The Forkhead Transcription Factor Foxo1 Stephen R Farmer  Molecular Cell  Volume 11, Issue 1, Pages 6-8 (January 2003) DOI: 10.1016/S1097-2765(03)00003-0

Figure 1 A Role for Insulin and Foxo1 in Regulating the Switch from Clonal Expansion to Differentiation during Adipogenesis Exposure of confluent, quiescent preadipocytes (G0) to insulin along with other hormones stimulates their transition through G1 phase of the cell cycle, which involves phosphorylation of Rb pocket proteins (Rb, p107, and p130) and a corresponding activation of the E2F family of transcription factors. E2F1 and E2F3 along with Rb cooperate with C/EBPβ and C/EBPδ to induce expression of the adipogenic transcription factors, PPARγ and C/EBPα. In addition to stimulating progression through clonal expansion (G1 to S phase of the cell cycle), insulin suppresses Foxo1 activity to prevent the activation of the cyclin-dependent kinase inhibitor p21 until growth has subsided. At this stage of adipogenesis, Foxo1 is activated and cooperates with PPARγ to trigger a postmitotic growth arrest (GD), which is required for terminal differentiation. Molecular Cell 2003 11, 6-8DOI: (10.1016/S1097-2765(03)00003-0)