Abstract

Gibel carp farming suffers severe economic losses due to Carassius auratus herpesvirus (CaHV) infection in China. CRISPR/Cas9-mediated genome editing is a potential tool to improve fish resistance to virus infection; however, lack of available genes limits its application. In humans, ISG15-deficient individuals are not reported to suffer overt viral diseases. Here, we report that genome editing of ISG15 genes could genetically improve viral resistance in gibel carp. Unlike human harboring one ISG15 gene, gibel carp possesses 19 homologs including three older genes (ISG15a, ISG15b and ISG15s) and 16 younger genes. Combined editing of ISG15a and ISG15b in gibel carp (CAS III) generated a mutant with normal phenotypes in growth and reproduction, but with a high survival against CaHV infection (nearly no deaths in artificial infection experiments). Transcriptome analysis of mutant carp revealed an increased basal expression of selected interferon (IFN)-stimulated genes (ISGs), a typical characteristic of ISG15-deficient humans. Consistently, gibel carp ISG15 homologs are inhibitors of fish IFN response and thus are proviral factors, despite displaying functional divergences. Our results indicate that fish ISG15 is an ideal target gene for precise antiviral breeding and thus we have created a gibel carp mutant with genetical resistance to CaHV infection.