Using the same approach, 20 genes with strong membership for M15 across brain regions and weak membership for M13C were identified (Supplementary Table 12). One such gene was ALDH1L1, which was recently identified as a highly specific marker for astrocytes30. Consistent with this report, we observed that ALDH1L1 possessed strong membership for M15 in CTX (RMM = 117, P = 5.7 × 10−14; Supplementary Table 3), CB (RMM = 72, P = 1.1 × 10−6; Supplementary Table 6) and CN (RMM = 17, P = 4.3 × 10−9; Supplementary Table 5). However, membership of ALDH1L1 for M13C was not significant (RMM = 3,104, P = 0.12; Supplementary Table 5), suggesting that this gene is not expressed by astrocytes in the SVZ. To test this hypothesis, we carried out immunostaining for ALDH1L1 in adult human brain. Notably, expression of ALDH1L1 was absent from layer II processes in the SVZ (Fig. 6l), despite robust staining of astrocytic processes in parenchyma (Fig. 6l).
