Effects of Exogenous Thyroxine on Statolith Synthesis and Resorption in Aurelia

Aurelia ephyrae which were maintained in thyroxine during theirmetamorphosis from the polyp state and another group of ephyraewhich were in thyroxine forfour and eight days of starvation,had significantly reduced numbers of statoliths as comparedwith control ephyrae in equimolar concentrations of iodine andin artificial sea water. We conclude, therefore, that thyroxinesignificantly affects the mineralization and demineralizationof statocytes resulting in changes in statolith numbers. A mineralization role of thyroxine in other invertebrates hasnot been reported in spite of the fact that thyroxine and itsprecursors, monoiodotyrosine and diiodotyrosine, have been locatedin numerous invertebrates, particularly in mineralizing areassuch as developing shells. On the other hand, an important roleof thyroxine in mineralization and demineralization of bonesand teeth of vertebrates including humans, has been known forsome time. The specific role of thyroxine in affecting mineralizationin vertebrates is not known, due perhaps to the presence ofmany other hormones and second messengers which also affectmineralization. The use of the relatively simple Aurelia statolithtest systems and the exploration for other invertebrate mineralizingsystems which respond to thyroxine will hopefully lead to abetter understanding of the basic mechanisms of thyroxine actionin mineralizing systems in the future.