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Our laboratory has recently developed approaches using growth factors that allow for the generation of self-renewing extra-embryonic endoderm cells without the requirement for gene manipulation (Cho et al., 2012; Niakan et al., 2013).

A notable advantage of this approach is potential application to mutant mESCs, allowing genetic study of extra-embryonic endoderm development.

Extracellular signalling and exit from stem cell self-renewal

Extracellular signalling and exit from stem cell self-renewal.

While we have discovered that paracrine FGF-signalling compensates for the loss of endogenous Fgf4, which is necessary to exit mESC self-renewal, but not for extra-embryonic endoderm cell maintenance, several questions remain: Are downstream MAP kinases the main effectors of FGF signalling? How rapidly is FGF/MAP kinase signalling transmitted? What is the specific effect of MAP kinase activation on the pluripotency gene regulatory network?

Moreover, our method has revealed that distinct pluripotent stem cells respond uniquely to differentiation promoting signals. Extra-embryonic endoderm cells can be derived from mESCs cultured with LIF and either serum or Erk- and Gsk3-inhibitors (2i). However, we find that epiblast stem cells (EpiSCs) derived from the post-implantation embryo are refractory to extra-embryonic endoderm cell establishment in this assay, further demonstrating that EpiSCs represent a pluripotent state distinct from mESCs. Using this approach we seek to further dissect the genetic network and signalling environments that influence stem cell differentiation and to determine whether extra-embryonic stem cells can be derived from human embryonic stem cells. These experiments will provide novel insight into the impact of signal transduction on the pluripotency gene regulatory network.
 
How does stem cell state and signalling influence lineage decisions? We have established a novel directed differentiation approach, which redefines the differentiation potential of mouse embryonic stem (mES) cells to include the capacity to give rise to both embryonic and extra-embryonic lineages. We hypothesise that FGF signalling is required to exit mES cell self-renewal but not for extra-embryonic endoderm stem cell (XEN) maintenance.