bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induced root differentiation in sycamore callus
Authors: Wright K. , Northcote D. H. 
Published: April 2021

ABSTRACT
A sycamore callus (S 4) has been isolated and grown on a medium containing salts, vitamins, a casein digest, 2 % sucrose and 1 mg/1. NAA. The callus, which would not grow in the absence of the added auxin, was much firmer in texture than a sycamore callus (S 2) isolated in this laboratory in 1958 which has not been induced to differentiate. When kinetin over the range 0·05–0·5 mg/1. was included in the growth medium of S 4 nodules of xylem and phloem were induced within the tissue and roots frequently grew from the surface of the callus. Some roots developed geotropic sensitivity although the majority grew radially outwards from the callus surface. The roots also varied with respect to the number of root hairs they carried. No roots were produced at sucrose concentrations less than 2%, although histological examination revealed extensive xylem and phloem differentiation relative to the amount of growth which had taken place. When sugars other than sucrose were supplied in the medium at a concentration of 3 % (w/v) roots were also induced in those calluses where the carbon source had supported good growth. Sucrose, glucose and fructose were identified in the ethanol-soluble extracts of all these calluses. Radioactivity was incorporated into sucrose when S 4 was incubated on a medium containing D-[U-14C]glucose for 24 h.
Any sugar which supported growth and differentiation was therefore one which was capable of entering the common metabolic pathway used by the plant for glucose and sucrose. The cells could undergo differentiation so long as the sugar they were supplied with supported active growth and division. The possibility of a physiological role for sucrose is discussed.
The basis of cell-to-cell transformation in Paramecium bursaria: I. transfer of cytoplasmic material
Authors: Cullis C. A. 
Published: April 2021

ABSTRACT
A mating type transformation, involving cell-to-cell contact (abortive conjugation) in syngen 4 of Parameciwn bursaria has been investigated. By autoradiography, transfer of material between the conjugants in normal and abortive conjugation has been shown to occur. The transfer of this material, which includes protein, RNA and DNA, during abortive conjugation has been shown to be necessary if the transformation is to occur.
The mating type substances produced by sexually competent cells of different mating types have been characterized with respect to their thermal stability. In all cases examined there appeared to be 3 mating type substances produced which had different temperature stabilities. No differences could be shown between the transformed cells and normal cells of the same mating type in relation to stability of mating type substance.
The Organization and Polarity of Pollen Mother Cells of Triticum Aestivum
Authors: Dover G. A. 
Published: April 2021

ABSTRACT
Colchicine has been applied to young developing anthers of Triticum aestivuni at varying stages of maturity from the last premeiotic mitoses of the archesporial and tapetai cells to the second meiotic divisions of the pollen mother cells. The developmental stage of the archesporium at which colchicine took effect was determined by cytological examination of the ploidy levels of the nuclei of the adjacent tapetai cells. The type of pollen abnormality induced depended on the time of application and the concentration of colchicine. Uninucleate monads with 4 randomly positioned pores and uninucleate monads without pores were obtained with 0·5 % colchicine. Multipored polyads and multipored uninucleate monads were observed together in anthers treated with 0·01 % colchicine. Naturally occurring aberrant pollen types in hybrids of Triticum aestivuni × Aegilops rnutica or T. aestivum x Aegilops sharonensis have revealed a constant relationship between the disposition of the meiotic spindles and the siting of the pollen pores. The colchicine-induced abnormalities have further clarified the nature of this relationship leading to the interpretation that both the positioning of the spindles and the siting of the pores are predetermined by events taking place in the premeiotic interphase at a time just after the last mitosis of the pollen mother cells and the penultimate mitosis of the tapetum. A reorganization of the archesporial cells (sensitive to colchicine) possibly occurs at this time. Various subsequent meiotic events are dependent on the reorganization. Two of these events - the organization of meiotic spindles and the establishment of pollen symmetry - are discussed.
Timing of Nucleolar Activity in Meristems
Authors: Torre C. De La , Clowes F. A. L. 
Published: April 2021

ABSTRACT
The nucleoli in 4 regions of the root meristem of Zea mays have been examined and the time spent in each of the phases of the nucleolar cycle has been calculated from estimates of the rates of mitosis and the fraction of cycling cells in each region. The nucleolar cycles have been fitted to the mitotic cycles of cycling cells in the same regions.
The timing of activity of the r-RNA genes differs in relation to the chromosomal cycles of condensation and movement in the different regions of the meristem. In the stelar regions disorganization of the nucleolus starts in the middle of prophase and reorganization starts towards the end of telophase and is completed in the following interphase. In the quiescent centre of the meristem the phases of both cycles are lengthened except for telophase and reorganization of the nucleolus does not start until after the end of telophase. The acceleration of telophase in the quiescent centre is discussed in relation to inhibition of protein synthesis. In the adjacent cap initials, which have the shortest mitotic cycle, the nucleolus starts to disorganize before the onset of prophase and reorganization is completed halfway through telophase. This fits with the fact that DNA synthesis is advanced into the telophase of the previous cycle in these cells.
Symmetric and Asymmetric Mitosis and Cytokinesis in the Root Tip of Hydrocharis Morsus-Ranae L.
Authors: Cutter Elizabeth G. , Hung Ching-Yuan 
Published: April 2021

ABSTRACT
In the roots of Hydrocharis morsus-ranae, certain cells of the protoderm divide asymmetrically to form a small, highly cytoplasmic trichoblast proximally, and a larger, more vacuolate epidermal cell distally. The former develops as a root hair without further division; the latter divides several times to form ordinary epidermal cells. During mitosis, presumed dictyosome vesicles and fragments or sections of reticulated or serrate sheets of ER, aligned with the spindle microtubules, were observed among the chromosomes as early as metaphase, suggesting that the portions of ER were involved in formation of the cell plate or in some other function in the equatorial region. A pre-prophase band of microtubules was not observed. Asymmetric divisions differ from symmetric ones in the skewed orientation of the metaphase plate, the formation of a curved, rather wavy cell wall and the slightly greater vacuolation of one daughter cell. Less difference in the ultrastructure of the daughter cells resulting from an asymmetric division was observed in this rather slowly growing material than in other examples previously described in the literature.
A Gradient of Positional Information in an Insect, Rhodnius
Authors: Lawrence P. A. , Crick F. H. C. , Munro M. 
Published: April 2021

ABSTRACT
Locke discovered a segmental gradient in Rhodnius which controls the polarity of the epidermal cell and gives positional information. The polarity is expressed by the orientation of folds in the adult epicuticle, which are aligned parallel to the contours in the gradient. It was later suggested that this gradient could be of a concentration of a diffusible substance. Because concentration gradients could be maintained in various ways we have simulated several models in the computer, and examined the results of rotating square pieces of model landscape through 90° and allowing diffusion. The gradient landscapes after different times and at equilibrium are plotted as contour maps and are compared with cuticle patterns from adult insects after rotation of square pieces of epidermis in larvae.
One simple model, where the gradient depends only on the activities of a line of source cells at one end of the segment and a line of sink cells at the other, is eliminated by 2 observations: (1) the theoretical and experimental patterns are consistently different; and (2) when adults developing from operated larvae are made to form a supernumerary cuticle the first and second cuticles have almost identical patterns. This suggests that the gradient landscape has reached a steady state.
In another model the cells are considered to act as homeostatic units in the gradient, and when moved to a new position they each attempt to maintain their original or ‘set’ concentration. Simulation of this model gives equilibrium patterns which are similar to the experimental results. It is suggested that the cells become ‘set’ at some stage in the cell cycle to the ambient concentration. This hypothesis predicts that after reaching initial equilibrium the pattern should change only if there are cell divisions. Adult insects are made to moult again under different conditions and it is found that pattern change is correlated with cell divisions.
Locke also observed an asymmetry in the patterns after rotation of squares through 180°. Simulation showed that such asymmetry would result from each cell acting as a better homeo-static unit when moved one way in the gradient (for example when acting as a sink) than when moved the other (acting as a source).
We do not claim that these comparisons eliminate all other classes of model, and present our conclusions in as general a form as possible.
Patterns of Particle Movement in Nerve Fibres In Vitro-An Analysis by Photokymography and Microscopy
Authors: Berlinrood M. , McGee-Russell S. M. , Allen R. D. 
Published: April 2021

ABSTRACT
Tissue-cultured nerve fibres derived from 3 species of amphibian embryos were composed of bundles of neurites, when viewed by electron microscopy, and contained particles moving in both directions by saltations. Photokymographic analysis of ciné microscopy records taken with Zeiss differential interference optics demonstrated instantaneous particle velocities ranging from 0·15 to 1·8 μm s-1 (13–155 mm/day) in Rana pipiens cultures; 0·16–0·8 μm s-1 (14–74 mm/day) in Ambystoma tigrinum cultures and 0·6—2·25 μm s-1 (45—194 mm/day) in Xenopus laevis cultures. Measured pathlengths for particles saltations ranged from 4 to 63 μm. No correlations between particle velocity and pathlength were found.
Calcium ions and tyrosine phosphorylation interact coordinately with actin to regulate cytoprotective responses to stretching
Authors: Glogauer M. , Arora P. , Yao G. , Sokholov I. , Ferrier J. , McCulloch C. A. G. 
Published: April 2021

ABSTRACT
The actindependent sensory and response elements of stromal cells that are involved in mechanical signal transduction are poorly understood. To study mechanotransduction we have described previously a collagenmagnetic bead model in which application of well-defined forces to integrins induces an immediate (&lt;1 second) calcium influx. In this report we used the model to determine the role of calcium ions and tyrosine-phosphorylation in the regulation of force-mediated actin assembly and the resulting change in membrane rigidity. Collagen-beads were bound to cells through the focal adhesion-associated proteins talin, vinculin, α2-integrin and β-actin, indicating that force application was mediated through cytoskeletal elements. When force (2 N/m2) was applied to collagen beads, confocal microscopy showed a marked vertical extension of the cell which was counteracted by an actin-mediated retraction. Immunoblotting showed that force application induced F-actin accumulation at the bead-membrane complex but vinculin, talin and α2-integrin remained unchanged. Atomic force microscopy showed that membrane rigidity increased 6-fold in the vicinity of beads which had been exposed to force. Force also induced tyrosine phosphorylation of several cytoplasmic proteins including paxillin. The force-induced actin accumulation was blocked in cells loaded with BAPTA/AM or in cells preincubated with genistein, an inhibitor of tyrosine phosphorylation. Repeated force application progressively inhibited the amplitude of force-induced calcium ion flux. As force-induced actin reorganization was dependent on calcium and tyrosine phosphorylation, and as progressive increases of filamentous actin in the submembrane cortex were correlated with increased membrane rigidity and dampened calcium influx, we suggest that cortical actin regulates stretch-activated cation permeable channel activity and provides a desensitization mechanism for cells exposed to repeated long-term mechanical stimuli. The actin response may be cytoprotective since it counteracts the initial force-mediated membrane extension and potentially strengthens cytoskeletal integrity at force-transfer points.
Subpellicular microtubules associate with an intramembranous particle lattice in the protozoan parasite Toxoplasma gondii
Authors: Morrissette Naomi S. , Murray John M. , Roos David S. 
Published: April 2021

ABSTRACT
Application of Fourier analysis techniques to images of isolated, frozen-hydrated subpellicular microtubules from the protozoan parasite Toxoplasma gondii demonstrates a distinctive 32 nm periodicity along the length of the microtubules. A 32 nm longitudinal repeat is also observed in the double rows of intramembranous particles seen in freezefracture images of the parasite’s pellicle; these rows are thought to overlie the subpellicular microtubules. Remarkably, the 32 nm intramembranous particle periodicity is carried over laterally to the single rows of particles that lie between the microtubule-associated double rows. This creates a two-dimensional particle lattice, with the second dimension at an angle of ∼75° to the longitudinal rows (depending on position along the length of the parasite). Drugs that disrupt known cytoskeletal components fail to destroy the integrity of the particle lattice. This intramembranous particle organization suggests the existence of multiple cytoskeletal filaments of unknown identity. Filaments associated with the particle lattice provide a possible mechanism for motility and shape change in Toxoplasma: distortion of the lattice may mediate the twirling motility seen upon host-cell lysis, and morphological changes observed during invasion.
SFV infection in CHO cells: cell-type specific restrictions to productive virus entry at the cell surface
Authors: Marsh Mark , Bron Romke 
Published: April 2021

ABSTRACT
Alphaviruses, such as Semliki Forest virus, normally enter cells by penetration from acidic organelles of the endocytic pathway. The virions are internalised intact from the cell surface before undergoing acidinduced fusion in endosomes. To investigate the possibility that endocytosis might play a role in delivering virions to specific sites for replication, we compared SFV infection of baby hamster kidney (BHK) cells and Chinese hamster ovary (CHO) cells following either normal virus fusion in endosomes or experimentallyinduced fusion at the cell surface. Whereas baby hamster kidney cells were infected efficiently following fusion in endosomes or at the plasma membrane, Chinese hamster ovary cells were only infected following fusion from endocytic organelles. Virions fused at the plasma membrane of CHO cells failed to initiate viral RNA and protein synthesis. Similar results were observed when CHO cells were challenged with a rhabdovirus, vesicular stomatitis virus.
These data suggest that in certain cell types a barrier, other than the plasma membrane, can prevent infection by alpha- and rhabdoviruses fused at the cell surface. Moreover, they suggest the endocytic pathway provides a mechanism for bringing viral particles to a site, or sites, in the cell where replication can proceed.
Plasma membrane targetting, vesicular budding and release of galectin 3 from the cytoplasm of mammalian cells during secretion
Authors: Mehul Bruno , Hughes R. Colin 
Published: April 2021

ABSTRACT
Galectin 3, a 30 kDa galactoside-binding protein distributed widely in epithelial and immune cells, contains no signal sequence and is externalized by a mechanism independent of the endoplasmic reticulum (ER)-Golgi complex. We show here that hamster galectin 3 overexpressed in transfected cos-7 cells is secreted at a very low rate. A chimaera of galectin 3 fused to the N-terminal acylation sequence of protein tyrosine kinase p56lck, Nt-p56lck-galectin 3, which is myristoylated and palmitoylated and rapidly transported to plasma membrane domains, is efficiently released from transfected cells indicating that movement of cytoplasmic galectin 3 to plasma membrane domains is a rate limiting step in lectin secretion. N-terminal acylation is not sufficient for protein secretion since p56lck and the chimaera Nt-p56lck-CAT are not secreted from transfected cells. The amino-terminal half of galectin 3 is sufficient to direct export of a chimaeric CAT protein indicating that part of the signal for plasma membrane translocation lies in the N-terminal domains of the lectin. Immunofluorescence studies show that Nt-p56lck-galectin 3 aggregates underneath the plasma membrane and is released by membrane blebbing. Vesicles of low buoyant density isolated from conditioned medium are enriched in galectin 3. The lectin is initially protected from exogenous collagenase but is later released in soluble protease-sensitive form from the lectin-loaded vesicles. Using murine macrophages, which secrete their endogenous galectin 3 at a moderate rate especially in the presence of Ca2+-ionophores, we were also able to trap a galectin 3-loaded vesicular fraction which was released into the culture supernatant.
Localization of five annexins in J774 macrophages and on isolated phagosomes
Authors: Diakonova Maria , Gerke Volker , Ernst Joel , Liautard Jean-Pierre , van der Vusse Ger , Griffiths Gareth 
Published: April 2021

ABSTRACT
Annexins are a family of structurally related proteins which bind phospholipids in a calcium-dependent manner. Although the precise functions of annexins are unknown, there is an accumulating set of data arguing for a role for some of them in vesicular transport and, specifically, in membrane-membrane or membrane-cytoskeletal interactions during these processes. Here we describe our qualitative and quantitative analysis of the localization of annexins I-V in J774 macrophages that had internalized latex beads, both with and without IgG opsonization. Our results show that whereas all these annexins are present on both the plasma membrane and on phagosomes, the localization on other organelles differs. Annexins I, II, III and V were detected on early endosomes, while only annexin V was seen on late endocytic organelles and mitochondria. Annexins I and II distributed along the plasma membrane non-uniformly and co-localized with F-actin at the sites of membrane protrusions. We also investigated by western blot analysis the association of annexins with purified phagosomes isolated at different time-points after latex bead internalization. While the amounts of annexins I, II, III and V associated with phagosomes were similar at all times after their formation, the level of annexin IV was significantly higher on older phagosomes. Whereas annexins I, II, IV and V could be removed from phagosome membranes with a Ca2+ chelator they remained membrane bound under low calcium conditions. In contrast, annexin III was removed under these conditions and needed a relatively high Ca2+ concentration to remain phagosome bound. Because of their purity and ease of preparation we suggest that phagosomes are a powerful system to study the potential role of annexins in membrane traffic.
Fibroblast growth factor receptor signalling has a role in lobuloalveolar development of the mammary gland
Authors: Jackson David , Bresnick Janine , Rosewell Ian , Crafton Tracy , Poulsom Richard , Stamp Gordon , Dickson Clive 
Published: April 2021

ABSTRACT
We have used the mouse mammary tumor virus promoter to express two dominant negative (DN) fibroblast growth factor receptor (FGFR) isoforms in the mammary epithelium of transgenic mice. While expression of DN-FGFR1(IIIc) showed no discernible phenotype, a similar kinase negative form of FGFR2(IIIb) caused a marked impairment of lobuloalveolar development. The growth retardation was apparent by mid-pregnancy and persisted in the post-partum glands. Despite the substantial underdevelopment of the mammary gland there was a measurable lactational response, but it was insufficient to properly sustain the new-born pups. These findings demonstrate that fibroblast growth factor signalling is necessary for pregnancy dependent lobuloalveolar development of the mammary gland.
Differentiation of embryonic stem cells into adipocytes in vitro
Authors: Dani C. , Smith A. G. , Dessolin S. , Leroy P. , Staccini L. , Villageois P. , Darimont C. , Ailhaud G. 
Published: April 2021

ABSTRACT
Embryonic stem cells, derived from the inner cell mass of murine blastocysts, can be maintained in a totipotent state in vitro. In appropriate conditions embryonic stem cells have been shown to differentiate in vitro into various derivatives of all three primary germ layers. We describe in this paper conditions to induce differentiation of embryonic stem cells reliably and at high efficiency into adipocytes. A prerequisite is to treat early developing embryonic stem cell-derived embryoid bodies with retinoic acid for a precise period of time. Retinoic acid could not be substituted by adipogenic hormones nor by potent activators of peroxisome proliferator-activated receptors. Treatment with retinoic acid resulted in the subsequent appearance of large clusters of mature adipocytes in embryoid body outgrowths. Lipogenic and lipolytic activities as well as high level expression of adipocyte specific genes could be detected in these cultures. Analysis of expression of potential adipogenic genes, such as peroxisome proliferator-activated receptors γ and δ and CCAAT/enhancer binding protein β, during differentiation of retinoic acidtreated embryoid bodies has been performed. The temporal pattern of expression of genes encoding these nuclear factors resembled that found during mouse embryogenesis. The differentiation of embryonic stem cells into adipocytes will provide an invaluable model for the characterisation of the role of genes expressed during the adipocyte development programme and for the identification of new adipogenic regulatory genes.