disease. Both extrinsic and intrinsic modulation of pathological and physiological stimulation prevent the progenitor cell from differentiating into dopamine cells. Further research must be done to understand factors that affect progenitor cell differentiation in order to treat Parkinson's disease. Despite the difficulties in replacing compromised dopamine neurons through endogenous sources, recent work suggests that pharmacological activation of endogenous neural stem cells or neural precursor cells results in powerful neuronal rescue and motor skill improvements through a signal transduction pathway that involves the phosphorylation of STAT3 on the serine residue and subsequent Hes3 expression increase (STAT3-Ser/Hes3 Signaling Axis). References Developmental biology