Recent insight into the functions of insulin receptor substratesIRS1 and IRS2 indicate that both coordinate responsesto insulin via FoxO1 (68, 69). During the re-fed state, insulinactivates IRS1 to suppress FoxO1 and allow an increase in glucokinaseand sterol regulatory element-binding transcriptionfactor 1 (SREBF1, a.k.a. SREBP1) expression that promotes glycolysisand lipid biosynthesis, respectfully. In contrast, insulininhibits IRS2. Because IRS2 stimulates gluconeogenesis byinducing PCK1 and G6PC in liver through FoxO1, the relativelylow levels of insulin in the fasted state allow IRS2 to inducegluconeogenesis. Based on these insights, the higher insulin levelsin the re-fed state would function through IRS1 to suppressRDH expression, whereas the lower insulin levels in the fastedstate would allow IRS2 to induce RDH expression.