Gene expression changes in asb2b mutant heart

Tissue integrity is critical for organ formation and function1. During heart development, cardiomyocytes have to differentiate and integrate to form a coherent tissue that contracts synchronously2,3. However, the molecular mechanisms regulating cardiac tissue integrity are poorly understood. Here, we show that proteolysis, via the E3 ubiquitin ligase ASB2, regulates cardiomyocyte maturation and tissue integrity. Cardiomyocytes in asb2b mutants fail to terminally differentiate, exhibit disorganized sarcomeres and cell-cell junctions, as well as defects in tissue polarity, resulting in reduced cardiac contractility and output. Mosaic analyses reveal a cell-autonomous requirement for Asb2b in cardiomyocyte integration, as asb2b mutant cardiomyocytes are unable to meld into wild-type myocardial tissue. In vitro and in vivo data indicate that ASB2 negatively regulates TCF3, a bHLH transcription factor. We further show that TCF3 must be degraded for cardiomyocyte maturation, as TCF3 gain-of-function causes a number of phenotypes associated with cardiomyocyte dedifferentiation. Overall, our results indicate that proteolysis has an important role in cardiomyocyte maturation and the formation of a coherent myocardial tissue. 50 hpf WT and asb2b mutant fish hearts were isolated and RNA expression levels were analyzed by microarray