Cancer is characterized by unrestricted, self-renewing cells, eventually forming tumors that deprive healthy tissues of resources. Albeit in a controlled fashion, the ability to self-renew is shared by pluripotent stem cells and naturally present progenitors in the adult. This shared ability to self-propagate led to the hypothesis that progenitor cells may be more apt to transformation into cancer or apt to transform with distinct tumor phenotypes. Work in several tumor types (rhabdomyosarcoma, clear cell sarcoma, etc.) has confirmed the hypothesis, while results in brain cancer contradict. Recent work by other labs has established the presence of multipotent melanocyte progenitors within the epidermis of adult humans, opening up the possibility for melanoma genesis from a more pluripotent and less differentiated cell. Uncovering the importance of cell of origin will test the hypothesis that the ell in which melanoma arises dictates its subsequent clinical behavior; providing insights on treating malignant melanomas based on their cell of origin and not just the bulk population. To address the impact of the differentiation status of the cell of origin on melanoma this study will utilize two complementary systems: human melanocytes derived from iPS cells and a transgenic zebrafish model of melanoma. We have generated a robust and repeatable protocol for the production of pigmented melanocytes via melanocyte progenitors from human pluripotent cells. We will introduce oncogenic mutations (including BRAFv600e) at defined stages of differentiation and characterize the tumorigenic phenotypes both in vitro and in vivo. To complement the human cell culture work, we will utilize the well-established in vivo zebrafish melanoma model to drive tumorigenesis in cells at each progenitor stage. By expressing BRAFv600e under promoters for lineage specific genes we can query the importance of differentiation status of the cell of origin on melanoma phenotypes in vivo.