PROJECT SUMMARY Malformation of the biliary system could lead to cholestatic liver diseases, including biliary atresia, the most common infantile liver disease. A developmental anomaly of the biliary system could lead to biliary atresia and other cholestatic liver diseases. To understand the genetic factors that contribute to the pathogenesis of biliary atresia, we undertook a forward genetic screen to identify previously unappreciated genes and pathways responsible for biliary system formation in zebrafish. We have successfully established new 24 zebrafish mutants, which specifically affect the biliary system. We will investigate the molecular mechanisms underlying biliary system phenotypes in zebrafish by using our innovative computational algorithms to quantify subtle differences in three-dimensional biliary branching patterns and utilize machine-learning-based algorithms to characterize their phenotypes unbiasedly. Building on this work, we will extend our studies to human biliary atresia and other biliary system disease patient samples to investigate the pathology. Successful execution of this collaborative scientific endeavor promises to develop important new scientific insights into biliary system formation. It may have profound implications for our understanding of the pathology of biliary system diseases.