UCLA

The study of fat tissue or adipose over the last half century has dramatically altered the perception of the fat cell, also known as the adipocyte. Once only thought to store fat, the adipocyte is currently recognized to be a highly critical and important metabolically active cell. Adipogenesis, the process of adipocyte formation, has now become an intense subject of basic scientific research in large part due to the up-surge in obesity and metabolic disease in modern day society. PPARgamma is the master regulator of adipogenesis and is also a validated target of anti-diabetic drug therapy. However, a renewed sense of urgency in discovering novel factors and mechanisms that regulate the expression and/or activity of PPARgamma now exists due to recent scrutiny in the clinical use of molecules that directly activate PPARgamma. Therefore, this thesis attempts to address this need by investigating and uncovering entirely new modes of regulation in the differentiating adipocyte.

Part one of this thesis presents the construction of a transgenic mouse line that carries a reporter vector containing a cloned set of highly conserved non-coding genomic sequences endogenously found within and adjacent to the PPARgamma locus in the mouse genome. This examination represents an effort to identify a genomic regulatory sequence that confers tissue selective expression of adipose-specific genes such as PPARgamma. Identification of such an enhancer would undoubtedly shed new light on the regulation of gene expression in adipocytes and usher in a new paradigm in the study of adipose tissue.

Part two of this thesis presents the identification of Vestigial-like 3 (Vgll3) as an inhibitor of adipocyte differentiation. Vgll3 is a conserved transcriptional co-activator that is down-regulated during adipogenesis. This gene was initially observed to be differentially regulated between pre-adipocyte cell lines that exhibit contradictory potential to become lipid-laden adipocytes. When overexpressed in differentiating adipocytes in vitro, Vgll3 induces a potent block in PPARgamma expression and adipocyte formation. Furthermore, ectopic expression of Vgll3 was observed to up-regulate the expression of genes previously determined to be inhibitors of adipogenesis and genes associated with other mesenchymal-derived cellular differentiation programs. These results point to Vgll3 as a gene whose expression must be carefully modulated during the formation of fully differentiated, mature adipose tissue.