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  • 1
    Electronic Resource
    Electronic Resource
    Role of calcium in the localization of maternal poly(A)+RNA and tubulin mRNA in Xenopus oocytes (1988)
    Springer
    Development genes and evolution 197 (1988), S. 175-183 
    Details
    ISSN: 1432-041X
    Keywords: Ca2+/Cl1− transmembrane flux ; Oocytes ; Meiotic maturation ; mRNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Poly(A)+RNA and tubulin mRNA are localized in the periphery of Xenopus oocytes and become delocalized during meiotic maturation. Delocalization of this RNA can be triggered by incubation in agents which reduce entry of calcium ions into the cell (e.g. lanthanum chloride and verapamil). Although these agents ordinarily promote meiotic maturation, addition of theophylline to the medium will inhibit maturation but not delocalization. Manipulations which prevent calcium entry without inducing meiotic maturation (e.g. calcium-free buffer) are also shown to trigger disruption of the RNA localization. In addition, manipulations which reduce chloride efflux from the cell (e.g. increasing the external chloride ion concentration with choline chloride) result in disruption of the localization of poly (A)+ RNA and tubulin mRNA without inducing meiotic maturation. The calcium-dependent chloride efflux present in Xenopus oocytes disappears after the oocyte has been stimulated to proceed through meiotic maturation. We show that reduction of the influx of calcium ions or efflux of chloride ions induces the delocalization of poly (A)+RNA and tubulin mRNA without inducing meiotic maturation. We suggest, therefore, that reducing the transmembrane movement of these ions is likely to be the natural trigger for the delocalization of poly(A)+RNA and tubulin mRNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00427921
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  • 2
    Electronic Resource
    Electronic Resource
    Freeze-fracture analysis of structural reorganization during meiotic maturation in oocytes of Xenopus laevis (1988)
    Springer
    Cell & tissue research 251 (1988), S. 129-136 
    Details
    ISSN: 1432-0878
    Keywords: Amphibian oocytes ; Meiotic maturation ; Annulate lamellae ; Cortical endoplasmic reticulum ; Freeze fracture ; Xenopus laevis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary During meiotic maturation, the cortex of oocytes of Xenopus laevis undergoes structural reorganization, visualized in this study by freeze-fracture electron microscopy. In the full-grown but immature oocyte, annulate lamellae are dispersed throughout the subcortex of the egg, 5 to 20 μm from the plasma membrane. The annulate lamellae consist of well-organized stacks of membrane with visible pores. Stimulation of meiotic maturation by progesterone leads to disruption of the annulate lamellae and formation of an elaborate cortical endoplasmic reticulum which surrounds the cortical granules and intertwines throughout the cortex of the mature egg. Pore-like structures similar to those previously observed in the subcortical annulate lamellae are observed in the mature cortical endoplasmic reticulum. The cortical endoplasmic reticulum is often in close apposition with the plasma membrane and with membranes of cortical granules, but no junctions are visualized. This study provides further evidence that the cortical endoplasmic reticulum develops during progesterone-stimulated meiotic maturation in vitro, and that the annulate lamellae are precursors to the cortical endoplasmic reticulum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00215457
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  • 3
    Electronic Resource
    Electronic Resource
    The sea urchin egg jelly coat is a three-dimensional fibrous network as seen by intermediate voltage electron microscopy and deep etching analysis (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 35 (1993), S. 181-188 
    Details
    ISSN: 1040-452X
    Keywords: Sea urchin ; Fertilization ; Extracellular Matrix ; Egg jelly ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The egg jelly (EJ) coat which surrounds the unfertilized sea urchin egg undergoes extensive swelling upon contact with sea water, forming a threedimensional network of interconnected fibers extending nearly 50 μm from the egg surface. Owing to its solubility, this coat has been difficult to visualize by light and electron microscopy. However, Lytechinus pictus EJ coats remain intact, if the fixation medium is maintained at pH 9. The addition of alcian blue during the final dehydration step of sample preparation stains the EJ for visualization of resin embedded eggs by both light and electron microscopy. Stereo pairs taken of thick sections prepared for intermediate voltage electron microscopy (IVEM) produce a threedimensional image of the EJ network, consisting of interconnected fibers decorated along their length by globular jelly components. Using scanning electron microscopy (SEM), we have shown that before swelling, EJ exists in a tightly bound network of jelly fibers, 50-60 nm in diameter. In contrast, swollen EJ consists of a greatly extended network whose fibrous components measure 10 to 30 nm in diameter. High resolution stereo images of hydrated jelly produced by the quick-freeze/deep-etch/rotary-shadowing technique (QF/DE/RS) show nearly identical EJ networks, suggesting that dehydration does not markedly alter the structure of this extracellular matrix. © 1993 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080350212
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