Evidence for an evolutionary conserved role of bone morphogenetic protein growth factors and Phox2 transcription factors during noradrenergic differentiation of sympathetic neurons - Induction of a putative synexpression group of neurotransmitter-synthesizing enzymes

The noradrenergic transmitter phenotype in postganglionic sympathetic neuro ns is induced early during embryonic development in avian and mammalian pri mary sympathetic ganglia. The simultaneous expression of tyrosine hydroxyla se and dopamine beta -hydroxylase, enzymes of the noradrenaline biosynthesi s pathway, indicates that different genes contributing to the noradrenergic transmitter phenotype are regulated as a synexpression group. This conclus ion is supported by the demonstration of bone morphogenetic protein (BMP) g rowth factors and Phox2 transcription factors being necessary for the expre ssion of both tyrosine hydroxylase and dopamine beta -hydroxylase in differ entiating sympathetic neurons. The close similarity in the expression patte rns of the relevant genes as well as in the function of BMPs and Phox2s bet ween avian and mammalian embryos strongly suggests that noradrenergic induc tion occurs along a conserved signalling pathway in these vertebrate classe s.