library_construction_protocol: After deep anesthetizing the entire mouse, its brain/forelimb was immediately removed and immersed in ice-cold Hanks balanced salt solution (Gibco 14175-095). The dorsal cortex/humerus was dissected into small pieces and dissociated into single-cell suspensions using a papain cell dissociation kit (Miltenyi Biotec, catalog number 130-092-628) or collagenase type 2 according to the manufacturer's instructions. Single-cell RNA sequencing (scRNA-Seq) libraries were prepared using the Chromium droplet-based sequencing platform (10X Genomics), in accordance with the manufacturer's guidelines (manual document part number: CG00052 Rev C). The cDNA libraries were purified, quantified using an Agilent 2100 Bioanalyzer, and sequenced on an Illumina HiSeq 6000. The Chromium dropletbased sequencing platform (10X Genomics) was used to generate scRNA-Seq libraries, following the manufacturer's instructions