An attractor state zone precedes neural crest fate in melanoma initiation
Field cancerization posits that groups of cells harboring oncogenic mutations create a permissive landscape predisposed to malignant transformation. We previously identified rare single cells in BRAFV600E;p53-/- zebrafish that reactivate an embryonic neural crest program prior to melanoma initiation. Here, we identify a specific field of BRAFV600E;p53-/-melanocytes with altered differentiation, morphology and cell-cycle regulatory programs that predates the neural crest activation. Based on single cell analysis, these cells form a cancer precursor zone (CPZ) from which a single clone ultimately stabilizes a neural crest-like state and expands to form melanoma. Using in vivo cellular barcoding combined with single-cell RNA-seq and ATAC-seq, we identify a transcriptionally distinct attractor state specific to oligoclonal CPZs that is modulated by BMP signaling. Mechanistically, BMP-dependent induction of the transcriptional repressor ID1 sequesters TCF12, thereby inhibiting lineage-specific targets required for maintenance of melanocyte identity and for clonal selection. Single cells from the CPZ initiate neural crest reprogramming and become tumorigenic. Analysis of a large human patient cohort reveals high ID1 expression in precursor melanocytes as early as dysplastic nevi and atypical melanocytic proliferations, implicating ID1 in early human melanomagenesis. This work identifies BMP signaling and ID1 as early, targetable vulnerabilities with potential for improved diagnosis and prevention of melanoma. Together, these findings uncover a previously unrecognized field effect during melanoma initiation, in which tumors emerge from an oligoclonal attractor-state zone of morphologically distinct yet clinically covert precursor cells with a defined altered transcriptional fate.