Channel catfish (Ictalurus punctatus) proopiomelanocortin (POMC) cDNA was cloned to investigate its structure, evolution, and expression in different tissues. POMC is an important gene in the hypothalamus-pituitary-adrenal axis, the main mediator of the stress response. POMC gene was isolated from a pituitary cDNA library and nucleotide sequence was determined. POMC cDNA is composed of 1164 nucleotides with a 639 nucleotide open reading frame encoding a protein of 212 amino acids. Catfish POMC protein contains a signal peptide (SP, Met1-Ala28), N-terminal peptide (Gln29- Glu101), adrenocorticotropic hormone (ACTH, Ser104- Met142), α-melanocyte stimulating hormone (α-MSH, Ser104-Val116), corticotropin-like intermediate lobe peptide (CLIP, Arg121-Met142), β-lipotropin (β-LPH, Glu145-His212), γ-lipotropin (γ-LPH, Glu145- Ser177), β-MSH (Asp 161-Ser177), and β-endorphin (β-EP, Tyr 180-His212). Catfish POMC protein does not contain a γ-MSH region and most of the joining peptide and part of the γ-LPH are deleted. Protein sequence alignment showed the highest similarity with the carp (Cyprinus carpio) POMC I (66.5%) and POMC II (67%), while the sea lamprey (Petromyzon marinus) POC (17.9%) and POM (18.8%) were the most divergent. The average similarity was 46.95% among the 44 POMC proteins from 36 different species analyzed. Compared to the POMC mRNA levels in the pituitary, the concentration of the POMC mRNA was 0.0594% in the anterior kidney and 0.0012-0.0045% in all the other tissues except in the skin where the lowest expression (0.0005%) was observed. Overall architecture of channel catfish POMC is highly similar to those from other teleosts.
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