Single nuclei dissociated with Papain + DNAse for organoids. For bulk RNA-sequencing, cortices were dissociated embryonically or perinatally and either flash frozen or RNA extracted by Qiagen RNAeasy kit. If frozen, samples place in RNA later and then extracted at later date using Qiagen RNAeasy kit 10X Chromium Single Cell 3' Standard library construction from JP Sulzberger genomics core at Columbia University. For bulk RNA sequencing Poly-A pull-down was used to enrich mRNAs from total RNA samples and libraries were constructed using Illumina TruSeq chemistry. Libraries were then sequenced using Illumina NovaSeq 6000