Despite the enormous medical potential of ESCs, the molecular mechanisms conferring the ability to differentiate into all cell types of the embryo remain elusive. We used an in silico approach to identify genes expressed exclusively in mouse preimplantation embryos and pluripotent cell lines. Two of these genes were developmental pluripotency-associated gene 2 (Dppa2) and Dppa4, which we show are closely linked genes encoding putative nuclear SAP domain proteins expressed in human and mouse pluripotent stem cells and germ cell tumor-derived embryonal carcinoma cells. In the mouse, these genes are transcribed in germinal vesicle-stage oocytes and throughout the cleavage stages of embryogenesis. They then become restricted to the pluripotent inner cell mass of blastocysts and are subsequently downregulated. After gastrulation, Dppa2 and Dppa4 are expressed only in the developing germ line, showing that these genes mark cells of the pluripotent cycle. In the germ line, both genes are downregulated as the germ cells commit to the oogenic pathway or soon after commitment to the spermatogenic pathway. We have observed similar germ line expression profiles for other pluripotent markers, and these results are consistent with the hypothesis that pluripotent markers must be downregulated during fetal germ line development, a process that may be required to facilitate appropriate germ line differentiation. The study of expression and function of pluripotent markers such as Dppa2 and Dppa4 is likely to unveil new aspects of the regulation of pluripotency and germ line development in mammals. STEM CELLS 2007;25:19 -28

Establishment of pluripotent epiblast cells is a critical event during early mammalian development because all somatic lineages and the primordial germ cells (PGCs) are derived from them. The epiblast and PGCs are in turn the precursors of pluripotent embryonic stem cells and embryonic germ cells, respectively. Although PGCs are specialized cells, they express several key pluripotency-related genes, such as Oct4 and Sox2. We have analyzed Esg1 expression in mouse and human cells and shown that in the mouse the gene is specifically expressed in preimplantation embryos, stem cells, and the germline. Moreover, Esg1 coexpresses with Oct4 and Sox2, confirming its identity as a marker of the pluripotent cycle. Esg1 is also expressed with Oct4 and Sox2 by human embryonic stem cells and in germ cell carcinoma tissue but not by all human embryonal carcinoma cell lines. These data suggest that together with Oct4 and Sox2, Esg1 plays a conserved role in the pluripotent pathway of mouse and human stem and germ cells.