Dax1, an atypical orphan nuclear receptor expressed in steroidogenic tissues, has recently been shown to be expressed in mouse embryonic stem (mES) cells and is required for pluripotency. While the mechanisms of transcriptional regulation of Dax1 in steroidogenic organs have been well characterized, those in mES cells have not. Here we report that 500 bp of the Dax1 gene promoter sequence are sufficient to drive expression in mES cells. In steroidogenic tissues, NR5A1 (Sf1) binds to nuclear receptor binding sites within this sequence to regulate Dax1 expression. In mES cells, while NR5A1 (Sf1) is not expressed, NR5A2 (LRH-1) expression is robust. Luciferase assays, EMSA and overexpression/knockdown studies demonstrate that LRH-1 binds the -128 site and regulates Dax1 in mES cells. Predicated on recent work indicating that Nanog binds to the Dax1 intron, we have used chromatin immunoprecipitation experiments (ChIP) to define an intronic site that is bound by Nanog. Overexpression and knockdown of Nanog in mES cells result in alteration of Dax1 expression, and luciferase assays reveal that this sequence can enhance transcription of a Dax1 reporter construct. These data indicate that LRH-1 and Nanog cooperate to regulate Dax1 expression in mES cells.
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