bluuebunny/crossref_metadata_2025_split huggingface dataset:
Movement of the cell surface and change in surface area during cleavage in the newt’s egg
Authors: Sawai Tsuyoshi 
Published: April 2021

ABSTRACT
In cleaving eggs of the newt, Cynops pyrrhogaster, the behaviour of the egg surface was analysed by observing linear and area changes in a transplanted piece of cortex which differed in pigmentation from the background.
Results from the animal hemisphere showed that the surface in the cleavage plane shrank extensively in the region where the early cleavage furrow was being formed. On both sides of the cleavage plane, the surface began to shrink in a direction parallel to the cleavage furrow and to stretch perpendicularly to the furrow, simultaneously with the onset of cleavage. The nearer the grafted region was to the furrow, the greater the change. These changes continued until about the time of the appearance of unpigmented surface on both walls of the furrow, when a maximum was reached. Thereafter a slight reversal was observed. Similar changes of lesser magnitude were encountered in regions remote from the cleavage plane. The surface area decreased in the vicinity of the furrow during the early phase of cleavage and returned roughly to its original value during the late phase, while, in the distant region, only an increase occurred.
Results from the vegetal hemisphere showed that little linear change of surface occurred even in the region adjacent to the furrow, while the surface area changed in the furrow region similarly to the animal half. In the vegetal hemisphere remote from the furrow, the changes took place to a lesser extent.
Pinocytosis and intracellular digestion of 125I-labelled haemoglobin by trophoblastic cells in tissue culture in the presence and absence of serum
Authors: Contractor S. F. , Krakauer Kathryn 
Published: April 2021

ABSTRACT
One aspect of human placental function which has not hitherto been studied is the ability of the placenta to digest proteins intracellularly and use the products of hydrolysis to supply its own and foetal needs for nutrition and protein synthesis. Placental lysosomes have a full complement of hydrolytic enzymes, including the acid proteases cathepsin C and D. We have used trophoblast cells in monolayer tissue culture as a model for the study of endocytosis and intracellular digestion of 125I-haemoglobin. The normal use of serum in tissue culture medium has shown up differences from the pattern observed with other phagocytic cells such as macrophages, in that serum allows endocytosis but prevents intracellular digestion 125I- haemoglobin. Replacement of serum by lactalbumin hydrolysate enables both endocytosis and intracellular digestion of 125I-haemoglobin to occur as in other phagocytic cells. Digestion is followed by release into the medium of acid-soluble, lower-molecular-weight compounds. The reasons for this major difference between trophoblast and other cells are discussed in the light of our results and their possible relevance to placental function.
Studies on the template activity of ‘isolated’ Xenopus erythrocyte nuclei: II. the effects of cytoplasmic extracts
Authors: Maclean Norman , Hilder Vaughan A. 
Published: April 2021

ABSTRACT
The effects of exposing nuclei isolated from Xenopus erythrocytes to cytoplasmic extracts prepared from various sources on their template activity are described. The cytoplasm of rat liver cells and the immature blood cells of Xenopus contain factors which stimulate RNA synthesis in these essentially inactive nuclei, whereas the cytoplasm of many other cells does not yield such factors. The active factors in rat liver cytoplasmic extracts appear to be proteins of molecular weight about 40000 Daltons. The implications of these results for genetic control in eukaryotes are discussed.
Calcium-rich, refractile granules in Tetrahymena pyriformis and their possible role in the intracellular ion-regulation
Authors: Nilsson Jytte R. , Coleman James R. 
Published: April 2021

ABSTRACT
Tetrahymena pyriformis GL is known to accumulate small, refractile granules during unfavourable growth conditions. Furthermore, electron microprobe analysis of granules in situ has shown them to be calcium-rich, with calcium bound in an apatite-like material.
The present study deals with the identification of these granules in the electron microscope. During granule formation Tetrahymena contains several structures with increased electron density, e.g. mitochondria, lipid droplets, and autophagic-like vacuoles; however, the most conspicuous feature is a membrane-bound structure with amorphous contents of varying electron density. These structures are believed to represent the calcium-rich granules. Their limiting membrane resembles the cell membrane in structure and polarization, i.e. one side of the membrane bilayer is thick and electron-dense. The electron-dense layer of the granule membrane faces the lumen of the granule (high content of calcium) and that of the cell membrane faces the external medium (high concentration of calcium); in both cases the less electron-dense layer of the membrane borders the cytoplasm (low concentration of calcium). This polarization is believed to be connected with the functions of the membrane. The cells also contain small tubular structures with a membrane similar in structure to that of the granules and with an amorphous content similar to that of the granules. These tubular structures are often found close to or in direct connexion with the granules and their possible involvement in granulogenesis is proposed.
The calcium-rich granules may play a role in the regulation of the intracellular concentration of calcium. Their formation correlates with a decrease in the general metabolism of the cells, i.e. conditions during which the intracellular concentration of calcium is likely to increase. A model is proposed for the possible pathways of calcium in Tetrahymena during normal and unfavourable growth conditions. In addition, the possible involvement of other cytoplasmic inclusions, e.g. mitochondria, in this regulation is discussed.
Linear increase in glycolytic activity through the cell cycle of Schizosaccharomyces pombe
Authors: Hamburger Kirsten , Kramhøft Birte , Nissen Susanne B. , Zeuthen Erik 
Published: April 2021

ABSTRACT
The glycolytic activity of 3 different synchronous systems in S. pombe was studied. Synchronous cultures were produced by a selection procedure, by cyclic heat treatment, or by cloning cells from an exponentially multiplying culture. In all experiments a complex medium with 3 % glucose was used. The glycolytic activity was recorded with a gasometric method, the gradient diver. A single cell in exponential growth or a small number of synchronized cells were placed in ampulla divers in which the cells progressed undisturbed through a number of cycles. An ampulla diver is in principle a narrow pipette by which a single or a few cells are removed from the mother culture. It serves next as an axenic growth chamber and at the same time as a gasometer. The divers were placed in linear saline density gradients and the gaseous exchanges taking place in the divers resulted in migration of the divers. The migration rate is a measure of the glycolytic activity of the cells. Our results show that the glycolytic activity increases in a linear fashion between successive divisions. The rate of increase doubles at each division. This is true in all 3 synchronous systems, and we take this as an indication that the cell cycles of heat-synchronized cells do not deviate seriously from the normal.
High-density induction of a quiescent cell state in Physarum Polycephalum
Authors: Mcalister L. E. , Allison V. F. , Jeter J. R. , Nations C. 
Published: April 2021

ABSTRACT
The non-histone protein complement of Physarum polycephalum changes rapidly when microplasmodia are subjected to conditions of high density. The changes in these proteins induced by high density are similar to the changes observed during starvation-induced encystment. A 50% decrease in DNA synthesis, observed after 7 h of starvation, is observed after only 1 h of high density. High density also results in a decrease in RNA synthesis comparable to decreases induced by prolonged starvation. Total heterochromatin increases in response to either high density or starvation. Increased heterochromatization is preceded by an increase in nuclear actin. Mitochondrial morphology and cytoplasmic organization are also similarly altered by starvation and high density. These observations suggest the possibility of a generalized mechanism for cellular transition from active growth to a non-proliferative cell state.
The ultrastructure of the somatic cortex of Pseudomicrothorax Dubius-: Structure and function of the epiplasm in ciliated protozoa
Authors: Peck Robert K. 
Published: April 2021

ABSTRACT
The ultrastructure of the somatic cortex of the ciliate Pseudomicrothorax dubius is studied with emphasis on the epiplasm layer which lies immediately under the inner alveolar membrane and is continuous with the terminal plates of cortical basal bodies.
In addition to a clearly demonstrable cytoskeletal role, the epiplasm appears to function as a cementing substance which integrates numerous cortical fibres and membranes. The kinetodesmal, postciliary and transverse fibre systems which originate at the proximal ends of basal bodies extend toward the cell surface and end at or in the epiplasm. Inner alveolar membranes and trichocyst membranes are attached to the epiplasm. Basal bodies are anchored into the epiplasm via their terminal plates.
The epiplasm appears to be morphogenetically important as a matrix into which newly formed basal bodies insert. Electron-opaque arms occur at the terminal plate level of new basal bodies, and these arms fuse with the epiplasm when basal body insertion occurs. The position of trichocysts in the cortex is specified by the epiplasm.
Evidence from numerous other ciliates tends to confirm both structural and morphogenetic roles of the epiplasm.
Evidence from serial sections that some cells contain large numbers of mitochondria
Authors: Heywood Peter 
Published: April 2021

ABSTRACTThree-dimensional reconstructions based on serial sections through cells of the chloro-monadophycean alga Gonyostomum semen Diesing indicate that there are many small unbranched mitochondria in log-phase cells. These organelles are approximately ellipsoid in shape with their longest axis usually ranging from 0 7 to 2·0 μm in length. Occasionally mitochondria reaching up to 3·6 μm in length have been observed: these have the same general morphology as their smaller counterparts. Preliminary observations indicate that cells of a related alga, Vacuolaria virescens Cienkowsky, also possess many small unbranched mitochondria.These observations are discussed in relation to recent reports that some cells contain a single branched mitochondrion or, at most, a small number of these organelles. It is suggested that mitochondrial number may be related to cell volume and that large cells may contain many mitochondria.
Outgrowth of human fibroblast aggregates on a substratum triggers a wide variety of morphogenetic properties in the cells
Authors: Schueren Bernadette Van Der , Cassiman Jean-Jacques , Berghe Herman Van Den 
Published: April 2021

ABSTRACTTwenty-four-hour-old aggregates of human diploid skin fibroblasts are allowed to attach to a glass or plastic substratum. As a result of this attachment the cells in the aggregate demonstrate rapid and generalized changes in cell shape, cell surface and cytoplasm ultrastructure and in their ability to incorporate [3H]thymidine. Within 24 h they grow out on the substratum to attain the regular monolayer configuration. During the process of leaving the aggregate for the substratum a great number of different morphogenetic properties are displayed by the cells, resembling the properties of embryonic or epithelial cells. The simultaneous occurrence of this great variety of cell shape and cell surface changes, many of them unusual for fibroblasts, as well as the concurrent formation of organized cytoplasmic structures — microfilaments, microtubules –at localized areas of the cells, makes this system a potentially useful tool in the study of cell behaviour.
Structural changes in the epidermal cells of Rhodnius during tracheole capture
Authors: Wigglesworth V. B. 
Published: April 2021

ABSTRACT
Epidermal cells deprived of their oxygen supply by tracheal section give off cytoplasmic processes which become attached to air-filled tracheoles in neighbouring areas and draw these into the oxygen-deficient zone.
Many of these cytoplasmic strands exceed 100 μm in length but may be no more than 50 nm in diameter; they contain mitochondria, ribosomes, microtubules and microfilaments. In basic structure they resemble the tendon cells; and also the tapering conical epidermal cells along the intersegmental borders of the abdomen, the terminal strands of which are inserted into the basement membrane behind and in front of the segmental boundaries.
The cytoplasmic walls of those tracheoles most exposed to tension during the process of tracheole capture become thickened and packed with microtubules.
In all these structures the microtubules are believed to be concerned in resistance to tension. Contraction is presumably effected by microfilaments, but no new evidence is given. The possible role of the epidermal strands in the transport of energy-rich metabolites is discussed.
Intercellular junctions in the central nervous system of insects
Authors: Lane Nancy J. , Skaer Helen Le B. , Swales Esley S. 
Published: April 2021

ABSTRACT
The intercellular junctional complexes in the central nervous system (CNS) from a variety of insect species have been examined by thin-sectioning and freeze-fracturing techniques. Of particular concern has been the fine-structural basis of the blood-brain barrier observed to be present in the outer perineurial layer around the avascular insect CNS. The basis of this has been found in the form of tight junctions (zonulae occludentes) present both in sections and in replicas of the perineurium. In the latter, they appear as one or two simple linear ridges, lying parallel to the outer surface, which occasionally display overlapping. The complex geometry of the interdigitating perineurial cells apparently permits such a relatively simple series of ridges to function as a barrier, since tracers are found not to penetrate beyond this level into the underlying nervous tissue. Such evidence is supported by microprobe X-ray analysis of lanthanum-incubated tissues, the perineurium compared with the glia-ensheathed axons showing the presence and absence of lanthanum, respectively. Possible physiological mechanisms that could operate ‘in vivo’ to maintain the blood-brain barrier are also considered. Other intercellular junctions such as desmosomes, septate junctions and gap junctions are found in the perineurial layer too, the last exhibiting EF particle plaques and PF pits. Glia-glia junctions also occur in some insect species; they include desmosomes, inverted gap junctions and occasional tight junctions. Septate, gap and tight junctions are also found on the membranes of trecheóles penetrating the CNS. Short, ridge-like elaborations and other particle arrays are found on the PF of the axon surfaces and the significance of these structures is discussed.
Combined histochemical and x-ray microanalytical studies on the copper-accumulating granules in the mid-gut of larval Drosophila
Authors: TAPP R. L. , Hockaday Austin 
Published: April 2021

ABSTRACT
The copper-containing granules in the mid-gut epithelium of larval Drosophila melanogaster were examined for acid phosphatase by combined histochemistry and energy-dispersive, X-ray microanalysis. After incubation, many of the granules were shown to contain simultaneously copper and sulphur (which are normal constituents), and lead and phosphorus (which are the detectable elements of the reaction product). Earlier work has been consolidated and extended and the evidence that the granules are formed as cytolysosomes is reviewed.
Effects on cell adhesion and membrane fluidity of changes in plasmalemmal lipids in mouse l929 cells
Authors: Schaeffer Barry E. , Curtis A. S. G. 
Published: April 2021

ABSTRACTIt has recently been shown that the lipid composition of the plasmalemma may be altered by taking advantage of the acyltransferase system to incorporate selected fatty acids into phosphatidyl lipids of the plasmalemma. Such lipid alterations have been shown to effect changes in cell adhesion in chick neural retina cells. Based on the fluid-mosaic model, it has been suggested that such changee in cell behaviour may be related to the degree of plasmalemmal fluidity. In the present study, when mouse L929 cells are incubated in the presence of stearic or arachidic acid (saturated), cell adhesion levels, as measured by an assay based on cellsubstrate interaction, increase. Similar incubation with linoleic or linolenic acid (unsaturated) decreases cell adhesion.In addition, we have found significant changes in plasmalemmal fluidity, using an assay based on patching of fluorescent antibody. Unsaturated fatty acids have a fluidizing effect on the membrane, while saturated fatty acids exert a solidifying effect, when substituted into the membrane. Although alternative interpretations are possible, we suggest that membrane fluidity changes are induced by alterations in lipid thermal transition temperatures of plasmalemmal phosphatidyl compounds, in which fatty acid substitutions were made. We also suggest that changes in membrane fluidity might affect adhesion by altering the aggregability of any membrane sites that may be involved in adhesion. Although a very fluid membrane may allow rapid lateral migration of sites, it might also aid their rapid dispersal, thereby reducing adhesion.
Role of Ca2+ In preserving viability of friend erythroleukaemic cells after ultramicroinjection
Authors: Wasserman Moshe , Loyter Abraham , Kulka Richard G. 
Published: April 2021

ABSTRACT
Ca2+ facilitated the fusion by Sendai virus of Friend erythroleukaemic cells and Ehrlich ascites tumour cells but not that of hepatoma tissue culture cells. In the absence of Ca2+ Sendai virus caused the complete depletion of ATP and abolished protein synthesis in Friend erythroleukaemic cells fused with each other. Addition of high concentrations of Ca2+ (10 – 20 mM) partially protected the cells from ATP depletion. After a further incubation of cells in complete medium plus 0 ·2 MM adenine, ATP levels and protein synthesis were restored to 60 – 85 % of those of the untreated control. The protective effect of Ca*÷ was used to improve the ultramicroinjection method which involves the fusion of human erythrocyte ghosts with cells. When human erythrocyte ghosts containing high K+ were fused with Friend erythroleukaemic cells in the presence of 10 mM Ca2+ ATP levels and protein synthesis after recovery were about 60 – 85 % of the control. Friend erythroleukaemic cells subjected to ultramicroinjection under these conditions had a cloning efficiency of 75 – 95 % of that of the untreated controls. In these experiments 70 · 100 % of the cells had fused with ghosts. Induction of haemoglobin synthesis by dimethylsulphoxide was unimpaired in cells subjected to ultramicroinjection under the same conditions.
Behaviour of kinetochore fibres in Haemanthus katherinae during anaphase movements of chromosomes
Authors: Hard Robert , Allen Robert D. 
Published: April 2021

ABSTRACT
A laser light source along with a new method of preparing endosperm cells of Haemanthus katherinae for differential interference contrast (DIC) microscopy has led to increased visibility of kinetochore fibres. Little information is available concerning the behaviour of these fibres during anaphase in living cells. In metaphase, kinetochore fibres are seen as distinct bundles of microtubules, here referred to as ‘filaments ‘, extending from the kinetochore to the ‘diffuse ‘pole. They possess an apparent globular substructure which corresponds to the moving ‘particles or states’ described previously from ciné films. In early anaphase, the filaments of each kinetochore fibre lose their parallel orientation characteristic of metaphase and splay out so that the more peripheral filaments intermingle with those of other kinetochore fibres. This process begins at the poles and proceeds as a wave toward the kinetochores as chromosomal movement progresses. This behaviour has been examined in relation to a number of proposed models for the mechanism of chromosome movement and has been found to place some constraints on some models but to be consistent with any model that hypothesizes that chromosomes move as a consequence of cumulative cohesive lateral interactions of microtubules.
Localization of histone gene transcripts in newt lampbrush chromosomes by in situ hybridization
Authors: Old R. W. , Callan H. G. , Gross K. W. 
Published: April 2021

ABSTRACT
Denatured 3H-labelled DNAs containing histone gene sequences originating from the echinoderms Psammechinus miliaris, Echinus esculentus and Strongylocentrotus purpuratus have been in situ hybridized to RNA transcripts on newt lampbrush chromosomes. Autoradiographs of the hybridized lampbrush preparations show labelling restricted to four or fewer lateral loop pairs all lying within the heteromorphic regions of chromosome I, also one or two loop pairs on chromosome VI, one loop pair on chromosome X and one loop pair on chromosome XI. For oocytes from a single newt, coincident label distribution is found with DNAs of diverse echinoderm origin; however different newts show some specific individual diversity in label distribution, including heterozygosity in the case of loops on bivalents VI and X. The more conspicuously labelled loops, particularly those on chromosome I, show a pattern of labelling which is explicable if the newt histone DNA sequences are confined to short intercepts of lateral loop axis. Transcription is initiated prior to the histone DNA sequences, proceeds through the histone DNA sequences, and beyond, and the histone RNA sequences are cut from the transcripts before the termination of transcription.
An inhibitor of cell cohesion from axenically grown cells of the slime mould, dictyostelium discoideum
Authors: Swan Alma P. , Garrod D. R. , MORRIS D. 
Published: April 2021

ABSTRACT
Medium from a stationary phase culture of axenically grown D. discoideum cells contains an inhibitor of cohesion of log phase cells. The inhibitor is a heat-stable, low molecular weight substance. Its biological effects include inhibition of cohesion of aggregation-competent cells, of cells of other slime mould species, the blocking of development on Millipore filters and a reduction in adhesiveness of slime mould cells to glass. Present evidence suggests that the inhibitor may bind to the cell surface.
Immunofluorescent anti-tubulin staining of spindles during meiotic maturation of mouse oocytes in vitro
Authors: Wassarman Paul M. , Fujiwara Keigi 
Published: April 2021

ABSTRACT
Immunofluorescent anti-tubulin staining has been used to follow nuclear progression from dictyate to metaphase II during meiotic maturation of mouse oocytes in vitro. Antibody directed against tubulin isolated from sea-urchin eggs decorates the metaphase I and metaphase II spindles, as well as the cytoplasmic bridge, midbody, and polar body of the maturing mouse oocyte. Changes in the tubulin-specific staining pattern during meiotic maturation in vitro take place in a highly reproducible manner. Oocytes exposed continuously to cytochalasin B arrest at metaphase I and display a spindle which by immunofluorescent staining is virtually indistinguishable from the spindle of untreated oocytes.