Abstract 749: herzbuckel - A Novel Regulator Of Cardiac Contractility
Despite intensive efforts and immense medical and economic interests the genetic causes of dilated cardiomyopathy (DCM) are mostly unknown. To identify novel disease causing genes and afterwards to define the disease gene-associated signalling pathways, the zebrafish has become a powerful model organism. We recently isolated the zebrafish mutation herzbuckel (hzbma10h) in a large-scale ENU-mutagenesis screen for recessive lethal mutations that perturb cardiac function. As shown by fractional shortening measurements hzb mutant embryos display progressive, ventricle-specific reduction of cardiac contractility leading to embryonic death 6 days after fertilization. Overall morphology of the heart remains unaffected in hzb mutant zebrafish embryos. Histological and ultrastructural analyses demonstrate the proper development of myocardial, endocardial and epicardial layers as well as intact organisation of myofibrils in hzb mutant hearts. By a positional cloning approach we demonstrate that the herzbuckel phenotype is caused by a nonsense-mutation in a zebrafish gene encoding for a novel E3-ubiquitin-and SUMO-E3-ligase. Gene specific knock-down studies by means of modified antisense oligonucleotides reveal a phenocopy of the hzb mutant phenotype whereas injection of the gene-specific mRNA in hzb mutant embryos restores the mutant phenotype indicating that hzb is indeed responsible for the observed phenotype. herzbuckel is highly expressed in cardiomyocytes of zebrafish and humans and by immunohistological analyses we demonstrate for the first time that herzbuckel is associated with the sarcomeric Z-disc. Post-translational modification of proteins by ubiquitinylation and SUMOylation is essential for the proper function of a multiplicity of cardiac-specific proteins and thereby for the proper function of cardiac-specific signalling pathways. Here we show for the first time that the novel E3-ubiquitin and SUMO-E3-ligase herzbuckel is important for the preservation of cardiac contractility.