Zebrafish rhabdomyosarcoma reflects the developmental stage of oncogene expression during myogenesis

Rhabdomyosarcoma is a pediatric malignancy thought to arise from the uncontrolled proliferation of myogenic cells. Here, we have generated models of rhabdomyosarcoma in the zebrafish by inducing oncogenic KRAS^G12D expression at different stages during muscle development. Several zebrafish promoters were used, including the cdh15 and rag2 promoters, which drive gene expression in early muscle progenitors, and the mylz2 promoter, which is expressed in differentiating myoblasts. The tumors that developed differed in their ability to recapitulate normal myogenesis. cdh15:KRAS^G12D and rag2:KRAS^G12D fish developed tumors that displayed an inability to complete muscle differentiation as determined by histological appearance and gene expression analyses. By contrast, mylz2:KRAS^G12D tumors more closely resembled mature skeletal muscle and were most similar to well-differentiated human rhabdomyosarcoma in terms of gene expression. mylz2:KRAS^G12D fish showed significantly improved survival compared with cdh15:KRAS^G12D and rag2:KRAS^G12D fish. Tumor-propagating activity was enriched in myf5-expressing cell populations within all of the tumor types. Our results demonstrate that oncogenic KRAS^G12D expression at different stages during muscle development has profound effects on the ability of tumor cells to recapitulate normal myogenesis, altering the tumorigenic capability of these cells.