ISL1 and Merkel cell skin cancer: Cells in cluster 0 were enriched for 6 genes that included 3 markers of normal Merkel cells (ATOH1, SOX2, and KRT8), the Hes family BHLH transcription factor 6 (HES6), insulin gene enhancer protein (ISL1), previously shown to be highly expressed in MCC and other NE cancers (19, 42, 43), and coiled-coil glutamate-rich protein 2 (CCER2), not previously associated with MCC or NE transcriptional programs.