Germinal layers contain various cortical progenitors including RG in the VZ, intermediate progenitors (IP) in the SZi, and ORG in the SZo (reviewed in41), and these RG may be quite diverse42. To search for coherent expression profiles marking putative progenitor populations, we created a consensus co-expression network using samples from VZ, SZi, and SZo in the 15/16 pcw brains, only including genes differentially expressed between these layers (Fig. 3d; Suppl. Table 7; Suppl. Methods). This network will only identify intergenic relationships common to both brains, and should therefore produce robust co-expression relationships that exclude specimen-specific features or changes with age. We found eight co-expression modules with selective enrichment in either the SZ or the VZ (Fig. 3d,e), highly conserved between brains (p<10−50), and highly distinct. Both VZ-enriched modules (G7, G8) contained cell cycle genes and many astrocyte markers, suggesting that these modules may represent different RG populations. Fluorescent ISH (FISH) confirmed that representative genes in both G7 (NR2E1) and G8 (SPATA13) are enriched in VZ versus SZ (Fig. 3f; Extended Data Fig. 7). Surprisingly, rather than labeling distinct cell populations
