We were particularly interested in identifying differences between the SZi and the SZo, which is absent in mice. Modules G2 and G3 are enriched in the SZi (Fig. 3d, white bars in bottom two rows), and G3 is enriched for genes marking Svet1+ IPs in E14 mouse SZ43, including ELAVL4, LRP8, NEUROD1, NRN1, SLC17A6, SSTR2, and TP53INP1. Modules G4-G6 are enriched in the SZo (Fig. 3d, gray bars); however, these modules are enriched for neuron-associated categories likely expressed in postmitotic cells during their radial migration. To identify expression specific to SZo or SZi using a more targeted approach, we searched for genes both maximally expressed in the SZ and differentially expressed between SZo and SZi (Fig. 3g; t>4, p<0.01, log2(FC)>0.5). Remarkably, few genes met both criteria at 15–16 pcw: 39 genes were enriched in SZi (including several in module G3), while only eight were specifically enriched in SZo. These results are consistent with a previous study of laminar enrichment in 13–16pcw human prenatal cortex, which also found few genes specifically enriched in SZo (55) or SZi (61)2.
