Characterization of two channel catfish, Ictalurus punctatus, glucocorticoid receptors and expression following an acute stressor

Authors: SMALL, BRIAN - University Of Idaho; Quiniou, Sylvie

Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2017
Publication Date: 2/1/2018
Citation: Small, B.C., Quiniou, S. 2018. Characterization of two channel catfish, Ictalurus punctatus, glucocorticoid receptors and expression following an acute stressor. Comparative Biochemistry and Physiology. 216:42-51.

Interpretive Summary: Suboptimal environmental conditions are common in aquaculture systems. When fish are exposed to these stressors, a series of physiological changes occur that help the animal cope with the stressor in the short run but may have long-term detrimental effects. Among the long-term consequences of stress are reduced growth and increased susceptibility to infectious disease. Therefore, understanding and managing the effects of stress is an important goal in aquaculture research. One of the first response to stress in fish is release of cortisol, which then activates other physiological responses. Cortisol acts by first binding to the Glucocorticoid Receptor (GR), which is present in almost every cell in the body. When cortisol binds with GR, the bound complex regulates genes controlling the development, metabolism, and immune response. In this study two glucocorticoid receptors were identified in catfish (ipGR1 and ipGR2). Both receptors were shown to be expressed in most tissues but to varying degrees. Following an acute stress event, ipGR1 was shown to be the major receptor modulating acute stress response. This is the first study of the identity and roles of GR in channel catfish and will add to our understanding of the stress response and how it can be managed in the most important aquaculture species in the United States.

Technical Abstract: Two channel catfish glucocorticoid receptor genes, ipGR1 (NR3C1_1) and ipGR2 (NR3C1_2) were partially characterized. Identification and analysis of the genomic organization of two channel catfish glucocorticoid receptors (GRs) revealed differences in the lengths of exons 1 and 2 and the addition of an extra 27-bp exon inserted after exon 2 in the GR1 gene, yielding a 9-aa insert in the receptor protein. Sequence of the 9-aa insert in ipGR1 (WRARQNTHG) is unique compared to other teleost fish GRs. Amino acid sequence alignment of the two channel catfish GRs, revealed 55% sequence identity between them, with a high degree of sequence conservation (82%) in the DNA binding and ligand binding domains. Real-time PCR indicated that ipGR1 and ipGR2 were expressed in all tissues evaluated. Channel catfish GR1 was predominantly expressed in the gills, nearly 25-fold higher than in the liver. GR1 expression was higher than GR2 expression in gills, intestine, head kidney and heart (P < 0.05). Channel catfish hepatic GR1 mRNA expression was significantly (P < 0.05) increased from pre-stress expression 30 min following removal of the acute stressor. After 30 minutes of stress and during the 2 h recovery period, ipGR1 mRNA expression was higher relative to ipGR2 expression. Hepatic ipGR2 expression was not affected (P > 0.05) by the acute stress event. The present study adds to the growing body of information on GR evolution and function and further demonstrates the unique regulation of the GC/GR system in teleost fish.