bluuebunny/crossref_metadata_2025_split huggingface dataset:
A scanning electron-microscopic study of the local degeneration of cilia during sexual reproduction in Paramecium
Authors: Watanabe Tsuyoshi 
Published: April 2021

ABSTRACT
The location and extent of local degeneration of cilia during sexual reproduction of Paramecium was studied using scanning electron microscopy to examine cells undergoing conjugation and autogamy. At some time during the mating reaction, but prior to conjugant pair formation, ciliary degeneration begins at the antero-ventral tip of cells and proceeds posteriorly along the suture. In the anterior part of the cell, degeneration occurs on both sides of the suture, but in the posterior part it is restricted to the right side of the suture. In 5 species of Paramecium examined, degeneration occurred in nearly the same region. No degeneration of cilia is observed in natural autogamy of P. tetraurelia, whereas in chemically induced autogamy of P. caudatum degeneration occurs as in ordinary conjugation. Conjugant pairs never expose any deciliated cell surface except at the poetero-ventral tip. The maximum extent of ciliary degeneration is best seen in the chemically induced autogamous cells: 7 kineties (rows of unit teritories) at the anterior-left, 4 kineties at the anterior-right, 10 or more kineties at the posterior-right and the right wall of the vestibule of the mouth. Before complete disappearance of the cilia, many short cilia are observed. This suggests that ciliary degeneration is due to resorption. Degeneration extends more rapidly in cells with stronger mating reactivity. The relations between mating reactivity, ciliary degeneration and nuclear activation are discussed.
Adenosinetriphosphate, calcium and temperature requirements for the final steps of exocytosis in Paramecium cells
Authors: Matt H. , Bilinski M. , Plattner H. 
Published: April 2021

ABSTRACT
In Paramecium cells a synchronized discharge of trichocysts (which involves only the final exocytosis steps of membrane fusion, content discharge and membrane resealing) was achieved with ATPase-blockers, Ca3+-ionophores, lipid solvents (including lysolecithin), polyethyleneglycol, anaesthetics (Dibucain) and cationic detergents (cetyltrimethylammonium bromide (CTMAB) and cetylpyridinium chloride (CPC)). Only Dibucain - and to some extent cationic detergents -can trigger exocytosis independently of extracellular Ca2+, possibly by mobilizing intracellular Ca2+. The internal free [Ca2+] necessary for exocytosis can be estimated to be &gt; 10−6 to 10−4 M. Membrane-free trichocyst contents were isolated by density gradient centrifugation; they are converted from the contracted to the expanded state by Dibucain, CTMAB and CPC, and also by exogenous ATPase (Apyrase). Thus, it is possible to de-couple the discharge (stretching) process from membrane-related phenomena. Since only the latter are inhibited by low temperature (0°C), membrane lipids probably have to be in a fluid state for exocytosis to occur. At least 2 steps appear to be involved: when membrane fusion is initiated, an independent matrix-bound system is activated for the synchronized stretching process. The energy requirement for one discharge event is estimated to be about 14 × 106 ATP molecules.
Microtubules in protozoan cells: III. ultrastructural changes during disintegration and reformation of heliozoan microtubules
Authors: Toyohara A. , Shigenaka Y. , Mohri H. H. 
Published: April 2021

ABSTRACT
In the heliozoan, Echinosphaerium nucleofilum strain MA, cold temperature (2 °C) induced axopodial retraction to about 36% of the initial length after 3 h. By electron microscopy, it was found that such axopodial shortening is accompanied by degradation of axonemal microtubules (25 nm in diameter), followed by the appearance of macrotubules (37 nm in diameter) and filamentous structures (14 nm in diameter) of a tubular and twisted appearance. All of these structures (microtubules, macrotubules and filamentous structures) were found to be depolymerized completely by applying 10 MM colchicine for 1–2 h, and to be replaced by regions with low electron density. Axopodial re-extension was induced rapidly by returning the cold-treated organisms to room temperature (20 °C). At a very early stage of axopodial re-extension, the filamentous structures were often observed to be continuous with the macrotubules. At a late stage of axopodial re-extension, the reforming axoneme was composed only of normal microtubules, while the macrotubules and filamentous structures had disappeared. On the basis of these results, the processes of disintegration and reformation of microtubules are discussed.
A collision analysis of lymphoid cell aggregation
Authors: Evans Clive W. , Proctor John 
Published: April 2021

ABSTRACT
We have obtained data on the frequency of aggregates of different size classes and on the maximum aggregate diameter of lymphoid cells subjected to aggregation in the laminar shear field of a Couette viscometer. Maximum aggregate diameter reached a plateau level during aggregation. This plateau is considered to be the result of a balance between the hydrodynamic shear forces tending to resist the formation of aggregates, and the adhesive forces of the aggregated cells tending to resist dissociation. Stepwise increases in the shear rate produced aggregates of progressively smaller maximum diameter until the limiting (i.e. control equivalent) diameter was reached. Equations governing these stepwise changes in aggregate diameter were obtained by regression analysis, and an estimate of the force of dissociation (FD,) was made from derived values of the critical shear rate. Thymocytes (FD= 2 ·54 × 10−6 N m−2 /cell) were found to be more adhesive than lymphocytes (FD = 2 ·05 × 10−6 N m−2 /cell), in agreement with current concepts.
The observed data on aggregate frequency were seen to be of poor fit with a model of aggregation derived by collision analysis of the aggregation process. This led us to consider the possibility that all cells may not share the same probability of forming an adhesion. We thus derived further models of aggregation in which some fraction of the total cells was considered to have enhanced possibilities of a collision producing an adhesion. Of the models we considered, a 15% preferred fraction offered best agreement with the experimental observations. We therefore conclude that the populations of cells studied in this report are not ‘homogenous’ in that some cells are more adhesive than others. Alterations in the percentage of the preferred fraction of cells will lead to different aggregate-frequency indices. Such changes might be expected to occur during the initial stages of carcinoma development.
Contact behaviour and pattern formation of bhk and polyoma virus-transformed bhk fibroblasts in culture
Authors: Erickson C. A. 
Published: April 2021

ABSTRACT
Certain behavioural and morphological aspects of cellular transformation have been studied, using baby hamster kidney cells (BHK21/13) and polyoma virus-transformed BHK cells. BHK cells grow to monolayers arranged in parallel arrays, whereas the transformed cells show a much greater incidence of crisscrossing and multilayering. Time-lapse cinemicrography and scanning electron microscopy were used to examine the behaviour producing these striking differences in cellular pattern.
It was found, contrary to previous thought, that in both cell lines, when contact is made ruffle to ruffle, ruffling is inhibited. When BHK cells contact each other ruffle to side, strong adhesions always occur, as evidenced by a large deformation of the contacted cell margin, with accompanying paralysis of ruffling. Then, the contacting cell either changes direction, usually spreading along the side of the contacted cell, or occasionally continues to protrude and underlap the other cell, although the original adhesions are seen to remain. Transformed cells never form strong rufHe-to-side adhesions, and usually underlap each other totally. When the cells were filmed, fixed and the same cells relocated in the scanning electron microscope, neither cell type was seen to move over the surface of another (overlap). Rather, all cells crisscross by underlapping (moving under the other cell). SEM also reveals PyBHK cells to have many fewer side-to-substratum adhesions than BHK cells. The smaller number of these attachments could explain the ease with which PyBHK cells underlap.
Regulation of interstitial cell differentiation in Hydra Attenuata : III. Effects of I-Cell and nerve cell densities
Authors: Yaross Marcia S. , Bode Hans R. 
Published: April 2021

ABSTRACT
The interstitial cell (i-cell) of hydra, a multipotent stem cell, produces two classes of differentiated cell types, nerve cells and nematocytes, throughout asexual growth. Using a new assay, the regulation of i-cell commitment to either nerve cell or nematocyte differentiation was investigated. This assay was used to determine the fractions of i-cells differentiating into nerve cells and nematocyte precursors in a variety of in vivo cellular milieus produced by hydroxyurea treatment, differential feeding, and reaggregation of dissociated cells.
Nematocyte commitment was found to be positively correlated with the size of the i-cell population and independent of the axial position of the i-cells along the body column. This indicates that i-cell commitment to nematocyte differentiation may be regulated by feedback from the i-cell population. Nerve cell commitment was found to be correlated with regions of high nerve cell density. This suggests that nerve cell commitment is regulated by feedback from the nerve cell population or is dependent on axial position. Implications of such mechanisms for the regulation of i-cell population size and distribution are discussed.
An analysis of con A-mediated agglutination in a chinese hamster ovary subclone which responds morphologically to growth in dibutyryl cyclic amp: III. The role of microvilli in the agglutination process
Authors: Noonan Kenneth D. , Ukena Thomas 
Published: April 2021

ABSTRACT
We have used the H-7 subclone of a Chinese hamster ovary cell line (K1) to investigate the role of cell surface architecture (specifically microvilli, blebs, and sheets) in determining the relative agglutinability of a cell line with Con A. Our evidence clearly demonstrates that no specific, immediately recognizable surface architecture is associated with the agglutinable or non-agglutinable phenotype. Our data suggest that the expression of microvilli on the cell surface is neither necessary to nor sufficient for the phenotype described by enhanced agglutinability with Con A. Furthermore our work demonstrates that cells covered with blebs are as agglutinable as cells covered with microvilli thereby suggesting that the intertwining of microvilli may not be an essential facet of the agglutination phenomenon.
Change of the nuclear pore frequency during the nuclear cycle of Physarum polycephalum
Authors: Schel Jan H. N. , Steenbergen Leo C. A. , Bekers A. G. M. , Wanka Friedrich 
Published: April 2021

ABSTRACT
The change of the nuclear pore frequency during the nuclear cycle of synchronous plasmodia of Physarum polycephalum was investigated. Counts were made on platinum-carbon replicas of isolated nuclei. Pore numbers varied markedly at any given time of the nuclear cycle, possibly due to the variable DNA contents of the nuclei. The average pore frequency per nucleus increased from 336 at 1 h after mitosis to 770 at 50 min before the subsequent mitosis. The results suggest a quantitative relation between the nuclear DNA content and pore frequency. This is compatible with the hypothesis that pore complexes serve as attachment sites for nuclear DNA.
RNA transcription on the giant lateral loops of the lampbrush chromosomes of the american newt Notophthalmus viridescens
Authors: Hartley S. E. , Callan H. G. 
Published: April 2021

ABSTRACT
By counting silver grains in autoradiographs of lampbrush chromosomes the rates of incorporation of [3H]adenine, [3H]cytidine, [3H]guanosine and [3H]uridine, administered separately, into RNA on the giant loops of chromosome II of Notophthalmus viridescens, were compared with the rates of incorporation of these same precursors into RNA on other, unidentified loops. The overall rate of RNA transcription on the giant loops is only about half that on the generality of other loops, and the RNA transcribed on the giant loops is computed to have a base ratio of approximately 25 A:39 C:9 G:27 U, implying that there must be about 4 times as many guanine residues on the transcribed as on the non-transcribed strand of the giant loops’ DNA.
Evidence for centriolar region RNA functioning in spindle formation in dividing PTK2 Cells
Authors: Peterson Scott P. , Berns Michael W. 
Published: April 2021

ABSTRACT
The light-activated, nucleic acid-binding drugs, psoralens, were used in conjunction with a 365-nm laser microbeam to selectively bind to any nucleic acids in the centriolar region. 4′-aminomethyl-4,5′,8-trimethyl-psoralen (AMT) has a high affinity for both RNA and DNA and can be shown to cause mitotic abortion when centriolar regions of prophase PTK, cells are reacted with AMT and 365-nm laser light. Other psoralen derivatives which have a high affinity for DNA and a low affinity for RNA are not effective in blocking mitosis in dividing PTK, cells. Examination of psoralen-bound centriolar regions by single-cell electron microscopy shows that at various times after treatment, the number of microtubules associated with the irradiated poles is much lower than in normal, dividing cells. Light-activated psoralen binding of the centriolar regions does not seem to affect the condensation or structure of mitotic chromosomes. It is concluded that there is an RNA in the centriolar region that is responsible for the formation of the spindle in dividing cells.
Associated changes in the size and number of mitochondria present in the midgut of the larvae of the housefly, Musca domestica and phospholipid composition of the larvae
Authors: Sohal R. S. , Bridges R. G. 
Published: April 2021

ABSTRACT
A possible relationship between the phospholipid base composition of larvae of the housefly and the size, number and total volume of midgut mitochondria was examined. The phospholipid composition of the larvae was altered by restricting the amount of choline, substituting choline by N-dimethylethyl-(2-hydroxyethyl)-ammonium salt or 2-N-dimcthylaminoethanol and by the addition of 2-aminobutan-1-01 to the larval diet. Mitochondrial measurements were made on electron micrographs of the epithelial cells in the midgut of third instar larvae. Reduction in the normal proportion of phosphatidylcholine in the phospholipids of the larvae was associated with an increase in the average size of the mitochondria and a decrease in their number, probably due to enhanced mitochondrial fusion. The opposite effect was noted when phosphatidyl-2-aminobutan-1-01 was present as a part replacement of the phosphatidylethanolamine normally present in the larvae. Larvae which contained both phosphatidyl-2-aminobutan-1-01 as well as reduced amounts of phosphatidylcholine, contained mitochondria which were intermediate in both size and number. The effects associated with the changes in phosphatidylcholine and phosphatidyl-2-aminobutan-1-01 were independent of each other. The presence of the analogue of phosphatidylcholine and phosphatidyldimethylaminoethanol had no significant effect on the mitochondrial distribution. Total mitochondrial volume remained unaffected by alterations in the phospholipid composition of the larvae.
The distribution of spectrin along the membranes of normal and echinocytic human erythrocytes
Authors: Ziparo Elio , lemay André , Marchesi Vincent T. 
Published: April 2021

ABSTRACT
Spectrin molecules are distributed uniformly throughout the submembranous regions of intact human erythrocytes. Spectrin does not appear to extend into the red blood cell cytoplasm to any significant extent. Thus, it does not form a recognizable internal scaffolding nor does it seem to connect distant segments of the cell membrane. Spectrin retains its submembranous location in the spiny processes of echinocytes produced by ATP depletion. Thus, these processes do not seem to form by a simple extrusion mechanism powered by contraction of the spectrin network. Spectrin seems to be important for the stability of the lipid bilayer of the red cell membrane, and it probably also plays a role in regulating red cell shape. How it performs either function is still unknown.
Do human spermatozoa reactivate in the cytoplasm of somatic cells?
Authors: Van Meel F. C. M. , Pearson P. L. 
Published: April 2021

ABSTRACT
The morphological changes following Sendai virus-enhanced interaction of purified fractions of human spermatozoa with various types of fibroblast lines were examined over a period of several days. The incorporation of spermatozoa was monitored by a variety of immunofluorescent staining techniques, including one for protamin. The initially high incorporation frequency (30–40 %) was accompanied by swelling of the acrosome and nucleus, which, in most instances, was followed by gradual lysis of the sperm components. However, a small proportion of all incorporated spermatozoa (2 %) exhibited chromatin decondensation, accompanied by a shift from a protamin to histone content and induction of RNA and DNA synthesis. These latter cells appear to fit the criteria for true reactivation and electron-microscope studies show that they do not undergo phagocytosis as do the majority of incorporated spermatozoa.
The route of entry of cytoplasmic ally synthesized proteins into: Chloroplasts of algae possessing chloroplast ER
Authors: Gibbs Sarah P. 
Published: April 2021

ABSTRACT
In 8 classes of algae, namely the Cryptophyceae, Raphidophyceae, Haptophyceae, Chryso-phyceae, Bacillariophyceae, Xanthophyceae, Eustigmatophyceae and Phaeophyceae, the chloroplasts, in addition to being surrounded by a double-membraned chloroplast envelope, are also enclosed by a cisterna of endoplasmic reticulum called the chloroplast ER. Often this ER cisterna is continuous with the outer membrane of the nuclear envelope in such a manner that the nuclear envelope forms a part of the ER sac enclosing the chloroplast. In all these classes of algae except the Cryptophyceae, a regular network of tubules and vesicles, named the periplastidal reticulum, is present at a specific location between the chloroplast envelope and the chloroplast ER. In the Cryptophyceae, scattered vesicles are found between the chloroplast envelope and the chloroplast ER.
Ribosomes which have been shown to be arranged in polysomes are found on the outer membrane of the chloroplast ER. It is proposed that nuclear-coded proteins which are destined for the chloroplast are synthesized on these polysomes, passing during synthesis into the lumen of the ER cisterna. Vesicles containing these proteins then pinch off the chloroplast ER and form the periplastidal reticulum. Vesicles then fuse with the outer membrane of the chloroplast envelope thereby delivering their contents to the lumen of the chloroplast envelope. Proteins then cross the inner membrane of the chloroplast envelope in an as yet unknown manner.
Experimental evidence for this hypothesis comes from studies on Ochromonas danica using chloramphenicol and spectinomycin, which inhibit protein synthesis on plastid ribosomes, and cycloheximide, which inhibits protein synthesis on cytoplasmic ribosomes. In cells of Ochromonas exposed to chloramphenicol or spectinomycin, the periplastidal reticulum proliferates markedly becoming several layers thick. Presumably this build up of periplastidal reticulum occurs because the transport of cytoplasmically synthesized plastid proteins is slowed down when protein synthesis in the chloroplast is inhibited. Conversely, when cells of Ochromonas are treated with cycloheximide, there is a reduction in the amount of periplastidal reticulum presumably because there are no cytoplasmically synthesized proteins to be transported into the chloroplast.
On the reduced intercellular adhesiveness of virally transformed BHK21 cells
Authors: Edwards J. G. , Dysart J. Mck. , Edgar D. H. , Son R. T. Rob 
Published: April 2021

ABSTRACT
Baby hamster kidney fibroblasts (BHK21 cells) transformed by polyoma or Rous sarcoma viruses aggregate less than the untransformed parental cells when incubated in growth medium in a gyratory shaker for 18–24 h. This difference can be measured by electronic particle counting, or by filtering aggregated suspensions of 32 P-labelled cells through bolting fabric. The aggregation of transformed derivatives is not enhanced by the presence, during aggregation of ∈-amino caproic acid, an inhibitor of plasmin activation. Some lines of transformed BHK21 cells do not appear less adhesive than untransformed cells in a short-term aggregation assay, and none adheres markedly less well when seeded onto homotypic cell sheets. The decreased aggregation of transformed cells is consistent with suggestions that LETS protein is involved in intercellular adhesion of fibroblasts as well as in attachment of cells to non-cellular substrates. If so, the short-term aggregation of freshly trypsinized cells may depend on secretion of LETS from an intracellular pool.
Growth of human diploid cells (Strain MRC-5) in defined medium; replacement of serum by a fraction of serum ultrafiltrate
Authors: Lambert Kathleen , Pirt S.J. 
Published: April 2021

ABSTRACT
A calf serum ultrafiltrate fraction permitted growth for at least 3 · 5 generations, including one subculture, of MRC-5 cells in defined medium in the absence of whole serum. The active material has a molecular weight of 10000 Daltons or less. This suggests that there may be no requirement for a large macromolecular component of serum. The ultrafiltrate was assayed by maximum cell yield from a serum-limited inoculum in a defined medium containing nonlimiting amounts of vitamins, amino acids, glucose, a 68-component supplement, iron and methylcellulose. The levels of vitamins, amino acids and glucose were based on quantitative measurements of uptake and the levels of the other components by minimum amount required for maximum yield in defined medium without ultrafiltrate or serum. With excess ultrafiltrate maximum cell yield was limited by the defined part of the medium, probably the supplement. The cell doubling time in defined medium with ultrafiltrate fractions was 70 h compared with 27 h in the medium with serum. Excess ultrafiltrate did not inhibit growth. The lowered growth rate is attributed to a nutritional deficiency in the supplement.
Experimentally induced differentiation of slow tonic and fast twitch muscles in the chick
Authors: Ashhurst Doreen E. , Vrbová Gerta 
Published: April 2021

ABSTRACT
The anterior latissimus dorsi (ALD) muscle of chickens is a slow tonic muscle, while the posterior latissimus dorsi (PLD) is a fast twitch muscle. These muscles on opposite sides of a 3-week-old chick were removed, minced and replaced in the site of the other muscle and left to regenerate. The regenerating muscles were examined at various periods from 4 days onwards and their contractile properties were found to resemble those typical of the muscle they replaced and not the original muscle. The regenerating muscles from 8 days onwards displayed the morphological features of the control muscles in the contralateral site. By 14 days, differentiation was almost complete and neuromuscular junctions were seen.
It is suggested that the physiological and morphological characteristics of a muscle are determined by its position and possibly also by its innervation.