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  • 1965-1969  (3)
  • 1
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The development of the pineal organ in the newt Taricha torosa has been studied utilizing cell counts and radioautography following single injections of tritiated thymidine. Embryos injected two weeks before hatching (series I) demonstrated a grain distribution pattern in the pineal organ and its underlying proliferation zone characteristic of continuous availability of isotope. Larvae injected at hatching (series II) or two weeks after hatching (series III) displayed the expected pulse label pattern for these same regions. With the possible exception of some mitosis insituin the youngest organs, pineal cells originate from a mitotically active cell population which comprises the pineal proliferation zone. After cell division some daughter cells migrate into the pineal organ, moving into the posterior part of the organ during the prehatching period, while from hatching onward the predominant migration is into the anterior part of the organ. Both the pineal photoreceptors and supportive cells arise in this manner with labeled cells of both types found in all three series, but in decreasing numbers from the youngest to the oldest series.Cell counts disclose an approximate ten-fold increase in the number of cells within the pineal organ from embryonic to adult stages, but the rate of cell addition slows with increasing age. Both photoreceptors and supportive cells show this increase in number with the photoreceptor population being maintained at a constant 14%-18% of the total pineal population over this entire five-year period.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 163 (1969), S. 403-425 
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Developing myotubes in skeletal muscle tissue from the limbs of larval newts have been examined with respect to the ultrastructure and sequence of events accompanying myofibril formation. A population of filaments having a diameter of 100 Å is found to occur throughout and beyond the period of myofibrillogenesis. This population is in addition to developing actin and myosin filaments and probably does not contribute directly to myofibril formation. Rather it may represent a cytoskeletal network which ultimately becomes principally disposed around and at right angles to older myofibrils at the level of their Z-bands.Assembly of thick and thin filaments into myofibrils seems to occur, in this muscle, predominantly near the periphery of the cell with registration of these components into A-, I-, and Z-bands being accomplished as they assume progressively more internal locations. Z-bands appear to develop by coalescence of Z-bodies which in turn are earlier related to skeins of fine filamentous material which commonly occupy the most peripheral cytoplasm of these and other mesenchymally derived cells. Fine structural details of these skeins, Z-bodies, and Z-bands have been analyzed with regard to the several prevailing concepts of Z-band architecture. An hypothetical sequence for myofibril formation and Z-band differentiation is presented which takes into account several observations and relates them to the looping filament configuration previously proposed for mature Z-band structure.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 154 (1966), S. 685-699 
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The large, presumably mucus and/or fluid secreting cells of Leydig have been studied in the epidermis of the newt, Taricha torosa, by light and electron microscopy. Mitotic activity in visibly differentiated Leydig cells results in their increasing numbers so that by mid-larval stages they comprise the major cellular component of tailfin skin. Subsequently, the number of these cells diminishes as the epidermis thickens; their final disappearance coincides with metamorphosis and epidermal cornification. During the course of larval life, clear vesicles within Leydig cell cytoplasm accumulate granular material and, in time, assume the morphology of typical mucous aggregates. Concomitantly, the cytoplasm progressively becomes clear in appearance and nearly devoid of organelles.The surface of larval skin is normally provided with a thin mucous coat by continual production on the part of apical epidermal cells. When this surface is exposed to air, observation over a period of time reveals that the outer mucous coat hardens rapidly. There is no indication that additional fluid or mucus is provided to the drying surface from Leydig cells. Rather, light and electron micrographs of epidermis after various degrees of desiccation suggest that Leydig cells do respond to drying, but do so by adding fluid and perhaps mucous material to subsurface, extracellular compartments of the epidermis. The concept that Leydig cells provide an internal fluid reserve is discussed in relation to epidermal development and prevailing physiological and structural evidence bearing on intercellular compartments.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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