TH and Parkinson disease: For example, in a study, iPSCs were transplanted into the putamen of MPTP-treated PD monkeys, which were then divided into two groups on the basis of whether they had excellent or poor TH+ cell innervation; the PD monkeys that had excellent innervation exhibited the upregulation of 11 specific genes, among which the most prominent was Dlk1, a gene that has a role in facilitating the migration of dopaminergic neurons in the midbrain.