1. Raldh2+ arachnoid meningeal fibroblasts formed a sheet of cells 194 located just above the pial-located PNVP (Fig. 3C). Rdh10 and Raldh2 are both needed to make retinoic 195 acid however our data show that Rdh10 is expressed by the pial fibroblasts, while Raldh2 is enriched in 196 arachnoid fibroblasts. This expression pattern is consistent with a mechanism where the pial and arachnoid 197 fibroblasts work in conjunction to make retinoic acid, with each layer responsible for a different synthesis 198 step. This observation is further supported by GSEA that demonstrate significant enrichment for retinoic 199 acid synthesis genes in pial and arachnoid cluster but;We confirmed Raldh2 (Aldh1a2) protein expression in arachnoid cells using whole mount 193 immunostaining of E15.5 meninges,2019
2. Because these molecules are needed for brain 203 growth and homeostasis, transporters such as like solute carrier (SLC) influx transporter proteins are 204 highly expressed in CNS endothelial cells and choroid plexus epithelia to ensure regulated delivery of 205 essential molecules into the brain and CSF;Saunders;Barriers at the blood-brain (CNS endothelium) and blood-CSF interfaces (choroid plexus or CP) 201 prevent uncontrolled intercellular movement of essential nutrients, ions and amino acids from the blood 202 into the CNS (reviewed in (Hladky and Barrand,2013
3. GSEA using a geneset of SLC genes expressed in the meningeal fibroblast clusters confirmed enrichment 213 of SLC genes in the arachnoid cluster (Fig. 3F);Slc16a9 (monocarboxylate transporter) and Slc38a2 (amino acid 215 transporter) (Fig. 3E, Fig. S3E) whereas the pial cluster was enriched for Slc1a3