Location, Location, Location: Spatio-Temporal Cues That Define the Cell of Origin in Melanoma.

It is unclear whether melanoma initiates from mature melanocytes or stem cell precursors. In this issue of Cell Stem Cell, Moon et al. (2017) and Köhler et al. (2017) use in vivo lineage tracing to demonstrate that these two possibilities may occur downstream of the same pro-tumorigenic lesions, depending on environmental factors or the anatomical location.