design: Whole fetal brains were randomly chosen from each litter, dissected, and immediately placed into 400L RNAlater (ThermoFisher Scientific) and stored at -80C. RNA was extracted using the PureLink RNA Mini Kit (Invitrogen). Equal amounts of RNA were pooled from 2 brains per litter, resulting in 3000ng RNA per sample. An RNA integrity number (RIN) of at least 9.7 was confirmed for each sample using the 4200 Tapestation system (Agilent). Sequencing library was made with QuantSeq 3 mRNA-Seq V2 Library Prep Kit.