Development of the amphibian pineal organ; cell proliferation and migration


  • Anita E. Hendrickson,

    1. Department of Biological Structure, University of Washington, Seattle, Washington
    Current affiliation:
    1. Department of Ophthalmology, University of Washington School of Medicine, Seattle, Washington 98105
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  • Douglas E. Kelly

    1. Department of Biological Structure, University of Washington, Seattle, Washington
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  • This investigation was supported by a research grant (GB-6910) from the National Science Foundation. The authors are indebted to Dr. N. B. Everett and Mrs. Ruth Tyler for their critical review of the manuscript, to Mrs. Sandra Kunz and Mrs. Nancy Gross for their able technical assistance and to Mrs. Doris Ringer for secretarial help.


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.