Figure 1.

Up-regulation of TRα genes during late embryogenesis correlates with TR and RXR binding to TR target genes. (A) TRα mRNA expression increases between embryonic and tadpole stages. Total RNA was isolated from stage 20 embryos and stage 47 tadpoles and used for PCR analysis of TRα and TRβ mRNA levels. PCR products (10 μl) were electrophoresed on 2% agarose gels, and the gels were stained with ethidium bromide. The expression of ribosomal protein gene Rpl8 was used as an internal control. (B) TR and RXR binding to T₃ response gene promoters increases between embryonic and tadpole stages. Chromatin from stage 20 embryo and stage 47 tadpole nuclei was immunoprecipitated with antibodies against TR or RXR and analyzed by PCR for the presence of the fragments containing the TREs of the two T₃ response genes. Aliquots of the chromatin before immunoprecipitation were used directly for PCR as control (input). The figure represents one of three independent experiments with different batch of animals, all yielding same results.