Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2004
Publication Date: 7/1/2004
Citation: Karsi, A., Waldbieser, G.C., Small, B.C., Liu, Z., Wolters, W.R. 2004. Molecular Cloning of Proopiomelanocortin cDNA and Multi-Tissue mRNA Expression in Channel Catfish. General and Comparative Endocrinology. 137:312-321. Interpretive Summary: Channel catfish are subject to a variety of environmental stressors during commercial culture, and establishment of stress responses is important for efficient performance during culture. Researchers at the USDA, ARS Catfish Genetics Research Unit, in collaboration with researchers at Auburn University, identified the DNA and protein sequences of the pro-opiomelanocortin (POMC) gene and measured gene expression in catfish tissues. Levels of POMC expression were high in the pituitary gland as expected, but the POMC gene was also expressed at significant levels in tissues related to immune responses. This research has provided molecular tools for measuring POMC gene expression that can permit researchers to develop catfish broodstock with higher tolerance to environmental stressors.
Technical Abstract: Channel catfish (Ictalurus punctatus) proopiomelanocortin (POMC) complementary DNA (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), alpha-melanocyte stimulating hormone ('-MSH, Ser**104-Val**116), corticotropin-like intermediate lobe peptide (CLIP, Arg**121-Met**142), beta lipotropin (ß- LPH, Glu**145- His**212), gamma-lipotropin ('-LPH, Glu**145- Ser**177), ß-MSH (Asp**161-Ser**177), and beta-endorphin (ß-EP, Tyr**180-His**212). Catfish POMC protein does not contain a '-MSH region and most of the joining peptide and part of the '-LPH are deleted. Protein sequence alignment showed the highest similarity with the carp (Cyprinus carpio) POMC I (67%) and POMC II (66.5%) genes, while the sea lamprey (Petromyzon marinus) POC (17.9%) and POM (18.8%) genes were the most divergent. The average similarity was 46.95% among the 44 POMC genes 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.