Co-localization of NANOG and OCT4 in human pre-implantation embryos and in human embryonic stem cells

NANOG and OCT4 are required for the maintenance of pluripotency in embryonic stem cells (ESCs). These proteins are also expressed in the inner cell mass (ICM) of the mouse pre-implantation embryo. Immunohistochemistry was used to show the presence of NANOG and OCT4 protein, and in situ hybridization was used to localize NANOG mRNA in human embryos from two-cell to blastocyst stage, and in human ESCs (hESCs). Nanog and Oct4 were co-localized in human embryos from morula and blastocyst stages. NANOG mRNA was detected in a group of cells in the morula, in cells of the ICM of blastocysts, and evenly in hESCs. All non-differentiated hESCs expressed NANOG and OCT4 protein. Pluripotent cells expressing NANOG and Oct4 were eccentrically localized, probably in polarized cells in a human compacted morula, which appears to be different from expression in murine embryos. In this study, we demonstrate that whole mount in situ hybridization is amenable to localization of mRNAs in human development, as in other species.