Which actin genes are necessary for zebrafish heart development and function?

Heart failure is the number one cause of mortality in the world, contributed to by cardiovascular disease. Many diseases of the heart muscle are caused by mutations in genes encoding contractile proteins, including cardiac actin mutations. Zebrafish are an advantageous system for modeling cardiac disease since embryos can develop without a functional heart. However, genome duplication in the teleost lineage creates a unique obstacle by increasing the number of genes involved in heart development. Four actin genes are expressed in the zebrafish heart: acta1b; actc1c; and duplicates of actc1a on chromosome 19 and 20. Here, we characterize the actin genes involved in early zebrafish heart development using in situ hybridization and CRISPR targeting to determine which gene is best to model changes seen in human patients with heart disease. The actc1a and acta1b genes are predominant during embryonic heart development, resulting in severe cardiac phenotypes when targeted with CRISPRs. Targeting these two cardiac genes with CRISPRs simultaneously results in a more severe phenotype than their individual counterparts, with the results suggesting compensation for lost actin genes by other actin paralogues. Given the duplication of the actc1a gene, we recommend acta1b as the best gene for targeted cardiac actin research.