design: Nuclei were stained with Sytox blue (Thermo Fisher Scientific) and sorted         on a BD FACSAria Fusion Flow Cytometer (BD Biosciences). For each sample, we collected         Sytox+, NeuN+, and Olig2- nuclei. Single-nucleus cDNA libraries were constructed using the         Chromium Single Cell 3 Reagent Kit V3 (10X Genomics). Samples were pooled and sequenced         targeting at least 30k reads per cell on a NextSeq 2000 system         (Illumina).