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Fig. 5. A low level of T3 (1 nM) can activate T3-inducible genes and metamorphosis in early premetamorphic tadpoles. (a) T3 activates various T3-response genes in early premetamorphic tadpoles. Wild type tadpoles at stage 46 were reared in the water with or without 1 nM T3. Total RNA was isolated from individual animals after 0, 1, 3, and 5 days. Each group had four individual animals. The cDNAs reverse-transcribed from the total RNAs were subjected to quantitative PCR. T3-response genes TRβ, stromelysin-3 (ST3), T3-responsive basic leucine zipper transcription factor (TH/bZip), and sonic hedgehog (xhh), were examined. A retinoic acid-response gene (HoxA1) was analyzed as a negative control. The expression level of each gene was normalized to that of rpL8 and expressed in arbitrary units. Note that expression of T3-response genes was significantly upregulated by T3 treatment (∗p < 0.05), whereas HoxA1 was unaffected. The xhh gene is an organ-specific T3-response gene and thus the upregulation was not very dramatic when analyzed in whole animals (Stolow and Shi, 1995). Similar results were obtained from another experiment with an independent batch of animals. (b) T3 accelerates hind limb development in premetamorphic tadpoles. A wild type tadpole reared in (1 nM) T3-containing water for 5 days had larger hind limbs (arrowhead) compared to a control tadpole without T3 treatment. Image published in: Sato Y et al. (2007) Copyright © 2007. Image reproduced with permission of the Publisher, Elsevier B. V. Larger Image Printer Friendly View

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