Gene expression profile in the liver of Rana catesbeiana tadpoles exposed to low temperature in the presence of thyroid hormone.

Amphibian metamorphosis, which is controlled by thyroid hormone (TH), is highly temperature-sensitive. Using real-time PCR, we investigated the gene expression profile in the liver of Rana catesbeiana tadpoles kept at 28 and 4 °C and treated with 5 nM 3,3',5-triiodothyronine (T3). Out of the 48 genes tested, 12 were up-regulated at 4 °C in T3-treated or untreated tadpoles. These included genes involved in energy metabolism, transcription, and translation. Four TH-response genes, including TH receptor β (TRβ) gene, showed no response to T3 at 4 °C. Deiodinase III was the only gene down-regulated at 4 °C. Chromatin immunoprecipitation assays showed that CCAAT/enhancer-binding protein 2 gene activation by cold exposure was associated with an increase in the acetylation of histone H3 at lysine 9, whereas TRβ gene activation by T3 at 28 °C was associated with an increase in the methylation of histone H3 at lysine 36 with no T3-dependent changes in methylation states on cold exposure. Our results suggest that the transfer of TH signal to chromatin modifications on a primary early TH response gene was specifically blocked by exposure to cold.