HES6 and Merkel cell skin cancer: We confirmed that MCC nature of the selected cells by expression of the established marker genes CCER2 (coiled-coil glutamate-rich protein 2), SOX2 (SRY-box transcription factor 2), and HES6 (Hes family BHLH transcription factor 6) (Fig. 1D) (refs. [19, 20]).