Genetic analysis of cardiac patterning in zebrafish

The zebrafish system provides a powerful model to investigate the cellular mechanisms regulating cardiac patterning. This study addresses three different aspects of cardiovascular development in zebrafish and seeks to further elucidate the genetic requirements for vertebrate cardiac patterning.;A limitation of the zebrafish system as a model for cardiac disease is the lack of quantitative means to assess cardiac function. In Chapter 2, I describe the zebrafish Cardiac Analysis System, which enables the visualization and quantification of cardiac function. An additional advantage of the zebrafish Cardiac Analysis System is its ability to facilitate high throughput screening of small molecules or mutations affecting cardiac function.;One facet of cardiac patterning is the determination of cardiac laterality. In Chapter 3, I characterize a previously unknown function for Fused in regulating left-right patterning by modulating cilia biogenesis in the Kupffer's vesicle. This role for Fused is independent from its previously described activity downstream of the Hedgehog signaling pathway in zebrafish, demonstrating that Fused function has diverged from Drosophila to vertebrates.;Cardiac function requires specification and differentiation of not only the atrial and ventricular chambers but of the atrioventricular (AV) boundary as well. Cardiomyocytes exhibit different conducting properties at the AV boundary than in the rest of the heart, and cardiac valve formation requires intricate signaling between the myocardium and the endocardium located at the AV boundary. In the last part of this study (Chapter 4), I characterize and clone the leo1 mutant, which displays cardiac and neural crest phenotypes. I further demonstrate that Leo1 is a conserved member of the PAF1 complex but is not required for all PAF1 complex-mediated transcription. Analysis of leo1 mutants indicates that Leo1 is required for differentiation of the AV boundary and of neural crest cells into pigmentation cells and cartilage.;Overall, my study has expanded our understanding of the genetic mechanisms underlying cardiac patterning in zebrafish.