bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three-dimensional analysis of morphogenesis induced by mating pheromone α factor in saccharomyces cerevisiae
Authors: Baba Misuzu , Baba Norio , Ohsumi Yoshinori , Kanaya Koichi , Osumi Masako 
Published: April 2021

ABSTRACT
Ultrastructural analyses of cytoplasmic changes in Saccharomyces cerevisiae X2180-1A (MATa) that had been treated with α factor were performed by using the freeze-substitution fixation method. After α factor treatment, cells exhibited a pointed projection, which is a unique pattern of oriented cell surface growth. The relationship between projection formation and intracellular organelles was examined using serial thin sections and computer-aided three-dimensional reconstructions. Using these analyses membrane vesicles and other organ-elles were detected, and studies on their dynamic structural reorganization became feasible. Production of membrane vesicles (average 65 nm in diameter) was induced upon exposure of the cells to afactor before projection emergence. The total number of membrane vesicles increased at the early stage and decreased at the late stage of projection formation. Three-dimensional analysis indicated that the vesicles were at first dispersed throughout the cell, then accumulated at the site where the projection formed. Morphological changes and multiplication of the Golgi body were seen during the process of projection formation. Other intracellular organelles (nucleus, vacuole, rough endoplasmic reticulum and mitochondria) were also rearranged, showing a polar organization of the cytoplasm during projection formation.
Mechanically cut mitotic spindles: clean cuts and stable microtubules
Authors: Nicklas R. Bruce , Lee Greta M. , Rieder Conly L. , Rupp Gerald 
Published: April 2021

ABSTRACT
We have discovered an easy way to cut through the mitotic spindle at any desired place. Spindles of demembranated cricket or grasshopper spermatocytes were severed with a microneedle between the chromosomes and one pole, and the cut-off polar piece was swept away. Spindle structure and microtubule dynamics in cut spindles were studied by anti-tubulin immunostaining and electron microscopy. The cut is clean: all microtubules are severed and only a few extend beyond the others. This provides the basis for a clear test of whether traction fibers pull chromosomes to the pole in anaphase, because the putative traction fiber is cleanly severed. Cutting creates new plus ends on microtubules in the cut-off polar piece and new minus ends on microtubules in the main spindle body. The microtubules with new plus ends are unstable, as expected from the dynamic instability of microtubules. However, the microtubules with new minus ends are as stable as uncut microtubules in the same spindle. Our mechanical method of cutting microtubules very likely creates native, reactive ends, and therefore the surprising stability of new minus ends is genuinely interesting, not an artifact of cutting.
Replication occurs at discrete foci spaced throughout nuclei replicating in vitro
Authors: Mills A. D. , Blow J. J. , White J. G. , Amos W. B. , Wilcock D. , Laskey R. A. 
Published: April 2021

ABSTRACT
Demembranated Xenopus sperm nuclei were induced to replicate synchronously in a low-speed supernatant (LSS) of Xenopus eggs by preincubation in a high-speed supernatant (HSS). DNA replication was observed by incorporation of [α-32P]dATP, BrdUTP or biotin-dUTP.
Biotin-dUTP incorporation, visualised with fluorescent streptavidin, reveals a striking pattern of replication foci throughout replicating nuclei. We show that this represents a precursor to the bright uniform fluorescence seen later. Confocal micro-scopic analysis of nuclei fixed early in replication reveals that these foci of DNA replication number about 100–300 for each nucleus and probably represent the replicon clusters already described for tissue culture cells. Foci are evenly distributed throughout the nuclei and are not concentrated at or near the nuclear envelope.
Complete replication of each nucleus occurs in an average time of only one hour in this system. Hence we calculate that there must be at least 300–1000 replication forks together in each cluster. Further-more, pulse labelling at later times in the period of replication reveals a similar pattern of foci indicating that replication forks remain tightly clustered in groups of at least 300 throughout the period of DNA replication.
Origin of type i collagen localized within oviduct epithelium of quail hyperstimulated by progesterone
Authors: Perche O. , Hayashi M. , Hayashi K. , Birk D. , Trelstad R. L. , Sandoz D. 
Published: April 2021

ABSTRACT
Bird oviduct development is controled by sex steroid hormones. Estrogens (E) induce cell proliferation, formation of tubular glands by epithelial cell évagination and cell differentiation. Progesterone (P) strongly increases secretory processes in Etreated quails, but inhibits cell proliferation and cell évagination. The balance between E and P is very critical for the development and morphogenesis of the oviduct. After six daily injections of low doses of E (10 μg day−1) and high doses of P (5 μg day−1) into ovariectomized quails, cell proliferation and secretory process are stimulated but cell évagination is totaly inhibited and distribution of striated collagen is perturbed. Using antibodies against type I collagen the stroma, which is mainly composed of fibroblasts, is brightly stained, as are some regions within the epithelium. Electron microscopy shows that bundles of striated collagen fibrils appear in extracellular spaces between the lateral membranes of the epithelial cells or between the basal lamina and the epithelial basal membrane.
After in situ hybridization using a 35S riboprobe specific for mRNA of the α 2 chain of type I collagen, mRNA was detected only in the fibroblasts of the stroma and not in epithelial cells. Furthermore electron microscope studies of collagen bundles in serial sections clearly show collagen fibrils passing through the basal lamina. It is assumed that the type I collagen between epithelial cells originates from mesenchymal cells.
In the oviduct of immature birds or after physiological E+P stimulation, striated collagen is localized only in the stroma and never within the epithelium. These results indicate a modulation of extracellular matrix by sex steroid hormones in the quail oviduct.
Evidence that cryptomonad chloroplasts evolved from photosynthetic eukaryotic endosymbionts
Authors: Mcfadden Geoffrey Ian 
Published: April 2021

ABSTRACT
Unicellular algae of the division Cryptophyta possess an unusual subcellular compartment of unknown derivation. This compartment, which is partitioned off from the main cytoplasm by two membranes, contains a chloroplast and a small nucleus-like organelle surrounded by ribosomelike particles. Electron-microscopic in situ hybridization has been used to show that the ribosomes in this subcellular compartment are eukaryotic. In addition, eukaryotic rRNA has been localised within the nucleus-like organelle, suggesting that the rRNAs may be transcribed from genes in this nucleus. This identification of a second, nucleuscontaining eukaryotic compartment within these cells supports the hypothesis that cryptomonads contain a reduced photosynthetic eukaryotic endosymbiont.
Cellulose synthesizing complexes in some giant marine algae
Authors: Itoh Takao 
Published: April 2021

ABSTRACT
The structure of putative cellulose synthesizing complexes (TCs) has been studied in giant marine algae and is discussed in relation to the assembly of cellulose microfibrils. Including previous work, 14 species belonging to nine genera in the Siphonocladales and two species in the Cladophorales are known to have linear TCs on both E- and P-fracture faces of the plasma membrane. Species studied in the present paper included Boodlea composita, Dictyosphaeria cavernosa, Ernodesmis verticillata, Siphonocladus tropicus, Struvea elegans, Valoniopsis pachynema and Chaetomorpha aerea. Contrary to their fairly consistent width (30–36 nm), TCs have a wide distribution of length among indIvidual species and at various stages of development in the same species. Most of the TCs have a random arrangement of subunits, but sometimes they are arranged in three rows. The mean TC length is greater during secondary wall synthesis than in primary wall synthesis in all of the following species: Boodlea composita, Dictyosphaeria cavernosa, Siphonocladus tropicus, Valonia macrophysa, Valonia ventricosa and Chaetomorpha aerea. These results support previous results suggesting that the linear TCs increase their length during cell wall development. The size of TC subunits, ranging from 7.3 to 8.9 nm, was smaller than the structural membrane particles on the plasma membrane in all of the species examined. It is suggested that the spacing between individual glucan chains will be reduced to half after crystallization of cellulose microfibrils, on the basis of evidence that the width of microfibrils is as wide as that of TC. The width of microfibrils ranged from 11.2 to 23.6 nm, while most of the species had microfibrils with a width in the range 14 to 16 nm. The width of microfibrils in Boergesenia was the largest among the giant marine algae. The formation of TCs from subunits, which are transmembrane particles, is characteristic of Siphonocladales in spite of their varying cell morphology.
Cells of the cellular immune and hemopoietic system of the mouse lack lamins A/C: distinction Versus other somatic cells
Authors: Rober Ruth-Ariane , Sauter Auhelmut , Weber Klaus , Osborn Mary 
Published: April 2021

ABSTRACT
Almost all somatic cells in adult murine tissues express all three nuclear lamins (A, B, C). Here we demonstrate that cells of the hemopoietic system of the adult mouse are an exception in that they express only lamin B. Thus T and B lymphocytes as well as granulocytes and monocytic cells directly isolated from spleen, thymus, blood or bone marrow do not express lamin A/C but only lamin B. In agreement with this observation the murine hemopoietic cell lines EL4, BW5147, HK22, 70Z/3, SP2/0 and PAI express only lamin B. In immunoblotting experiments used to confirm the immunofluorescence data no lamin A/C expression was detected.
However, we noticed that murine lamin B occurs in two isoforms, which can be distinguished immunologically. These results reinforce the idea that a functional nuclear lamina can be formed from lamin B alone. They also pose the question of whether cells lacking lamin A/C are more plastic in their developmental programs than those that express all three lamins.
Molecular traffic through plasma membrane disruptions of cells in vivo
Authors: McNeil Paul L. , Ito Susumu 
Published: April 2021

ABSTRACT
We have recently shown that mechanical forces, experimentally imposed or physiologically generated, transiently disrupt or wound the plasma membranes of epithelial cells of the gut and that cultured endothelial cells similarly wounded mechanically at their plasma membranes release a potent basic fibroblast growth factor-like molecule. Here we show that mechanical forces generated by experimental manipulation (tape stripping and needle puncture), or by animal locomotion, transiently wound the plasma membranes of various cells of skin, allowing otherwise impermeant tracer molecules to enter and become trapped within cell cytoplasm. We estimate that the epidermis of digits from actively locomoting animals is composed of 10.5% (±4.9% S.D.) wounded cells, and that from quiescent animals has 3.7% (±2.5%) wounded cells. Wounded fibroblast, glandular and endothelial cells were also identified in mechanically stressed skin. Cells retaining fluorescein dextran, used as a label for wounding, were observed 24 h after the imposition of mechanical force, and wounded cells were generally of normal ultrastructure, indicating that cells in skin can survive membrane wounding. We propose that plasma membrane disruptions are an overlooked but probably common occurrence in cells residing in tissues such as gut and skin that are normally exposed to mechanical stress in vivo, and that such disruptions provide the physical basis in vivo for a previously unrecognized and diffusion-mediated route for molecular traffic directly across the plasma membrane into and out of living cell cytoplasm.
Effects of agents that modulate intracellular signal transduction, macromolecule synthesis and cytoskeleton assembly
Authors: Rosen Eliot M. , Meromsky Leonid , Goldberg Itzhak , Bhargava Madhu , Setter Eva 
Published: April 2021

ABSTRACT
Scatter factor (SF) is a cytokine that causes cohesive epithelial colonies to ‘scatter’ into isolated cells and stimulates epithelial cell migration. To investigate SF’s mechanism(s), we screened agents that modulate various intracellular processes for effects on scattering of Madin-Darby canine kidney (MDCK) cells. Selected agents were studied in quantitative migration assays using microcarrier beads. Agents that activate the adenylate cyclase (AC) pathway caused mild to moderate inhibition of scattering and migration, while modulators of Ca2+/calmodulin pathways had little effect on scattering. In contrast, phorbol esters (PMA, PDD) and protein kinase C (PKC) inhibitors (staurosporine, H-7, 7,8-dihydroxy-chlorpromazine) markedly enhanced and accelerated scattering; PMA and staurosporine also stimulated migration. Diacylglycerol analogues (e.g. diC8), naphthalenesulfonamide PKC activators (SC-9, SC-10) and inactive phorbol esters (e.g. 4a-PDD) did not potentiate scattering, while PKC depletion by 48 h pre-incubation with PMA markedly stimulated scattering. Thus, PMA-enhanced scattering may be related to down-modulation of PKC. Scattering was blocked by inhibitors of protein and RNA but not DNA synthesis; SF- and agent-stimulated migration were ablated by cycloheximide. Scattering and migration were inhibited by an anti-microfilament (cytochalasin B) but not anti-microtubule (e.g. colce-mid) agents. These findings suggest that SF-induced epithelial mobility may be mediated, in part, by protein synthesis, alterations in protein phosphorylation (?inhibition of PKC), and actin filament reorganization. They indicate directions for further studies.
Chemotaxis to cyclic AMP and folic acid is mediated by different G proteins in Dictyostelium discoideum
Authors: Kesbeke Fanja , Van Haastert Peter J. M. , De Wit René J. W. , Snaar-Jagalska B. Ewa 
Published: April 2021

ABSTRACT
Mutant Frigid A (fgdA) of Dictyostelium discoideum is defective in a functional Ga2 subunit of a G protein and is characterized by a complete blockade of the cyclic AMP-mediated sensory transduction steps, including cyclic AMP relay, chemotaxis and the cyclic GMP response. Folic acid-mediated transmembrane signal transduction was investigated in this mutant; the results show that: (1) cell surface folic acid receptors are present in fgdA mutants. (2) Folic acid induces intracellular responses, including activation of guanylate cyclase and chemotaxis. (3) The inhibitory effect of GTP on folic acid binding to membranes is present. (4) GTPγS binding and high-affinity GTPase are stimulated by folic acid. These data strongly suggest that folic acid receptors are coupled to guanylate cyclase and chemotaxis via a Ga protein that is different from Ga2. The results imply that surface receptors for cyclic AMP and folic acid are coupled to different G proteins.
Taxol influences control of protofilament number at microtubule-nucleating sites in Drosophila
Authors: Mogensen Mette M. , Tucker John B. 
Published: April 2021

ABSTRACT
Control of protofilament number has been investigated using Drosophila wings at a stage when 15-protofilament microtubules assemble under normal conditions. Microtubule nucleation still progressed at the usual microtubule-nucleating sites in the presence of taxol. However, provided taxol was introduced before microtubule nucleation began, few microtubules with 15 protofilaments assembled. Most microtubules were composed of 12 protofilaments (a previously undetected value for Drosophila) or 13 protofilaments (which is the value for micro tubules in most eukaryotic cells). Unexpectedly, a comparatively mild challenge to control of nucleation (in vitro wing culture) also promoted assembly of 13-protofilament microtubules. Hence, the microtubule-nucleating sites may possess a relatively labile control specifying 15 protofilaments superimposed upon that for maintaining 13-proto-filament fidelity.
An endogenous carbohydrate-binding protein of baby hamster kidney (BHK21 C13) cells : Temporal changes in cellular expression in the developing kidney
Authors: Foddy Louise , Stamatoglou Stamatis C. , Hughes R. Colin 
Published: April 2021

ABSTRACT
Asialofetuin (ASF) coupled to Sepharose has been used to isolate a Af r30000 protein from Triton X-100 extracts of the baby hamster kidney cell line BHK21 C13. Binding to ASF-Sepharose was specific for terminal β-galactosyl residues. The lectin requires detergent for optimal solubilization and binding is independent of Ca 2+ or reducing reagents. The lectin was labelled in a lactoperoxidase-catalysed iodination of intact BHK21 C13 cells, suggesting that it is associated with the cell surface. Antibodies to the lectin identify in Western blotting cross-reactive components in established cell lines of kidney (MDCK, NRK) and non-kidney (L, CHO, 3T3) origin. In young adult hamsters, the lectin is expressed in colon and duodenum and in lesser amounts in ileum, stomach, lung, liver and testes but is absent in kidney. The lectin is expressed in late embryonic and newborn hamster kidney but expression declines during 14 days after birth. Immunofluorescent staining of cryostat sections of newborn hamster kidney and intestine show that the lectin is expressed at apical epithelial surfaces. The presence of the lectin at the luminal surface of kidney tubules suggests a tubular origin for the BHK21 C13 cell line. Possible functions of the Mr30000 lectin in kidney development are discussed.
Desmoplakin II expression is not restricted to stratified epithelia
Authors: Angst Bright D. , Nilles Laura A. , Green Kathleen J. 
Published: April 2021

ABSTRACT
Desmosomes are major intercellular junctions found in association with intermediate filaments in epithelial, cardiac and arachnoidal tissue. Desmoplakins I and II (DPI and II) are highly related proteins localized in the innermost part of the desmosomal plaque and are candidates for linking intermediate filaments (IF) to the desmosomal complex. While investigators agree that DPI is present in all epithelia, they disagree on the distribution of DPII. Some have reported DPII to be restricted to stratified tissue and have furthermore suggested that the expression of DPII may be linked to stratification.
We have compared the expression of DPI and II at the mRNA and protein levels in cell lines derived from simple, transitional and stratified epithelia. Northern blot analysis revealed DPI and II mRNA to be present in all cell lines as well as simple and stratified epithelial tissues. However, DPII mRNA could not be detected in cardiac muscle tissue. Immunoblotting and immunoprecipitation demonstrated the presence of DPI and II in all cell lines at the whole-cell protein level as well as in association with cytoskeletal fractions. Immunofluorescence staining was used to correlate the biochemical findings with the localization of DPI and II. While most cell lines exhibited typical intercellular and in many cases cytoplasmic DP staining, T24 cells exhibited predominantly diffuse and dotty cytoplasmic staining. In addition, we investigated whether changes in DPI and II expression occurred following calcium-induced cell contact formation and stratification in the human pharyngeal cell line, FaDu. No significant changes in mRNA or whole-cell protein levels were observed during a period of 5 days following the calcium switch. However, immunoblotting revealed a significant increase in DPI and II levels in the insoluble protein pool during desmosome formation. These observations indicated a possible recruitment of soluble DPI/H into an insoluble pool after induction of desmosome assembly by the calcium switch, consistent with earlier reports for MDCK cells.
In summary, our results suggest that the expression of DPII is not strictly linked to stratification or differentiation; however, the apparent absence of DPII mRNA from cardiac muscle suggests it may not be a constituent of all desmosomes.
The influenza resistance murine Mx1 gene is constitutively expressed in the epithelia of the gastrointestinal, respiratory and uterine tracts
Authors: Chang Kin-Chow , Gerlach Gerald , Fernandes Kenneth , Lida Joshua , Goldspink Geoffrey 
Published: April 2021

ABSTRACT
The murine Mxl gene confers specific resistance against influenza in the inbred A2G mice and in vitro have been shown to be inducible with type I but not type II interferons. Contrary to expectation, we found by in situ hybridisation widespread Mxl expression along the epithelia of the gastrointestinal, uterine and respiratory tracts in uninduced A2G mice. Several lines of evidence, including further enhancement of Mxl expression during organ culture and gnotobiotic mice analyses, indicated that this apparent constitutive epithelial Mxl expression was a locally induced response to stimuli present in the respective lumina. This phenomenon may be a feature found in other interferon-inducible and interferon genes.
The importance of mitotic control for establishment of developmental competence in Acanthamoeba castellanii
Authors: Jantzen Helga , Schulze Ingrid , Stöhr Michael 
Published: April 2021

ABSTRACT
Acanthamoeba castellanii cells become growth arrested at different positions of the G2 phase of the cell cycle. Cells arresting at the competence position of G2 either develop into cysts in response to starvation or enter the mitotic division cycle in response to fresh nutrient medium. In cells arresting elsewhere in G2 growth can be initiated. The cell cycle position at which cells become growth arrested is dependent on the mode of cell cycle progression which, in turn, is strongly dependent on physical parameters of the cultivation conditions. Cells arresting at the competence position progress through cell cycles in which developmental competence and the so-called ‘growth-associated’ or ‘M phase-specific’ histone Hl kinase activity oscillate in levels. Hl kinase activity increases rapidly at the onset of mitosis and decreases to its basal level immediately after the completion of mitosis. In this case, peak levels of developmental competence slightly precede peak levels of Hl kinase activity. In contrast, cells arresting elsewhere in G2 are advanced through their cell cycle, i.e. undergo mitosis at reduced G2 phase length and smaller cell size compared with normal. The premature mitosis correlates in time with a rapid increase of Hl kinase activity. However, the extent of its activation is increased and its inactivation is slower so that Hl kinase activity does not decrease to its basal level during the shortened G2 phase. Ln this case a cell cycle period in which establishment of developmental competence takes place is lacking. In response to cycloheximide or vanadate, which delay the onset of premature mitosis, the competence period can be restored. Hl kinase activity is likely to represent p34cdc2 protein kinase activity, which has been shown in a wide variety of eukaryotic cell types to play a key role in regulating mitosis. Therefore, the results indicate that the mechanisms regulating development are coupled to controls acting over mitosis. In vitro translation patterns suggest that the length of G2 and/or a low basal level of Hl kinase activity is (are) important for regulating the cellular content of competence- and development-specific RNA species.