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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Age 12 (1989), S. 83-88 
    ISSN: 1574-4647
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Recently eight-to 16-cell stage embryos from rabbits, sheep, and cattle have been cloned using nuclear transplantation technology. Early developmental studies indicate that when a nucleus from an early embryonic cell is transferred to the cytoplasm of a freshly ovulated unfertilized oocyte, the nucleus undergoes reprogramming events and these nuclear transplant embryos are similar to newly fertilized oocytes in growth and development. Nuclear reprogramming by factors within the oocyte offers the opportunity to study dedifferentiation and cellular aging events in nuclear transplant embryos. Also, nuclear transplantation technology may enable commercial animal breeders to produce a large number of genetically valuable livestock and reduce animal usage in biomedical research. The effects of serial transfers and cell cycle length and stage on the success of cloning animals using advance cell stage donor nuclei are discussed. The use of nuclear transplantation in mammals may lead to new inroads into understanding and retarding the aging process in the future.
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  • 2
    ISSN: 1040-452X
    Keywords: nucleus ; replication ; transcription ; MPM-2 ; rabbit embryo ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Mechanisms of nuclear reprogramming and assessment of potential malfunctions that could be deleterious for development were evaluated in rabbit zygotes, parthenotes, and nuclear transfer embryos by analysis of DNA replication, nucleolar fibrillarin label, and localization of nuclear material reactive to the MPM-2 antibody. Nuclear transfer embryos were derived from G1/early S-phase donor nuclei and MII oocytes. In nuclear transfer embryos, DNA rerelication was likely to have occurred because label was incorporated, possibly in the centromeric regions of the chromosomes, prior to premature chromosome condensation and again following pronuclear formation. In parthenotes, DNA replication began very late in the cell cycle, which may be due to deficiencies in the artificial activation stimulus. The presence of fibrillarin label in the nucleolus was used as an indication of nucleolar transcriptional activity. Fibrillarin label was absent in embryos of all types up to the 16-32-cell stage. Although fibrillarin reappeared in nuclear transfer and parthenote embryos at the appropriate stage, not all blastomeres showed label indicating impaired development in these embryos. Labelling of phosphorylated epitopes by MPM-2 antibody showed a change in pattern of labelling during early development. Early cleavage stage embryos did not exhibit labelling over the spindle poles as did blastomeres from 32-cell embryos and tissue culture cells. All cell types exhibited labelling during interphase as dots located primarily over the nucleus in blastomeres from 32-cell embryos and in tissue culture cells, together with cytoplasmic label in embryos at early cleavage stages. Nuclear transplant embryos had a normal pattern of MPM-2 label. In contrast, the appearance of MPM-2 label in parthenotes depended on the type of calcium stimulation. These results demonstrate defects in DNA synthesis, nucleolar activity, and specific phosphorylation events, likely resulting from an improper activation stimulus and chromosome condensation in the transplanted nucleus. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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  • 3
    ISSN: 1040-452X
    Keywords: Oocyte activation ; Calcium ; Maturation promoting factor ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The present study investigated the role of intracellular Ca2+ (Ca2+i) elevation on the inactivation of maturation promoting factor (MPF) in rabbit oocytes. The effects of the number of Ca2+ stimulations and of the amplitude of Ca2+i elevation on the profile of histone H1 kinase activity were determined. A Ca2+ stimulation consisted of transferring mature oocytes from culture medium to 0.3 M mannitol containing 0.1-1.0 mM CaCl2, and pulsing them at 1.25 kV/cm for 10 μsec, or microinjecting 2-8 mM CaCl2 into the oocyte cytoplasm. The number of electrically-induced Ca2+ stimulations was varied, and amplitude of the Ca2+i rise was controlled by altering Ca2+ concentration in the pulsing medium or the injection pipette. Ca2+i concentration was determined with fura-2 dextran; oocytes were snap-frozen at indicated time points and assayed for H1 kinase activity. The activity was quantified by densitometry and expressed as a fraction of activity in nonstimulated oocytes. Electrically-mediated Ca2+i rises inactivated H1 kinase in a manner dependent on the number of Ca2+ stimulations. A single Ca2+ stimulation inactivated H1 kinase to 30-40% of its initial activity. However, H1 kinase inactivation was only transient, regardless of the amplitude of the electrically- or injection-mediated Ca2+i elevation. Increasing the number of Ca2+ stimulations helped to maintain H1 kinase activity at basal (pronuclear) levels. The results show the necessity of a threshold of Ca2+i concentration to trigger MPF inactivation, and suggest a role for the extended period of time over which Ca2+i oscillates at fertilization. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Gamete Research 10 (1984), S. 415-422 
    ISSN: 0148-7280
    Keywords: mouse ; fertility ; fertilization ; sperm ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: This study was conducted to determine the optimal concentration of sperm to use for the insemination of females to detect differences among strains of mice in the percentage of eggs fertilized. Female ICR mice were inseminated with sperm of concentrations ranging from 0.25 to 8 × 106/50 μl from males of either DBA/2N, CF1, or C57BL/6N strains. Differences among strains were detected only when approximately 50% of the eggs were fertilized but not when each of the strains fertilized either a high or low percentage of eggs. The optimal concentration of sperm therefore was the concentration that gave approximately 50% fertilized eggs.
    Additional Material: 1 Ill.
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  • 5
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] We have developed a method, using nuclear transplantation, to produce transgenic embryonic stem (ES)-like cells from fetal bovine fibroblasts. These cells, when reintroduced into preimplantation embryos, differentiated into derivatives from the three embryonic germ layers, ectoderm, mesoderm, and ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature biotechnology 17 (1999), S. 636-637 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Reading the recent paper by Matthew Perry et al., "Mammalian Transgenesis by Intracytoplasmic Sperm Injection," brought back memories from the early 1980s when Ralph Brinster and Richard Palmiter injected a foreign gene construct into the pronuclei of mouse embryos and produced offspring that ...
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  • 7
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Gene targeting is accomplished using embryonic stem cells in the mouse but has been successful, only using primary somatic cells followed by embryonic cloning, in other species. Gene targeting in somatic cells versus embryonic stem cells is a challenge; consequently, there are few reported ...
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  • 8
    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.
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  • 9
    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.
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  • 10
    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.
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