Abstract 048: Identifying Genetic Modifiers for Cardiomyopathy via Mutagenesis Screening

Abstract

Rationale: The generation of animal models for human cardiomyopathy creates opportunities to uncover mechanisms of diseases’ pathogenesis and to identify genes that modify the progression of pathogenesis. In contrast to candidate gene-based approaches, the phenotype-based forward genetic screening approach is less effectively employed in a vertebrate, mainly due to the prohibitively enormous colony management efforts. Objective: To identify genetic modifiers of cardiomyopathy through developing an unbiased forward genetic approach in the vertebrate Danio rerio. Methods and Results: Using an expression-based insertional mutagenesis screening strategy, we identified 49 Zebrafish Insertional Cardiac (ZIC) mutants from a collection of ~300 gene break-transposon (GBT) lines. By applying doxorubicin (DOX) stress to these heterozygous ZIC mutants, we initially identified four GBT lines that either enhanced or suppressed DOX-induced cardiomyopathy phenotypes. Here, we focus on the GBT0411 line which significantly enhances DOX-induced cardiomyopathy phenotypes. We cloned the gene and identified a single transposon insertion that disrupts the long nuclei isoform of dnajb6b in this GBT0411 mutant. Consistent with its cardiomyopathy modifier function, we detected a predominant expression of dnajb6b in the heart. While mutations affecting the cytoplasmic functions of DNAJB6 were recently reported to cause limb-girdle muscular dystrophy type 1D, our study suggested that the impaired balance between Dnajb6b long (nuclei) and short (cytoplasmic) isoform accounted for the cardiomyopathy modifier effect. Conclusions: Our results demonstrated the feasibility of identifying genetic modifiers of cardiomyopathy using a forward genetic approach in a vertebrate. Specifically, our data implicate DNAJB6 as a new genetic risk factor for DOX-induced cardiomyopathy. Without any presumption, this forward genetic strategy opens the door to systematically identify genetic factors that modify the progression of cardiomyopathy, which will facilitate the practice of personalized medicine and the development of novel therapies.