Differential regulation of dopaminergic gene expression by Er81

A recent study proposed that differentiation of dopaminergic neurons requires a conserved "dopamine motif" (DA-motif) that functions as a binding site for ETS DNA binding domain transcription factors. In the mammalian olfactory bulb (OB), the expression of a set of five genes [including tyrosine hydroxylase (Th)] that are necessary for differentiation of dopaminergic neurons was suggested to be regulated by the ETS-domain transcription factor ER81 via the DA-motif. To investigate this putative regulatory role of ER81, expression levels of these five genes were compared in both olfactory bulbs of adult wild-type mice subjected to unilateral naris closure and the olfactory bulbs of neonatal Er81 wild-type and mutant mice. These studies found that ER81 was necessary only for Th expression and not the other cassette genes. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays (EMSA) experiments showed that ER81 bound directly to a consensus binding site/DA-motif in the rodent Th proximal promoter. However, the ER81 binding site/DA-motif in the Th proximal promoter is poorly conserved in other mammals. Both ChIP assays with canine OB tissue and EMSA experiments with the human Th proximal promoter did not detect ER81 binding to the Th DA-motif from these species. These results suggest that regulation of Th expression by the direct binding of ER81 to the Th promoter is a species-specific mechanism. These findings indicate that ER81 is not necessary for expression of the OB dopaminergic gene cassette and that the DA-motif is not involved in differentiation of the mammalian OB dopaminergic phenotype.