Specifically, the abundance of a proliferating (MKI67+) microglial subtype was found to be significantly lower after MPTP treatment, indicating a putative trajectory toward functional PD-associated microglia (e.g., the GPNMB+ or VAV3+ microglia) by quickly consuming this progenitor population (Supplementary Fig. 7). The gene discussed is GPNMB; the disease is Parkinson disease.