The Phox2 homeodomain proteins are sufficient to promote the development of sympathetic neurons

The development of sympathetic neurons is controlled by a network of transc riptional regulators, including the paired homeodomain proteins Phox2a and Phox2b, To understand the role of Phox2 proteins in more detail, the effect of Phox2 overexpression was analysed in the avian peripheral nervous syste m. Phox2a expression in neural crest cultures elicited a strong increase in the number of sympathoadrenergic cells. Expression of Phox2a in the chick embryo promoted the generation of additional neurons expressing the noradre nergic marker genes DBH and TH, pan-neuronal genes SCG10 and NF160 and chol inergic genes ChAT and VAChT. Phox2a-induced neurons were found in ectopic locations such as dorsal root ganglia and peripheral nerve. Sympathoadrener gic development could be elicited in cultures of E5 dorsal root ganglia, de monstrating the presence of Phox2a-responsive cells in non-autonomic periph eral ganglia, Phox2b induced ectopic neurons in the chick embryo in the sam e way as Phox2a, These results show that Phox2 proteins are sufficient to p romote sympathetic neuron generation and control, directly or indirectly, t he expression of a large number of genes characteristic for sympathetic neu rons.