The reprogramming factor nuclear receptor subfamily 5, group A, member 2 cannot replace octamer‐binding transcription factor 4 function in the self‐renewal of embryonic stem cells

Although octamer‐binding transcription factor 4 (Oct‐4) is one of the most intensively studied factors in mammalian development, no cellular genes capable of replacing Oct‐4 function in embryonic stem (ES) cells have been found. Recent data show that nuclear receptor subfamily 5, group A, member 2 (Nr5a2) is able to replace Oct‐4 function in the reprogramming process; however, it is unclear whether Nr5a2 can replace Oct‐4 function in ES cells. In this study, the ability of Nr5a2 to maintain self‐renewal and pluripotency in ES cells was investigated. Nr5a2 localized to the nucleus in ES cells, similarly to Oct‐4. However, expression of Nr5a2 failed to rescue the stem cell phenotype or to maintain the self‐renewal ability of ES cells. Furthermore, as compared with Oct‐4‐expressing ES cells, Nr5a2‐expressing ES cells showed a reduced number of cells in S‐phase, did not expand normally, and did not remain in an undifferentiated state. Ectopic expression of Nr5a2 in ES cells was not able to activate transcription of ES cell‐specific genes, and gene expression profiling demonstrated differences between Nr5a2‐expressing and Oct‐4‐expressing ES cells. In addition, Nr5a2‐expressing ES cells were not able to form teratomas in nude mice. Taken together, these results strongly suggest that the gene regulation properties of Nr5a2 and Oct‐4 and their abilities to confer self‐renewal and pluripotency of ES cells differ. The present study provides strong evidence that Nr5a2 cannot replace Oct‐4 function in ES cells. Although Nr5a2 is reported to replace Oct‐4 in reprogramming of murine somatic cells to pluripotent cells, whether Nr5a2 can replace Oct‐4 in the maintenance of self‐renewal and pluripotency mediated in ES cells has not been determined. To examine whether Nr5a2 can replace Oct‐4 function in ES cells, we performed an ES cell‐based complementation assay using ZHBTc4 ES cells. In contrast to the reprogramming process, the nuclear receptor Nr5a2 cannot replace Oct‐4 function in ES cells.