Expression of TGFβ family factors and FGF2 in mouse and human embryonic stem cells maintained in different culture systems

Mouse and human embryonic stem cells are in different states of pluripotency (naive/ground and primed states). Mechanisms of signaling regulation in cells with ground and primed states of pluripotency are considerably different. In order to understand the contribution of endogenous and exogenous factors in the maintenance of a metastable state of the cells in different phases of pluripotency, we examined the expression of TGFβ family factors (ActivinA, Nodal, Lefty1, TGFβ1, GDF3, BMP4) and FGF2 initiating the appropriate signaling pathways in mouse and human embryonic stem cells (mESCs, hESCs) and supporting feeder cells. Quantitative real-time PCR analysis of gene expression showed that the expression patterns of endogenous factors studied were considerably different in mESCs and hESCs. The most significant differences were found in the levels of endogenous expression of TGFβ1, BMP4 and ActivinA. The sources of exogenous factors ActivnA, TGFβ1, and FGF2 for hESCs are feeder cells (mouse and human embryonic fibroblasts) expressing high levels of these factors, as well as low levels of BMP4. Thus, our data demonstrated that the in vitro maintenance of metastable state of undifferentiated pluripotent cells is achieved in mESCs and hESCs using different schemes of the regulations of ActivinA/Nodal/Lefty/Smad2/3 and BMP/Smad1/5/8 endogenous branches of TGFβ signaling. The requirement for exogenous stimulation or inhibition of these signaling pathways is due to different patterns of endogenous expression of TGFβ family factors and FGF2 in the mESCs and hESCs. For the hESCs, enhanced activity of ActivinA/Nodal/Lefty/Smad2/3 signaling by exogenous factor stimulation is necessary to mitigate the effects of BMP/Smad1/5/8 signaling pathways that promote cell differentiation into the extraembryonic structures. Significant differences in endogenous FGF2 expression in the cells in the ground and primed states of pluripotency demonstrate diverse involvement of this factor in the regulation of the pluripotent cell self-renewal.