We collected publicly available single-cell RNA-seq data from different studies. The core dataset of our analysis is a study that sampled more than 500K single cells from the entire mouse nervous system (19 regions) and identified 39 broad categories (level 4) and 265 refined cell types (level 5) 30. The 39 cell types expressed a median of 16417 genes, had a median UMI total count of ~8.6M and summed the expression of a median of 1501 single cells (Table S14). The replication datasets were: 1) a mouse study that sampled 690K single cells from 9 brain regions and identified 565 cell types 91 (note that we averaged the UMI counts by broad categories of cell type in each brain region, resulting in 88 different cell types); 2) our prior mouse study of ~10K cells from 5 different brain regions (and samples enriched for oligodendrocytes, dopaminergic neurons, serotonergic neurons and cortical parvalbuminergic interneurons) that identified 24 broad categories and 149 refined cell types 12; 3) a study that sampled 19,550 nuclei from frozen adult human post-mortem hippocampus and prefrontal cortex and
