Abstract

A unique and complex signaling network allows embryonic stem cells (ESCs) to undergo extended proliferation in vitro, while maintaining their capacity for multilineage differentiation. Genuine ESC identity can only be maintained when both self-renewal and suppression of differentiation are active and balanced. Here we identify Pramel7 (Preferentially expressed antigen in melanoma-like 7) as a novel factor crucial for maintenance of pluripotency and LIF-mediated self-renewal in ESCs. In vivo, Pramel7 expression was exclusively found in the pluripotent pools of cells, namely the central part of the morula and the inner cell mass (ICM) of the blastocyst. Ablation of Pramel7 induced ESC differentiation, while its overexpression was sufficient to support long-term self-renewal in the absence of exogenous LIF. Furthermore, Pramel7 overexpression suppressed differentiation in ESCs in vitro and in vivo. This process was reversible, as upon transgene excision cells reverted to a LIF-dependent state and regained their capacity to participate in the formation of chimeric mice. Molecularly, LIF directly controls Pramel7 expression, involving both STAT3-dependent transcriptional regulation and PI3K-dependent phosphorylation of GSK3β. Pramel7 expression in turn confers constitutive self-renewal and prevents differentiation through inactivation of ERK phosphorylation. Accordingly, knockdown of Pramel7 promotes ESC differentiation in presence of LIF and even upon forced STAT3-activation. Thus, Pramel7 represents a central and essential factor in the signaling network regulating pluripotency and self-renewal in ESCs.