduced capacity to form tumours. Clones of EC cells exposed to retinoic acid for longer than 96 h are unable to form tumours in a 30-day period, whilst 87 % of their untreated counterparts are able to do so.
Temporal relationships of host cell and algal mitosis in the green hydra symbiosis
Authors: McAuley P. J. 
Published: April 2021

ABSTRACT
In fed hydra or excised regenerating peduncles there are increases in the mitotic indices of both digestive cells and the symbiotic algae that reside within them. Conversely, algal and digestive cell mitotic indices decrease in starved hydra. The temporal relationships of algal and host cell division differ in fed hydra and regenerating peduncles. After feeding, algal and digestive cell mitotic indices both reach a peak at about the same time; during regeneration, first the algae and then the digestive cells divide. Thus, mitotic digestive cells in regenerating peduncles contain more algae than those in gastric regions of fed hydra. However, in both cases mitotic digestive cells contain more algae than non-mitotic cells. The algae appear to be partitioned at random between daughter digestive cells at teleophase.
It is suggested that the division of the symbiotic algae is closely related to that of the digestive cells in which they are maintained. Mitosis of algae is stimulated by host cell mitosis, but in non-dividing cells algal mitosis is restricted. Possible mechanisms by which the host digestive cells could restrict algal division are discussed.
Hyperimmune human abo blood-typing sera: Reactivity with murine laminin and cytotoxicity for metastatic murine tumour cells
Authors: McCOY J. P. , Schrier D. , Lovett E. J. , Judd W. J. , Varani J. 
Published: April 2021

ABSTRACT
Commercially prepared ABO blood-typing antisera have been tested for their ability to bind to murine laminin and their cytotoxic effects upon high and low metastatic variants of a murine fibrosarcoma. Previous studies have shown that α-D-galactopyranosyl end-groups comprise the major antigenic determinants on type B erythrocytes and that these same end-groups are present on murine laminin purified from the EHS sarcoma and on a laminin-like glycoprotein on the surface of the high, but not low, metastatic fibrosarcoma cells. In the present study we found that all sera containing anti-B activity were cytotoxic to the high, but not the low, metastatic cells and that all of these sera reacted strongly against immobilized murine laminin in an enzyme-linked immunosorbent assay. Sera lacking anti-B activity, i.e. anti-A antisera, were much less cytotoxic to either cell line and three of the four anti-A sera did not bind to murine laminin. The laminin reactivity and cytotoxic effect of the anti-B sera were specifically abrogated by preincubation of the sera with watersoluble blood group B substance or with murine laminin but not with water-soluble blood group A substance.