bluuebunny/crossref_metadata_2025_split huggingface dataset:
Non-random chromosome segregation in Neocurtilla hexadactyla is controlled by chromosomal spindle fibres: An ultraviolet microbeam analysis
Authors: Wise Dwayne , Sillers Peggy J. , Forer Arthur 
Published: April 2021

ABSTRACT
Single spindle fibres in Neocurtilla spermatocytes were irradiated by means of an ultraviolet microbeam. Irradiations were with monochromatic ultraviolet light. The single sex chromosome (the X1 univalent) reoriented after irradiation of its spindle fibre or of any of the spindle fibres associated with the heteromorphic bivalent (the X2Y bivalent): the X1 moved toward the Y half-spindle, and sometimes rotated as it moved. Irradiations of autosomal spindle fibres did not induce X1 movements, and hence the induction of reorientation is specific to irradiation of the spindle fibres associated with X1 or X2Y. In no case did the X2Y bivalent reorient; hence, the X1 is the active chromosome in ensuring that there is non-random segregation in Neocurtilla spermatocytes. The irradiations sometimes caused the X2Y bivalent to contract, but the reorientation movements of the X1 were independent of the contraction of the X2Y bivalent. We suggest that the X1 and X2Y chromosomal spindle fibres form a network that is able to send signals to the X1 univalent to cause it to reorient.
Quick-freeze, deep-etch rotary replication ofTrypanosoma cruziandHerpetomonas megaseliae
Authors: Souto-Padrón Thais , Souza Wanderley De , Heuser John E. 
Published: April 2021

ABSTRACTThe fine structure of epimastigotes of Trypanosoma cruzi and promastigotes of Herpetomonas megasehae was analysed in replicas of quick-frozen, freeze-fractured, deeply etched and rotary-replicated cells. Using control cells and cells treated with Triton X-100 before glutaraldehyde fixation, images were obtained that showed connections of the sub-pellicular microtubules with each other, with the plasma membrane, and with the endoplasmic reticulum. Images were also obtained that showed the DNA network in the kinetoplast. Filamentous structures were found to connect the kinetoplast to the basal body, and to connect the main basal body to the accessory one. In addition, deep-etch images of detergent-extracted flagella display dynein arm substructure and the filamentous architecture of the paraxial structures.
Behaviour of thymocyte nuclei in non activated and activated mouse oocytes
Authors: Czołowska Renata , Modliński Jacek A. , Tarkowski Andrzej K. 
Published: April 2021

ABSTRACT
Cells originating from the thymus of newborn mice were fused with mouse oocytes using polyethylene glycol. The behaviour of thymocyte nuclei was studied in non-activated metaphase II oocytes, and in oocytes activated in vitro with ethanol.
In non-activated oocytes all thymocyte nuclei undergo premature chromosome condensation with individualization of chromosomes; the chromosomes form separate groups in the cytoplasm, or are assembled around the metaphase II spindle, or located on the extra-spindle.
In activated oocytes thymocyte nuclei start to develop along a pronucleus-like pathway (decon-densation, visualization of nucleoli, swelling) and increase up to 200 times in volume during 24h culture in vitro, eventually reaching the size of a fully grown pronucleus. Activation/fusion timing seems to be critical for the full remodelling of thymocyte nuclei. Nuclei introduced before (10–30 min) or shortly after (up to 60 min) activation often grow larger than the female pronucleus. Those introduced into oocytes long before activation (&gt;30min) undergo premature condensation with subsequent reformation of nuclei that are sometimes deficient (as indicated by the presence of micronuclei), or of hybrid character. Nuclei introduced late after activation (&gt;60min) are mostly doomed to retarded development.
The implications of the present observations for nuclear transfer experiments in mammals are discussed.
The synaptology of the granule cells of the olfactory bulb
Authors: Price J. L. , Powell T. P. S 
Published: April 2021

ABSTRACT
The synapses related to the granule cells of the olfactory bulb of rat brain have been studied in aldehyde-fixed material. The synapses can be divided into three classes: (1) those which have asymmetrical synaptic membrane thickenings and spheroidal synaptic vesicles; (2) those with symmetrical synaptic thickenings and flattened vesicles; and (3) the reciprocal synapses, one half of which (from mitral to granule cell) has an asymmetrical synaptic thickening associated with spheroidal vesicles, while the other half (from granule to mitral cell) has a symmetrical synaptic thickening and flattened vesicles. Qualitative observations, supported by preliminary quantitative measurements, suggest that it may be possible to divide both the spheroidal and flattened-vesicle types into two further varieties, on the basis of size, The smaller variety of spheroidal vesicles is found in most axon terminals, while the larger spheroidal vesicles are present in mitral cell dendrites and in some of the axon terminals. The flattened vesicles associated with symmetrical synapses which are oriented on to the granule cells are smaller than the spheroidal vesicles, but the flattened vesicles in the spines and gemmules of the granule cells are the same size or larger than the spheroidal vesicles. The division of flattened vesicles into two sizes is supported by statistical analysis of measurements of these vesicles, but because of difficulty in identifying the axon terminals with asymmetrical synapses there is no quantitative evidence for such a division of spheroidal vesicles.
The asymmetrical synapses are found predominantly on spines, gemmules, and dendritic varicosities, although they are occasionally present on shafts of dendrites and on the cell somata. The symmetrical synapses are almost completely restricted to the shafts of the peripheral processes and the deep dendrites, and to the cell somata; only very rarely are synapses of this type found on spines, and then always in conjunction with an asymmetrical synapse.
The haemoglobin in the condensed chromatin of mature amphibian erythrocytes: a further study
Authors: Small J. V. , Davies H. G. 
Published: April 2021

ABSTRACT
The condensed chromatin in mature nucleated erythrocytes is surrounded by nuclear haemo-globin at a concentration about equal to that in the cytoplasm. New measurements employing improved fixation, glutaraldehyde instead of OsO4, and microspectrophotometnc analyses instead of photographic photometry at one wavelength, show that previously reported values for the content of haemoglobin in the mass of the chromatin in Triturus crutatus, 45–50%, were far too high. In the condensed chromatin of 3 species of amphibia the concentrations of intrachromatin haemoglobin relative to the cytoplasm are 10% (Triturus crutatus), 10% (Necturus maculosa) and 8 % (Amphtuma trtdactylum). It is concluded that haemoglobin is only a minor component of chromatin, and this result is discussed in relation to the condensation of erythrocyte chromatin and observations on its ultrastructure.
The spindle as a basal body distributor: a study in the meiosis of the male silkworm moth, Bombyx mori
Authors: Friedländer M. , Wahrman J. 
Published: April 2021

ABSTRACT
The spindle of metazoan cells functions as a dual distributor that guarantees the accurate segregation of both chromosomes and centnoles (basal bodies). This combined mechanism may have evolved from the separate distribution devices for chromosomes and basal bodies found in Protozoa.
Typical eupyrene spermatocytes of the silk moth were compared with atypical apyrene spermatocytes. (a) Long microtubules, persisting during centnolar movements, develop in the meiotic prophases in continuity with the centrtoles (b) There is no longer a centriole-microtubule continuity at metaphase-anaphase (c) Spindles comprise microtubules and endoplasmic reticulum (ER). The microtubules form a barrel-shaped structure terminating far in front of the centrioles. The two types of spermatocytes differ in the structure of the ER, which is vesicular in the eupyrene and lamellar in the apyrene line. It is suggested that the ER influences the anaphase movement of chromosomes, (d) The chromosomes lack localized centromeres. Microtubules penetrate all along the polar faces of the eupyrene metaphase chromosomes. The apyrene chromosomes form irregular blocks that are penetrated by microtubules all around their periphery, (e) The centriole comprises 3 concentric zones. Typical changes in the centnole are correlated with changes in the cell cycle. Replication, de novo formation and disappearance of centrioles are manifestations of the state of flux of the microtubules.
Low-angle x-ray diffraction and electron-microscope studies of isolated erythrocyte membranes
Authors: Knutton S. , Finean J. B. , Coleman R. , Limbrick A. R. 
Published: April 2021

ABSTRACT
Two alternative sequences of low angle X-ray diffraction patterns (Type I and Type II) have been observed during the controlled dehydration of rat (and human) erythrocyte ghost preparations in which the residual haemoglobin content has varied.
The Type I sequence has been obtained when haemoglobin has comprised more than 30 % of the total protein of the membrane preparation. It features an initial lamellar pattern that has been interpreted in terms of a predominantly continuous lipoprotein sandwich structure. Subsequent changes in diffraction pattern have been suggested to represent a partial breakdown of the lipoprotein structure to give a multiphase system.
The Type II sequence was most readily obtained from haemoglobin-free ghosts. At no stage during the dehydration of these ghosts did the diffraction feature a stable lamellar pattern. At all levels of hydration the X-ray reflections appeared to represent independent lipid and lipoprotein phases. Osmium tetroxide fixation of haemoglobin-free membranes prevented the separation of lipid and lipoprotein phases during dehydration.
Comparisons of electron micrographs of condensed membrane preparations have revealed some structural differences between membranes which give rise to the Type I and Type II diffraction sequences.
Growth and macromolecular synthesis in the 3T6 mouse fibroblast: I. general description and the role of ascorbic acid
Authors: Levene C. I. , Bates C. J. 
Published: April 2021

ABSTRACT
The growth of the 3T6 mouse fibroblast and synthesis of macromolecules has been studied over the last 6 days of the cultures’ 14-day life span. The effect of ascorbic acid was also tested.
During this period, the cells synthesized collagen, as judged by the appearance of non dialysable hydroxyproline, which was identified by chemical assay and by radioactive incorporation studies. A high proportion of the collagen in the cell layer was insoluble in 0·1 N acetic acid. Of the hydroxyproline synthesized in the presence of ascorbic acid, about 75 % was eventually liberated into the growth medium, and about 25–30% of the liberated material behaved as free hydroxyproline. In the absence of ascorbic acid, the cell layer hydroxyproline was reduced to one-third, but the growth medium hydroxyproline was unaffected.
The cells also synthesized glycosaminoglycans, as judged by the appearance of cetyl pyri dinium-precipitable uronic acid, and the incorporation of labelled glucosamine into macro molecules. A large proportion of this material has the properties of hyaluronic acid. Ascorbic acid had no detectable effect on overall glycosaminoglycan synthesis, in contrast to healing tendonectomy wounds in guinea-pigs.
Cell proliferation and general protein synthesis were virtually unaffected by ascorbic acid. Whereas general protein synthesis, like cell proliferation, declined in the ageing culture, glycosaminoglycan synthesis and collagen synthesis continued at a steady or increasing rate.
Maturation of the reticulocyte in vitro
Authors: Gronowicz Gloria , Swift Hewson , Steck Theodore L. 
Published: April 2021

ABSTRACT
The maturation of reticulocytes into erythrocytes was demonstrated in vitro. Reticulocytosis was induced in rats by repeated bleeding or by phenylhydrazine injections. Whole blood samples were then incubated for 2 days at 37 °C. Reticulocytes in culture changed from poly tabulated, monoconcave or triconcave forms to biconcave disks. During the first 12h in vitro, the average reticulocyte count decreased from 39% to 12%, and the membrane-bound organelles, ribosomes and exocytic figures in the remaining reticulocytes were markedly diminished. In contrast, the number of red cells containing inclusions of denatured haemoglobin (Heinz bodies) in phenylhydrazine-treated blood did not decline. The reduction in reticulocyte count was not the result of differential cell destruction, since little haemolysis occurred in vitro.
During red cell maturation three modes of organelle removal were observed particularly well when mitochondria were followed by cytochrome oxidase cytochemistry. First, some mitochondria degenerated, presumably through autolysis, by swelling, losing cristae and forming small single membrane-bound vesicles. Second, individual mitochondria became enclosed in vacuoles that fused with the plasma membrane and expelled their mitochondria by exocytosis. Third, autophagic vacuoles containing mitochondria, cytosol and membrane fragments fused with existing lysosomes. We conclude that all aspects of normal reticulocyte maturation occur in vitro, independent of the spleen, including the removal of organelles and the assumption of the mature biconcave disk shape.
Regulation of a ribonucleoside reductase during the early generative phase in Acetabularia
Authors: Groot Egon J. De , Schweiger Hans-Georg 
Published: April 2021

ABSTRACT
The activity of a ribonucleoside reductase was estimated during the life cycle of Acetabularia. During the early generative phase the enzyme activity was dramatically increased. Regulation of the ribonucleoside reductase was observed even in the absence of the nucleus. The increase in activity was inhibited by chloramphenicol but not by cycloheximide. These results indicate that the enzyme is translated on 70S ribosomes.
Chemotactic factor binding by metastatic tumour cells: Evidence for a formyl-peptide receptor on a non-myelogenous cell
Authors: Marasco Wayne A. , Ward Peter A. , Feltner Douglas E. , Varani James 
Published: April 2021

ABSTRACT
Analysis of fMet-Leu-[3H]Phe binding to Walker 256 carcinosarcoma cells demonstrated both saturable and reversible binding, and indicated the presence of a single population of binding sites having an equilibrium dissociation constant: KD = 15·7 ± 3·3× 10−9M, and with 2425 +204 binding sites per cell. The specificity of the binding site was investigated by competitive inhibition of fMet-Leu-[3H]Phe binding studies using 10 oligoformyl peptides. These results demonstrated an order of peptide reactivity with marked similarity in specificity to the leucocyte binding sites for the formyl-peptides. The most active peptides also had potent agonist activity as determined by their ability to increase the cells’ adherence response to nylon-wool fibres. In addition, a competitive antagonist of the formyl-peptide receptor, tert-butoxy-Phe-Leu-Phe-Leu-Phe, completely abolished the adherence response induced by fMet-Leu-Phe, but had no inhibitory effect on the adherence response caused by the tumour-promoting agent, phorbol myristate acetate.
These data demonstrate that formyl-peptide receptors may be more common than we have anticipated and may be found on cells not derived from the myeloid series. Furthermore, these studies advance our understanding of stimulus-coupled responses in tumour cells.
Biochemical evidence for the presence of an actin protein in Tetrahymena pyriformis
Authors: Mitchell E. Jane , Zimmerman Arthur M. 
Published: April 2021

ABSTRACT
A protein from an ATP extract prepared from an acetone powder of Tetrahymena pyrifonnis GL was identified as actin. The protein migrated slightly behind muscle actin on sodium dodecyl sulphate (SDS)/10% polyacrylamide gels (SDS/PAGE) with an apparent molecular weight of 47500 (47·5 ×103Mr). Partial proteolysis of this band with Staphylococcus aureus V-8 protease followed by electrophoresis revealed a pattern of peptides in which at least four peptides were similar to those observed after digestion of rabbit skeletal muscle actin. The 47·5 × 103 Mr protein appeared particularly susceptible to endogenous proteolvtic cleavage, which was inhibited by leupeptin. An ATP extract prepared with leupeptin was applied to a DNase I-affinity column and a distinct peak was eluted with 3 xi-guanidincHCl; the DNase I-binding protein appeared as a distinct band on SDS/PAGE with an apparent molecular weight of 47·5× 103. Mr. In the absence of leupeptin, the DNase I-binding protein appeared as a broad 34×103Mr band on gels. Both the ATP extract and the DNase I-binding protein showed reactivity with commercially available antiserum raised against native chicken skeletal muscle actin as determined bv an enzvme-linked immunosorbance assay (ELISA). Immuno-blotting-studies and affinity purification of this antiserum showed that the recognition was not specific to the 47·5×103 Mr protein. However, using affinity-purified anti-actin antibodies raised against denatured actin from chick smooth muscle, recognition of the 47’5×103Mr protein and a 34×103Mr protein was shown. In negatively stained preparations from an ATP extract after two cycles of polymerization and depolymerization there were filaments, 8–12nm diameter, which did not decorate with subfragment S-l of myosin, but which resembled intermediate filaments. Analysis of these filaments on SDS/PAGE indicated an intensely stained 54×103Mr band. It is suggested that, in vitro, Tetrahymena intermediate filaments assemble under conditions expected to assemble actin filaments. Thus, in Tetrahymena there is a protein that resembles actin in its extractability, molecular weight, peptide pattern after partial proteolysis, DNase I-binding capacity and reactivity with anti-actin antibodies. However, this protein did not assemble into actin filaments in crude extracts.
Binding of Tetrahymena dynein to axonemes of Marsilea vestita lacking the outer dynein arm
Authors: Hyams Jeremy S. 
Published: April 2021

ABSTRACT
Axonemes from the heterosporous water fern Marsilea vestita were fixed in the presence of tannic acid and examined by thin-section electron microscopy. Transverse sections revealed the normal 9+2 configuration except for the absence of the outer of the two dynein arms. Both arms were normally preserved in parallel preparations of Chlamydomonas axonemes. Isolated dynein from the ciliated protozoon Tetrahymena bound to Marsilea axonemes at the site normally occupied by the outer arm. Dynein binding was partially reversed by ATP as judged by both electron microscopy and polyacrylamide gel electrophoresis. This system should provide a valuable insight into the biochemistry and function of the inner dynein arm and the relationship of the two arms to motility in more conventionally equipped axonemes.
Differentiation in Trypanosoma brucei: Host-parasite cell junctions and their persistence during acquisition of the variable antigen coat
Authors: Tetley L. , Vickerman K. 
Published: April 2021

ABSTRACT
Acquisition of the variable antigen-containing surface coat of Trypanosoma brucei occurs at the metacyclic stage in the salivary glands of the tsetse fly vector. The differentiation of the metacyclic trypanosome in the gland has been studied by scanning electron microscopy and by transmission electron microscopy of thin sections and freeze-fracture replicas. The uncoated epimastigote trypanosomes (with a prenuclear kinetoplast) divide while attached to the salivary gland epithelium brush border by elaborate branched flagellar outgrowths, which ramify between the host cell microvilli and form punctate hemidesmosome-like attachment plaques where they are indented by the microvilli. These outgrowths become reduced as the epimastigotes transform to uncoated trypomastigotes (with postnuclear kinetoplast), which remain attached and capable of binary fission. The flagellar outgrowths disappear but the attachment plaques persist as the uncoated trypomastigotes (premetacyclics) stop dividing and acquire the surface coat to become ‘nascent metacyclics’. Coat acquisition therefore occurs in the attached trypanosome and not, as previously believed, after detachment. Coating is accompanied by morphological changes in the glycosomes and mitochondrion of the parasite. Freeze-fracture replicas of the host-parasite junctional complexes show membrane particle aggregates on the host membrane but not on the parasite membrane. It is suggested that disruption of the complex occurs when maximum packing of the glycoprotein molecules has been achieved in the trypanosome surface coat, releasing the metacyclic trypanosome into the lumen of the gland.
Regulation of cell shape in Euglena gracilis. iii. involvement of stable microtubules
Authors: Lachney Carole L. , Lonergan Thomas A. 
Published: April 2021

ABSTRACT
The role of cytoplasmic microtubules in a recently reported biological clock-controlled rhythm in cell shape of the alga Euglena gracilis (strain Z) was examined using indirect immunofluorescence microscopy. The resulting fluorescent patterns indicated that, unlike many other cell systems, Euglena cells apparently change from round to long to round cell shape without associated cytoplasmic microtubule assembly and disassembly. Instead, the different cell shapes were correlated with microtubule patterns, which suggested the movement of stable microtubules to accomplish cell shape changes. In live intact cells, these microtubules were demonstrated by immunofluorescence to be stable to lowered temperature and elevated intracellular Ca2+ levels, treatments that are commonly used to depolymerize microtubules. In cells extracted in detergent at low temperature or in the presence of elevated Ca2+ levels, the fluorescent image of the microtubules was disrupted. Transmission electron microscopy confirmed the loss of one subset of pellicle microtubules. The difference in microtubule stability to these agents between live intact cells and cells extracted in detergent suggested the presence of a microtubule-stabilizing factor in live cells, which is released from the cell by extraction with detergent, thereby permitting microtubule depolymerization by Ca2+ or lowered temperature. The calmodulin antagonist trifluoperazine prevented the Ca2+-induced disruption of the fluorescent microtubule pattern in cells extracted in detergent. These results implied the involvement of calmodulin in the sensitivity to Ca2+ of the microtubules of cells extracted in detergent.