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  • Activation  (2)
  • Centrosome  (2)
  • 1
    ISSN: 1040-452X
    Keywords: Sperm ; Aster ; Bovine ; Centrosome ; Polyspermy ; Adrogenote ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Chromatin and microtubule configurations during the first cell cycle of bovine zygotes were analyzed by DNA staining and microtubule immunolocalization using an IVM/IVF system and oocytes matured and fertilized in vivo, in order to investigate the origin of the active centrosome and to characterize the nuclear and the cytoplasmic changes following bovine fertilization. Our results suggest that the paternal centrosome is active during early zygotic development, forming a conspicuous sperm aster soon after fertilization. We also report that polyspermy in bovine eggs, leads to the formation of numerous sperm asters with different degrees of association with the chromatin. The maternal structures in both monospermic and polyspermic zygotes can be lost or degenerate. Consequently, these cells may resume the first cell cycle as androgenotes, very often with several types of mitotic activity taking place in different regions of the cell cytoplasm at the same time. As indicated by a comparison of monospermic and polyspermic fertilization rates to rates of development, it is possible that some androgenetic embryos cleave and develop to the blastocyst stage. © 1993 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 25 (1990), S. 272-280 
    ISSN: 1040-452X
    Keywords: Activation ; Rabbit ; Sperm ; Oocyte ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In this study a fraction was prepared from rabbit sperm that activated rabbit and mouse oocytes following injection into the cytoplasm. The sperm factor activated oocytes exhibited cortical granule exocytosis, pronuclear formation, and cleavage. The sperm factor was soluble in aqueous solution and was not active extracellularly. Unlike most artificial activation methods that are only effective with aged oocytes, the sperm factor activated recently ovulated oocytes. The factor appears to be a protein or associated with a protein but not an acrosomal protein. Fractions from both mouse and bull sperm did not activate rabbit or mouse oocytes. Their inactivity may be owing to the techniques used to recover the fractions or differences between species in sperm morphology and fertilization processes. These observations support the hypothesis that oocyte activation is induced by a factor within sperm that is released into the cytoplasm of the oocyte at the time of sperm-oocyte fusion.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    ISSN: 1040-452X
    Keywords: Activation ; Calcium ; Fura-2 ; Electrical pulse ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Electrical stimulation is known to cause activation in mammalian oocytes, possibly by eliciting an elevation in intracellular calcium (Ca2+). This study reports intracellular Ca2+ concentrations in mature rabbit oocytes using the Ca2+ indicator fura-2. Calcium levels were determined prior to, during, and after the administration of an electrical pulse (3.6 kV/cm for 60 μsec). Baseline Ca2+ levels ranged from 30 to 90 nM. The intracellular Ca2+ transient evoked by a pulse, peaked at 11 sec, was highly variable in amplitude (40-300 nM) and returned to prepulse levels within 300 sec. Electrically stimulated oocytes did not exhibit repetitive Ca2+ transients. The size of the cytoplasmic Ca2+ rise was influenced by the duration of the pulse, the field strength and the concentrations of external Ca2+ (P 〈 0.05). Oocytes electrically stimulated in the presence of 100 μM CaCl2, which evoked Ca2+ transients with a mean magnitude of 120 nM, activated at a higher rate (P 〈 0.05) than oocytes stimulated in the presence of either higher or lower levels of external Ca2+. Although oocytes electrically shocked at 16-18 hr after administration of human chorionic gonadotropin (hphCG) activated at a lower rate than oocytes stimulated at 22-24 hphCG (P 〈 0.05), their intracellular Ca2+ response to the pulse was similar (P 〈 0.05). These results indicate that electrical pulse parameters and extracellular Ca2+ concentrations can be used to modulate intracellular Ca2+ levels and optimize oocyte activation rates. Furthermore, the data suggest that as the oocyte ages it becomes more responsive to a given intracellular Ca2+ elevation. © 1992 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
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  • 4
    ISSN: 1040-452X
    Keywords: Spindle ; Oocyte ; Mammalian ; Centrosome ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Artificial activation and nuclear transfer in rabbit oocytes have been used in past years in an attempt to develop viable techniques for cloning in cattle. The procedures established in our laboratory, using the rabbit as a model, consistently lead to high rates of development to the blastocyst stage. However, the rate of embryos developing to term is considerably lower. In the present study, we undertook a detailed immunocytochemical study of the patterns of both microtubules and chromatin during the first cell cycle of electrical pulse-activated oocytes and of nuclear transfer embryos. Our goal was to investigate the responses of the cell to the different stimuli applied and to establish the sequence of events leading to first cleavage in the absence of normal fertilization. Our results show that, in both electrically activated oocytes and nuclear transfer embryos, although the initial development patterns are rather unusual, embryos become synchronized at the time of the formation of a pronuclear-like structure, and then organize metaphase spindles and cleave. These spindles consistently present small defects, suggesting that problems in the formation of the mitotic apparatus during the first cell cycle may have a long-term effect leading to embryo mortality. © 1993 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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