ABSTRACT
Pluripotent mouse embryonic stem cells (mESCs), maintained in the presence of the leukemia inhibitory factor (LIF) cytokine, provide a powerful model with which to study pluripotency and differentiation programs. Extensive microarray studies on cultured cells have led to the identification of three LIF signatures. Here we focus on muscle ras oncogene homolog (MRAS), which is a small GTPase of the Ras family encoded within the Pluri gene cluster. To characterise the effects of Mras on cell pluripotency and differentiation, we used gain- and loss-of-function strategies in mESCs and in the Xenopus laevis embryo, in which Mras gene structure and protein sequence are conserved. We show that persistent knockdown of Mras in mESCs reduces expression of specific master genes and that MRAS plays a crucial role in the downregulation of OCT4 and NANOG protein levels upon differentiation. In Xenopus, we demonstrate the potential of Mras to modulate cell fate at early steps of development and during neurogenesis. Overexpression of Mras allows gastrula cells to retain responsiveness to fibroblast growth factor (FGF) and activin. Collectively, these results highlight novel conserved and pleiotropic effects of MRAS in stem cells and early steps of development.
Subject(s)
Embryonic Stem Cells/enzymology , Gene Expression Regulation, Developmental , Monomeric GTP-Binding Proteins/metabolism , Xenopus laevis/embryology , Activins/pharmacology , Amino Acid Sequence , Animals , Biomarkers/metabolism , Brain/embryology , Brain/enzymology , Conserved Sequence , Embryonic Induction , Embryonic Stem Cells/drug effects , Embryonic Stem Cells/metabolism , Female , Fibroblast Growth Factors/pharmacology , Gastrula/cytology , Gastrula/drug effects , Gastrula/enzymology , Gene Knockdown Techniques , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Leukemia Inhibitory Factor/pharmacology , Mice , Molecular Sequence Data , Monomeric GTP-Binding Proteins/genetics , Nanog Homeobox Protein , Neurogenesis , Octamer Transcription Factor-3/genetics , Octamer Transcription Factor-3/metabolism , Ovary/enzymology , Xenopus laevis/genetics , Xenopus laevis/metabolism , ras ProteinsABSTRACT
LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.
