Defective adipocyte differentiation in mice lacking the C/EBPβ and/or C/EBPδ gene

To investigate the role of C/EBP family members during adipocyte differentiation in vivo, we have generated mice lacking the C/EBP beta and/or C/EBP delta by gene targeting, Approximately 85% of C/EBP beta(-/-).delta(-/-) mice died at the early neonatal stage, By 20 h after birth, brown adipose tissue of the interscapular region in wild-type mice contained many lipid droplets, whereas C/EBP beta(-/-).delta(-/-) mice did not accumulate droplets. In addition, the epidydimal fat pad weight of surviving adult C/EBP beta(-/-).delta(-/-) mice was significantly reduced compared with wild-type mice. However, these adipose tissues in C/EBP beta(-/-).delta(-/-) mice exhibit normal expression of C/EBP alpha and PPAR gamma, despite impaired adipogenesis. These results demonstrated that C/EBP beta and C/EBP delta have a synergistic role in terminal adipocyte differentiation in vivo. The induction of C/EBP alpha and PPAR gamma does not always require C/EBP beta and C/EBP delta, but co-expression of C/EBP alpha and PPAR gamma is not sufficient for complete adipocyte differentiation in the absence of C/EBP beta and C/EBP delta.