RBP4 and vitamin A deficiency: Of note, Bco2−/− (single knockout) embryos from dams fed the VAD diet and supplemented with β-carotene from 6.5–9.5 dpc developed normally (51 normal embryos from 8 dams), indicating that this role of BCO2 may be specific to conditions of vitamin A deficiency (in this case, modeled on the Rbp4−/− background).