Abstract

Infections with several flatworm parasites represent group 1 biological carcinogens, i.e. definite causes of cancer. Infection with the food-borne liver fluke Opisthorchis viverrini causes cholangiocarcinoma (CCA). Whereas the causative agent for most cancers, including CCA in the West, remains obscure, the principal risk factor for CCA in Thailand is opisthorchiasis. We exploited this established link to explore the role of the secreted parasite growth factor termed liver fluke granulin (Ov-GRN-1) in pre-malignant lesions of the biliary tract. We targeted the Ov-grn-1 gene for programmed knockout and investigated gene-edited parasites in vitro and in experimentally infected hamsters. Both adult and juvenile stages of the liver fluke were transfected with a plasmid encoding a guide RNA sequence specific for exon 1 of Ov-grn-1 and the Cas9 nuclease. Deep sequencing of amplicon libraries from genomic DNA from gene-edited parasites exhibited programmed, Cas9-catalyzed mutations within the Ov-grn-1 locus, and tandem analyses by RT-PCR and western blot revealed rapid depletion of Ov-grn-1 transcripts and protein. Newly excysted juvenile flukes that had undergone editing of Ov-grn-1 colonized the biliary tract, grew and developed over a period of 60 days, were active and motile, and induced a clinically relevant pathophysiological tissue phenotype of attenuated biliary hyperplasia and fibrosis in comparison to infection with wild type flukes. This is the first report of gene knock-out using CRISPR/Cas9 in a parasitic flatworm, demonstrating the activity and utility of the process for functional genomics in these pathogens. The striking clinical phenotype highlights the role in virulence that liver fluke growth factors play in biliary tract morbidity during chronic opisthorchiasis.