MITF deficiency and oncogenic GNAQ each promote proliferation programs in zebrafish melanocyte lineage cells

Uveal melanoma (UM) is the most common primary malignancy of the eye in adults, but lacks any FDA-approved therapy for the deadly metastatic disease. Thus, there is great need to dissect the driving mechanisms for UM, and develop strategies to evaluate potential therapeutics. Using a zebrafish model, we previously identified MITF, the master melanocyte transcription factor, as a tumor suppressor in GNAQQ209L-driven UM. Here, we show that zebrafish mitfa-deficient GNAQQ209L-driven tumors significantly up-regulate neural crest markers, and higher expression of a melanoma-associated neural crest signature correlates with poor UM patient survival. We further determined how the mitfa-null state, as well as expression of GNAQQ209L, YAPS127A;S381A, or BRAFV600E oncogenes, impacts melanocyte lineage cells before they acquire the transformed state. Specifically, examination 5 days post-fertilization showed that mitfa-deficiency is sufficient to upregulate pigment progenitor and neural crest markers, while GNAQQ209L expression promotes a proliferative phenotype that is further enhanced by YAPS127A;S381A co-expression. Finally, we show that this oncogene-induced proliferative phenotype can be used to screen chemical inhibitors for their efficacy against the UM pathway. Overall, this study establishes that a neural crest signature correlates with poor UM survival, and describes an in vivo assay for pre-clinical trials of potential UM therapeutics. Overall design: Four replicates each of 5 dpf larval cells expressing a mitfa:GFP reporter on wild-type and null mitfa backgrounds compared to similar groups with added BRAF, GNAQ and YAP transgenes.