bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phylogenetic relationships within the invertebrata in relation to the structure of septate junctions and the development of ‘occluding’ junctional types
Authors: Green Colin R. , Bergquist Patricia R. 
Published: April 2021

ABSTRACT
The structures of 13 variants of invertebrate septate junction are reviewed on the basis of freeze-fracture, lanthanum tracer and thin-section studies. In addition, a simple type of occluding junction in the phylum Porifera, a variation of tight junction in the phylum Tunicata and the vertebrate tight junction are covered. All the junctions considered form a belt around the apical circumference of cells lining a lumen or an exterior surface. The large number of these junctions now recognized permits discussion relating to invertebrate classification and suggested phylogenetic relationships, and to the development of intercellular junctions. The relationships revealed are discussed under three headings: Coelenterates and lower invertebrates, Proterostomia (the annelid, molluscan and arthropod lineage) and the Deuterostomia (the echinoderm and chordate lineage).
It is proposed that the pleated septate junction of the lower invertebrates resembles that of the hydrozoan rather than anthozoan Coelenterates. This lower invertebrate pleated septate junction occurs in several lower invertebrate phyla including the Annelida (of the proterostome lineage), but also occurs in the Sipunculoidea, a group supposedly on the deuterostome lineage. The proterostome line includes the molluscs and the arthropods, which have the molluscarthropod pleated septate junction. Several variations of the smooth septate junction are also seen in Arthropoda. Among the deuterostomes the Chaetognatha have both a paired septate junction and a pleated junction and are therefore considered to be not very far removed from the Sipunculoidea. The echinoderms and hemichordates also have double-septum septate junctions. In addition however, these two phyla have anastomosing septate junctions that are very similar, varying only in their final configuration. Of the two, the echinoderm anastomosing septate junction most closely resembles the tight junction seen in the tunicates, and the Hemichordata are therefore considered to be a lateral development from the main line of chordate evolution. The tunicates have a tight junction similar to that seen in vertebrates; it is however more ‘leaky’ and has distinctive freeze-fracture characteristics.
In the phylum Porifera a form of simple parallel membrane junction appears to serve an occluding function. This junction has regular intercellular spacing in the absence of any septa and it is suggested that the spacing in septate junctions is probably not dictated by the septa. This interpretation is reasonable particularly when the diversity of septal types in conjunction with stable intercellular spacing is considered. Finally, a theory is put forward suggesting that in evolution a change from the septate to the tight junction could simply involve a modification of a ‘membrane spacing factor’, which allows the membranes of adjacent cells to come together at intervals, in the normal tight junction pattern.
The fusion of trout spermatozoa with chinese hamster fibroblasts
Authors: Yip J. H. K. , Bols N. C. 
Published: April 2021

ABSTRACT
Polyethylene glycol (PEG) was used to fuse trout sperm with Chinese hamster fibroblasts (CHW-1102). As judged by light microscopy, PEG significantly increased the number of associations between the two cell types. Electron microscopy revealed that the sperm nuclei were in the cytoplasm of CHW-1102 in cultures that had been treated with PEG and in phagosomes of CHW-1102 in cultures not treated with PEG.
In the cytoplasm many sperm nuclei had an extensive network of fibres whereas before fusion the sperm nuclei contained chromatin blocks which were packed together tightly. In phagosomes they consisted of dispersed blocks of chromatin. The chromatin of the few sperm that were found outside CHW-1100 cells but in the same culture that was treated with PEG also lacked fibres and consisted of loosely packed blocks. Most nuclei were unaltered by PEG treatment alone although in a few the packing of the chromatin blocks was loosened. Thus the decondensation of sperm nuclei within CHW-1102 cells appears to be brought about by the mammalian cytoplasm rather than by digestion in phagosomes, the culture conditions, or the treatment used to induce fusion.
Intake of phosphatase-active plasma membrane into the cytoplasm of oocytes from sexually immature hamsters
Authors: Weakley Brenda S. , Webb Pauline , James John L. 
Published: April 2021

ABSTRACT
When thiamine pyrophosphate is used as substrate, heavily stained complexly branching cytoplasmic structures are seen in developing oocytes of the hamster between 8 and 12 days after birth. This coincides with the onset of the dictyate stage of first meiotic prophase. The structures appear to arise from the oocyte plasma membrane in two ways: (1) by proliferation and infolding of the membrane, and (2) by membrane being pushed into the cytoplasm by invaginating follicle cell processes. This appears to be followed by proliferation of the 1n-vaginated plasma membrane within the oocyte cytoplasm.
Incubations with ATP or β-glycerophosphate, with and without the inhibitor L-p-bromo-tetramisole, indicate that the staining is not due to the action of either ATPase or alkaline phosphatases.
The origin and possible developmental significance of the reactive structures are discussed.
Heterogeneity of the kinetics of proliferation within human skin fibroblastic cell populations
Authors: Azzarone B. , Macieira-Coelho A. 
Published: April 2021

ABSTRACT
Human adult fibroblasts from the papillary layer of the skin showed increased survival in vitro when compared to reticular fibroblasts from the same biopsy. Fibroblasts of the papillary layer were also analysed in vitro to study the kinetics of proliferation between subcultivation and resting phase. It was found that the growth fraction and maximum cell densities vary as a function of the initial inoculum. The results are compatible with the presence of two cell populations with different growth potentials. The heterogeneity of these populations has to be taken into account when studying cellular aging.
Osteoblasts release osteoclasts from calcitonin-induced quiescence
Authors: Chambers T. J. 
Published: April 2021

ABSTRACT
There is an increasing body of indirect evidence that suggests that the localization and activity of osteoclasts, the major agents of bone resorption, are controlled by osteoblasts. In this paper I provide direct evidence that osteoblasts are indeed able to alter the behaviour of osteoclasts. I used calcitonin (CT) to suppress the cytoplasmic activity of osteoclasts isolated on glass or plastic substrates, and found that, while isolated osteoclasts remain quiescent in CT for as long as the hormone is present, they regain activity when osteoblasts are added to the culture. ‘Escape’ from CT-induced quiescence could not be transmitted by supernatants from cultures of osteoblasts, was not due to inactivation of CT by osteoblasts, and did not occur if osteoblasts were separated from osteoclasts by a Millipore filter. When osteoblasts and osteoclasts were cultured together at low cell density in CT, I found that while those osteoclasts in the culture that remained isolated also remained inactive, osteoclasts that were in contact with osteoblasts showed a return to activity. This return to activity was most marked in the portion of osteoclast periphery in direct contact with an adjacent osteoblast. Although contact with osteoblasts did not abrogate the sensitivity of osteoclasts to added calcitonin, osteoclasts were found to escape inhibition by calcitonin at a rate proportional to the number of osteoblasts with which they were in contact.
Intermediate (10 nm) filament proteins and the Ca2+-activated proteinase specific for vimentin and desmin in the cells from fish to man: an example of evolutionary conservation
Authors: Nelson W. James , Traub Peter 
Published: April 2021

ABSTRACT
Cultured cells from representative species of the five main Classes of Chordates (Mammalia, Aves, Reptilia, Amphibia and Pisces) were examined for the presence of intermediate (1o nm) filament proteins. Using a combination of morphological and immunological methods and detailed protein-chemical characterization it is demonstrated that intermediate filament proteins, as shown also for actin and tubulin, are highly conserved during evolution. This conclusion is based on the following observations: (1) intermediate (10 nm) filaments were found in all the cell lines examined from taxonomically distant species; (2) the intermediate filaments were stable in buffers of low ionic strength in the presence of 4 mM-Mg2+ and Triton X-100; (3) under these ionic conditions, detergent-resistant residual cell structures were formed in which the intermediate filament morphology was highly preserved; (4) the intermediate filaments could be completely solubilized in the absence of Mg2+; (5) all intermediate filament proteins were quantitatively precipitated by (NH4)2SO4 at 25% saturation; (6) the intermediate filament proteins, with the exception of some of the proteins from Xenopus and viper cells, all bound to single-stranded DNA-cellulose, and could be eluted at various NaCl concentrations depending on the individual proteins; (7) the intermediate filament proteins had similar molecular weights (50 000 to 58 000), isoelectric points (pl 5·6–5·3) and isoelectric variants, probably due to different degrees of phosphorylation; (8) the major intermediate filament proteins were degraded by the vimentin-specific, Ca2+-activated proteinase and had similar peptide patterns; (9) all the intermediate filament proteins had an antigenic determinant in common and cross-reacted with the monoclonal antibody α-IFA.
In addition, the presence of intermediate filament proteins in taxonomically distant species was indirectly supported by the finding that a Ca2+-activated proteinase activity could be detected in the cells from fish to man. This proteinase had identical characteristics in all the cells examined. It had a molecular weight of 100000, a pl of 5·2, Ca2+ dependence, neutral pH optimum and degraded Ehrlich ascites tumour cell-vimentin with the production of a specific and characteristic peptide pattern. The proteinase was also classified as a thiol-type enzyme. The proteinases from the taxonomically distant species had, therefore, identical properties to the vimentin-specific, Ca2+-activated proteinase purified from Ehrlich ascites tumour cells.
Locomotory invasion of human cervical epithelium and avian fibroblasts by hela cells in vitro
Authors: Stephenson E. M. 
Published: April 2021

ABSTRACT
The locomotory invasive ability of HeLa cells was tested against: (a) embryonic chick heart fibroblasts (CHF); and (b) normal epithelial cells from human cervix (HCE) in explant confrontations. Data for analyses were obtained from replicate cultures fixed 24 h after junction and from 24-h time-lapse films.
The mean invasion index for HeLa versus CHF did not indicate significant obstruction but analyses of hourly radial advance and orientation frequencies showed that obstruction eventually developed as postjunctional incubation time increased. Early contacts between HeLa and CHF demonstrated non-reciprocity of type I contact inhibition of locomotion by the tumour cells, which continued moving in their original direction to underlap contact-inhibited fibroblasts and eventually to occupy spaces vacated by them. When CHF population density increased and free space diminished, HeLa cells displayed directional and probably substratedependent contact inhibition.
The high invasion index of HeLa versus HCE was largely due to occupation of previous HCE territory by tumour cells and only occasionally to actual infiltration of the epithelial sheet. After contact with HeLa, ruffling substrate-adherent marginal epithelial cells displayed contractile, type 1 contact inhibition of locomotion. After orientation changes, they gradually retreated. Against HCE, HeLa cells exhibited non-reciprocity of type I contact inhibition and continued radially forward, following the retreating epithelial margin. They did not move onto exposed upper surfaces of epithelial cells and did not underlap marginal cells firmly adherent to the substratum. Invasion of the epithelial sheet was seen only when initial access beneath a cell with a non-adherent margin was available. The contact relationships of isolated invading HeLa cells with their epithelial neighbours suggested successive non-reciprocal contact inhibition reactions.
Structure of Drosophila polytene chromosomes : Evidence for a toroidal organization of the bands
Authors: Mortin Lawrence I. , Sedat John W. 
Published: April 2021

ABSTRACT
Avoiding acid fixation or squashing, the structure of Drosophila salivary gland polytene chromosomes has been examined in detail in nuclei, with special emphasis on the organization of the DNA in the chromosome bands. Cut serial sections, optical serial sections, scanning electron microscopy (SEM) on whole mounts, high-voltage electron microscopy (HVEM) on whole mounts, and pancreatic DNase I digestion monitored by fluorescent microscopy have been used to complement one another in this analysis. With all five of these techniques, stereo pairs were used to aid in the three-dimensional reconstruction of chromosomal structures.
Evidence is presented that most, if not all, of the polytene chromosome bands are torusshaped. The DNA of these bands is largely confined to the rim, with the interior essentially DNA-free. The chromatin in each polytene band is also seen to have an extremely regular and highly ordered substructure. This substructural organization is largely radially symmetric in the bands and generally parallel to the chromosome axis. In addition, each band appears to be a distinct architectural entity with regard to its exact structural features and dimensions. A model is presented that follows these organizational boundary conditions.
Growth and observations of chinese hamster seminiferous epithelium in vitro
Authors: Ellingson D. J. , Yao K. T. S. 
Published: April 2021

ABSTRACT
Seminiferous tubules from 1- to 3·5-month-old Chinese hamsters were cultivated under dialysis membranes in Rose chambers. The growth and development of the germinal cells was followed daily with phase-contrast microscopy and time-lapse cinemicrography. Spermatogonia lived for 2 or 3 weeks and underwent frequent mitoses. Spermatocytes in metaphase at culture initiation completed their meiotic division. These cells remained healthy for 3–4 days. Such phenomena as germinal cell/Sertoli cell association, nuclear rotation, multinucleated cell formation and spermatid formation were studied and photographed.
Pollen-wall proteins: localization and enzymic activity
Authors: Knox R. B. , Heslop-Harrison J. 
Published: April 2021

ABSTRACT
Cytochemical methods have been used to examine the distribution of acid phosphatase, ribonuclease, esterase, amylase and protease activity and protein in the walls of pollen grains and spores. Enzyme activity was detected in the walls of 50 angiosperm pollens, in pine, and in the spore wall of a species of Equisetum. Activity was absent from the 2 species of ferns examined. The survey covered all major structural pollen types. In all cases enzyme activity was associated principally with the intine, the inner cellulosic part of the wall. In all aperturate grains activity was concentrated in or around the apertural intine; that is, over or near the potential sites of emergence of the pollen tube. Protein concentrations in the intine at these sites could be demonstrated in several pollen types by staining methods and by absorption at 285 nm.
Developmental study showed that the enzymes are incorporated in the intine during the early period of wall growth following the release of the spores from the meiotic tetrads. During this period, stratified ribosomal endoplasmic reticulum lies adjacent to the inner spore wall over the areas of incorporation. In Cosmos bipinnatus, a composite, the material is incorporated as ribbons or leaflets, which interleave with cellulose lamellae. In other species the wall protein may take the form of granules, tubules or vesicles, embedded in the intine cellulose. At maturity the intine is separated from the spore cytoplasm by an intact plasmalemma, so the wall enzymes are to be regarded as being extracellular.
In some species enzyme activity was detected in materials on the surface of the pollen exine derived probably from the surrounding tapetal tissue; however, this was usually insignificant compared with that shown by the intine.
The intine enzymes are very readily leachable, and their function is probably connected with the early nutrition of the pollen tube and the penetration of the stigma. It is likely that the wall proteins make up a very large proportion of mobile protein of the pollen grain, and they may therefore be important in pollen allergenicity.
The development and structure of pyrenoids in Bulbochaete hiloensis
Authors: Retallack B. , Butler R. D. 
Published: April 2021

ABSTRACT
Chloroplasts in zoospore mother cells, zoospores, and sporelings of Bulbochaete are shown to possess spherical granular areas which are interpreted as incipient pyrenoids, which arise de novo within the stroma. Very young pyrenoids are often seen adjacent to pale, fibril-containing areas of the chloroplast. Later, the incipient pyrenoids are often associated with a single thylakoid and become invested with starch grains and cytoplasmic channels as they develop into forms morphologically indistinguishable from the mature pyrenoids of the vegetative cell. In young oogonia, degenerating pyrenoids are seen to possess much starch. Infrequently, the matrix of a degenerating pyrenoid is invaded by the stroma, its dimensions decreasing to those of an incipient pyrenoid. The appearance of young pyrenoid-like structures within lateral outgrowths of the chloroplasts of young oogonia and sporelings may represent a further method of pyrenoid formation.
Relationships between intramembranous particles and surface coat carbohydrates in cells of a compact tissue
Authors: Murphy C. R. , Swift J. G. 
Published: April 2021

ABSTRACT
The structural relationships between intramembranous particles (IMPs) and surface carbohydrates have been studied in cells of a compact tissue — uterine epithelial cells – using an in vivo technique. This involves introducing small amounts of glycerol into the uterine lumen of anaesthetized rats. The treatment results in extensive aggregation of IMPs in the apical plasma membrane of the epithelial cells, but no change in the distribution of several surface carbohydrates could be detected.
Our findings indicate that, in this case, the carbohydrates are not the surface expression of the IMPs, which are generally believed to represent integral membrane proteins. We suggest that the structural relationships between IMPs and surface carbohydrates in the plasma membrane of this compact tissue cell are more similar to those in membranes of free-floating nucleated cells than to those in the much-studied erythrocyte membrane.
Thymidylate kinase from Acetabularia I. Properties of the enzyme
Authors: Groot Egon J. De , Schweiger Hans-Georg 
Published: April 2021

ABSTRACT
The occurrence of a dTMP kinase as well as a dTDP kinase in Acetabularia mediterranea has been demonstrated. A test system was developed by which it was possible to estimate the enzyme activity in an individual Acetabularia cell or even in a cell fragment.
The enzyme catalyses the phosphorylation of dTMP in the presence of ATP. In the test system described, dTTP is formed as well as dTDP. This indicates that there is also a dTDP kinase present in the enzyme preparation. Characteristics of the enzyme such as pH optima at pH 7·0 and 8·75, a temperature optimum at 45 °C, a Km value of 3·3 × 10−6M and a high specificity for ATP were established. In homogenates that were preserved at −70°C the enzyme activity was retained even after many weeks. Freezing at −70°C and then thawing resulted in an increase in enzyme activity. The enzyme was inhibited by low concentrations of dTTP. After centrifugation of homogenates the greater part of the enzyme activity was found in the sediment. From the observation that purified chloroplast preparations contained most of the dTMP kinase activity, and that chlorophyll and enzyme activity cosedimented in a linear sucrose gradient, it was concluded that the enzyme is located in the chloroplasts.
The positions of centromeres on the somatic metaphase plate of grasses
Authors: Heslop-Harrison J. S. , Bennett M. D. 
Published: April 2021

ABSTRACT
Centromere positions on the metaphase plate of 48 root-tip cells of four grass species were analysed using metaphases reconstructed from electron micrographs of serial thin sections.
Centromere alignment was almost perfect on a plane in 15 untreated metaphases of cereals where 2n = 14; only 2% of the total variance in centromere position was out of the plane of the metaphase plate. In 23 similar cells pretreated with ice-water, the mean out-of-plate variance was 9%, compared to an expectation of 18% if centromeres were positioned randomly in space. In cold-treated cells of Zea mays (2n = 20), the out-of-plate variance (14%) was significantly less than a random expectation of 20%.
The distances of centromeres from the mean centromere position (MCP) were also analysed. They showed that the centromeres tended to be normally distributed about a circle around the MCP in all the species. Thus centromeres tend towards a ring arrangement in metaphase cells.
Analysis of separation distances of all pairs of centromeres in each reconstructed cell showed that the distribution of distances between centromeres is not random: there are significantly fewer centromeres that are close together and more that are at medium separation distances than is expected on a random basis. This is different from previously published assumptions about centromere disposition in squashed metaphases.
Changes in the synthesis, distribution and sulphation of glycosaminoglycans of cultured human skin fibroblasts upon ascorbate feeding
Authors: Edward Michael , Oliver Roy F. 
Published: April 2021

ABSTRACT
The effect of ascorbic acid on the synthesis, distribution and sulphation of glycosaminoglycans by human skin fibroblasts has been examined. Medium was supplemented with ascorbate over several days, and cultures incubated with [* 3H]glucosamine and Na235SO4 for 48 h, followed by analysis of the glycosaminoglycans in the medium, in collagenase and trypsin extracts, and in cell fractions. Ascorbate feeding resulted in a reduction in hyaluronate synthesis, which was the main 3H-labelled component and was distributed mainly in the medium fractions. Sulphated glycosaminoglycans showed a reduction in incorporation of 3H label, but increased sulphation following ascorbate feeding. In control cultures 53% of 3H-labelled sulphated glycosaminoglycans and 63% of 35S-labelled glycosaminoglycans were present in the medium fraction, while in ascorbate-fed cultures, 41% of 3H label and 38% 35S label were incorporated into medium-sulphated glycosaminoglycans. Ascorbate also caused an increase in cell density and in collagen production and deposition.