A cellular and spatial map of the choroid plexus across brain ventricles and ages

Abstract

The choroid plexus (ChP), located in each brain ventricle, produces cerebrospinal fluid (CSF) and forms the blood-CSF barrier, but is under-characterized. Here, we combine single cell RNA-Seq and spatial mapping of RNA and proteins to construct an atlas of each ChP in the developing and adult mouse brain. Each ChP comprises of epithelial, endothelial, mesenchymal, immune, neuronal, and glial cells, with distinct subtypes, differentiation states and anatomical locations.Epithelial, fibroblast, and macrophage populations had ventricle-specific, regionalized gene expression programs across the developing brain. Key cell types are retained in adult, with loss of developmental signatures and maturation of ventricle-specific regionalization in the epithelial cells. Expression of cognate ligand-receptor pairs across cell subtypes suggests substantial cellcell interactions within the ChP. Our atlas sheds new light on the development and function of the ChP brain barrier system, and will facilitate future studies on its role in brain development, homeostasis and disease. of mice and profiled them by droplet-based single cell RNA-seq (scRNA-Seq, Methods, Fig. 1B, S1A). We partitioned the cells into clusters (Methods) followed by post hoc annotation by expression of canonical cell markers, which identified epithelial, mesenchymal (mural and fibroblast), endothelial, immune, neuron and glia-like cell types in each ChP from all ventricles ( Fig. 1C,D, S1B), and associated each cell type with marker genes (Fig. 1D). We used canonical markers to determine the spatial positions of each major cell type within the ChP tissue from each ventricle ( Fig. 1E, S1C). Notably, actively cycling cell subsets were present within each of the six major cell classes (Fig. S1D), and positionally enriched along the base of the ChP proximal to the brain based on staining for the proliferation marker Ki67 (Fig. S1E). Neurogenic and gliogenic cell populations are found within all developing ChPsIn agreement with previous studies documenting the presence of neuronal cell bodies and neural innervation of the ChP 23 , we captured both neuronal (Tubb3 expressing) and glial-like (Slc1a3/EAAT1 expressing) populations in each developing ChP (Fig. S1F,G) in all developing ChPs (Fig. S1B). Subsets of glial-like cells expressed markers of glia-neuron progenitors/stemlike cells (Rspo2/3, Nes, Sox2, Fabp7, Hes1, Pax6) as well as oligodendrocyte precursor cells (OPCs, Olig1, Olig2) 24 (Fig. 1F, S1H). Subsets of neurons expressed markers of immediate progenitor (Eomes/Tbr2) and immature neurons (Neurod1/2, Dlx1/2, Fig. 1F, S1H), which also expressed a range of neuropeptides ( Fig. S1H). We confirmed the presence of differentiated neurons using whole LV ChP explants (Methods, Fig. 1G), leveraging the relatively simpler three-dimensional structure of LV ChP (Fig. 1A) to facilitate whole tissue imaging, reconstruction and cell identification. Moreover, some of the neuronal cell bodies with processes within the LV ChP stained positive for the neurotransmitter s...

Release of insulin produced by the choroid plexis is regulated by serotonergic signaling

“…Using FISH for Ins2 mRNA in sagittal sections of mouse brains, we show that brain insulin mRNA is predominantly expressed not in the brain parenchyma, but in the epithelial layer of the ChP, where we also detected expression of enzymes needed for maturation of preproinsulin into its mature, bioactive form. In agreement with our findings, Ins2 expression by EChP was also detected by single-cell RNA sequencing, as described recently by Dani et al (37).…”

Angiomodulin (IGFBP7) is a cerebral specific angiocrine factor, but is probably not a blood–brain barrier inducer

“…According to mRNA profiling in another study, AGM mRNA levels are also relatively high in ECs and mature astrocytes, and detectable in neurons also in human brains [31]. AGM expression such as that found by us in non-BBB vasculature at the choroid plexus is also in line with mRNA profiling of the embryonic and adult choroid plexus [32].…”

Broad transcriptional dysregulation of brain and choroid plexus cell types with COVID-19

“…At the same time, no snRNA-seq study exists on the human choroid plexus, in health or disease. This could, as we discovered, be because enzymatic and dounce homogenization techniques successfully used to process mouse tissue 29 resulted in a near complete loss of genes in isolated human choroid nuclei. We thus generated a method involving successive gentle triturations in mild detergent (Methods), yielding 24,052 nuclei across 7 major epithelial, mesenchymal, immune, and glial cell types (6 non-viral, 4 COVID-19, 1 influenza; Fig.…”

“…This is in part because high-quality human brain tissue from patients for such studies is largely inaccessible 21,23,24 . Furthermore, several brain regions highly relevant to COVID-19, such as the choroid plexus 23,24 , have not yet been successfully profiled in humans at single-cell resolution, in health or disease 29 .…”