oa Analysis of Human Endoderm Development Using Lineage-specific Reporter hESCs

Human induced pluripotent stem cells (hiPSCs), derived by the in vitro reprogramming of somatic cells, resemble embryonic stem cells (hESCs) derived from the inner cell mass of the pre-implantation blastocyst stage embryo. In vitro, these pluripotent stem cells (PSCs) can be directed to differentiate toward specific lineages and, therefore, represent a tractable platform for the study of important events during the specification of early human cell types. A key step in differentiation is the commitment of PSCs to mesendoderm formation and the subsequent emergence of lineage-restricted progenitors. Studies from both embryology and from in vitro ESC differentiation systems have identified BMP4 and Activin A as important factors that control the direction of differentiation within nascent mesendoderm. Using a completely defined recombinant protein based differentiation medium, we have examined requirements for each of these factors in the generation of a variety of endodermal lineages, including thymus, lung and pancreas. This analysis has been aided by suite of genetically tagged hESC lines that enable precursors representing these cell types to be easily identified.

Human cells generated from differentiated PSCs represent a new tool for medical research as well as an avenue toward potential cell-based therapies of the future. In addition to the cellular products of PSC differentiation, findings from these experiments have interesting parallels with embryology and provide clues to some of the important events surrounding lineage commitment during early human development.