Effects of heat stress on the expression of crh and its receptor genes and the concentration of cortisol in largemouth bass （Micropterus salmoides）

【Objective】To investigate the effects of heat stress on the expressions of the corticotropin-releasing hormone gene（crh） and its receptor genes （crhr1 and crhr2） and the concentration of cortisol in largemouth bass （Micropterus salmoides）, and to further analyze the interaction between crh, crhr1 and crhr2 genes and cortisol, which would lay a foundation for revealing the molecular regulatory mechanism of stress response in largemouth bass. 【Method】The open reading frames （ORF） of crh, crhr1 and crhr2 genes were amplified by PCR amplification, and the expression of the 3 genes in different tissues of largemouth bass was detected by real-time fluorescence quantitative PCR （q RT-PCR）. The blood samples and brain tissues of largemouth bass were collected after acute heat stress, the relative expressions levels of crh,crhr1 and crhr2 genes in brain tissues and the concentration of serum cortisol of largemouth bass were measured at different treatment time points, with 25.0 ℃ as the initial water temperature set as control（CK）.【Result】The ORF sequences of the crh, crhr1 and crhr2 genes of largemouth bass were obtained as 510, 1392 and 1245 bp, encoding 169, 463 and 414 amino acids respectively. The phylogenetic tree based on the nucleotide sequence similarity of crh, crhr1, and crhr2 genes showed that largemouth bass was clustered with percoid fish, especially close to smallmouth bass. The genes of crh, crhr1 and crhr2 were expressed in heart, liver, intestine, kidney, brain, gill and muscle, and the relative expressions were higher in brain. After acute heat stress, the relative expressions of crh, crhr1 and crhr2 genes in brain and the concentration of serum cortisol increased first and then decreased with time. Among these, the relative expressions of crh and crhr1 genes and the concentration of serum cortisol reached the peak at 3 h post heat （33.0 ℃）. There was a lag in the expression of crhr2 gene, and its relative expression reached its peak at 6 h （30.4 ℃） stress.【Conclusion】After acute heat stress in largemouth bass, the expressions of crh and crhr1 genes were consistent with the changing trend of the concentration of serum cortisol after acute heat stress, while the expression of crhr2 gene lags behind the change in the concentration of cortisol. Therefore, it is speculated that crh and crhr1 genes are involved in the synthesis and secretion of cortisol and related to stress initiation. While crhr2 gene is involved in the decomposition of cortisol, associated with stress recovery.