bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear volume control by nucleoskeletal DNA, selection for cell volume and cell growth rate, and the solution of the DNA C-value paradox
Authors: Cavalier-Smith T. 
Published: April 2021

ABSTRACT
The 40000-f0ld variation in eukaryote haploid DNA content is unrelated to organismic complexity or to the numbers of protein-coding genes. In eukaryote microorganisms, as well as in animals and plants, DNA content is strongly correlated with cell volume and nuclear volume, and with cell cycle length and minimum generation time. These correlations are simply explained by postulating that DNA has 2 major functions unrelated to its proteincoding capacity: (1) the control of cell volume by the number of replicon origins, and (2) the determination of nuclear volume by the overall bulk of the DNA; cell growth rates are determined by the cell volume and by the area of the nuclear envelope available for nucleocytoplasmic transport of RNA, which in turn depends on the nuclear volume and therefore on the DNA content. During evolution nuclear volume, and therefore DNA content, has to be adjusted to the cell volume to allow reasonable growth rates.
The great diversity of cell volumes and growth rates, and therefore of DNA contents, among eukaryotes results from a varying balance in different species between r-selection, which favours small cells and rapid growth rates and therefore low DNA C-values, and K-selection which favours large cells and slow growth rates and therefore high DNA C-values. In multicellular organisms cell size needs to vary in different tissues: size differences between somatic cells result from polyteny, endopolyploidy, or the synthesis of nucleoskeletal RNA. Conflict between the need for large ova and small somatic cells explains why lampbrush chromosomes, nurse cells, chromatin diminution and chromosome elimination evolved. Similar evolutionary considerations clarify the nature of polygenes, the significance of the distribution of haploidy, diploidy and dikaryosis in life cycles and of double fertilization in angiosperms, and of hetero-ploidy despite DNA constancy in cultured cells, and other puzzles in eukaryote chromosome biology.
Eukaryote DNA can be divided into genic DNA (G-DNA), which codes for proteins (or serves as recognition sites for proteins involved in transcription, replication and recombination), and nucleoskeletal DNA (S-DNA) which exists only because of its nucleoskeletal role in determining the nuclear volume (which it shares with G-DNA, and performs not only directly, but also indirectly by coding for nucleoskeletal RNA). Mechanistic and evolutionary implications of this are discussed.
Membrane recycling at the cytoproct of Tetrahymena
Authors: Allen Richard D. , Wolf R. W. 
Published: April 2021

ABSTRACT
Exocytosis and membrane recycling at the cytoproct (cell anus) of Tetrahymena pyriformis were studied using thin-section electron microscopy. Single cells were fixed at specific times relative to the elimination of the vacuole’s contents —before elimination, at elimination, 3–5 s and 10–15 8 following elimination. The closed cytoproct is distinguished from other pellicular regions by a single membrane at the cell surface which is circumscribed by an electron-opaque flange that links or welds the plasma membrane to the underlying alveolar margins. Microtubules originating in the flange pass inward where they lie over, and possibly guide, the approaching food vacuoles to the cytoproct. Food vacuoles near the cytoproct are also accompanied by coats of microfilaments. These microfilaments appear to be active in the channelling and endocytosis of food vacuole membrane. Upon cytoproct opening the plasma membrane and food vacuole membrane fuse. Elimination seems to be essentially passive and is accomplished by re-engulfment of the old food vacuole membrane which is constantly associated with microfilaments. Re-engulfment of all the food vacuole membrane requires 10–15 s and results in a closed cytoproct. The membrane remnants embedded in microfilaments form a cluster under the closed cytoproct. At the periphery of this cluster remnants take the shape of 70–130-nm spherical vesicles or 0 · 2-μm-long flattened vesicles.
Extent and rate of chromosome segregation in two intraspecific mouse cell hybrids: A9 × diploid foetal erythrocyte and A9 × B82
Authors: Russell M. H. , McGEE B. J. , Engel E. 
Published: April 2021

ABSTRACT
Patterns of chromosome segregation were studied in 2 different intraspecific mouse cell hybrids: (1) A9 × B82, formed by fusing 2 cell lines of heteroploid fibroblasts, and (2) UWE, originating from the fusion of A9 cells with euploid foetal erythrocytes. Detailed analyses of Giemsa (G)-banded chromosomes and chromosome arms of both parental and hybrid cells were made for each hybrid type, in order to determine the specificity of the losses and to assess the influence of ploidy and cell differentiation.
Unlike the A9 × B82 hybrids, which revealed a significant chromosome loss under selective tissue culture pressures only after 9 months, the UWE hybrids showed a sharp reduction in the total chromosome number during the initial 2 months under similar pressures. However, with no additional cloning, UWE remained karyotypically stable after that time. This rapid chromosomal segregation in UWE hybrids may be caused by properties of the parental foetal erythrocytes.
In UWE cells, the majority of the chromosome arms were retained or duplicated. Less than a quarter of the total number of chromosome arms were segregated or lost, and these were all chromosome arms with abnormal mouse G-banding patterns, present only in the heteroploid A9 parental cells. In two of the four A9 × B82 hybrid lines, there was marked segregation of chromosome arms whose banding patterns were identical to those of wild type mouse telocentric chromosomes. For both types of intraspecific cell hybrids, two thirds or more of the chromosome arms had banding patterns which were the same as those of the wild type genome.
Cell-associated proteases affect tumour cell migration in vitro
Authors: Varani J. , Orr W. , Ward P. A. 
Published: April 2021

ABSTRACT
The in vitro migratory activity of mouse fibrosarcoma cells in medium containing either foetal calf serum or normal human serum was studied. These 2 sera were studied because foetal calf serum contains high levels of protease inhibitor activity while human serum contains much less. The cells migrated actively in medium with foetal calf serum but migration was greatly inhibited in human serum-containing medium. When protease inhibitors such as soybean trypsin inhibitor, lima bean trypsin inhibitor and bovine pancreas trypsin inhibitor were added to human serum-containing medium cell migration was supported almost as effectively as in medium with foetal calf serum. Addition of є-amino-n-caproic acid to human serum or depletion of the plasminogen from human serum did not enable it to support enhanced migration, є-amino-n-caproic acid actually inhibited migration. A variant cell population with elevated levels of caseinolytic activity and elevated levels of activity against the substrate n-acetyl-DL-phenylalanine-β-naphthyl ester (a substrate specific for chymotrypsin-like enzymes) was isolated from the parent cells. When the variant cells were compared to the parent cells regarding migratory activity in foetal calf serum or human serum-containing medium, the variant cells showed much less activity. Only a few, widely scattered variant cells migrated in the human serum-containing medium. These data suggest that a cell-associated factor interferes with the migration of the cells in medium with human serum. This factor apparently is neutralized in medium containing human serum to which protease inhibitors with antitrypsin activity have been added.
The evolution of excitable behaviour in Dictyostelium
Authors: Lax Alistair J. 
Published: April 2021

ABSTRACT
Aggregation of Dictyostelium discoideum amoebae is effected by relayed cyclic AMP (cAMP) signals. The period of this wave propagation drops abruptly at the transition from aggregative to post-aggregative development. In this paper I demonstrate that the light-scattering response induced by a low concentration pulse of cAMP evolves from one lasting 5 min to one lasting 2 min. The definitive establishment of the 2-min response coincides with the beginning of post-aggregative gene expression. Amoebae at the aggregative stage are unable to respond to a second cAMP pulse delivered less than 4 min after the first, whereas at the post-aggregative stage they can respond to 2 pulses separated by 1 min or longer. Addition of cAMP phosphodiesterase to amoebae at the aggregative stage can in part mimic the change in excitable behaviour: the response is shortened and the amoebae can respond more frequently. However the shortened response is not post-aggregative in shape and the prolonged presence of cyclic nucleotides induces different responses at the aggregative and post-aggregative stage. Both these results suggest that the rate of destruction of the relayed signal is not solely responsible for the change in excitability.
Studies of membrane fusion.: III. fusion of erythrocytes with polyethylene glycol
Authors: Knutton S. 
Published: April 2021

ABSTRACT
Freeze-fracture electron, microscopy has been used to investigate the mechanism of polyethylene glycol-induced cell fusion. Interaction of cells with the high concentrations of polyethylene glycol required for cell fusion results in cell agglutination with large planar areas of very close contact between adjacent cell membranes. An aggregation of intramembrane particles into large patches at the sites of cell-cell contact accompanies cell agglutination. Fusion occurs following the removal of most of the PEG when cells only remain in close contact at small (∼ 0·1 μm diameter) plaques of smooth particle-denuded membrane. Membrane fusion occurs at these plaques of smooth membrane resulting in cells connected by one (or more) small cytoplasmic connexions. Expansion to form spherical fused cells occurs by a process of cell swelling.
Actin in spindles of Haemanthus Katherinae endosperm : II. distribution of actin in chromosomal spindle fibres, determined by analysis of serial sections
Authors: Forer Arthur , Jackson W. T. , Engberg A. 
Published: April 2021

ABSTRACT
We have studied the arrangements of actin-containing filaments in 13 bundles of kinetochore microtubules in glycerinated, heavy meromyosin-treated Haemanthus endosperm cells : 7 bundles were in a cell at anaphase, and 6 were in a cell at metaphase. Actin-containing filaments were present in each of the 13 bundles of kinetochore microtubules : they were in amongst the microtubules in the bundle and seemed to be associated with the microtubules. Actin-containing filaments in each bundle seemed to terminate at the kinetochores. Actin-containing filaments associated with the kinetochore microtubules were of consistent polarity (the arrowheads pointed towards the kinetochores) whereas those associated with other microtubules and those not associated with microtubules did not have consistent polarity (some pointed towards the spindle pole, others pointed away from it). Roughly, there were as many individual stretches of actin-containing filaments identified per bundle of kinetochore microtubules as there were microtubules which terminated at the kinetochore. These data suggest that actin-containing filaments in spindles have a functional role.
We used 2 glycerination procedures in our studies (one for each cell), and neither seemed to disrupt the basic microtubule arrangements : the arrangements of spindle microtubules seen after glycerination of Haemanthus endosperm were identical to those described previously by others in non-glycerinated glutaraldehyde-fixed Haemanthus endosperm. Thus we argue that spindle structure is not disrupted by the procedures, and therefore that the arrangements of actin-containing filaments are not artifacts of the glycerination procedures. The only difference between microtubules in glycerinated cells and microtubules in untreated cells is that there seem to be fewer in the glycerinated cells.
The possible role of actin-containing filaments in the spindle is discussed.
An abnormality of cell behaviour in human dystrophic muscle cultures: A time-lapse study
Authors: Yasin Rose , Beers G. Van , Riddle P. N. , Brown D. , Widdowson G. , Thompson E. J. 
Published: April 2021

ABSTRACT
The initiation of monolayer mass cell cultures from adult human biopsies has revealed a striking abnormality in the growth and development pattern of muscle cultures from Duchennetype dystrophy. This abnormality in cell behaviour was seen as early as 4 days in culture, well before myotubc formation or confluence, and consisted of areas where cells clustered together in a multilayered mass rather than showing the typical monolayer distribution normally ob served.
To gain some insight into the mechanism of cell cluster development, we have examined such a culture by time-lapse cinematography and also the cell behaviour of other control cultures. The results of this study show that the clusters enlarged primarily by cell division and, to a lesser extent, by the acquisition of neighbouring cells. Furthermore, none of the single cells surrounding the clusters exhibited contact inhibition of movement. This behaviour was not observed in the other cultures examined. These findings could be indicative of an abnormality in the cell surface or cell-locomotory machinery of dystrophic cells.
The time course of male meiosis in the red-backed salamander, Plethodon cinereus
Authors: Morgan Garry T. 
Published: April 2021

ABSTRACT
Tritiated-thymidine autoradiography was used to follow the progress of cells through meiosis in male P. cinereus at 20 °C. Spermatocytes spend 7 days in leptotene, 5 days in zygotene and 3 days in pachytene before entering the diffuse stage. Diffuse lasts for 8 days and is followed by a diplotene of 2 days. First and second meiotic metaphase occur a total of 26 days after the end of premeiotic S.
Considering the information for P. cinereus together with that for 3 other species, it appears that in amphibians the duration of meiosis does not show the linear relation with C-value that has been described for other groups of organisms.
Effect of temperature on dry mass of polytene nuclei in Drosophila
Authors: Hartmann-Goldstein Ingeborg J. , Goldstein D. J. 
Published: April 2021

ABSTRACTNuclei were isolated by an aqueous detergent method from Drosophila prepupal salivary glands, and measured by integrating interference microscopy. There was a highly significant correlation between nuclear volume and dry mass. Dry masses fell into 2, 3 or 4 distinct groups corresponding to polytene replication classes; the mean of a given dry mass group was between 8 and 30% less than twice that of the group below, indicating that the ratio of DNA:dry mass increases during polytenic growth.The proportion of nuclei in the higher mass groups, the mean dry mass of nuclei within a given mass group, and the percentage loss of nuclear dry mass in the first hour after isolation were all higher when animals were reared at 150 instead of 25 °C. Nuclear dry mass in prepupae was affected by the temperature during both the embryonic and larval periods, and also to some extent by the nutrition and degree of crowding of the cultures.
The effect of cell mass on the cell cycle timing and duration of S-phase in fission yeast
Authors: Nasmyth Kim , Nurse Paul , Fraser R. S. S. 
Published: April 2021

ABSTRACT
Two isotopic methods for measuring DNA replication in the fission yeast Schizosaccharomyces pombe are described. The first is a method for measuring the total quantity of [3H]uracil incorporated into DNA after pulse labelling. The second is a means of detecting DNA replication in single cells by autoradiography. Both of these techniques have been used to investigate the timing and duration of S-phase in a series of mutant strains whose cell mass at division varies over a 3-fold range. The results support the hypothesis that in S. pombe there are 2 different controls over the timing of S-phase: an attainment of a critical cell mass and a dependency upon the completion of the previous mitosis coupled with a short minimum time in G1. Strains whose cell mass at birth is above this critical level initiate DNA replication almost immediately after septation, that is, very soon after the previous mitosis. Strains whose cell mass at birth is below the critical level do not initiate replication until the critical cell mass is attained. The duration of S-phase has been estimated from the proportion of cells whose nuclei are labelled after a pulse of given duration. S-phase is short in S. pombe, lasting only about 0·1of a cell cycle in wild type. Cell mass at S-phase does not have any consistent effect on this length. We have also investigated the degree of synchrony of S-phase initiation in daughter cells, and have found that, in a cell cycle 240 min long, their S-phases are initiated within 1-2 min of each other. This result indicates that between sisters variability in the duration of the G1 phase is small compared with variability in the total cell cycle time, and argues against the hypothesis that the rate of cell cycle traverse is determined by a random transition in G1.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: III. radioautographic distribution of [14C]sucrose
Authors: Appleton T. C. , Pelc S. R. , Dingle J. T. , Fell Honor B. 
Published: April 2021

ABSTRACT
Earlier experiments have shown that when limb-bone rudiments from day embryonic chicks are cultivated in medium containing an indigestible sugar, the perichondrial cells become intensely vacuolated, but this vacuolation does not appear in the chondrocytes, except in the articular region. Appleton’s radioautographic method for demonstrating water-soluble materials was used to study the uptake, distribution and loss of 14C-labelled sucrose in day limb-bone rudiments cultivated in a chemically denned medium (BGJ5).
After 48 h exposure to [14C]sucrose, both perichondrium and cartilage were heavily labelled. When such explants were either washed for 1 h in BGJ5 or cultivated for a further 24 h in non-radioactive medium, labelling was almost unaffected in the perichondrial cells but was greatly reduced in the cartilage, the cells of which were almost devoid of radioactivity.
The presence in the medium of 0·08 M ‘cold’ sucrose did not alter the perichondrial grain counts in the washed explants. This finding supports the view that in the perichondrial cells sucrose is taken up non-specifically by endocytosis, and that the intense vacuolation of the cytoplasm is due to abnormal persistence of the pinocytotic vesicles in the presence of the sugar.
It is concluded that failure of the chondrocytes to take up sucrose is due, not to lack of penetration of the sugar into the cartilage, but to a weak endocytotic activity of the cells.
Endocytosis of sugars in embryonic skeletal tissues in organ culture: IV. lysosomal and other biochemical effects. general discussion
Authors: Dingle J. T. , Fell Honor B. , Glauert Audrey M. 
Published: April 2021

ABSTRACT
Cultivation of limb-bone rudiments in medium containing various non-metabolizable or poorly metabolizable sugars caused vacuolation of the perichondrial and articular cells and was accompanied by an increased synthesis and profuse secretion of lysosomal enzymes. Experiments with [14C]dextran indicated that the cytoplasmic vacuolation was due not to a higher rate of endocytosis, but rather to an abnormally long persistence of the pinocytotic vacuoles. Meta-chromatic material was lost from the cartilage only in the immediate vicinity of the vacuolated articular chondrocytes and the amount of hexosamine and hydroxyproline released into the medium was not much increased. However, the hexosamine and hydroxyproline of the sucrosetreated rudiments was much more susceptible to extraction with neutral salt than those of paired controls.
Sucrose taken up by the cells was liberated when the rudiments were returned to normal medium; this release, unlike the secretion of lysosomal enzymes, was unaffected by the presence of hydrocortisone. It is probable that the primary lysosomes, formed in the enlarged Golgi region, are the vehicles for the secretion of lysosomal enzymes. No appreciable amount of enzymic activity was released into the medium from rudiments grown in the presence of 0·08 M sucrose, before 36 h; at, or just before this time, however, a net increase in synthesis of enzyme was observed. The role of endocytosis in the resorption of skeletal matrix is discussed.
The effect of enucleation on flagellar regeneration in the protozoon Peranema trichophorum
Authors: Tamm S. L. 
Published: April 2021

ABSTRACT
A rotocompressor was used to enucleate the flagellate protozoon Peranema trichophorum at known stages in the mitotic cycle. This new enucleation technique, combined with recently devised methods for amputating the flagellum and recording its regeneration in single living cells, permitted the investigation of the role of the nucleus in flagellar regeneration at different cell ages.
The flagellar regeneration capacity of an enucleate Peranema depended on the stage in the cell cycle when the nucleus was removed. Post-division enucleate cells regenerated about half the length reached by sham-operated controls, and at slower rates, while predivision enucleate cells regenerated flagella equally as well as the controls.
Therefore, the nucleus is making an immediate contribution to flagellar regeneration early in the cell cycle, but not late in the cell cycle.
Nuclear morphology and the ultra-structural localization of deoxyribonucleic acid synthesis during interphase
Authors: Milner Gillian R. 
Published: April 2021

ABSTRACTThe ultrastructural localization of deoxyribonucleic acid (DNA) synthesis was studied by electron-microscope autoradiography in human transforming lymphocytes, embryonic lung fibroblasts, epithelial cells and normoblasts. Euchromatin was found to be active in DNA synthesis in all cell types studied, whereas heterochromatin was inactive. However, DNA synthesis was also prominent in the regions where heterochromatin was thought to be decondensing to form euchromatin. Analysis of sequential changes in nuclear morphology of the transforming lymphocyte suggested that there is decondensation of heterochromatin during the S-phase until none is left. In nuclei with no heterochromatin a prominent localization of DNA synthesis was at the nuclear membrane. This sequence of complete decondensation of hetero-chromatin also seemed likely for fibroblasts and epithelial cells. Normoblasts however showed no stage where the nucleus was wholly euchromatic and it is suggested that in this cell decondensation of heterochromatin for replication is localized and transient.
Natural segregation of the ribonucleoprotein components of the nucleoli of chloragogen cells in Tubifex
Authors: Djaczenko W. , Grabska J. , Filadoro F. 
Published: April 2021

ABSTRACT
Nucleolar ribonucleoprotein (RNP) components of the chloragogen cells of normal untreated specimens of Tubifex tubifex (Mull.) were found to be segregated, there being separate zones for each RNP species. There were external and internal zones, containing granular RNP, and a fibrillar zone located between them in which only filamentous RNP components were’found. The innermost part of the nucleolus was formed by one or more vacuole-like structures which occasionally contained 350-A granules of high electron opacity. In the vicinity of the nucleolus a spherical mass, called the ‘paranucleolar body’ and composed of densely packed granules and filaments, was constantly encountered.