The melanocortin system. Top, the proopiomelanocortin (POMC) gene produces the melanocortins (α-, β- and γ-MSH and ACTH) which bind to melanocortin receptors. Amino acid sequences of the melanocortin peptide and core heptapeptide aminoacids are highlighted (a). The tissues were we have localized three MCRs receptors are shown, along with the functions they control; upward arrow means "increased function". Total RNA screened for MC1R mRNA transcripts by real-time RT-PCR, much increased expression of MC1R transcripts is evident in the skin of island lizards (b). Brain and testis expression of the melanocortins receptors as evidenced by western blotting with anti-MC3R and anti-MC4R antibodies: c and d respectively. T, lizard testis; B, lizard brain; SH, human neuronal cells. Actin and SH were used as controls.