Directed differentiation of human embryonic stem cells into haematopoietic and definitive endodermal lineages

Abstract

Human Embryonic Stem Cells (hESCs) possess the potential to form, under the right experimental conditions, the roughly 220 cell types that comprise the human adult. My dissertation research focused on the early differentiation of hESCs into two of the primary germ layers, the mesoderm and definitive endoderm. My initial studies of mesoderm differentiation into haematopoietic lineages revealed that hESCs form CD45+ progenitors but fail to efficiently develop into terminally differentiated cells such as dendritic cells (DCs). Endodermal differentiation, in contrast, proceeds robustly when aggregates of hESCs are confronted with a combination of two Transforming Growth Factor B (TGF beta) related growth factors, Activin A and Bone Morphogenetic Protein 4 (BMP4). I have employed this experimental paradigm to characterise in detail the formation of definitive endoderm from hESCs. Transcriptional profiling has identified a number of novel, differentially expressed genes in conditions that promote endoderm formation. Homologs of these genes were analyzed for their expression during key developmental stages in the mouse embryo in an effort to further elaborate the mechanisms governing in vivo definitive endoderm formation downstream of Activin/Nodal and BMP4.