The XXXX in Rana catesbeiana tadpoles is encoded by a thyroid hormone-responsive gene.

@entity73281 @entity1238 @entity24284 @entity16266
We have recently reported that the @entity1238 complementary DNA (cDNA), @entity24284 , encodes a selenoprotein that is a 5-deiodinase (5D). @entity24284 represents a gene that is up-regulated by thyroid hormone in this species. We now report the isolation from a Rana catesbeiana (RC) cDNA library of a cDNA for the @entity73281 ( @entity73281 ). @entity73281 a 1534-base pair cDNA that exhibits 78% identity to @entity24284 in the coding region, including the TGA codon, which in @entity24284 encodes @entity16266 , and a putative @entity16266 insertion sequence (SECIS) located in the 3'-untranslated region. Transcripts of @entity73281 , synthesized in vitro, induce 5D activity after their injection into @entity1238 oocytes. @entity73281 hybridizes to a 2.2-kilobase messenger RNA (mRNA) species in RC tissues. The expression of @entity73281 was studied in 10 tissues from untreated and T3-treated premetamorphic tadpoles. @entity73281 mRNA transcripts and 5D activity were detected in most tissues examined, and the levels of both were greatly increased in T3-stimulated tadpoles. Furthermore, the levels of @entity73281 mRNA transcripts correlated closely with 5D, but not with 5'-deiodinase (5'D), activity. 5'D was not enhanced by a 4-day exposure of the tadpoles to T3. The up-regulation of @entity73281 gene expression by T3 was demonstrable in tadpoles by stage V, but was found to be transient. The levels of @entity73281 transcripts and 5D activity were highest after 2-3 days and 5 days of T3 exposure, respectively, but had fallen by 10 days to levels comparable to those in unexposed tadpoles. It is concluded that @entity73281 encodes a selenoprotein that is a 5D, and it represents a gene that is up-regulated by T3. On the basis of the findings presented herein, it is suggested that the 5D system plays a major role in regulating intracellular T3 levels in developing tadpoles.
