The development of obesity requires the continuous differentiation of new adipocytes throughout life, and this process of adipocyte differentiation from preadipocytes is called adipogenesis. Many studies have demonstrated the importance of transcription factors, especially nuclear receptors and their coactivators, in adipocyte proliferation, gene expression regulation, and differentiation. In adipocytes, PPARgamma regulates the expression of genes involved in lipid synthesis, storage, and transportation. This invention relates generally to compositions and methods which utilization nuclear receptors for regulating adipogenesis in cells. Specifically, the invention is directed to compositions which regulate transcription factor PPARgamma.sub and enhance or inhibit the transcription of genes responsible for directing cell differentiation towards a pathway of adipogenesis. More specifically, disclosed herein is a novel polypeptide coactivator of PPARgamma, and fragments thereof, which possess coactivator or corepressor activity. The invention includes interfering RNA that may be used to inhibit adipogenesis.