Cloning and expression of two proopiomelanocortin mRNAs in the common carp (Cyprinus carpio L.)

Proopiomelanocortin (POMC) is the precursor for a number of biologically active peptides such as adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin. It is well known that these peptides are involved in the stress response in fish as well as in mammals. We have cloned two different carp POMC cDNAs called, POMC-I and POMC-II. The nucleotide sequences of 955 bp for POMC-I and 959 bp for POMC-II share 93.5% identity in their cDNAs, and the deduced amino acid sequences (both 222 amino acids) are 91.4% identical. In the ACTH and beta-MSH domain, two amino acid substitutions are found, whereas alpha-MSH and beta-endorphin are identical. For beta-MSH, the serine replacement (in POMC-I) by a glycine (in POMC-II) results in a putative amidation site Pro-X-Gly for POMC-II. We used RT-PCR to show that both POMC mRNAs are expressed in the hypophysis, hypothalamus and other parts of the brain of a single fish. Furthermore, in a phylogenetic tree based on POMC sequences the divergence of carp POMC-I and -II from tetraploid animals (salmon, trout and xenopus) is demonstrated.