bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of multiciliogenesis by miR-34/449 in the male reproductive tract through enforcing cell cycle exit
Authors: Wu Yu-Jie , Liu Yue , Hu Yan-Qin , Wang Li , Bai Fu-Rong , Xu Chen , Wu Jing-Wen 
Published: April 2021

ABSTRACT
Multiciliated cells (MCCs) are terminally differentiated postmitotic cells that possess hundreds of motile cilia on their apical surface. Defects in cilia formation are associated with ciliopathies that affect many organs. In this study, we tested the role and mechanism of the miR-34/449 family in the regulation of multiciliogenesis in EDs using an miR-34b/c−/−; miR-449−/− double knockout (dKO) mouse model. MiR-34b/c and miR-449 depletion led to a reduced number of MCCs and abnormal cilia structure in the EDs starting from postnatal day (P)14. However, abnormal MCC differentiation in the dKO EDs could be observed as early as P7. RNA-seq analyses revealed that the aberrant development of MCCs in the EDs of dKO mice was associated with the upregulation of genes involved in cell cycle control. Using a cyclin-dependent kinase inhibitor to force cell cycle exit promoted MCC differentiation, and partially rescued the defective multiciliogenesis in the EDs of dKO mice. Taken together, our results suggest that miR-34b/c and miR-449 play an essential role in multiciliogenesis in EDs by regulating cell cycle exit.
An ancient glaucophyte c6-like cytochrome related to higher plant cytochrome c6A is imported into muroplasts
Authors: Kleiner Friedrich Hans , Vesteg Matej , Steiner Jürgen Michael 
Published: April 2021

Abstract
Cytochrome c6 is a redox carrier in the thylakoid lumen of cyanobacteria and some eukaryotic algae. Although the isofunctional plastocyanin is present in land plants and the green alga Chlamydomonas reinhardtii, these organisms also possess a cytochrome c6-like protein designated as cytochrome c6A. Two other cytochrome c6-like groups, c6B and c6C, have been identified in cyanobacteria. In this study, we have identified a novel c6-like cytochrome called PetJ2, which is encoded in the nuclear genome of Cyanophora paradoxa, a member of the glaucophytes – the basal branch of the Archaeplastida. We propose that glaucophyte PetJ2 protein is related to cyanobacterial c6B and c6C cytochromes, and that cryptic green algal and land plant cytochromes c6A evolved from an ancestral archaeplastidial PetJ2 protein. In vitro import experiments with isolated muroplasts revealed that PetJ2 is imported into plastids. Although it harbors a twin-arginine motif in its thylakoid-targeting peptide, which is generally indicative of thylakoid import via the Tat import pathway, our import experiments with isolated muroplasts and the heterologous pea thylakoid import system revealed that PetJ2 uses the Sec pathway instead of the Tat import pathway.
Physiological requirements for ciliary reactivation of bracken fern spermatozoids
Authors: Wolniak Stephen M. , Cande W. Zacheus 
Published: April 2021

ABSTRACT
Physiological parameters affecting reactivated ciliary beat in spermatozoids of bracken fem (Pteridium aquilinum) were studied using a Triton/glycerol permeabilized cell model system. Reactivation frequencies of polylysine-tethered cells equalled in vivo rates at neutral pH. Frequency was dependent on ATP and Mg!+ concentration, and reactivation was inhibited by millimolar or greater free calcium. Reactivation was reversibly inhibited by micromolar concentrations of sodium ortho-vanadate, while intact cells were not affected by millimolar levels of the inhibitor. This is the first characterization of in vitro ciliary beat in a non-algal plant cell and demonstrates that the nucleotide and ionic requirements for reactivation of bracken cilia are similar to those of other systems.
Karyotype analysis of the plant-parasitic nematode Heterodera glycines by electron microscopy: II the tetraploid and an aneuploid hybrid
Authors: Goldstein Paul , Triantaphyllou A. C. 
Published: April 2021

ABSTRACT
In the plant-parasite nematode Heterodera glycines, 2 forms, in addition to the diploid (9 bivalents), have been isolated and analysed: a tetrapioid (18 bivalents) and an aneuploid (14 bivalents, hybrid between the diploid and the tetrapioid). Observations on the formation of their karyotypes indicates normal and non-homologous pairing. Eighteen normal synaptonemal complexes (SC) are present in pachytene nuclei of the tetrapioid. Two of the SCs are enclosed in a large heterochromatin mass that is displaced to one side of the nucleus. Such a mass has not been observed in the diploid or the aneuploid. Another 2 normal SCs of the tetrapioid have each a ‘modified SC region’ (MSC) within which the SC appears disorganized. The aneuploid has 14 SCs that are unattached at either end. Only 25% of the karyotype length is normal in the appearance of the SCs. The rest can be traced by the presence of disorganized SC material and condensed chromatin. Four MSCs are present in the hybrid nuclei. The possible role of the MSCs in the sex determination system is discussed.
Quantitative demonstration of cell surface involvement in a plant-animal symbiosis: Lectin inhibition of reassociation
Authors: Meints R. H. , Pardy R. L. 
Published: April 2021

ABSTRACT
The freshwater hydra, Hydra viridis is normally associated with Chlorella like, algal symbionts which inhabit the host’s digestive cells. Under experimental conditions bleached hydra will reassociate with algae harvested from green hydra, but not from our cultures of wild type Chlorella or strain NC64A which when originally isolated from Paramecium bursaria was symbiotically competent. Because of its demonstrated selectivity, the reassociation process is hypothesized to involve a recognition interface whose active participants are the algae cell wall and the digestive cell membrane. The data presented here confirm the hypothesis and suggest some potential molecular characteristics of the interacting partners.
Concanavalin A (Con A), a plant lectin, used widely for similar studies in other systems totally inhibits reassociation; Wheat Germ Agglutinin (WGA), ricin and Lens culinaris lectin do so to a lesser degree. These results are consistent with the hypothesis that glycoproteins on the cells’ peripheries are involved in cell-cell recognition in this system.
Protein labelling with 3H-NSP (N-succinimidyl-[2,3-3H]propionate)
Authors: Müller G. H. 
Published: April 2021

ABSTRACTA tritium compound with low molecular weight and diameter, N-succinimidyl-[2,3-3H]-propionate (3 H-NSP), was used to label histones and nonhistone proteins from calf thymus, and nuclear and total salivary gland proteins from larvae of the midge Chironomus thummi. Labelled proteins were visualized after electrophoresis in 10% polyacrylamide slab gels by fluorography. The method is much more sensitive than staining procedures, allowing to discern approx, 0.1 μg protein.
The relationship between the excess-delay phenomenon and temperature-sensitive periods in Tetrahymena thermophila
Authors: Frankel Joseph , Mohler Jym , Frankel Anne Koopmans 
Published: April 2021

ABSTRACT
Although temperatures of 37·5 and 39 °C allow continuous and rapid exponential growth of wild type Tetrahymena thermophila, sudden shifts up to these temperatures can bring about long excess-delays of cell division with accompanying resorption of developing oral primordia. A characteristic parameter of this delay-phenomenon is the physiological transition point, before which delays are maximal and after which they are negligible. When measured at a restrictive temperature that does not induce excess delays (36 °C), the end of the temperature-sensitive period of the cell division arrest of mutant cdaAI precedes the physiological transition point, that of cdaHI roughly coincides with it, while the entire temperature-sensitive period of cdaC2 comes after the physiological transition point. When cdaAI cells are exposed to 37·5 °C or above, the manifestations of temperature sensitivity are drastically affected: the estimate of the end of the temperature-sensitive period (the execution point) becomes spuriously late, and the characteristic division arrest following heat shocks is not manifested. The differential effects of the higher restrictive temperatures on cdaHI are more subtle, whereas those on cdaC2 are negligible. We conclude that the excess-delay phenomenon involves a set-back of gene-mediated processes occurring at specific stages of the cell cycle.
Characterization and localization of adenylyl cyclase in membrane vesicles and intact boar and human spermatozoa
Authors: Peterson R. N. , Russell L. , Hook L. , Bundman D. , Freund M. 
Published: April 2021

ABSTRACT
The enzymic properties of adenylyl cyclase in purified membrane vesicles from human and boar spermatozoa are described. Plasma membrane vesicles, which appear to be right-side-out, show a marked increase in activity in the presence of the detergent Triton X-100, manganous ion and alkaline pH. Electron-microscope cytochemical assays indicated the presence of adenylyl cyclase in boar and human sperm plasma membranes and also within the axoneme of intact human spermatozoa. The significance and precautions in the evaluation of the cytochemical data are discussed.
Genetic dissection of the final exocytosis steps in Paramecium tetraurelia cells: cytochemical determination of Ca2+-ATPase activity over preformed exocytosis sites
Authors: Plattner H. , Reichel K. , Matt H. , Beisson J. , Lefort-Tran M. , Pouphile M. 
Published: April 2021

ABSTRACT
In different Paramecium tetraurelia strains the occurrence of a Ca’+-ATPase (or p-nitro-phenylphosphatase) activity at the preformed attachment and exocytosis sites of the secretory vesicles (trichocysts) was analysed by electron-microscopic cytochemistry and X-ray micro analysis. In conjunction with freeze-fracture studies it was found that only those strains, which contain rosette particles, display this Ca,+-ATPase activity (7S, K 401, nd 9 (18 °C)), while other strains (nd 6, nd 9 (27 °C), tarn 38) are devoid of both these characteristics. The presence (absence) of rosette particles and of Ca,+-ATPase activity at the preformed exocytosis sites is correlated with the capability (incapability) of performing exocytosis in these strains. We discuss several possible interpretations of this structure-function correlation.
Cell migration through three-dimensional gels of native collagen fibres: collagenolytic activity is not required for the migration of two permanent cell lines
Authors: Schor Seth L. , Allen Terence D. , Harrison Christine J. 
Published: April 2021

ABSTRACT
Three-dimensional gels of native type I collagen fibres have been used as a substratum for the growth and migration of Chinese hamster ovary cells (fibroblastoid cell line) and RPMI–3460 melanoma cells (tumorigenic cell line from Syrian hamster). Quantitative data concerning the migration of these cells from the gel surface into the 3-dimensional collagen gel matrix have been obtained. The migration of both cell types into the collagen gel matrix is not accompanied by the degradation of collagen fibres. The possible implications of these observations for tumour cell invasion in vivo are discussed.
Human diploid fibroblast-like cells (CF-3) as a model system for the study of Golgi biogenesis
Authors: Dell’orco R. T. , Terracio L. , Douglas W. H. J. 
Published: April 2021

ABSTRACT
Human diploid fibroblast-like cells were maintained in an arrested, essentially non-mitotic state for extended periods of time in culture by lowering the serum concentration in the medium from 10 to 0·5 %. These arrested cells re-entered the proliferative state when subcultivated in medium containing 10 % serum. The morphological distribution and enzymic activities associated with the Golgi complex were examined during growth, arrest, and recovery. Cells grown in medium containing 10 % serum possessed a well-developed Golgi complex consisting of parallel arrays of membranes and associated vesicles. Galactosyl transferase activity was highest after 3 days growth (17·5 ±5·0 nmol galactose transferred/45 min/mg protein) and decfined to 9·8 ± 30 at day 7. When the serum concentration was reduced to 0·5 %, Golgi complexes were rarely observed by electron microscopy and galactosyl transferase activity was further reduced to 4·6 ± 1·2 and 3-2 ± 1·4 after 3- and 7-day arrests, respectively. Arrested cells subcultured into medium containing 10 % serum recovered from the arrested state and ultrastructurally resembled cells continuously cultured at the higher serum level. Numerous Golgi complexes reappeared and galactosyl transferase activity increased to 13·0 ± 3·34 days after subcultivation. These results indicate that the Golgi complex can be experimentally manipulated in human diploid fibroblast-like cells in a manner which may be useful for the study of the biogenesis of this organelle.
Three-dimensional reconstruction of organelles in Euglena gracilis Z.: II. Qualitative and quantitative changes of chloroplasts and mitochondrial reticulum in synchronous cultures during bleaching
Authors: Pellegrini Max 
Published: April 2021

ABSTRACT
By ultrathin serial sectioning, morphological and volumetric changes of the plastidome and chondriome have been observed in Euglena gracilis Z during bleaching in darkness with addition of sodium acetate to the culture medium. In order not to introduce any modification to the synchronization pattern during bleaching, green cells were previously grown photoauto-trophically on Cramer&Myers medium under continuous illumination and synchronized by temperature cycles. They were then cultivated (1) photoheterotrophically with sodium acetate added to the culture medium and (2) heterotrophically by keeping the culture in darkness. This regime allowed observation of the influence (1) of synchronization by temperature cycles and (2) of sodium acetate and darkness on the plastidome and chondriome of photoautotrophic cells synchronized by light-dark cycles as described previously. In photoautotrophic cells, the plastidome, consisting of about ten diskoidal chloroplasts, occupies 15 % of the cell volume. The chondriome, in the form of one single giant mitochondrion branched throughout the cell, represents 6 % of the cell volume.
The synchronization by temperature cycles in continuous illumination does not change the morphology and volume of these organelles. However, pyrenoids disappear. In photohetero-trophic culture with sodium acetate added, the plastidome fine structure does not vary but its volume decreases by 19–25 %. At that time, the plastidome thus occupies 12–13 % of the cell volume. Sodium acetate provokes, on the contrary, hypertrophy of the delicate threads of the mitochondrial reticulum which appears as a network with narrow meshes around other organelles. The chondriome thus comes to occupy 10–11 % of the cell volume. In heterotrophic cells, the combined effects of sodium acetate and darkness emphasize the regression of the plastidome volume and hypertrophy of the chondriome. The plastidome occupies 6–7 % of the cell volume while the chondriome appears as a fenestrated parietal shell occupying 15—16% of the cell volume. Maximal hypertrophy is obtained in 24 h. Total dedifferentiation of chloroplasts requires 6—9 successive generations in heterotrophic conditions.
These results are discussed in relation to numerous light-microscopic and ultrastructural observations. It has been demonstrated, as in photoautotrophic Euglena cells synchronized by light-dark cycles, that the plastidome of heterotrophic cells consists of about ten organelles, whereas the chondriome contains one single giant mitochondrion. Contrary to the opinion that the variations of the plastidome and chondriome are reciprocally related, it is proved here that dedifferentiation of chloroplasts and hypertrophy of the chondriome occur at different rates, and may be independent of one another.
A cell cycle study of the effects of Con A on synchronized mouse embryo fibroblasts: arrest at two specific stages of the cycle and dissociation between uptake of thymidine and DNA synthesis
Authors: Mallucci L. , Dunn M. , Wells V. , Delia D. 
Published: April 2021

ABSTRACT
We have examined the effects of 50 µg m1−1 of Con A added to synchronized mouse embryo fibroblasts at different times during the cell cycle. We found that Con A caused arrest of growth not solely by preventing G1-G0 cells from entering the S-phase but also by exerting a G1 block. We also found that Con A, which prevented commencement of S-phase, did not arrest cells already in S from reaching the G2 stage but inhibited the S-phase associated process of thymidine uptake. The inhibition was greater when the Con A receptors were extensively clustered.
DNA is replicated at the nuclear cage
Authors: Mccready S. J. , Godwin J. , Mason W. , Brazell I. A. , Cook P.R. 
Published: April 2021

ABSTRACT
Structures resembling nuclei are released when HeLa cells are lysed in a detergent and 2 M salt. These nucleoids, which lack any organized membrane structure, contain all the nuclear DNA packaged within a cage of RNA and protein. Their DNA is supercoiled so that the linear DNA must remain unbroken and looped during lysis. Following digestion with the restriction endonuclease, EcoRI, cages and associated DNA were filtered free of unattached DNA. Pulse-labelled (i.e. newly synthesized) DNA remains preferentially associated with the cages. This association has been confirmed by autoradiography. When nucleoids are prepared for electron microscopy by the Kleinschmidt procedure the DNA spills out to form a skirt around the flattened cage. Labelling, which is restricted to the region of the cage after short pulses, extends out into the skirt as the labelling time increases. A model, based on the premise that replication takes place at the nuclear cage, is presented in the Appendix. The results of the biochemical experiments and electron microscopy both indicate that the average size of the unit of replication is ∼ 20 μm. This is about one-quarter the size of the average structural unit -the loop. Therefore sequences in the loop must become attached to the nuclear cage prior to the initiation of DNA synthesis.
Genetic dissection of the final exocytosis steps in Paramecium tetraurelia cells: trigger analyses
Authors: Matt H. , Plattner H. , Reichel K. , Lefort-Tran M. , Beisson J. 
Published: April 2021

ABSTRACT
A variety of trigger procedures were applied to analyse the exocytotic capability of different Paramecium tetraurelia strains. 7,S K 401, kin 241, nd g (18 °C) arecapable of exocytosis (permissive strains), in contrast to nd 6, nd 7, nd g (27 °C), tarn 38 and ftb A, although all procedures used enhance [Ca3+] in the cytoplasm of all strains tested and although strains nd 6, nd 7 and nd g (27 °C) contain a full set of morphologically normal trichocysts attached to the cell membrane. The results show that only those strains are permissive which were shown previously to contain a rosette of membrane-integrated particles and a Ca2+-ATPase activity in the cell membrane over the trichocyst attachment (exocytosis) sites. The results from trigger experiments with permissive and non-permissive strains would be compatible with a dual function of rosette particles as Ca2+ pumps and Ca2+ channels. Nevertheless, the latter aspect remains uncertain since we show that experiments along these lines published by others (introducing a Ca,+ ionophore from the outside) involve a solvent-induced artifact (pseudoexocytosis: matrix stretching in the absence of membrane fusion). In all strains, except for tarn 38 and ftb A (which have abnormal trichocysts incapable of being attached to the cell membrane), the isolated trichocyst matrix can be transferred from the contracted to the expanded state in vitro with certain trigger procedures. Our data clearly show that an increase of [Ca3+]t in the cytoplasm is not sufficient for exocytosis to occur and that non-permissivity is somehow due to an inability to perform membrane fusion. It remains open whether the lack of rosettes and Ca2+-ATPase activity at trichocyst attachment sites are the primary cause of non-permissivity’.
Packing DNA into chromosomes
Authors: Mullinger A. M. , Johnson R. T. 
Published: April 2021

ABSTRACT
Electron microscopy of HeLa metaphase nucleoids (i.e. whole metaphase cells exposed to 2 M salt and non-ionic detergent) spread by the Kleinschmidt technique, reveals a variety of protein-depleted structures (spreads) derived from chromosomes. Spreads vary in size and shape. At one extreme are oval structures with one or more cores surrounded by a network of supercoiled fibres. These fibres are probably arranged as loops and we estimate that 600-1000 may emerge from a single, large core region. At the other extreme are chromosome-shaped spreads with an elongated core which takes the form of a multifibred axis. At intervals groups of lateral fibres appear to emerge from each axis to produce the network. Spreads intermediate between these 2 extremes occur in which axial fibres can be resolved in only part of the elongated core.
Similar structures are observed in chromosomes deproteinized and spread after isolation by a procedure which preserves high molecular weight DNA. The appearance of chromosomes isolated by the Wray-Stubblefield hexylene glycol procedure agrees in general with previous findings of others, except that in some more extended spreads axial fibres are visible.
We believe our observations are consistent with the idea that the chromonema of each metaphase chromatid contains regions of multistranded DNA. We do not propose, however, that the chromatid is functionally multineme, but rather that axial fibre folding either within or between chromomere regions contributes to packing of DNA in the metaphase chromosome. These regions of constraint are also postulated as the locations of emergence of lateral loops. In spread preparations the axial fibres are seen clearly only when chromatids have been elongated beyond the contracted metaphase length. Elongation would be produced both by relaxation of chromosomal coils (gyres) and by extension of the chromonema upon deproteinization and spreading. Whereas in deproteinized nucleoids the long axis is labile and liable to elongate, fragment or collapse, the chromonema of Wray-Stubblefield chromosomes is locked at the metaphase (gyred) length and axial fibres are generally not visible. We propose that the assembly of the complex DNA axis of the metaphase chromosome from its extended interphase counterpart plays a major part in increasing the DNA packing ratio in the mitotic cell.
Ultrastructure of multiple microtubule initiation sites in mouse neuroblastoma cells
Authors: Sharp Gaynor A. , Osborn Mary , Weber Klaus 
Published: April 2021

ABSTRACT
Morphologically undifferentiated and differentiated mouse neuroblastoma N115 and N18 cells were examined after serial sectioning by electron microscopy. A sizeable percentage of the cells revealed multiple centrioles, usually clustered together in the perinuclear area with 2 preferential locations, i.e. above and below the largest nuclear diameter. These results indicate that the multiple microtubule- organizing centres previously visualized by immunofluorescence microscopy with tubulin antibody in neuroblastoma cells recovering from Col-cemid poisoning are most likely in majority related to multiple centrioles. This interpretation is further strengthened by experiments in which cells are first recorded in the fluorescence microscope and then after serial sectioning in the electron microscope. The results show that under optimal conditions immunofluorescence microscopy is able to visualize single centrioles. The possible biological significance of the combined electron and immunofluorescence microscopical results is discussed.