The “cancerized field” concept posits that cells in a given tissue share an oncogenic mutation or insult and are thus cancer-prone, yet only discreet clones within the field initiate tumors. Nearly all benign nevi carry oncogenic BRAFV600E mutations, but they only rarely become melanoma. The zebrafish crestin gene is expressed embryonically in neural crest progenitors (NCP’s) and is specifically re-expressed in melanoma. We show by live imaging of transgenic zebrafish crestin reporters that, within a cancerized field (BRAFV600E-mutant; p53-deficient), a single melanocyte reactivates the NCP state, and this establishes that a fate change occurs at melanoma initiation in this model. We show the crestin element is regulated by NCP transcription factors, including sox10. Forced sox10 overexpression in melanocytes accelerated melanoma formation, consistent with activation of a NCP gene signature and super-enhancers leading to melanoma. Our work highlights the importance of NCP state reemergence as a key event in melanoma initiation.

Summary CRISPR/Cas9 technology of genome editing has greatly facilitated the targeted inactivation of genes in vitro and in vivo in a wide range of organisms. In zebrafish it allows the rapid generation of knock-out lines by simply injecting a guide RNA (gRNA) and Cas9 mRNA into one-cell stage embryos. Here, we report a simple and scalable CRISPR-based vector system for tissue-specific gene inactivation in zebrafish. As proof of principle, we used our vector with the gata1 promoter driving Cas9 expression to silence the urod gene, implicated in heme biosynthesis, specifically in the erythrocytic lineage. Urod targeting yielded red fluorescent erythrocytes in zebrafish embryos, recapitulating the phenotype observed in the yquem mutant. While F0 embryos displayed mosaic gene disruption, the phenotype appeared very penetrant in stable F1 fish. This vector system constitutes a unique tool to spatially control gene knock-out and greatly broadens the scope of loss-of-function studies in zebrafish.

BACKGROUND & AIMS: Patients with cirrhosis are at high risk for hepatocellular carcinoma (HCC) and often have increased serum levels of estrogen. It is not clear how estrogen promotes hepatic growth. We investigated the effects of estrogen on hepatocyte proliferation during zebrafish development, liver regeneration, and carcinogenesis. We also studied human hepatocytes and liver tissues. METHODS: Zebrafish were exposed to selective modifiers of estrogen signaling at larval and adult stages. Liver growth was assessed by gene expression, fluorescent imaging, and histologic analyses. We monitored liver regeneration after hepatocyte ablation and HCC development after administration of chemical carcinogens (dimethylbenzanthrazene). Proliferation of human hepatocytes was measured in a coculture system. We measured levels of G-protein–coupled estrogen receptor (GPER1) in HCC and nontumor liver tissues from 68 patients by immunohisto-chemistry. RESULTS: Exposure to 17β-estradiol (E2) increased proliferation of hepatocytes and liver volume and mass in larval and adult zebrafish. Chemical genetic and epistasis experiments showed that GPER1 mediates the effects of E2 via the phosphoinositide 3-kinase–protein kinase B–mechanistic target of rapamycin pathway:gper1-knockout and mtor-knockout zebrafish did not increase liver growth in response to E2. HCC samples from patients had increased levels of GPER1 compared with nontumor tissue samples; estrogen promoted proliferation of human primary hepatocytes. Estrogen accelerated hepatocarcinogenesis specifically in male zebrafish. Chemical inhibition or genetic loss of GPER1 significantly reduced tumor development in the zebrafish. CONCLUSIONS: In an analysis of zebrafish and human liver cells and tissues, we found GPER1 to be a hepatic estrogen sensor that regulates liver growth during development, regeneration, and tumorigenesis. Inhibitors of GPER1 might be developed for liver cancer prevention or treatment. TRANSCRIPT PROFILING: The accession number in the Gene Expression Omnibus is GSE92544.