Expression of thyroid hormone receptor beta A gene assayed by transgenic Xenopus laevis carrying its promoter sequences

The responsiveness of thyroid hormone responsive element (TRE)-containing p romoter sequence to thyroid hormone (TH) was studied utilizing Xenopus laev is carrying a transgene containing 5 ' -upstream region of TR beta A1 gene and green fluorescent protein (EGFP) gone. EGFP-expression was seen first i n neurulae, which continued to stage 45, then became weak, and again starte d to increase at the prometamorphic stage, culminating at the metamorphic c limax stage. Immunohistochemistry identified eyes, viscera, and muscles as the EGFP-expressing larval tissues. The treatment of premetamorphic tadpole s with TH induced the precocious EGFP-expression. We also showed that the t ransgenic Xenopus adults were responsive to exogenous TH, a high responsive ness being seen in brain, small intestine, kidney, and bone. TR beta -expre ssion in the embryo, larva, and adult was verified by Western blotting. Thu s, TH not only regulates the metamorphosis, but also might play some biolog ical role(s) in embryos and adults. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.