Human and mouse embryonic stem (ES) cells are permanent cell lines derived from pre-implantation embryos that display the peculiarities of combining unlimited self-renewal and pluripotency abilities while retaining a normal karyotype.
In practical terms, these peculiarities mean that ES cells can be maintained in culture for indefinite periods of time while conserving their ability to differentiate into any cell type if the appropriate context is provided, either in vivo or in vitro.
Our laboratory is interested in understanding the molecular bases of ES cell pluripotency. For this purpose, we use both mouse and human ES cells. Most of our current knowledge regarding ES cell pluripotency comes from studies of mouse ES cells.
In this system, propagation of undifferentiated cells depends on the presence of a fibroblast feeder layer and the addition of fetal bovine serum.
The activities of both requirements has been pinpointed to specific molecules, the cytokine leukemia inhibitory factor (LIF) and ligands of the transforming growth factor- (TGF ) superfamily (such as BMP2, BMP4, and GDF6), respectively. The pluripotency of mouse ES cells has also been shown to depend on intrinsic determinants, such as the expression of the POU transcription factor Oct4 and the divergent homeodomain-containing factor Nanog. The relationships between extrinsic and intrinsic determinants of mouse ES cell identity are only recently beginning to be understood, and several projects in our laboratory are aimed to address this question. The maintenance of human ES cell pluripotency also appears to depend on the expression of Oct4 and Nanog, but, unlike the case of mouse ES cells, LIF or STAT3 signaling is not required. Instead, signaling by the fibroblast growth factor (Fgf) pathway needs to be exogenously activated by addition of Fgf2.
Also unlike mouse ES cells, it is not presently possible to maintain undifferentiated human ES cells in chemically-defined media. Several projects in our laboratory are pursuing the identification of specific extrinsic and intrinsic requirements of human ES cell pluripotency, and the subsequent optimization of chemically-defined media for their propagation.
Overall, the questions we are approaching include: