To begin to understand the molecular organization of the mammalian nervous system, we calculated a robust dendrogram of cell types (Figure 1C and STAR Methods), showing relationships between cell types based on gene expression distance. The resulting arrangement of cell types revealed that the mammalian nervous system is organized according to three overlapping and interacting principles: major class (e.g., neurons, astrocytes), developmental origin (e.g., telencephalon, diencephalon, midbrain, hindbrain) and neurotransmitter type (e.g., GABA, glutamate).
