bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structure of syncytia induced by the phytoparasitic nematode Nacobbus aberrans in tomato roots, and the possible role of plasmodesmata in their nutrition
Authors: Jones M. G. K. , Payne H. L. 
Published: April 2021

ABSTRACT
The structure of syncytia induced within galls in tomato roots by the false root-knot nematode Nacobbus aberrans has been examined by light and electron microscopy. A syncytium develops by breakdown of individual cell walls, which allows movement of cytoplasmic contents between transformed cells. The wall breakdown takes place at pit fields, where the plasmodesmata may be protected from digestion until the surrounding wall is removed. Numerous sieve elements differentiate in the cells outside the syncytium. These sieve elements, and also plasmodesmata in pit fields, are demonstrated by fluorescence microscopy. The possibility of a symplastic pathway of solute movement from the phloem to the syncytium is suggested. A massive accumulation of starch occurs in the gall cells and syncytial cells, which may be related to the proliferation of phloem. Wall ingrowths typical of transfer cells are absent, and a comparative survey of the structure and mode of solute entry into nematode-transformed cells in which ingrowths are present or absent is presented.
Hijacking of the host cell Golgi by Plasmodium berghei liver stage parasites
Authors: De Niz Mariana , Caldelari Reto , Kaiser Gesine , Zuber Benoit , Heo Won Do , Heussler Volker T. , Agop-Nersesian Carolina 
Published: April 2021

ABSTRACT
The intracellular lifestyle represents a challenge for the rapidly proliferating liver stage Plasmodium parasite. In order to scavenge host resources, Plasmodium has evolved the ability to target and manipulate host cell organelles. Using dynamic fluorescence-based imaging, we here show an interplay between the pre-erythrocytic stages of Plasmodium berghei and the host cell Golgi during liver stage development. Liver stage schizonts fragment the host cell Golgi into miniaturized stacks, which increases surface interactions with the parasitophorous vacuolar membrane of the parasite. Expression of specific dominant-negative Arf1 and Rab GTPases, which interfere with the host cell Golgi-linked vesicular machinery, results in developmental delay and diminished survival of liver stage parasites. Moreover, functional Rab11a is critical for the ability of the parasites to induce Golgi fragmentation. Altogether, we demonstrate that the structural integrity of the host cell Golgi and Golgi-associated vesicular traffic is important for optimal pre-erythrocytic development of P. berghei. The parasite hijacks the Golgi structure of the hepatocyte to optimize its own intracellular development.
This article has an associated First Person interview with the first author of the paper.
A twelve-channel automatic device for continuous recording of cell aggregation by measurement of small-angle light-scattering
Authors: Thomas William A. , Steinberg Malcolm S. 
Published: April 2021

ABSTRACT
We describe here a 12-channel aggregometer, evolved from the instrument described by Beug & Gerisch in 1972, which records the course of aggregation or agglutination of cells or other particles by following the changes in light-scattering of the aggregating suspension. The instrument incorporates a simple memory system for condensing the data, introduces an improved cuvette design, and can be adjusted in its responsiveness to light-scattering by particles of different sizes.
In our aggregometer, a vertical wheel in an opaque thermostatted chamber accommodates up to 12 cuvettes each containing a cell suspension and an air bubble. The constant rising of the bubble as the wheel rotates causes the stirring action which promotes aggregation. At a certain point in its rotational path, each cuvette is penetrated by a beam of light focused upon an absorbing beam stop centred in front of a photomultiplier tube. Particles suspended in the cuvette scatter a portion of the light beyond the beam stop into the photomultiplier tube to produce an electrical pulse proportional to the photon input. Collection of these pulses with the wheel in continuous motion avoids any disturbance of the course of aggregation. The pulses are routed to memory circuits for summation and eventual recording by a 12-channel printing potentiometer which automatically colour-codes and numbers each curve.
The cuvettes consist of 2 glass microscope coverslips affixed with silicone grease over a hole in a thin, stainless steel blank. They are very durable and are easily dismantled and reassembled for cleaning. The coverslips are replaced after each use. The discoid chamber of our cuvette permits uniform circulation of the bubble, which in turn causes gentle stirring of the aggregating suspension at a rate that is a direct and continuous function of rev/min.
Measurement of light-scattering at small angles (3–5·5°) provides great sensitivity to the disappearance of single cells and progressively less sensitivity to the coalescence of aggregates of progressively larger size. The signal generated by the photomultiplier tube decreases as aggregation proceeds.
At 32 rev/min, one data point per channel, representing the sum (average) of 24 successive measurements, is printed every 45 s. In the course of a 60-min assay under standard conditions, up to 23040 individual readings can be automatically taken, summed and plotted. In a comparison of 8 identical samples run simultaneously, the printed values after 60 min agreed with a standard deviation of ± 2 %.
In situ hybridization to lampbrush chromosomes: A potential source of error exposed
Authors: Callan H. G. , Old R. W. 
Published: April 2021

ABSTRACT
Denatured 3H-labelled DNAs containing Xenopus or human globin sequences hybridize to RNA transcripts on a single pair of lateral loops on lampbrush chromosome IX of Triturus cristatns carnifex, and to no other loops on this chromosome or the rest of the complement. However they do so, not because of the globin sequences in the probes, but rather because the plasmids from which the probes were prepared were constructed with G.C homopolymer tails. Simple sequence poly d(C/G)n probes also hybridize with RNA transcripts on this same pair of loops, and with no others.
Cell proliferation and migration on collagen substrata in vitro
Authors: Schor Seth L. 
Published: April 2021

ABSTRACT
Quantitative data are presented regarding cell proliferation and migration on (a) collagen films (b) the surface of 3-dimensional gels of native collagen fibres and (c) within the 3-dimensional collagen gel matrix, as part of a study of the effects of the extracellular matrix on cell behaviour. The nature of the collagen environment was found to influence the proliferation of certain cell types, but not of others. For example, HeLa cells proliferate at approximately the same rate and reach the same saturation cell densities on all of the collagen substrata, while human skin fibroblasts grow more slowly within the 3-dimensional collagen gel matrix compared with cells either on the gel surface or on collagen films. The 3-dimensional gels of native collagen fibres may also be used to study cell migration on the gel surface, as well as cell migration (or ‘infiltration’) from the gel surface into the 3-dimensional collagen matrix. Two methods have been used to obtain quantitative information concerning cell infiltration into the collagen gel, one involving the selective removal of cells from the gel surface, while the other relies on direct microscopic examination. Of the cells examined to date, epithelial cells (both normal and tumour) do not show infiltrative behaviour, while both normal and virally transformed fibroblasts, as well as tumour cells of non-epithelial origin (e.g. melanoma), do infiltrate into the collagen gel matrix, at rates which vary considerably according to cell type.
Clonal death associated with the number of fissions in Paramecium caudatum
Authors: Takagi Yoshiomi , Yoshida Michiko 
Published: April 2021

ABSTRACT
Contrary to an earlier report suggesting clonal immortality in Paramecium caudatum, the clones of the same species in this study terminated inevitably with a maximal life-span of 658 fissions and showed, prior to clonal death, decreased fission rate, increased probability of the appearance of non-dividing or dead cells after cell division, and increased frequency of morphological abnormality and of division asynchrony. Clonal senescence and death after a limited number of fissions was reproducible even if subclones derived from the original clone of a known fission age were examined again after a lag of 468 days. These results indicate that clones of P. caudatum are mortal and that they use fissions, not days, to measure life-span. Possible causes for the discrepancies between the earlier report and the present one are discussed.
Ultrastructure of modified root-tip cells in Ficus carica, induced by the ectoparasitic nematode Xiphinema index
Authors: Wyss U. , Lehmann H. , Jank-Ladwig R. 
Published: April 2021

ABSTRACT
The migratory ectoparasitic root nematode Xiphinema index, added to Ficus carica seedlings in. sterile agar culture, fed exclusively on the tips of the roots. As a response the tips started to swell and became transformed into terminal galls as long as feeding was continued.
When the cytology of swollen root-tips was examined 24 h after the first nematode attack, necrotic cells, scattered singly or in small groups within the root apex, were found in ultrathin sections. These cells, whose protoplasts showed features of a hypersensitive reaction, were most probably those fed upon by the nematodes. Each necrotic cell was surrounded by several enlarged, mostly binucleate cells with dense cytoplasm. One day later the binculeate cells were multinucleate, containing 4 or even 8 nuclei. The clear-cut demarcation between necrotic and modified cells indicated that only the stimulus for the induction of modified cells but not the stimulus for cell necrosis passed into neighbouring cells.
Root-tip galls that provided the appropriate food for egg production in nematodes contained greatly enlarged multinucleate cells between necrotic cells. The modified cells showed features of high metabolic activities, expressed in nuclear and nucleolar hypertrophy, invagination of the nuclear envelope, increased cytoplasmic density, abundance of mitochondria, plastids and rough endoplasmic reticulum. Wall ingrowths, typical of transfer cells, were rare and if present occurred only adjacent to necrotic cells. In older modified cells new cell plates, surrounded by phragmoplasts, were formed.
Euglena plasma membrane during normal and vitamin B12 starvation growth
Authors: Lefort-Tran M. , Bre M. H. , Ranck J. L. , Pouphile M. 
Published: April 2021

ABSTRACT
Freeze-fracture and optical diffraction techniques were used to study the organization of the Euglena pellicle during the normal and replicative stages of the cell cycle and during vitamin B12 starvation. It was shown that the diffuse layer underlying the tripartite structure has a fibrillar structure. Despite the absence of homology in the 2 fracture faces of the pellicle, the EF striated and the PF particulate ones appear complementary as shown by optical diffraction studies; it must therefore be considered as a true membrane. The grooves are free from such particles and striations. They appear as a specific pattern of the cortex, different from the ridges in their structural organization and their replicative capacity as observed during vitamin B12 starvation. This notion is confirmed by the mode of pellicular growth which is characterized by 2 steps. The first occurs during the early replicative stage (pre-mitotic phase of the cell cycle) when the formation of a new ridge is correlated with the appearance of the ‘minor’ orientation of a 2-dimensional lattice on the EF and the PF faces and the spread of the particles over the PF face of the space between the old ridges. The second takes place during the lengthening of the ridges from the initiating posterior side (non-replicative stage).During this second step, the ‘major’ orientation of the lattice is preferentially observed in control cells and exclusively in starved cells.
The striking differences between the grooves and the ridges is discussed, as well as the 2 modes of growth and their significance in morphogenesis.
The nucleolus in telophase, interphase and prophase
Authors: Ashraf Mohammad , Godward M. B. E. 
Published: April 2021

ABSTRACT
The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the ‘pale fibrillar material’ occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described.
It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription.
A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the model, and the contrary views, implicating the use of the term ‘nucleolar organizer’, that are still current at the present time.
Nematocyte migration in hydra: evidence for contact guidance in vivo
Authors: Campbell Richard D. , Marcum Beverly A. 
Published: April 2021

ABSTRACT
Nematocytes rapidly emigrate from normal tissue implanted into an epithelial hydra, which lacks its own nematocytes. We observed emigrating nematocytes, both in time-lapse movies and in fixed whole mounts, to learn what controls directionality. The cells migrate at speeds of 10—30μm/min with a pseudopod forward and the capsule trailing. Migration is aligned parallel to the polyp axis, but cells move both proximally and distally and often shuttle back and forth. Thus, migration is strongly bidirectional, with a slight distal bias since at any time more cells are moving towards the tentacles. Nematocytes freely migrate through tissue of reversed polarity. No evidence was found for a chemotactic stimulus emitted from the tentacles. The bidirectional movement pattern appeared to be imposed by epithelial muscle processes, which form an axial, fibrous mat on which nematocytes migrate. Experimental deformation of the muscle alignment results in a corresponding deformation of nematocyte migration. Thus, nematocyte migration appears to be bidirectionally oriented through contact guidance by epithelial muscle processes.
ATP-driven tubule extrusion from axonemes without outer dynein arms of sea-urchin sperm flagella
Authors: Hata H. , Yano Y. , Mohri T. , Mohri H. , Miki-Noumura T. 
Published: April 2021

ABSTRACT
We have prepared axonemes without outer dynein arms from sea-urchin (Pseudocentrotus depressus, Hemicentrotus pulcherrimus) sperm flagella by selective solubilization with NaCl. Electron microscopy revealed that the axonemes gradually lost their outer arms in 0·5 M NaCl during 10 min. Such axonemes retained 42·8 ±7·3 % of their total axonemal ATPase activity and showed C, A, D and B bands in the dynein region of 4 % SDS-gel, while a solubilized fraction of the outer arms consisted almost entirely of A band polypeptide. We have succeeded in causing extrusion of the outer doublets from such axonemes by addition of ATP and trypsin. A bundle of outer doublets was sometimes observed to be extruded first from an axoneme and to show bending motion for a while, subsequently followed by a sliding of separate doublets past each other. The speed of the tubule extrusion process was slower and around 60 % of that of intact axonemes having both types of arm.
These observations indicate that the inner arms have a function equivalent to that of the outer arms, of sliding on adjacent doublets, although the inner arms seem to be constituted from polypeptide(s) different from that of the outer arms.
Structural responses of amoebae to the injection of heterologous cytoplasm
Authors: Flickinger Charles J. , Read Graham A. , Kabana Ellen M. 
Published: April 2021

ABSTRACT
Responses to the introduction of heterologous cytoplasm and the fate of foreign organelles were investigated in amoebae. Heterologous cytoplasm was transferred by microinjection from Pelomyxa carolinensis to Amoeba discoides. In control experiments, homologous cytoplasm was transferred from one A. discoides to another. Recipient cells were observed by light microscopy, and samples were prepared for ultrastructural study at intervals between 15 min and 3 days after operation. Recipients of heterologous cytoplasm showed two main responses. First, about 40 % recipients expelled small amounts of cytoplasm by a blebbing process within 30 min after injection. Second, organelles were segregated and broken down in membrane-bounded cytoplasmic vacuoles between 6 h and 2 days after operation. Acid phosphatase reaction product was observed in these vacuoles along with altered organelles. Use of electron-dense thoria particles to mark donor cells demonstrated the presence of injected cytoplasm in the vacuoles. In contrast, when amoebae were injected with homologous cytoplasm, none was expelled and vacuoles containing degenerating organelles were uncommon. The survival rate and general appearance of recipients of heterologous cytoplasm were much poorer than those of homologous recipients, and most of the former died by 1 week after operation. It is postulated that amoebae are capable of recognizing heteiologous organelles introduced into the cytoplasm and that they respond by expulsion and/or destruction of the foreign cellular components. The previously described lethal effect of heterologous cytoplasm was confirmed.
Isolation and characterization of membranes from the cells of maize root tips
Authors: Baydoun Elias A-H. , Northcote D. H. 
Published: April 2021

ABSTRACT
A discontinuous sucrose density gradient was used to separate membrane fractions from a homogenate of maize rcottips. Endoplasmic reticulum-, Golgi apparatus-, plasma membrane- and mitochondria-rich fractions were identified by their enzymic characteristics and by their appearance under the electron microscope. Maize roots were incubated in vivo with D-[U-14C]glucose, [Me-14C]choline chloride and diazotized [U-3H]sulphanilic acid. The pattern of incorporation of radioactivity into the various membrane fractions was investigated. Analyses of the polypeptide chains of the membrane fractions by SDS-polyacrylamide gel electrophoresis showed that the mitochondria-rich fraction had a different pattern of polypeptides from that of the other membrane fractions. The results are discussed in relation to the hypotheses of endomembrane flow and differentiation.
On the role of small peptides in the regulation of rna synthesis in Tetrahymena pyriformis
Authors: Andersen H. A. , Lykkesfeldt Anne E. , Nielsen S.J. 
Published: April 2021

ABSTRACT
Tetrahymena cells secrete a factor which inhibits RNA synthesis in vivo and in vitro. The factor is a relatively small peptide with a molecular weight between 300 and 1500 Daltons. Other, non-specific peptides in the broth medium or added to a chemically defined medium have a stimulatory effect on RNA synthesis in vivo and such peptides also stimulate the in vitro synthesis of RNA in an r-chromatin preparation. On the basis of these results we conclude that such extracellular small peptides compete with a specific factor which is part of the intracellular regulatory mechanism controlling the rate of RNA synthesis. The consequence of such competition is a high overproduction of ribosomal RNA in cells inoculated on peptide-rich broth media.
Effects of Colchicine on the Golgi Complex and Gerl of Cultured Rat Peritoneal Macrophages and Epiphyseal Chondrocytes
Authors: THYBERG JOHAN , PIASEK ANDRZEJ , MOSKALEWSKI STANISLAW 
Published: April 2021

Thioglycollate-elicited rat peritoneal macrophages and epiphyseal chondrocytes were cultured in vitro, treated with colchicine, and then studied by electron-microscopic and cytochemical techniques. Colchicine, but not lumicolchicine, caused disappearance of cytoplasmic microtubules and breakup of the Golgi complex with spreading of its dictyosomes from a well defined juxta nuclear area throughout the cytoplasm. There was also an altered distribution of lysosomes, which oriented themselves close to the dictyosomes both in controland colchicine-treated cells. Further, the structure of the individual dictyosomes was changed, especially in the chondrocytes. GERL equivalents were observed in control cells but were difficult to detect after exposure to colchicine. Reaction product for thiamine pyrophosphatase was found in narrow cisternae on the inner side of the dictyosomes in control cells but invacuole-like structures in colchicine-treated cells. Reaction product for acid phosphatase was present in GERL equivalents and lysosomes in control cells but mainly in lysosomes incolchicine-treated cells. Nevertheless, the total specific activities of these enzymes as well as of 5â&#x80;²-nucleotidase, a plasma membrane marker, remained unaffected by the drug treatment.
These observations show that cytoplasmic microtubules play an important and, in many respects similar, cytoskeletal role in two so functionally diverse cell types as macrophages and chondrocytes. They are particularly important for the structural integrity of the Golgi complex, which in both cells is normally organized in the area around the centrioles, from which numerous microtubules radiate into the cytoplasm. The observations further suggest that GERL is an integrated part of the Golgi complex in these cells.
Effects of colchicine on endocytosis of horseradish peroxidase by rat peritoneal macrophages
Authors: Piasek Andrzej , Thyberg Johan 
Published: April 2021

ABSTRACT
Horseradish peroxidase (HRP) was used as an exogenous marker to study the effects of microtubule-disruptive drugs on endocytosis in cultures of thioglycollate-elicited rat peritoneal macrophages. Colchicine and vinblastine, but not lumicolchicine or cytochalasin B, reduced HRP uptake by about 30–40 %. However, as determined by stereological measurements, the size of the HRP-containing compartment within the cells remained unaltered. In both control cells and cells treated with colchicine or vinblastine the HRP-reactive vesicles were preferentially located close to the dictyosomes (stacks of cistemae) despite the fact that the Golgi complex was disorganized in the treated cells. These results suggest that intact cytoplasmic microtubules are required to maintain a normal rate of fluid phase endocytosis in macrophages. On the other hand, it seems as if microtubules are not necessary for the translocation of newly formed endocytic vesicles/lysosomes to the dictyosomes, from which they probably are supplied with digestive enzymes.