The nucleic acid sequence of the POMC enhancer is disclosed herein. Sequences from the human, rat, rabbit, hamster, mouse, and cow POMC enhancer are disclosed. Hybrid transgenes, comprising a POMC transcriptional control element operably linked to a nucleic acid sequence encoding a marker are also enclosed. In addition, transgenic mice carrying a hybrid transgene including a POMC control element operably linked to a marker are disclosed herein.