Figure 1. Experimental strategies for the identification of bipotent adipocyte progenitors. Initial experiments used tracing techniques (top panel) to investigate the origin of brown adipoyctes that are induced by the ADRB3 agonist stimulation (green box). (A) In vivo tagging with thymidine analogs demonstrated that iBA come from proliferating cells. (B) Immunotyping of cells tagged with thymidine analogs indicated that iBA are derived from progenitors that express PDGFRα⁺. (C) Inducible genetic tagging with the PDGFRα-CreER reporter model proved that PDGFRα⁺ cells become iBA during CL stimulation. Prospective analysis (lower panel) of FACS-isolated cells indicate that PDGFRα⁺ have the potential to become either brown and white adipocytes. (D) FACS-isolated cells formed colonies that contain both brown and white adipocytes, and following transplantation became white adipocytes. (E) Lineage tracing using the PDGFRα-CreER reporter model demonstrated that high fat feeding greatly increases the recruitment of white adipocytes from PDGFRα⁺ progenitors.