Abstract
Truncating mutations in the tumor suppressor gene adenomatous polyposis coli (APC) are the initiating step in the vast majority of sporadic colorectal cancers, and they underlie familial adenomatous polyposis (FAP) syndromes. Modeling of APC- driven tumor formation in the mouse has contributed substantially to our mechanistic understanding of the associated disease, but additional models are needed to explore therapeutic opportunities and overcome current limitations of mouse models. We report on a novel and penetrant genetic cancer model in Xenopus tropicalis, an aquatic tetrapod vertebrate with external development, diploid genome and short life cycle. Tadpoles and froglets derived from embryos injected with TAL effector nucleases targeting the apc gene rapidly developed intestinal hyperplasia and other neoplasms observed in FAP patients, including desmoid tumors and medulloblastomas. Bi-allelic apc mutations causing frame shifts were detected in the tumors, which displayed activation of the Wnt/β-catenin pathway and showed increased cellular proliferation. We further demonstrate that simultaneous double bi-allelic mutation of apc and a non-relevant gene is possible in the neoplasias, opening the door for identification and characterization of effector or modifier genes in tumors expressing truncated apc. Our results demonstrate the power of modeling human cancer in Xenopus tropicalis using mosaic TALEN-mediated bi-allelic gene disruption.
Highlights
familial adenomatous polyposis (FAP) is an autosomal dominant disorder characterized by the presence of hundreds to thousands of benign, adenomatous polyps in the colon, which over time can progress to malignant adenocarcinomas
Using TALEN-mediated targeting of the mutation cluster region (MCR) of the apc allele, we developed a model that mimics the human FAP syndrome and remarkably recapitulates several of the tumor types observed in FAP patients
Most truncating adenomatous polyposis coli (APC) mutations occur between the first and third 20-aa repeats [15]. We first sequenced this region from four frogs in our colony to detect any single nucleotide polymorphisms (SNPs) that might interfere with TALEN binding, but none were found
Summary
FAP is an autosomal dominant disorder characterized by the presence of hundreds to thousands of benign, adenomatous polyps in the colon, which over time can progress to malignant adenocarcinomas. In the Gardner syndrome (OMIM 175100, 135290), gastrointestinal adenoma formation is frequently accompanied by extra-colonic manifestations, such as congenital hypertrophy of the retinal pigment epithelium (CHRPE), desmoid tumors, osteomas, dental anomalies, epidermal cysts, and soft tissue tumors. In patients diagnosed with the Turcot syndrome (OMIM 276300), central nervous system malignancies, such as medulloblastomas, are observed. Prophylactic colorectal surgery significantly reduces the mortality associated with FAP, the other less penetrant signs and symptoms are becoming more clinically relevant, most prominently the desmoid tumors, which are hard to treat and are a major cause of death in FAP patients [1, 2]
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