Date of Award


Document Type


Degree Name

Master of Science



First Advisor

Dr. Gary P. Radice

Second Advisor

Dr. Francis B. Leftwich

Third Advisor

Dr. Rafael O. de Sa


It has long been known that thyroid hormone (TH) is responsible for metamorphosis in tadpoles. It is also known that A7 MHC, an adult muscle isoform, is expressed in adult Xenopus laevis frogs, but not in larvae. Furthermore, the appearance of A7 corresponds with the onset of metamorphosis. The present study investigated the relationship between TH and the expression of A7 MHC mRNA in Xenopus laevis. Isolated tails in culture and 6-n-propyl 2-thiouracil (PTU) treated tails were treated with TH and the presence of A7 mRNA analyzed with in-situ hybridization, and RT-PCR. It was found that TH caused substantial regression of tails. It was also found that A7 was expressed in tails treated with TH and was located primarily in a region rich in slow twitch fibers near the base of the tadpole tail. Finally, A7 is also expressed in PTU treated tadpoles, which suggests a novel mechanism is involved.

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