SPATIOTEMPORAL DEVELOPMENT OF SPARSE EXCITATORY NEURONAL TYPES WITHIN THE DEEP MOUSE CORTEX

The developing brain comprises a diverse array of cell types that emerge in a tightly regulated spatiotemporal manner. Understanding the spatiotemporal organization of cell-type development is therefore critical for elucidating cortical patterning and function. Here, we integrate single-cell spatial transcriptomics to map the temporal evolution and spatial organization of cell types in the developing mouse brain. Across four developmental time points and both sexes, we profile ~1.5 million cells spanning embryonic and postnatal stages, with a focus on sparse deep cortical populations, including the subplate and claustrum. These neuronal populations are often thought to share similar developmental patterns due to overlapping molecular features in adulthood. In contrast to current thinking, we identify marked differences between the developing subplate and claustrum, including distinct cellular origins, transcriptomic and spatiotemporal maturation patterns. These findings suggest that subplate and claustrum neurons play critical yet divergent roles during cortical development. Beyond these insights, our comprehensive single-cell spatial transcriptomics dataset provides a valuable resource for investigating cell-type–specific developmental programs across the brain, enabling future studies of cellular diversity and organization during neurodevelopment.