Figure 9. Transcriptional regulation of adipogenesis as determined in vitro in a fibroblast-like preadipocyte clonal cell line. Preadipocytes are grown to confluence and become growth arrested. Following induction of differentiation, they re-enter the cell cycle and undergo several rounds of proliferation, a process known as mitotic clonal expansion. At the end of this short proliferative phase, preadipocytes terminally differentiate into adipocytes as they begin synthesizing lipid and assume characteristics of mature fat cells. Numerous transcription factors have been determined to promote (green arrows) or inhibit (orange horizontal ended line) adipogenesis either during clonal expansion or at later stages of terminal differentiation. The timing of activation (i.e. when each transcription factor is turned on and off) is critical to the progression of adipocyte differentiation.