Small Increases in the Level of Sox2 Trigger the Differentiation of Mouse Embryonic Stem Cells

¹ Eppley Institute for Research in Cancer and Allied Diseases; Department of Pathology and Microbiology
² Eppley Institute for Research in Cancer and Allied Diseases
³ Eppley Institute for Research in Cancer and Allied Diseases; Department of Pathology and Microbiology; Department of Biochemistry and Molecular Biology; University of Nebraska Medical Center; 986805 Nebraska Medical Center; Omaha, Nebraska 68198–6805

^* To whom correspondence should be addressed. E-mail: arizzino{at}unmc.edu.

	Abstract

Previous studies demonstrated that the transcription factor Sox2 is essential during the early stages of development. Furthermore, decreasing the expression of Sox2 severely interferes with the self-renewal and pluripotency of embryonic stem (ES) cells. Other studies have shown that Sox2, in conjunction with the transcription factor Oct-3/4, stimulates its own transcription as well as the expression of a growing list of genes (Sox2:Oct-3/4 target genes) that require the cooperative action of Sox2 and Oct-3/4. Remarkably, recent studies have shown that overexpression of Sox2 decreases expression of its own gene, as well as four other Sox2:Oct-3/4 target genes (Oct-3/4, Nanog, Fgf-4 and Utf1). This finding led to the prediction that overexpression of Sox2 in ES cells would trigger their differentiation. In the current study, we initially engineered mouse ES cells for inducible overexpression of Sox2. Using this model system, we demonstrate that small increases in Sox2 protein (two-fold or less) trigger the differentiation of ES cells into cells that exhibit markers for a wide range of differentiated cell types, including neuroectoderm, mesoderm and trophectoderm, but not endoderm. We also demonstrate that elevating the levels of Sox2 quickly down-regulate several developmentally regulated genes, including Nanog, and a newly identified Sox2:Oct-3/4 target gene, Lefty1. Together, these data argue that the self-renewal of ES cells requires that Sox2 levels are maintained within narrow limits. Thus, Sox2 appears to function as a molecular rheostat that controls the expression of a critical set of embryonic genes, as well as the self-renewal and differentiation of ES cells.