The present invention relates to isolated Nato3 mutant polypeptides. Methods for stimulating a brain cell to differentiate into a dopaminergic progenitor neuronal cell or a dopaminergic neuron comprises increasing phosphorylation of Nato3 in the brain cells and culturing the brain cells until a progenitor dopaminergic neuronal cell marker or a dopaminergic neuronal cell marker is expressed in the cultured brain cells. Methods for treating Parkinson's disease (PD) in a subject comprises administering to the subject in need thereof, a composition comprising progenitor dopaminergic neuronal cells and/or dopaminergic neuronal cells expressing a Nato3 mutant polypeptide to the brain of the subject.