bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relative significance of growth rate and interdivision time in the size control of cultured mammalian epithelial cells
Authors: Hola M. , Riley P. A. 
Published: April 2021

ABSTRACT
Genealogies of a line of mammalian epithelial cells (GPK) have been constructed from timelapse film of monolayer cultures and measurements made of initial (post-divisional) cell size, final (pre-divisional) cell size and interdivision time (IDT). The mean initial cell volume was 2696 ±404 (S.D.) μm3, the mean final volume was 5247 ± 696 μm3 and the mean IDT was 985 ± 84 min.
Cell size regulation must be by modulation of either the growth rate or the length of the growth period. Increase in size was strongly correlated with the average rate of growth (increase in volume per unit time) (R = 0·94, P &lt;4 0·001), whilst no correlation was found between increase in size and IDT.
Although a negative correlation was found between initial volume and IDT (P&lt;0·02), this appeared to be due to differences in IDT between sister cells being correlated with differences in their initial volumes (P&lt;0·02), as indicated by the lack of correlation between mean sister IDT and mean sister initial volume.
The regulatory effect of growth rate was demonstrated by a negative correlation between growth rate and the initial volume of the cell (P&lt; 0·005), which is independent of differences between siblings. The mean growth rate of sibling cells was found to be negatively correlated with both the maternal growth rate (P&lt;0·01) and the maternal volume increase (P&lt;0·005). This implies that the growth rate of division products (which manifest similar growth rates) is influenced by the growth of the progenitor cell.
Key words: cell size regulation, growth rates, interdivision times.
Turnover of the carboxy-terminal tyrosine of α-tubulin and means of reaching elevated levels of detyrosination in living cells
Authors: Wehland Juergen , Weber Klaus 
Published: April 2021

ABSTRACT
Monoclonal antibodies specific for either the tyrosinated (Tyr) or the detyrosinated (Glu) form of α-tubulin were elicited with synthetic peptides spanning the carboxy-terminal sequences of the two forms. While almost all microtubules (MTs) are usually of the Tyr-tubulin type (Tyr-rich MTs) some MTs containing noticeable amounts of Glu-tubulin (Glu-rich MTs) were found in many but not all cell lines studied. Glu-rich MTs seemed absent from proliferating CHO and N115 neuroblastoma cells. When differentiation of these cells was initiated by the addition of forskolin for CHO, or by serum deprivation for N115, elevated levels of microtubular Glu-tubulin were observed. In differentiated N115 cells Glu-tubulin was restricted to MT of elongated cell processes and was not found in growth cones and many MT of the cell body. Elevated levels of Glu-tubulin were also characteristic of other differentiated cell types, including neurones and myotubes but were not found in glial cells, astrocytes and fibroblasts in the same primary cultures.
Additional experiments suggested that the restricted distribution of Glu-tubulin is the result of MT subsets with different stabilities. Results with mitotic drugs indicated that detyrosination occurs on MTs rather than on soluble tubulin and that stabilization of MTs usually favours the detyrosination process. Evidence for a functional α-tubulin cycle involving an inherent carboxypeptidase and a recharging ligase was apparent in 3T3 cells from the preponderance of Glu-rich MTs induced by taxol treatment or the microinjection of certain antibodies either protecting the detyrosinated form (Glu-tubulin antibodies) or inhibiting retyrosination (ligase antibodies). As the same treatment of CHO cells resulted in comparable arrays of Glu-rich MTs only when forskolin was also present, different cell types may differ in the level of active carboxypeptidase.
The results are discussed in terms of possible functions of the tyrosination/detyrosination cycle of α-tubulin. While most results can be explained on the basis of‘older’ and, consequently, more detyrosinated MTs, others raise the possibility that cyclic-AMP-dependent events and certain environmental influences known to induce either a morphological transformation or a differentiation event may influence the carboxypeptidase inherent in the α-tubulin cycle.
Preliminary characterization of maturation-promoting factor from yeast Saccharomyces cerevisiae
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Authors: Tachibana Kazunori , Yanagishima Naohiko , Kishimoto Takeo 
Published: April 2021

ABSTRACT
It has been known for some time that maturation-promoting factor (MPF) appears in a wide variety of eukaryotic cells at M phase and exerts equal M-phase-promoting activity in both meiotic cells and mitotic cells in a non-specific manner. MPF was extracted from cdc20 mutant cells of the yeast Saccharomyces cerevisiae synchronized at M phase by incubation at the restrictive temperature. When injected into immature oocytes of Xenopus laevis, yeast MPF caused meiosis re-initiation in a dose-dependent manner and even in the presence of cycloheximide. Yeast MPF exerted its activity in starfish oocytes as well. MPF activity was obtained only from cells in M phase and not from G1, S or G2 phase cells, indicating cyclical changes during the yeast mitotic cell cycle. Preliminary characterization of yeast MPF revealed that its activity was associated with a heat-labile protein having a sedimentation coefficient value of 6S. In contrast to the current assumption that MPF is a Ca-sensitive phospho-protein stabilized by phosphorylated small molecules, such as ATP and Na-β-glycerophosphate, the present study revealed that yeast MPF was still active even after treatment with either Ca2+ or alkaline phosphatase. Furthermore, it was found that yeast MPF and these phosphorylated small molecules were complementary in inducing reinitiation of meiosis, since the meiosis-reinitiating activity was detected only when both were present simultaneously and almost un-detectable when either of them was present alone. These facts suggest that yeast MPF need not necessarily be in a phosphorylated form in order to be active and that the phosphorylated small molecules have another effect, such as preventing the activity of phosphatases that might be present in recipient Xenopus oocytes rather than stabilizing the MPF molecule itself.
Characterization and origin of extrachromosomal DNA granules in Sarcophaga bullata
Authors: Bultmann Hermann , Mezzanotte Roberto 
Published: April 2021

ABSTRACT
We have used endonuclease treatment in situ, followed by Giemsa or ethidium bromide staining, for mapping repetitive sequences on the chromosomes of the flesh fly Sarcophaga bullata and thus for studying extrachromosomal DNA granules in this species. All three restriction enzymes employed (HaeIII, AluI and HindIII) show the same cytological effects, except for a single interstitial band. In both polytene and mitotic chromosomes, chromatin resistant to these endonucleases presumably includes at least three previously unrecognized buoyant density satellites (1·663, 1·670 and 1· 692 g ml−1 in neutral CsCl), and is predominantly localized in the pericentric regions of all five autosomes. Mitotic treated chromosomes show that the entire rodshaped X chromosome, but no part of the dot-like Y chromosome, consists of endonuclease-resistant chromatin. The most unusual heterochromatic component of polytene nuclei in this species, the‘extrachromosomal DNA granules’, are also entirely resistant to digestion with endo-nucleases. We think that these DNA granules represent dispersed X chromatin and not, as previously assumed, extruded autosomal hetero-chromatin.
Observations on rRNA gene replication in Chara vulgaris evaluated by in situ [3H] rRNA-DNA hybridization
Authors: Kwiatkowska Maria , Kononowicz A. K. , Janas Krystyna 
Published: April 2021

ABSTRACT
In situ [3H]rRNA-DNA hybridization showed that: (1) during the cell cycle in antheridial filaments of Chara vulgaris the rDNA gene content doubles during a 2h period in mid-S-phase, which corresponds to about 13% of the duration of this phase; (2) doubling of the number of grains occurs during mid-S-phase irrespective of the developmental stage of the antheridial filaments; (3) the numbers of autoradiographic grains in comparable phases of successive cell cycles preceding spermatid formation are the same. Thus the gradual reduction of total nucleolar volume (estimated per nucleus) occurring in successive cell cycles preceding spermatid formation is not associated with a decrease in the number of rDNA genes.
MHC control of cell position in vitro
Authors: Birkby C. A. , Curtis A. S. G. , McGrath M. , Ripley B. D. 
Published: April 2021

ABSTRACT
Two-dimensional sorting-out behaviour (segregation) in mixtures of pulmonary endothelial cell lines derived from congenic strains of mice was examined using dense confluent cultures in which mitosis is rare. Cell MHC type was detected by autoradiographic labelling or by immunofluorescence techniques. For autoradiography cultures of one type were previously labelled with [3H] thymidine and one component of the mixed cell types was prepared from these cultures. Autoradiographs were prepared from the fixed cultures. Counts of contiguous neighbours (labelled or unlabelled around a randomly chosen central labelled cell) were made: these were analysed statistically using a new model for such a system. The results show that segregation of a clustering type took place if the alleles of the D locus in the H-2 complex were mismatched in the mixed strains, but that matching at the IC locus (or some locus to the right of IJ) overrides the effect of D mismatch. After 2 days culture sorting-out was easily detectable when the cells were stained for their histocompatibility antigens and groups of up to 12 cells of the same type were associated together.
Ultrastructural aspects of encystation and cyst-germination in Phytophthora parasitica
Authors: Hemmes D.E. , Hohl H.R. 
Published: April 2021

ABSTRACT
Encystation in Phytophthora parasitica can be divided into 3 stages. In the first, the zoospores line their peripheries with flattened vesicles and nbrillar vacuoles in preparation for encystation. In the second stage, as the zoospores round up and shed their flagella, an initial wall is produced which takes the form of the mature cyst wall in thickness, but not in density. The participation of the flattened vesicles and fibrillar vacuoles in the formation of this initial wall is suggested by the disappearance of these organelles concomitant with wall formation. The third stage involves the maturation of the cyst wall and occurs only after dictyosomes produce vesicles which move to the cyst periphery and fuse to the plasmalemma.
Germ tubes are formed in direct and indirect germination and involve the evagination of the plasmalemma and cyst wall proximal to an accumulation of dictyosome-derived vesicles. These vesicles remain at the germ-tube tip as it extends. In indirect germination the germ tube stops after having attained an average length of 6 μm and the vesicles appear to fuse at the hyphal apex, thus forming a cap.
Lomasomes do not appear to be cell organelles with a specific function such as wall synthesis, but rather seem to represent aggregations of excess membranous material that have formed as a result of the discharge of vesicles at the cell periphery during wall formation. When dictyosome vesicles are inhibited from forming and moving toward the cell periphery, lomasomes are not formed.
Macromolecular dynamics of the cell surface during the formation of coated pits is revealed by fracture-flip
Authors: Fujimoto Kazushi , Silva Pedro Pinto Da 
Published: April 2021

ABSTRACT
We report here the macromolecular dynamics of the cell surface of rat alveolar macrophages during spreading on a substratum, a process that involves the formation of numerous coated pits. We used ‘fracture-flip’ to prepare high-resolution platinum-shadowed replicas of membrane surfaces. Our observations show the following sequence of events associated with coated pit formation: at 4°C the cell surface of macrophages is covered with a moderate density of particulate components, with most ranging from 10 to 25 nm in diameter. These particles appear to be randomly distributed over the cell surface. Incubation of adherent cells at 37°C for 15 min results in the formation of large loose clusters (area 0·5–4 μm2) of particles on the adherent surfaces. After incubation of macrophages for 30 min at 37°C, these clusters become tighter andeventually form circular depressions (200·300 nm in diameter), which we interpret as part of a process of invagination. After 60 min, the depressions become much steeper. At this time surface particles can be observed on the intervening non-invaginated regions, and the peripheral region of the adherent membrane, as well as the free membrane. Fractureflip reveals the presence of structures undetected in previous electron-microscopic studies and provides ultrastructural evidence for the clustering of surface macromolecules that is involved in the formation of coated pits.
Cell adhesion to hydroxyl groups of a monolayer film
Authors: Owens Norman F. , Gingell David , Trommler Annette 
Published: April 2021

ABSTRACT
We have studied cells on chemically defined mono-molecular films of the long-chain alcohol docosanol. Langmuir-Blodgett films of the alcohol were deposited on glass coverslips, previously made hydrophobic with octadecyl groups. This gives films in which the alcohol headgroups face outwards to the water. Molecular orientation and film integrity were shown by a fluorescence adsorption test. Cell contacts on the films were observed in media without proteins by interference reflection microscopy (IRM) and the mechanics of detachment were examined by hydrodynamic shearing in a flow chamber. Cell contact with docosanol was compared with that on an adjacent area of octadecyl glass without a monolayer.
Dictyostelium amoebae settled and spread on both docosanol and octadecyl glass, but little or no locomotion was seen on docosanol. On octadecyl glass the amoebae moved actively, forming ultrathin cytoplasmic lamellae, which look dark under IRM, and left distinctive trails of membranous debris. Hydrodynamic shearing showed that the amoebae stuck strongly to both surfaces and could not be removed from either at the maximum attainable wall shear stress of 6Nm−2. Red blood cells also adhered to both surfaces and removal from both occurred between 1 and 3Nm−2. IRM and scanning electron microscopy (SEM) studies indicated that this force leads to a minimal measure of red cell adhesion, since removal often involved the breakage of cytoplasmic tethers.
Our results show that alcoholic -OH groups, in a two-dimensional array, provide a surface that is strongly adhesive for cells. No other method has made it possible to demonstrate cell adhesion purely to -OH groups, in a known orientation and density, and in the absence of any other functional groups on the interface.
Differentiated membrane specializations and myofibrillar breakdown and recovery in cultured adult cardiac myocytes treated with TPA and diacylglycerol
Authors: Moses R. L. , Claycomb William C. 
Published: April 2021

ABSTRACT
Cultured adult rat ventricular cardiac muscle cells were treated with either 12-O-tetradecanoyl-phor-bol-13-acetate (TPA) or diacylglycerol (DAG) and observed by in situ transmission electron microscopy. Membrane specializations present in untreated cells (intercalated discs, transverse tubules, plasmalemmal couplings) were also present after TPA and DAG treatment. In the case of the transverse tubular system, there was morphological evidence for active growth. Our studies showed that myofilaments began to become disorganized after 12–24 h of TPA treatment and that after 2 days of exposure to TPA the breakdown of sarcomeres was essentially complete. Myocytes that were treated with TPA for 2 days and then allowed to recover in control medium for 5 days contained sarcomeres in various stages of reassembly. These data indicate that TPA-treated cardiac myocytes retain several membrane specializations, suggesting that there are separate controls for myofilament organization and the maintenance of these differentiated plasmalemmal regions. Furthermore, the ability of the myocytes to recover from TPA treatment may provide investigators with a useful model with which to study myofibrillogenesis.
Subfractionation of the endocytic pathway: Isolation of compartments involved in the processing of internalised epidermal growth factor-receptor complexes
Authors: Futter Clare E. , Hopkins Colin R. 
Published: April 2021

ABSTRACT
The aim of the present study was to isofate different parts of the endocytic pathway in order to examine the rofe of epidermal growth factor (EGF)-receptor internalisation in mediating the biofogical effects of EGF. We have used an antibody to the transferrin receptor complexed with cofloidal gold to modify the density of the endocytic compartments so that they can be purified by sucrose density centrifugation. Using this technique, we have been able to isofate a highly purified preparation of endocytic vesicles from H.Ep.2 cells that contain internalised EGF. By employing pulse-chase protocofs, it is possible to isofate the different parts of the endocytic pathway and show that they are temporally distinct with regard to the processing of EGF. It should now be possible to examine interactions between the EGF receptor and intracellular substrates in different parts of the endocytic pathway.
Extracellular ciliary axonemes associated with the surface of smooth muscle cells of ctenophores
Authors: Tamm Signhild , Tamm Sidney L. 
Published: April 2021

ABSTRACT
We describe the first example of bare ciliary axonemes existing outside eukaryotic cells. The axonemes run in longitudinal invaginations of the surface membrane of giant smooth muscle cells in ctenophores. No motility of the surface-associated axonemes has been detected in living muscles. The axonemes are truly extracellular and in direct contact with the extracellular matrix (mesoglea), as shown by the ultrastructural tracer horseradish peroxidase. The axonemes appear partially degraded and disorganized, and individual doublet microtubules are difficult to distinguish. Nevertheless, immunofluorescence microscopy shows that the axonemes retain antigenic sites reacting with mouse monoclonal anti-beta-tubulin. The origin of the extracellular axonemes is unknown: no attached basal bodies (extracellular or intracellular) have been found. The muscle-associated axonemes may play a unique role in smooth muscle function and/or development, and may be related to the evolution of muscle cells in soft-bodied invertebrates that exploit cilia for a wide variety of functions.
Normal chemotaxis in Dictyostelium discoideum cells with a depolarized plasma membrane potential
Authors: Duijn Bert Van , Vogelzang Sake A. , Ypey Dirk L. , Molen Loek G. Van Der , Haastert Peter J. M. Van 
Published: April 2021

ABSTRACT
We examined a possible role for the plasma membrane potential in signal transduction during cyclic AMP-induced chemotaxis in the cellular slime mold Dictyostelium discoideum. Chemotaxis, cyclic GMP and cyclic AMP responses in cells with a depolarized membrane potential were measured. Cells can be completely depolarized by two different methods: (1) by treatment with azide; this probably causes inhibition of the electrogenic proton pump, which was shown earlier to regulate plasma membrane potential in D. discoideum. (2) By electroporation, which causes the formation of large non-ion-selective pores in the plasma membrane.
It was found that in depolarized cells the cylic AMP-mediated cyclic AMP accumulation was inhibited. In contrast, chemotaxis to a cyclic AMP source was normal; the cyclic AMP-induced accumulation of cyclic GMP, which is known to mediate the chemotactic response, was also not affected. We conclude that membrane-potential-regulated processes, such as voltage-gated ion channels, do not play an essential role in chemotaxis in D. discoideum.
Spreading of trypsinized cells: Cytoskeletal dynamics and energy requirements
Authors: Bereiter-Hahn Jürgen , Lück Michaela , Miebach Toni , Stelzer H. K. , Vöth Monika 
Published: April 2021

ABSTRACT
The spreading of trypsinized XTH-2 cells (a line derived from Xenopus laevis tadpole heart endothélia) on glass was investigated. Three phases can be distinguished: (1) blebbing of rounded cells, first attachment to a solid substratum and formation of a broad smooth contact area; (2) organization of a peripheral zone of actin fibrils and reinforcement of the basal cytoplasm by a stress fibre-like pattern; (3) extension of lamellae.
The first phase seems to be independent of a supply of metabolic energy, while the others clearly depend on it. This is concluded from the close relationship between cellular projection area and energization of mitochondria as revealed by (a) the fluorescence intensity of cells vitally stained with the mitochondria-specific fluorochrome DASPMI (2–4-(dimethyl-amino)-styryl-l-methylpyridinium-iodine); (b) the degree of spreading in the presence of inhibitors of respiration; (c) effective amelioration of spreading (phases (2) and (3)) under conditions of high ATP content.
In phase (2) the extension of the central part of the cells becomes stabilized, the cell body settles on the basal cytoplasmic layer and further expansion of the projection area is achieved by lamella formation (phase (3)); motile and stabile regions of the cells become separated. This sequence of events is interpreted as a self-organizing process based on the development of internal hydraulic pressure, actin polymerization and contraction of the newly developed actomyosin network.
During trypsinization, depolymerization of actin does not occur but rather on addition of Ca2+-containing media. Cellular ATP content drops as well on trypsinization, as on addition of Ca2+. Manganese promotes spreading by decreasing F-actin disassembly and maintaining a high level of cytosolic ATP, most probably because it is not accepted by the calcium pumps. Regarding the association of glycolytic enzymes with F-actin and their influence on actin assembly, lactate dehydrogenase has been inhibited with oxamic acid. This treatment improves the correlation between F-actin content and the degree of spreading; however, the total amount of F-actin remains smaller and the cells spread more.
Isolation of microtubule motors from an insect ovarian system: Characterization using a novel motility substratum
Authors: Anastasi Angela , Hunt Cherryl , Stebbings Howard 
Published: April 2021

ABSTRACT
The ovaries of hemipteran insects contain massive microtubule-based translocation channels known as nutritive tubes, linking nurse cells to the developing oocytes. Translocation, which is in a retrograde direction along the nutritive tube microtubules, has previously been reactivated in vitro. Here, ATP-sensitive microtubule-associated proteins (MAPs) have been isolated from the insect ovaries, and beads coated with such proteins applied to salt-treated, detergent-extracted nutritive tube microtubules microdissected from the insect ovaries. These motility substrata are composed of many thousands of parallel microtubules, all with a common known polarity, so that not only are they easily observed, but the direction of any translocation along their length can be readily interpreted.
ATP extracts of insect ovarian MAPs, containing both kinesin and dynein, were seen to promote bidirectional movements of beads. Movements in the two directions differed in both rate and form. On fractionation of the ATP extract, those fractions containing kinesin brought about bead movement in an anterograde direction. Fractions containing dynein failed to promote movement of beads, and no single fraction promoted movement of beads in a retrograde direction.
Kinesin, while clearly present in the insect ovary, is absent from the nutritive tube translocation channels. The nutritive tubes, however, contain a polypeptide that co-electrophoreses with insect ovarian dynein, making dynein a possible candidate for the motor that drives the retrograde translocation along nutritive tubes.