Parthenogenetic embryonic stem (pES) cells isolated from parthenogenetic activation of oocytes and embryos,also called parthenogenetically induced pluripotent stem cells,exhibit pluripotency evidenced by both in vitro and in vivo differentiation potential.Differential proteomic analysis was performed using differential in-gel electrophoresis and isotope-coded affinity tag-based quantitative proteomics to investigate the molecular mechanisms underlying the developmental pluripotency of pES cells and to compare the protein expression of pES cells generated from either the in vivo-matured ovulated (IVO) oocytes or from the in vitro-matured (IVM) oocytes with that of fertilized embryonic stem (fES) cells derived from fertilized embryos.A total of 76 proteins were upregulated and 16 proteins were downregulated in the IVM pES cells,whereas 91 proteins were upregulated and 9 were downregulated in the IVO pES cells based on a minimal 1.5-fold change as the cutoff value.No distinct pathways were found in the differentially expressed proteins except for those involved in metabolism and physiological processes.Notably,no differences were found in the protein expression of imprinted genes between the pES and fES cells,suggesting that genomic imprinting can be corrected in the pES cells at least at the early passages.The germline competent IVM pES cells may be applicable for germ cell renewal in aging ovaries if oocytes are retrieved at a younger age.