Laminar organization of pyramidal neuron cell types defines distinct CA1 hippocampal subregions

Investigating the cell type organization of hippocampal CA1 is essential for understanding its role in memory and cognition and its susceptibility to neurological disorders like Alzheimer's disease and epilepsy. Multiple studies have identified different organizational principles for gene expression and how it reflects cell types within the CA1 pyramidal layer including gradients or mosaic. Here, we identify sublaminar gene expression patterns within the mouse CA1 pyramidal layer that span across the entire hippocampal axis. Our findings reveal that CA1 subregions (CA1d, CA1i, CA1v, CA1vv) contain differentially distributed layers of constituent cell types and can be identified by regional gene expression signatures. This work offers a new perspective on the organization of CA1 cell types that can be used to further explore hippocampal cell types across species.