Functional genomics in zebrafish to disset the pathogenesis of myofibrillar myopathies

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In an attempt to develop within this consortium novel targeted treatment strategies for human myofibrillar myopathies (MFMs) our research within the first funding period aimed to elucidate the genetic basis and the mechanisms that translate known MFM mutations into the myopathic phenotype using forward and reverse genetic approaches in the zebrafish model. Loss-of-function studies of known MFM disease genes reveal that MFM genedeficient zebrafish develop heart and skeletal muscle myopathies without signs of protein aggregations, suggesting that aggregates are not the main trigger of myopathy in the zebrafish. We find that targeted depletion of putative MFM disease genes identified within this consortium (e.g. Strumpellin, KIAA1033) lead to severe myopathic phenotypes affecting both, heart and skeletal muscle, in zebrafish embryos. Additionally, we generated zebrafish that overexpress selected human MFM mutations transiently or in an inducible and stable (transgenic) manner. The transgenic lines will now allow us to evaluate MFM pathophysiology for selected human mutations.Within the second funding period we will focus on the detailed characterization of the novel MFM disease gene, Nexilin, identified by this consortium. Specific aim 1 of this project is to functionally, structurally, molecularly as well as biomechanically characterize Nexilinknockout mice which we generated during the first funding period, as well as zebrafish stably overexpressing human Nexilin mutations associated with myopathies. Specific aim 2 is to decipher the direct effects of MFM disease gene deficiency on myofiber function and structure in selected loss-of-function and transgenic zebrafish MFM disease models. Finally, specific aim 3 is to evaluate the impact/relevance of potential novel MFM disease genes recently identified within this consortium by various approaches on heart and skeletal muscle function in zebrafish.