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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 39 (1994), S. 375-383 
    ISSN: 1040-452X
    Keywords: In vitro fertilization ; Bovine ; Embryo ; Genome Activation ; Transcription ; 3H-Uridine ; α-Amanitin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The timing of genome activation in bovine embryos is still not well defined. The objective of this study was therefore to investigate transcription in bovine embryos with a high potential to develop in culture after in vitro fertilization, by examining, autoradiographically, their incorporation of 3H-uridine. Initial experiments determined that developmental potential in vitro could be related to the time of first division of the zygote. Embryos that completed their first cleavage within 30 hours of exposure to sperm were more likely to develop into blastocysts (65.7%) and to hatch (50.9%). Using such embryos, it was found that 10 of 12 8-cell and all 11 4-cell stage embryos were labeled after a 2-4-hr exposure to 3H-Uridine. Among 2-cell stage embryos, 0 of 23, 3 of 17, 8 of 15, and 3 of 4 were labeled after exposure to 3H-uridine of 2, 4, 7, and 10 hr, respectively. Treatment with α-amanatin (10-100 m̈g/ml) blocked 3H-uridine incorporation but did not inhibit cleavage during the first 4 cell cycles. It was concluded that transcription occurs as early as the 2-cell stage in bovine embryos in vitro but is not critical to the first four cell cycles. © 1994 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 24 (1993), S. 106-112 
    ISSN: 1059-910X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Additional Material: 1 Tab.
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  • 3
    ISSN: 1040-452X
    Keywords: Cell cycle ; DNA synthesis ; NEBD ; Nuclear transplantation ; Bovine ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Nuclear transplantations into metaphase II (MII) and S phase oocyte cytoplasm were performed to investigate the influence of recipient cell cycle stage on nuclear function and development of bovine nuclear transplant (NT) embryos. Rate of inactivation of histone H1 kinase and duration of DNA synthesis in activated oocytes were determined. The proportion of S phase blastomeres in in vivo produced day 5.5 bovine embryos was measured. DNA synthesis was also assessed in NT embryos after transfer into MII and S phase cytoplasm. MII NT embryos were produced by fusing a blastomere into a MII oocyte; the fusion pulse served to activate the oocyte. S NT embryos were produced by fusing a blastomere into an early S phase oocyte electrically activated 4 h prior to fusion. Nuclear envelope structure, chromosome constitution, and extent of development were examined in MII and S NT embryos. Histone H1 kinase activity dropped to baseline within 2 h of electrical activation. A second electrical pulse did not alter H1 kinase activity when delivered 4 h after the first pulse. The frequency of S phase blastomeres in day 5.5 bovine embryos ranged from. 79% to 100%, depending on the duration of culture in 3H-thymidine. Nuclear transplantation into MII cytoplasm resulted in a transient drop in DNA synthesis over 3.5 h. DNA synthesis resumed at 4.5 h post activation (hpa), concomittantly with initiation of DNA replication in activated oocytes. In contrast, DNA synthesis was not interrupted after transfer into S phase cytoplasm. DNA synthesis persisted until 13.5 hpa, as in activated oocytes. Partial or complete nuclear envelope breakdown (NEBD) occurred after transfer into MII cytoplasm, whereas the nuclear envelope remained intact in 50% of the embryos or underwent partial breakdown in S phase cytoplasm. A greater proportion of S NT embryos was diploid (50% vs. 23% MII NT embryos, P 〈 0.001), and a higher frequency of S NT embryos developed to the morula or blastocyst stage (22% vs. 5%, P 〈 0.001). The data indicate that DNA synthesis is regulated differently if the recipient oocyte is in MII or in S phase at the time of fusion. Extended DNA synthesis after transfer into MII cytoplasm suggests a re-replication of the donor chromatin. Re-replication, presumably, does not occur after transfer into S phase cytoplasm. Re-replication is likely to be a consequence of permeabilization of the nuclear envelope upon NEBD in MII cytoplasm. Improved regulation of DNA synthesis after transfer into S phase cytoplasm and reduced incidence of chromosome damage in the first cell cycle may have been responsible for increased frequency of development of S NT embryos to the morula/blastocyst stage. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 13 (1991), S. 65-72 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: There is a growing recognition, stemming from work with both vertebrates and invertebrates, that the capacity for neuronal regeneration is critically dependent on the local microenvironment. That environment is largely created by the non-neuronal elements of the nervous system, the neuroglia. Therefore an understanding of how glial cells respond to injury is crucial to understanding neuronal regeneration. Here we examine the process of repair in a relatively simple nervous system, that of the insect, in which it is possible to define precisely the cellular events of the repair process. This repair is rapid and well organised; it involves the recruitment of blood cells, the division of endogenous glial elements and, possibly, migration from pre-existing glial pools in adjacent ganglia. There are clear parallels between the events of repair and those of normal glial development. It seems likely that the ability of the insect central nervous system to repair resides in the retention of developmental capacities throughout its life and that damage results in the activation of this potential.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 16 (1994), S. 457-459 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Insect neurogenesis has been subjected to extensive study and as a result is regarded as being well understood. It is, therefore, all the more surprising when a fundamentally novel aspects of the process is uncovered. Until recently it was thought that the production of central neurons ceased before the emergence of the adult. Recently, however, Cayre et al. have shown that neurogenesis also occurs in the adult brain. Their studies also show that the rate at which adult neuroblasts divide is controlled by hormones, suggesting that hormones may play a more important role in regulating neurogenesis than previously suspected.
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