An electrical switch for melanoma: biologists at Tufts University have discovered that a change in membrane voltage in newly identified "instructor cells" can cause stem cells' descendants to trigger melanoma-like growth in pigment cells (melanocytes). Hyperpigmentation can be seen in the treated tadpole embryo (B, red arrows), but not in the control embryo (A). The pigment cells not only grew in greater numbers but also formed long, branch-like shapes and invaded neural tissues, blood vessels and gut in a pattern typical of metastasis. Discovery of this novel bioelectric signal and cell type could aid in the prevention and treatment of diseases like cancer and vitiligo as well as birth defects. Tufts biologists manipulated the electrical properties of a special, sparse cell population present throughout the embryo by using the common anti-parasitic drug ivermectin to open the glycine gated chloride channel (GlyCl). The GlyCl channel is one of the many ion channels that control cellular membrane voltage and is a marker of this unique "instructor cell" population. Changing the chloride ion level to hyperpolarize or depolarize the cells in turn triggered abnormal growth in distant pigment cells derived from the neural crest stem cells.