Figure 1. TRα2 shows dominant negative activity on positively and negatively regulated T3 target genes in vivo.
A: TRα2 exerts dominant negative activity on positively ME-tk-luc transcription. ME-tk-luc transcription was measured in hypothyroid (PTU) 2 days old mice treated with T3 (2.5 µg/g b.w.) (PTU+T3) or saline (PTU), 18 h after hypothalamic injection of 1 µg reporter construct and 100 ng expression vector (empty pSG5 (Ct) or pSG5-TRα1 (TRα1) or pSG5-TRα2 (TRα2)). Transcription from ME-tk-luc is significantly increased in the presence of T3 when TRα1 is overexpressed (as compared to Ct) (p<0.001). In contrast TRα2 overexpression significantly increases basal, T3-independent ME transcription as compared to Ct and TRα1 (p<0.001), but addition of T3 does not modify transcription further. B: TRα2 exerts dominant negative activity on negatively Trh-luc transcription. Trh-luc transcription was measured in hypothyroid (PTU) 2 days old mice as described above (100 ng expression vector and 1 µg reporter gene, Trh-luc per pup). Transcription from a Trh-luc construct is significantly decreased both in absence (PTU) and presence of T3 (PTU+T3) when TRα1 is overexpressed (as compared with Ct). In contrast, overexpression of TRα2 has no effect on T3-independent Trh transcription, but blocks its T3-dependent repression. SEMs are given, n≥10 per point. In each case, the whole experiment was repeated twice giving similar results. *, p<0.05; **, p<0.01; ***, p<0.001.