eSPN subclusters (Figure S7F–H) were divided into two major groups (Figure 7H), separated by a gene set that included markers used to distinguish canonical iSPNs from dSPNs, such as Drd1 and Adora2a (Figure 7I). Expression of markers associated with canonical SPNs suggests eSPNs have been molecularly “camouflaged,” including in studies using mice that have employed Drd1 and Adora2a driven–transgenes to label and manipulate dSPNs or iSPNs (Heiman et al., 2008; Kozorovitskiy et al., 2012; Kravitz et al., 2012). Despite sharing markers, Adora2a+ eSPNs and Drd1+ eSPNs are distinguished from their canonical SPN counterparts by expression levels of many genes (Adora2a+ SPNs: 35 genes; Drd1+ SPNs: 96 genes; Figure S7I). We validated additional eSPN diversity predicted by Drop-seq, including an ultra-rare eSPN Adora2a±/Th±/Npffr1+ subtype (13–5) that accounts for just 0.3% of all SPNs (n=88 cells)(Figure 7J). One clue about the anatomical identity of eSPNs comes from this small Th+ population, as spiny Th+ principal cells with similar spatial arrangement to eSPNs have been observed in striatum and appear to be dynamically regulated by dopamine (Darmopil et al., 2008). Subsets of the eSPN class share markers previously reported to distinguish SPN subtypes (Gökce et al., 2016).
