Fig. 4.

Of the two histone marks associated with gene silencing, H3K9me3 and H3K27me3, only H3K27me3 was reduced upon gene activation by T₃ during metamorphosis. Premetamorphic tadpoles at stage 54 were treated with T₃ for 2 d. The intestine was isolated and subjected to a ChIP assay with anti-H3K27me3 (A) or anti-H3K9me3 antibody (B). ChIP signals were normalized with the ChIP signals of histone H3 in Fig. 2 for the corresponding promoter/exon regions. Note that surprisingly, the amount of H3K9me3 was increased in the downstream transcribed region of the TRβ gene (exon 5) upon gene activation by T₃. Error bars indicate sem (n = 3). A Student's t test was carried out between pairs of control and T₃-treated groups. The one and two stars indicate pairs of samples with significant differences (P < 0.05 and P < 0.01, respectively).