Maternal-effect Floped gene is essential for the derivation of embryonic stem cells in mice

Floped (official name Ooep) is specifically and abundantly expressed in mouse oocytes and embryonic stem cells (ESCs). Depletion of Floped from oocytes leads to early embryonic arrest at the 2-cell stage. Although crucial in cleavage stage development, its roles in early embryos as well as in ESCs remain completely unknown. Here, we compared the efficiency of mouse ESC derivation from inner cell mass (ICM) with and without Floped to study its possible roles in mESCs. Derivation rates of mESC from wild-type, heterozygous, and homozygous blastocysts were 33.3%, 21.43%, and 3.85%, respectively, indicating that Floped-/- blastocysts had significantly decreased derivation rates. Respective outgrowth appearing rate five days after blastocyst attachment were 83.3%, 85.7%, and 15.4%. Morphologically, the outgrowth of ICM from Floped-/- blastocysts appeared severely death three to five days after blastocyst attachment, and the respective derived stem cells showed long-term instability with long-standing epithelial-like colonies. This result suggests a possible role of Floped in the course of ICM-ESCs transition.