To characterize pMGLs we used a consensus subset of genes that is highly expressed in microglia but poorly expressed in other macrophages, combining the most relevant genes of the microglial sensome 11, the unique TGFβ-dependent signature of microglia 29, and the microglial cassette found to be upregulated in TMEM119+ microglia during postnatal mouse development 10 (see Suppl. Table 8 for microglial genes compounded from Bennett et al. 2016). These include genes coding for the transmembrane protein TMEM119, the proto-oncogene MERTK, the phospholipid binding protein PROS1, the putative synaptic-tagging complement factor C1QA, the inhibitory receptor LAIR1, the GPCR GPR34, the ectonucleotidase ENTPD1, the purinergic sensors P2Y12/13, and the main TGFβ signaling partners TGFβ1 and TGFβR1. The expression of these markers appears to be positively correlated with maturation time in vivo, increasing in adult animals as compared to newborns 29. Conversely, their expression seems to be negatively correlated with time in culture, being highest in freshly isolated cells and lowest in maintained primary cells and transformed lines. Most of these genes are in fact expressed at higher levels in pMGLs than in
