Identification and Characterization of a LIF-STAT3/Activin-Smad2/3 Dual Responsive Pluripotent Stem Cell State

Abstract

The medical and bioindustrial applications of pluripotent stem cells rely on our understanding of their biology. Pluripotent stem cell lines derived from embryos in different stages depend on distinct signalling pathways. Embryonic stem cells (ESCs), derived from the inner cell mass (ICM) of preimplantation embryos, are dependent on LIF/STAT3 signalling, while epiblast stem cells (EpiSCs), established from the postimplantation embryos, require Activin A/Smad2/3 signalling. Recent studies revealed the presence of intermediate pluripotent stem cell populations. Their growth factor responsiveness, gene expression pattern and associated chromatic signatures, are compatible with the state intermediate between ESCs and EpiSCs. However, it remains unknown whether such cell populations represent a stable clonally intermediate cell state. In this thesis, I describe the discovery and characterization of novel stem cell lines displaying gene expression pattern intermediate between ESCs and EpiSCs. These cells respond to LIF/STAT3 as well as Activin/Smad2/3 signalling at single cell level. They can integrate into the ICM and generate chimeric embryos. In keeping with a more advanced differentiation stage than that of ESCs, the LIF/Activin dual responsive stem cells showed accelerated temporal gene expression kinetics during in vitro differentiation in embryo bodies. I found that these properties are shared by some induced pluripotent stem cell (iPSC) lines. The notion of an intermediate state was consolidated by a genome-wide microarray profiling. The hierarchical clustering analysis grouped LIF/Activin dual responsive stem cells together into a cluster intermediate between ESCs and EpiSCs. These findings advanced our understanding of the regulation of pluripotency. A better understanding of distinct differentiation state of pluripotent stem cells and their signalling responsiveness is crucial for developing tailored strategies for lineage/cell type differentiation.