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  • Coelenterates  (3)
  • Springer  (3)
  • International Union of Crystallography
  • 1990-1994  (3)
  • 1970-1974
Collection
Keywords
Publisher
  • Springer  (3)
  • International Union of Crystallography
Years
  • 1990-1994  (3)
  • 1970-1974
Year
  • 1
    Electronic Resource
    Electronic Resource
    Pulses of ammonia and methylamine induce down-regulation of nematocyte and nerve cell populations in Hydrozoa (Hydra; Hydractinia) (1990)
    Springer
    Development genes and evolution 199 (1990), S. 123-133 
    Details
    ISSN: 1432-041X
    Keywords: Ammonia ; Methylamines ; Glutamine ; Nematocytes ; Nerve cells ; Coelenterates ; Hydra ; Hydractinia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Hydrozoa replace used-up nematocytes (cnidocytes) by proliferation and differentiation from interstitial stem cells (i cells). Repeated pulsed exposure ofHydra to elevated levels of unprotonated ammonia leads to successive loss of the various types of nematocytes: first of the stenoteles, then of the isorhizas and finally of the desmonemes. The loss is due to deficits in supply; the number of nematoblasts and differentiating intermediates is reduced. In the hydroidHydractinia the main process leading to numerical reduction was observed in vivo: mature nematocytes as well as precursors emigrate from their place of origin into the gastrovascular channels where they are removed by phagocytosis. This is a regular means by which these animals down-regulate an induced surplus of nematocytes. With lower effectiveness, pulses of methylamine, trimethylamine and glutamine also induce elimination of the nematocyte lineages. In the long term the population of nerve cells, which are permanently but slowly renewed from interstitial neuroblasts, decreases, too. After 2 months of daily repeated treatment the density of the Arg-Phe-amide-positive nerve cells was reduced to 50% of its normal level. Thus, ammonia induces down-regulation of all interstitial cell lineages. The temporal sequence of the ammonia-induced loss reflects the diverse rates with which the various i cell descendants normally are renewed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01681485
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  • 2
    Electronic Resource
    Electronic Resource
    Signal transmission and covert prepattern in the metamorphosis of Hydractinia echinata (Hydrozoa) (1990)
    Springer
    Development genes and evolution 198 (1990), S. 245-251 
    Details
    ISSN: 1432-041X
    Keywords: Coelenterates ; Metamorphosis ; Pattern formation ; Neuropeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Planulae are simply structured larvae lacking an overt longitudinal organization. In the course of a rapid metamorphosis, however, they transform into polyps, which display striking structural patterns. Metamorphosis takes place only in response to external stimuli. Surgical removal and transplantation of larval parts reveal that external stimuli, including artificial inducers such as cesium ions, tumor promoters and diacylglycerol, act on the anterior quarter of the larva where sensory cells containing Arg-Phe-amide-like peptides are located. The external stimuli initiate the release of an internal signal, which is transmitted to the posterior end causing the successive transformation of larval into adult tissue. The transformation front moves from the anterior to the posterior quarter in 60 min. The internal signal can be released or bypassed by a transitory lowering of the Mg2+ content of the seawater. By using this procedure, or by administering an extract containing the putative internal signal substance, each isolated part of the larva can be induced to metamorphose separately. Provided there is no time for regeneration after cutting before metamorphosis is initiated, the most anterior fragment forms only stolons, the most posterior fragment forms only a head. The overt pattern of the polyp is, therefore, generated under the influence of a covert anterior-posterior prepattern of the larva.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377390
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  • 3
    Electronic Resource
    Electronic Resource
    Arachidonic acid and the control of body pattern inHydra (1993)
    Springer
    Development genes and evolution 202 (1993), S. 70-76 
    Details
    ISSN: 1432-041X
    Keywords: Arachidonic acid ; HETE ; Protein kinase C ; Lipoxygenase ; Hydra ; Coelenterates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Repeated stimulation ofHydra magnipapillata with the diacylglycerol (DG) 1,2-sn-dioctanoylglycerol (diC8) induces an increase in positional value and eventually the development of ectopic heads. Upon stimulation, the polyps release [14C]-arachidonic acid from previously labelled endogenous sources. Arachidonic acid (AA) is not released into the external medium but remains within the animal, AA, linoleic acid and their lipoxygenase products were identified by gas chromatography-mass spectrometry. Several metabolites were found, most abundantly 12-HETE (hydroxy-eicosa-tetraenoic acid), 8-HETE, 9-HODE (hydroxy-octadecadienoic acid), and 13-HODE; this is the first evidence of their presence in coelenterates. Externally applied AA causes ectopic head formation, though less effectively than diC8. When administered simultaneously, (diC8) and AA, which both are known to activate protein kinase C (PKC), act synergistically in inducing ectopic head formation. Since released endogenous AA can spread in tissues, it may mediate a temporal and spatial extension of PKC activation and, hence, broaden the range in which positional value increases. However, in addition to the activation of PKC, the generation of AA metabolites appears to be essential for the induction of ectopic head formation, since not only a selective inhibitor of PKC, chelerythrine, but also an inhibitor of lipoxygenases, NDGA (nordihydroguaiaretic acid), significantly reduces the effectiveness of both AA and DG.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00636531
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