FIG. 2.

Knocking out TRβ in the homozygous TRα mutant background derepresses the expression of T3-inducible genes in premetamorphic tadpoles with little effect on premetamorphic development. (A) Representative photos of tadpoles at stage 54. Note that the TRα ^(−/−)TRβ ^(+/+) and TRα ^(−/−)TRβ ^(−/−) tadpoles at stage 54 have a similar head (dorsal view) and hind limb morphology (lateral view). Scale bars: 1 mm. (B) TRα ^(−/−)TRβ ^(+/+) and TRα ^(−/−)TRβ ^(−/−) tadpoles have similar developmental rates (age, days to stage 54), total body length, snout-vent length, and intestinal length (normalized against the total body length) at stage 54. These results are plotted as the mean, marked as a line, and SE. (C) Increased basal expression of known T3 target genes due to TRβ knockout in premetamorphic tadpoles. Total RNA from three different organs, intestine, tail, and hind limb, of stage 54 tadpoles of the three genotypes, was used for qRT-PCR analysis of the expression of four well-known T3 direct target genes: TRβ, klf9, mmp11, and TH/bzip. The expression levels were normalized against that of ef1α. Different lowercase letters denote statistically significant differences (p < 0.05). qRT-PCR, quantitative real-time PCR.