Liver and pancreas development in the zebrafish, Danio rerio

My thesis work has been focused on understanding the processes involved in liver and pancreas organogenesis. With its amenability to forward genetic screens and external fertilization of its eggs, the zebrafish is a useful and practical model system in which to investigate aspects of liver and pancreas development. Taking advantage of the embryos' optical clarity and a transgenic line that expresses GFP throughout the endoderm, I have been able to characterize the morphogenesis of these organs in zebrafish embryos.; Liver development has not previously been characterized in the zebrafish. Using confocal microscopy with the GFP transgenic line mentioned above I identified three morphologically distinct stages of liver budding and characterized the behavior of the hepatocytes as the liver undergoes organogenesis.; Morphogenesis of the zebrafish pancreas has been previously described, with all studies indicating that pancreas development in zebrafish occurs from a single pancreatic anlage. My work has led to the realization that there are in fact two pancreatic anlagen that join to form the pancreas. The posterior bud contains only endocrine tissue, and the anterior bud gives rise to the pancreatic duct and exocrine cells. Interestingly, at later stages the anterior bud also gives rise to a small number of endocrine cells that can be seen near the pancreatic duct. Observations regarding the location and timing of endocrine cell development have led us to hypothesize that there are two distinct origins for endocrine cells in the zebrafish. Future directions of the lab will include genetic analyses to determine whether these populations do indeed come from different precursor populations, and whether different genetic programs regulate their differentiation.