GRM1 and melanoma: It was discovered that a gain-of-function of the murine form of a neuronal receptor, metabotropic glutamate receptor 1 (gene: GRM1, protein: mGluR1), when ectopically expressed in melanocytes, was sufficient to induce in vitro melanocytic transformation and spontaneous malignant melanoma development in vivo in a transgenic mouse model, TG-3 (Pollock et al., 2003; Ohtani et al., 2008; Shin et al., 2008).