Submitted to: General and Comparative Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/11/2005
Publication Date: 4/9/2005
Citation: Karsi, A., Waldbieser, G.C., Small, B.C., Wolters, W.R. 2005. Genomic structure of the proopiomelanocortin gene and expression during temporal stress in channel catfish, Ictalurus punctatus. General and Comparative Endocrinology. Interpretive Summary: Stressors in production systems lead to lowered efficiency of catfish production. This research was designed to develop a tool for characterizing levels of physiological stress in catfish. The proopiomelanocortin (POMC) gene was cloned which provided DNA sequence useful for studying factors which regulate POMC gene activity. This molecular tool will allow us to measure variation in stress responses between fish, and correlate the responses of catfish with resistance to diseases and efficient growth.
Technical Abstract: Proopiomelanocortin (POMC) is an important gene involved in the stress response of the hypothalamus-pituitary-adrenal axis (HPA). It is a precursor of important peptide hormones including adrenocorticotropic hormone (ACTH), melanocyte stimulating hormones (MSH), and b-endorphin (b-EP). The present research was designed to determine genomic structure and expression of the POMC gene during temporal stress in channel catfish (Ictalurus punctatus). The catfish POMC gene consisting of three exons and two introns has a similar structural organization to that of other species. However, DNA sequence conservation within the catfish and mammalian POMC promoter region was low. Genomic southern blot analysis indicated POMC is present as a single copy gene in the catfish genome. Real-time PCR permitted monitoring of temporal expression of the POMC mRNA in catfish pituitary during low-water stress, and plasma cortisol concentrations were also measured as an indicator of stress. Within 15 min after the onset of low water stress, POMC mRNA expression was elevated 1.87 fold above the control value. The POMC mRNA level had declined after 30 min (1.29 fold) and 1 h (1.1 fold) at which stress was removed. After 1 h recovery, a significant increase in the POMC mRNA expression was detected (2.44 fold, P<0.05) followed by a decline 2 h later (1.52 fold) when the experiment was terminated. We conclude that POMC and cortisol are both involved in the low-water stress response during which cortisol may serve as a negative regulator of POMC expression in catfish.