My group is working to understand how the vertebrate pancreas normally develops using zebrafish as a model. Zebrafish combines forward and reverse genetics with optically clear embryos that are accessible from the earliest stages of development. It lends itself to a variety of approaches, including sophisticated cell manipulations, generation of fluorescent reporter lines, and detailed imaging analysis – approaches that are unfeasible in internally developing mammals. Importantly, the zebrafish pancreas has the same cell types as a mammalian pancreas, and because developmental mechanisms are highly conserved across all vertebrates our findings can often be extrapolated to humans. Our ongoing projects focus on understanding the mechanisms through which pancreatic progenitors are specified from undifferentiated endoderm.
We have established that retinoic acid (RA) signaling is a critical component of normal pancreas development in zebrafish and other vertebrates. Recently, published protocols to produce endocrine pancreas cells from stem cells have featured RA treatment, confirming that the information provided by our zebrafish research is of direct relevance to the production of pancreatic islets in vitro for use in transplantation therapies. We continue to explore the signaling pathway downstream of RA. In a second ongoing project, we have found that the Cdx4 transcription factor functions to set the posterior limit of the pancreas, and thus to limit the normal size of the pancreas progenitor pool. By developing a novel transplantation approach to target reagents to endoderm, we have shown that both RA receptors, and Cdx4, function directly in the endoderm to regulate pancreas development.
A. Confocal image of 72 hour zebrafish larva fore-gut. Gut-GFP transgene expression (green) reveals liver and pancreas. Islet expression (blue) labels the pancreatic islet (right hand side) and associated mesenchyme. Rhodamine dextran (red) labels a clone of endoderm cells derived from a single labeled blastomere.
B. Zebrafish larva with GFP expression targeted to beta cells.