Because astrocytes derived from adult human brain parenchyma lack neurogenic potential39,40,45, we wanted to identify genes with expression patterns that might distinguish these cells from SVZ astrocytes, as there are no known genes that provide such a distinction in the human brain. We reasoned that comparisons on the basis of module membership can be used to identify genes with expression patterns that distinguish subpopulations of cells in brain regions, and therefore compared membership for M13C with membership for M15, which was highly conserved across brain regions and enriched with markers of astrocytes in every network (Figs. 2 and 5, Table 1 and Supplementary Table 2). This comparison identified genes with strong membership for either M13C or M15, but not both (Supplementary Table 12 online; Methods). The genes with the strongest membership for M13C (SVZ) relative to M15 (astrocyte) included CD24, IQCG, STK38L, CETN2, FLJ22167 and NEK1 (Supplementary Table 12). Consistent with these results, CD24 expression was not observed in parenchymal astrocytes in human caudate nucleus (data not shown).
