Expression of erbAα and β mRNAs in regions of adult rat brain

The proto-oncogenes erbAa and erbAβ together encode three functional thyroid hormone receptors (erbAol, β1, and β2), as well as two proteins (erbAσ 2 and α3) that do not bind T3. The erbAα2 protein has been shown to inhibit the T3 inductive effects of functional receptors, and α2 mRNA is expressed at high levels in adult rat brain. Thus, expression of erbAα2 may explain the observation that adult rat brain is not a T3 responsive organ, despite the presence of T3 receptors. However, expression of the different erbA mRNAs has not been studied within distinct regions of rat brain. To gain further insight into the roles of these molecules, we have used polymerase chain reaction to investigate the expression of all five erbA mRNAs within discrete regions of adult rat brain. The results indicate that all three erbAa mRNAs are expressed in all regions studied (brainstem, cerebellum, cortex, hippocampus, pituitary, quadrigeminal plate, striatum, and thalamus). All regions contained less erbAα3 RNA than either α1 or α2. Expression of α2 exceeded that of αl in all regions except striatum. ErbAβl was expressed in all brain regions, whereas erbAβ2 was confined to the pituitary.