Evolution of the cellular landscape in mammalian striatum

Abstract

The dorsal striatum is important for highly specialized functions including movement, learning, and habit formation. However, it is not known if species-specialized behaviors are associated with cellular specializations in the striatum. Here, we compared single-nucleus RNA sequencing (snRNA-seq) data from human, chimpanzee, rhesus macaque, common marmoset, and pale spear-nosed bat caudate (CN) and putamen (Pu) separately as well as mouse caudoputamen (C-Pu), which represents divergence among species spanning approximately 94 million years of evolution. We observed a lower neuron-to-glia ratio in primate striata compared to non-primates, reflecting the allometric scaling of neuron density and relative glia density invariance in larger brains. Among neurons, eccentric spiny projection neurons (eSPNs) - an SPN of unknown function - showed significantly lower proportions in non-primate striata for both CN and Pu. Focusing on the heterogeneity within interneurons, we identified two bat striatal interneuron cell types that are nearly absent in other species: which express LMO3, and co-express FOXP2 and TSHZ2. Other striatal interneurons also showed significantly differential abundance between primates and non-primates. In summary, we provide a comprehensive snRNA- seq dataset of dorsal striatum, identify novel interneuron innovations in bat, and uncover fundamental cellular composition differences between primate and non-primate striata.