When the dams were fed a VAD diet, the mRNA levels of several oxidative stress response genes were slightly but significantly higher in Bco2−/−Rbp4−/− than in Rbp4−/− embryos at 14.5 dpc (Fig. 1C), suggesting that the double-knockout embryos experienced higher levels of oxidative stress than their Rbp4−/− counterparts by virtue of their more severe vitamin A deficiency (Fig. 1A). Here, RBP4 is linked to vitamin A deficiency.