C/EBPβ and δ are transiently induced during the early stages of adipocyte differentiation (adipogenesis), while C/EBPα is upregulated during the terminal stages of adipogenesis. In vitro and in vivo studies have demonstrated that each plays an important role in this process. For example, Murine Embryonic Fibroblasts (MEFs) from mice lacking both C/EBPβ and C/EBPδ show impaired adipocyte differentiation in response to adipogenic stimuli. In contrast, ectopic expression of C/EBPβ and δ in 3T3-L1 preadipocytes promotes adipogenesis, even in the absence of adipogenic stimuli. C/EBPβ and δ promote adipogenesis, at least in part by inducing the expression of the "master" adipogenic transcription factors C/EBPα and PPARγ.
C/EBPα is required both for adipogenesis and for normal adipocyte function. For example, mice lacking C/EBPα in all tissues except the liver (where it is needed to avoid postnatal lethality) show abnormal adipose tissue formation. Moreover, ectopic expression of C/EBPα in various fibroblast cell lines promotes adipogenesis. C/EBPα probably promotes adipogenesis by inducing the expression of PPARγ.