Spatiotemporal single-cell analysis of gene expression in the mouse suprachiasmatic nucleus

Mammalian circadian behaviors are orchestrated by suprachiasmatic nucleus (SCN) in the hypothalamus. Yet basic SCN cell types and their roles in circadian pacemaking are still unclear. In this study, we comprehensively characterized the basic cell types of SCN and their circadian and light-induced gene expression. In SCN, we identified seven major cell types among which neurons, astrocytes, ependymocytes and endothelial cells display cell-type specific circadian gene expression. We found that five SCN neuron subtypes, Avp+/Nms+, Vip+/Nms+, Vip+/Grp+, Cck+/C1ql3+ and Cck+/Bdnf+, differ in their spatial distribution, circadian rhythmicity and light responsiveness. Among the rhythmic neuron subtypes, we observed a wave of circadian gene expression propagating from the subtypes in posterior SCN  to the subtypes in anterior SCN. Such wave can be explained by the neuropeptide-receptor signaling network in which Avp+/Nms+ subtype is the leader of circadian oscillations. Our study provides insights into the basic neural mechanism of circadian pacemaking in mammals. Drop-seq of mice SCN at 12 circadian time points and 1 flash stimulate time point