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Thyroxine induced metamorphosis in Aurelia.

The functional activity of thyroxine in strobilation initiation in Aurelia is explored. Low temperature preconditioned jellyfish polyps are consistently induced to metamorphose by administration of triiodothyronine, diiodotyrosine, monoiodotyrosine, and thyroglobulin, as well as by previously reported iodide and thyroxine (Spangenberg, ′67). Jellyfish synthesize three protein-bound iodocompounds during strobilation and excrete one protein-bound compound into the medium. The culture medium containing the iodocompound induced strobilation in the absence of iodide. The protein-bound compound found in the culture medium and in the polyps is tentatively identified as thyroxine since it consistently was co-chromatographed with thyroxine in five different solvent systems. 
 
 
 
No localized site of intense concentration of 131NaI or of 125I-T4 was found in the polyps during initiation of strobilation. Both substances were present in greater amounts at the distal, differentiating end of the organisms than at the base, particularly during the early pre-segmentation strobilation period. Distribution of these two substances between the tissue layers during strobilation indicates that thyroxine may be ingested orally and iodide taken up across the epidermis. 
 
 
 
The strobilation system of Aurelia represents the simplest system in which thyroxine is functional and is probably synthesized. This system, therefore, offers new opportunities for the study of the action of thyroid hormone under less complicated developmental conditions than are found in higher organisms.