Growth factor that exhibits neurotrophic activity on mesencephalic dopaminergic and motor neurons (PubMed:11116144, PubMed:9491986). Acts by binding to its coreceptor, GFRA4, leading to autophosphorylation and activation of the RET receptor (PubMed:11116144). {ECO:0000269|PubMed:11116144, ECO:0000269|PubMed:9491986}. This is the function of ENSG00000125650 (PSPN, persephin).