Cellular plasticity is a state in which cancer cells exist along a reversible phenotypic spectrum, and underlies key traits such as drug resistance and metastasis.,Melanoma plasticity is linked to phenotype switching, where the microenvironment induces switches between invasive/MITFLO versus proliferative/MITFHI states.,Since MITF also induces pigmentation, we hypothesize that macrometastatic success should be favoured by microenvironments that induce a MITFHI/differentiated/proliferative state.,Zebrafish imaging demonstrates that after extravasation, melanoma cells become pigmented and enact a gene expression program of melanocyte differentiation.,We screened for microenvironmental factors leading to phenotype switching, and find that EDN3 induces a state that is both proliferative and differentiated.,CRISPR-mediated inactivation of EDN3, or its synthetic enzyme ECE2, from the microenvironment abrogates phenotype switching and increases animal survival.,These results demonstrate that after metastatic dissemination, the microenvironment provides signals to promote phenotype switching and provide proof that targeting tumour cell plasticity is a viable therapeutic opportunity.,Phenotype switching is a form of plasticity that allows melanoma cancer cells that leave the primary tumour to invade secondary sites, to switch from an invasive to a proliferative state.,Here the authors identify EDN3, and its synthetic enzyme ECE2, as a regulator of melanoma plasticity in the microenvironment.
Cancers contain a wide diversity of cell types that are defined by differentiation states, genetic mutations and altered epigenetic programmes that impart functional diversity to individual cells.,Elevated tumour cell heterogeneity is linked with progression, therapy resistance and relapse.,Yet, imaging of tumour cell heterogeneity and the hallmarks of cancer has been a technical and biological challenge.,Here we develop optically clear immune-compromised rag2E450fs (casper) zebrafish for optimized cell transplantation and direct visualization of fluorescently labelled cancer cells at single-cell resolution.,Tumour engraftment permits dynamic imaging of neovascularization, niche partitioning of tumour-propagating cells in embryonal rhabdomyosarcoma, emergence of clonal dominance in T-cell acute lymphoblastic leukaemia and tumour evolution resulting in elevated growth and metastasis in BRAFV600E-driven melanoma.,Cell transplantation approaches using optically clear immune-compromised zebrafish provide unique opportunities to uncover biology underlying cancer and to dynamically visualize cancer processes at single-cell resolution in vivo.,Direct visualisation of heterogeneous cell populations in live animals has been challenging.,Here, the authors optimize cell transplantation into optically clear immune-deficient zebrafish, and use intravital imaging to track and to assess functional diversity of individual cancer cells in vivo.