Year 3
Toward a goal of developing endodermal lineages from hESCs, including liver, pancreas, lung and intestine, we have developed new tools and approaches to identify these subtypes as well as a molecular understanding of how these subtypes emerge. These advances are highlighted in three papers which are currently under review for publication and one in preparation. Two of these papers redefine endodermal subtypes derived from hESCs, including new methods to isolate lineage restricted endodermal populations and a means to distinguish between single endodermal cells. The third paper provides an unprecedented view of the Nodal signaling pathway and its intersection with bivalent domains in both hESCs and derived endoderm. This chromatin signature which consists of Smad transcription factors and both histone repressive and active marks is the most conducive for mediating downstream targets of Nodal, providing inroads into how signaling pathways and chromatin cooperate during fate specification in hESCs. This analysis has led to the elucidation of new proteins that mediate Nodal signaling; ones that play a key role in endoderm specification.