Identification of developmental pluripotency associated 5 expression in human pluripotent stem cells.

Pluripotent embryonic germ cells (EGCs) can be derived from the culture of primordial germ cells (PGCs). However, there are no reports of gonocytes, following the stage of PGC development, becoming stem cell lines. To analyze the gene expression differences between PGCs and gonocytes, we performed cDNA subtractive hybridization with mouse gonads containing either of the two cell populations. We confirmed that developmental pluripotency associated 5 (Dppa5), originally found in mouse embryonic stem cells (ESCs) and mouse embryonic carcinoma cells (ECCs), was strongly expressed in mouse PGCs and the expression was rapidly downregulated during germ cell development. A human sequence homologous to Dppa5 was identified by bioinformatics approaches. Interestingly, human Dppa5 was expressed only in human PGCs, human EGCs, and human ESCs and was not detected in human ECCs. Its expression was downregulated during induced differentiation of human ESCs. These findings confirmed that Dppa5 is specifically and differentially expressed in human cells that have pluripotency. The results strongly suggest that Dppa5 may have an important role in stemness in human ESCs and EGCs and also can be used as a marker of pluripotent stem cells. Human pluripotent stem cells may have their own ways to be pluripotent, as opposed to the much uniform mouse stem cells.