D3 mouse embryonic stem cell line either untreated (dark orange filled histogram) or treated with retinoic acid for 3 days (light orange filled histogram) was stained with Goat Anti-Mouse Nanog APC-conjugated Antigen Affinity-purified Polyclonal Antibody (Catalog # IC2729A) or isotype control antibody (Catalog # IC108A, blue open histogram). To facilitate intracellular staining, cells were fixed with Flow Cytometry Fixation Buffer (Catalog # FC004) and permeabilized with Flow Cytometry Permeabilization/Wash Buffer I (Catalog # FC005). View our protocol for Staining Intracellular Molecules.