Spatiotemporal development of sparse excitatory neuronal types within the deep mouse cortex

Revealing the spatiotemporal organization of cell-type development is critical for understanding cortical patterning and function. To map the temporal evolution and spatial patterning of cell types in the developing mouse brain, here we employ single-cell spatial transcriptomics across four developmental time points and both sexes. We generate a dataset of >1.5 million brain cells across embryonic and postnatal time points and focus on deep cortical neurons of the subplate and claustrum, which have typically been thought to have similar developmental patterns due to shared molecular properties in adulthood. We find significant differences between the developing subplate and claustrum, including distinct origins, transcriptomic evolution, and spatiotemporal maturation, illustrating that these neurons likely play critical yet distinct roles in development. Our single-cell spatial transcriptomics dataset, encompassing a variety of cell types across time points and sexes, will facilitate future study of cell types in brain development.