The human cytomegalovirus immediate-early promoter is transcriptionally active in undifferentiated mouse embryonic stem cells.

It has been reported recently that the cytomegalovirus (CMV) immediate-early promoter is transcriptionally inactive in undifferentiated mouse embryonic stem (ES) cells. This result is surprising, since the CMV promoter is used to express transgenes in a variety of cell lines. We studied the expression of a human CMV-driven enhanced green fluorescent protein (EGFP) reporter gene (pEGFP-N1) in five undifferentiated mouse ES cell lines (BL/6III, D3, E14TG2a, MESC20, and 129) and found EGFP expression in all of these cell lines. Under optimal conditions, between 50%-80% transfection efficiencies could be achieved, and EGFP expression levels were maintained for at least 72 hours. Therefore, the human CMV promoter remains a useful system for transgene expression in undifferentiated ES cells.