bluuebunny/crossref_metadata_2025 huggingface dataset:
Repair of strand breaks in superhelical dna of ataxia telangiectasia lymphoblastoid cells
Authors: Lavin M. F. , Davidson M.
Published: April 2021

A number of different assay methods have been used to study repair of strand breaks in DNA after exposure of cells to ionizing radiation. Use of these methods indicates that fibroblasts from patients with ataxia telangiectasia (AT), a multiform genetic disease exhibiting high sensitivity to ionizing radiation, have a normal ability to repair strand breaks in DNA. All of these methods determine the extent of breakage of DNA and the resealing of these breaks but do not provide information on restoration of DNA configuration in the nucleus.

In this report we have used a sensitive technique to investigate restoration of the 3-dimensional structure of DNA in AT lymphoblastoid cells after exposure to ionizing radiation. This technique provides a means of lysing cells using a high concentration of salt and a non-ionic detergent, giving rise to structures called nucleoids which contain nuclear RNA and DNA, are depleted in protein, and sediment in a manner characteristic of supercoiled DNA. We have shown that the degree of supercoiling is the same in control and AT lymphoblastoid cells using sedimentation in the presence of ethidium bromide. The extent of breakage after exposure of cells to y-radiation, and the rate of repair of these breaks are similar in both cell types. Rate of repair of strand breaks is dose dependent and the restructured rapidly sedimenting complex behaves similarly, on sucrose gradients containing ethidium bromide, to that extracted from unirradiated cells.
Dna synthesis and mitosis in fused cells: I. hela homokaryons
Authors: Johnson R. T. , Harris H.
Published: April 2021

When HeLa cells growing in asynchronous culture are fused together by inactivated Sendai virus, synchrony of DNA synthesis and mitosis is rapidly imposed in the resultant multinucleate cells, even though the single cells which fuse to form these multinucleate cells are at different stages of the cell cycle. Some measure of nuclear co-ordination can already be observed within a few hours of cell fusion, and maximal synchrony is achieved within 2 days. By the end of the second day after fusion, asynchronous DNA synthesis or mitosis is rare. In binucleate cells this high order of synchrony is maintained for at least 5 days, but in cells containing greater numbers of nuclei some loss of synchrony begins to appear after the third day. The results indicate that the ability of the multinucleate cell to co-ordinate nuclear events is not impaired by the use of virus to facilitate cell fusion.
Dna synthesis and mitosis in fused cells: II. hela-chick erythrocyte heterokaryons
Authors: Johnson R. T. , Harris H.
Published: April 2021

When chick erythrocyte nuclei are introduced into the cytoplasm of HeLa cells they resume the synthesis of DNA. The reactivated nuclei synthesize DNA in a highly co-ordinated manner and essentially in synchrony with the HeLa nuclei. Asynchronous DNA synthesis is rare. The erythrocyte nuclei in the HeLa cytoplasm respond to the signals which regulate DNA synthesis in the same way as the HeLa nuclei; and they do not, for at least 2 days after cell fusion, interfere in any way with the synthesis of DNA in the HeLa nuclei.
Dna synthesis and mitosis in fused cells: III. HeLa-Ehrlich heterokaryons
Authors: Johnson R. T. , Harris H.
Published: April 2021

Unlike HeLa homokaryons and HeLa-erythrocyte heterokaryons, heterokaryons made by fusing HeLa cells with Ehrlich ascites cells do not, in general, succeed in synchronizing DNA synthesis or mitosis. Indeed, a form of antisynchrony is observed in which most of the Ehrlich nuclei synthesize DNA and most of the HeLa nuclei do not. This anomalous situation appears to be the consequence of competition between the Ehrlich nuclei and the HeLa nuclei for some factor or factors essential for DNA synthesis. In this competition the Ehrlich nuclei are overwhelmingly successful, so that synthesis of DNA in the HeLa nuclei is largely inhibited. The patterns of DNA synthesis in these heterokaryons are thus essentially determined by the proportions of the two kinds of nuclei in the cell.
Lavender, a chick melanocyte mutant with defective melanosome translocation: a possible role for 10nm filaments and microfilaments but not microtubules
Authors: Mayerson Paula L. , Brumbaugh John A.
Published: April 2021

Lavender is a mutation of chick neural-crest-derived melanocytes showing dilute feather pigmentation. This defect, previously attributed to a lack or attenuation of dendrites, was found to be due to a defect in melanosome translocation. The mutant phenotype, of melanin-congested perikarya and pigmentless dendrites is expressed both in vivo and in vitro. Studies with colcemid and cytochalasin B suggest that the avian melanocyte resembles a dispersing amphibian melanophore in its requirement for microfilaments but not microtubules.

Ultrastructural analysis revealed a normal complement of intracellular filaments. Microtubules, however, are scarce. Intermediate (10 nm) filaments surround and are closely associated with intracellular organelles, while microfilaments interconnect all filaments and organelles. Whole-cell centrifugation at 300 g showed that 10 nm filaments stream behind and appear to attach to mobile membrane-bound organelles including the nucleus, lipid granules and mitochondria, as well as melanosomes. It is suggested that all intracellular filaments, especially microfilaments and intermediate filaments, interconnect forming a network responsible for organelle motility.
DNA replication in Chironomus polytene chromosomes during treatment with ethanol
Authors: Lönn Ulf
Published: April 2021

DNA replication in Chironomus polytene chromosomes was investigated. The results show that during treatment with ethanol there is an accumulation of newly synthesized DNA with the size expected of replicons. These and previous results indicate that it is possible that in polytene chromosomes the termination of replication and merging of adjacent replicons is more sensitive to damage than the initiation and/or elongation steps.
Sequential alterations in the nuclear chromatin region during mitosis of the fission yeast Schizosa Ccharomyces Pombe-: Video fluorescence microscopy of synchronously growing wild-type and cold-sensitive cdc mutants by using a dna-binding fluorescent probe
Authors: Toda Takashi , Yamamoto Masayuki , Yanagida Mitsuhiro
Published: April 2021

Video-connected fluorescence microscopy was introduced to study the yeast nuclear chromatin region. It was defined as the nuclear area where a DNA-binding fluorescent probe 4′,6-diamidino-2-phenylindole specifically bound and fluoresced. The 3-dimensional feature of the mitotic chromatin region was deduced by analysing the successive video images of a cell viewed at different angles. By investigating synchronous culture of the wild-type fission yeast Schizosaccharomyces pambe, we found sequential structural alterations in the chromatin region during mitosis. The steps found include the compaction of the chromatin region from the regular hemispherical form, the formation of a U-shaped intermediate and the rapid segregation into 2 daughter hemispherical forms. Six cs cdc mutants, apparently blocked in mitosis, were observed by fluorescence microscopy. Under the restrictive conditions their chromatin regions exhibited either hemispherical, compact, disk-like, U-shaped or partially segregated chromatin regions. Two mutants showed anomalous nuclear locations. The results of the temperature shift-up experiments of the highly reversible KM52 and KM108 strains supported the above scheme of sequential alterations in the chromatin region.
A biochemical dissection of the cardiac intercalated disk: isolation of subcellular fractions containing Fascia Adherentes and gap junctions
Authors: Colaco C. A. L. S. , Evans W. Howard
Published: April 2021

In view of our limited knowledge of the biochemical composition of intercellular junctions, a method was developed for the preparation from rats and mice of plasma membranes containing cardiac intercalated disks. When these membranes were extracted with detergents, e.g. N-lauryl sarcosinate or deoxycholate, the detergent-insoluble material contained structures derived mainly from fascia adherentes junctions, but a few gap junctions and maculae adherentes were also present. When the detergent extraction was carried out at an alkaline pH, the maculae adherentes junctions were dissolved. Fractionation of the detergentinsoluble extract on a sucrose gradient yielded a fraction containing fascia adherentes junction of density 1.20–1.26 g/cm*. Gap junctions banded at a lower density, 1.16–1.20 g/cm3. Polyacrylamide gel electrophoresis showed that the major polypeptide bands in the fascia adherentes-enriched fraction were of molecular weights 134000, 108000, 62–64000, 58000, 47000 and 43000. Although fractions with the gap junctions were contaminated by fascia adherentes junctions, the major polypeptides were calculated by subtraction to be of mol. wt 37000, 26000 and 19000. Two glycoproteins corresponding to minor polypeptides visualized by Coomassie Blue staining were present in the fascia adherentes fraction. Comparison of the fasci aadherentes-enriched fraction with a Z-disc fraction prepared from rabbit hearts indicated a different morphology and polypeptide composition.
Stability ratio of red blood cells: Its dependence on temperature and its relationship to the erythrocyte sedimentation rate
Authors: Sewchand Lionel S.
Published: April 2021

The theory of the coagulation of particles in laminar shear flow was applied in a study of the aggregation of red blood cells. The theory predicts that in a system of initially dispersed particles the total particle concentration would decay (because of aggregation) logarithmically with time with the decay rate, depending on the adhesiveness of the particles. The applicability of this theory was tested at 4 different shear rates (G = 5.0 s-1, 12.6 s-1, 15.7 s-1 and 23.3 s-1) for normal red blood cells in plasma. At every shear rate it was found that an equilibrium condition was approached after 10–20 min, suggesting that the equation is valid only during the first 10–20 min of the aggregation process. Having established the time period over which the theory is valid, values for the stability ratio of red blood cells were computed. The stability ratio, which is essentially a measure of the adhesiveness of the cells, is defined as the ratio of the number of effective collisions (collisions resulting in adhesion) to the total number of collisions.

A very simple shearing technique was used. The suspension of red blood cells was placed in a small weighing bottle and the shearing force was provided by a small magnetic stirring rod, whose rotational frequency could be controlled. The mixing chamber was clamped in a small water bath, which in turn rested on a heated magnetic stirrer. Samples for microscopic viewing and counting were prepared by transferring a very small volume of the suspension onto a microscope slide and preserving it by placing an identical slide on top.

The stability ratio (α) was found to have a negative linear relationship with shear rate (regression line α = 0.02640 — 0.00084 G, r = 0.94) and extrapolation to a = o suggests that a minimum shear rate of ∼ 32 s-1 is required to prevent re-aggregation of the red blood cells. For 10 healthy men and women the stability ratio, calculated at a shear rate of 12.6 s−l, was found to be 0.0129 ±0.0009 (S.E.M.).

The stability ratio was also found to be temperature-dependent. It increased linearly with temperature from 4 °C to 41 °C and then decreased at higher temperatures, becoming zero at a temperature of 52 °C.

Results obtained from a group of patients with high erythrocyte sedimentation rate (e.s.r.) were combined with those from normal, healthy subjects and a positive linear relationship between α, and e.s.r. was obtained. This finding suggests that the stability ratio might be a valuable measurement in comparing red blood cells in disease with normal red blood cells.
Effects of 5-bromo-2′-deoxyuridine on friend erythroleukaemia cells : II. oxidative metabolism and enzyme content of whole cells and isolated mitochondria
Authors: Walter Robert J.
Published: April 2021

Untreated or bromodeoxyuridine (BrdUrd)-treated Friend erythroleukaemia (EL) cells from 15- and 72-h cultures were harvested and the mitochondria were isolated by homogenization and differential centrifugation. Aliquots of the original cell suspensions or the final mitochondrial suspensions were either fixed for electron microscopy, assayed for enzyme activities, or introduced into a i-ml Clarke oxygen electrode chamber. Whole BrdUrd-treated cells exhibited notable morphological alterations (see accompanying paper) but no effect was observed on whole-cell respiration. Morphologically, isolated mitochondria exhibited a highly condensed matrix and a greatly expanded outer compartment. Functionally, these mitochondria oxidized a variety of substrates at high state-3 (ADP-stimulated) rates (60–210 ng atoms O/min per mg protein) and displayed adequate respiratory control and ADP/O ratios. In the mitochondria isolated from BrdUrd-treated EL cells (both 15- and 72-h cultures), the state-3 oxygen consumption rates, respiratory control ratios, and ADP/O ratios generally decreased compared to their matched controls. These functional deficiencies coincided with in situ increases in the volume of the mitochondrial compartment and conspicuous (30–100%) increases in the specific and total activities of several mitochondrial enzymes. In addition, the mitochondria isolated from the 72-h group (treated and untreated) displayed immediate alterations when BrdUrd was added to the electrode chamber. Oxygen consumption rates dropped, respiratory control ratios changed moderately, and ADP/O ratios increased. BrdUrd may act both as an inhibitor of oxidative phosphorylation and perhaps as a sink for some of the high energy phosphate that is being generated. Thus, BrdUrd may exert its inhibitory effect on cell differentiation by interfering with mitochondrial function.
Identification of a microfilament-enriched, motile domain in amoeboflagellates of Physarum Polycephalum
Authors: Pagh Kathryn , Adelman Mark r.
Published: April 2021

A distinctive, transient cytoplasmic domain was identified in haploid cells of Physarum polycephalum that are transforming from amoebae into flagellate swimming cells. As revealed by light microscopy, this region, termed the ridge, is a flattened cytoplasmic extension that displays a specific form of motility, characterized by undulations that propagate rapidly down its long axis. The ridge was further examined by scanning electron microscopy of whole cells, and by transmission electron microscopy of serial sections and negative stain preparations of amoeboflagellate cytoskeletons. We identified three distinct components possibly related to ridge motility: a short flagellum closely associated with the ridge surface, an array of micro-tubules that is part of a complex microtubular apparatus and a network of filaments that forms a well-defined laminar core within the ridge.

Labelling studies with heavy meromyosin subfragment 1 (S-1) indicated that a major portion of the filament network is actin. Peripheral microfilaments appeared to have a uniform orientation in that arrowheads pointed towards the cell body. Other ordered filament arrangements were apparent with a modified extraction protocol using phalloidin. Similar microfilament organization has been reported in motile regions of other systems, such as the lamellipodia of tissue culture cells. However, the ridge can be distinguished from such other motile regions in that it forms independently of contact with a substratum and is only present in a specific region of amoeboflagellates. Moreover, the ridge appears at a specific time during the course of the transformation.

The ridge constitutes a new system for studying the structural basis of cell motility. The arrangements of actin- and microtubule-containing ridge components suggest several testable hypotheses concerning their involvement in cytoskeletal or motile functions.
The course of the acrosome reaction in guinea-pig sperm
Authors: Green D. P. L.
Published: April 2021

The acrosome reaction in guinea-pig sperm is accompanied by a marked cavitation of the acrosomal contenta. Two divergent views are held as to whether this cavitation precedes or follows the membrane fusion that occurs in the reaction. To distinguish between these 2 views cavitation was induced in media containing a colloid, either Ficoll 70 or inulin, either by inducing a normal acrosome reaction using the calcium ionophore A2 3187 or by using the detergent Triton X100. Both Ficoll 70 and inulin, when incorporated into media of normal osmolality, were able to suppress various features of the cavitation. Complete retention of acrosomal shape was achieved in sperm treated with detergent in 30% (w/v) Ficoll 70 solution despite the absence of the limiting acrosomal and plasma membranes. This evidence supports the suggestion that the cause of the cavitation is a colloid osmotic pressure within the acrosomal matrix. This in turn supports one of the 2 proposed mechanisms for the temporal sequence of events occurring in the acrosome reaction.
Cell volume and the control of the Chlamydomonas cell cycle
Authors: Craigie R. A. , Cavalier-smith T.
Published: April 2021

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
A massive system of microtubules associated with cytoplasmic movement in telotrophic ovarioles
Authors: Macgregor H. C. , Stebbings H.
Published: April 2021

The telotrophic ovary of Notonecta glauca glauca consists of 7 ovarioles. Each ovanole comprises, from front to rear, a terminal filament, a trophic region, a prefolhcular region, and a series of 10-15 follicles of progressively increasing size The trophic region is largely syncytial and is made up of polyploid trophic nuclei packed around a central trophic core The cytoplasm of the trophic core is continuous with the cytoplasm of each oocyte through a system of trophic tubes. There is one trophic tube per oocyte. The trophic nuclei have large nucleoh. There are a few small nucleoh in the oocyte nuclei The cytoplasm of the trophic core, the trophic tubes, and the oocytes is rich in RNA. Autoradiographs of sections of ovarioles fixed 2 h after injection of PHjundine into animals show label over the trophic nuclei only. Eight-hour autoradiographs show heavy labelling of the trophic region and label over the front ends of the trophic tubes, but little label over the posterior regions of the tubes or the oocyte cytoplasm. Later autoradiographs indicate that label gradually spreads backwards from the trophic core, along the trophic tubes, and progressively builds up in the oocyte cytoplasm These observations are thought to indicate synthesis of RNA in the trophic region and movement of RNA from the trophic core along the trophic tubes to the oocytes The trophic core and tubes show brilliant positive form birefringence with respect to their lengths. This birefringence can be reduced by keeping animals at 2 °C for 12 h, and eliminated by placing ovanoles in 1 % colchicine for 6 h. Electron micrographs of thin sections of ovanoles show that trophic core and tubes are densely and uniformly packed with nbosomes and microtubules The latter are lined up along the trophic tubes. There are about 30000 microtubules evident m a TS through a trophic tube 15 fim wide. Lengths of microtubules up to 2 /*m have been observed. Ribosomes are packed between the microtubules but are excluded from regions where the spacing between adjacent microtubules is less than 25 ran The contribution of the trophic region to the oocytes and the role of the microtubules in maintaining or facilitating the movement of nbosomes along the trophic tubes is discussed
Genetic recombination in Coprinus II. its relations to the synaptinemal complexes
Authors: Lu B. C.
Published: April 2021

The frequency of genetic recombination in Coprinus lagopus may be modified by heat and cold shock. By removal of samples from a fruiting body before and after temperature treatment, it is possible to study the ultrastructure of chromosomes at the time recombination frequency (between den+ × +me—1) can be modified. The sensitive period for temperature effects and, therefore, probably the time of crossing over, commences with the formation of the synaptinemal complex (s.c.) and ends with its disappearance, i.e. during the entire existence of the s.c. It is concluded that recombination is an event subsequent to the formation of the s.c. and is independent of the process of its formation. It is suggested that the event takes place at the synaptic centre.
Absence of step changes in activity of certain enzymes during the cell cycle of budding and fission yeasts in synchronous cultures
Authors: Creanor J. , Elliott S. G. , Bisset Y. C. , Mitchison J. M.
Published: April 2021

Synchronous cultures prepared by selection from an elutriating rotor were used to measure activity changes during the cell cycle of the following enzymes: acid phosphatase in Schizosac-charomyces pontbe and Saccharomyces cerevisiae, a-glucosidase in S. cerevisiae and /Lgalacto-sidase in Kluyveromyces lactis. There was no sign of step rises in activity in acid phosphatase but there were indications in S. cerevisiae of the linear pattern with rate doublings once per cycle that had been found previously in S. pombe. There was also no sign of step rises in the other two enzymes, in contrast to earlier results using different techniques. Asynchronous control cultures showed little or no perturbations after the first hour.
Stromal colonies from mouse marrow: Characterization of cell types, optimization of plating efficiency and its effect on radiosensitivity
Authors: Xu C. X. , Hendry J. H. , Testa N. G. , Allen T. D.
Published: April 2021

Modifications to the colony assay in vitro for stromal progenitor cells in mouse femoral marrow have been studied so as to optimize the efficiency of colony formation (CFE). The highest reproducible concentration achieved was about 30 colonies (containing fibroblasts, macrophages and endothelioid cells) per 106 nucleated marrow cells (range 20—50) in mice 3—4 months old, and higher by 50% in mice 14–15 months old. Each of many slight technical modifications could reduce these values by more than 30%.

The importance of optimization was demonstrated by a reduced radiosensitivity when the CFE was reduced by a factor of 3 using a-medium stored at 4°C for 15 days. The Do value was 3·9 ± 0·8 Gy compared to 1·6 ± 0·1 Gy using freshly prepared medium, and this could be due to the selection of a radioresistant subpopulation.

The modifications studied may partly explain the marked variations in CFE and in radiosensitivity reported in the literature.
Circadian rhythm of protein synthesis activity in the exocrine pancreas of fed and starved rats
Authors: Völkl A. , Poort C.
Published: April 2021

Rats, either fed a solid standard chow ad libitum or starved for 24 h prior to the beginning of the experiments, were kept in a normal light-dark cycle of 12 h. At certain times over a total period of 24 h, three animals of each group were killed, their pancreata were excised and the protein synthetic capacity was determined, measuring both the amount of cellular RNA and the percentage of ribosomes active in protein synthesis. A clear-cut circadian rhythm in the synthetic activity was found, well expressed in the fed animals but less evident and shifted in time in the starved ones. The RNA/DNA ratios in the two sets of animals remained fairly constant throughout the day, but were somewhat lower in the fasted rats.
Higher-Order Structure Of Chromatin From Resting Cells : Ii. High-Resolution Computer Analysis Of Native Chromatin Fibres And Freeze-Etching Of Nuclei From Rat Liver Cells
Authors: Nicolini C. , Cavazza B. , Trefiletti V. , Pioli F. , Beltrame F. , Brambilla G. , Maraldi N. , Patrone E.
Published: April 2021

Non-destructive electron microscopy of native chromatin from rat liver nuclei reveals that the 30 nm fibre is formed of four 11 nm nucleofilaments, arranged in a coiled-coil (or rope-like) conformation. At low ionic strength, native fibres show an alternating pattern of compact and unwound regions. Freeze-etching experiments carried out on the same nuclei are compatible with the existence of periodic attachments of the fibres to the nuclear envelope near the pores in a regular, drapery-like fashion.

For the first time, computer image analysis has been applied to electron micrographs of giant chromatin fibres and a few essential geometrical parameters characterizing the conformation of the higher-order structures have been determined. No significant difference has been found between calf thymus and rat liver chromatin.
Changes In Poly(A)+ Rna During Male Meiosis In Lilium
Authors: Porter E. K. , Parry D. , Dickinson H. G.
Published: April 2021

Levels of poly(A)+ RNA have been investigated at each stage of male meiosis in Lilium (var. Firecracker). Two methods were employed in this work: in one extracts from labelle’d meiocytes were passed through oligo(dT) columns, while in the other the specific probe [3H]poly(U) was hybridized in situ with resin-embedded sections of pollen mother cells. The label contained in the eluate from the oligo(dT) columns was measured by liquid scintillation, and the quantity of [3H]-poly(U) hybridized was determined by statistical analysis of light microscopic autoradiographs. Both techniques revealed a dramatic decline in detectable poly(A)+ RNA during prophase. Lowest levels are reached in the pachytene stage, following which a gradual restoration of this species of RNA takes place in both nucleus and cytoplasm. The data presented here provide no clear indication as to whether this fall in RNA levels is caused by the action of novel enzymes specific to the meiotic prophase, by a cessation of synthesis and the activity of normal turnover processes, or by a combination of the two. Although there is some evidence from the [3H]poly(U) hybridization study that a small peak of poly(A)+ RNA synthesis may take place in leptotene, both methods indicate that there is a very low level of poly(A)+ RNA synthesis throughout prophase. The presence of poly(A)+ RNA was not detected in either the accessory nucleoli or the cytoplasmic nucleoloids that characterize the nucleus and cytoplasm of these cells. These events are considered in terms of the juncture at which they occur in the plant life-cycle.