Fig. 6.

TR strongly associates specifically with the TRE in the IYD promoter in the intestine but not the tail in vivo. Stage 54 premetamorphic tadpoles were treated with or without T₃ for 2 d, and the intestine (A) and tail (B) were isolated for ChIP assay with the anti-TR antibody (top panel) or anti-Id14 antibody (bottom panel), which served as a negative control for antibody specificity. The immunoprecipitated DNA was analyzed by qPCR for the presence of the TRE region of IYD promoter. A region of IYD exon 3 with no TRE was analyzed as a negative control for binding specificity. Note that little or no TR was bound to the TRE of the IYD gene in the absence of T₃ in premetamorphic tadpoles. In the presence of T₃, TR binding to the TRE in the intestine was strongly increased in the intestine, but not the tail, in agreement with the specific, strong regulation of IYD mRNA expression by T₃ in the intestine but not the tail. There was no TR binding to IYD exon 3 in the presence or absence of T₃. Only background signals were observed with the anti-ID14 antibody. Error bars indicate sem (n = 3). *, P < 0.05.