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  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 183 (1977), S. 207-214 
    ISSN: 1432-041X
    Keywords: Hydra mutant ; Morphogenetic substances ; Bud formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Non-budding mutants ofChlorohydra viridissima regenerate heads 6 h faster thanHydra attenuata and the number of tentacles per head is higher. The polarity in pieces from the gastric region is the more labile, the smaller the pieces are. In regenerates heads and tentacles form much more frequently than feet, giving rise to bipolar or multiheaded structures. Buds very seldom form under normal conditions, but they occasionally occur in regenerating animals with two cut surfaces. The higher head-forming potential in the mutant is paralleled by a higher head-activator concentration (20-fold in head, 4-fold in body), than inHydra attenuata, which is not accompanied by an equivalent increase in head-inhibitor concentration (1.4-fold in head, 2-fold in body). The foot-activator concentration is slightly reduced (1.3-fold), the foot-inhibitor concentration is higher (1.6-fold) than inH. attenuata. The mutant is extremely insensitive to head activator, relatively insensitive to head inhibitor and foot inhibitor, but sensitive to foot activator.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 186 (1979), S. 139-149 
    ISSN: 1432-041X
    Keywords: Hydra ; Morphogenetic substances ; Regeneration ; Budding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A procedure is presented by which four previously described morphogenetic substances can be purified from hydra: an activator and an inhibitor of head formation and an activator and an inhibitor of foot formation. We show that all four substances act specifically. At low concentrations, the head factors only influence head and not foot formation, and the foot factors only influence foot and not head formation.
    Type of Medium: Electronic Resource
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 194 (1985), S. 453-461 
    ISSN: 1432-041X
    Keywords: Hydra ; Peroxidase activity ; Foot cell differentiation ; Foot activator ; Foot inhibitor ; Head inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mucous cells in the basal disk of hydra contain a peroxidase-like enzyme allowing specific staining of these cells with substrates for peroxidases. The peroxidase activity provides an excellent marker for foot mucous cell, differentiation and was used to follow the reappearance of footspecific cells during foot regeneration after amputation. By choosing the appropriate either soluble or precipitable substrate the peroxidase reaction was used both for a qualitative and for a quantitative evaluation of foot-specific differentiation in hydra. For histological studies diaminobenzidien was found to be a suitable substrate which forms a dark brown precipitate within the cells containing the peroxidase activity. For a quantitative evaluation of foot regeneration the soluble substrate 2,2-azino-di(3-ethyl-benzthiazoline-sulfonic acid-6) ammonium salt was used which after reaction with the enzyme gives rise to a diffusible green reaction product the concentration of which can be measured by its specific absorption at 415 nm. Based on the diffusible enzyme product a new quantitative assay for foot regenration was developed and applied to confirm the effect and specificity of morphogenetic substances which either inhibit or activate foot or head regeneration in hydra.
    Type of Medium: Electronic Resource
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  • 14
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 171 (1973), S. 269-285 
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tissue maceration was used to determine the absolute number and the distribution of cell types in Hydra. It was shown that the total number of cells per animal as well as the distribution of cells vary depending on temperature, feeding conditions, and state of growth. During head and foot regeneration and during budding the first detectable change in the cell distribution is an increase in the number of nerve cells at the site of morphogenesis. These results and the finding that nerve cells are most concentrated in the head region, diminishing in density down the body column, are discussed in relation to tissue polarity.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 190 (1981), S. 191-196 
    ISSN: 1432-041X
    Keywords: Morphogenetic mutants ; Hydra ; Head regeneration ; Morphogens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mutantreg-16 is deficient in head regeneration and abnormal in size regulation. The gastric region becomes twice as long as that of normal animals before the first bud is produced. Both mutant characteristics are due to changes in head-specific morphogen concentrations.Reg-16 contains twice as much head inhibitor and only half as much head activator in its head as normal animals. This leads to a higher level of free head inhibitor in the whole animal resulting on one hand in a greater distance of buds from the head, and on the other hand in a total blockage of release of head activator and head inhibitor which would be necessary to initiate head regeneration.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 188 (1980), S. 133-139 
    ISSN: 1432-041X
    Keywords: Hydra ; Morphogenetic substances ; Regeneration ; Pattern formation ; Sea anemones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A substance was isolated from crude extracts of hydra that inhibits foot regeneration. This substance, the foot inhibitor, has a molecular weight of ≦500 daltons. It is a hydrophilic molecule, slightly basic in character and it has no peptide bonds. The pruified substance acts specifically and at concentrations lower than 10−7 M. At this low concentration only foot and not head regeneration is inhibited. Hydra are sensitive to purified foot inhibitor between the second and eight hour after initiation of foot regeneration by cutting. In normal animals the foot inhibitor is most likely produced by nerve cells. A substance with similar biological and physico-chemical properties is found in other coelenterates.
    Type of Medium: Electronic Resource
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  • 17
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 193 (1984), S. 117-118 
    ISSN: 1432-041X
    Keywords: Hydra ; Regeneration ; Head inhibitor ; Foot inhibitor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In a recent publication in this journal (Berking 1983) it was claimed (1) that the head inhibitor we isolated from hydra is a Dowex artefact, (2) that a separate foot inhibitor does not exist in hydra and (3) that the only inhibitor that has so far been isolated from hydra is one which inhibits head and foot regeneration equally well. These statements are incorrect and require a response. In the following, I would like to summarise our evidence that the inhibitors isolated from hydra, including Berking's inhibitor, have different specificities for head and foot regeneration. In addition, I would like to show that none of our substances are Dowex artefacts.
    Type of Medium: Electronic Resource
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  • 18
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Empirical Finance 1 (1994), S. 193-209 
    ISSN: 0927-5398
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Economics
    Type of Medium: Electronic Resource
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  • 19
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Physics, Section A 278 (1977), S. 163-176 
    ISSN: 0375-9474
    Keywords: Nuclear reactions
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 20
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    BBA Section Nucleic Acids And Protein Synthesis 138 (1967), S. 466-473 
    ISSN: 0005-2787
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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