factors. Activation of one of these factors, the nuclear hormone receptor PPARγ, is known to
promote fat cell differentiation in vitro. Whether PPARγ is required for this process in vivo has
remained an open question because a viable loss-of-function model for PPARγ has been
lacking. We demonstrate here that mice chimeric for wild-type and PPARγ null cells show
little or no contribution of null cells to adipose tissue, whereas most other organs examined …