<p class="first" id="d698769e309">The choroid plexus (ChP) in each brain ventricle
produces cerebrospinal fluid (CSF)
and forms the blood-CSF barrier. Here, we construct a single-cell and spatial atlas
of each ChP in the developing, adult, and aged mouse brain. We delineate diverse cell
types, subtypes, cell states, and expression programs in epithelial and mesenchymal
cells across ages and ventricles. In the developing ChP, we predict a common progenitor
pool for epithelial and neuronal cells, validated by lineage tracing. Epithelial and
fibroblast cells show regionalized expression by ventricle, starting at embryonic
stages and persisting with age, with a dramatic transcriptional shift with maturation,
and a smaller shift in each aged cell type. With aging, epithelial cells upregulate
host-defense programs, and resident macrophages upregulate interleukin-1β (IL-1β)
signaling genes. Our atlas reveals cellular diversity, architecture and signaling
across ventricles during development, maturation, and aging of the ChP-brain barrier.
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