Development of FGF2-dependent pluripotent stem cells showing naive state characteristics from murine preimplantation inner cell mass

• We have established a unique pluripotent cell line from the murine ICM.
• Self-renewal of the cells was maintained with FGF2/MEFs but not LIF/2i.
• The cells have the capacity to contribute chimeric animal including germ cells.
• Gene expression patterns of the cells are distinct from murine ESC or EpiSC.
• The cells can self-renew with FGF2, ActivinA and LIF in the absent of MEF.

Two distinct types of embryonic pluripotent stem cells can be established from either the inner cell mass (ICM) of preimplantation blastocyst (leukemia inhibitory factor (LIF)-dependent embryonic stem cell, ESC, called naive state) or the epiblast of postimplantation fetuses (fibroblast growth factor 2 (FGF2)-dependent epiblast stem cells, EpiSC, called primed state). Here, we report that naive pluripotent stem cell was established from the ICM, but maintained its self-renewal by treatment with FGF2 and mouse embryonic fibroblasts (MEFs) when they were exposed FGF2 during establishment. This cell line is competent to contribute to chimeric animals, including germ cells, at high efficiency. The ERK1/2, SMAD2/3, and JAK/STAT3 pathways are essential to maintain self-renewal. Inhibition of ERK1/2 or SMAD2/3 initiates transition to a naive state ESC-like state, whereas inhibition of JAK/STAT3 promotes a primed EpiSC-like character. Our present results could provide novel insights into understanding the growth factor environment and ICM plasticity, and mechanisms which orchestrate the pluripotency of embryonic stem cells and the capacity for chimeric contributions.