NANOG is a direct target of TGFbeta/activin-mediated SMAD signaling in human ESCs.

Self-renewal of human embryonic stem cells (ESCs) is promoted by FGF and TGFbeta/Activin signaling, and differentiation is promoted by BMP signaling, but how these signals regulate genes critical to the maintenance of pluripotency has been unclear. Using a defined medium, we show here that both TGFbeta and FGF signals synergize to inhibit BMP signaling; sustain expression of pluripotency-associated genes such as NANOG, OCT4, and SOX2; and promote long-term undifferentiated proliferation of human ESCs. We also show that both TGFbeta- and BMP-responsive SMADs can bind with the NANOG proximal promoter.

Basic FGF and suppression of BMP signaling sustain undifferentiated proliferation of human ES cells.

Human embryonic stem cells (hESCs) are routinely cultured on fibroblast feeder layers or in fibroblast-conditioned medium (CM). Bone morphogenetic proteins (BMPs) have previously been shown to induce hESC differentiation, in apparent contrast to mouse embryonic stem (ES) cells, in which BMP4 synergizes with leukemia inhibitory factor (LIF) to maintain self-renewal. Here we demonstrate that hESCs cultured in unconditioned medium (UM) are subjected to high levels of BMP signaling activity, which is reduced in CM.