Leukemia Inhibitory Factor Is Essential for the Self-Renewal of Embryonic Stem Cells from Nile Tilapia (Oreochromis niloticus) Through Stat3 Signaling

To date, little is known about the mechanisms underlying the self-renewal of embryonic stem (ES) cells from fish species. In this study, we report that the leukemia inhibitory factor (LIF; named as OnLif) from a teleost fish, Nile tilapia (Oreochromis niloticus), is essential for the proliferation, survival, and pluripotency maintenance of Nile tilapia ES cells (TES1) by activating the signal transducer and activator of transcription 3 (Stat3). This protein has 221 amino acid residues with similar sequence features to mammalian LIF. By fusing to a small ubiquitin-related modifier and inducing expression at 16 degrees C, the soluble tag-free protein had been successfully obtained. Further investigation indicates that OnLif could significantly enhance the proliferation and survival of TES1. Moreover, it contributed to the pluripotency maintenance of TES1 characteristic of high expression of pluripotency genes, no or low expression of differentiation genes, and strong alkaline phosphatase activity. Notably, it mediated Stat3 phosphorylation, whose inhibitor treatment could lead to apoptosis. In addition, OnLif significantly enhanced the proliferation of ES cells from medaka (Oryzias latipes), suggesting its potential role in other fish ES cells. These data first suggest that Lif/Stat3 signaling has an essential role in the self-renewal of ES cells from fish, just like that in the ground state pluripotency maintenance of mouse and human ES cells. Our study would not only be helpful for the understanding of molecular mechanisms underlying self-renewal of ES cells from the perspective of evolution but also facilitate ES-based biotechnology application in fishery.