PTGDS and melanoma: We identified within this group melanocytes, which produce a high level of pigmentation genes (Ptgds, Pmel, Mlana) consistent with the highly pigmented nature of nevus melanocytes12; a Schwann cell population (marked by Mpz); and several tumor-enriched cell populations that clustered separately from melanocytes, and expressed melanoma markers (Plp1, Gpm6b, Postn, Mcam35) (Fig. 2c, d).