design: Dorsal skin was excised with micro scissors and treated overnight in Dispase (Stem Cell Technologies). Epidermal sheets, comprised of keratinocytes and migrating melanoblasts, were isolated by gentle scraping with a No.15-blade scalpel and dissociated with trypsin. 2.5 million cells were resuspended in TRIzol and total RNA was isolated using a Directzol RNA mini column used to construct a strand-specific RNA sequencing library. The library was sequenced to generate 52 million 150 nucleotide paired-end reads on a partial lane of an Illumina Novaseq sequencer.