Furthermore, we discovered two additional related cell types that shared expression of the canonical VLMC markers. We identified one (ABC) as arachnoid barrier cells based on the expression of Abcg2 and Pgp. These two genes encode drug and xenobiotic transporters known as BCGP and P-gp, respectively, which are expressed on barrier cells of the arachnoid mater of the meninges (Yasuda et al., 2013). The most specific gene expressed in ABCs was Slc47a1, which encodes the multidrug and toxin extrusion protein MATE1, reinforcing the putative function of ABCs to cleanse the cerebrospinal fluid of toxic substances. In contrast to all other VLMC-like cell types, ABCs did not express Lum and showed only very low levels of Pdgfra.
