Sahmyook University 1 article published in JoVE Developmental Biology Loss- and Gain-of-function Approach to Investigate Early Cell Fate Determinants in Preimplantation Mouse Embryos Jae H. Lee1,2, Yong II Cho5, Sung S. Choi4, Hae-Won Kim1,2, Churl K. Min3, Sang J. Lee5 1Department of Nanobiomedical Sciences and BK21 PLUS NBM Global Research Center for Regenerative Medicine, Dankook University, 2Insititute of Tissue Regeneration Engineering, Dankook University, 3Department of Biological Sciences, Ajou University, 4Department of Pharmacy, Sahmyook University, 5Department of Animal Biotechnology, Sahmyook University The goal of this protocol is to describe a loss- and gain-of function method that is applicable to identify neogenin as a stage-specific receptor that leads to trophectoderm and inner cell mass differentiation in preimplantation mouse embryos.