Fig. 8. Model of the regulation of prestin and Kcnq4 gene expression by an interplay of TH and distinct TR isoforms in a single OHC. (A) In the absence of TH, apo-TRß exerts only a weak repression of prestin, allowing basal transcription. (B) Transcription is activated in the presence of TH by TRß. (C) In the absence of TH, apo-TR1 represses Kcnq4. (D) In the presence of TH, TR1 activates Kcnq4. Putative co-repressors (CoR) and co-activators (CoA) and transient local peak of cochlear D2 activity may be involved. D2 activity is depicted according to data from Campos-Barros et al. (Campos-Barros et al., 2000). D2, 5'-deiodinase type 2; PIC, pre-initiation complex.