Molecular cloning of proopiomelanocortin cDNA and multi-tissue mRNA expression in channel catfish

Abstract

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, Met 1–Ala 28), N-terminal peptide (Gln 29–Glu 101), adrenocorticotropic hormone (ACTH, Ser 104–Met 142), α-melanocyte stimulating hormone (α-MSH, Ser 104–Val 116), corticotropin-like intermediate lobe peptide (CLIP, Arg 121–Met 142), β-lipotropin (β-LPH, Glu 145–His 212), γ-lipotropin (γ-LPH, Glu 145– Ser 177), β-MSH (Asp 161–Ser 177), and β-endorphin (β-EP, Tyr 180–His 212). 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.