A nuclear receptor atlas: 3T3-L1 adipogenesis

The differentiation of a preadipocyte into a mature adipocyte represents a fundamental process in biology that requires a scripted program of transcriptional events leading to changes in gene expression. As part of our contribution to the Nuclear Receptor Signaling Atlas (NURSA), we used quantitative real-time PCR to profile the temporal expression of all 49 members of the mouse nuclear receptor superfamily at selected time points during differentiation of 3T3-L1 cells into mature, lipid-bearing adipocytes using two differentiation inducers [DMI ( a cocktail of dexamethasone, 3-isobutyl-1- methylxanthine, and insulin) and rosiglitazone]. We also included a comparative analysis of nuclear receptor expression in mouse primary preadipocytes and mature adipocytes. In addition to confirming the expression of receptors known to be required for adipogenesis, this analysis revealed the existence of a tightly regulated transcriptional cascade that appeared in three distinct temporal phases. The first phase began within 4 h of adipogenic initiation with the transient, sequential expression of four previously uncharacterized receptors, followed by biphasic expression of a second subset, and ended with the sequential increase in a third receptor subset over a period of 2 wk after initiation. The discovery that these receptors may serve as adipogenic biomarkers and as potential therapeutic targets in adipose- related diseases highlights the utility of quantitative expression profiling as a method for directing mechanism-based approaches to study complex regulatory pathways.