Melanocortin receptor genes in the chicken--tissue distributions

Two receptor genes belonging to the melanocortin receptor (MC-R) family were isolated in the chicken, the CMC4 and CMC5, each of which is a chicken homologue of the mammalian MC4-R and MC5-R, respectively. The CMC4 encodes a 331 amino acid protein, sharing 86. 4-88.1% identity with mammalian analogs, and the CMC5 encodes a 325 amino acid protein, which is 72.3-79.1% identical to mammalian counterparts. Both genes contain no intron in their coding regions and exist in the chicken genome as single copy genes. Reverse transcription-PCR analysis revealed that the CMC4 mRNA is expressed in a wide variety of peripheral tissues, including the adrenal, gonads, spleen, and adipose tissues, as well as in the brain, where mammalian counterparts are exclusively expressed in the brain, indicating that the regulation of MC4-R gene expression differs between mammals and chickens. The CMC5 mRNA, on the other hand, is expressed in the liver, gonads, adrenal, kidney, brain, and adipose tissues as well as in the uropygial gland. These findings raise the possibility that melanocortins affect a variety of functions both in the brain and in the peripheral tissues of the chicken.